Tooling apparatus for composite fabrication

Abstract: The present invention relates to tooling for the fabrication of composite materials, particularly layered composite materials. The tooling apparatus encapsulates the composite material and uses an applied pressure, either atmospheric, induced gaseous or mechanical, to the material to retain it in place during off-gassing and/or consolidation. The apparatus is made of a material having a low interstitial gas content.

Description: Field of the Invention The present invention is directed to a tooling apparatus for composite fabrication and, more particularly, to a tooling which encapsulates the composite material to be fabricated and holds it in place during fabricating processing steps such as off-gassing and consolidation. Background Art In the prior art, it is known to consolidate composite materials comprising layers of fibers and a matrix together by first off-gassing the composite material followed by consolidation. These types of composite materials are shown in Figure 1 wherein the composite material is designated by the reference numeral 10. The composite material 10 comprises a series of layered fibers 1 surrounded by a matrix 3. Typically, the fibers 1 and matrix 3 are held together with an adhesive 5 in what is typically called a green form, see Figure 2, reference numeral 20. The adhesives 5 are usually organic materials which have been dissolved in a solvent. The green form 20 is placed in a tool and is subject to a vacuum to remove any moisture in the green form 20 as well as the organic material of the adhesive 5. The off-gas processing volatizes the water and adhesives by heating the green form to the appropriate volatizing temperature. A tooling according to the preamble of claim 1 is known for instance from US 5 370 760. One of the problems with prior art tooling in this regard is the inability to allow the volatized water and adhesives to be removed while holding the composite material in place so that it can be subsequently consolidated. In prior art apparatus, the composite material is subjected to shifting which disrupts the orientation and spacing of the reinforcing materials therein, for example, the fibers 1 in the composite 10 of Figure 1. With this disruption, the consolidated composite material has less than desirable product characteristics. As such, a need has developed to provide an improved tooling apparatus which not only allows the volatized water and adhesives to be removed but also keeps the green form in place during off-gassing and consolidation. Responsive to this need, the present invention provides a tooling apparatus which overcomes the deficiencies in the prior art apparatus discussed above. That is, according to the invention, the inventive tooling apparatus includes features which not only permit off-gassing to occur but also hold the composite material in place so that the composite can be subjected to both off-gassing and consolidation. Summary of the Invention Accordingly, it is a first object of the present invention to provide a tooling apparatus for the fabrication of layered or composite materials. A further object of the present invention is to provide a tooling apparatus which encapsulates the composite material to be off-gassed and consolidated by using means for applying pressure to the composite material during off-gassing and consolidation. A still further object of the present invention is to provide a tooling apparatus which facilitates evacuating a tooling apparatus cavity for off-gassing. Yet another object of the present invention is to provide an apparatus which utilizes atmospheric pressure as a loading means in combination with evacuation to hold or secure a composite material to be off-gassed and subsequently consolidated. Other object and advantages of the present invention will become apparent as a description thereof proceeds. In satisfaction of the foregoing objects and advantages, the present invention provides, in its broadest sense, a vacuum tooling apparatus which utilizes a flexible bag, the flexible bag made of a metallic material having a low interstitial gas content. The bag forms a cavity which is sized to receive an organic material-containing composite material which it to be subjected to off-gassing and consolidation. The bag has a thickness and flexibility which permits atmospheric pressure to retain the composite material in place when the cavity is subjected to a vacuum. The tooling apparatus also includes at least one evacuation port in the bag to permit evacuation of the cavity. The bag is sealed along its periphery except for the one or more evacuation ports. The evacuation port comprises tubing which is attached to the flexible bag. The cavity receiving the composite material for evacuation is formed by a frame, plungers, an encapsulating bag and one or more evacuation ports. The frame surrounds the composite material to be off-gassed and consolidated. The plungers provide a loading force/restraint on the top and bottom of the composite material. The encapsulating bag in combination with the frame forms the cavity enclosing both the composite material and plungers for evacuation. Evacuation ports may be made part of the frame to evacuate the cavity. The frame also may include one or more spacers, generally in the configuration of a picture frame which provide thickness adjustment for the tooling apparatus to accommodate the plunger thicknesses as well as the green and final thicknesses of the composite material being fabricated. Mechanical loading means are provided in conjunction with one or both of the plungers to adjust the loading on the composite material during evacuation. These mechanical loading means are used in the apparatus according to the third embodiment. Brief Description of the Drawings Reference is now made to the drawings of the invention wherein: Figure 1 is a sectional view of a composite material adaptable for use in the inventive tooling apparatus; Figure 2 is a sectional view of a green form the composite material of Figure 1; Figure 7a is a sectional view of a third embodiment of the inventive tooling apparatus; Figure 7b is a top view of the embodiment depicted in Figure 7a; Figure 9 is a sectional view of a fifth embodiment of the inventive tooling apparatus. Description of the Preferred Embodiment In its broadest sense, the inventive tooling apparatus provides a way to retain a composite material in place during off-gassing and subsequent consolidation. A vacuum is formed in a space surrounding the composite material so that atmospheric pressure, an applied gaseous pressure, a mechanical loading or a combination thereof applied to the composite material holds it in place. The pressure from either the atmosphere, the applied gaseous pressure or the mechanical loading retains the composite material in place during off-gassing and subsequent consolidation. Thus, any movement of precisely aligned composite material components is avoided during both off-gassing and consolidation, thereby producing a high quality composite material. It should be understood that the composite material which is adaptable for use with the inventive tooling apparatus can be any known composite material which is subjected to off-gassing and consolidation. Typically, these composite materials include a reinforcing material which could be either a fiber, whisker, powder or the like. The reinforcing materials could include carbon, silicon carbide, boron, alumina, graphite, silicon nitride. Generally, the reinforcing materials are combined with a matrix which could be metallic or non-metallic. Typically, examples of matrix materials include aluminum, magnesium, titanium alloys or the like. It should be understood that the tooling apparatus of the invention is not limited to any specific type of composite material. The techniques used to off-gas or consolidate the composite material when placed in the inventive tooling apparatus are also conventional in the art and require no further description for understanding of the invention. Any conventional type of off-gassing and/or consolidation processing can be utilized with the inventive tooling apparatus. For this application, a "low interstitial gas content material" is one that has less than 2,000 ppm total of a reactive gas therein. Typically, these reactive gasses include oxygen, nitrogen, carbon-containing gasses and hydrogen or hydrogen-containing gasses. The material of the inventive tooling apparatus should be a low interstitial gas content material so that when the material is subjected to a vacuum, the composite material is not adversely affected by any gas contained within the bag or tube material. Typically, the encapsulating bags range from 0.002 to 0.060" thick, more preferably, 0.005" to 0.03". Preferably, the encapsulating bag should have the following characteristics: 1. Ductile enough at room temperature to form around the article being manufactured, 2. be available with a low interstitial gas content, 3. able to be welded to itself and to the off-gas tube material, 4. will not contaminate or alloy with the product material, 5. be available in the proper thickness range (0.002" to 0.060"), and 6. able to be withstand the processing temperature of the product without tearing or cracking. The requirements of the evacuation tube material are the following: 1. Ductile enough at room temperature to be flattened without cracking, 2. be available with a low interstitial gas content, 3. able to be welded to itself and the bag material, 4. able to be mechanically worked, e.g. hot or cold crimped to form a diffusion bond with itself, and 5. able to withstand the processing temperatures of the product without tearing or cracking. Typically, the evacuation tube is welded to one piece of the bag material followed by centering the composite material on that piece. The second piece of bag material is then welded to the first piece and the evacuation tube. The encapsulating bag, when welded, must be helium-leak tight for the tool to work properly. Once the encapsulating bag and evacuation tube are formed to be helium-leak tight, the evacuation bag forming a cavity for the composite material, the composite material is subjected to off-gassing to remove any adhesive, moisture or the like therefrom. When evacuating the encapsulating bag, atmospheric pressure on the encapsulating bag causes the bag to form around the composite material, thereby locking it in place. Consequently, the composite material is retained and no shifting of its components can occur during the off-gassing step. Although welding is disclosed as one means for forming the cavity for the composite material, any known means can be used to form the leak tight cavity for receiving the composite material. Referring now to Figures 7a and 7b, an embodiment of the invention is generally designated by the reference numeral 80 and includes a frame 81, a pair of plungers 83, an encapsulating bag 85 and evacuation tubes 87. All materials of this embodiment are made from the low interstitial gas content material, e.g. a 620 steel or vacuum degassed 1018 steel. The frame 81 can be a single piece of material which surrounds the composite material 33 but can also be made from four individual pieces that are welded together along the outside seams. The plungers 83 can be stacked thin sheets or a single piece of plate stock. Encapsulating bags 85, typically 0.120" thick can also be made from multiple layers which are welded along the edge thereof. The vacuum tubes 87 are seamless-thick wall tubing which is welded to the frame. The frame 81 also includes a passageway 89 which allows for evacuation of the cavity 91 formed by the frame 81 and the encapsulating bag 85. The apparatus 80 can also includes one or more strips of sheet material 93 which are picture frame in configuration and are disposed between the frame 81 and the bag 85. The strips 93 are made in thickness and number to accommodate the plunger thicknesses 83. Of course, the bag 85 could be welded to the appropriately sized frame 81 without the spacers 93, if desired. The size of the apparatus 80 depends on the number and the green and final thicknesses of the composite material 33 being fabricated. The total green stack thickness and final stack thickness, including plungers and any spacers is calculated. The frame thickness is chosen so that there is a minimal interference between the plunger and the frame. The requirements for the frame, the plunger, the bag and the evacuation tubes are the same as that disclosed above except that the bag does not need the above ductility. According to this embodiment, during off-gassing the frame which surrounds the composite material 33 and the plungers which provide a loading on the top and/or bottom prevent the composite material 33 from movement during off-gassing. The frame 81 prevents movement by its physical presence surrounding the composite material with the plunger doing this via the atmospheric pressure applied thereto via the encapsulating bag 85. After off-gassing, the evacuation tubes 87 are crimped and sealed to maintain the vacuum inside the tool. Referring now to Figure 9, a variation of the fourth embodiment is generally designated by the reference numeral 110. In this embodiment, a clamping force can be applied to the plungers 83, the clamping force independently adjustable from the induced atmospheric force. More specifically, bent metal sheets 111, typically 0.030", are placed between the plungers 83 and the outer bags 85. The bent metal sheets 111 are positioned in such a way so as to apply a constant spring force to the plungers but not allow direct contact between the outer bags and plungers. In this embodiment, the volume 91 can be evacuated as described in the embodiment depicted in Figure 7a in combination with applying a mechanical force against the plungers 83 by reason of the bent metal sheets 92. It should be understood that the sheet material gauge can be varied to vary the applied spring force as is well known in the art. As such, an invention has been disclosed in terms of preferred embodiments thereof which fulfill each and every one of the objects of the present invention as set forth herein above and provides a new and improved vacuum tooling apparatus for off-gassing and consolidation of composite materials. Of course, various changes, modifications and alterations from the teaching of the present invention may be contemplated by those skilled in the art without departing from the intended spirit and scope thereof. Accordingly, it is intended that the present invention only be limited by the terms of the appended claims.

Claims: A vacuum tooling apparatus (80, 110) for a composite material (33) comprising: a) a frame (81) sized to peripherally surround said composite material, b) a pair of plungers (83) sized to contact upper and lower surfaces of said composite material, c) encapsulating sheets (85) attached to said frame, said encapsulating sheet and said frame forming a cavity (91) containing said plungers and said composite material, d) at least one evacuation port (87) in communication with said cavity for evacuating said cavity wherein atmospheric pressure on said encapsulating sheets and the mass of said plungers hold said composite material in place during said evacuating, characterised in that said frame, plungers, encapsulating sheets and evacuation port are each made of a material having a content of less than 2000 ppm of a reactive gas. The tooling apparatus (80, 110) of claim 1 wherein said at least one evacuation port is a tubing connected to a passageway (89) in said frame which is in communication with said cavity (91). The tooling apparatus (80, 110) of claim 1 further comprising at least one spacer positioned between said frame and a respective encapsulating sheet (85), said spacer, said frame (81) and said encapsulating sheets forming said cavity (91). The tooling apparatus (80,110) of claim 1 further comprising means (111) for applying a force to at least one of said plungers, that is independently adjustable from the atmospheric pressure force, said force applying means positioned within said cavity (91) and between a said encapsulating sheet (85) and one of said plungers (83) adjacent thereto. The tooling apparatus (80, 110) of claim 4 wherein said force applying means (111) is a spring. The tooling apparatus (80,110) of claim 5 wherein said spring a bent sheet metal spring. The tooling apparatus (80, 110) of claim 4 comprising a pair of force applying means (111), each force applying means positioned against a respective said plunger (83).

Inventors: HANUSIAK LISA B, HANUSIAK WILLIAM M, PARNELL JEFFREY M, ROWE CHARLES R, SPEAR STEVEN R, HANUSIAK, LISA B., HANUSIAK, WILLIAM M., PARNELL, JEFFREY M., ROWE, CHARLES R., SPEAR, STEVEN R.
Applicants: ATLANTIC RES CORP, ATLANTIC RESEARCH CORPORATION
Application year: 1997
Main classification: B22F3
IPC codes: B29C33, B22F3, B29C70, B29C37, B29C43