Gas-assisted laser cutting of medium-section metals using spherically aberrated beams

Abstract

Abstract. We analyzed the effects of the focal point aberrational offset in optical transport systems for highpower lasers. Transverse and near-axial laser intensity distribution transformations in the presence of both positive and negative spherical aberrations were numerically calculated and experimentally demonstrated for different strengths. We show that spherical aberration yields considerable asymmetry of the focused beam's caustic. Several optical transport systems with identical optical parameters (excluding the noncorrected axial beam spherical aberration) were designed. We examined the effects of the laser intensity profiles produced by these systems on the quality of oxygen-assisted laser cutting of medium-section mild steel. We show that high-quality cuts can be obtained for different shapes of laser intensity distribution. However, the greater the refocusing magnitude introduced by the spherical aberration correction, the more precisely the focal point position must be maintained during the laser cutting process. © The Authors. Published by SPIE under a Creative Commons 1 Introduction Laser cutting of metals and alloys is one of the most commercially valuable laser technology processes. Originating from basic research on laser-matter interaction, 1 the field has significantly developed, now offering a large arsenal of state-of-the-art techniques.2-5 Omitting the energy and resource efficiency issues, 6 the performance of laser cutting can be captured by only two output parameters. These are the cutting speed and kerf quality. Thus, laser cutting optimization reduces to achieving the maximal cutting speed with the best kerf quality. As far as the material separation is concerned, 7 the speed can be dramatically increased. On the other hand, the cutting quality depends on many parameters. The most important and frequently discussed are the kerf geometry (accuracy, width, and taper), the surface quality (cut-edge roughness, striations morphology, and dross and burr inclusions), and the mechanical and metallurgical properties (hardness and strength, heat-affected zone, and oxide layer). 8 The number of parameters dramatically affecting the cutting quality ranges from 25 9 to 75. 4,5 These are nearly evenly divided between the workpiece properties, assist gas parameters, laser machine, and laser beam characteristics. Input-output parameters relationships are mostly nonlinear and exhibit strong interdependence. In this regard, maximal precision is provided by the studies that focus on only one input-output parameter pair. Yet, this "one parameter at one time" approach does not provide complete information on the process as a whole.