Plastic and nonmetallic article shaping or treating: processes – Direct application of fluid pressure differential to... – Producing multilayer work or article
Reexamination Certificate
1999-01-11
2003-04-29
Walker, W. L. (Department: 1722)
Plastic and nonmetallic article shaping or treating: processes
Direct application of fluid pressure differential to...
Producing multilayer work or article
C264S571000, C264S316000, C425S389000, C425S405100
Reexamination Certificate
active
06555045
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to fiber-reinforced resin structures, and more particularly to an apparatus used to fabricate a fiber-reinforced resin structure using a mold having a grooved surface, and the method of using the same.
BACKGROUND OF THE INVENTION
Vacuum assisted resin transfer molding (VARTM) and related processes and techniques have been widely used to fabricate relatively large fiber-reinforced composite articles. Such articles may include coach chassis for buses and trailers and fiber glass boat hulls, for example.
In general, the VARTM process includes the distribution of dry, fiber strips, plies or mats about the surface of a female mold to form a fiber lay-up of a desired thickness. The fiber strips or plies may take the form of a cloth or sheet of fibers of glass, carbon or other suitable material. In addition, one or more rigid core layers may be included. The core layers may be formed of a solid foam material or balsa wood. The core layers may be sandwiched between the fiber plies to form a fiber/core composite lay-up or laminate.
A flexible, fluid impermeable bag or sheet is positioned atop the exposed lay-up and sealed about the periphery thereof. A relative vacuum is drawn between the mold and the bag, thereby causing the bag to compress against the fiber lay-up. A chemically catalyzed liquid resin is introduced into the evacuated bagged mold through a series of resin supply lines or conduits. A multitude of individual resin supply lines may be used so as to facilitate distributed wetting or infusion of the liquid resin about the fiber lay-up. The vacuum source and resin supply lines are strategically positioned relative to one another in a manner which encourages controlled wetting. In this respect, the vacuum source may be applied at one side of the fiber lay-up and the resin introduced at an opposing side, and thus tending to cause the resin to be pulled across and wet portions of the fiber lay-up therebetween.
Underwetting and overwetting of the fiber lay-up are particularly problematic, as such conditions may result unacceptable structural weaknesses and deficiencies of the resultant article. In addition, nonuniform resin distribution may also result unacceptable structural weaknesses and deficiencies of the resultant article.
Contemporary techniques for facilitating more uniformed or homogeneous resin distribution include the use of cloth material adjacent the fiber lay-up. The cloth forms a screen or matrix of open spaces which tends to wick the resin, and thereby facilitates resin flow. The cloth is removed or peeled away prior to the resin fully curing. Other techniques for enhancing more uniformed resin distribution focus on the resin delivery apparatus, such as specially formed resin supply conduit manifolds and manifolds which are integrated into the vacuum bag itself. While these and other techniques enhance the distribution of resin about the fiber lay-up, they each require the positioning and application of a particular type of cloth or conduit manifold or the like, each time the article is formed. In addition, specialized procedures for disposal and/or clean-up of such additional apparatus must be addressed as well. As such, use of such apparatus increases the time and skill requirements in order to fabricate a resultant article to desired quality control standards.
Where resin overwetting is detected prior to the resin curing, excess resin may be removed via skilled labor intensive steps. Where underwetting is detected in a cured lay-up, the structure may be required to undergo additional processing in the form of reinfusion of liquid resin and subsequent curing of the resin. While such labor intensive steps, including inspection tasks, may result in a structure which conforms to desired mechanical requirements, such a process so limits the production efficiency so as to make the process economically nonfeasible.
As such, based upon the foregoing, there exists a need in the art for an improved method and device, for enhancing resin distribution in comparison to the prior art.
SUMMARY OF THE INVENTION
In accordance with the present invention, there is provided a process for forming a fiber-reinforced resin structure against a mold surface of a rigid mold by vacuum bag forming. The process includes grooving the mold surface of the rigid mold to form resin distribution conduits therein. A fiber-reinforced ply is distributed adjacent the mold surface. A flexible covering is placed over the fiber-reinforced ply and the rigid mold to form a chamber therebetween. The chamber is evacuated. Resin is dispensed into the evacuated chamber such that the resin enters the resin distribution conduits and is thereby distributed about the ply. After the resin is distributed about the ply, the resin is allowed to cure to form a resultant fiber-reinforced resin structure.
In another embodiment of the present invention, there is provided an improvement for an apparatus or tool used in the forming of fiber-reinforced resin structures as described in the above process. The apparatus is provided with a flexible covering and a mold surface which is formed to support a fiber-reinforced ply thereon and over which the covering may be placed to form a chamber therebetween. A vacuum port is further provided for evacuating the chamber to collapse the covering against the ply and the mold surface. The apparatus improvement comprises a plurality of resin distribution conduits formed in the mold surface for distributing the resin about the ply when the resin is dispensed into the evacuated chamber. In this respect, the resin distribution conduits may take the form of straight grooves which are formed to intersect one another in a criss-crossed or grid-like pattern. In the preferred embodiment, at least one of the resin distribution conduits is disposed adjacent a resin port and at least one is disposed adjacent a vacuum port.
The apparatus improvement constructed in accordance with the present invention and the process of fabricating fiber-reinforced structures using the same presents numerous advantages not found in the related prior art. In this respect, the present invention is particularly adapted to provide enhanced resin distribution by the incorporation of the resin distribution conduits or grooves about the mold surface. Such enhanced resin distribution tends to increase the structural integrity of the resultant fiber-reinforced resin structures and reduce the time and skill fabrication requirements. As such, the resultant structures can be produced at rates which make the technology more economically viable.
As such, the present invention represents an advance in the art.
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paten
Jackson Steven Alan
McClure Edward Norman
Sweesy Philip J.
Nguyen Thu Khanh T.
Northrop Grumman Corporation
Stetina Brunda Garred & Brucker
Walker W. L.
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