HF welding techniques are based on dielectric heating of the materials to be welded. Dielectric heating occurs when a conductor containing polar molecules is placed in an alternating current field. The electrical charges in the material then try to follow the changes in direction of the field. In the process, friction occurs between the molecules, creating internal heat.
When HF welding is done, the plastic materials to be welded are inserted between two metal plates (electrodes) that are powered up at high frequency (generally at 27.2 MHz). The molecules in the materials to be welded start to vibrate and heat up, causing the materials to soften. The technique of placing two layers of plastic in a high-frequency field like this and squeezing them together produces a very strong weld.
Some plastic materials heat up better than others in a high-frequency field. The following thermoplastics lend themselves particularly well to this type of welding: