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Major advances have been made in a RIM process which permits low viscosity reactives to be injected onto preshaped fiber reinforcement in a mold. Interest from a large number of end-users and in a wide variety of automotive parts has spawned a rapid increase in process technology and composite performance. Comparison of fiber types, fiber orientation, processing aids and techniques with resulting effects on physical properties will be discussed. Processing technology required to RIM large parts for structural applications has been defined. Strength to thickness ratios allow an overall weight savings in a tire cover application. Excellent wet-out without fiber movement in the mold has led to nearly isotropic properties; therefore over design to account for fiber orientation by other molding techniques has not been needed.

The production of FRP Class A surface parts for the automotive industry has been limited to high temperature SMC molding which requires chrome plated steel tooling and large hydraulic presses. The cost of this type of operation limits the economics of the process to a minimum of 30,000 parts/yr. Production runs of 3,000 to 20,000 parts/yr cannot justify hard tooling so other methods of production are used. These alternate methods have not offered the same quality of surface as the high temperature molding does. A new resin transfer molding resin. Arotran™ 50437, has been developed which can be used at mold temperatures as low as 120°F. Parts have been produced at tool temperatures between 120°F and 200°F with a surface comparable to that obtained with SMC. Molding produced at 120°F have utilized plastic tooling. Processing at 200°F, however, will undoubtedly require more durable tooling such as nickel shell molds.