SINTERING ADDITIVELY MANUFACTURED PARTS IN MICROWAVE OVEN
A method comprising supplying a first brown part and a second brown part, each of the first and second brown parts formed from a material in which more than 50 percent of powder particles of a second powdered metal have a diameter less than 10 microns, in a first mode, loading the first brown part into a fused tube, and ramping a temperature inside the fused tube at greater than 10 degrees C. per minute but less than 40 degrees C. per minute to a first sintering temperature from 500-700 degrees C., and in a second mode, loading the second brown part into the fused tube, and ramping the temperature inside the fused tube at greater than 10 degrees C. per minute but less than 40 degrees C. per minute to a second sintering tempering temperature from 1000-1200 degrees C.
This application claims the benefit under 35 U.S.C. § 119(e) of U.S. provisional application Ser. No. 62/489,410 filed Apr. 24, 2017, entitled “SINTERING ADDITIVELY MANUFACTURED PARTS IN MICROWAVE OVEN”; 62/505,081 filed May 11, 2017, entitled “RAPID DEBINDING VIA INTERNAL FLUID CHANNELS”; 62/519,138 filed Jun. 13, 2017, entitled “COMPENSATING FOR BINDER-INTERNAL STRESSES IN SINTERABLE 3D PRINTED PARTS”; 62/545,966 filed Aug. 15, 2017, entitled “BUBBLE REMEDIATION IN 3D PRINTING OF METAL POWDER IN SOLUBLE BINDER FEEDSTOCK”; and 62/575,219 filed Oct. 20, 2017, entitled “3D PRINTING INTERNAL FREE SPACE WITH A SINTERABLE POWDER FEEDSTOCK”, the disclosures of which are herein incorporated by reference in their entireties. This application is also a continuation of each of U.S. patent application Ser. No. 15/829,472 filed on Dec. 1, 2017, entitled “SINTERING ADDITIVELY MANUFACTURED PARTS WITH A DENSIFICATION LINKING PLATFORM”; Ser. No. 15/829,486 filed on Dec. 1, 2017, entitled “STRESS RELAXATION IN ADDITIVELY MANUFACTURED PARTS”; Ser. No. 15/829,500 filed on Dec. 1, 2017, entitled “ADDITIVELY MANUFACTURED PARTS WITH DEBINDING ACCELERATION”; and Ser. No. 15/831,995 filed on Dec. 5, 2017, entitled “ADDITIVE MANUFACTURING WITH HEAT-FLEXED MATERIAL FEEDING”, the disclosures of which are herein incorporated by reference in their entireties.
FIELDAspects relate to three dimensional printing of composite metal or ceramic materials.
BACKGROUND“Three dimensional printing” as an art includes various methods for producing metal parts.
In 3D printing, in general, unsupported spans as well as overhanging or cantilevered portions of a part may require removable and/or soluble and/or dispersing supports underneath to provide a facing surface for deposition or to resist deformation during post-processing.
SUMMARYAccording to a first aspect of the embodiments of the present invention, a method of depositing part layers to form a part in additive manufacturing may include depositing a part layer of green material including a first binder and a sinterable powder.
A release layer of release material including a second binder and a release powder is deposited upon the part layer of green material. A portion of the first binder is debound from the part layer of green material before depositing a subsequent layer of green material.
Optionally, a plurality of part layers of green material is deposited, and the plurality of part layers of green material is debound before depositing a subsequent plurality of part layers of green material.
Further optionally, the part layer of green material may be deposited with a print head, and the portion of the first binder may be debound by immersing the part in solvent before depositing a subsequent plurality of part layers of green material.
Still further optionally, the part layer of green material may be deposited with a print head, and the portion of the first binder debound with a debinding head following a same trajectory as the print head.
Alternatively, or in addition, a portion of the first binder is debound with a debinding head scanning across a part layer of green material. Following debinding all part layers of green material of the part, the entire part may be sintered.
In another aspect of the embodiments of the present invention, a method of depositing material for additive manufacturing may include depositing a part layer of green material including a first binder and a sinterable powder. A portion of the first binder may be debound from the part layer of green material to form a layer of brown material, and a release layer of release material may be deposited including a second binder and a release powder upon the layer of brown material. A part layer of green material may be deposited upon the part layer of brown material.
Optionally, following depositing a plurality of part layers of brown material, further the brown material may be further debound. Following depositing a plurality of part layers of brown material, the entire part may be sintered. Following depositing a plurality of part layers of brown material, the second binder may be pyrolysed during sintering to leave a loose layer of the release powder.
In still another aspect of the embodiments of the present invention, an apparatus for additive manufacture of parts may include a sealed chamber in which a part is deposited, and a heated build plate for receiving a deposited part. A print head may deposit part layers of model material containing a binder and a sinterable powder upon the heated build plate and upon prior deposited part layers. A debinding applicator may substantially continuously debind the binder from the model material as it is deposited on the heated build plate. A fume extractor may remove the debound binder from the sealed chamber.
Optionally, the fume extractor includes a vacuum pump that maintains the sealed chamber under vacuum.
Alternatively, or in addition, the debinding applicator may include a debinding head that substantially continuously follows a trajectory of the print head. A portion of the fume extractor may be transported together with the debinding head to remove debound binder from a position continuously adjacent the debinding head. The debinding applicator optionally operates upon one or more part layers, but fewer than all part layers, at one time. The debinding head may a solvent nozzle (such as a spray or drip) that releases debinding fluid upon a part layer of green material, and/or a heat energy projector (such as a heat gun, or a laser) that projects heat energy upon a part layer of green material.
Optionally, the debinding applicator include may a debinding carriage that main scans a part layer at a time (e.g., sprays and/or heats across the width of a layer) to debind the debinder, and a portion of the fume extractor is transported together with the debinding carriage to remove debound binder from a position continuously adjacent the debinding carriage.
Further optionally, the debinding applicator may include a solvent bath into which the part is immersed and removed before subsequent part layer deposition by the print head.
Still further optionally, the print head may deposit part layers of model material upon prior deposited part layers that have not been debound by the debinding applicator as well as upon layers that have been debound by the debinding applicator.
According to another aspect of the embodiments of the present invention, a method of reducing distortion in an additively manufactured part may include forming a shrinking or densification linking platform of successive layers of composite, the composite including a metal particulate filler in a debindable matrix. The debindable matrix may include different components so as to be a one or two stage binder. Shrinking or densification linking supports are formed of the same composite above the shrinking platform. A desired part of the same composite is formed upon the shrinking platform and shrinking supports, substantially horizontal portions (e.g., overhangs, bridges, large radius arches) of the desired part being vertically supported by the shrinking platform (e.g., directly, via the shrinking supports, or via a release layer). A sliding release layer may be formed below the shrinking platform of equal or larger surface area than a bottom of the shrinking platform (e.g., as shown in
An apparatus of similar advantage may include a print head that deposits the shrinking platform, the shrinking supports, and the desired part, a second printhead that forms the sliding release layer, a debinding wash that debinds the shape-retaining brown part assembly, and a sintering oven to heat and shrink the shrinking platform, the shrinking supports, and the desired part together at a same rate. Optionally, an open cell structure including interconnections among cell chambers is deposited in at least one of the shrinking platform, the shrinking supports, and the desired part; and a fluid debinder is penetrated into the open cell structure to debind the matrix from within the open cell structure. Additionally, or alternatively, the shrinking platform, shrinking supports, and desired part may be formed to substantially align a centroid of the combined shrinking platform and connected shrinking supports with the centroid of the part. Further additionally or in the alternative, the shrinking supports may be interconnected to a side of the desired part by forming separable attachment protrusions of the same composite between the shrinking supports and the side of the desired part. Still further additionally or in the alternative, a lateral support shell may be formed of the same composite following a lateral contour of the desired part, and the lateral support shell may be connected to the lateral contour of the desired part by forming separable attachment protrusions of the same composite between the lateral support shell and the desired part.
Further optionally, soluble support structures of the debindable matrix may be formed, without the metal particulate filler, that resist downward forces during the forming of the desired part, and the matrix debound sufficient to dissolve the soluble support structures before heating the shape-retaining brown part assembly. Alternatively, or in addition, soluble support structures of a release composite may be formed, the release composite including a ceramic particulate filler and the debindable matrix, the soluble support structures resisting downward forces during the forming of the desired part. Before heating the shape-retaining brown part assembly, the matrix may be debound sufficient to form a shape-retaining brown part assembly including the shrinking platform, shrinking supports, and desired part, and to dissolve the matrix of the soluble support structures.
Additionally, or in the alternative, the underlying surface may include a portable build plate. In this case, the shrinking platform may be formed above the portable build plate, and the sliding release layer formed below the shrinking platform and above the portable build plate with a release composite including a ceramic particulate and the debindable matrix. The shape-retaining brown part assembly may be sintered during the heating. The build plate, sliding release layer, and shape-retaining brown part assembly may be kept together as a unit during the debinding and during the sintering. After sintering, the build plate, sliding release layer, shrinking platform, and shrinking supports may be separated from the desired part.
Optionally, part release layers may be formed between the shrinking supports and the desired part with a release composite including a ceramic particulate filler and the debindable matrix, and the shape-retaining brown part assembly sintered during the heating. The part release layers and shape-retaining brown part assembly may be kept together as a unit during the debinding and during the sintering. After sintering, separating the part release layers, shrinking platform, and shrinking supports may be separated from the desired part. In this case, an open cell structure including interconnections among cell chambers in the shrinking supports may be deposited, and a fluid debinder may be penetrated into the open cell structure to debind the matrix from within the open cell structure.
According to another aspect of the embodiments of the present invention, a method of reducing distortion in an additively manufactured part includes depositing, in successive layers, a shrinking platform formed from a composite, the composite including a metal particulate filler in a debindable matrix, and depositing shrinking supports of the same composite and above the shrinking platform. An open cell structure including interconnections is deposited among cell chambers in the shrinking supports. From the same composite, a desired part is deposited upon the shrinking platform and shrinking supports. The shrinking platform, shrinking supports, and desired part are exposed to a fluid debinder to form a shape-retaining brown part assembly. The fluid debinder is penetrated into the open cell structure to debind the matrix from within the open cell structure. The shape-retaining brown part assembly is sintered to shrink at a rate common throughout the shape-retaining brown part assembly.
Optionally, a sliding release layer is deposited below the shrinking platform of equal or larger surface area than a bottom of the shrinking platform that reduces lateral resistance between the shrinking platform and an underlying surface. Additionally, or in the alternative, part release layers are deposited between the shrinking supports and the desired part with a release composite including a ceramic particulate filler and the debindable matrix, and the part release layers and shape-retaining brown part assembly are kept together as a unit during the exposing and during the sintering. After sintering, the part release layers, shrinking platform, and shrinking supports are separated from the desired part. Further optionally, as shown in, e.g.,
Alternatively, or in addition, as shown in, e.g.,
Further optionally, as shown in, e.g.,
According to another aspect of the embodiments of the present invention, a method of reducing distortion in an additively manufactured part includes depositing, in successive layers, a shrinking platform formed from a composite, the composite including a metal particulate filler in a debindable matrix. Shrinking supports of the same composite may be deposited above the shrinking platform. As shown in, e.g.,
Optionally, one or more separation clearances are formed as vertical clearance separating neighboring support columns and extending for substantially an height of the neighboring support columns, and further comprising, and the neighboring support columns are separated from one another along the vertical clearances. Alternatively, or in addition, within a cavity of the desired part, interior shrinking supports are formed from the same composite. Among the interior shrinking supports, parting lines may be formed as separation clearances dividing the interior shrinking supports into subsection fragments separable along the separation clearances. The subsection fragments may be separated from one another along the separation clearances.
Alternatively, or in addition, the fragments are formed as blocks separable from one another along a separation clearance contiguous within a plane intersecting the shrinking supports. A lateral support shell of the same composite as the shrinking supports may be formed to follow a lateral contour of the desired part. Optionally, the lateral support shell may be connected to the lateral contour of the desired part by forming separable attachment protrusions of the same composite between the lateral support shell and the desired part. Further optionally, in the lateral support shell, parting lines may be formed dividing the lateral support shell into shell fragments separable along the parting lines. The matrix may be debound sufficient to form a shape-retaining brown part assembly including the shrinking platform, shrinking support columns, lateral support shell, and desired part. The lateral support shell may be separated into the shell fragments along the parting lines. The shell fragments may be separated from the desired part.
Further optionally, at least one of the shrinking platform, the shrinking supports, and the desired part may be deposited with interconnections between internal chambers, and a fluid debinder penetrated via the interconnections into the internal chambers to debind the matrix from within the open cell structure. Alternatively, or in addition, soluble support structures of the debindable matrix without the metal particulate filler may be formed that resist downward forces during the forming of the desired part, and the matrix debound sufficient to dissolve the soluble support structures before sintering the shape-retaining brown part assembly.
Still further optionally, a sliding release layer may be formed below the shrinking platform of equal or larger surface area than a bottom of the shrinking platform that reduces lateral resistance between the shrinking platform and build plate, and the shrinking platform may be formed above the portable build plate. The sliding release layer may be formed below the shrinking platform and above the portable build plate with a release composite including a ceramic particulate and the debindable matrix, the build plate, sliding release layers and shape-retaining brown part assembly may be kept together as a unit during the debinding and during the sintering.
Further alternatively or in addition, part release layers may be formed between the shrinking supports and the desired part with a release composite including a ceramic particulate filler and the debindable matrix, and the part release layers and shape-retaining brown part assembly may be kept together as a unit during the debinding and during the sintering. After sintering, the part release layers, shrinking platform, and shrinking supports may be separated from the desired part.
According to another aspect of the embodiments of the present invention, in a method for building a part with a deposition-based additive manufacturing system, a polymer-including material is deposited along a first contour tool path to form a perimeter path of a layer of the green part and to define an interior region within the perimeter path. In a second direction retrograde the first direction, the material is deposited based on a second contour tool path to form an adjacent path in the interior region adjacent the perimeter path. The deposition of the adjacent path in the second direction stresses polymer chains in the material in a direction opposite to stresses in polymer chains in the material in the perimeter path, and reduces part twist caused by relaxation of the polymer chains in the part.
