High frequency (HF) welding process, also known as Radio Frequency (RF) and Dielectric welding, consists of amalgamation of material by supplying HF energy in the form of an electromagnetic field (27.12 MHz) which is normally applied between two metal electrodes, plates or moulds. HF welding is accompanied with certain pressure on the material surfaces to be joined. For this purpose the HF welding machine are constructed.
HF Welding relies on certain properties of the material being welded to cause the generation of heat in a rapidly alternating electric field, so called dielectric heating of the material to be welded. This means that only certain materials can be welded using this technique. The dynamic electric field causes the molecules in polar thermoplastics to oscillate. Depending on their geometry and dipole moment, these molecules may translate some of this oscillatory motion into thermal energy and cause heating of the material. A measure of this interaction is the loss factor, which is temperature and frequency dependent.
Advantage of high frequency welding
The great advantage of HF welding is the speed of welding: the material is heated from the inside and fuses quickly, within few seconds. In comparison with HF, in all other kinds of welding methods (with filaments, hot air or infrared radiation) the heat has to be added from the outside. It means the heat must first penetrate the material in order to make it plastic enough to form a weld. The main risk of this kind of treatment is burning the top layer of welded material.