Study On The Effect Of Spot Welding Process On Stainless Steel Spot Welding Indentation And Methods To Reduce Indentation

In recent years,the city development of urban rail transportation demand has greatly promoted the development of stainless steel rail bus manufacturing.The stainless steel rail bus body is a welded structure made of tens of thousands of resistance spot welding joints,and it is important to ensure the intrinsic and appearance quality of the spot welding joints in the spot welding forming process to meet the structural strength and surface aesthetics of the stainless steel body.In this paper,for stainless steel rail passenger cars commonly used SUS301 L stainless steel sheet,we studied the methods to reduce the surface indentation of resistance spot welded joints from the perspective of controlling the parameters of the spot welding process and changing the electrode structure,respectively.For the traditional RSW using spherical electrodes,this paper designed a spot welding process control test,we collected the spot welding joint surface indentation datas and use MATLAB design algorithm for data processing,and finally generated the average indentation depth H curve,indentation area S curve and indentation threedimensional image,these images can visually reflect the welding current,welding time,electrode pressure on the surface of the spot welding joint indentation.Combining these images with the maximum tensile shear force curve,we develop the optimal spot welding process parameters that will ensure adequate mechanical properties and the smallest possible surface indentation of the spot welded joint.A numerical model of spherical electrode resistance spot welding indentation is established using ABAQUS finite element software.The simulated average indentation depth H* and simulated indentation area S* calculated by this model are consistent with the average indentation depth H and indentation area S within a certain error range,and this model achieves the prediction of the surface indentation of the RSW using spherical electrodes using a computer.This paper designs a new RSW with ring-shaped nugget process and simulates the process using ABAQUS finite element software.The analysis of the changes in current density and temperature field during the spot welding process reveals the nucleation mechanism of the RSW with ring-shaped nugget process,which verifies the conjecture of designing this process,that is,to reduce the surface indentation by changing the current distribution to ensure the reduction of heat input without reducing the diameter of the nugget.For the RSW with ring-shaped nugget,this paper designed a spot welding process control test,the results show that the process can significantly reduce the average indentation depth but has no significant effect on the indentation area compared with the traditional RSW using spherical electrodes process.This paper further investigates the effects of spot welding current and welding time on the surface indentation,and combines the analysis of nugget morphology and maximum tensile-shear force curves to develop reasonable welding process parameters of the RSW with ring-shaped nugget to reduce indentation.This paper further analyzes the nuggte morphology of spot welding joint of the RSW with ring-shaped nugget,the results show that when the heat input is sufficient,with increased heat input spot welding joint will first generate an annular nugget,followed by the nugget while expanding inward and outward,eventually forming a flatter circular nugget,when the heat input is insufficient,ultimately only annular nugget can be maintained.This process is also able to significantly reduce the penetration rate while maintaining the mechanical properties of the spot welded joint.