Dynamic phenomena in laser cutting and cut quality

Abstract

The quality obtained with laser cutting, one of the most important processes of laser machining, is characterized by a nearly periodic pattern of striations that cause a certain roughness of the cut surfaces. Improvements of the cut quality, that would be of major technical importance, can only be obtained if the mechanism that leads to the formation of these striations is entirely understood. The present author has argued already in 1984 that temporal fluctuations of laser power can induce oscillations of the liquid layer formed at the momentary end of the cut and its temperature, thus causing distortions of the cut surfaces due to the movement of that layer in cutting direction. The numerical evaluation of the theoretical model yields satisfactory agreement of the “wavelength” of the striations and their dependance on the thickness of the workpiece with experimental values. So far, no attempt has been made to calculate not only the wavelength but also the depth of these striations. It is the purpose of this paper to determine the depth of the striations and to compare the numerical values with the experimental situation. Moreover, the paper is devoted to the explanation of the fact that the laser cut surfaces are showing not only one but usually two different striation patterns, one with a finer structure adjacent to the upper surface and one with a coarser pattern adjacent to the lower surface of the workpiece.