Optionally, one of a start of deposition or a stop of deposition is adjusted to be located within the interior region of the layer. Further optionally, the locations of the start point and the stop point define an arrangement selected from the group consisting of an open-square arrangement, a closed-square arrangement, an overlapped closed-square arrangement, an open-triangle arrangement, a closed-triangle arrangement, a converging-point arrangement, an overlapped-cross arrangement, a crimped-square arrangement, and combinations thereof. Alternatively, or in addition, a contour tool path between the start point and the stop point further defines a raster path that at least partially fills the interior region.
According to another aspect of the embodiments of the present invention, in a method for building a part with a deposition-based additive manufacturing system having a deposition head and a controller, a first tool path for a layer of the part is received by the controller, wherein the received first tool path comprises a perimeter contour segment. A second tool path for a layer of the part is received by the controller, wherein the received second tool path comprises an interior region segment adjacent the perimeter contour segment. A deposition head is moved in a pattern that follows the perimeter contour segment of the received first tool path to produce a perimeter path of a debindable composite including sinterable powder; and moving the deposition head in a pattern that follows the interior region segment of the received second tool path to produce an interior adjacent path of the debindable composite, wherein the perimeter path and the adjacent path are deposited in directions so that directions of residual stress within a binder of the debindable composite are opposite in the perimeter path and the adjacent path.
According to still another aspect of the embodiments of the present invention, in a method for building a part with a deposition-based additive manufacturing system, a digital solid model (e.g., 3D mesh or 3D solid) of the part is received, and the digital solid model is sliced into a plurality of layers. A perimeter contour tool path is generated based on a perimeter of a layer of the plurality of layers, wherein the generated perimeter contour tool path defines an interior region of the layer. An interior adjacent path is generated based on the perimeter contour tool path within the interior region. A debindable composite is extruded including sinterable powder in a first direction based on the perimeter contour tool path to form a perimeter of the debindable composite for the layer. The debindable composite is extruded in a second direction based on the perimeter contour tool path to form an interior adjacent path of the debindable composite for the layer, wherein the deposition of the perimeter contour tool path and the interior adjacent path are traced in retrograde directions to one another so that directions of residual stress within a binder of the debindable composite are opposite in the perimeter contour tool path and the interior adjacent path. Optionally, a start point of the perimeter contour tool path and a stop point of the perimeter contour tool path are adjusted to locations within the interior region.
According to still another aspect of the embodiments of the present invention, in method for building a part with an deposition-based additive manufacturing system having a deposition head and a controller, a first tool path for a layer of the part is received by the controller, wherein the received first tool path comprises a contour segment. A second tool path for a layer of the part is received by the controller, and the received second tool path may overlap the first tool path over at least 90 percent of a continuous deposition length of the second tool path. The deposition head is moved in a pattern that follows the first tool path to produce a perimeter path of a debindable composite for the layer. The deposition head is moved in a pattern that follows the second tool path in a retrograde direction to the first tool path to produce a stress-offsetting path adjacent the perimeter path of debindable composite, such that directions of residual stress within a binder of the debindable composite are opposite in the perimeter path and the stress-offsetting path. Optionally, the second tool path is continuously adjacent at least 90 percent of the first tool path within the same layer, and comprises an interior region path. Further optionally, the second tool path is continuously adjacent over at least 90 percent of the first tool path within an adjacent layer, and comprises a perimeter path of the adjacent layer.
According to yet another aspect of the embodiments of the present invention, in a method for building a part with a deposition-based additive manufacturing system having an deposition head and a controller, a tool path is generated with a computer. Instructions for the generated tool path are transmitted to the controller, and a debindable composite is deposited from the deposition head while moving the deposition head along the generated tool path to form a perimeter path of a layer of the part. The perimeter path may include a first contour road portion, and a second contour road portion, each of the first contour road portion and the second contour road portion crossing one another with an even number of X-patterns, forming an even number of concealed seams for the layer.
According to yet another aspect of the embodiments of the present invention, in a method for building a part with a deposition-based additive manufacturing system having a deposition head and a controller, the deposition head is moved along a first tool path segment to form a perimeter road portion for a layer of the part, and is moved along a direction changing tool path segment. The deposition head may be moved along a second tool path segment to form a stress-balancing road portion adjacent to the perimeter road portion. Optionally, the direction changing tool path segment is a reflex angle continuation between the first tool path segment and the second tool path segment within the same layer. Further optionally, a debindable composite including a binder and a sinterable powder is deposited in a first direction about a perimeter. An interior path is deposited along the perimeter in a direction retrograde the first direction. The deposition of the adjacent path stresses long-chain molecules in the binder in a direction opposite to stresses in the perimeter path, and reduces part twist during sintering caused by relaxation of the long-chain molecules in the part.
According to yet another aspect of the embodiments of the present invention, in a method of depositing material for additive manufacturing, a composite material is fed including a binder matrix and a sinterable powder. Successive layers of a wall of a part are deposited to form a first access channel extending from an exterior of the part to an interior of the part. Successive layers of honeycomb infill in the interior of the part are deposited to form a distribution channel connecting an interior volume of the honeycomb infill to the first access channel. The binder matrix is debound (e.g., dissolved) by flowing a debinding fluid through the first access channel and the distribution channel within the interior volume of the honeycomb infill.
Optionally, successive layers of the wall of the part are deposited to form a second access channel extending from the exterior of the part to the interior of the part, and the binder matrix is debound by flowing a debinding fluid in through the first access channel, via the distribution channel, and out through the second access channel. Further optionally, the first access channel is connected to a pressurized supply of debinding fluid to force debinding fluid through the first access channel, distribution channel, and second access channel. Alternatively, or in addition, successive layers of honeycomb infill are deposited in the interior of the part to form a plurality of distribution channels connecting an interior volume of the honeycomb infill to the first access channel, at least some of the plurality of distribution channels being of different length from other of the distribution channels.
According to another aspect of the embodiments of the present invention, in a method of depositing material for additive manufacturing, a metal material including a binder matrix and sinterable powdered metal having an average particle diameter lower than 8 micrometers are fed, the metal material having a first sintering temperature. A ceramic material is fed including a same binder matrix and a sinterable powdered ceramic, the ceramic material including a mixture of a first ceramic having a higher sintering temperature than the metal material with a second ceramic having a lower sintering temperature than the metal material, the ceramic material substantially matching a shrinking behavior of the metal material and having a second sintering temperature substantially in a same range as the first sintering temperature. Layers of the metal material are formed by deposition upon a prior deposition of layers of the metal material, and layers of the metal material are formed by deposition upon prior deposition of layers of the ceramic material. At least a portion of the binder matrix is debound from each of the metal material and ceramic material. A part so formed from the metal material and ceramic material is heated to the first sintering temperature, thereby sintering the first material and the second material. Successive layers of a wall of a part are deposited to form a first access channel extending from an exterior of the part to an interior of the part, as well as to form a distribution channel connecting an interior volume of the honeycomb infill to the first access channel. A binder matrix retaining sinterable powder is debound by flowing a debinding fluid through the first access channel and the distribution channel within the interior volume of the honeycomb infill.
According to a further aspect of the embodiments of the present invention, in method of depositing material to form a sinterable brown part by additive manufacturing, a first filament feeding along a material feed path, the first filament including a binder matrix and sinterable spherized and/or powdered first material having a first sintering temperature. A green layer of first material is formed by deposition upon a brown layer of first material. At least a portion of the binder matrix is debound from each green layer of first material to debind each green layer into a corresponding brown layer. Following the formation of substantially all brown layers of the part, the part may be sintered at the first sintering temperature.
In an alternative, or in addition, in a method of depositing material to form a sinterable brown part by additive manufacturing, a first filament is fed including a binder matrix and sinterable spherized and/or powdered first material having a first sintering temperature. A second filament is fed including a second material having a second sintering temperature more than 300 degrees C. higher than the first sintering temperature. Layers of second material are formed by deposition upon a build plate or prior deposition of first or second material. Green layers of first material are formed by deposition upon prior deposition of a brown layer or second material, and at least a portion of the binder matrix from each green layer of first material is debound, to debind each green layer into a corresponding brown layer. Following the formation of substantially all brown layers of the part, the part may be sintered at the first sintering temperature but below the second sintering temperature, thereby sintering the first material without sintering the second material.
According to another aspect of the embodiments of the present invention, in a method of sintering a brown part article formed from a powdered sinterable material, a brown part integrally formed from a first powder having a first sintering temperature in a powder bed is placed within a crucible, the powder bed including a second powder having a second sintering temperature more than 300 degrees C. higher than the first sintering temperature. The second powder is agitated to fill internal cavities of the brown part. A weight of an unsupported portion of the brown part is continually resisted with the second powder. The brown part is sintered at the first temperature without sintering the second powder to form a sintered part. The sintered part is removed from the powder bed.
Optionally, the agitating includes fluidizing the second powder by flowing a pressurized gas into the bottom of the crucible. Alternatively, or in addition, the weight of an unsupported portion of the brown part is continually resisted with the second powder, at least in part by maintaining a buoyant force having an upward component in the fluidized second powder.
According to another aspect of the embodiments of the present invention, in a method of fabricating a 3D printed from a powdered sinterable material, a first filament is fed including a binder matrix and sinterable spherized and/or powdered first material having a first sintering temperature. A second filament is fed including a second material having a second sintering temperature more than 300 degrees C. higher than the first sintering temperature. Layers of second material are formed by deposition upon a build plate or a prior deposition of first or second material, and green layers of first material are formed by deposition upon prior deposition of a brown layer or second material. At least a portion of the binder matrix from each green layer of first material is debound, to debind each green layer into a corresponding brown layer. The part is placed integrally in a powder bed within a crucible, the powder bed including a third powder having a third sintering temperature more than 300 degrees C. higher than the first sintering temperature. The third powder is agitated to fill internal cavities among the brown layers, and a weight of an unsupported portion of the brown layers is continually resisted with the third powder. The part is sintered at the first temperature without sintering the third powder to form a sintered part, and the sintered part is removed from the powder bed.
According to another aspect of the embodiments of the present invention, in a method for additive manufacturing, a material is supplied containing a removable binder and greater than 50% volume fraction of a powdered metal having a melting point greater than 1200 degrees C., in which more than 50 percent of powder particles of the powdered metal have a diameter less than 10 microns. The material is additively depositing in successive layers to form a green body, and the binder is then removed to form a brown body. The brown part or body is loaded into a fused tube formed from a material having an operating temperature less than substantially 1200 degrees C., a thermal expansion coefficient lower than 1×10-6/° C. and a microwave field penetration depth of 10 m or higher. The fused tube is sealed and internal air is replaced with a sintering atmosphere. Microwave energy is applied outside the sealed fused tube to the brown part. The brown part is sintered a temperature lower than 1200 degrees C.
According to a further aspect of the embodiments of the present invention, in a method for additive manufacturing, a material is supplied containing a removable binder and greater than 50% volume of a powdered metal having a melting point greater than 1200 degrees C., in which more than 50 percent of the powder particles have a diameter less than 10 microns. The material is additively deposited with a nozzle having an internal diameter smaller than 300 microns. The binder is removed to form a brown body or part. The brown part or body is loaded into a fused tube formed from a material having a thermal expansion coefficient lower than 1×10-6/° C. The fused tube is sealed, and internal air replaced with a sintering atmosphere. Radiant energy is applied from outside the sealed fused tube to the brown part. The brown part or body is sintered at a temperature higher than 500 degrees C. but less than 1200 degrees C.
According to a further aspect of the embodiments of the present invention, in a method for additive manufacturing, a first brown part may be supplied formed from a first debound material including a first powdered metal, in which more than 50 percent of powder particles of the first powdered metal have a diameter less than 10 microns. A second brown part may be supplied formed from a second debound material including a second powdered metal, in which more than 50 percent of powder particles of the second powdered metal have a diameter less than 10 microns. In a first mode, the first brown part may be loaded into a fused tube formed from a material having a thermal expansion coefficient lower than 1×10-6/° C., and a temperature inside the fused tube may be ramped at greater than 10 degrees C. per minute but less than 40 C degrees C. per minute to a first sintering temperature higher than 500 degrees C. and less than 700 degrees C. In a second mode, the second brown part may be loaded into the same fused tube, and a temperature inside the fused tube may be ramped at greater than 10 degrees C. per minute but less than 40 degrees C. per minute to a second sintering tempering temperature higher than 1000 degrees C. but less than 1200 degrees C.
Optionally, in the first mode, a first sintering atmosphere is introduced into the fused tube including inert Nitrogen being 99.999% or higher free of Oxygen. Further optionally, in the second mode, a second sintering atmosphere comprising at least 2%-5% (e.g., 3%) Hydrogen may be introduced into the fused tube. Optionally, the fused tube is formed from a fused silica having a microwave field penetration depth of 10 m or higher, and microwave energy is applied to the first and/or second material brown parts within the fused tube, raising the temperature of same. Microwave energy may alternatively, or in addition applied to, to raising the temperature of, susceptor material elements placed outside the fused tube and outside any sintering atmosphere within the fused tube.
In these aspects, optionally, the material is additively deposited at a layer height substantially ⅔ or more of the nozzle width. Optionally, a material is supplied in which more than 90 percent of powder particles of the powdered metal have a diameter less than 8 microns. Further optionally, microwave energy is applied from outside the sealed fused tube to susceptor material members arranged outside the sealed fused tube. Microwave energy may be the radiant energy applied from outside the sealed fused tube to the brown part. Susceptor material members arranged outside the sealed fused tube may be resistively heated. Optionally, a temperature inside the fused tube may be ramped at greater than 10 degrees C. per minute but less than 40 degrees C. per minute. The material of the fused tube may be amorphous fused silica, and the sintering atmosphere may comprise at least 2% Hydrogen and no more than 5% Hydrogen (e.g., 3% Hydrogen). The powdered metal may be a stainless steel or a tool steel. The susceptor material may be one of SiC or MoSi2.
According to an additional aspect of the embodiments of the present invention, a multipurpose sintering furnace, includes a fused tube formed from a fused silica having a thermal expansion coefficient lower than 1×10-6/° C., and a seal that seals the fused tube versus ambient atmosphere. An internal atmosphere regulator is operatively connected to an interior of the fused tube to apply vacuum to remove gases within the fused tube and to introduce a plurality of sintering atmospheres into the fused tube, and heating elements are placed outside the fused tube and outside any sintering atmosphere within the fused tube. A controller is operatively connected to the heating elements and the internal atmosphere regulator, the controller in a first mode sintering first material brown parts within a first sintering atmosphere at first sintering temperature higher than 500 degrees C. and less than 700 degrees C., and in a second mode sintering second material brown parts within a second sintering atmosphere at a second sintering temperature higher than 1000 degrees C. but less than 1200 degrees C.
