Numerical Simulation For The Process Of Spot Welding In The Low-carbon Steel

Resistance spot welding has a wide range of applications in the welding of steel sheet. For the invisibility in the process of spot welding nugget forming and the transient of welding process , it is difficult to control the quality of spot welding process and optimize welding parameters , especially in special condition spot welding,such as unequal thickness steel sheets , three layers equal thickness steel sheets and sheets with znic-coated layer ,these problems are more obvious. The means of numerical simulation replaces technics experiment ,which has not only a importmant economic value but also the meaning of academic guidance in the forecast of spot welding defect and the control of spot quality, and practically applied outlook.ANSYS software is used here to simulate the process of spot welding in two layers equal thickness, two layers unequal thickness, three layers equal thickness low-carbon steel sheets and sheets with znic-coated layer, the finite element model is built aiming at the characteristic in geometry of spot welding joint and pyrogenation of the spot welding process,including the enactment of boundary condition, the mesh of gridding and the choice of element. The impact of contact resistance, phase change latent, water cooling of electrode and air cooling etc on the growth process of nugget is considered adequately. Besides, the temperature-dependent electrical, thermal and mechanical properties are taken into account considered in detail. The method of active and deactive element was employed to simulate the problem of molten zinc on galvanized steel sheet on the simulation of spot welding, which make the model tallys with the practical thing.In this simulation, transmitting electricity and conducting thermal are nonlinear problems and mechanical behave is an elastic-plasticity problem with contacting condition, calculation uses full Newton-Rophson iterative method. Because of material nonlinear, geometry nonlinear and contacting nonlinear, the small time step is adopted to improve convergence of the calculation.The content of study in this paper : The electrical-thermal simulation in the temperature field of the process of resistant spot welding is to analyze the distributing law of voltage and current density, variational law in the temperature field and the problem of electrode longevity ; the nugget shape and dimension were displayed and analyzed theoretically by post-process of simulating result. Theanalysis of the electrical- thermal-mechanical coupling is to discuss the variational law of contact state in contact surfaces respectively and the effect of thermal expansion for the deformation of electrode and workpiece. It is validated that the model is reasonable and the simulating result is exact by the checking of nugget shape and dimension in practical spot welding .