Insert molding is a process that allows plastic to bond to an insert (usually metal) placed within a mold cavity. For example, adding a threaded brass insert to a plastic faceplate.

This process eliminates assembly steps and reduces costs. You can use inserts for:

• Threaded screw fittings (Nutserts)
• Electrical contacts
• Wire connectors
• Warnings labels

While useful, there are some concerns with insert molding:

• Labor Cost: Hand-loading inserts slows down production.
• Stress Cracks: Resin shrinks while metal does not, causing stress cracks (especially in Polycarbonate).
• Volume: Hand-loading is only efficient for low volumes (up to 50,000). High volume requires automation.

Overmolding (also known as Two-Shot or 2K molding) is a process where a rubber or elastomer (like TPE/TPU) is permanently molded onto a rigid plastic substrate.

It is commonly used to improve grip, feel, and aesthetics (two-tone effect). Examples include toothbrush handles and power tool grips.

• Strong Bond: Chemical bond between materials is very strong.
• Aesthetics: Allows for contrasting colors and improved product look.
• Functionality: Provides soft grip, vibration dampening, and water seals.
• Automation: Ideal for large production runs as the process is automated.

Overmolding uses a special machine with two barrels. One holds the rigid plastic, and the other holds the elastomer.

The mold tool typically has 3 halves instead of two. The substrate is molded first, then rotated to the second cavity where the overmold material is injected.