Optionally, the internal atmosphere regulator is operatively connected to an interior of the fused tube to introduce a first sintering atmosphere comprising inert Nitrogen being 99.999% or higher free of Oxygen. Further optionally, the controller in the first mode sinters brown parts primarily formed with Aluminum powder in which more than 50 percent of powder particles have a diameter less than 10 microns, within the first sintering atmosphere comprising inert Nitrogen being 99.999% or higher free of Oxygen, at the first sintering temperature higher than 500 degrees C. and less than 700 degrees C. Alternatively, or in addition, the controller in the second mode sinters brown parts primarily formed with Steel powder in which more than 50 percent of powder particles have a diameter less than 10 microns, within the second sintering atmosphere comprising at least 3% Hydrogen, at the second sintering temperature higher than 1000 degrees C. and less than 1200 degrees C.
The controller may ramp a temperature inside the fused tube at greater than 10 degrees C. per minute but less than 40 degrees C. per minute. The internal atmosphere regulator may be operatively connected to an interior of the fused tube to introduce a second sintering atmosphere comprising at least 3% Hydrogen. The controller may ramping a temperature inside the fused tube at greater than 10 degrees C. per minute but less than 40 degrees C. per minute. The fused silica tube may be formed from a fused silica having a thermal expansion coefficient lower than 1×10-6/° C. and a microwave field penetration depth of 10 m or higher, and wherein the heating elements further comprise a microwave generator that applies energy to, and raises the temperature of, the first and/or second material brown parts within the fused tube. Susceptor material heating elements may be placed outside the fused tube and outside any sintering atmosphere within the fused tube, wherein the microwave generator applies energy to, and raises the temperature of, one or both of (i) the first and/or second material brown parts within the fused tube and/or (ii) the susceptor material heating elements. The heating elements further comprise susceptor material heating elements placed outside the fused tube and outside any sintering atmosphere within the fused tube. A small powder particle size (e.g., 90 percent of particles smaller than 8 microns) of metal powder embedded in additively deposited material may lower a sintering temperature of stainless steels to below the 1200 degree C. operating temperature ceiling of a fused silica tube furnace, permitting the same silica fused tube furnace to be used for sintering both aluminum and stainless steel (with appropriate atmospheres), as well as the use of microwave heating, resistant heating, or passive or active susceptor heating to sinter both materials.
According to an another aspect of the embodiments of the present invention, in a composite material including >50% metal or ceramic spheres, and optionally with a two stage binder, a spool of filament material is wound and unwound at a temperature higher than room temperature but less than a glass transition temperature of a binder material, e.g., 50-55 degrees Celsius. It may be transported in at room temperature. Upper spools in a model material chamber may include the model material and the release material. The spools may be kept in a joint heated chamber which keeps the spools at the 50-55 degrees Celsius contemplated by this example. A build plate may be heated by a build plate heater to similar or higher temperature (e.g., 50-120 degrees C.) during printing. The heating of the build plate may help maintains the temperature within the printing compartment at a level above room temperature.
Optionally, each spool of material may be kept in its own independent chamber. A heater for maintaining the spool temperature may be passive, e.g., radiant and convection heater, or include a blower. Heated air may be driven through Bowden tubes or other transport tubes through which the filament material is driven. The spools may be vertically arranged on a horizontal axle, and the filament dropped substantially directly down to the moving printing heads so as to have a large bend radius in all bends of the filament. The material may be maintained with no bend more of smaller than a 10 cm bend radius, and/or no bend radius substantially smaller than that of the spool radius).
According to an another aspect of the embodiments of the present invention, in a method for 3D printing green parts, a binder is jetted onto successive layers of powder feedstock to form a 2D layer shape of bound powder per layer. A 3D shape is additively deposited (e.g., built up) of a desired 3D green part from interconnected 2D layer shapes of the bound powder. A 3D shape of sintering supports is additively deposited (e.g., built up) from interconnected 2D layer shapes of the bound powder, and a 3D shape of a shrinking platform is additively deposited (e.g., built up) from interconnected 2D layer shapes of the bound powder. A release material is additively deposited (e.g., built up) upon shapes of bound powder to form 2D layer shapes of release material, and a 3D shape of release surfaces additively deposited (e.g., built up) from interconnected 2D layer shapes of the release material. A placeholder material is additively deposited (e.g., built up) upon shapes of bound powder to form 2D layer shapes of placeholder material, and a 3D shape of placeholder volumes is additively deposited (e.g., built up) from interconnected 2D layer shapes of the placeholder material. The bound powder, release material, and placeholder material are debound to form a green part assembly including the desired 3D green part, the sintering supports, the release surfaces, and internal cavities corresponding to the 3D shapes of the placeholder material before debinding.
According to this aspect, for 3D printing green parts to be debound and sintered, a binder may be jetted into successive layers of sinterable powder feedstock to build up a 3D shape of a desired 3D green part, associated sintering supports, and an associated shrinking platform. A release material may be deposited to intervene between the 3D green parts and the sintering supports. A placeholder material may be deposited upon bound powder to form 2D layer shapes of placeholder material, and the sinterable powder feedstock refilled and leveled about the placeholder material. Upon debinding, internal cavities corresponding to the 3D shapes of the placeholder material are formed.
According to an another aspect of the embodiments of the present invention, an apparatus for additive manufacturing by depositing sinterable powdered metal in a soluble binder include a nozzle assembly, including a nozzle body within which is formed a first central cylindrical cavity of substantially constant diameter and a nozzle outlet connected to the cylindrical cavity, the nozzle outlet being of 0.1-0.4 mm diameter. A heat break member abuts the nozzle assembly, the heat break member including a heat break body having a narrowed waist portion, a second central cylindrical cavity of substantially constant diameter being formed through the heat break body and narrowed waist portion. A melt chamber is formed shared by the first and second central cylindrical cavity, the melt chamber being of 15-25 mm̂3 volume and 1 mm or less in diameter.
According to an another aspect of the embodiments of the present invention, a 3D printer may deposit, from the powdered metal (or ceramic) and binder composites discussed herein, a densification linking platform that is equal to or larger than a lateral or horizontal extent of a desired part, e.g., a minimum size that corresponds to the envelope of the part, at least partially separated from the part by a ceramic release layer. The thickness of the densification linking platform should be at least ½ mm-10 mm thick such that the forces developed during the shrinking process from atomic diffusion in the raft substantially counteract the friction force between the brown body assembly and a plate or carrier upon which sintering is performed. The desired part may be optionally tacked to the densification linking platform with small-cross sectional area (e.g., less than ⅓ mm diameter) connections of the metal composite material that penetrate the ceramic release layer vertically in order to ensure that the part shrinks in the same geometric manner as the densification linking platform that it is resting on. The densification linking platform is optionally formed having a cross-sectional area in the shape of a convex shape (a polygon or curved shape without concavities), and/or in a symmetric shape having a centroid aligned with that of the part above. The densification linking platform tends to densify and shrink in a regular or predictable manner due to its simple geometry, and if as the desired part is connected to the raft it decreases geometry specific part distortion that arises from the friction forces between the desired part and the densification linking platform, especially in the case of asymmetric parts, parts with high aspect ratio cross sections, and parts with variable thicknesses. The number and placement of tack points between the part and the raft may be selected such that the raft can be suitably removed after the sintering process. Optionally, vertical walls outside the perimeter of the part that are solidly attached to the densification linking may extend at least partially up the sides of the desired part to further reduce distortion. These vertical supports may also be separated from the desired by the ceramic release layer.
It is expressly contemplated that the foregoing examples of aspects of embodiments of the present invention, when combined individually or in multiple combinations, form additional examples of aspects of embodiments of the present invention.
At least one aspect of the invention is directed to a method for additive manufacturing, the method comprising supplying a first brown part formed from a first debound material including a first powdered metal, in which more than 50 percent of powder particles of the first powdered metal have a diameter less than 10 microns, supplying a second brown part formed from a second debound material including a second powdered metal, in which more than 50 percent of powder particles of the second powdered metal have a diameter less than 10 microns, in a first mode, loading the first brown part into a fused tube formed from a material having a thermal expansion coefficient lower than 1×10-6/° C., and ramping a temperature inside the fused tube at greater than 10 degrees C. per minute but less than 40 degrees C. per minute to a first sintering temperature higher than 500 degrees C. and less than 700 degrees C., and in a second mode, loading the second brown part into the fused tube, and ramping the temperature inside the fused tube at greater than 10 degrees C. per minute but less than 40 degrees C. per minute to a second sintering tempering temperature higher than 1000 degrees C. but less than 1200 degrees C.
According to one embodiment, the method further comprises, in the first mode, introducing into the fused tube a first sintering atmosphere comprising inert Nitrogen being 99.999% or higher free of Oxygen. In one embodiment, the method further comprises, in the second mode, introducing into the fused tube a second sintering atmosphere comprising at least 3% Hydrogen.
According to another embodiment, the fused tube is formed from a fused silica having a microwave field penetration depth of 10 m or higher, and the method further comprises applying microwave energy to, and raising the temperature of, the first and/or second brown parts within the fused tube. In one embodiment, the method further comprises applying microwave energy to, and raising the temperature of, susceptor material elements placed outside the fused tube and outside any sintering atmosphere within the fused tube.
According to one embodiment, the method further comprises additively depositing the first brown part with a nozzle having an internal diameter smaller than 300 microns. In one embodiment, the method further comprises additively depositing the first brown part at a layer height substantially ⅔ or more of an internal diameter of the nozzle. In another embodiment, more than 90 percent of the powder particles of the second powdered metal have a diameter less than 8 microns. In one embodiment, the material of the fused tube is amorphous fused silica.
Another aspect of the invention is directed to a multipurpose sintering furnace comprising a fused tube formed from a fused silica having a thermal expansion coefficient lower than 1×10-6/° C., a seal configured to seal the fused tube versus ambient atmosphere, an internal atmosphere regulator operatively connected to an interior of the fused tube and configured to apply vacuum to remove gases within the fused tube and to introduce a plurality of sintering atmospheres into the fused tube, heating elements placed outside the fused tube and outside any sintering atmosphere within the fused tube, and a controller operatively connected to the heating elements and the internal atmosphere regulator, the controller configured to operate the heating elements and the internal atmosphere regulator, in a first mode, to sinter first brown parts, formed from a first material, within a first sintering atmosphere at a first sintering temperature higher than 500 degrees C. and less than 700 degrees C., and in a second mode, to sinter second brown parts, formed from a second material, within a second sintering atmosphere at a second sintering temperature higher than 1000 degrees C. but less than 1200 degrees C.
According to one embodiment, the internal atmosphere regulator is further configured to introduce the first sintering atmosphere comprising inert Nitrogen being 99.999% or higher free of Oxygen.
According to another embodiment, the controller is further configured to operate the heating elements and the internal atmosphere regulator, in the first mode, to sinter the first brown parts, primarily formed with Aluminum powder in which more than 50 percent of the powder particles have a diameter less than 10 microns, within the first sintering atmosphere comprising inert Nitrogen being 99.999% or higher free of Oxygen, at the first sintering temperature higher than 500 degrees C. and less than 700 degrees C. In one embodiment, the controller is further configured to operate the heating elements to ramp a temperature inside the fused tube at greater than 10 degrees C. per minute but less than 40 degrees C. per minute. In another embodiment, the internal atmosphere regulator is further configured to introduce the second sintering atmosphere comprising at least 3% Hydrogen.
According to one embodiment, the controller is further configured to operate the heating elements and the internal atmosphere regulator, in the second mode, to sinter the second brown parts, primarily formed with Steel powder in which more than 50 percent of powder particles have a diameter less than 10 microns, within the second sintering atmosphere comprising at least 3% Hydrogen, at the second sintering temperature higher than 1000 degrees C. and less than 1200 degrees C. In one embodiment, the controller is further configured to operate the heating elements to ramp a temperature inside the fused tube at greater than 10 degrees C. per minute but less than 40 degrees C. per minute.
According to another embodiment, the fused silica tube is formed from a fused silica having a thermal expansion coefficient lower than 1×10-6/° C. and a microwave field penetration depth of 10 m or higher, and the heating elements further comprise a microwave generator that is configured to apply energy to, and raise the temperature of, the first and/or second brown parts within the fused tube. In one embodiment, the method further comprises susceptor material heating elements placed outside the fused tube and outside any sintering atmosphere within the fused tube, wherein the heating elements further comprise a microwave generator that is configured to apply energy to, and raise the temperature of, one or both of (i) the first and/or second brown parts within the fused tube and/or (ii) the susceptor material heating elements. In one embodiment, the heating elements further comprise susceptor material heating elements placed outside the fused tube and outside any sintering atmosphere within the fused tube.
This patent application incorporates the following disclosures by reference in their entireties: U.S. Patent Application Ser. Nos. 61/804,235; 61/815,531; 61/831,600; 61/847,113; 61/878,029; 61/880,129; 61/881,946; 61/883,440; 61/902,256; 61/907,431; and 62/080,890; 14/222,318; 14/297,437; and Ser. No. 14/333,881, may be referred to herein as “Composite Filament Fabrication patent applications” or “CFF patent applications”. Although the present disclosure discusses various metal or ceramic 3D printing systems, at least the mechanical and electrical motion, control, and sensor systems of the CFF patent applications may be used as discussed herein. In addition, U.S. Pat. Nos. 6,202,734; 5,337,961; 5,257,657; 5,598,200; 8,523,331; 8,721,032, and U.S. Patent Publication No. 20150273577, are incorporated herein by reference in their entireties. Further, U.S. Patent Application Nos. 62/429,711, filed Dec. 2, 2016; 62/430,902, filed Dec. 6, 2016; 62/442,395, filed Jan. 4, 2017; 62/480,331, filed Mar. 31, 2017; 62/489,410, filed Apr. 24, 2017; 62/505,081, filed May 11, 2017; 62/519,138, filed Jun. 13, 2017; 62/545,966, filed Aug. 15, 2017; 62/575,219, filed Oct. 20, 2017; and Ser. No. 15/722,445, filed Oct. 2, 2017 include related subject matter and are incorporated herein by reference in their entireties.
