Striation-free Laser Cutting of Mild Steel Sheets

Striation, i.e. periodic lines appearing on the cut surface, is one of the most important quality factors in laser cutting. It affects the surface roughness, appearances and geometry precision of laser cut products. Despite various efforts over the last 30 years to understand striation formation mechanisms and to optimise laser parameters, no reported work has so far shown striation-free cutting. This paper reports an investigation into achieving striation-free laser cutting of EN43 mild steel sheets of 2 mm thickness. A 1 kW single mode fibre laser was used in this work. Specific operating conditions have been determined which enable high-speed, striation-free laser cutting. A theoretical model is proposed to predict the critical cutting speed at which striation-free cutting occurs. It is also observed that at cutting speeds above the critical cutting speed, striation reappears and surface roughness increases with the cutting speed, a phenomenon not observed before.