High-Frequency Welding

a welding method in which metals are heated by high-frequency currents. The parts that are to be joined are placed at a small angle to one another and come in contact in the welding area, where the metal is heated rapidly to its melting point, squeezed together by compression rollers, and upset, thus forming a strong welded joint. There are two types of high-frequency welding—induction and contact. In induction heating, a current is induced at the point of welding by an inductor, and in the contact method the current is supplied through contacts. High-frequency welding is used extensively in the production of welded tubes. The tube is moved continuously, and a ferrite magnetic core is inserted in the workpiece to increase the heating rate. For welding tubes of small diameter (up to 76 mm), valve oscillators having a frequency of 440 kilohertz (kHz) are used to supply the current; for large-diameter tubes (up to 426 mm) the current is obtained from AC generators at a frequency of 8 kHz. The welding rate is 30-50 m/min.