In 3D printing, in general, overhanging or jutting portions of a part may require removable and/or soluble and/or dispersing supports underneath to provide a facing surface for deposition. In metal printing, in part because metal is particularly dense (e.g., heavy), removable and/or soluble and/or dispersing supports may also be helpful to prevent deformation, sagging, during mid- or post-processing—for example, to preserve shape vs. drooping or sagging in potentially deforming environments like high heat.
Printing a sinterable part using a 3D printing material including a binder and a ceramic or metal sintering material is aided by support structures that are able to resist the downward pressure of, e.g., extrusion, and locate the deposited bead or other deposition in space. A release layer intervening between the support structures and the part includes a higher melting temperature material—ceramic or high temperature metal, for example, optionally deposited with a similar (primary) matrix or binder component to the model material. The release layer does not sinter, and permits the part to “release” from the supports. Beneath the release layer, the same model material as the part is used for the support structures, promoting the same compaction/densification during sintering. This tends to mean the part and the supports will shrink uniformly, maintaining dimensional accuracy of the part. At the bottom of the support, a release layer may also be printed. In addition, the support structures may be printed in sections with release layers between the sections, such that the final sintered support structures will readily break into smaller subsections for easy removal, optionally in the presence of mechanical or other agitation. In this way, a large support structure can be removed from an internal cavity via a substantially smaller hole. In addition, or in the alternative, a further method of support is to print soluble support material that is removed in the debinding process. For catalytic debind, this may be Delrin (POM) material.
One method to promote uniform shrinking or densification is to print a ceramic release layer as the bottom most layer in the part. On top of the sliding release layer (analogous to microscopic ball bearings) a thin sheet of metal—e.g., a raft—may be printed that will uniformly shrink with the part, and provide a “shrinking platform” or “densification linking” platform to hold the part and the related support materials in relative position during the shrinking or densification process. Optionally staples or tacks, e.g., attachment points, connect and interconnect (or link as densification linking) the model material portions being printed.
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A long or continuous fiber reinforced composite filament is fully optional, and when used, is fed, dragged, and/or pulled through a conduit nozzle optionally heated to a controlled temperature selected for the matrix material to maintain a predetermined viscosity, force of adhesion of bonded ranks, melting properties, and/or surface finish. After the matrix material or polymer of the fiber reinforced filament is substantially melted, the continuous core reinforced filament is applied onto a build platen 16 to build successive layers of a part 14 to form a three dimensional structure. The relative position and/or orientation of the build platen 16 and print heads 18, 18a, 18b, and/or 10 are controlled by a controller 20 to deposit each material described herein in the desired location and direction. A driven roller set 42, 40 may drive a continuous filament along a clearance fit zone that prevents buckling of filament. In a threading or stitching process, the melted matrix material and the axial fiber strands of the filament may be pressed into the part and/or into the swaths below, at times with axial compression. As the build platen 16 and print head(s) are translated with respect to one another, the end of the filament contacts an ironing lip and be subsequently continually ironed in a transverse pressure zone to form bonded ranks or composite swaths in the part 14.
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All of the printed structures previously discussed may be embedded within a printed article during a printing process, as discussed herein, expressly including reinforced fiber structures of any kind, sparse, dense, concentric, quasi-isotropic or otherwise as well as fill material (e.g., including model material and release material) or plain resin structures. In addition, in all cases discussed with respect to embedding in a part, structures printed by fill material heads 18, 18a, 18b using thermoplastic extrusion deposition may be in each case replaced with soluble material (e.g., soluble thermoplastic or salt) to form a soluble preform which may form a printing substrate for part printing and then removed. All continuous fiber structures discussed herein, e.g., sandwich panels, shells, walls, reinforcement surrounding holes or features, etc., may be part of a continuous fiber reinforced part. The 3D printer herein discussed with reference to
Commercially valuable metals suitable for printing include aluminum, titanium and/or stainless steel as well as other metals resistant to oxidation at both high and low temperatures (e.g., amorphous metal, glassy metal or metallic glass). One form of post-processing is sintering. By molding or 3D printing model material as described herein, a green body may be formed from an appropriate material, including a binder or binders and a powdered or spherized metal or ceramic (of uniform or preferably distributed particle or sphere sizes). A brown body may be formed from the green body by removing one or more binders (e.g., using a solvent, catalysis, pyrolysis). The brown body may retain its shape and resist impact better than the green body due to remelting of a remaining binder. In other cases the brown body may retain its shape but be comparatively fragile. When the brown body is sintered at high temperature and/or pressure, remaining or second stage binder may pyrolyse away, and the brown body substantially uniformly contracts as it sinters. The sintering may take place in an inert gas, a reducing gas, a reacting gas, or a vacuum. Application of heat (and optionally) pressure eliminates internal pores, voids and microporosity between and within the metal or ceramic beads through at least diffusion bonding and/or atomic diffusion. Supporting material, either the same or different from model material, supports the part being printed, post-processed, or sintered versus the deposition force of printing itself (e.g., green body supports) and/or versus gravity (e.g., green body supports or sintering supports), particularly for unsupported straight or low-angle spans or cantilevers.
Printing a part is aided by the support structures, able to resist the downward pressure of, e.g., extrusion, and locate the deposited bead or deposition in space. As discussed herein a release layer includes a higher melting temperature or sintering temperature powdered material—ceramic for example, optionally deposited in or via a similar (primary) matrix component to the model material. Beneath the release layer, the same (metal) material is used as the part, promoting the same compaction/densification. This tends to mean the part and the supports will shrink uniformly, maintaining overall dimensional accuracy of the part. At the bottom of the sintering support, a release layer may also be printed. In addition, the sintering support structures may be printed sections with release layers, such that the final sintered support structures will readily break into smaller subsections for easy removal, optionally in the presence of mechanical or other agitation. In this way, a large support structure can be removed from an internal cavity via a substantially smaller hole. In addition, or in the alternative, a further method of support is to print soluble support material that is removed in the debinding process. For catalytic debind, this may be Delrin (POM) material. One method to promote uniform shrinking is to print a ceramic release layer as the bottom most layer in the part. On top of the sliding release layer (analogous to microscopic ball bearings) a thin sheet of metal—e.g., a raft—may be printed that will uniformly shrink with the part, and provide a “shrinking platform” or “densification linking platform” to hold the part and the related support materials in relative position during the shrinking or densification process. Optionally staples or tacks, e.g., attachment points, connect and interconnect the model material portions being printed.
As noted, in one example, green body supports may be printed from a thermal, soluble, pyrolytic or catalytically responsive material (e.g., polymer or polymer blend) and leave behind only removable byproducts (gases or dissolved material) when the green body supports are removed. In another example, green body supports may optionally be printed from a matrix of thermal, soluble, or catalytic debindable composite material (e.g., catalytic including Polyoxymethylene—POM/acetal) and high melting point metal (e.g., molybdenum) or ceramic spheres, and leave behind a powder when debound. The green body supports may be formed to be mechanically or chemically or thermally removed before or after debinding, but preferably are also made from thermal, soluble, pyrolytic or catalytically responsive material, and may be fully removed during the debinding stage (or immediately thereafter, e.g., subsequent powder cleaning to remove remainder powder). In some cases, the green body supports are removed by a different chemical/thermal process from the debinding, before or after debinding.
An exemplary catalytically debindable composite material including POM or acetal is one example of a two-stage debinding material. In some cases, in a two-stage debinding material, in a first stage a first material is removed, leaving interconnected voids for gas passage during debinding. The first material may be melted out (e.g., wax), catalytically removed (e.g., converted directly into gas in a catalytic surface reaction), or dissolved (in a solvent). A second stage binder, e.g., polyethylene, that is not as responsive to the first material process, remains in a lattice-like and porous form, yet maintaining the shape of the 3D printed object awaiting sintering (e.g., before the metal or ceramic balls have been heated to sufficient temperature to begin the atomic diffusion of sintering). This results in a brown part, which includes, or is attached to, the sintering supports. As the part is sintered at high heat, the second stage binder may be pyrolysed and progressively removed in gaseous form.
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“Tacked” sintering supports, in contrast, may be similarly formed from the model material, i.e., the same composite material as the part, but may connect to the part either by penetrating the release layer or without a release layer. The tacked sintering supports are printed to be contiguous with the part, via thin connections, i.e., “tacked” at least to the part. The tacked sintering supports may in the alternative, or in addition, be printed to be contiguous with a raft below the part that interconnects the part and the supports with model material. The raft may be separated from a build plate of a 3D printer by a layer or layers of release layer material.
A role of tacked and untacked of sintering supports is to provide sufficient supporting points versus gravity to prevent, or in some cases remediate, sagging or bowing of bridging, spanning, or overhanging part material due to gravity. The untacked and tacked sintering supports are both useful. Brown bodies, in the sintering process, may shrink by atomic diffusion, e.g., uniformly about the center of mass or centroid of the part. In metal sintering and some ceramics, typically this is at least in part solid-state atomic diffusion. While there may be some cases where diffusion-based mass transport among the many interconnected metal/ceramic spheres does not transport sufficient material to, e.g., maintain a very thin bridge joining large masses, this is not necessarily the case with supports, which may be contiguously formed connected at only one end as a one-ended bridge (or connected at two ends as two-ended bridges; or interconnected over the length).
In those cases where tacked sintering supports are tacked to, or connected to, or linked to, a model material raft or shrinking platform or densification linking platform upon which the part is printed, the interconnection of model material among the tacked sintering supports and the raft can be arranged such that the centroid of the raft-supports contiguous body is at or near the same point in space as that of the part, such that the part and the raft-support contiguous to the part each shrink during sintering uniformly and without relative movement that would move the supports excessively with respect to the part. In other cases, the part itself may also be tacked to the model material raft, such that the entire contiguous body shrinks about a common centroid. In another variation, the part is interconnected to the raft via tacked sintering supports tacked at both ends (e.g., to the raft and to the part) or and/along their length (e.g., to the part and/or to each other).
In other cases, untacked sintering supports may be confined within a volume and contiguous with the raft and/or the part, the volume formed from model material, such that they may shrink about their own centroids (or interconnected centroid) but are continually moved through space and kept in a position supporting the part by the surrounding model material. For example, this may be effective in the case of the internal volume V2 of
In the alternative, or in addition, support or support structures or shells may be formed from model material following the form of the part in a lateral direction with respect to gravity, e.g., as shown in certain cases in
Any of the support structures discussed herein—e.g., tacked or untacked sintering supports, and/or support shells, may be printed with, instead of or in addition to intervening separation material, a separation clearance or gap (e.g., 5-100 microns) between the part and support structure (both being formed from model material). In this manner, individual particles or spheres of the support structure may intermittently contact the part during sintering, but as the separation clearance or gap is preserved in most locations, the support structures are not printed with compacted, intimate support with the part. When and if bonding diffusion occurs at intermittently contacting particles, the separation force required to remove the separation clearance support structures after sintering may be “snap-away” or “tap-away”, and in any case far lower than an integral or contiguous extension of the part. Larger separation clearances or gaps (e.g., 200-300 microns) may permit debinding fluid to penetrate and/or drain.
In an alternative, separation gaps or clearances between the part and support structures may be placed in partial segments following the contour, with some of the remainder of the support structures following the e.g., lateral contour of the part more closely or more distantly, or both. For example, support structures may be printed with a small separation gap (5-100 microns) for the majority of the support structure, but with other sections partially substantially following the contour printed yet closer to the part (e.g., 1-20 microns) providing increased rigidity and support during sintering, yet generally over a set of limited contact areas (e.g., less than 5% of contact area), permitting removal. This may also be carried out with large and medium gaps (e.g., 100-300 microns separation for the larger clearance support structures, optionally with separation material intervening, and 5-100 microns for the more closely following support structures). Further, this may be carried out in three or more levels (e.g., 100-300 micron gaps, 5-100 micron gaps, and 1-20 micron gaps in different portions of the support structures following the contour of the part).
Optionally, the sintering support structures may include a following shell with an inner surface generally offset from the e.g., lateral part contour by a larger (e.g., 5-300 microns) gap or clearance, but will have protrusions or raised ridges extending into the gap or clearance to and separated by the smaller gap (e.g., 1-20 microns), or extending across the gap or clearance, to enable small point contacts between the part and support structures formed from the same (or similar) model material. Point contacts may be easier to break off after sintering than compacted, intimate contact of, e.g., a following contour shell. Optionally, a neat matrix (e.g., green body supports formed from one or more of the binder components) support structure may be printed between model material (e.g., metal) parts and model material (e.g., metal) support structures to maintain the shape of the part and structural integrity during the green and brown states, reducing the chance of cracking or destruction in handling.
While several of the Figures are shown in side, cross section view,
In the case of complex geometries, as noted above, support structures may be printed with parting lines, sectioned into smaller subsections (e.g., as PL-1 in
In some cases, particularly in the case of a small number of parting lines (e.g., halves, thirds, quarters) the support structures, at least because they are form following structures, may be preserved for later use as a workholding fixture, e.g. soft jaws, for holding a sintered the part in secondary operations (such as machining). For example, if a support structure were to support a generally spherical part, a support structure suitable for later use as a workholding jaw or soft jaw, the structure should retain the part from all sides, and therefore extend past the center or half-way point of the sphere. For the purposes of sintering and supporting vs. gravity, the support structure need not extend past the halfway point (or slightly before), but for the purposes of subsequent workholding for inspection and post processing, the support structure would continue past the half way point (e.g. up to ⅔ of the part's height, and in some cases overhanging the part) enabling positive grip in, e.g., a vise.
Further, attachment features to hold the workholding fixture(s) or soft jaw(s) in a vise (or other holder) may be added to the support structure for the purpose of post processing, e.g., through holes for attachment to a vise, or dovetails, or the like. Alternatively, or in addition, a ceramic support may be printed, and sintered, to act as a reusable support for the sintering step of many 3D printed parts. In this case, upwardly facing surfaces of the reusable support may be printed to shrink to the same height as the matching or facing surface of the part being supported.
