Study on supplying method of assist gas in precision cutting with pulsed YAG laser

YAG laser has widely been used for precision micro machining in many fields. However, adhesions of dross and spatter to base material due to high energy beam machining lead to the deterioration of surface integrity. It is important to understand the assist gas flow from the tip of a convergent nozzle in order to improve the machining accuracy, since most materials are removed away by gas flow. In this paper, the effects of assist gas flow on machined results in micro machining with pulsed YAG laser are investigated using Schlieren method. Experimental analysis made it clear that there was a region in which the pressure on workpiece didn't increase linearly with an increase of cylinder gas pressure. Mach shock disk repeatedly appeared and disappeared under this condition, and the pressure on workpiece changed periodically. The fluctuation of assist gas flow led to the irregular dross generation. On the other hand, there was no unstable region under small gap and/or high pressure conditions, in which the assist gas flow was stable and the height of dross became smaller. Consequently, it is recommended to use the assist gas under higher pressure condition more than 300kPa on workpiece for fine precision machining.