Laser power requirement for cutting thick-section steel and effects of processing parameters on mild steel cut quality

The high-power fibre laser presents a possibility for the application of solid-state lasers in thick-section metal cutting, a field which has been dominated by high-power CO2 lasers. The current paper presents the lumped-parameter formulation of the laser power requirement as a function of cutting speed for oxygen-assisted laser cutting of mild steel and nitrogen-assisted laser cutting of stainless steel. The calculated laser power requirement is compared with the incident laser power used in the cutting of 15 mm mild steel with oxygen assist gas and 10 mm stainless steel with nitrogen assist gas using a multi-mode 5kW fibre laser and a 4kW CO2 laser. The incident laser power required for cutting at a given cutting speed is found to be lower for fibre laser cutting than for the CO2 laser cutting, indicating a higher absorption of the fibre laser beam. The effects of process parameters on the cut kerf quality in mild steel laser cutting with oxygen assist gas using the high-power fibre laser are presented. The critical process parameters affecting the quality of the cutting process and the resulting cut kerf are the cutting speed, oxygen pressure, and nozzle diameter.