MULTIPLE FLUX CONCENTRATOR HEATING
A heating method is described. A plurality of flux concentrators and at least one part may be held in proximity to one another. One or more alternating electric current may be generated to generate a plurality of alternating magnetic fields by the respective flux concentrators.
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This application claims priority from U.S. Provisional Patent Application No. 61/885,806, filed on Oct. 2, 2013; U.S. Provisional Patent Application No. 61/896,896, filed on Oct. 29, 2013; U.S. Provisional Patent Application No. 61/898,054, filed on Oct. 31, 2013 and U.S. Provisional Patent Application No. 61/977,399, filed on Apr. 9, 2014, each of which are incorporated herein by reference in their entirety.STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Certain aspects of this invention were developed with support from the DARPA (Defense Advanced Research Projects Agency). The U.S. Government may have rights in certain of these inventions.BACKGROUND OF THE INVENTION
1). Field of the Invention
This invention relates to a sintering apparatus and its use.
2). Discussion of Related Art
It has become common place to fabricate three-dimensional components using Computer Numerical Control (CNC) systems. State of the art solid freeform fabrication (SFF) methods span a number of technologies including stereolithography, 3D printing, selective laser sintering, direct metal deposition, electron beam melting, and microplasma powder deposition. Thermoplastic-based SFF technologies allow designers to verify product design with three-dimensional models at an early stage, but are not capable of fabricating high-strength end products. In principle, metal-based SFF technologies allow for the rapid manufacture of structurally sound, dimensionally accurate metallic parts directly from computer aided design (CAD) models. Laser-based SFF technologies (e.g. DMD and SLS) are highly dependent on specific process parameters to achieve structurally sound parts. These process parameters are specific to the composition, morphology, and materials properties of the metallic powder, as well as the characteristics of the laser beam used to consolidate the powder. Selective Laser Sintering (SLS) and Direct Metal Deposition (DMD) are examples of three-dimensional additive manufacturing systems wherein a high power laser is used to fuse components or particles, such as metal powders or ceramic/metal composite powders, to one another as a means of building up a macroscopic part. These components or particles to be fused may be located in a dense particle bed, as in SLS, or may be entrained in a gas flow and fused in a weld pool on the surface of the part being manufactured, as in DMD. However, in both SLS and DMD technologies, the entire unfused components or particles that comprise the powdered material is heated indiscriminately by the high intensity laser beam. In certain applications, such as when the powdered material includes a ceramic component, the laser may cause thermal decomposition of the ceramic part resulting in the degradation of the physical characteristics of the macroscopic part.SUMMARY OF THE INVENTION
The invention provides a method including holding a plurality of flux concentrators and at least one part in proximity to one another, generating at least a first alternating electric current to generate a plurality of alternating magnetic fields by the respective flux concentrators, each alternating magnetic field heating a respective region of the at least one part to create a phase change in the region and moving the flux concentrators in unison relative to the at least one part to create trailing paths of the regions that overlap one another.
The invention also provides a heating apparatus including a holder capable of holding at least one part, an electric current generator generating at least a first alternating electric current, a plurality of flux concentrators electrically connected to the electrical current generator, the at least first alternating electric current driving the flux concentrators so that the flux concentrators generate a plurality of respective alternating magnetic fields, each alternating magnetic field heating a respective region of the at least one part to create a phase change in the region and a movement imparting device, the flux concentrators being mounted to the movement imparting device, the movement imparting device causing relative movement of the flux concentrators on the holders so that the flux concentrators move in unison relative to the at least one part to create trailing paths of the regions that overlap one another.
The invention is further described by way of example with reference to the accompanying drawings, wherein:
Micro-Induction Sintering (MIS) is a new additive manufacturing process described herein in which a metallic powder is consolidated via high frequency induction heating. Unlike laser- or electron beam-based additive manufacturing techniques in which the metal powder is heated indiscriminately by an external energy source, the MIS technique allows for the selective heating of individual particles by tailoring the frequency of an applied magnetic field. A localized high frequency magnetic field is produced at the powder bed using a specifically designed flux concentrator (FC) system.
