Study On The Laser Beam Brazing Process And Defect Inhibition Mechanism Of Galvanized Steel

As a combined technology of laser welding and brazing, laser beam brazing hasadvantages of high quality of welding, flexible joints form, small deformation of the workpiece, as well as the high welding efficiency. Laser brazing not only retains the advantagesof laser autogenous welding, but it also overcomes the defect of laser autogenous welding,like processing accuracy of work piece, high fixture demanding and so on. Currently, laserbrazing galvanized steel inland is little researched. In this paper,4kW fiber laser and wirefeeder with a hot wire function is used to build up experimental platform, with which laserbrazing crimping butt and lap joint is researched for its process feature. What’s more, a trialwelding of trunk lid is designed and implemented.For crimping butt and lap joints, the increase with laser power and defocussing amountincreasing, the brazing seam width showed an increasing trend; while welding speedincreasing result in the brazing seam width decreasing; wire feed speed has little effect onbrazing seam width. For crimping butt joints, the increase of laser power and wire feedspeed, help to increase the filling depth; with the welding speed and defocussing amountincreasing, filling depth is reduced. Weld reinforcement increases with the increase ofwelding speed and defocussing amount, while decreases with the decrease of wire feedspeed. Hot wire brazing can significantly increase the brazing seam width and help toincrease the filling depth and decrease the weld reinforcement to a certain extent. Comparedwith crimping butt, it’s more sensitive to welding speed for lap joint, but a wider range ofvariation is obtained for defocussing amount. For the crimping butt joint, the weld tensilestrength is most sensitive to the variation of wire feed speed and increases while it increases.Under the experimental conditions and parameters herein, shear tensile strength is abovethe base metal for all samples of lap joint.The common weld defects in laser brazing can be summarized as four categories aspoor solder melting, poor solder spreading, holes and zinc coating loss. The main factorsthat determine the effect of laser brazing forming are the solder surface spreadability andspreading time. The whole welding process is accompanied by volatilization of zinc vapor.According to the formation mechanism for each type of defect, the corresponding process parameters can be adjusted to reduce or avoid the occurrence of defects.Finally, based on the study of process characteristics, a scheme of laser brazing for cartrunk lid was made and a trial welding was implemented. In the track setting, the posture ofwelding head was considered importantly. T-joint is the primarily important joint form inthe trunk lid. According to process analysis, a large process window was obtained and evenwhen the value of the beam incident angle varied from15°to30°, uniform weld formingwas obtained. In this study, some problems still exist on the seam forming of the trunk lid,but an almost complete weld was obtained. It was found that the design of split stampingsand joint method of laser brazing are reliable. The flexibility of laser brazing makes thetrunk lid design more freedom and diversity.