As discussed herein, a feedstock material for forming the part and/or the sintering supports may include approximately 50-70% (preferably approx. 60-65%) volume fraction secondary matrix material, e.g., (ceramic or metal) substantially spherical beads or powder in 10-50 micron diameter size, approximately 20-30% (preferably approx. 25% volume fraction of soluble or catalysable binder, (preferably solid at room temperature), approximately 5-10% (preferably approx. 7-9%) volume fraction of pyrolysable binder or primary matrix material, (preferably solid at room temperature), as well as approximately 0.1-15% (preferably approx. 5-10%) volume fraction of carbon fiber strands, each fiber strand coated with a metal that does not react with carbon at sintering temperatures or below (e.g., nickel, titanium boride). As discussed herein, the “primary matrix” is the polymer binder and is deposited by the 3D printer, holding the “secondary matrix” beads or spheres and the fiber filler; and following sintering, the (ceramic or metal) material of the beads or spheres becomes the matrix, holding the fiber filler.
Alternatively, a feedstock material for forming the part and/or the sintering supports may include approximately 50-70% (preferably approx. 60-65%) volume fraction secondary matrix material, e.g., (ceramic or metal) substantially spherical beads or powder in 10-50 micron diameter size, approximately 20-30% (preferably approx. 25% volume fraction of soluble or catalysable binder, (preferably solid at room temperature), approximately 5-10% (preferably approx. 7-9%) volume fraction of a pyrolysable binder or secondary matrix material approximately 1/10- 1/200 the elastic modulus of the (ceramic or metal) secondary matrix material, and approximately 0.1-15% (preferably approx. 5-10%) volume fraction of particle or fiber filler of a material approximately 2-10 times the elastic modulus of the secondary, (metal or ceramic) matrix material. As discussed herein, the “primary matrix” is the polymer binder and is deposited by the 3D printer, holding the “secondary matrix” beads or spheres and the fiber filler; and following sintering, the (ceramic or metal) material of the beads or spheres becomes the matrix, holding the particle of fiber filler.
A comparison of elastic modulus may be found in the following table, with polymer/binder primary matrices of 1-5 GPa elastic modulus
The spheres, beads or powder (e.g., particulate) may be a range of sizes. A binder may include dispersant, stabilizer, plasticizer, and/or inter-molecular lubricant additive(s). Some candidate secondary matrix-filler combinations that may be deposited by a 3D printer within a binder or polymer primary matrix include cobalt or bronze beads with tungsten carbide coated graphite (carbon) fibers; aluminum beads with graphite (carbon) fibers; steel beads with boron nitride fibers; aluminum beads with boron carbide fibers; aluminum beads with nickel coated carbon fibers; alumina beads with carbon fibers; titanium beads with silicon carbide fibers; copper beads with aluminum oxide particles (and carbon fibers); copper-silver alloy beads with diamond particles. Those fibers that may be printed via the techniques of the CFF Patent Applications may also be embedded as continuous fibers. Carbon forms for particles or fibers include carbon nanotubes, carbon blacks, short/medium/long carbon fibers, graphite flakes, platelets, graphene, carbon onions, astralenes, etc.
Some soluble-pyrolysable binder combinations include polyethylene glycol (PEG) and polymethyl methacrylate (PMMA) (stearic acid optional, PMMA in emulsion form optional); waxes (carnauba, bees wax, paraffin) mixed with steatite and/or polyethylene (PE); PEG, polyvinylbutyral (PVB) and stearic acid. Some pyrolysable second stage binders include: polyolefin resins polypropylene (PP), high-density polyethylene (HDPE); linear low-density polyethylene (LLDPE), and polyoxymethylene copolymer (POM). As noted, in thermal debinding, a part containing binder is heated at a given rate under controlled atmosphere. The binder decomposes by thermal cracking in small molecules that are sweep away by the gas leaving the oven. In solvent debinding, a part containing binder is subject to dissolving the binder in appropriate solvent, e.g., acetone or heptane. In catalytic debinding, the part is brought into contact with an atmosphere that contains a gaseous catalyst that accelerates cracking of the binder, which can be carried away.
In a composite material including >50% metal or ceramic spheres, as well as a two stage binder, advantageous mechanical properties for 3D printing, debinding and sintering (including melt viscosity, catalytic behavior and the like) may result in a printing material that—while having properties suitable or advantageous for other parts of the process, may be claylike and/or brittle at room temperature, even though the material becomes suitably fluidized but also suitably viscous and self-supporting for 3D printing when at a printing temperature (above one or more glass transition temperatures or melting temperatures of the material).
Suitable structures for handling materials brittle at room temperature are shown in
Each spool/material may be kept in its own independent chamber rather than the joint chamber HC1, and each may be heated by its own heater rather than the joint heater HT1. Heater HT1 may be a passive, e.g., radiant and convection heater, or include a blower. As shown in
In one alternative embodiment, rather than debinding an entire part after printing, at least a portion of the debinding is performed while or after printing layers of the part and/or supports. As discussed herein, debinding may be performed by solvent, heating and/or applying vacuum evaporation or sublimation, catalysis, or other means of removing or decomposing a binder, in each case removing at least a part of the matrix material for subsequent processes such as sintering. It may be more advantageous to debind less than a layer at a time (e.g., with a directed debinding head optionally travelling with the print head) or a layer, a few layers, or several layers at a time (e.g., with a full-enclosure debinding system or a region-at-a-time or scannable debinding system).
Full part molding technologies using debinding, in contrast to additive or 3D printing technologies, necessarily apply debinding processes to a full molded part. As discussed herein, full part debinding is similarly useful for additive or 3D printed parts as well, and may offer advantages versus molded parts in the case of additive or 3D printed parts (e.g., weight may be reduced and/or debinding accelerated when internal honeycomb, access channels, open cells, and other debinding acceleration structures are printed).
In contrast, layer-by-layer debinding (e.g., not limited to one layer at a time—continuous debinding while printing, or debinding part of a layer at a time, or debinding a set of layers are each possible) may have unique advantages in the case of 3D printed or additive technologies. As with molding, a purpose of a first stage binder in the case of extrusion 3D printing (e.g., using spooled or coiled filament, spooled or foldable tapes, or feedable rods) is delivery of the sinterable powder into the desired shape, while a purpose of a second stage binder is adhesion and shape retention in the brown part versus gravity and system/process forces. After delivery, the first stage binder need only be retained so long as is necessary or useful for adhesion and shape retention versus these forces. In the case of molding, this would be at least until after the green part is formed, and in most cases until after the green part is removed from the mold. In the case of 3D printing, depending on the debinding system and binder material properties, the binder can be removed substantially immediately after deposition (e.g., if some first stage binder remains, and/or a second stage binder or other component retains structural integrity versus gravity and printing/processing forces). If sufficient structural integrity remains, a debinding head may continuously debind “behind” a deposited road that has solidified, or even one that has not yet solidified or cooled to solidification. As another example, a debinding head may independently track or scan a portion of a layer, a full layer, or a set of layers; or a volumetric or bulk process (e.g., heating, vacuum) in the printing chamber may continuously debind or debind in duty cycles. In all of these cases of substantially layer-by-layer debinding, several advantages result. Significantly, the process of debinding is accelerated because internal surfaces are directly available for debinding. Similarly, structures impractical to debind in full-part process (e.g., dense or large parts) may be debound. No additional time or transport is necessary following printing, as the printer continuously transforms (continuously, region by region, layer by layer, or layer set by layer set) green layers of the part into brown layers, and a printed part is a brown part. Even partial debinding may accelerate the overall process by increasing the available surface area for whole part debinding. For example, a partial debinding sweep may be conducted upon a printed layer or set of layers, temporarily exposing some surfaces to debinding fluid (gas or liquid).
In one example, as shown in
In the case of a heat gun or radiant element, the layer or road of first material deposited may be heated to temperature of 200-220 degrees C. to debind the material. Optionally, the fume extractor FE1 or vacuum may be concentric or partially concentric with a heat source, such that fumes are extracted similarly without dependence on the direction of travel of the debinding head DBH1. Similarly, the debinding head DBH1, with or without the fume extractor FE1, may be concentric with the printing head 180 or 180a, again so that debinding may “follow” or track the print head 180 or 180a in any direction, and/or may perform similarly in any Cartesian direction of movement. Alternatively, either of the debinding head DBH1 or the fume extractor FE1 may be mounted onto a side of the print head 180 or 180a (with or without independent articulation for direction) and may be mounted on a separately or independently movable carriage. In each case described herein (concentric, adjacent, or main scan) the fume extractor FE1 is preferably proximate to an output of the debinding head DBH1 (e.g., spray, heat radiator, etc.), e.g., no more than 0.1-10 mm from the debinding head DBH1.
Alternatively, as shown in
Further alternatively, as shown in
Still further alternatively, as shown in
As shown in
When sintering supports are used, the apparatus (and/or process) may include a second print head along a material feed path, and the apparatus can feed a second filament including the binder matrix and sinterable spherized and/or powdered second material having a second sintering temperature higher than the first sintering temperature (optionally, e.g., more than 300, or more than 500 degrees C. higher). The apparatus forms layers of the second material—the separation layer material—which may have a second sintering temperature more than 300 degrees C., or more than 500 degrees C. higher than the first sintering temperature. Green layers of model material are deposited upon a by deposition upon a build plate or prior deposition of a brown layer (previously debound layer-by-layer as discussed herein) or separation material, and at least a portion of the binder matrix from each green layer is debound to convert that layer or layers into a corresponding brown layer. Layers of the separation material are deposited upon a build plate or first or second material, and layers of first material by deposition upon prior deposition of model material or separation material as appropriate, to permit sintering supports to be later removed or build up separation material. When all brown layers of the part have been so converted, the part may be sintered at the first sintering temperature but below the second material. The apparatus (including an additional station of the apparatus) debinds at least a portion of the binder matrix from each of the first material and second material. The apparatus (including an additional station of the apparatus) then heats a part so formed from first and second material to the first sintering temperature, thereby sintering the first material without sintering and decomposing the second material (the separation material) The second stage binder in the separation material, is, however pyrolysed, leaving an unsintered powder behind.
In the present disclosure, a vacuum-assisted debinding process using a high vapor pressure first stage binder subject to sublimation (e.g., naphthalene) may be particularly effective in the case where interconnected channels are printed. The 3D printing model material may include a binder and a ceramic or metal sintering material, and a release layer intervenes between infill cells or honeycomb or open cells in the part interior that connect to support structures and the part exterior. As discussed herein, open cell holes may optionally form, be formed by, or be connected to access and/or distribution channels for debinding fluid penetration and draining. “Vacuum-assisted” may mean debinding in gaseous pressure below ambient, optionally below 0.1-5 mm Hg, where any remaining gas may be air or inert, with or without added heat by a debinding head, heated printbed, and/or heated printing/debinding chamber. All or some, each of the channels/holes may be sized to remain open during debinding under vacuum, yet close during the approximately 20% size (approximately 20% may be 12-24%) reduction or densification of sintering. In such a case, the first stage binder may include chemically compatible solid, liquid and/or paste-like higher hydrocarbon and ester binder components having a measurable vapor pressure at the low end of the debinding temperatures (support structures and thus readily removable), especially under reduced pressure and elevated temperature conditions, prior to or without the use of extracting solvents. Preferably, such total or partial wax replacement components in the binder fraction would be characterized by a low-lying triple point which would make the removal of the component feasibly by sublimation, i.e., directly from the solid into the vapor phase, and thus preserving the open structure of the polyolefin binder phase.
In the present disclosure, binder compositions suitable for room temperature filament winding, commercial range shipping, and room temperature storage and unspooling may be formed by combining low melting point waxes and other compatible materials into a first stage binder. A problem to be overcome is brittleness, which prevents bending or winding of relatively high-aspect ratio filament (e.g., 1-3 mm) without breaking.
Solvent-debinding MIM feedstocks often include three distinct components. One component is the solvent-extractable partially miscible lower molecular weight component, such as petroleum wax (PW), microcrystalline wax (MW), crystalline wax (CW), bee's wax, C15-C65 paraffins and the like. The first stage binder component may serve as a pore former that can be rapidly and conveniently removed from the green part without changing its dimensions and integrity but that also facilitates a controlled and uniform removal of gaseous thermal decomposition products from the brown part body without deforming it. A second component may be a non-extractable, later pyrolysed second stage binder, which may be a thermoplastic polymer selected from various grades of polyethylene (PE), such as LDPE, HDPE, LLMWPE, etc., polypropylene, poly(methyl pentene) or other nonpolar hydrocarbon polymer. A third component may be a minor fraction of a powder dispersing component, such as long-chain saturated fatty acids (for example, stearic (SA) or palmitic (PA) acid) that act as disaggregating surface active agents for the inorganic or metal powder, alternatively a polar and tacky copoly(ethylene-vinyl acetate) (PEVA) in place of a fatty acid as the powder dispersing component.
In these examples, binder compositions may contain a first stage binder of 50-70 vol.-% of hydrocarbon solvent-soluble wax or fatty acid components. In order to be more flexible or pliable in room temperature or shipping conditions, the first stage binder may include low-melting binder components, such as higher alkanes, petrolatum, paraffin waxes and fatty acid esters and other compatible liquid plasticizers to increase the flexibility of the polymeric binder system. These components may improve spool winding on small-diameter spools and to resist impact during handling and shipping (including in colder ambient temperatures, e.g., below freezing), and may also increase the rate of extraction during the solvent debinding step.
In one particular example, a measurably volatile plasticizing binder component may have relatively volatility under ambient storage, e.g., such as naphthalene, 2-methylnaphthalene or another hydrocarbon having a triple point temperature in the vicinity of room temperature as a component of a primarily polyolefin binder, or as the majority component or entire component of a first stage binder. Due to its aromaticity and low polarity, naphthalene is compatible with a polyethylene (polyolefin) melt and has naphthalene has a relatively very low temperature triple point and thus very high vapor pressure over the solid phase up to the melting point at 80 degrees C. In another example, a polyolefin binder is blended with a straight- or branched chain higher (10<n<26) alkane or a mixture of such alkanes, with or without a fraction of naphthalene, in which the alkanes or their mixture is selected from compounds having a measurable vapor pressure at temperatures below the melting point of the polyolefin or below the dissolution temperature of said polyolefin in the alkane or its mixture. “Measurable vapor pressure” means a saturated vapor pressure higher than 0.1 Pa (1 μm Hg) at 20 degrees C.)
