PERIMETER RESIN FEEDING OF COMPOSITE STRUCTURES

Abstract: A resin transfer molding system includes a plurality of ports (24) for injecting resin into reinforcement material (54,56), which preferably comprises fabric, disposed between upper and lower mold pieces (58,62) to form a structural part. Channels (30) are provided adjacent the fabric reinforcement material (54,56) and act as reservoirs to permit relatively fast and efficient injection of the resin without excessive applied pressure.

Description: The invention relates to a method of forming a fiber-reinforced structure. The publications Modern Plastics International, Feb. 1981, p. 42 and Plastverarbeiter, 32. Jahrgang 1981, Nr. 2, p. 186, 188, describe a method of forming a fiber-reinforced structure wherein a mold is provided having a plurality of inlet ports connected to a source of resin and upper and lower pieces with one of said pieces including one channel for receiving resin, fibrous material is placed along the inner walls of said upper and lower pieces adjacent said channel, resin is injected through said inlet ports and said channel into said fibrous material, and said resin is cured to form said fiber-reinforced structure. According to such a method known from the above publications the channel through which the resin is injected into the said fibrous material extends around the perimeter of the fiber-reinforced structure to be formed as a minigroove for linear gating, the cross section of which corresponds to the wall thickness of the structure to be formed. Air is vented during resin injection through a vent arranged centrally in relation to the perimeter. Secondary vacuum sinks may be provided at the edge of the mold avoiding entering of air bubbles. As the flow resistance for the resin is high in the minigroove which cannot act as a resin reservoir a relatively high injection pressure is required to inject resin, especially if large structures are to be formed. The object of the invention is to provide a method of forming a solid fiber-reinforced structure which permits forming large structures whithin a short time using relatively low input pressure for the injection of the resin. This object is obtained by a method of forming a fiber-reinforced structure comprising the steps of: a) providing a mold having upper and lower pieces with one of said pieces including at least one channel into which open a plurality of inlet ports connected to a source of resin, wherein a second channel is provided in one of said mold pieces to vent air as said resin is being injected, b) placing fibrous material along the inner walls of said upper and lower pieces adjacent said channel(s) and placing an inflatable member between said fibrous material within said mold, closing said mold and inflating said inflatable member, c) injecting resin through said inlet ports and said channel (s), which act(s) as a reservoir for receiving the resin, into said fibrous material and d) curing said resin to form a reinforced hollow structure. Advantageously, said fiber-reinforced structure comprises foam disposed within said mold. Embodiments of the invention are described in the following by means of drawings. Fig. 1 is a side view, partly broken away, of an automotive side frame structure, of the type which may be formed using the present invention; Fig. 2 is a cross-sectional view, taken along lines 2-2 of Fig. 1, including upper and lower molds not illustrated in Fig. 1; Fig. 3 is a cross-sectional view of the part formed, as illustrated in Fig. 2; Fig. 4 is a cross-sectional view of a sandwich panel structure. Referring to Fig. 1, an automotive frame 10 is illustrated. The frame may include front post 12, center post 14 and rear post 16. The frame is designed to provide door openings 18 and 20 and a window opening 22. In the copending European application 86108600.7/0 212 140 a portion of an automobile structure is illustrated which forms part of a door frame for an automobile. The frame may include various joints, curved surfaces and areas of irregular cross sections. A singular integral cured structure was formed from several prelocated, but unimpregnated, fiber pieces which were subsequently injected with resin and suitably molded and cured. The structure included a hollow area extending thereto. The present invention includes many of the steps illustrated in the copening patent application. In the present invention, however, the structure 10 is much larger than the structure illustrated in the copending application. Because of the relatively large structure involved in the present application, if a single source of resin was used to impregnate the structure 10, a relatively long time would be involved to complete the impregnation of a single structure. Also, a relatively high amount of pressure would be required to inject the resin. High input pressures may collapse the inflatible bag used or may displace the fabric material. Referring again to Fig. 1, along with Figs. 2 and 3, a source of resin is connected to a plurality of inlet ports 24 to impregnate the fiber material 26 which ultimately forms the solid structures. Between the resin inlet ports 24 and the fibrous material 26, there are provided a plurality of channels or reservoirs 28, 30, 32, 34 and 36. The grooves or reservoirs are disposed adjacent the fibrous material 26. Channels or reservoirs receive the resin from the ports 24. When the resin is applied under pressure, the fibrous material 26 is impregnated with the resin. A plurality of air vents 38 is provided to vent the air as the resin is injected into the fibrous material. Vent groove 48 is disposed about the periphery of the frame, vent groove 50 is disposed at the center post 14, and vent groove 52 is disposed at the end post 16 to facilitate the venting of the air to the vent ports 38. In Fig. 1, for purpose of explanation, the pieces are not illustrated. However, the various channels for reservoirs for receiving the resin are actually part of the mold involved, and may be in the upper or lower mold piece. Likewise, the air vent grooves also form part of the mold involved. Referring to Figs. 2 and 3, a single integrally cured structure then is developed from several prelocated fibrous pieces, such as pieces 54 and 56. The piece 54 is placed within the inner wall of the piece 58 of a mold 60 and is lapped over the piece 56. The piece 56 is disposed on the inner wall of the lower piece 62 of the mold 60. A hollow area 64 extends through the structure, as in the aforementioned copending patent application. Prior to closing the mold 60, an inflatible bladder 66, is inserted between pieces 54 and 56. The bladder may comprise a plurality of pieces cut to suitable shapes and sizes, corresponding to the shape and size of the structure to be formed. Air, or other suitable gas from a pressurized source, is applied through a conduit 68 into the inflatible bladder 66 causing it to inflate to force it against the fibrous pieces 54 and 56. With the mold 60 closed, resin under pressure is forced through the inlet ports 24 into the various reservoirs or channels into the fibrous material. Air is vented from the fibrous material from ports 38 as the resin is being injected to insure that there are no voids in the fibrous material. Following are steps for impregnating the fibrous material with resin, a curing operation is performed. Depending upon the chosen resin, the curing could be done either at room temperature or an elevated temperature, which involves heating the fibrous material with the resin while under pressure. The curing completes the formation of the structure 10, which is the side frame illustrated in Fig. 1. Referring to Fig. 4, a sandwich panel structure is formed between a mold 72, which includes upper and lower pieces 74 and 76. The sandwich panel structure includes urethane material 78 at a core surrounded by fiberglass or other fibrous material skins 80. A channel or reservoir 82 is disposed about the periphery of the main panel structures. Resin is injected to the skin 80 from resin inlet ports to the reservoir 82 to the skin 80. It is noted that resin is injected completely around the panel or structure edge to allow molding of the complete structural edging as well as the sandwich skin. In one embodiment of the invention, the skins were .035 inches (0.9 mm) thick fiberglass, which is relatively thin with to respect to RTM. The perimeter resin feeding permitted such a thin skin to be completely impregnated. An air vent 84 disposed toward the center of the panel is centrally disposed. The single air vent 84 is relatively close to all the inlet resin ports 83. This permits relatively fast injection of the resin under relatively low pressure. The vent port 84 extends completely through the foam core as illustrated by the dotted lines.