Heating of metallic particles by induction is a result of both Joule heating due to eddy currents in non-magnetic metallic particles and hysteresis loss in magnetic particles, both of which result from the application of a high frequency magnetic field. For non-magnetic metals, eddy currents flow within a certain distance from the surface of the material. The distance within the metal at which the eddy current is reduced to approximately 37% of the value at the surface is called the skin depth δ and can be written as,
where ρ is the resistivity and μ is the permeability of the material, and f is the selected frequency of the magnetic field. In order to heat a metal particle by induction, it is important to immerse the particle in a high frequency magnetic field such that the skin depth is less than one half the diameter of the particle. As shown in
For simple shaped (e.g. flat or cylindrical) materials placed in a uniform alternating magnetic field, the power absorbed by the part (Pw) can be written as:
where ρ is the resistivity of the material, δ is the skin depth, A is the surface of the part exposed to the magnetic field, K is a power transfer factor that depends on a geometry of the part relative to the applied magnetic field, and H is the magnetic field strength. In principle, it is possible to calculate the power absorbed by a given metallic part in an induction heating process using modern finite element analysis methods. As a rule of thumb, with a fixed resistivity, magnetic permeability, and part dimensions, the power absorbed by the part in an induction heating process increases with increasing frequency and magnetic field strength.
In equation , the only ill-defined quantities are A and K, which describes how well the high-frequency magnetic field couples to an individual part. For a given component geometry and form factor of the applied AC magnetic field, A can be calculated. The power transfer factor K, on the other hand, depends on the “electrical dimension” of the part being heated, which is defined as the ratio of the diameter (outside dimension) of the part to the skin depth, d/δ. This is shown in
Unlike plates or cylinders, metal powders typically used in additive manufacturing processes consist of spherical particles. Consider a metallic sphere immersed in a high frequency magnetic field as shown in
The effective heating of spherical particles can be achieved by selecting the frequency of the applied magnetic field to maximize the overall power transfer to the particle. This is illustrated in
In general, the reduced effective diameter near the “poles” of the spherical particle will require higher induction frequencies to cause bulk heating of the entire particle. It is estimated that the “electrical dimension” appropriate for the efficient heating of spherical metal particles will be between 4 and 8. The determination of the frequency dependent K appropriate for the bulk heating of spherical metal powders is of critical importance to the MIS additive manufacturing method. A detailed model of K for a sphere will guide the continued design of power supplies for the MIS flux concentrator.Induction Heating of Composite Powders
Equations  and , along with the functional dependence of K(d/δ), provide a powerful toolbox for the selective heating of individual particles in composite materials. This is a distinctive advantage of the MIS method over competing metal-based additive manufacturing techniques such as selective laser sintering (SLS) and electron beam deposition (EBD). Here, we describe two conceptual composite architectures with an emphasis on the selective heating of individual components of the composite during the consolidation process.
where d is the diameter of the particle. Thus, for a given particle size and magnetic permeability, the ideal induction frequency to achieve bulk heating of a particle scales linearly with the resistivity of the material. In this case, the thin circle particles can be selectively heated in bulk using an oscillating magnetic field with a frequency 10 times smaller than that which would be used to bulk heat the thick circle particles. This is illustrated in
In this example, the consolidation of the composite is driven by the selective sintering of the thin circle particles, with the thick circle particles remaining as inclusions in the solid. This is illustrated in
The coupling and de-coupling of the high frequency magnetic field based on the domain size of the metallic material allows for real-time diagnostics of the MIS consolidation process through the monitoring of the forward and reflected power to the powder bed. In addition, it allows for the rapid and automatic de-coupling of the external heat source (i.e. the high frequency magnetic field) upon consolidation of the particles. This is an important control feature in the consolidation of heat sensitive materials or composite materials that may degrade upon exposure to elevated temperatures.
