Research On MS1180/DP780 Heterogeneous Advanced High Strength Steel Spot Welding Process

In recent years,the rapid development of the automotive industry has facilitated our transportation,but it has also produced three inevitable social problems: energy consumption,emissions and safety.In order to solve these problems,it is particularly important to find high-quality materials that can achieve lightweight vehicles.Advanced high-strength steel can achieve the required strength and even higher strength with lighter weight,and also has the advantages of good forming performance and good anti-collision performance that ordinary steel does not have.Therefore,advanced high-strength steel is currently in the automotive industry.The required body materials solved the problem to a certain extent and met the current requirements.If the advanced high-strength steel of different materials is spot-welded,the thickness of the plate,the composition of the structure,the properties and the processing technology are different during the spot welding process,which makes the process parameters difficult to control,and it is easy to produce defects such as splashes and shrinkage holes,which ultimately makes high quality spot welding head cannot be obtained.Therefore,the exploration of heterogeneous advanced high-strength steel spot welding technology has become an urgent problem to be solved.The research experiment used the spot welding robot welding system provided by Kaierda for spot welding experiments.For the equipment and system,the spot welding robot welding system is perfected to enable normal and stable spot welding;Various signal detection sensors are installed,and the data acquisition and analysis system is improved through debugging,so that it can accurately collect and analyze electrical signal related to welding quality.For the spot welding process,two kinds of fracture modes during the breakage were explored and analyzed.The related contents of the spot weld defects of shrinkage and splash were studied.The orthogonal welding experiment was used and the spot welding process parameters were optimized by the variance analysis method;The orthogonal test was again designed to optimize the process parameters of the tempering pulse.The influence of process parameters and heat on the characteristic size of solder joints was studied.Through the research on the spot welding process of the advanced high-strength steel,some conclusions are summarized as follows:(1)The microstructure of the nugget in the spot weld joint is larger than that of the other two regions;the grain in the heat affected zone becomes larger and larger as the distance from the center of the nugget decreases;the nugget area of the spot weld joint The microhardness is generally higher than the heat affected zone and the parent metal zone.For the electrical signal waveform,the spattered solder joint has a sudden change in the voltage of the solder joint voltage compared to the non-splash solder joint,and the current pulse has a small pulse protrusion.(2)The orthogonal experiment was designed to optimize the spot welding process parameters.The optimum process parameters were obtained by variance analysis.The welding current was 8.5kA,the welding time was 400 ms,and the electrode pressure was 7.5kN.The tempering pulse orthogonal optimization test shows that the optimal tempering process parameters for double-pulse spot welding are cooling time 800 ms,tempering current 4250 kA,and tempering time 200 ms.The influence degree of the tempering process parameters on the maximum shear force is obtained by the range analysis: the cooling time has the most significant influence,the tempering current is second,and the tempering time has a weak influence.(3)Through the research,the regular relationship between the average power and heat and the cross-sectional characteristic size is obtained.Solder joints that produce the same amount of heat may have different combinations of process parameters,and the cross-sectional dimensions formed by various aspects may also be different.Similarly,solder joints of the same cross-sectional dimension may have different combinations of process parameters,and the heat generated by various aspects may also be different.As the heat of the solder joint increases,the diameter of the nugget increases slowly and the fluctuations in the later period change smoothly.The diameters of the indentations on the MS1180 side and the DP780 side increase continuously and the changes on both sides are basically the same;the indentation rates on both sides are slow.Increased and the waveform jitter is large;the penetration rate on both sides is slowly reduced and the waveform jitter is large.This study provides good process parameters for MS1180/DP780 heterogeneous advanced high-strength steel spot welding,and puts forward some theoretical insights to avoid splashing,which is of great significance for practical industrial welding.The influence of process parameters and heat on the characteristic size of the solder joints was obtained,which provided a theoretical basis for further research.In the later research,in the spot welding of multi-pulses such as tempering pulses,further investigation is required to obtain better solder joints.