Dr. Dmitri Kopeliovich
Transfer Molding (Resin Transfer Molding) is a process in which a pre-weighed amount of a polymer is preheated in a separate chamber (transfer pot) and then forced into a preheated mold through a sprue, taking a shape of the mold cavity and performing curing due to heat and pressure applied to the material.
The picture below illustrates the Transfer Molding Process.
The method uses a split mold and a third plate equipped with a plunger mounted in a hydraulic press.
Transfer Molding process involves the following steps:
The charge may be in form of powders, pellets, putty-like masses or pre-formed blanks.
The charge is heated in the pot where the polymer softens.
The mold, equipped with a heating system, provides curing (cross-linking) of the polymer (if thermoset is processed).
If thermosetting resin is molded, the mold may be open in hot state – cured thermosets maintain their shape and dimensions even in hot state.
If thermoplastic is molded, the mold and the molded part are cooled down before opening.
Transfer Molding cycle time is shorter than Compression Molding cycle but longer than Injection Molding cycle.
The method is capable to produce more complicated shapes than Compression Molding but not as complicated as Injection Molding.
Transfer Molding is suitable for molding with ceramic or metallic inserts which are placed in the mold cavity. When the heated polymer fills the mold it forms bonding with the insert surface.
Transfer molding of thermosets is used for molding parts encapsulating metal inserts, wear plates, pins, studs, electronic components with molded terminals. Transfer molding is also used for manufacturing radio and television cabinets and car body shells.
Materials commonly processed by Compression Molding are: