Depositing heat-treated aluminum using ultrasonic consolidation

Abstract

A system, method, and articles are disclosed with respect to depositing aluminum or alloys thereof, utilizing ultrasonic object consolidation. The method aspect of the invention comprises the steps of heat-treating an aluminum-based feedstock and ultrasonically consolidating the feedstock to a substrate to produce a part or a repair of a part, as might be required in an aerospace or aircraft structure. The feedstock may be solution heat-treated. This would include situations wherein the feedstock is solution heat treated off-line and maintained under controlled temperature conditions to prevent precipitation of solutes prior to the ultrasonic consolidation. Alternatively, the feedstock may be heat-treated on-line by passing it through a temperature- and/or atmosphere-controlled chamber prior to ultrasonic consolidation. The feedstock may be supported to minimize slumping due to creep. The feedstock may be T4, or may be aged, to T6, for example. The feedstock may be allowed to age naturally at room temperature, or a heat source may be used to artificially age the consolidated feedstock. The substrate may be aged or unaged. The source of the aluminum-based feedstock is in the form of tapes, sheets, wires, or droplets.

Description

REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Patent Application Ser. No. 60/629,421, filed Nov. 19, 2004, the entire content of which is incorporated herein by reference.

FIELD OF THE INVENTION

This invention relates generally to ultrasonic object consolidation and, in particular, to the deposition of heat-treated aluminum using ultrasonic consolidation without disturbing the properties of the underlying material(s).

BACKGROUND OF THE INVENTION

Ultrasonic consolidation is an additive manufacturing technology used to produce objects of any geometry from uniform, featureless feedstocks, such as tapes, sheets, wires, or droplets. There are a range of methods for accomplishing the metallurgical consolidation of the feedstocks via ultrasonic energy. These include, but are not limited to, spot consolidation, continuous rotary consolidation, plate-type consolidation, and so forth.

My U.S. Pat. No. 6,519,500 is directed to a system and a method of fabricating an object by adding material layers incrementally and consolidating the layers through the use of ultrasonic vibrations and pressure. The layers are placed in position to shape the object by a material feeding unit. The raw material may be provided in various forms, including flat sheets, segments of tape, strands of filament or single dots cut from a wire roll. The material may be metallic or plastic, and its composition may vary discontinuously or gradually from one layer to the next, creating a region of functionally gradient material. Plastic or metal matrix composite material feedstocks incorporating reinforcement materials of various compositions and geometries may also be used.

If excess material is applied due to the feedstock geometry employed, such material may be removed after each layer is bonded, or at the end of the process; that is after sufficient material has been consolidated to realize the final object. A variety of tools may be used for material removal, depending on composition and the target application, including knives, drilling or milling machines, laser cutting beams, or ultrasonic cutting tools.

The consolidation is effected by ultrasonic welding equipment, which includes an ultrasonic generator, a transducer, a booster and a head unit, also called a horn or sonotrode. Ultrasonic vibrations are transmitted through the sonotrode to the common contact surface between two or more adjacent layers, which may include layers next to each other on the same plane, and/or layers stacked on top of each other. The orientation of the sonotrode is preferably adjusted so that the direction of the ultrasonic vibrations is normal to the contact surface when consolidating layers of plastic material, and parallel to the contact surface when consolidating layers of metal.

The layers are fed sequentially and additively according to a layer-by-layer computer model description of the object, which is generated by a computer-aided design (CAD) system. The CAD system, which holds the layered description of the object, interfaces with a numerical controller, which in turn controls one or more actuators. The actuators impart motion in multiple directions, preferably three orthogonal directions, so that each layer of material is accurately placed in position and clamped under pressure. The actuators also guide the motion of the sonotrode, so that ultrasonic vibrations are transmitted in the direction required through the common contact surfaces of the layers undergoing consolidation.

During the ultrasonic consolidation process, an ultrasonic power supply is used to drive the sonotrode to a particular amplitude when applying material to a structure. The amount of power required to accomplish this is constantly varying due to the constantly changing geometry of the structure. This is prevalent in free-form fabrication applications, in which an arbitrary geometry is supplied to a manufacturing system, which them produces that arbitrary article from an essentially featureless feedstock, such as tape, wire or other tiny volumes of material.

SUMMARY OF THE INVENTION

This invention is directed to a system, method, and articles produced by depositing aluminum or alloys thereof, utilizing ultrasonic object consolidation. The method aspect of the invention comprises the steps of heat treating an aluminum-based feedstock and ultrasonically consolidating the feedstock to a substrate to produce a part or a repair of a part, as might be required in an aerospace or aircraft structure.

