Subscribe to our newsletter to receive the latest news and events from TWI:

Subscribe >
Skip to content

What is hot plate welding of thermoplastics?


The parts to be welded are accurately held in fixtures with their weld faces pressed against an electrically heated tool. Heating takes place in two stages and is controlled either manually or by a microprocessor.

First, the heated tool melts the surfaces and material flows to the outside edges of the parts. This is to ensure that the joint interfaces are smooth and have intimate contact with the surface of the heated tool. Mechanical stops in the equipment, or a reduction in the force pressing the parts against the heated tool, prevent further flow of molten material.

In the second stage, known as the 'heat soak' stage, the parts continue to be heated by the tool until they are softened some distance away from it. Thermoplastics have a very low coefficient of thermal conductivity compared with metals, and the temperature gradient within the parts will decline steeply back from the surface of the heated tool. The parts are then moved slightly away from the heated tool which is then withdrawn. Next, the fixtures force the parts together to consolidate the weld. Finally, the assembly is allowed to cool before removal from the welding machine.

Applications of hot plate welding include pipes, battery cases, pallets, automotive trim and domestic appliances.

See further information about plastics welding and testing or please contact us.

For more information please email: