Transfer molding is similar to compression molding in that a carefully calculated, pre-measured amount of uncured molding compound is used for the molding process. The difference is, instead of loading the polymer into an open mold, the plastic material is pre-heated and loaded into a holding champer called the pot. The material is then forced/transferred into the pre-heated mold cavity by a hydraulic plunger through a channel called sprue. The mold remains closed until the material inside is cured.
Transfer molded parts inherently have less flash (excess material that runs along the parting line of the mold) than their compression molded counterparts because the mold remains closed when the plastic enters the mold cavity. However, transfer molding still produces more waste material than compression molding because of the sprue, the air holes and the overflow grooves that are often needed to allow air to escape and material to overflow.
| 1. |  | The pre-heated, uncured molding compound is placed in the transfer pot. |
| 2. |  | A hydraulically powered plunger pushes the molding compound through the sprue(s) into the pre-heated mold cavity. The mold remains closed until the material inside is cured (thermosets) or cooled (thermoplastics). |
| 3. |  | The mold is split to free the product, with the help of the ejector pins. |
| 4. |  | The flash and sprue material is trimmed off. |
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