Naoki Miyanagi

Effect of nozzle shape on surface integrity in microcutting with pulsed YAG laser

YAG laser has widely been used for precision micro machining in many fields. However, adhesions of dross and spatter to the base material due to high energy beam machining lead to the deterioration of the surface integrity. It is important to understand the assist gas flow from the tip of a convergent nozzle in order to improve the surface integrity, since material is mostly removed away by the gas flow spouted in the same direction of the laser beam. In this paper, effects of the nozzle shape on assist gas flow and the machined results were experimentally analyzed using the Schlieren method. There exists an unstable region in which the pressure on the workpiece changes periodically, and the region becomes wider with the reduction of the exit diameter. The pressure on the workpiece increases with an increase of the exit diameter, which makes the dross height smaller. However, it is necessary to select the nozzle shape according to the demand of the surface integrity, because the consumption of the assist gas increases and the kerf width becomes wider with an increase of the exit diameter. Moreover, it was pointed out that a kind of nozzle with a convex curve on inner wall of nozzle led to better surface integrity.