The feedstock may be solution heat-treated. This would include situations wherein the feedstock is solution heat treated off-line and maintained under controlled temperature conditions to prevent precipitation of solutes prior to the ultrasonic consolidation. Alternatively, the feedstock may be heat-treated on-line by passing it through a temperature- and/or atmosphere-controlled chamber prior to ultrasonic consolidation. The feedstock may be supported to minimize slumping due to creep.

The feedstock may be T4, or may be aged, to T6, for example. The feedstock may be allowed to age naturally at room temperature, or a heat source may be used to artificially age the consolidated feedstock. The substrate may be aged or unaged. The source of the aluminum-based feedstock is in the form of tapes, sheets, wires, or droplets.

A system for depositing aluminum or an alloy thereof according to the invention would include a source of aluminum-based feedstock, a subsystem for heat-treating the feedstock, and an ultrasonic consolidation subsystem for bonding the heat-treated feedstock to a substrate. Such apparatus may further include a temperature- and/or atmosphere-controlled chamber through which the feedstock passes prior to ultrasonic consolidation. A support may be provided to minimize slumping due to creep. A heat source may be provided to artificially age the consolidated feedstock. The subsystem for heat-treating the feedstock may additionally perform a solution heat-treatment process.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an automated ultrasonic consolidation system to which the invention is applicable;

FIG. 2 illustrates the use of support materials to fabricate an object with overhanging parts;

FIG. 3a shows a stacking pattern for tape lay-up;

FIG. 3b shows a basic feed arrangement for tape stock;

FIG. 3c is a drawing of a horizontal section of the object showing adjacent tape segments;

FIG. 3d is a drawing of a vertical section of the object showing the vertically stacked sections; and

FIG. 4 is directed to ultrasonically applying aluminum, in the form of foil, dots, or wires in a solution-heat-treated condition, over an existing structure which might be in an aged or unaged condition.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a schematic diagram of an automated ultrasonic consolidation system to which the invention is applicable. A computer-aided design unit 60 provides a layer-by-layer description of the object and of the support, as needed. The object material is fed onto the work area 75 by an object-material feed unit 64. The support material is fed onto the work area 75 by a support-material feed unit 62. The feed units may be combined into one when the shapes of the object and support layers are compatible, for instance sheets of plastic are used for the support and sheets of aluminum foil for the object. In general, two different feed units are required.

As shown in FIG. 2, the object may be fabricated by consolidating segments of tape 100 or filament or dots of material, as described below in other embodiments of the invention, while the support for overhanging parts 95 of the object may be constructed by adding layers of support material 90.

The object layers may be either precut, or excess object may be removed by an object removing unit 80, which could be a mechanical or ultrasonic knife, drill, or milling tool, or a laser beam. If used, support material may be removed by a removing unit 85. Sporadic ultrasonic spot-welding of the support material may be limited to the extent necessary to provide a rigid substrate for overhanging parts of the object, thereby facilitating rapid removal of the support by cutting through thin, unwelded sections of the support structure.

The CAD system 60 interfaces with a numerical controller 70, which controls an actuation system (not shown). The actuation system brings the support feed unit 62, the support ultrasonic welding unit 66, the object feed unit 64 and the object ultrasonic welding unit 68 into proper position in the work area 75, so that the ultrasonic consolidation of the layers takes place according to the CAD description of the object and support. The actuation system also controls the vertical motion of the substrate or anvil and the motion of any additional vertical clamps required by the application, so that clamping pressure may be applied on two layers undergoing consolidation.

Feedstock in the form of sheets is often difficult to handle and maintain under uniform in-plane tension and pressure orthogonal to its plane; it may require very wide rollers to be fitted to the sonotrode, and successive passes of the roller to cover the entire sheet. A preferred approach with respect to wide objects is to build such an object from layers of material which are cut from a roll of tape. FIGS. 3a through 3d illustrate the building of an object by tape lay-up. FIG. 3a shows a typical lamination stacking pattern, in which the layers of tape forming one section of the object have a direction which is at a 90 degree angle with the direction of the layers of tape forming the next section of the object.

The set-up of the operation is shown in FIG. 3b. A feed spool 120 holds the tape 110, which passes through a tension roll 130 and is fed on to the work area 75 to be consolidated with previous layers by the roller 44 of a sonotrode. The tape is usually 1 to 2 inches wide. FIG. 3c is a drawing of a horizontal section of the object showing adjacent tape segments, and FIG. 3d is a drawing of a vertical section of the object showing the vertically stacked sections.

For this process, ultrasonic vibrations are preferably transmitted in two orthogonal directions, namely, between the horizontal sections, and between the vertical surfaces of adjacent segments of tape forming each section. Such a configuration permits full consolidation, so that the bond lines which are visible in the stacking pattern of FIG. 7a, are no longer visible after consolidation.

