Compression Molding

Originally developed to manufacture composite parts for metal replacement applications, compression molding is mostly used to make larger flat or moderately curved parts such as hoods, fenders, scoops, spoilers, lift gates and the like for automotive end-uses.  Although this technology is the main processing method used with thermoset resins, it can also be employed to process themoplastic resins such as Ticona’s Compel® and Celstran® long fiber reinforced thermoplastics (LFRT), and GUR® ultrahigh molecular weight polyethylene (UHMWPE).  

The schematic below shows the process equipment.

The material to be molded is placed in the mold cavity and the heated platens are closed by a hydraulic ram.  Thermoset resins, either bulk molding compound (BMC) or sheet molding compound (SMC), are conformed to the mold shape by the applied pressure and heated until the curing reaction occurs.  SMC feed material usually is cut to conform to the surface area of the mold.  The mold is then cooled and the part removed.

Thermoplastic resins may be loaded into the mold either in the form of pellets or sheet, or the mold may be loaded from a plasticating extruder.  Thermoplastic materials are heated above their melting points, formed and cooled.  For both thermosets and thermoplastics, the better the feed material is distributed over the mold surface, the less flow orientation occurs during the compression step.