Reaction Injection Molding

Reaction injection molding OR RIM Molding is similar to injection molding except that a reaction occurs within the mold. The process uses thermoset polymers (commonly polyurethane) instead of thermoplastic polymers used in standard injection molding. Before injection of the polymer two components are mixed which react in the mold to form a solid thermoset polymer. The bi-component fluid is of much lower viscosity than molten thermoplastic polymer which enables the economical production of large parts with complex geometry.

Reaction injection molding is often used for vehicle bumpers and enclosures for electrical and computer equipment.

Tooling
Machined steel or aluminum; cast aluminum; silicone rubber. The machines can be large and also small depending on the size of part required.

Advantages
Strong, flexible, lightweight parts which can easily be painted. Quick cycle times compared to typical vacuum cast materials

Disadvantages
Slow cycle times compared to injection molding, expensive raw materials.