The previous example illustrates the selectivity that the MIS process has with powders that possess similar particle size distributions, but different materials properties. Here, we illustrate the selectivity of the MIS process simply based on the size of the particles in the powder. Consider the ideal metal powder shown in
In the composite architectures described above, the frequency of the induction heating process is used to selectively heat specific components of the composite based on the physical or materials characteristics of the powder. In the previous example, the small particles are selectively heated by induction, which results in the consolidation of the material. By changing the frequency of the magnetic field, however, the large particles could have been selectively heated by induction, which may lead to an improved density of the final part. In practice, the specific sintering characteristics of the material will determine the operating frequency and bandwidth of the MIS flux concentrator.General Aspects of the MIS Process
Micro-Induction Sintering is a unique additive manufacturing process capable, in principle, of producing complex parts and components directly from advanced metal and ceramic/metal matrix composite powders. The MIS process, however, is not without limitations imposed by the radio frequency (RF) power electronics, the electrical characteristics of the flux concentrator, the specific sintering characteristics of the metallic powders, and the fundamental physics of induction heating. In general, the MIS process is viable within the following approximate operational parameters:
- 1) Materials with electrical resistivities between 1 μΩ cm and 400 μΩ cm.
- 2) Powders with particle sizes between 1 μm and 500 μm.
- 3) MIS-FC operational frequencies between 0.5 MHz and 3 GHz.
Using this parameter space and equation , the operative phase space for the bulk heating of powders by high frequency induction can be determined.
- 1) High Frequency (HF)—frequencies less than 30 MHz and greater than 0.1 MHz.
- 2) Very High Frequency (VHF)—frequencies greater than 30 MHz and less than 300 MHz.
- 3) Ultra High Frequency (UHF)—frequencies greater than 300 MHz and less than 3 GHz.
The vast majority of materials used in additive manufacturing processes possess particle size distributions ranging between 50 μm and 150 μm with electrical resistivities less than 100μΩ cm. This operational space is highlighted by the box in
The Evolution of the Flux Concentrator
A central component in the MIS additive manufacturing system is the flux concentrator. This component focuses a high frequency magnetic field into a spatially compact region on a powder bed, resulting in the rapid joule heating of the individual metallic particles and subsequent sintering and consolidation.
Based on MIS-FC concepts that are modeled on a 3D computer aided design (CAD) platform and include advanced 3D magnetic field calculations at both DC and MHz frequencies and models that incorporate the measured physical properties of the material used to fabricate the MIS-FC. The following characteristics for a flux concentrator suitable for the MIS process:
- 1) 1 mT magnetic flux density at 0.5 mm distance
- 2) Induction heating spatial resolution of approximately 1 mm
- 3) Operating frequencies from 0.5 MHz to approximately 3 GHz, preferable at least 1 MHz.
- 4) A coil having a diameter of less than 10 mm.
- 5) Inductance of less than approximately 10 nH, preferably less than 5 nH
These performance characteristics not only determine the final configuration of the MIS-FC, but also the appropriate power supply for the MIS system.
The approach at the beginning of the development effort involved the use of magneto-dielectric materials and high amp-turn conductors to generate a localized, high frequency magnetic field at the air gap of the magnetic circuit. In general, the flux concentrators fabricated and tested along this path consisted of various permutations of the “horse shoe” design and the “pointed cylinder” design.
