Electron beam welding is a method of welding heat generated by concentrated high-speed electron beam bombardment of the workpiece surface. In electron beam welding, electron beam is generated and accelerated by electron gun. Commonly used electron beam welding are high vacuum electron beam welding, low vacuum electron beam welding and non vacuum electron beam welding. The first two methods are carried out in a vacuum chamber. The welding preparation time (mainly vacuum time) is longer, and the size of the workpiece is limited by the size of the vacuum chamber. Compared with arc welding, electron beam welding is characterized by high weld penetration, small weld width and high purity of weld metal. It can be used for precision welding of thin materials and for thick (300mm thick) components. All metals and alloys that can be melted and welded by other welding methods can be welded by electron beam. It is mainly used for welding of high quality products. It can also solve the welding of dissimilar metals, oxidizing metals and refractory metals. But it is not suitable for large quantities of products. Electron beam welder: the core is an electronic gun. It is a device that completes the generation of electrons and the formation and convergence of the electron beam. It is mainly composed of filament, cathode, anode and focusing coil. The filament is heating up and heating the cathode. When the cathode reaches about 2400K, the electron is emitted. Under the action of the high voltage electric field between the cathode and the anode, the electron is accelerated (about 1/2 light speed) and is ejected through the anode hole. Then the focusing coil will converge into the electron beam of 0.8 ~ 3.2mm diameter to the welding part, and the surface will be on the surface of the welding piece. The kinetic energy is transformed into heat energy, so that the joint of the welds is melted rapidly, and the weld is formed after cooling crystallization. According to the vacuum degree of welding workshops (welds placement), the classification of electron beam welding is: (1) high vacuum electron beam welding. The studio is in the same chamber as the electron gun, with a vacuum of 10-2 to 10-1Pa. It is suitable for precision welding of refractory, reactive, high purity metals and small parts. (2) low vacuum electron beam welding. The studio and the electronic gun are divided into two vacuum chambers, the vacuum degree of the studio is 10-1 ~ 15Pa, which is suitable for the larger structure parts and the refractory metals which are not too sensitive to oxygen and nitrogen. (3) non vacuum electron beam welding. It is necessary to add an inert gas shield or nozzle, and the distance between the welding part and the electron beam outlet should be controlled around 10mm to reduce the scattering caused by the collision between the electron beam and the gas molecules. Non vacuum electron beam welding is suitable for welding carbon steel, low alloy steel, stainless steel, refractory metal, copper and aluminum alloy, and the size of weldments is not limited. The advantages of vacuum electron beam welding (EB): (1) the energy density of the electron beam is large, up to 5 x 108W/cm2, about 5000~10000 times of the ordinary arc, the heat concentration, the high thermal efficiency, the small heat affected zone, the narrow and deep weld, and the minimal welding deformation. (2) welding in vacuum, the metal does not interact with the gas phase, and the joint strength is high.