CROSS-REFERENCES TO RELATED APPLICATIONS
- TECHNICAL FIELD
This application claims the benefit of U.S. Provisional Application No. 60/647,538 filed Jan. 26, 2005.
The present invention relates to gas valves, and more particularly to lightweight gas valves capable of withstanding the hot gas environment generated from burning propellants used in various systems such as divert and attitude control systems for missiles, interceptors, and space craft.
Space craft, missiles, and other projectiles are sometimes equipped with steering features that enable the projectiles to provide for their own guidance. Some of such features include various propellant output valves that operate by opening and closing to redirect propellant thrust and thereby steer the projectile.
Valves for propellant redirection are capable of withstanding the hot environment produced by engine gases since engine gas generators may use and exhaust gases at between about 1500 and 5000° F. Even if valves are only required to be briefly exposed to hot gases, the valves should be capable of withstanding such high temperatures for their short duty cycles. For this reason, high temperature divert and attitude control valves for space craft, missiles, interceptors, and other craft are sometimes formed from refractory metals that maintain their strength and form at high temperatures. Also, valves and valve components that are not subjected to hot environments are commonly made from refractory metals or other metals that have high strength and are metallurgically sound.
Although care is taken to produce hot gas valves and other valves that are structurally and metallurgically sound, the processes for manufacturing the valves can be somewhat inefficient in various aspects including time and expense. Refractory metal hot gas valve components are currently produced by performing electro-discharge machining and grinding processes on large refractory metal plates or bars. For example, one class of hot gas valve that may be incorporated into missiles includes a fluidic stack through which a fluid is introduced into a valve chamber. The fluidic stack is a stack of plates, each of which has a void that, together with voids from the other plates in the stack, forms a three-dimensional fluid passage. The plates and bars themselves are typically fabricated using sintered powder metallurgy processes. Although the valves that are formed from these combined processes are operable at high temperatures, the valve components may include micropores or other inconsistencies that are sometimes products of sintered powder metallurgy processes, and that may affect valve's mechanical integrity if the components are included in the valve. The component inconsistencies require screening prior to manufacturing and/or using a hot gas valve to assure that the valve will operate correctly at high temperatures.
- BRIEF SUMMARY
Hence, there is a need for methods for manufacturing hot gas valves and valve components that have high ductility and high strength. There is a particular need for methods that manufacture such components with high structural and metallurgical consistency so that the need for inefficient screening methods can be minimized.
The present invention provides a first method of manufacturing a hot gas valve for a divert and attitude control system in a propelled craft. The method comprises the steps of building a plurality of separate valve components using a solid free-form fabrication process, and assembling the plurality of separate valve components to produce the hot gas valve. The solid free-form fabrication process comprises the steps of forming successive feedstock layers by depositing the feedstock material into a predetermined region, the feedstock layers representing successive cross-sectional component slices, and modifying the feedstock by directing an energy source to the predetermined region and thereby creating modified regions in the successive feedstock layers, the combined modified regions defining an at least partially-formed valve component.
The present invention also provides a second method of manufacturing a hot gas valve for a divert and attitude control system in a propelled craft. The second method comprises the steps of forming successive feedstock layers by depositing the feedstock material into a predetermined region, the feedstock layers representing successive cross-sectional slices of the hot gas valve, and modifying the feedstock by directing an energy source to the predetermined region and thereby creating modified regions in the successive feedstock layers, the combined modified regions defining at least a segment of a hot gas valve in net or near-net shape.
The present invention also provides a third method of manufacturing a hot gas valve for a divert and attitude control system in a propelled craft. The third method comprises the steps of building a plurality of separate valve segments using a solid free-form fabrication process, and assembling the plurality of separate valve segments to produce the hot gas valve in net or near-net shape.
- BRIEF DESCRIPTION OF THE DRAWINGS
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.
FIG. 1 is an exploded perspective view of a disc switching element and its components, including a thruster, a hot gas valve disc, a disc seat, and a disc chamber;
FIG. 2 is a flow chart that outlines a method for manufacturing a hot gas valve by building individual valve components and then assembling the hot gas valve according to an embodiment of the invention;
FIG. 3 is an exploded view of an exemplary fluidic amplifier module, which when constructed is an assembly of stacked and joined plates;
FIG. 4 is a flow chart that outlines a method for manufacturing a hot gas valve or valve in net or near-net shape using a solid free-form fabrication process according to another embodiment of the invention; and
- DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
FIG. 5 is a flow chart that outlines a method for manufacturing a hot gas valve in net or near-net shape by building individual valve segments and then assembling the hot gas valve according to another embodiment 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.
