Study On The Monitoring And Controlling Of Penetration Condition Of Tailor Rolled Blank During Laser Deep Penetration Welding

With the rapid growth of car ownership,many problems,such as energy consumption and environmental pollution,are becoming more and more serious.Therefore,automobile lightening is one of the main measures to solve these problems.Tailor rolled plate can achieve the purpose of weight reduction and ensure the high strength of the body in the manufacture of automobile,so the connection problem of the tailor rolled plate become the key technology to realize the lightweight of the car.Laser welding has gradually become one of the main welding methods in automobile industry because of its fast welding speed,good weld formation,small welding deformation,little spatter and easy automation.However,due to the continuous and irregular change of the tailor rolled plate,the laser welding is difficult to be applied directly to the material connection.Therefore,it is necessary to monitor and control the welding process.In order to explore the thickness variation of the tailor rolled plate,this thesis first studied the rules of thickness variation of three tailor rolled plates.It was found that the plates had sudden changes of thickness in the longitudinal direction and uneven changes of thickness in the width direction.In order to eliminate the influence of defocus on laser welding tailor rolled plates,a special welding fixture was designed to ensure that the defocus of the laser welding process was kept constant.This thesis built an active coaxial monitoring platform,mainly included the laser welding system,displacement platform system and image acquisition system.Welding ability tests of three kinds of variable thickness plates were carried out and it was found that the width and penetration of laser welding on two sides of the tailor rolled plates were different.The laser variable power welding tests of the 1.2mm-2.0mm variable thickness plates were carried out and the power variable ranges were from 800W to 1700W.The images captured by the high-speed camera in the laser welding process were processed by image processing method,and the area information of small keyholes and through-holes were extracted.It was found that the result of the image processing algorithm agreed with the actual welding results.The surface topographies and welding profiles of welding under variable power welding were analyzed,and the power ranges of optimum laser welding quality were obtained at different thickness plates.The hardness of the weld section were carried out,and it was found that the weld hardness was increased by 60.54%through laser welding.The thickness,width and penetration data were measured by the super-depth deep microscopy system.Using the method of regression analysis to analyze the factors of the welding,and the regression power—weld width—prediction thickness deviation model was established.It could be obtained the predicted the optimal laser welding power under different thickness plates.According to the different thickness of the tailor rolled plates,the variable power laser welding experiments of the material were carried out,and the consistency of the weld width and penetration state in the full thickness range of the variable thickness panel were obtained.