Injection Molding of Thermosets

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Process Overview

Thermoset plastic can also be injection molded, although the process is generally more difficult than injection molding thermoplastics. The manufacturing is done on a slightly modified thermoplastic injection molding machine. This process is well suited to mass produce parts that require good dimensional stability, good high temperature properties, and good electrical insulation properties. This process also produces a lot a flash, which must be removed in a secondary operation in which the parts are usually bead blasted.

Materials

Thermoset materials irreversibly chemically react during the molding process. They cannot be remelted or recycled very easily. However, because they will not melt or soften, they are excellent plastics for high temperature environments. They also have excellent electrical insulation properties, and are commonly used in electrical applications.

As with thermoplastic, there is a host of thermoset materials, each with its own set of properties and applications.

Summary

The manufacturing process is nearly identical to injection molding thermoplastics. There are two major differences: the material is transferred into the molding machine differently, and the mold must be heated to start the chemical reaction.

Advantages of thermoset injection molding are:

· Process is suited for automation and high production volumes

· Parts have excellent high temperature properties (low creep, high dimensional stability)

· Material will not burn or melt

· Materials are excellent electrical insulators

· Complex geometry and fine features are easily formed

Disadvantages of thermoset injection molding

· Parts must be deflashed, adding a secondary operation

· The mold must be heated, either with oil, steam, or electric. This is energy intensive

· Because thermosets cannot be remelted, caution must be used to make sure the material does not cure in places where it should not (the machine’s barrel, inside of a mold manifold, in the hopper, etc.)

· The non-recyclable scrap is usually sent to land fills