Compression molding is a common process used for both thermoplastic and thermoset stock shape materials. Compression molding is accomplished by placing the plastic material (can be a granular or pelletized form) in a mold cavity to be formed by heat and pressure. The process is someone similar to making waffles. The heat and pressure force the materials into all areas of the mold. The heat and pressure cycle of the process will harden the material and then it can be removed.
Typically, thermosetting compounds like polyesters, phenolics, melamines and other resin systems are compression molded using alternating layers of different reinforcement materials to create a final product. However, there are various thermoplastics that are commercially compression molded as well.
Advantages of injection molding:
– Extremely low to zero residual stress left in stock shape.
– Can economically provide large parts.
– Tooling costs are relatively low.
– Flask may require trimming, can be sharp.
– Cycle times can be slow, a factor in producing larger volume orders.
– Can be higher priced than extruded products (when comparing thermoplastics).
Compression molding is a valuable tool where it has a fit. Obviously for thermosets, it is a primary process but in thermoplastics it can often times be useful in creating a base stock shape to machine extremely complex geometries without having to take excessive time and steps to anneal parts. This can increase production cycle time and reduce overall cost while delivering exceptional finished parts.