The present invention relates to the fabrication of parts and devices, and more particularly relates to solid free-form fabrication processes that create parts and devices by selectively applying feedstock material to a substrate or an in-process workpiece.
Solid free-form fabrication (SFF) is a designation for a group of processes that produce three dimensional shapes from additive formation steps. SFF does not implement any part-specific tooling. Instead, a three dimensional component is often produced from a graphical representation devised using computer-aided modeling (CAM). This computer representation may be, for example, a layer-by-layer slicing of the component shape into consecutive two dimensional layers, which can then be fed to control equipment to fabricate the part. Alternatively, the manufacturing process may be user controlled instead of computer controlled. Generally speaking, a component may be manufactured using SFF by successively building feedstock layers representing successive cross-sectional component slices. Although there are numerous SFF systems that use different components and feedstock materials to build a component, SFF systems can be broadly described as having an automated platform/positioner for receiving and supporting the feedstock layers during the manufacturing process, a feedstock supplying apparatus that directs the feedstock material to a predetermined region to build the feedstock layers, and an energy source directed toward the predetermined region. The energy from the energy source modifies the feedstock in a layer-by-layer fashion in the predetermined region to thereby manufacture the component as the successive layers are built onto each other.
One recent implementation of SFF is generally referred to as ion fusion formation (IFF). With IFF, a torch such as a plasma, gas tungsten arc, plasma arc welding, or other torch with a variable orifice is incorporated in conjunction with a stock feeding mechanism to direct molten feedstock to a targeted surface such as a base substrate or an in-process structure of previously-deposited feedstock. A component is built using IFF by applying small amounts of molten material only where needed in a plurality of deposition steps, resulting in net-shape or near-net-shape parts without the use of machining, molds, or mandrels. The deposition steps are typically performed in a layer-by-layer fashion wherein slices are taken through a three dimensional electronic model by a computer program. A positioner then directs the molten feedstock across each layer at a prescribed thickness.
There are also several other SFF process that may be used to manufacture a component. Direct metal deposition, layer additive manufacturing processes, and selective laser sintering are just a few SFF processes. U.S. Pat. No. 6,680,456, discloses a selective laser sintering process that involves selectively depositing a material such as a laser-melted powdered material onto a substrate to form complex, net-shape objects. In operation, a powdered material feeder provides a uniform and continuous flow of a measured amount of powdered material to a delivery system. The delivery system directs the powdered material toward a deposition stage in a converging conical pattern, the apex of which intersects the focal plane produced by a laser in close proximity to the deposition stage. Consequently, a substantial portion of the powdered material melts and is deposited on the deposition stage surface. By causing the deposition stage to move relative to the melt zone, layers of molten powdered material are deposited. Initially, a layer is deposited directly on the deposition stage. Thereafter, subsequent layers are deposited on previous layers until the desired three-dimensional object is formed as a net-shape or near net-shape object. Other suitable SFF techniques include stereolithography processes in which a UV laser is used to selectively cure a liquid plastic resin.
When building a metal component using many SFFF process, the mechanical properties of the metal product may be limited by the metal's grain size. Relatively large grains is sometimes an inherent trait of materials formed using SFFF. For example, IFF in essence is a weld deposition process, and welds tend to have somewhat large columnar grains. Metals having small equiaxed grains typically have higher strength than metals having relatively large grains.
Hence, there is a need for SFFF processes such as IFF that include a technique for improving a workpiece material's strength after heated feedstock is deposited onto a targeted surface to form the workpiece. There is a further need for a technique that optimizes grain size and thereby improves the workpiece material's mechanical properties.
The present invention provides a solid free form fabrication method for manufacturing a component from successive layers of metal feedstock material, with each of the successive layers representing a cross-sectional component slice. First, a first of the successive layers is formed by directing the feedstock material to a predetermined region, the layer comprising at least one crystal grain. Then, the at least one crystal grain is deformed to create dislocations therein. A second layer is formed on the first layer, and the first and second layers are heated to form new crystal grains that are differently sized than the at least one crystal grain.
The present invention also provides another solid free form fabrication method. First, successive layers are formed by directing the feedstock material to predetermined regions, the layers together comprising at least one crystal grain. Then, the at least one crystal grain is deformed to creating dislocations therein. Finally, the layers are heated to form new crystal grains that are smaller than the at least one crystal grain.
Other independent features and advantages of the preferred apparatus and method will become apparent from the following detailed description, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention.
The following detailed description of the invention is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any theory presented in the preceding background of the invention or the following detailed description of the invention.
