Study On Optimizing Process Parameters Of Laser Overlap Welding Of Galvanized Steel Plate Based On Response Surface Methodology

Galvanized steel sheet is widely used in automobile body manufacture because of its excellent corrosion resistance.However,because the boiling point of zinc(907?)on the surface of galvanized steel sheet is much lower than the melting point of steel(1530?),a large number of high temperature and high pressure zinc vapors are produced on the lap surface during the zero gap laser lapping process.If these zinc vapors cannot escape smoothly,serious welding defects such as voids,blowhole and spatter will occur.Solving the welding defects caused by zinc vapor can promote the development of automobile manufacturing industry and improve the economic benefits of various automobile enterprises,making it a research hotspot of automobile enterprises and universities.In order to solve the problem of welding defects caused by zinc vapor in zero-gap laser lap welding of galvanized steel sheet,a method of laser lap welding of galvanized steel sheet based on prefabricated slot is proposed in this paper.The effect of slot on the forming quality and mechanical properties of zero-gap laser lap welding seam of galvanized steel sheet is studied.The effects of slot size,laser power,welding speed and defocusing amount on galvanized steel sheet are investigated.On this basis,response surface methodology was applied to optimize the parameters of zero gap laser overlap welding of galvanized steel sheet.The results show that there are no gas holes in the inner structure of the weld and no serious welding defects such as holes and perforations on the surface of the weld under the condition with slot.In the absence of slot,the welding process is unstable and serious welding defects such as holes and perforations appear on the surface of the weld.Tensile test shows that the fracture position of overlap joint obtained under the condition of no slot appears in the weld zone,and its shear force is only 5.8 kN.Welding test under the condition with slot,the fracture position of overlap joint obtained appears in the base metal area far from the weld,and its maximum shear force is 6.5 kN.It proves that the existence of slot can improve the weld appearance and improve weld mechanical properties.The results show that the best process parameters are the slot size of 0.08mm,the laser power of 1900W,the welding speed of 2.4m/min and focal point position of 0.3.The results of optimization analysis by response surface method show that the optimum process parameters are as follows:the size of slot is 0.13 mm,the laser power is 2188 W,the welding speed is 2.63 m/min,and the corresponding shear force of the weld is 6.54 kN;The shear stress of the weld is 6.37 kN by welding test with the optimum technological parameters.Variance analysis shows that the size of the slot and the laser power have a significant impact on the shear force of the weld;response surface and contour plot indicate that the interaction between slot size and welding speed,laser power and welding speed is obvious,while the interaction between slot size and laser power is not obvious.