In our “horse shoe” shaped flux concentrators, a high current conductor that is located in the “yoke” of the “horse shoe” induces magnetic flux in the magneto-dielectric material. In this geometry, the flux density is increased as the cross-sectional area of the “horse shoe” arms decreases near the air gap in the magnetic circuit. At the air gap, the flux density “spills” out of the magneto-dielectric material and forms a localized high frequency magnetic field. The shape and magnitude of this high frequency magnetic field is determined by the shape of the “horse shoe” FC near the air gap, the amplitude of the current passing through the “yoke”, and the electromagnetic properties of the magneto-dielectric material. In general, this FC configuration could achieve the target flux densities only at very high amp-turns. By increasing the number of turns through the “yoke”, it was possible to significantly increase the flux density at the air gap and reduce the power requirements of the RF amplifier. Unfortunately, the increased number of turns in the “yoke” dramatically increased the inductance of the FC. This high inductance resulted in a MIS-FC with limited bandwidth that required a sophisticated multi-stage matching network. This approach was abandoned after we determined that the required flux densities could only be achieved at frequencies less than 100 MHz with very high RF power levels (e.g., greater than 500 W).
In our “pointed cylinder” shaped flux concentrators, several turns of a low current conductor wrapped around the cylindrical portion of the FC induces magnetic flux in the magneto-dielectric material. Similar to the “horse shoe” FC, the flux density is increased in this geometry as the cross-sectional area of the conical portion of the cylinder decreases near the very large air gap in the magnetic circuit. Near the point of the FC, the flux density “spills” out of the magneto-dielectric material and forms a localized high frequency magnetic field. The shape and magnitude of this high frequency magnetic field is determined by the shape of the cone, the amp-turns of the solenoid around the cylindrical portion of the FC, and the electromagnetic properties of the magneto-dielectric material. Overall, this FC configuration could achieve the target flux densities at modest currents. Unfortunately, this configuration has a very high inductance, which again resulted in a MIS-FC with limited bandwidth that required a sophisticated multi-stage matching network. In addition, we determined that the majority of the power from the RF amplifier was dissipated in the magneto-dielectric material through hysteresis. The magneto-dielectric material heated to approximately 400° C. after 30 seconds of 25 W RF power. This approach was abandoned after we determined that it was nearly impossible to keep the magneto-dielectric material cool during the MIS process.
In addition to these fundamental technical issues with the magneto-dielectric flux concentrators, we determined that the MIS of ScNc materials requires induction heating frequencies well in excess of 100 MHz. After an extensive search for high frequency magneto-dielectric material candidates, we established that no high permeability, low loss materials exist that are suitable for operation in an MIS flux concentrator. In the end, the technical push to VHF and UHF bands for the MIS of ScNc materials ultimately lead to the complete elimination of the magneto-dielectric material in the MIS-FC.Air-Core Flux Concentrators
In our air-core flux concentrators, a high current conductor is shaped into a coil and the turns in the coil form a localized magnetic field. Early versions of the air-core flux concentrator were simply the “pointed cylinder” flux concentrator without the magneto-dielectric material. The removal of the magneto-dielectric material from the conical coil FC resulted in a significant decrease in the inductance of the FC, as well as a large decrease in the flux density at the “tip” of the coil. The shape and magnitude of this high frequency magnetic field is determined by the shape and amp-turns of the conical coil. Overall, this FC configuration could achieve the target flux densities only at high currents. Unfortunately, the magnetic field produced by the current in the turns that are far from the “tip” of the conical coil do not contribute much flux density at the “tip”. This lead to the development of the “pancake” coil in which there are only two turns in the flux concentrator. This configuration resulted in the highest flux density per amp-turn at that time. In order to achieve the required flux densities, we determined that any air-core FC must be energized through a high frequency tank circuit. These circuits consist of a bank of capacitors in parallel to the inductive flux concentrator. This approach was successful and established our design trend for future MIS flux concentrators, which is characterized by a resonant tank circuit with an inductive FC that has the lowest inductance possible. In other words, a MIS-FC with a single turn.
