Numerical Simulation On Temperature And Stress Fields Of Low Carbon Sheet By Resistance Spot Welding

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. The means of numerical simulation replaces technologic experiment, which has not only a important economic value but also the meaning of academic guidance in the forecast of spot welding defect, the control of spot quality and practically applied outlook. At present, most of the study on the simulation of resistance spot welding process is limited to the preloading and the welding periods. There has been little research on the cooling and residual stresses field. However, the distribution of the residual stresses is the main causes to welding cracks and effect the solder joint lifetime. Therefore, It is difficult to simulate of the residual stress field.SYSWELD software is used to simulate the process of the spot welding in two layers equal thickness low-carbon steel sheets. The finite element model was 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 effect of contact resistance, phase change latent,water cooling of electrode and air cooling etc on the growth process of nugget was considered adequately.Based on mentioned above, the temperature field of resistant spot welding process was simulated to analyze the distributing law of temperature, the nugget shape and dimension were displayed and analyzed theoretically by post-process of simulating result. 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. The analysis of the electro-kinetics, heat transfer, metallurgy and mechanics coupling is to discuss the variational law of the stress field, especially the residual stresses of the spot welding process. The variational law of contact state in contact surfaces respectively and the effect of thermal expansion for the deformation and displacement of the worksheet were discussed.It is shown by analysis that the distribution of stress and strain on spot welding joints are uneven. During the welding process, the stress on nugget is smaller, and high stress is mainly in heat affected zone; the stress of the nugget changes from compressive stress to tension stress one; the maximum residual stress and strain appears at the vicinity of the edge of worksheet binding face.