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.
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.
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.
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.
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.
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
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.
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
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.
This application claims the benefit of U.S. Provisional Application No. 60/647,538 filed Jan. 26, 2005.
Number | Date | Country | |
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60647538 | Jan 2005 | US |