Reaction Injection Molding (RIM)

A fabrication technique involving the extremely rapid impingement mixing of two chemically reactive liquid streams, injected into a mold that results in the simultaneous polymerization, cross-linking and formation of the part. Typically, this low temperature process typically takes less than a minute to complete, including time for mixing, curing, and demolding.

This technique is a form of liquid injection molding (LIM). When short fibers (1.6 mm), carbon or mineral fillers are incorporated into one of the liquids to increase modulus and reduce coefficient of expansion the process is referred to as reinforced reaction injection molding (RRIM). RIM resin systems include epoxy which mold over continuous strand mat and preforms as well as polyurethane/polyester hybrids, polyurea and poly(DCPD).

Raw Materials
Liquid urethane in various combinations with liquid catalyst

Tooling
Machined steel or aluminum; cast aluminum.

Cost
Parts & tooling relatively high.

Advantages
Strong, flexible, lightweight parts which can easily be painted.

Disadvantages
Slow cycles, expensive raw materials.

Applications
Automotive spoilers, interior trim panels for automobiles and trucks.