| Resistance spot welding has a wide range of application in the processing industry, the quality of spot welding joint and applied field have been paid attention more and more. Not only satisfy intensity and appearance requirement, sometimes we need improve leakproof quality, sometimes the structure and position of workpiece is complex, we have to change the shape of electrode to adapt to the requirement of production. The solution is change the shape of electrode to rectangle surface of electrode. For the invisibility of nugget forming in the process of spot welding and the transient of welding process,it is difficult to control the quality of spot welding process and optimize welding parameters, especial the appearance of new material and new craftwork, these problem is more obvious. The integrating of numerical simulation and technics experiment, which not only shorten period of development but also have important economic value.The article adopt finite element method, build three-dimensional finite element model of rectangle surface electrode of stainless steel resistance spot welding for . The model can describe the stress and temperature field distribution exactly, taking into account the influence of temperature-dependent physical parameters, gridding, contact resistance, melting latent heat to melt nucleus forming process. Besides, the boundary condition is considered in detail. All of the above improvement make the model more close to real welding condition.The initialized conducting region and contact resistance distribution are determined in the pre-squeeze stage of RSW, which has great effect on the position of initialized nucleation, nugget forming process and weld quality. This article established contact analysis numerical model of the rectangular surface electrode in the pre-squeeze stage according to the plastic theory and the contact theory, created contact pair in contact region, setting load and boundary condition, obtained contact pressure distribution of workpiece interface and the electrode interface, had determined the initial electric conduction region, has laid the foundation for the melt nucleus forming process value simulation.The thermal-electrical coupling process of resistant spot welding for stainless steel was analyzed. In contact region extremely thin entity units are added to simulates the contact resistance, which relates to the effect of contact force,contact area between two sheets and temperature variation. Analyzed the distribution of current density,voltage and the temperature in the spot weldingprocess, and the temperature variation of some keypoints with the time. Through the post-processing of simulation result, obtained the differences in the process of nugget formation and determine the final shape of nugget. The experimental results show the model prediction agrees with the practice well. In this calculation, electricity transmitting and thermal conducting are nonlinear problems and mechanical behave is elastic-plasticity problem with contacting condition. Because of material nonlinear, geometry nonlinear, and contacting nonlinear, the cycle time step is 0.005S to improve convergence of the calculation.The result show that: in the stress field of early stage of the resistance spot welding, the contact stress at the edges and corners of electrode is very high on the contact surface between electrode and workpiece because of the special shape of electrode, contact pressure along X axis is higher on the contact surface between workpiece and workpiece. In the earlier stage of welding, the highest of temperature occurs in the electrode boundary vicinity on the contact surface between workpiece and workpiece as a result of distributed characteristic of the contact resistance and the contact pressure. With the time increasing, the highest of temperature shift to internal. The position which the melt nucleus first forms is not in the central, but in the vicinity of electrode boundary. The melt nucleus may complete in 4-5 cycle.
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