Effects of Angle of Incidence or Focal Position upon Spatter Reduction on Basis of Three-Dimensional X-Ray Transmission In-Situ Observation of Laser Welding Phenomena

摘要

The objective of this research is to reveal effects of angel of incidence or focal position upon spatter generation and reduction in melt-run welding of a SUS304 stainless steel plate with a 6-kW power laser beam on basis of a high-speed video camera and a three-dimensional X-ray transmission in-situ observation apparatus. The high-speed video images at 150 mm/s in welding speed show the convex molten-pool surface behind a keyhole inlet was elongated and scattered as large spatters over 0.1 mm in size. According to the X-ray images, a melt flew to the elongated part at approximately 2.3 m/s in velocity, which caused the rapid increase of the spatters in size. A 2-mm inner defocused position or a 20-degrees angle of advance for an incident laser beam decreased number of spatter by half or one third owing to circulating melt flow behind the keyhole inlet. It was revealed that the large spatter reduction was effective to deceleration or change in direction of the melt flows behind the keyhole inlet, which led to not only suppressing formation of the elongated surface but also improving the frequency that tire elongated went back to the molten pool.