How to Design a Thermoset Composite Part [Infographic]

As in all aspects of plastic molding, quality starts with design. A part designed for machining, thermoplastic molding, or metal casting will not necessarily be suitable for design in thermoset molding. Parts as simple as a 5-ounce thin disc, or as complex as high-appearance appliance parts and 35-pound Industrial/Electrical switchgear, vary widely in their design criteria for aesthetics, strength, and moldability.

Generally, thermoset plastic parts, when designed properly, can yield lower part cost, lower tooling cost, faster time to production, and higher strength when compared to other methods of production. Additionally, parts produced from the three thermoset molding processes—Injection, Compression, and Transfer--can be produced with a high degree of accuracy due to the stiffness and low shrinkage of the material.

Thermoset parts are not as prone to sink-marks and warpage as thermoplastic parts, especially when the part design requires changes in wall thicknesses.

Thermoset parts can hold tighter tolerances than most thermoplastic parts.

Thermoset parts do not require machining operations that are often required in cast metal parts.

Care should be taken to understand which materials and processes would be best utilized in the making of the part, and to design the part accordingly.

Some features and details that produce good part designs are:

• More draft is better. Low material shrinkage requires draft for better mold release and less stress during ejection.
• Large radii are better. All corners, inside fillets and outside rounds, should have as much radii as possible. This promotes good material flow into the mold and less stress in the mold tooling.
• Openings in the part should allow for proper shutoff design in the tooling.
• Side actions and undercut requirements can be designed into the tooling or produced in secondary operations.