Plastic and nonmetallic article shaping or treating: processes – Direct application of fluid pressure differential to... – Producing multilayer work or article
Reexamination Certificate
1999-06-18
2001-10-09
Davis, Robert (Department: 1722)
Plastic and nonmetallic article shaping or treating: processes
Direct application of fluid pressure differential to...
Producing multilayer work or article
C264S571000, C425S129100, C425S389000, C425S390000, C425S405100
Reexamination Certificate
active
06299819
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to composite fabrication and, more particularly, to a double chamber vacuum resin transfer molding scheme having applications in the fabrication of fiber reinforced polymer, ceramic matrix, and carbon-carbon composites.
A number of different resin transfer molding processes are described in the prior art. For example, U.S. Pat. No. 5,518,385, teaches a resin transfer molding process wherein the reinforcing material or preform is degassed in an uncompressed condition prior to impregnation of the material with the resin. A different method of fabricating a composite structure is described in U.S. Pat. No. 5,683,646, wherein is disclosed a specialized approach for fabricating long and narrow composite structures using fiber/matrix and foam materials. Despite the efforts evident in the teachings of these and other patent documents, there is a continuing need in the fiber reinforced composite industry for versatile, effective, and low cost methods for fabricating fiber reinforced composites.
BRIEF SUMMARY OF THE INVENTION
This need is met by the present invention wherein a double chamber vacuum resin transfer molding scheme is provided including a compressible seal defining the boundary between a mold cavity and a brim cavity of the molding apparatus. Specific embodiments of the present invention incorporate a hybrid process of vacuum bag molding and resin transfer molding.
In accordance with one embodiment of the present invention, a double chamber vacuum resin transfer molding apparatus is provided comprising a first mold portion and a second mold portion. The first mold portion and the second mold portion are configured such that, in an engaged state, the first mold portion and the second mold portion define a mold cavity and a brim cavity. The mold cavity is isolated from the brim cavity by a compressible seal. Either the first mold portion, the second mold portion, or both, are further configured to define an injection gate in communication with the mold cavity, a mold cavity vacuum port in communication with the mold cavity, and a brim cavity vacuum port in communication with the brim cavity. The first mold portion, the second mold portion, and the compressible seal are arranged such that a decrease in brim cavity pressure below atmospheric pressure causes a corresponding decrease in mold cavity volume.
Preferably, the brim cavity is arranged about the periphery of the mold cavity and the first and second mold portions define respective first and second complementary geometrical profiles. Either the first mold portion, the second mold portion, or both, may be configured to define a plurality of elongated mold portion voids formed in a surface bounding at least a portion of the mold cavity. The elongated mold portion voids may comprise a series of grooves formed in the mold portion.
The compressible seal may be arranged such that it defines either a U-shaped cross section, a V-shaped cross section, or a hollow cross section. Specifically, the compressible seal may be arranged such that it defines V-shaped cross section with a seal base or an inverted V-shaped cross section with a seal base and an open apex. The compressible seal preferably defines a compressible dimension extending between the first mold portion and the second mold portion. The first mold portion and the compressible seal are preferably arranged such that the first mold portion mass contributes to compression of the compressible seal. The compressible seal preferably defines the entire periphery of the mold cavity and the brim cavity surrounds the periphery of the mold cavity.
The brim cavity may be bounded by an inner compressible seal, an outer compressible seal, the first mold portion, and the second mold portion, and the mold cavity may be bounded by the inner compressible seal, the first mold portion, and the second mold portion. Alternatively, the mold cavity may be bounded by the inner compressible seal, the first mold portion, the second mold portion, and a vacuum bag defining an atmospheric hollow included in the mold cavity.
In accordance with another embodiment of the present invention, a double chamber vacuum resin transfer molding process is provided comprising the initial step of providing a double chamber vacuum resin transfer molding apparatus comprising a first mold portion and a second mold portion. The first mold portion and the second mold portion are configured such that, in an engaged state, the first mold portion and the second mold portion define a mold cavity and a brim cavity. The mold cavity is isolated from the brim cavity by a compressible seal. Either or both of the first mold portion and the second mold portion are further configured to define an injection gate in communication with the mold cavity, a mold cavity vacuum port in communication with the mold cavity, and a brim cavity vacuum port in communication with the brim cavity. The first mold portion, the second mold portion, and the compressible seal are arranged such that a decrease in brim cavity pressure below atmospheric pressure causes a corresponding decrease in mold cavity volume.
A preform is provided and the molding apparatus is arranged in the engaged state such that the preform is positioned in the mold cavity. A resin is injected into the mold cavity via the injection gate. The mold cavity and the brim cavity are evacuated so as to compress the compressible seal, decrease the brim cavity pressure, decrease the mold cavity volume, and cause the injected resin to infiltrate the preform. The resin is cured in the mold cavity by maintaining the evacuated state in the brim cavity for an amount of time sufficient to cure the resin. The process may further comprise the step of releasing the vacuum in the mold cavity prior to the resin curing step.
In accordance with yet another embodiment of the present invention, a double chamber vacuum resin transfer molding process is provided comprising the initial step of providing a molding apparatus comprising a first mold portion and a second mold portion. The first mold portion and the second mold portion are configured such that, in an engaged state, the first mold portion and the second mold portion define a mold cavity and a brim cavity. The mold cavity is isolated from the brim cavity by a compressible seal. Either or both of the first mold portion and the second mold portion are further configured to define an injection gate and a mold cavity vacuum port in communication with the mold cavity and a brim cavity vacuum port in communication with the brim cavity. The first mold portion, the second mold portion, and the compressible seal are arranged such that a decrease in brim cavity pressure below atmospheric pressure causes a corresponding decrease in mold cavity volume. A preform is provided and the molding apparatus is arranged in the engaged state such that the preform is positioned in the mold cavity. The mold cavity and the brim cavity are evacuated so as to compress the compressible seal, decrease the brim cavity pressure, and decrease the mold cavity volume. A resin is injected into the evacuated mold cavity via the injection gate so as to cause the injected resin to infiltrate the preform. The evacuated state is maintained in the brim cavity for an amount of time sufficient to cure the resin in the mold cavity.
The first mold portion and the second mold portion may be further configured to define a plurality of injection gates in communication with the mold cavity and the injection gates are arranged to create a substantially uniform infiltration of resin in the preform.
In accordance with yet another embodiment of the present invention, a double chamber vacuum resin transfer molding process is provided wherein the first portion or the second mold portion, or both, are further configured to define a plurality of elongated mold portion voids formed in a surface bounding at least a portion of the mold cavity. The mold cavity and the brim cavity are evacuated so as to compress the compressible seal, decrease the
Davis Robert
Killworth, Gottman Hagan & Schaeff, L.L.P.
The University of Dayton
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