At present, the welding heat source is very rich, such as flame, arc, resistance, ultrasonic, friction, plasma, electron beam, laser beam, microwave, etc., but the research and development of welding heat source has not been terminated, and its new development can be summarized. There are three aspects: first, the improvement of the existing heat source makes it more effective, convenient, and economical. In this regard, the development of electron beam and laser beam welding is more significant; the second is to develop a better and more effective heat source. The use of two heat sources is superimposed in order to obtain a stronger energy density, such as the addition of a laser beam in electron beam welding; the third is energy-saving technology. Since the energy consumed by welding is very large, many new technologies aiming at energy saving have emerged, such as the development of electronic technology in solar welding and resistance spot welding to increase the power factor of welding machines.