The principle of HF welding is based on the dielectric heating of the material being welded. The material is attached between two metal plates (electrodes) after which an HF voltage is connected up to the plates. This causes the molecules in the material to vibrate, which leads to heating up to the melting temperature. By bringing two layers of material simultaneously in the HF field and compressing them together, the layers fuse together and form a strong welded joint.
Some materials heat up better than others in an HF field, and therefore are more suitable for HF welding. This has to do with the extent to which the molecules of the material are made to vibrate by the HF field. This indicates the ''loss factor'’ of the material. The higher the loss factor of the material, the easier it is to weld the material with HF-welding. Thermoplastic polymers such as Polyvinyl Chloride (PVC) and Polyurethane (PU) are particularly good for welding; these materials are therefore ideally suited for welding with HF welding machines. Less HF weldable polymers are, for example, Polyethylene (PE) and various other hard polymers.
The big advantage of HF welding is the speed. Because the material is heated from within, fusion takes place within a few seconds. With all other types of heating, such as filaments, hot air or infrared radiation, the heat has to be applied from the outside. The heat then takes some time to penetrate the material.