Investigation of the piercing process in laser cutting of stainless steel

This paper investigates the laser piercing process which precedes nearly every laser cutting operation. The two most important aspects of the piercing process are: (a) How long does it take to pierce the material? and (b) How wide is the pierced hole? If the hole is no wider than the cut line, the material can be pierced on the line to be cut. In this paper, 10 mm thick stainless steel was pierced by a multikilowatt fiber laser to compare efficiency and quality when piercing with a continuous wave output and a selected range of power modulation parameters. The different processes were observed by high speed imaging and subsequently examined by visual observation. High speed imaging is used to time the penetration event and to study the laser-material interactions involved in drilling the pierced holes. The results show that appropriate laser power modulation settings can considerably reduce both the piercing time and the required energy to generate any piercing hole required for the subsequent cutting process. This pulse-pierce technique and the differences between piercing with a continuous and a power modulated laser beam are further explained and discussed. Also, the effect on the size of the entrance to the pierced hole depending on power modulation regimes was investigated in this paper.