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 (besleme geçidi), taking a shape of the mold cavity and performing curing due to heat and pressure applied to the material.
The method is used primarily for molding thermosetting resins (thermosets), but some thermoplastic parts may also be produced by Transfer Molding.
The picture below illustrates the Transfer Molding Process.
The method uses a split mold and a third plate equipped with a plunger (piston) mounted in a hydraulic press.
The method combines features of both Compression Molding (hydraulic pressing and the same molding materials - thermosets) and Injection Molding (ram-plunger and filling the mold through a sprue).
Note: the larger piston is called as a “ram” and small one a “plunger”
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 (vida), 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:
• Epoxies (EP)
• Unsaturated Polyesters (UP)
• Phenolics (PF)
• Vinylester