Response: All of these processes require matched metal dies designed to be clamped under pressure and heated to initiate the cross linking reaction. The key difference is how the molding compound is introduced into the mold, which affects flow patterns and glass integrity. Compression molding: · Requires dies with shear edges to contain the material in the mold as the mold closes. · A charge of the SMC, BMC, or TMC is placed on one half of the mold; the closing action of the two mold halves coming together forces the flow of the material. · Although historically more labor intensive than injection molding, robotic charge loaders and part unloaders can support full automation. · Compression molding is easily adapted to place molded-in inserts into the mold cavity for value-added features. Injection molding: · The two halves of the mold are clamped together by the action of the press before the material is introduced; shear edges are not required at the parting line. · The material is then injected through a sprue into the mold cavity by the action of an injection screw or plunger. · This process has a greater tendency to filamentize and break the glass fibers, resulting in lower part strength. · This process is easy to automate for good efficiency. Injection-compression molding: · Preserves glass fiber integrity compared to injection molding. · Requires molds with shear edges at the parting line. · Mold initially closes to engage the shear edges, but not to fully closed position. · Metered dose of the material is then injected into the mold by the injection screw or plunger. · Mold then is clamped to full closed position. · All the advantages of injection with improved strength. · Glass integrity is preserved and flow pattern around internal obstructions differs. · Requires precision control of the mold clamping function and shot size. Transfer molding: · Approximates injection molding in a compression press. · Effective for multiple-cavity molds; balances pressures between cavities. · Mold has a central “transfer pot” connected to each mold cavity by the runner system. · Charge of material is placed in transfer pot; mold is closed, then ram under the transfer pot injects material into the mold cavities.