Study On The Re-pressure Mechanism Of 22MnB5 Steel By Resistance Spot Welding

The 22MnB5 steel belongs to the low alloy and high strength steel,which is a high quality material for realizing light weight of automobile body.Its strength can guarantee the high strength of automobile body.Therefore,22MnB5 steel becomes the trend of automobile steel,and the main welding method of automobile Body is the Resistance Spot Welding,The high strength of 22MnB5 steel makes grain strcture of the solder molten core zone and heat affected zone changed in the process of cooling crystallization.There is a certain difference between the average class steel and22MnB5 steel,when the welding zone continuous cooling transformation law of CCT curve.The performance of strength matching requirements of 22MnB5 steel not completely conform to the ordinary class steel in the solder joint.Due to high temperature peak value of resistance spot welding heat cycle and uneven cooling rate inside and outside of molten core,the comprehensive mechanical properties and forming indexes of 22MnB5 steel resistance spot welding joint cannot meet the relevant requirements of certain automobile industry.In this paper,the thick 22MnB5 steel plate is 1mm that was used as experimental material.In order to obtain the same degree of plastic deformation as common steel,greater electrode pressure was needed to be applied,but the larger electric force directly caused the narrowing of the 22MnB5 steel welding process window.So this topic for22MnB5 steel resistance spot welding process was improved,using resistance spot welding robot servo electrode holder welding orthogonal experiments,in the process of welding when solder melt will be in nucleation of solidification sate,through adjusting torque servo electrode augment electrode pressure,on the basis of the original process increase pressure process again,and study solder joint nucleation mechanism of pressurization process condition.In the experiment,COMSOL Multiphysics finite element simulation software was used to simulate the spot-shaped nuclear process in the process of re-pressurization.The variation process of molten core size with welding time and the distribution of temperature field were analyzed,and the nucleation of solidification state of molten core in the simulated state was determined.In this paper,the process of welding spot nucleation was also photographed by high-speed camera,and compared with the simulation process.Through multi-channel temperature detector acquisition under the two states of solder heat affected zone temperature of each point in time,compare the simulation status under the temperature of heat affected zone,and analyze the differences of two state temperature,and then under the pressure of welding spot temperature of the heat affected zone and heat affected zone joint simulation of temperature difference,the accuracy of the simulation results verify the resistance spot welding.The experimental results show that the 22 mnb5 for 1 mm thick steel plate,when the welding current is about 6 kA ~ 8kA,the welding time is about 10 cyc ~ 20 cyc,the shape and mechanical properties of the welding spot after resistance spot welding and pressure molding process can be effectively improved.When the welding re-pressure time is about 6 cyc ~ 10 cyc,the shear strength of the welding spot can be increased by 20%,the diameter of nugget can be increased by 20% ~ 25%.According to the result of the simulation and temperature detector,the cooling rate of fusion core in the state of re-pressure is higher than the traditional process,the strength of the welding spot and refine the molten core grains can be effectively improved by the change of electricity in the state of re-pressure.