Laser Machining of Die Steel (EN-31): An Experimental Approach to Optimise Process Parameters using Response Surface Methodology

Experiments were performed based on response surface methodology (RSM) to investigate the process parameters effect on the features of hole geometry. Cutting speed (of 500-1000 mm/min), laser power (of 2000-4000 W), frequency (of 800-2000 Hz), duty cycle (of 75-95%), and gas pressure (of 0.05-0.15 bar) were considered as variable parameters. Deviation in the dimension of entrance and exit holes, heat affected zone (HAZ) on the upper & lower edge, and roughness were the output to analyse the cutting quality of 14 mm thick normal and heat-treated (HT) EN-31 die steel using 4 kW CO2 laser. For untreated plate, minimum taper angle was achieved with low cutting speed, higher laser power, and gas pressure. Higher cutting speed, low laser power, and higher gas pressure result in the minimum HAZ. For the HT plate, the mid-range of parameters results in the minimum taper angle and HAZ. An optimised model was developed, and the confirmatory test gives roughness up to 0.27 microns and it shows good agreement with the mathematical model. At the cross-section of holes, striation pattern, resolidified layer, and corner qualities were visually inspected. Surface damage near the cutting edge was observed using scanning electron microscopy.