Research On Resistance Annular Welding Technology

In order to meet the requirements of automotive high strength steel sheet welding and sheet metal welding,based on the ideas of the welding energy distribution control,we design a new ceramic core composite annular electrode.By inlaying a circular non-conductive ceramic rod in the center of the traditional copper electrode,this electrode changes the welding heat from the traditional spot welding to a more dispersed annular distribution in the center of the welding spot,and forms a annular welding spot corresponding to the annular copper end face.Due to the dispersion of energy,the threshold of forming current of circular solder joint is higher than that of traditional circular solder joint,but the surface indentation depth of solder joint decreases effectively.The annular electrode structure adjustment can realize the design of annular solder joint size,and the strength of the solder joint can be improved by forming a large size solder joint area.This topic first uses the ordinary annular electrode to conduct the welding to the Q235 steel plate,respectively taking the current percentage is 20%,30%,40%,50%,60%,70% welding current to obtain the relatively stable welding part.At the same time,another group of Q235 steel plates were welded with ordinary electrodes under the same welding parameters,as a comparative experiment.Then,the ceramic core composite annular electrode and circular electrode were used to weld 1.0mmq235 mild steel and 0.7mmdc06 steel respectively under the same welding time and welding pressure.Using 1.2mmdp980 steel,under the condition of the same pressure(150kg),the same current(8k A)and different time(40-210ms),the weld core forming and mechanical properties obtained from ordinary electrode and annular electrode were compared,and the following conclusions are obtained.(1)When the welding current is very small(less than 70%),the welding parts of the annular electrode resistance spot welding show interface fracture,while the joints welded with ordinary electrodes show pull-out fracture mode when the current strength is more than 30%.Therefore,the strength of the welded joint obtained by the annular electrode is far less than that obtained by the spot welding of the ordinary electrode resistance.When the current is large enough(more than 70%),the load and failure energy of the welding piece obtained under the annular electrode(without ceramic core)are higher than those obtained under the ordinary electrode welding.Therefore,under the condition of such welding parameters,the annular electrode resistance spot welding process improves the welding quality,and the strength and mechanical properties of the welded joint are also enhanced.(2)Compared with the circular electrode,the ceramic core composite annular electrode has a higher current threshold,but the surface indentation depth of the solder joint is reduced.Under the condition of the same end face diameter,the ceramic core composite annular electrode can provide a larger area of solder joint than the circular electrode.(3)When the ceramic core composite annular electrode is welded,the stable circular electrode can be formed with the increase of current,and the stable tensile strength and stripping strength can be obtained in the larger welding window.