Thermoset 101: How Are Thermosets Molded?

Thermosets are processed in similar functions to thermoplastics such as nylon, ABS, polypropylene, etc. Thermosets may be injection molded, compression molded, injection-compression molded, or transfer molded. Additionally thermosets can utilize molded-in inserts within the molding process.

Injection Molding

Thermoset Injection Molding with Edge Gate

Injection molding offers a cost-efficient option for large volume applications that require a high throughput. Injection molding offers a faster cycle time, allowing more parts to be produced per hour vs. a compression or transfer molding process. In addition to higher throughput, the faster cycle times of injection molding provides a low unit part cost. Injection molding also offers better opportunity for multi-cavity tooling.

Injection-Compression Molding

8-Cavity Injection-Compression Molding

Injection-compression is a hybrid molding process similar to injection, but where the mold opens slightly to degas after injection, and then closes as a compression type process. Injection-compression molding provides higher throughput similar to injection, but offers additional strength properties. Whereas straight injection molding will create a knit-line opposite the gate, injection-compression does not use gating to flow material directly to the parts, so there are no knit-lines or witness marks created.

Compression Molding:

Compression molding optimizes high strength characteristics. As with injection-compression, no knit-lines or witness marks are created. While straight compression offers the most compressive strength properties, the cycle times are much slower than injection processes, creating higher part costs and lower throughput. Compression molding is generally geared towards low volume applications requiring very high strength characteristics.

Insert Molding:

End Product Insert Molded with Two Molded-in Bushing Inserts

Insert molding may be used with either injection or compression molding, but includes molded-in inserts that are either hand loaded or automated within the mold before the molding process. Inserts are used to combine metal and thermoset components and also used for internal threading for product assembly. After the inserts are loaded, and the molding machine injects material, the resin flows over and secures the insert in place. By incorporating insert molding, product assemblies are able to reduce secondary operation costs used to assemble together components or manually install inserts.

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