This invention more specifically resides in the deposition of heat-treated aluminum using ultrasonic consolidation without disturbing the properties of the underlying material(s). Aluminum is a lightweight, structural material that can be strengthened through alloying and, depending upon composition, further strengthened by heat treatment and/or cold working. Among the advantages of aluminum are its low density; a high strength-to-weight ratio; good resistance to corrosion; and ease of fabrication and diversity of form. Wrought and cast alloys are identified by a four-digit number, the first digit generally identifying the major alloying element used in the process. For casting alloys, the fourth digit is separate from the first three digits by a decimal point and indicates the form of the raw material.

The tempered designation appears as a hyphenated suffix to the basic alloy number. Four basic tempered designations are used for aluminum alloys. They are F for “fabricated”; O for “annealed”; H for “strain-harden” and T for “thermally treated.” There are many T designations, including T4 which signifies solution heat-treated (SHT) and naturally aged to a substantially stable condition. This applies to products which are not cold worked after solution heat-treatment, or in which the affect of cold working flattened or straightening may not be recognized in mechanical property limits. T6, on the other hand, signifies solution heat-treated and then artificially aged. Mechanical property limits are not affected by cold-working. Most alloys in the —W and −T4 conditions are artificially aged to T6. There are many variations to both T4 and T6 treatments.

Referring to FIG. 4, the preferred embodiment of the invention is directed to ultrasonically applying aluminum, in the form of foil 402, dots, or wires in a solution-heat-treated condition, over an existing structure 404 which might be in an aged or unaged condition. The ultrasonically deposited SHT material is either allowed to age naturally at room temperature, or a heat source of some kind, whether general or local, is applied to achieve an artificially aged condition such as T-6. The invention is applicable to any aging or non-aging aluminum alloy system, or any other alloy system or alloy systems (since dissimilar metals could be used). One or more of the alloys employed may be deposited in a condition in which alloying elements are present in solid solution and thermo-mechanical treatment can be used to increase the strength of the material via precipitation hardening.

The build material may be generated in an SHT condition; for example, by solution heat treating of the feed stock off-line, and maintaining it under certain temperature conditions to prevent precipitation of solutes prior to ultrasonic consolidation of the SHT feedstock. Alternatively, the feedstock may be passed through a temperature- and/or atmosphere-controlled chamber 406 in an online process in which it is then fed directly into an ultrasonic consolidation system 410.

The apparatus further preferably includes a mechanism 412 for supporting the feedstock from slumping due to creep which may occur at the high temperatures employed to solution heat treat aluminum alloys. The feedstock may be quenched via an argon quench or other atmosphere controlled quenching technique to control feedstock surface condition as it is fed to the ultrasonic consolidation head, while maintaining the material in the SHT condition as it is cooled to the application temperature and deposited. The system and method have numerous important applications, including aircraft and aerospace structures.

Claims

1. A method depositing aluminum or an alloy thereof, comprising the steps of:

heat treating an aluminum-based feedstock; and

ultrasonically consolidating the feedstack to a substrate.

2. The method of claim 1, wherein the feedstock is solution heat treated.

3. The method of claim 1, wherein the feedstock is solution heat treated off line and maintained under controlled temperature conditions to prevent precipitation of solutes prior to the ultrasonic consolidation.

4. The method of claim 1, wherein the feedstock is heat-treated on-line by passing it through a temperature- and/or atmosphere-controlled chamber prior to ultrasonic consolidation.

5. The method of claim 1, wherein the feedstock is supported to minimize slumping due to creep.

6. The method of claim 1, wherein the feedstock is T4.

7. The method of claim 1, wherein the feedstock is aged.

8. The method of claim 1, wherein the feedstock is aged to T6.

9. The method of claim 1, wherein the feedstock is allowed to age naturally at room temperature.

10. The method of claim 1, wherein a heat source is used to artificially age the consolidated feedstock.

11. The method of claim 1, wherein the substrate is aged or unaged.

12. The method of claim 1, wherein the substrate forms parts of an aerospace or aircraft structure.

13. A product constructed using the process of claim 12.

14. A system for depositing aluminum or an alloy thereof, comprising:

a source of aluminum-based feedstock;

a subsystem for heat-treating the feedstock; and

an ultrasonic consolidation subsystem for bonding the heat-treated feedstock to a substrate.

15. The system of claim 14, wherein the feedstock is solution heat treated.

16. The system of claim 14, further including a temperature- and/or atmosphere-controlled chamber through which the feedstock passes prior to ultrasonic consolidation.

17. The system of claim 14, further including a feedstock support to minimize slumping due to creep.

18. The system of claim 14, further including a heat source to artificially age the consolidated feedstock.

19. The system of claim 14, wherein the subsystem for heat-treating the feedstock performs a solution heat-treatment process.

20. The system of claim 14, wherein the source of aluminum-based feedstock is in the form of tapes, sheets, wires, or droplets.