Claims: A method of forming a fiber-reinforced structure comprising the steps of a) providing a mold (60, 72) having upper and lower pieces (58, 62; 74, 76) with one of said pieces including at least one channel (28, 30, 32, 34, 36; 82) into which open a plurality of inlet ports (24) connected to a source of resin, wherein a second channel (48; 50; 52; 84) is provided in one of said mold pieces (58; 62; 74) to vent air as said resin is being injected, b) placing fibrous material (26; 54, 56; 80) along the inner walls of said upper and lower pieces (58, 62; 74, 76) adjacent said channel(s) (28, 30, 32, 34, 36; 82) and placing an inflatable member (66) between said fibrous material (54, 56) within said mold (60, 72), closing said mold (60, 72) and inflating said inflatable member (66), c) injecting resin through said inlet ports (24) and said channel(s) (28, 30, 32, 34, 36; 82), which act(s) as a reservoir for receiving the resin, into said fibrous material (54, 56; 80) and d) curing said resin to form a reinforced hollow structure (10). A method as set forth in claim 1, wherein said fiber-reinforced structure comprises foam (78) disposed within said mold (72).

Inventors: FREEMAN, RICHARD BENJAMIN
Applicants: THE BUDD COMPANY
Application year: 1987
Main classification: B29C67
IPC codes: B29C45, B29C70, B29C43, B29K101, B29C33, B29K105, B29L31