Now viewing: thermal insertion

Joe Miura
By Joe Miura
Sunday, April 7, 2013 - 17:49

At Elite Plastics we manufacture a multitude of plastic housings every day. Most of these housings go into assemblies and need to be joined together. In order to accomplish this many designers choose to go with inserts and screws. To achieve this design, we offer many ways to add inserts to our parts. 

Molded-In

Molding in the inserts is exactly as the process sounds.  We place brass inserts onto a pin inside the injection mold (Pic 1). When the plastic is injected into the mold, it surrounds the insert and molds the insert in place. By doing this we are able to eliminate a secondary post operation for the part, saving both time and money.

Heat Staking – thermal insertion

When it is not possible to mold-in the insert, a secondary process is used to achieve this. Heat staking, or thermal insertion is one way to do so. Heat staking uses a head, which includes probes or tips that are heated above the melting point of the plastic. The heat staking head is applied to the inserts and will transfer the heat to the insert. As the inserts heat up, they start to melt the plastic around them. Pressure is applied to drive the insert down. When the insert hits its correct location within the boss, cold air is applied to solidify it in place.  Heat staking is great for complex geometries with inserts on different levels. This process is also very useful for parts that have many inserts in them.

Ultrasonic Welding

The last way we insert parts at Elite Plastics is with ultrasonic welding.  Ultrasonic welding uses high frequency electrical energy, which is converted to high frequency mechanical energy.  It is applied to the insert and creates friction between the insert and the plastic. The resulting friction causes the plastic around the insert to melt and the insert is then driven down to the correct location. The process is very quick – it takes less than one second to insert. However, multiple inserts typically need to be on the same plane. Due to this constraint, it is difficult to ultrasonically weld a part with many inserts.