What is the difference between injection molding and transfer molding?

The difference is within the machine and process

The presses used for injection molding are horizontally operated with a unique material delivery system. The thermoset compound is fed and injected with a high speed reciprocating screw, or a plunger system that reduces glass degradation for better part strength. The major advantages of injection molding:

• Better for small to medium part sizes (0.1 lbs to 6 lbs) in high volume.
• Tight tolerances can be achieved with these low-shrink materials. Post curing is not needed.
• Consistent material delivery into the mold cavities.
• Good strength for small parts, especially when molded with Thick Molding Compound (TMC).

The presses used for transfer molding are vertically operated and equipped with a hydraulic transfer system and controls. The thermoset compound is loaded into a chamber known as the transfer pot. The mold is then closed and a transfer plunger forces the compound from the pot through the runner system and gates into the mold cavities. The major advantages of transfer molding:

• Better for small to medium part sizes in medium to high volume.
• Good for molding in complex metallic inserts into the part (encapsulation).
• Tight tolerances can be achieved with these low-shrink materials. Post curing is not needed.
• Consistent material delivery into the mold cavities.