The MIS-FC circuit is driven by COTS RF amplifiers (ENI 3100L, Amplifier Research 100W1000B, or Milmega AS0825) with an output impedance of 50Ω and operating bandwidth from 250 kHz up to 2.5 GHz. These amplifiers are driven by a high frequency function generator (Rohde & Schwartz SMIQ03) capable of producing a swept high frequency sine wave from 300 kHz to 3.3 GHz. The amplifier is connected directly to the MIS-FC assembly via a high-power SMA cable. As shown in
The circuit diagram for a 75 MHz MIS-FC is shown in
where L is the inductance of the MIS-FC (L1 coil) and C is the capacitance of the capacitor bank (C1) in parallel to L. The capacitors of the capacitor bank collect charge and release the charge to the MIS-FC. A plurality of capacitors are mounted in parallel to the plate 12. At fR, very large reactive currents flow between the capacitor bank and the MIS-FC, but the only power dissipated in the circuit is due to the resistive loss in R1 and R3 when K is zero. With a non-zero M, increased power is drawn from the power supply as power flows to the metal powder bed, R2. In general, the magnitude of these resistive and reactive currents depends on the voltage available from the RF power supply and the reactive current available from the capacitor at fR. The MIS-FC tank circuit minimizes the power draw from the RF amplifier by operating near the resonant frequency at all times. A large coil would result in high inductance. High inductance would reduce resonance frequency for a fixed capacitor bank. A reduction in resonance frequency would result in a larger skin depth, which results in a larger outer dimension.
This circuit design not only maximizes the current flow to the MIS-FC, but also is critical to the potential real-time diagnostic features of the MIS process. If the resonant frequency of the circuit does not couple well with the particle size distribution of the powder (see Equations  and ), then there is a reduced resistive load in the circuit, which corresponds to the case where M is equal to zero. If the resonant frequency of the circuit couples well with the particle size distribution of the powder (i.e. M˜1), however, an additional resistive load is introduced in the circuit and increased power will be drawn from the amplifier. In principle, this increased power will flow in the circuit only when the induction heating frequency (i.e. fR) is such that the “electrical dimension” d/δ is approximately 4 to 6 (Assuming spherical particles and an ideal “electrical dimension” of 6 for the maximum power transfer to a sphere.). The frequency dependence of the real power provided by the RF amplifier using this circuit design can be directly related to the real-time diagnostics and qualification of the MIS method.
A convenient method to determine the power transfer from a source to a load is to measure the Voltage Standing Wave Ratio (VSWR) of a device under test (DUT). In this case, the DUT is the MIS-FC. The VSWR is a measure of the amplitude of the reflected RF wave relative to the incident RF wave between an RF power supply and a DUT. In general, the VSWR can be calculated by measuring the reflection coefficient F of a DUT, which can be written as,
where Vreflected and Vincident are the voltage of the reflected and incident waves, respectively. Using this definition of F, the VSWR can be written as,
where |Γ| is the absolute value of Γ. As Γ is always between 0 and 1, the VSWR has a minimum of unity, which corresponds to 100% power transferred from the source to the load.
RF Flux Density Measurements of the “Solid-State” MIS-FC
In addition to measuring the electrical properties of the MIS-FC and high current tank circuit, a control code is also used to measure the flux density of the MIS-FC as a function of frequency to confirm the concentration of flux density in the single turn loop of the MIS-FC. Using an RF signal generator, amplifier, and a small RF field probe (Beehive Electronics 100B Probe), we have confirmed that the high frequency magnetic field is located primarily above the single turn circular loop in the solid-state MIS-FC configuration.
Early in the development of the MIS system, we focused on the development of a wide bandwidth MIS-FC as a means to couple effectively to all diameter particles in the metallic powder. While this approach is sound, in principle, it proved to be difficult to establish a low VSWR (i.e. high power transfer to the powder) over the entire bandwidth, in practice. As an alternative, the MIS-FC is designed to operate at sufficiently high frequencies such that the vast majority of particles in a given size distribution are heated by either bulk or surface heating. In this manner, a fixed parallel capacitor tank circuit can be designed specific to each powder. The resonant frequency of the MIS-FC component is easily adjusted by changing the capacitance in the tank circuit. This is illustrated in
ScNc Powder Deposition System
Superconducting Nanocomposite (ScNc) powder materials consist of superconducting magnesium diboride and gallium metal prepared using a milling process that results in an intimate, homogeneous mixture of both materials.
