Frequently, injection-molded parts will need features, such as threaded inserts. You’ll find threaded inserts in a variety of parts—housings, casings, electronic enclosures, appliance knobs and dials, and so on.

Typically, there are three ways to incorporate threaded inserts into a molded part—insert molding, heat staking, and ultrasonic welding. Heat staking and ultrasonic welding are considered finishing options and only used with rigid thermoplastic parts, not softer materials such as elastomers or highly rigid materials like thermosets. They are often used on parts with complex geometries. Both offer tightness, durability, and enhance the aesthetics of plastic parts.

With heat staking, a conductive surface is use to heat threaded inserts, which, once sufficiently hot, are then press fitted into the part. The process requires precise control of the temperature and pressure to reform the plastic without damage. It is often used on appliances, automotive parts, and components and equipment for the telecom industry.

The ultrasonic welding process uses high frequency acoustic vibrations to create enough heat to soften the molded part to install the insert. It creates a solid-state weld. This process is often used for parts in medical devices, automotive parts, aerospace components, and electronic assemblies.