Study On Powder Beam Form In Laser Welding Of Strength Galvanized Steel With Powder Filling And The Zinc Burnout

With the development of laser technology and the lightweight of car body, thelaser welding will take the place of resistance spot welding because the laser weldingcan reduce car body weight effectively. Yet laser welding workpiece weldcomposition is difficult to control, some derivative laser technology has been invented.Laser welding with powder filling is a high flexible welding technology due to itseffective control of the weld composition of workpiece. In order to explore therelationship between powder filling and the weld composition，hence the powderspraying process for the laser welding of galvanized steel with powder filling issimulated and experimental analyzed.Firstly, the powder beam profile has been studied on the basis of the gas-soliddiscrete phase model. The powder beam spatial distribution density on welding planehas been obtained by the analysis of the concentration of powder beam section. At thesame time, research has been given to the influence brought about by the correlationof different parameters on the powder focal length, maximum powder concentration,focal spot diameter and depth of focus powder process parameters. Powder nozzlediameter is the main process parameters affecting the powder focal length. Maximumpowder concentration is inverse proportional to protective gas flow, carrier gas flowrate, nozzle diameter and nozzle angle. The powder focal spot diameter isproportional correlation to carrier gas flow rate and nozzle angle. On the contrary，itis a positive correlation to protective gas flow and nozzle diameter. In order toachieve the best powder gathering effect, its found that the condition of a singlevariable of shielding gas flow and carrier gas flow rate is8L/min, powder sprayingmouth diameter of0.8mm and angle70°, with the best focal spot diameter of1.92mm and the focal depth of3.69mm.Simultaneously, based on the results of the theoretical calculation of the coaxialpowder spraying device combined with the powder, gas and water stable are designedaccording to the carrier gas drive and the principle of powder under its own gravity.To obtained the relationship between flour beam spatial distribution curve throughimage processing method including the gray processing, image enhancement andimage data feature after feeding experiment was carried out. The result shows that thepowder focal length and the focal spot diameter deviation value is less than10% between experimental and simulation results. Powder beam focal spot diameter isdecreased67%compared with the using powder spraying device.Finally, the relationships between process parameters and the spectral signals ofthe laser-induced plasma as well as the burnout of the zinc were experimentallystudied in laser lap welding of galvanized steel. The results are as following: Theimportant order of the relevant factors that affect the burnout of the zinc is: weldingspeed>laser power>auxiliary gas flow> defocus. At the same time, the test of thepowder filling welding galvanized steel was proved that powder filling cansignificantly improve the performance of the weld surface and reduce the burnout ofthe zinc.The research of the powder beam characteristics provides the theoretical andexperimental basis to select the powder utilization methods in the process of laserwelding with powder filling.