The alkane or its mixtures may be replaced in entirety or in part by mono-, di- or triesters of fatty acids and fatty alcohols, glycols or glycerol which also possess a measurable vapor pressure in the range from ambient temperature to the dissolution temperature of the polyolefin binder in the ester or its mixture. If the alkane, ester or its blend or a blend with a medium-size fatty acid has a measurable vapor pressure at ambient or higher temperature, but below the melting or dissolution point of the polymer binder, it can conveniently be removed from the blend by simply exposing the green part to low pressure environment, preferable at an elevated temperature, but at least initially at a temperature lower than the melting or dissolution temperature of the polyolefin binder. The sublimation or evaporation of the binder component will generate microporosity in the binder phase of the green part, thus facilitating subsequent thermal debinding of the green part and preventing its dimensional distortion due to the expansion of the trapped gaseous decomposition products.
The volatile binder component should have a vapor pressure at ambient temperature low enough so as not to vaporize to a significant degree during normal handling and use of the material in the open atmosphere. Volatile binder loss during long-term storage may be effectively prevented by storing the pellets, extruded filament or the like in sealed gas- and organic vapor-impermeable multilayer packaging. Polyolefin binders include polyethylene, polypropylene or their copolymers, as described with a wax component including a proportion of naphthalene, 2-methylnaphthalene. Sublimation of naphthalene during storage can be prevented by using an appropriate vapor impermeable packaging material such as an aluminum-polymer laminate, yet naphthalene can be relatively rapidly removed from the green part by moderate heating under low pressure, for example, in a vacuum oven at temperatures below the melting point of naphthalene and thus remove it without melting the binder phase.
As noted, in the case of
As shown in
As shown in
If the powder bed is to be fluidized, pressurized gas appropriate for sintering (e.g., typically an inert gas, or a reducing gas) may enter the fluidized bed vessel through numerous holes via a distributor plate 23-9 or a sparger distributor, the resultant gas-particle fluid being lighter than air and flowing upward through the bed, causing the solid particles to be suspended. Heat is applied to the crucible 23-1 containing the powder bed (optionally fluidized) and part 23-3. Any part of the system may be appropriately pre-heated, e.g., a pressurized gas 23-2 may be pre-heated to a temperature in the below, in the range of, or above the sintering temperature. As the part 23-3 is heated up to sintering temperature, the tendency is to deform downward under gravity, i.e., under the weight of the part 23-3 itself. In the system of
Optionally, in order to promote flow, and prevent entrapment of powder in orifices and compartments of the part, the powder may be substantially spherically shaped. Further, the powder bed can be fluidized to reduce viscosity through fluid inlet and/or distributor plate 23-9. Further optionally, the crucible 23-1 is positioned in a substantially gas-tight chamber 23-7 that seals the furnace to prevent the ingress of oxygen—which is usually detrimental to the physical properties of metallic powders during the sintering process. A refractory lining 23-5 is shown, which isolates the high-temperature crucible 23-1 from the (preferably stainless steel) walls of the furnace.
Further optionally, a crucible lid 23-6 may rests on top of the crucible 23-1 further limiting oxygen flow into the part 23-3. As the gas flows into the crucible 23-1, the pressure may slightly elevate the 23-1 lid to enable gas to escape. The resulting positive pressure flowing gas seal may reduce oxygen ingress, resulting in a more pure atmosphere around the part 23-3. Further optionally, in one embodiment, the fluidizing gas may be maintained at a flow rate below a point of mobility of the powder during an initial temperature ramp, and through the onset of necking among metal powder spheres in the process of sintering—the initial stages of the sintering process. When sufficient necking is achieved to connect many spheres and thereby maintain the structure of the part, the gas flow can be increased to the point of fluidizing the powder. Fluidizing (e.g., creating a fluidized bed) during the initial ramp (before necking) may have a destabilizing effect on the part, and may increase the likelihood of cracking or damage. However, once sintering or pre-sintering has enabled sufficient part strength (e.g., 0.1-10% part shrinkage), and before the part has contracted to fully sintered (e.g., 12-24%, or approximately 20% shrinkage) fluid flow may be increased to fluidize the support powder without damaging the part. Increasing fluid flow later in the process may require low viscosity powder to ensure egress of powder from holes, cavities and the like.
Further optionally, the properties of the powder, fluid flow, and printing (including part, supports, and auxiliary structures) may be configured to generate buoyancy of the part, on a scale from low buoyancy to neutral buoyancy in the fluidized bath. This effectively zero gravity sintering process may permit complex shapes with internal spans and bridges to be sintered without sagging or slumping. A mild amount of buoyancy will reduce the effective weight of the part or a portion of the part. However, the buoyancy may be up to neutral (the part tends to float within the fluidized bed) or above neutral (the part tends to float to the top of the fluidized bed). A supporting hanger 23-10 may counteract negative, neutral, or positive buoyancy and hold the part immersed in the fluidized bed. In addition, a hood guard 23-11 shaped to exclude powder directly above the contour of the part may reduce or eliminate the weight of a hood or stagnant cap of non-fluidized powder that may reside above the part. This hood or stagnant cap may reduce overall buoyancy or buoyancy in particular locations (see, e.g., https://rucore.libraries.rutgers.edu/rutgers-lib/26379/). The hood guard 23-11 may be 3D printed along with the part—e.g., the hood guard 23-11 may be determined according to the cross-sectional shape of a representative or maximum horizontal section of the part, projected upward for the expected depth of submersion in the fluidized bed. The hood guard 23-11 may then be 3D printed as a hollow or substantially hollow prism or shell from model material (or sintering support material), e.g., above the part with a separation layer, or a separate print job (subsequent or beside the part to be sintered). The hood guard 23-11 may also serve the role of a supporting hanger 23-10, and the part may be suspended via the hood guard 23-11. The hood guard 23-11 may be “sacrificial”, e.g., generated during printing but disposed of or recycled following sintering.
Further optionally, a gas outlet 8 may allow the exhaust of the sintering process to be removed from the oven. Alternatively, or in addition, the outlet 8 may be used to pull a vacuum on the furnace (e.g., use a vacuum pump to lower the ambient pressure toward vacuum) to remove a significant portion of the oxygen from the environment prior to flowing the inert or reducing gas for sintering and/or fluidizing the bed. Flowing gas through the powder agitates the powder in addition to fluidizing the powder. Further optionally, a fluidized bed may allow the part to contract or shrink during sintering without the powder exerting any resistance. While the necessary gas flow to enter a particulate regime and bubbling regime in fluidizing a particular particle size and type can be well characterized empirically or via modeling, mechanical agitation, including by stirring members, shaking members or chambers, ultrasonic, magnetic, inductive, or the like may reduce the gas velocity needed or provide fluidization in more inaccessible sections of the part.
Continuing with
With respect to sintering ovens, unlike solid metals (which may be opaque to or reflect microwaves at low temperatures), powdered metal may advantageously absorb microwaves. In addition, the resulting heating process may be volumetric or partially volumetric, and heat a body of powdered material evenly throughout, including to sintering temperatures (if a compatible chamber and atmosphere can be practically provided). Furthermore, as discussed herein, smaller powder sizes (e.g., lower than 10 micron, average or >90% count) may lower sintering temperatures to enable using lower temperature furnace and refractory materials. A soak in a forming or reducing gas (e.g., Hydrogen mixtures) may also be used.
A fused silica tube used for sintering (in combination with microwaves or otherwise) may be formed from very pure silica (e.g., 99.9% SiO2), and a crucible for holding the workpiece or part may be made from a similar material. In some cases, the optical transparency of fused silica may correlate to its microwave transparency and/or its coefficient of thermal expansion. A more optically transparent fused silica may have a lower degree of crystallization, and the crystal structures may scatter both light and RF.
Typical Thermal Expansion Coefficients and Microwave penetration depths
-
- Penetration depth (d) is the distance from the surface of the material at which the field strength reduces to 1/e (approximately 0.368) of its value at the surface. The measurements in this table are taken at or around 20 degrees C. As temperature increases, the penetration depth tends to decrease (e.g., at 1200 degrees C., the penetration depth may be 50-75% of that at 20 degree C.).
With respect to gas handling, different sintering atmospheres are appropriate for different metals (e.g., Hydrogen, Nitrogen, Argon, Carbon Monoxide, vacuum, reducing gases with small percentages of Hydrogen), and for different stages of a sintering process. The sintering atmosphere may help in different stages, e.g., in completing debinding, in cleaning away debinding remnant materials to avoid contamination in a sintering furnace, in reducing surface oxidation, in preventing internal oxidation, and/or to prevent decarburization. A atmosphere controlled furnace may be used before sintering as well, or different stages arranged in a muffle staged continuous furnace.
An atmosphere after initial debinding to clean away lubricants or remnant binder, but before sintering may be oxidizing (nitrogen saturated with water or with added air) through water to high temperature metal for example, optionally deposited with a similar (primary) matrix or binder component to the model material. After sintering, the release layer may become highly saturated, or by use of air additions. Temperatures may be 200-750 C with dew point of 0 to 25 C. An atmosphere in sintering, especially for stainless steels or some tool steels, may be highly reducing, e.g., pure Hydrogen, with dew point of −20 to −40 C. Nitrogen/hydrogen mixtures (3-40%) or Nitrogen/ammonia may be used, and hydrocarbons may add back surface carbon or prevent its loss. Atmospheres in post-sintering may be cooling (at very low Oxygen levels, e.g., 10-50 ppm) at a rate of, e.g., 1-2 degrees C. per second, and/or may be recarbonizing with a hydrocarbon-including atmosphere (forming some CO) at e.g., 700-1000° C. range for steels.
With respect to a microwave assisted sintering furnace 113, as shown in
As shown in
Smaller, e.g., 90 percent of less than 8 microns, particle sizes may lower the sintering temperature as a result of various effects including increased surface area and surface contact among particles. In some cases, especially for stainless and tool steel, this may result in the sintering temperature being within the operating range of a fused tube furnace using a tube of amorphous silica, e.g., below 1200 degrees C. Accordingly, in the process variation, as discussed herein, this smaller diameter powder material may be additively deposited in successive layers to form a green body as discussed herein, and the binder removed to form a brown body (in any example of deposition and/or debinding discussed herein).
As shown in
As shown in
As shown in
In a variation approach for producing finely detailed parts, again the material having a removable binder and greater than 50% volume of a powdered steel (or other metal) is supplied with more than 50 percent of the powder particles have a diameter less than 10 microns, advantageously more than 90 percent having a diameter equal to or less than substantially 8 microns. The material may be additively deposited with a nozzle having an internal diameter smaller than 300 microns, which provides fine detail but is 10-20 times the diameter of the larger particles of the powder (preventing jamming). Again, the binder is removed to form a brown body and the brown part loaded into the fused tube, e.g., amorphous silica, having a thermal expansion coefficient lower than 1×10-6/° C., and the is sealed and the atmosphere therein replaced with a sintering atmosphere. Radiant energy (e.g., radiant heat from passive or active susceptor rods or other resistive elements, and/or microwave energy) is applied from outside the sealed fused tube 113-5 to the brown part, sintering the brown part at a temperature higher than 500 degrees C. but less than 1200 degrees C. (a range enabling small particle aluminum as well as small particle steel powders). In this case, the nozzle may be arranged to deposit material at a layer height substantially ⅔ or more of the nozzle width (e.g., more than substantially 200 microns for a 300 micron nozzle, or 100 microns for a 150 micron nozzle).
In another variation suitable for sintering both aluminum and stainless steels (in addition to possible other materials) in one sintering furnace 113, parts formed from either small particle powder may be placed in the same furnace and the atmosphere and temperature ramping controlled substantially according to the material. For example, a first brown part may be formed from a first debound material (e.g., aluminum powder printing material) including a first powdered metal (e.g., aluminum), in which more than 50 percent of powder particles of the first powdered metal have a diameter less than 10 microns, and a second brown part formed from a second debound material (e.g., stainless steel powder printing material) including a second powdered metal (e.g., stainless steel) in which more than 50 percent of powder particles of the second powdered metal have a diameter less than 10 microns. In a first mode for the furnace, the aluminum brown part may be loaded into the amorphous silica fused tube discussed herein, and the temperature ramped at greater than 10 degrees C. per minute but less than 40 C degrees C. per minute to a first sintering temperature higher than 500 degrees C. and less than 700 degrees C. In a second mode, the stainless steel brown part may be loaded into the same fused tube, and the temperature inside the fused tube ramped (e.g., by the heat control HC and or microwave generator MG) at greater than 10 degrees C. per minute but less than 40 degrees C. per minute to a second sintering tempering temperature higher than 1000 degrees C. but less than 1200 degrees C.
The atmosphere may be changed by the pressure control 113-8 and/or flow control 113-9, operating the vacuum pump 113-10 or gas source 113-11. In the first mode for aluminum, a first sintering atmosphere may be introduced into the fused tube 113-5, including inert Nitrogen being 99.999% or higher free of Oxygen. In the second mode for stainless steel, a second sintering atmosphere comprising at least 3% Hydrogen may be introduced.
As shown in
As shown in
Accordingly, a small powder particle size (e.g., 90 percent of particles smaller than 8 microns, optionally including or assisted by particles of less than 1 micron) of metal powder embedded in additively deposited material lowers a sintering temperature of stainless steels to below the 1200 degree C. operating temperature ceiling of a fused silica tube furnace, permitting the same silica fused tube furnace to be used for sintering both aluminum and stainless steel (with appropriate atmospheres), as well as the use of microwave heating, resistant heating, or passive or active susceptor heating to sinter both materials.
As discussed herein, interconnected channels may be printed between infill cells or honeycomb or open cells in the part interior, that connect to the part exterior, and a shell (including but not limited to a support shell) may have small open cell holes, large cells, or a honeycomb interior throughout to lower weight, save material, and improve penetration or diffusion of gases or liquids (e.g., fluids) for debinding. These access channels, open cells, and other debinding acceleration structures may be printed in the part or supports (including shrinking/densification supports or shrinking/densification platform). All or some of the channels/holes may be sized to remain open during debinding (including but not limited to under vacuum), yet close during the approximately 20% size reduction of sintering. Internal volumes may be printed with a channel to the outside of the part to permit support material to be removed, cleaned away, or more readily accessed by heat transfer or fluids or gasses used as solvents or catalysis.
Debinding times for debinding techniques involving solvent or catalyst fluids (liquid, gas, or other) may be considered in some cases to depend on the part “thickness”. For example, a 4 cm thick or 2 cm thick part may debind more slowly than a 1 cm thick part, and in some cases this relationship is heuristically defined by a debinding time of, e.g., some number of minutes per millimeter of thickness. The time for removing debinding fluid (e.g., drying or cleaning) may also increase substantially proportionately with thickness. According to the present embodiment, the effective thickness of a part for the purposes of debinding time may be reduced by providing the aforementioned fluid access to an interior of the part, using channels from the exterior which may either remain open through sintering or be (effectively) closed following sintering.