Additional elements depicted in
A cross-sectional view of the torch 120 is depicted in detail in
A noble gas such as argon is preferably ionized using the arc electrode 150, although alternative inert gases, ions, molecules, or atoms may be used in conjunction with the torch 102 instead of argon. These alternative mediators of the plasma energy may include positive and/or negative ions, or electrons alone or together with ions. Further, reactive elements may be combined with an inert gas such as argon to optimize performance of the torch 102. The plasma generating process so energizes the argon gas that the gas temperature is raised to between 5,000 and 30,000 K. Consequently, only a small volume of energized argon gas is required to melt feedstock 160 from the wire feed mechanism 104. Nozzles of varying apertures or other orifices may be used to provide specific geometry and plasma collimation for the fabrication of different components. Direct beam nozzle orifices may contrast with nozzles having a fan shape or other shapes.
The ionized argon plasma, and all other ionized noble gases, has strong affinity for electrons and will obtain them from the surrounding atmosphere unless the atmosphere consists of gases having equal or higher electron affinity. One advantage of the exemplary IFF system depicted in the drawings does not require a pressurization chamber or other chamber in which the ambient gas is controlled. However, to prevent the ionized argon plasma from obtaining electrons and/or ions from the surrounding atmosphere, i.e. from nitrogen and oxygen typically present in ambient environments, the ionized argon plasma is sheathed or protected by a curtain of helium, another noble gas, or other inert gases flowing from the nozzle from a coaxial channel 172. Helium and other noble gases hold their electrons with a high degree of affinity, and are less susceptible than oxygen or nitrogen to having its electrons taken by the ionized argon plasma.
Collisions between the energetic argon atom and the nozzle 154 may substantially heat and damage the nozzle if left unchecked. To cool the nozzle 154, water or another cooling fluid is circulated in a cooling chamber 174 that surrounds the nozzle 154. A gas and water flow line 180 leads into the cooling chamber 174.
Any material susceptible to melting by an argon ion or other plasma beam may be supplied using a powder feed mechanism or the wire feed mechanism 104 as feedstock 160. Such materials may include steel alloys, aluminum alloys, titanium alloys, nickel alloys, although numerous other materials may be used as feedstock depending on the desired material characteristics such as fatigue initiation, crack propagation, post-welding toughness and strength, and corrosion resistance at both welding temperatures and those temperatures at which the component will be used. Specific operating parameters including plasma temperatures, build materials, melt pool parameters, nozzle angles and tip configurations, inert shielding gases, dopants, and nozzle coolants may be tailored to fit an IFF process. U.S. Pat. No. 6,680,456 discloses an IFF system and various operating parameters, and is hereby incorporated herein by reference.
As previously discussed, when building a component using IFF or any SFFF process, the mechanical properties of the metal product may be limited if the metal's grain size is too large. Metals having relatively small equiaxed grains typically have higher strength than metals having larger grains. Relatively large grains may be an inherent trait of materials formed using SFFF depending on deposition parameters. For example, metal components produced using IFF or other direct metal deposition processes may have somewhat large columnar grains.
As depicted in
According to a preferred embodiment, crystal deformation is performed at or below the metal's recrystallization temperature in order for the effects of crystal deformation to be maintained. The load may also be applied while the first layer 10 is higher than the metal's recrystallization temperature, and especially at temperatures significantly above the recrystallization temperature, and large crystal grains may thereby be formed in or restored into the first layer 10. In contrast, when performing crystal deformation at or below the metal's recrystallization temperature the small grains produced by the deformation process are preserved.
In
In a preferred method, the plunger or other device that causes crystal deformation is actuated automatically after each layer deposition, or after a predetermined number of layer depositions. The SFFF apparatus may be equipped with a mechanism that follows a layer deposition device and exerts a deformation stress between deposition passes once the previously-deposited layer is cooled to or below the recrystallization temperature for the metal in the layer.
Turning now to
Although all of the previously-described methods include a crystal deformation process that is performed at a feedstock layer surface, other exemplary methods include inducement of crystal deformation from a structure's interior.
Thus, the SFFF methods of the present invention include various mechanisms for inducing crystal deformation after heated feedstock is deposited to form a workpiece. The crystal deformation methods may be performed between successive feedstock depositions using some mechanisms, but may also be performed by creating stress between layers after two or more feedstock layers have been deposited. Exemplary methods incorporate the crystal deformation procedures while the component is positioned on a building platform, so all the manufacturing and deformation processes may be performed in-situ, without the need to move the workpiece from one station to another between each successive feedstock deposition. The SFFF methods, including the crystal deformation steps, enable the control and optimization of component grain size and thereby improve the component strength.
While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt to a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.