In general, particle size, morphology, and density determine the flow characteristics of a given powder or powder mixture. These characteristics are described using a classification scheme developed by Geldart for the fluidization of powders in air driven fluidized beds, but are also useful when describing the flow properties of any powder.
Table 1 lists the relevant properties of ScNc powders used herein as well as some commercially available metal powders. The large particle size and moderate density of both the commercially available Al and Ti powders, for example, place these materials well within the Geldart Class B limit, as shown in
Based on the observed ScNc particle/agglomerate morphology and the unknown “electrical dimension” of the ScNc powder, fabricated a series of MIS-FC assemblies and directly measured the power transfer by detecting heat from the ScNc material located over the MIS-FC. This method was very effective in determining the minimum frequency required for the ScNc MIS process. It was found experimentally that induction heating of the ScNc did not occur for frequencies less than approximately 700 MHz, which indicates that the “electrical dimension” of the ScNc is on the order of 35 μm, which is well below the physical size of the ScNc agglomerate.
After a series of measurements with increasing resonant frequencies, we fabricated an ultra-high frequency MIS-FC suitable for ScNc materials.
A particularly unique feature of the MIS process is the potential for real time diagnostics and monitoring of the sintering and consolidation of the metal particles during the additive manufacturing of a part. To illustrate this, consider the MIS tank circuit of
As discussed previously, bulk heating of the particles will only occur when the diameter d of the particles is on the order of 6δ. As the particles heat and sinter together, the effective diameter increases significantly and the bulk induction heating of the individual particles transforms into the surface heating of the consolidated powder in the region of the MIS-FC tip. This is illustrated schematically in
where VSWRK>0 is the VSWR of the MIS-FC circuit when it is coupled to the powder bed, and VSWRK=0 is the VSWR of the MIS-FC circuit when it is completely de-coupled from the powder bed. Similar to the VSWR, this normalized quantity is also independent of the level of RF power incident on the MIS-FC. Note that θ is unity if there is no coupling to the powder bed for all frequencies.
In addition to the high frequency VSWR spectroscopy, auxiliary low frequency induction heaters located near the MIS-FC assembly could be used to probe the quality of the consolidation over larger length scales and to locally heat treat the part during fabrication to reduce the mechanical stress on the part.
The low frequency coil 102 is driven by its own electric current generator (not shown) and exposes the part to an alternating magnetic field generated by the alternating electric current. The high frequency of the flux concentrator of the print head 32 heats only a portion of the particles that are in contact with the part so that the particles of the portion join with the part. The alternating electric current for pre-heating the part is a low frequency alternating electric current that exposes the part to a low frequency alternating magnetic field. The alternating current for heating the particles is a high frequency alternating electric current that exposes a portion of the particles that are in contact with the part to a high frequency alternating magnetic field.
The system 112 includes a frame 124, first and second tracks 126, a boom 128, and a plurality of rails 130. The tracks 126 are mounted to the frame 124 on opposing sides thereof and extend in an x direction. The boom 128 is mounted between the rails 130 and extends in a y direction. The boom 128 is movable in the x direction on the rails 130. An actuator (not shown) moves the boom 128 horizontally on the rails 130 in the x direction. The print head 32 is mounted to the boom 128 for movement in the y direction on the boom 128. An actuator (not shown) moves the print head 32 horizontally on the boom 128 in the y direction.
The container 114 is a horizontal bed with sides for containing and holding small particles 132 that contact one another. The rails 130 extend in a vertical z direction. The container 114 is mounted to the rails 130 for movement up and down in the vertical z direction. An actuator (not shown) moves the container 114 up and down the rails 130 in the vertical z direction.