Such channels may include at least one access channel to an exterior of the part, e.g., penetrating from the exterior of the part through wall structures of the 3D printed shape to one, several, or many infill cavities of the part; or may alternatively be surrounded by wall structures of the part. In some cases, an interconnected channel may include at least two access channels to an exterior of the part that similarly penetrate a wall, in order to provide an inlet and an outlet for fluid flow or simply to permit fluid to enter versus surface tension and/or internal gas. These inlet-honeycomb-outlet structures may be multiplied or interconnected. In some cases, the inlets may be connected to pressurized fluid flow (e.g., via either 3D printed or mechanically inserted flow channel structures). In some cases, the inlets may be connected to vacuum or a flushing gas. In some cases, “inlet” and “outlet” are interchangeable, depending on the stage of the process.
For example, the 3D printer according to
The 3D printer may deposit successive layers of honeycomb infill within the interior (e.g., between walls tracing positive and negative contours of the part), and the honeycomb infill may have a distribution channel (or several, or many distribution channels) connecting an interior volume of the honeycomb infill to the access channel. The 3D printer or subsequent debinding station or part washer may debind the binder matrix by flowing a debinding fluid through the access channel and/or distribution channel(s) and within the interior volume of the honeycomb infill.
As shown in
As shown in
Accordingly, as shown in
As shown in
In general, the substantial temperature ramp and environmental conditions (such as gases) for sintering a target metal part model material is presumed to be the temperature ramp to be used, because the part must sinter adequately with or without supports. Exceptions are possible (e.g., minor changes to the part model sintering temperature ramp to allow the supports to function better). Under these conditions (e.g., given a temperature ramp suitable for sintering a metal part model material), a candidate first ceramic material, e.g., α-alumina or other alumina, having a sintering temperature above that of the part model material may have its sintering temperature lowered and/or its shrinkage amount changed by (i) reducing average particle size (“APS”) or (ii) mixing in a compatible second or third lower temperature sintering material (e.g., silica, or yttria-silica-zirconia). These mixed materials would also be sintered. In addition, or in the alternative, a non-sintering filler that sinters at a significantly higher temperature may be mixed (which will generally decrease the amount of shrinking or densification). In general, homogeneous materials having a smaller APS will start densifying at lower temperatures and will attain a full density at a lower temperature than the larger APS materials.
In addition, or in the alternative, the sintering temperature, shrinking amount or the degree of densification can be changed by changing the particle size distribution (“PSD”, e.g., for the same average particle size, a different proportion or composition of larger and smaller particles). In addition, or in the alternative, when materials that may react are mixed, the sintering temperature, shrinking amount or the degree of densification of the mixture can be changed by using component mixing that may densify at a lower temperature than a chemical reaction, e.g., combining alumina and silica in a manner that densifies (sinters) at a temperature lower than that which forms mullite. For example, alumina-silica powder may be generated as alumina powder particles each forming an alumina core with a shell of silica, where the mixture first densifies/sinters between, e.g., 1150 and 1300 deg C, and converts to mullite only at higher temperatures, e.g., 1300-1600 degrees C.
In addition, or in the alternative, the sintering temperature, shrinking amount or the degree of densification can be changed by changing a degree of homogenization (molecular, nano-scale, core-shell structures) of dissimilar components. In the case of part shapes including either or both of convex or concave shapes (protrusions, cavities, or contours), as shown in
An appropriate sintering support material may have a final shrinkage amount over the same time-temperature sintering profile as the model material, as discussed herein. However, perfect matching of rate and final shrinkage percentage is not necessary. For example, the sintering support material should not shrink at a slower rate than the model material, or concave shapes on the part may be deformed and may not be restored by gravity. However, should the sintering support material shrink at a faster rate than the model material, printed sintering supports may not interfere with many concave shapes of the part (e.g., as shown in
As shown in
However, as shown in
In Step S342, the chamber may be filled with solvent or other debinding agent (alternatively, or in addition, the part is lowered or otherwise placed into a pre-filled bath). In Step S343 the part is kept in the debinding agent for a predetermined, modeled, calculated, or measured dwell time. The dwell time may be sufficient for, e.g., the debinding agent to permeate the channels. The dwell time may be additionally or alternatively sufficient for, e.g., the debinding agent to debind the first matrix material by a first effective amount (e.g., 5-30% or higher by volume of matrix material removal). The dwell time or period in Step S343 may be enhanced by, as shown in
In step S345, and as shown in
In step S346, and as shown in
In step S347, and as shown in
Extrusion type and other deposition 3D printers employ various printing approaches for completing perimeters, in particular for reducing seams resulting from extruding a closed perimeter path. Any path point not on a perimeter path is in an interior region, because the perimeter path constitutes the outermost path points (e.g., a new path that forms part of the outer perimeter renders previous paths to be interior regions). Accordingly, printing paths may form a seam with a butt joint or other than a butt joint (or example, overlapping, self-crossing, interlocking). Generally, one segment and one seam is preferred because fewer seams tend to have superior aesthetics, sealing, and dimensional stability. Further, wall or shell contour paths (in contrast to “raster” fill paths) have been deposited in a same rotational direction—either clockwise or counterclockwise. Paths are printed in the same clockwise or counterclockwise direction even if a perimeter path branches to the interior. This simplifies and speeds printing as perimeter paths can be continuously printed without reflex angle turns (e.g., turns of less than 180 degrees) from the current heading.
In the case where a printer deposits a composite feedstock intended to be debound then sintered, and a second stage binder in place during sintering includes retaining polymers of a common molecular lengths, deposition may create stress along the polymer molecule chains (e.g., HDPE etc.) within at least the second stage binder aligned to some extent along the deposition paths. In the green or brown state, the stresses may not have any particular effect on dimensional stability. However, as the part is heated in the sintering process, the stresses may relax or pull in each layer, cumulatively changing the shape of the part if many small changes add up in the many layers of the part.
In such a case, brown parts may be dimensionally consistent with the deposited green part, but may display a twist around a vertical axis after sintering. In a case where heating a brown part to mild levels (e.g., 150-200 C) causes twist, the second stage polymer binder may be considered to be heated to a level where residual stress can relax, causing the twist, as deposition stress built into the brown part is relaxed. As the printer deposits a layer, long chain molecules that compose the second stage binder polymer (the part of the binder that is left after the primary debind) may be strained along the printing direction. When heated to a relaxing temperature, the molecules may pull back, potentially causing a macroscopic twist in the part as pulls among many layers accumulate.
One countermeasure for twist is to print roads in a counteracting or retrograde direction. The three most common categories of roads are shells or walls, which are printed to form the perimeter of a sliced interior or exterior contour; “raster” fill, which is printed to fill interior volume in a solid manner, and infill honeycomb, which is printed to fill interior volume in a honeycomb. In addition, interior volume may be filled in any coverage pattern including non-raster or non-boustrophedon fills that cross road and/or are parallel or adjacent other roads or contours (e.g., random fill, wall-following fill, spiral fill, Zamboni-pattern fill, or the like), and may be filled in variable size, randomized, anisotropic, foam-like, sponge-like, 3-dimensional, or other versions of regular and irregular cellular (cell walls and low density or atmosphere cell interior) fills. For shells or walls, many or most parts are not formed from vertical prism shapes and through-holes, so layer to layer the shape of a slice and the shape of the shell or all incrementally changes for different wall slopes, concavities and convexities. Close to upper and lower surfaces, the incremental change in wall or shell shape may be more significant.
At a topmost horizontal or substantially horizontal flat layer with, e.g., protrusions or another shape beginning in the layer above, the shape of shells or walls may change completely from one layer to the next. Accordingly, it is optionally advantageous to print first and second sets of opposing direction walls or shells within one layer, so as to avoid layer-to layer comparison which may be more complex. One approach is to print each outer perimeter or negative contour inner perimeter with a companion, parallel, adjacent wall or shell road. In such a case, the length of the companion or offsetting road is not necessarily precisely the same, especially for small positive and negative contours (e.g., for a 3 mm diameter feature, the length of the perimeter road vs. a companion road may differ by 25 or 30%, while at 30 mm the length of the companion road may be 5% or less difference). In such a case an amount of overlap determined according to the difference in perimeter lengths may be effective at removing twist.
For raster fill within the shells or walls, a twisting effect from the relaxation of residual stress may not be as pronounced because raster rows may include some retrograde paths. However, as the filled interior area becomes smaller, differences in path length among raster rows and turns may be more pronounced. Overlap determined according to a difference in directional lengths (e.g., including straight rows as well as end-of-row turns) may be used to offset a length difference. In addition, raster-like or cellular patterns may be printed in tile patterns that each include main paths and parallel retrograde paths to relieve twisting stress relaxation within the tile and/or among tiles.
In one example of such an embodiment or expression of the invention, as shown in
While a butt joint as shown in
In another example of such an embodiment or expression of the invention, as shown in
In another example of such an embodiment or expression of the invention, as shown in
In another example of such an embodiment or expression of the invention, as shown in
Optionally, the second tool path may be continuously adjacent or overlap the first tool path within the same layer, and may include interior region path within the same layer. Alternatively, or in addition, the second tool path is continuously adjacent over at least 90 percent of the first tool path within an adjacent layer, and may include a perimeter path of the adjacent layer.
In another example of such an embodiment or expression of the invention, as shown in
In another example of such an embodiment or expression of the invention, as shown in
As shown in
If the melting point is low enough, or the material reactive enough, small bubbles or other discontinuities can form in the fluidized feedstock during the extrusion process when using ordinary extrusion-type nozzles, heat breaks, and heating. The bubbles create printing problems in several ways—for example, uneven printing in both gaps and drips, or uneven printing of adjacent roads or roads in different parts of the layer or part. The present disclosure provides a solution specifically for promoting even printing. Bubbles may be formed in many ways—for example gas dissolution from the solid phase, i.e. small amounts of moisture making steam. Alternatively, or in addition, micro bubbles may coalesce in the nozzle that entered the feedstock filament in a feedstock manufacturing phase—e.g., bubbles in pellet material converted into filament that are not removed during this process, or bubbles introduced during filament production. Alternatively, or in addition, air may be pulled into the system during a retract step following steady printing (an extrusion type 3D printer may be set to “retract”, i.e., reverse the filament drive direction, by a small amount—e.g., 1-5 mm—following steady printing or during a non-printing nozzle translation to relieve pressure in the melt zone). In addition, or in the alternative, bubbles may be caused by deformation due to the filament extruder hob (e.g., caused by any of grabbing teeth, pressure, or heating).
An additional benefit of the present system is decreasing the volume of melt for a practically sized heater block and nozzle system, providing more responsive extrusion control. Additional back pressure may also give better extrusion control given the very low viscosity of some MIM materials. In one implementation, for example for a MIM material which begins to melt or liquefy at around 130-150 C, the material may be heated in the print head to 180-230 C to promote adhesion. In this alternative, instead of reducing the volume of the melt zone using a long, thin melt channel (e.g., 1:10 width-height aspect ratio for diameter and a volume of 20 mm̂3, the melt zone may be a short 1:2 aspect ratio and a volume of 20 mm̂3—e.g., 3 mm of melt zone height, 1.5 mm of melt zone diameter. The longer, thin melt channel however allows more heating length for exposure to a heating element (e.g., as shown in the Figures, a short melt zone cannot necessarily accommodate a large and powerful heating cartridge). A reduced filament diameter (e.g. instead of a customary 3 mm or 1.75 mm, a 1 mm diameter filament) may permit a smaller bend radius for a given temperature, and better control over an amount extruded—for a given step size on the extruder, less material is extruded.
With respect to advised or advantageous dimensions, below a 10:1 nozzle to particle diameter ratio jamming may begin. Jamming is exacerbated by less spherical particles (e.g., platelets or flakes, which can be created during mixing or screw extrusion). Traditional MIM (or CIM) materials may be between 55% and 65% metal (or ceramic) powder loading by volume, but at this level of loading, separation layer material in small powder sizes (e.g., less than 1 um diameter) of alumina ceramic may tend to sinter at steel sintering temperatures. As the size of powder increases slightly to 2 um, the separation layer may become chalk-like. Accordingly, 15-35% powder by volume with a powder diameter of 5 um or higher for alumina or similar ceramic powder loaded in a MIM binder (e.g., wax-polyethylene, as discussed herein) may perform well as a separation layer. Alternatively, 10-20% powder by volume with a powder diameter of 2 um or lower (or 1 um or lower) for alumina or similar ceramic powder loaded in a MIM binder may perform well as a separation layer. Further, these may be combined (e.g., some particles smaller than 1 um and some particles larger than 5 um).
A conventional FDM/FFF filament or melt chamber may be approximately 1.7-3 mm, and in the present invention the melt chamber may be 0.6-1 mm in diameter for a tip outlet diameter of 0.1-0.4 mm (for a filament diameter of 1.0-2 mm). The volume of the melt chamber (the heated substantially cylindrical chamber of constant diameter extending from adjacent the nozzle tip to a melt interface) the may be approximately 15-25 mm̂3 vs. a melt chamber in conventional FDM/FFF of approximately 70 mm̂3.
As shown in
As shown in
With respect to the binder jetting example shown in
In some layers, differing amounts of binder may be jetted depending on whether a 2D layer shape segment being formed is an external wall, internal wall, or honeycomb wall, or internal bulk material (or depending on the printing location relative to such perimeters or areas). This results in differing (optionally a continuous or stepwise gradient) of volume fraction proportions of binder to powder, e.g., from 90% binder to 100% powder through 50:50 up to 10% binder to 90% powder. For example, a higher volume fraction of binder may be located on an outer shell (and/or inner shell), progressively reducing inward toward, e.g., area centroids.
In some layers, a release material (including another powder that does not sinter at the sintering temperature of the feedstock powder) may also be applied in a complementary 2D shape (e.g., jetted in a binder, extruded in a binder) for example, intervening between a support shape in a lower layer and a part shape in a layer two above.
