Abstract
In YAG laser cutting process of thin plate, it is important to understand the assist gas flow from the tip of a convergent nozzle in order to improve the machining accuracy, since melted material is mostly carried away downward by the gas flow. Besides, it is considered that the nozzle shape influences the assist gas flow. In this paper, the effects of the nozzle shape on assist gas flow and machining results in micro machining by a pulsed YAG laser are experimentally investigated. There is an unstable region where the pressure on a workpiece changes periodically regardless of the internal shape and exit diameter of nozzle. The unstable region starts at low cylinder gas pressure and becomes smaller in range with increasing the exit diameter. Under middle and high cylinder gas pressure conditions over 300kPa, height of dross becomes smaller with the increase of the exit diameter for a nozzle of conical internal shape, since the pressure on workpiece increases. Furthermore, when the conical inner wall of nozzle is changed to a convex inner wall, it is possible to reduce the height of dross. Additionally, the height of dross becomes lower, when the curvature of the inner wall increases under the high pressure condition.