The apparatus 110 further includes two powder reservoirs 134. The powder reservoirs 134 are also movable in a vertical z direction. By raising the powder reservoirs 134 and/or lowering the container 114, a height differential can be created between the particles 132 in the container 114 and particles held in the powder reservoir 134 so that particles can be scraped from the powder reservoirs 134 into and over the particles 132 already in the container 114.
It can thus be seen that the system 112 provides for movement in three-dimensions of the print head 32 relative to the particles 132. In use, a thin layer of particles 132 is scraped from the reservoirs 134 onto the container 114. The electric current generator 116 is connected through the lead 118 to the print head 32. When the electric current generator 116 is operated, it generates an alternating electric current and provides the alternating electric current through the lead 118 to an area adjacent the print head 32. The print head 32 is held close to the particles 132 and focuses an alternating magnetic field generated by the alternating magnetic current within a small first portion of the particles 132. The alternating magnetic field heats the particles so that they join. Joining of the particles occurs due to sintering and or melting of the material. The flux concentrator is then moved in x and/or y directions so that the alternating magnetic field is reduced from the first portion of the particles while exposing a second, adjacent portion of the particles to the alternating magnetic field. A reduction in the alternating magnetic field strength at the first portion of particles that has been joined allows the first portion to cool. In reality, there is a transition from the first portion to the second portion, and then to a third portion and so on so that an elongate part can be formed. The elongate part can have a two-dimensional profile in x and y directions.
After the part is formed within the particles 132, the container 114 is lowered and a new layer of particles is scraped onto the particles 132 from the reservoirs 134. The process hereinbefore described is then repeated. The particles that are heated in the second cycle are not only fused to one another, but are also fused to the part that has been manufactured in the first cycle. Should a circular plate for example be manufactured during the first cycle, the second cycle will add another layer to the circular plate and if the process is repeated, a cylinder may be manufactured. It may also be possible to manufacture more complex, three-dimensional shapes in this manner.
The instructions 160 include a recipe data store 164, a recipe selector 166, an interface 168, a selected recipe 170, a frequency modulation module 172, selected 3D parameters 174, and a CNC module 176.
In use, an operator can view the interface 168 on a display device. The interface 168 gives the operator access to the recipe selector 166 and the selected 3D parameters 174. The recipe selector 166 includes inputs for materials and particle sizes. A plurality of recipes are stored in the recipe data store 164. The recipe selector 166 selects one of the recipes in the recipe data store 164 based on the input provided by the operator through the interface 168. The recipe that is selected by the recipe selector 166 is then stored as the selected recipe 170.
The operator also enters 3D parameters through the interface 168, for example the manufacture of a cylinder as hereinbefore described. The parameters that are entered by the operator are then stored as the selected 3D parameters 174. The frequency modulation module 172 then utilizes the parameters of the selected recipe 170, including frequency, to modulate a frequency generated by the electric current generator 116. The CNC module 176 simultaneously operates the actuators 162 to create a desired two-dimensional, and ultimately three-dimensional part.
ρ is the resistivity of the material of the plate,
μ is the permeability of the material of the plate; and
f is the frequency of the magnetic field.
The holes 184 are spaced from one another by a distance s. In order for the currents of the holes 184 to remain separate from one another, s≥2δ. In
In general, each flux concentrator heats a respective region of the underlying part or parts. A respective heat affected zone is thereby created in the respective region where atom movement causes a change in a property of a material the part or parts. The material may or may not melt. A plurality of particles may be sintered together due to migration of atoms between the particles, which is an example of a non-melting change in properties of a material. A non-melting change in properties of a material may include a change in microstructure of the material. Such a change in microstructure may for example include a phase change of the material wherein a crystal structure of the material is changed. Such a change in crystal structure may involve a change in lattice structure with or without the inclusion of additional or replacement atoms or may include the inclusion or replacement of atoms without a change in the lattice structure. A phase change may involve a change in the grain size.
