Study On Resistance Spot Welding Process Of Stainless Steel With Ring-shaped Nugget

The resistance spot welding process is a connection technology with the advantages of low cost,high efficiency,easy realization of mechanization and automation,etc.And it is widely used in the connection of body structures of stainless steel railway vehicle.Based on the research of the traditional resistance spot welding process,in order to further improve the joint performance and reduce the indentation and deformation of the solder joint,this paper proposes an electrode that uses an insulating film to make the core non-conductive and a new resistance spot welding process with ring-shaped nugget from the perspective of nugget shape control.Because the resistance spot welding is a complex process involving the interaction of multiple physical fields such as heat,electricity and force,and the process of nugget formation is invisible and instantaneous,it is difficult to conduct a comprehensive and in-depth study on the preloading process and nugget formation mechanism simply by theoretical or experimental methods.The computer numerical simulation method can be more intuitive and efficient to simulate the preloading process and nugget formation process,which has important guiding significance for the in-depth study of the spot welding process of stainless steel with ring-shaped nugget.In this paper,based on the principle of resistance spot welding with ring-shaped nugget,the corresponding spot welding electrodes are designed.The welding experiment is used to determine the reasonable electrode form.Then a threedimensional axisymmetric numerical model of stainless steel double-sided single spot welding is established by using the finite element simulation software ABAQUS.The model was used to numerically simulate the preloading stage and electric heating stage.The distribution of electric field,temperature field and stress field in the process is analyzed,and the formation mechanism of ring-shaped nugget is explored.By analyzing the simulation results of different welding process parameters,the reasonable process parameters are obtained.Finally,combined with the process test,the numerical simulation results are compared with the test results in this paper.The numerical simulation results show that compared with the traditional resistance spot welding process,the resistance spot welding process of stainless steel with ring-shaped nugget shows characteristics compatible with the structure of the thinfilm insulated core non-conductive electrode.In the preloading stage,the equivalent stress distribution of the whole workpiece is relatively uniform.Due to the electrode structure and shape,the equivalent stress value in the center area of the solder joint is relatively low.There is a peak stress at the contact edge between the electrode and the workpiece and between the two workpieces,and there is an obvious stress concentration phenomenon.With the increase of electrode pressure,the contact stress value of the contact surface between the electrode and the workpiece and the contact surface between the upper and lower workpiece increases continuously,but the contact range of each contact surface is basically unchanged,indicating that the initial conductive area of resistance spot welding is unchanged.During the electric heating process,the temperature field and the current density distribution are highly consistent,both of which are annular.With the increase of the energization time,the nugget starts to appear and grows to the center and periphery of the solder joint at the same time,eventually forming a ring-shaped nugget.At the end of this paper,the effect of resistance spot welding process parameters on the formation of ring-shaped nuggets is further explored,which has important guiding significance for optimizing the resistance spot welding process of stainless steel with ring-shaped nugget.