The following description includes several methods for manufacturing hot gas valves and valve components that have high ductility and high strength. Although the discussion is directed specifically toward such components, the manufacturing methods are not limited to the particular hot gas valves depicted in the drawings, and can be used to manufacture a variety of other elevated temperature valves and valve components that are used in various industries. The manufacturing methods include solid-free-form fabrication processes, alone or in combination with machining, bonding, and or heating steps, to build the valve components or even the entire valve in net or near-net shape.
FIG. 1 is an exploded perspective view of a high temperature divert and attitude control disc switching element 100 and its components for propelled craft. The disc switching element 100 includes first and second side thrusters 10 and 18, and a disc chamber 16. The first side thruster 10 includes a first disc seat 12 that is housed inside the disc chamber 16, and the second side thruster 18 also includes a non-illustrated second disc seat. A hot gas valve disc 20 is also housed inside the disc chamber 16 between the side thrusters 10 and 18. The disc chamber 16 includes first and second gas inlet ports 14 a and 14 b and the hot gas valve disc 20 is positioned between the first and second gas inlet ports 14 a and 14 b. The side thrusters control a propelled craft's roll, pitch, and yaw movements, and can be powered by the same engine propellant as the main rearward-thrust engine. When propellant gas enters one of the gas inlet ports 14 a and 14 b, the hot gas valve disc 20 is pneumatically pushed toward one of the disc seats and the propellant gas exits the side thruster that is on the same side as the gas inlet port by which the propellant gas entered the disc chamber 16. For example, if the propellant gas enters the disc chamber 16 by way of the second gas inlet port 14 b, the pressure from the propellant gas pushes the disc 20 away from the second gas inlet port 14 b and toward the disc seat 12 to thereby effectively cause the propellant gas to exit only through the second side thruster 18.
Many refractory metals and alloys are high strength, making them suitable hot gas valve materials. Pure rhenium and rhenium alloys are exemplary refractory metals. Some exemplary rhenium alloys include one or more of tungsten, tantalum, molybdenum, or other high temperature elements. Other suitable metals and alloys may be tungsten or tungsten-based alloys, tantalum or tantalum-based alloys, or other high temperature metals and alloys of the same.
FIG. 2 is a flow chart that outlines a general method for manufacturing a hot gas valve by building individual valve components and then assembling the hot gas valve. Step 30 comprises fabricating a starting material using a solid-free-form fabrication (SFF) process. 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 such as laser additive manufacturing, 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.
Returning to the method outlined in FIG. 2, after manufacturing a starting material using a SFF process, any necessary machining is performed on the starting material to form a valve component as step 32. The starting material may be a block, sheet, plate, rod, cylinder, or another fundamental shape. For example, one class of fluidic diverter valves that may be incorporated into a missile or space vehicle flight control system includes a fluidic amplifier module through which a fluid is introduced into a valve chamber. FIG. 3 is an exploded view of an exemplary fluidic amplifier module 50, which when constructed is an assembly of stacked and joined plates 60A-F. Each of the plates 60A-F in the fluidic amplifier module 50 includes fluid pathways 52A-F that together form a three-dimensional fluid passage. During use, a hot gas flows through the fluid passage and into one of the gas inlet ports 14 a and 14 b,the hot gas valve disc 20 is pneumatically pushed toward one of the disc seats and the propellant gas exits the side thruster that is on the same side as the gas inlet port by which the propellant gas entered the disc chamber 16.
The plates 60A-F are conventionally fabricated using sintered powder metallurgy processes, and may consequently include micropores or other inconsistencies that are sometimes products of the sintered powder metallurgy process. As step 32, after one of the plates 60A is manufactured, a fluid pathway 52A and other contours are formed in the plate 60A using one or more suitable machining process such as electro-discharge machining and/or grinding processes.