As shown in
As shown in
In one example, the power supply can provide the same alternating electric current to the terminals 188 in
- Simultaneous and Time-delayed excitation of adjacent flux concentrators;
- Unequal duty cycles of adjacent flux concentrators;
- Simultaneous and Time-delayed excitation of next nearest-neighbor flux concentrators;
- Unequal duty cycles on next nearest-neighbor flux concentrators;
- Flux concentrator diameter (e.g. equal or mixed diameter of flux concentrators in an array); and
- Flux concentrator consolidation points operating a different frequencies.
While certain exemplary embodiments have been described and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative and not restrictive of the current invention, and that this invention is not restricted to the specific constructions and arrangements shown and described since modifications may occur to those ordinarily skilled in the art. A system has been described that uses relative movement of flux concentrators to create overlapping heat affected zones. Another system may not make use of relative movement without departing from the scope and spirit of the inventions. A static system may for example make use of an array of flux concentrators that create an array of heat affected zones. Although an array is generally rectangular, other layouts may be used depending on the intended purpose.
1. A method comprising:
- holding a plurality of flux concentrators and at least one part in proximity to one another;
- generating at least a first alternating electric current to generate a plurality of alternating magnetic fields by the respective flux concentrators, each alternating magnetic field heating a respective region of the at least one part to create a heat affected zone in the region where atom movement causes a change in a property of a material of the at least one part, the heat affected zones created by respective flux concentrators overlapping one another.
2. The method of claim 1, wherein the flux concentrators are formed by respective holes in a plate, the holes being spaced from one another by a spacing s, wherein δ = ρ π f μ
- s≥2δ, and
- ρ is the resistivity of the material of the plate,
- μ is the permeability of the material of the plate; and
- f is the frequency of the magnetic field.
3. The method of claim 1, further comprising:
- generating a plurality of different alternating electric currents, each electric current generating a respective one of the alternating magnetic fields.
4. The method of claim 1 further comprising:
- moving the flux concentrators in unison relative to the at least one part to create trailing paths of the regions that overlap one another.
5. The method of claim 4, wherein the holes are in a row at right angles to the relative movement.
6. The method of claim 5, wherein the holes are in at least two rows.
7. The method of claim 1, wherein the material does not melt.
8. The method of claim 7, wherein the at least one part includes a plurality of particles that are sintered together due to migration of atoms between the particles.
9. The method of claim 7, wherein the change in the property of the material includes a change in a microstructure of the material.
10. The method of claim 9, wherein the material undergoes a phase change.
11. The method of claim 10, wherein the material undergoes a change in crystal structure of the material.
12. The method of claim 9, wherein the material undergoes a change in grain size.
13. The method of claim 1, wherein the material melts.
14. A heating apparatus comprising:
- a holder capable of holding at least one part;
- an electric current generator generating at least a first alternating electric current;
- a plurality of flux concentrators electrically connected to the electrical current generator, the at least first alternating electric current driving the flux concentrators so that the flux concentrators generate a plurality of respective alternating magnetic fields, each alternating magnetic field heating a respective region of the at least one part to create a heat affected zone in the region where atom movement causes a change in a property of a material of the at least one part, the heat affected zones created by respective flux concentrators overlapping one another.
15. The heating apparatus of claim 14, further comprising: δ = ρ π f μ
- a plate with a plurality of holes therein, wherein the flux concentrators are formed by the respective holes, the holes being spaced from one another by a spacing s, wherein s≥2δ, and
- ρ is the resistivity of the material of the plate,
- μ is the permeability of the material of the plate; and
- f is the frequency of the magnetic field.
15. The heating apparatus of claim 14, further comprising:
- a movement imparting device, the flux concentrators being mounted to the movement imparting device, the movement imparting device causing relative movement of the flux concentrators relative to the holder so that the flux concentrators move in unison relative to the at least one part to create trailing paths of the regions that overlap one another.