Research Of Quality Insurance Technology Of Sheet Metal Electromagnetic Forming

Electromagnetic forming is a new kind of forming method with high energy and high forming velocity, by which the metal is loaded under strong impulse magnetic field and deformed plastically. The advantages of the method are as follows. There is no physical contact during forming process, so the workpiece can be polished or grinded before forming or assembling. There is no static force exerted during forming, so relatively light frame structure can be used for die supporting. Magnetic impulse pressure time can be in the order of microsecond, and the intensity of electromagnetic impulse pressure can be controlled electrically to very high precision. There is no friction during forming, so lubricant is not necessary, and cleaning of workpiece after operation is also not necessary. Material with high strength and bad formability, such as aluminum alloy can be used since material's formability can be increased under high forming velocity. Forming sheet metal of aluminum alloy using electromagnetic forming method, and substituting it for steel to use for body structure and other parts of automobile, can decrease the weight of the automobile 30 percent. It, in turn, can decrease the oil assumption and exhausts. It will be more and more important for electromagnetic forming process to apply in automobile field.The main research of this dissertation is as follows. Based on investigation of the development status of the area in China and oversea countries, electromagnetic forming of sheet metal was selected as main research work. Theory analysis, experiment research and finite element simulation were carried out to study the process factors with strong affect to the forming quality, such as impulse current frequency, forming voltage, mould design, sheet thickness, and so on. Therefore the design methods of forming coil, circuit parameters of forming equipment, forming voltage and the mould, which are necessary for the electromagnetic forming process design, were acquired. It is important for the quality insurance of the workpiece and the promoting of its application in industry. And the application of sheet metal electromagnetic forming in combined forming process (conventional drawing + electromagnetic forming) can promote the application of combined forming of aluminum alloy parts of automobile body.In the dissertation, the distribution of magnetic induction intensity induced by intense winding conductor plane coil was deduced, and the distribution of the electromagnetic pressure on the sheet metal was analyzed. On this basis, minimum size of the coil was proposed so that electromagnetic pressure at the edge of the sheet was zero. If coil size is smaller than the minimum size, the direction of electromagnetic pressure at the edge of the sheet will be upward, and it is disadvantageous to the deformation of the sheet. The dichotomy method and complex method were used for the calculation of the minimum size of circular coil and elliptic coil. Using box die and hole die, the experimental research to sheet forming with circular coil and elliptic coil were carried out, and the suitable cases of the application of the two kinds of coil were acquired. For the long workpiece, elliptic coil is more suitable than circular coil. For the workpiece that has much demand for the deformation of its center area, circular coil should be selected. All of these are important for coil shape selection and coil size calculation during electromagnetic forming process design.In the dissertation, sheet metal electromagnetic free forming and die forming experiments were discussed in detail. And based on the experiments, the affect of forming voltage, die structure, and sheet thickness to deformation was analyzed, and the deformation process of sheet metal electromagnetic forming was preliminarily acquired. For free forming, deformation during loading time is small, and most of the deformation happens during the inertia stage. For die forming, the sheet moves toward the opposite direction after its impact with the bottom of the d...