After the valve component is formed from the starting material, it is determined as step 33 whether additional valve components should be fabricated. If so, another block, sheet, plate, rod, cylinder, or other starting material is manufactured using a SFF process by repeating step 30, and any necessary machining is performed on the starting material by repeating step 32 to build another valve component. Continuing with the example of the fluidic amplifier module 50, the individual plates 60B-F are made in the same manner as the plate 60A by first forming the plates by a SFF process and then machining the plates 60B-F as necessary to include the fluid pathways 52B-F and other contours. Further, steps 30 and 32 are repeated to form the disc switching element components including the first and second side thrusters 10 and 18, the disc chamber 16, the valve disc 20, and any other valve components.
After forming the valve components, the hot gas valve is completed by assembling the individual valve components as step 34. Diffusion bonding or other bonding means may be employed to assemble the valve components. Assembling the valve components to complete the hot gas valve may also include any desirable machining to the assembled components.
FIG. 4 is a flow chart that outlines another exemplary method for manufacturing a hot gas valve in net or near-net shape using a solid free-form fabrication process. As step 40, Instead of fabricating and machining starting materials such as blocks, sheets, plates, rods, cylinders, and so forth, the entire hot gas valve is built in a layer-by-layer fashion to net or near-net shape using a SFF process. According to one exemplary embodiment, the hot gas valve includes the disc switching element 100 and the fluidic amplifier module 50 as a continuous and unitary structure rather than an assembly of separate valve components. For example, the fluidic amplifier module 50 is a continuous and unitary structure instead of a laminate formed from a plurality of individual plates. The fluid pathways are built up onto each other layer-by-layer, and together provide the three-dimensional fluid passage into the gas inlet ports 14 a and 14 b.
Even if the disc switching element 100, the fluidic amplifier module 50, or other valve components are built from different materials, a SFF process enables on-demand adjustments to the material being deposited. For example, an IFF process may utilize a plurality of wire and/or powder feeding devices. Each feeding device may introduce a different material into the hot plasma stream produced by the torch. A feeding rate for one or more feedstock materials may be adjusted between deposition of two layers, or even as an intralayer compositional change. Feedstock temperatures may also be adjusted on demand during deposition by adjusting the torch temperature, feedstock feed rates, and so forth. In this way, each valve component may be built to have a particular composition, grain size, density, ductility, and so forth.
After building the hot gas valve to net or near-net shape, any final machining is performed on the valve as step 42. Electro-discharge machining, a grinding process, or other suitable machining steps may be performed to bring the valve to its completed form.
Alternatively, a valve segment may be fabricated using a SFF process as step 40 instead of the entire valve. A valve segment is different from a rod, sheet, block, plate, cylinder, or other starting material in the sense that a valve segment resembles a portion of the completed valve in net or near-net shape, and is built as a unitary and integral structure and not as an assembly of starting materials. However, it may be advantageous to perform some machining as step 42 after a segment of the valve has been fabricated. For example, machining may be performed on an fluid passageway or other interior valve component after fabricating several layers of the valve but before the valve is entirely fabricated. If so, valve segments are build to near-net shape and machining is performed between formation of valve segments as step 44 until the valve is brought to its completed form.
will be appreciated by those skilled in the pertinent art that the hot gas valve depicted in FIGS. 1 and 3 is just one type of hot gas valve that may be fabricated using the methods of the present invention. For example, U.S. Pat. Nos. 6,926,036 and 5,927,335 describe other hot gas valves that, along with numerous other hot gas valves, may be fabricated using the SFF processes described herein.
FIG. 5 is a flow chart that outlines another exemplary method for manufacturing a hot gas valve. Instead of fabricating and machining starting materials such as blocks, sheets, plates, rods, cylinders, and so forth, a segment of a hot gas valve is built to net or near-net shape using a SFF process as step 61. The valve is fabricated in the same manner as set forth in the method outlined in FIG. 4, although instead of fabricating the entire valve before performing any machining, valve segments are separately manufactured in a layer-by-layer fashion and then machined as step 62. After the valve segment is fabricated and any machining is performed, it is determined as step 63 whether additional valve segments should be fabricated. If so, steps 60 and 62 are repeated and additional valve segments are fabricated to net or near-net shape, and any necessary machining is performed for each segment. When all the valve segments are fabricated, the valve is assembled as step 64 from all the valve segments.
The preceding description thus includes several SFF methods for manufacturing hot gas valves and valve components in a manner that reduces the amount of machined and/or discarded structural material. The SFF methods produce high quality valve components with reduced porosity or tailoring inconsistencies that are sometimes associated with powder metallurgy methods.
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.