Composition and surface state influence in laser process for steel sheets

Laser cutting process is highly influenced by material composition and surface state before cutting. Variability in these elements involve changes in cutting parameter values (productivity) and cut quality (part acceptance or rejection). The vast majority of studies on this matter have been conducted employing CO2 lasers, therefore, the aim of this analysis is to complete existing literature and update it with actual industrial trends which move towards the use of fibre lasers. For this purpose, behaviour of three steel types (pickled steel, Ruukki and Hardox) with thicknesses of 6mm, 10mm and 15mm has been analysed, using the sheets just as they left the mill, with a superficial machining and superficial rust. Quality of obtained parts has been measured visually and through a confocal microscope, comparing roughness results with the standard UNE-EN ISO 9013 for thermal cuts. Results have revealed three different existing quality zones (upper, centre, bottom) for thick materials (>6mm) and a single quality for the thin ones (s6mm). Differences in quality and cutting parameter values between pickled steel and Hardox have been noticed, but not between pickled steel and Ruukki. Moreover, significant variations in cutting process have been observed when previous superficial rust is present, while machined surface has no effect on it.