A Guide to Thermoset Plastic Injection Molding

April 22nd, 2025

Thermoset plastic injection molding is used to produce high-strength plastic components. Working with thermoset materials for decades we provide industrial customers nationwide with durable injection-molded thermoset components for a wide range of applications. Here’s a quick guide to thermoset injection molding.

What Is the Thermoset Injection Molding Process?

• Thermoset materials begin as ground powder or as a liquid resin that is inserted into a mold.
• During the molding process, the material is heated and fills the void of the mold, taking its shape.
• Then the material undergoes a chemical change, transforming into a hardened state.
• Thermoset injection molding process is irreversible as the polymers become cross-linked.

Benefits of Injection Molding Thermosets:

• Excellent strength-to-weight ratio with high load-bearing capacity
• Thermosets retain their properties in extreme thermal environments
• Many thermoset materials have excellent dielectric properties
• Can resist exposure to oils, solvents, and corrosive substances
• Thermoset injection molding is an excellent solution for high-volume manufacturing

Thermoset Injection Molding vs. Thermoplastic Injection Molding

Both thermoset and thermoplastic molding are plastic manufacturing processes, but they are used for different applications.

• Thermoplastics are solid at room temperature, but they can be repeatedly melted, reused, and remolded.
• Thermosets can’t as they undergo an irreversible chemical reaction during molding.
• Thermoplastics can't be used for applications that require high levels of strength or resistance to heat.
• Thermosets are used for components requiring structural integrity and heat resistance.

Common Thermoset Injection Molding Materials

• Epoxy: High strength, low shrinkage, excellent chemical resistance, and good electrical insulation properties
• Phenolic: Excellent heat resistance, good insulating ability, lightweight, good tensile and impact strength
• Polyester (BMC/SMC): Cost-effective with good mechanical properties and geometric stability
• Silicone: Flexible, temperature-resistant, highly versatile, good all-around properties

Industries using Thermoset Injection Molding

• Aerospace
• Automotive
• Construction
• Electrical
• Marine
• Medical
• Military & Defense

Southwest Plastics is Your Source for Thermoset Injection Molding Services