In some layers, placeholder material (without either the green part powder or the release material powder) may also be applied in a complementary 2D shape of desired free space within the green part and/or sintering supports (e.g., jetted or extruded). In some layers, the placeholder material may also or alternatively be applied in a wall or “mold” shape, e.g., occupying external free space to the part shape, capturing unbound sinterable powder inside the mold shape. In other words, an external shell (e.g., wax) may be formed of the placeholder material. The external shell 2D shapes are deposited in each candidate layer on top of the preceding powder (e.g., bound powder, unbound powder, and/or release material) layer, then a subsequent layer of unbound powder feedstock is wiped on. As shown in
The binder may be jetted into roofs, floors, lattice, honeycomb, or skeletal reinforcement shapes within the mold shape (e.g., starting spaced away from the mold shape) to help hold the unbound sinterable powder versus gravity, or mechanical disturbance during downstream processes such as leveling or moving the part from station to station. For example, in some 2D layers, an internal holding pattern such as hexagon, triangle, or as previously describe lower density or high volume fraction of binder may be used as a holder, in combination with either an outer shell formed from bound composite, an outer shell formed from high volume fraction binder bound composite (e.g., 70% binder), and/or a mold shape formed from the placeholder material. As noted, this may help prevent motion of parts during printing/or during layer re-application.
Further, in some layers, the placeholder material may also or alternatively be applied in a complementary 2D shape of adhesive between, e.g., the shrinking platform formed from bound powder and the underlying build platform, or between a plurality of adjacent or stacked 3D green parts and associated sintering supports to allow multiple parts to be built up per run. The adhesive function may, again, help hold the any of the shapes versus mechanical disturbance during downstream processes such as leveling or moving the part from station to station. It should be noted that the binder jetting into sinterable powder may also be used to form adhering tacks as described herein between the shrinking platform and build platform, as well as or alternatively between a plurality of adjacent or stacked 3D green parts and associated sintering supports. In other words, the part may be anchored part with (e.g., solvent removed) binder to a ground plane (e.g., build plate) and/or parts to each other (e.g., in the Z axis, when printing one on top of another).
After each layer, the powder bed is refilled and releveled/wiped (with a doctor blade 138, roller, wheel or other powder leveling mechanism) flush with the green part shape, the release material shape, and/or the free space placeholder material shape. Optionally, a surface finishing mechanism flattens or shapes (rolling, shaving, ironing, abrading, milling) a recent or a most recent layer of green part shape, release material shape, and/or placeholder material shape before the powder bed is refilled about them.
The 3D shapes of each of the green part, sintering supports, intervening release material, and placeholder free space material are built up in successive layers, and in 3D space may take essentially any interlocking 3D forms. In many cases, the green part is formed as a recognizable 3D object, with separation material forming planes, arches, hemispheres, organic shapes or the like separating the 3D object from columns of sintering supports below, leading down to a shrinking platform as described herein, which is adhered to a build platform via placeholder material and/or bound composite tacks. Optionally, as described, within the recognizable 3D object, desired free space may be filled with placeholder material and/or unbound sinterable powder. Among the placeholder material and/or unbound sinterable powder may be deposited bound composite honeycomb or lattice or the like containing or entraining either or both of the placeholder material or unbound sinterable powder. Optionally, as described, about the recognizable 3D object, a mold shape defining the outer skin of the 3D object may be formed of the placeholder material. Additionally, or in the alternative, a skin shape forming the outer skin of the 3D object may be formed of the bound composite.
Subsequently, the 3D green part(s) together with sintering supports, release shapes, and placeholder or adhesive shapes is removed from the powder, and cleaned of remaining unbound powder. Unbound powder may be removed from the surroundings of the 3D green part(s) and sintering supports via outlets formed in the bound composite, or left entrained within the desired green part. Subsequently, the green part and its sintering supports may be handled as otherwise described in this disclosure. Bound composite outer and inner walls and internal honeycomb walls will be debound as described to form the brown part assembly. Release material will be debound as described, become separation powder for removing the sintering supports, and is retained for sintering and removed following sintering. Placeholder material may be debound (including in a solvent, catalytic, or thermal process) or even, if a different material from the binder, removed before or after debinding. In some cases, high temperature placeholder material that retains its shape at high heat but may be disassembled by further vibration, mechanical, radiation, or electrical processing (e.g., carbon or ceramic composite) may be retained through sintering.
Alternatively, the debinding step may not be necessary, for the green part shape and/or sintering supports if a single stage binder can be pyrolysed in a sintering furnace. In such a case, the green part assembly is taken directly to the furnace. Bound composite outer and inner walls and internal honeycomb walls are debound and sintered in an integrated process. Release material may be debound prior to the integrated debinding and sintering in the furnace, or at may be debound in the furnace as well. Placeholder material may be debound (including in a solvent, catalytic, or thermal process) prior to the integrated debinding and sintering in the furnace, or at may be debound in the furnace as well.
A material may be supplied (pellet extruded, filament extruded, jetted or cured) containing a removable binder as discussed herein (two or one stage) and greater than 50% volume fraction of a powdered metal having a melting point greater than 1200 degrees C. (including various steels, such as stainless steels or tool steels). The powdered metal may have which more than 50 percent of powder particles of a diameter less than 10 microns, and advantageously more than 90 percent of powder particles of a diameter less than 8 microns. The average particle size may be 3-6 microns diameter, and the substantial maximum (e.g., more than the span of +/−3 standard deviations or 99.7 percent) of 6-10 microns diameter.
Smaller, e.g., 90 percent of less than 8 microns, particle sizes may lower the sintering temperature as a result of various effects including increased surface area and surface contact among particles. In some cases, especially for stainless and tool steel, this may result in the sintering temperature being within the operating range of a fused tube furnace using a tube of amorphous silica, e.g., below 1200 degrees C. Smaller diameter powder material may be additively deposited in successive layers to form a green body as discussed herein, and the binder removed to form a brown body (in any example of deposition and/or debinding discussed herein).
DefinitionsA “sintering temperature” of a material is a temperature range at which the material is sintered in industry, and is typically a lowest temperature range at which the material reaches the expected bulk density by sintering, e.g., 90 percent or higher of the peak bulk density it is expected to reach in a sintering furnace.
“Honeycomb” includes any regular or repeatable tessellation for sparse fill of an area (and thereby of a volume as layers are stacked), including three-sided, six-sided, four-sided, complementary shape (e.g., hexagons combined with triangles) interlocking shape, or cellular. “Cells” may be vertical or otherwise columns in a geometric prism shape akin to a true honeycomb (a central cavity and the surrounding walls extending as a column), or may be Archimedean or other space-filling honeycomb, interlocking polyhedra or varied shape “bubbles” with a central cavity and the surrounding walls being arranged stacked in all directions in three dimensions. Cells may be of the same size, of differing but repeated sizes, or of variable size.
“Extrusion” may mean a process in which a stock material is pressed through a die to take on a specific shape of a lower cross-sectional area than the stock material. Fused Filament Fabrication (“FFF”), sometimes called Fused Deposition Manufacturing (“FDM”), is an extrusion process. Similarly, “extrusion nozzle” shall mean a device designed to control the direction or characteristics of an extrusion fluid flow, especially to increase velocity and/or restrict cross-sectional area, as the fluid flow exits (or enters) an enclosed chamber.
“Shell” and “layer” are used in many cases interchangeably, a “layer” being one or both of a subset of a “shell” (e.g., a layer is an 2.5D limited version of a shell, a lamina extending in any direction in 3D space) or superset of a “shell” (e.g., a shell is a layer wrapped around a 3D surface). Shells or layers are deposited as 2.5D successive surfaces with 3 degrees of freedom (which may be Cartesian, polar, or expressed “delta”); and as 3D successive surfaces with 4-6 or more degrees of freedom.
In the present disclosure,” In the present disclosure, “3D printer” is inclusive of both discrete printers and/or toolhead accessories to manufacturing machinery which carry out an additive manufacturing sub-process within a larger process. A 3D printer is controlled by a motion controller 20 which interprets dedicated G-code and drives various actuators of the 3D printer in accordance with the G-code. “Fill material” includes composite material formed of a debindable material and a sinterable powder, e.g., before debinding.
“Fill material” includes material that may be deposited in substantially homogenous form as extrudate, fluid, or powder material, and is solidified, e.g., by hardening, crystallizing, or curing. “Substantially homogenous” includes powders, fluids, blends, dispersions, colloids, suspensions and mixtures.
“3D printer” meaning includes discrete printers and/or toolhead accessories to manufacturing machinery which carry out an additive manufacturing sub-process within a larger process. A 3D printer is controlled by a motion controller 20 which interprets dedicated G-code (toolpath instructions) and drives various actuators of the 3D printer in accordance with the G-code.
“Deposition head” may include jet nozzles, spray nozzles, extrusion nozzles, conduit nozzles, and/or hybrid nozzles.
“Filament” generally may refer to the entire cross-sectional area of a (e.g., spooled) build material.
Claims
1. A method for additive manufacturing, the method comprising:
- supplying a first brown part formed from a first debound material including a first powdered metal, in which more than 50 percent of powder particles of the first powdered metal have a diameter less than 10 microns;
- supplying a second brown part formed from a second debound material including a second powdered metal, in which more than 50 percent of powder particles of the second powdered metal have a diameter less than 10 microns;
- in a first mode, loading the first brown part into a fused tube formed from a material having a thermal expansion coefficient lower than 1×10-6/° C., and ramping a temperature inside the fused tube at greater than 10 degrees C. per minute but less than 40 degrees C. per minute to a first sintering temperature higher than 500 degrees C. and less than 700 degrees C.; and
- in a second mode, loading the second brown part into the fused tube, and ramping the temperature inside the fused tube at greater than 10 degrees C. per minute but less than 40 degrees C. per minute to a second sintering tempering temperature higher than 1000 degrees C. but less than 1200 degrees C.
2. The method according to claim 1, further comprising, in the first mode, introducing into the fused tube a first sintering atmosphere comprising inert Nitrogen being 99.999% or higher free of Oxygen.
3. The method according to claim 1, further comprising, in the second mode, introducing into the fused tube a second sintering atmosphere comprising at least 3% Hydrogen.
4. The method according to claim 1, wherein the fused tube is formed from a fused silica having a microwave field penetration depth of 10 m or higher, and wherein the method further comprises:
- applying microwave energy to, and raising the temperature of, the first and/or second brown parts within the fused tube.
5. The method according to claim 1, further comprising:
- applying microwave energy to, and raising the temperature of, susceptor material elements placed outside the fused tube and outside any sintering atmosphere within the fused tube.
6. The method according to claim 1, further comprising:
- additively depositing the first brown part with a nozzle having an internal diameter smaller than 300 microns.
7. The method according to claim 6, further comprising:
- additively depositing the first brown part at a layer height substantially ⅔ or more of an internal diameter of the nozzle.
8. The method according to claim 1, in which more than 90 percent of the powder particles of the second powdered metal have a diameter less than 8 microns.
9. The method according to claim 1, in which the material of the fused tube is amorphous fused silica.
10. A multipurpose sintering furnace comprising:
- a fused tube formed from a fused silica having a thermal expansion coefficient lower than 1×10-6/° C.;
- a seal configured to seal the fused tube versus ambient atmosphere;
- an internal atmosphere regulator operatively connected to an interior of the fused tube and configured to apply vacuum to remove gases within the fused tube and to introduce a plurality of sintering atmospheres into the fused tube;
- heating elements placed outside the fused tube and outside any sintering atmosphere within the fused tube; and
- a controller operatively connected to the heating elements and the internal atmosphere regulator, the controller configured to operate the heating elements and the internal atmosphere regulator, in a first mode, to sinter first brown parts, formed from a first material, within a first sintering atmosphere at a first sintering temperature higher than 500 degrees C. and less than 700 degrees C., and in a second mode, to sinter second brown parts, formed from a second material, within a second sintering atmosphere at a second sintering temperature higher than 1000 degrees C. but less than 1200 degrees C.
11. The multipurpose sintering furnace according to claim 10, wherein the internal atmosphere regulator is further configured to introduce the first sintering atmosphere comprising inert Nitrogen being 99.999% or higher free of Oxygen.
12. The multipurpose sintering furnace according to claim 11, wherein the controller is further configured to operate the heating elements and the internal atmosphere regulator, in the first mode, to sinter the first brown parts, primarily formed with Aluminum powder in which more than 50 percent of the powder particles have a diameter less than 10 microns, within the first sintering atmosphere comprising inert Nitrogen being 99.999% or higher free of Oxygen, at the first sintering temperature higher than 500 degrees C. and less than 700 degrees C.
13. The multipurpose sintering furnace according to claim 12, wherein the controller is further configured to operate the heating elements to ramp a temperature inside the fused tube at greater than 10 degrees C. per minute but less than 40 degrees C. per minute.
14. The multipurpose sintering furnace according to claim 10, wherein the internal atmosphere regulator is further configured to introduce the second sintering atmosphere comprising at least 3% Hydrogen.
15. The multipurpose sintering furnace according to claim 11, wherein the controller is further configured to operate the heating elements and the internal atmosphere regulator, in the second mode, to sinter the second brown parts, primarily formed with Steel powder in which more than 50 percent of powder particles have a diameter less than 10 microns, within the second sintering atmosphere comprising at least 3% Hydrogen, at the second sintering temperature higher than 1000 degrees C. and less than 1200 degrees C.
16. The multipurpose sintering furnace according to claim 15, wherein the controller is further configured to operate the heating elements to ramp a temperature inside the fused tube at greater than 10 degrees C. per minute but less than 40 degrees C. per minute.
17. The multipurpose sintering furnace according to claim 10, wherein the fused silica tube is formed from a fused silica having a thermal expansion coefficient lower than 1×10-6/° C. and a microwave field penetration depth of 10 m or higher, and wherein the heating elements further comprise a microwave generator that is configured to apply energy to, and raise the temperature of, the first and/or second brown parts within the fused tube.
18. The multipurpose sintering furnace according to claim 10, further comprising susceptor material heating elements placed outside the fused tube and outside any sintering atmosphere within the fused tube, wherein the heating elements further comprise a microwave generator that is configured to apply energy to, and raise the temperature of, one or both of (i) the first and/or second brown parts within the fused tube and/or (ii) the susceptor material heating elements.
19. The multipurpose sintering furnace according to claim 10, wherein the heating elements further comprise susceptor material heating elements placed outside the fused tube and outside any sintering atmosphere within the fused tube.
Type: Application
Filed: Apr 24, 2018
Publication Date: Aug 23, 2018
Inventor: Gregory Thomas Mark (Brookline, MA)
Application Number: 15/961,384
