1、 General introduction of electromagnetic assisted forming system Electromagnetic forming belongs to high-energy (high-speed) forming technology. Firstly, the electric energy should be stored in the high-voltage capacitor. When the high-voltage switch is closed, the capacitor can discharge the coil quickly (US level) and generate a changing pulse magnetic field around it. When the pulse magnetic field passes through the workpiece, the induced current (eddy current) will be generated in the metal workpiece, and the charged metal workpiece will be in a rapidly changing magnetic field When the magnetic pressure reaches the yield strength of the material, the metal workpiece will have plastic deformation to achieve the purpose of forming metal parts. Electromagnetic forming technology has the characteristics of easy and accurate control of processing energy, fast forming speed, high precision of forming workpiece, small elasticity of parts after forming, improvement of plastic deformation ability of materials, simple mold and strong universality of equipment, easy to adopt composite process and realize automatic production, green and environmental protection in the whole forming process, which has been widely used in aviation, aerospace, weapon industry Automobile manufacturing, light chemical industry, instruments and electronics and many other fields. Electromagnetic forming can be widely used in plate forming, sheet punching, punching, electromagnetic bulging and reducing of pipe, flanging and connection, stamping and forming, multi process composite forming, assembly of assembly parts, powder compaction, electromagnetic riveting, electromagnetic welding and storage of radioactive materials, etc. it is the preferred forming method for some special parts. For example, precision sizing of large components, burr free punching of diaphragm, processing of complex shape pipe fittings, forming of missile clamp, sizing of instrument cabin, forming of aircraft turbine engine room, assembling of torque shaft and connecting rod; connection of automobile air-conditioning reservoir, heat exchanger, universal joint frame, cam, gear, etc. with drive shaft or universal shaft pipe; assembly of electronic components such as fuse, insulator, etc In the nuclear industry, fuel rod forming, nuclear waste container sealing, electromagnetic riveting have been widely used in Boeing 737, 747, 767, and electromagnetic powder pressing has opened up a broad application prospect for electromagnetic forming technology in the functional ceramics industry, sensitive components and sensors industry. 1.1 brief introduction of EMP welding machine Electromagnetic welding aid is generally considered to be the same as explosive welding mechanism. Whenever the energy storage capacitor is discharged, the coil produces a transient, high-voltage and high-speed stamping wave which acts on a metal accessory and causes it to crash violently into another metal base at a high speed. At some initial impact points of the two metal contact interfaces, there will be "jet" and high strain rate metal plastic flow. The result of "jet" action is to wash or remove the oxide layer and adsorption layer of the two metal surfaces to be compounded, so that the two clean metal surfaces are closely combined under high pressure to form metal bond connection. With the deformation, i.e. the compounding process, the metal bond is gradually extended to the whole connection surface to achieve the purpose of compounding or welding. The deformation force required for electromagnetic welding is provided by solenoid coil. The traditional methods to remove welding stress are: prestressing method and pretensioning method, vibration aging stress relief method, impact rolling method with welding, temperature difference stretching method, hammering method with welding, etc. Although these methods have achieved good results in some occasions, there are some shortcomings due to their own characteristics. (1) the prestressing method and the pretensioning method are difficult to be widely used due to the limitations of the stretching equipment and the weld forms; (2) if the vibration is not proper, the fatigue performance of the structure will be affected; (3) with the change of welding specifications and welding materials, the size of impact roller needs to be redesigned and manufactured; (4) the temperature difference tensile method can not reduce the transverse shrinkage of the weldment, but will increase the transverse shrinkage, so it is not suitable for the welding of closed weld; (5) with the welding hammering method, the hammering surface is rough and the surface finish of the workpiece is poor, so it is difficult to realize the actual welding of closed weld. According to the characteristics of welding residual stress and deformation of thin plate components, the method of controlling welding stress and deformation by electromagnetic impact is put forward. The control of welding stress and deformation by electromagnetic impact is a method based on the principle of electromagnetic induction. The main principle is: using the electromagnetic force exerted by the coil on the workpiece, the residual compressive plastic deformation in the weld can be fully extended, so as to reduce the residual stress of the weld and reduce the welding deformation. When welding thin plates, there is often deflection, so the maximum deflection of deflection can be used to measure the effect of controlling welding deformation.