The effects of gas composition on the CO₂ laser cutting of mild steel

The importance of the exothermic reaction to CO₂ laser cutting was found by many previous researchers and this reaction was also investigated widely over the years. However, a systematic investigation about the effects of gas composition on high power CO₂ laser cutting has not yet been performed. Therefore, an attempt to systematically examine the effects of gas composition on the CO₂ laser cutting of mild steel is carried out from the experimental point of view. There are many non-linear interacting factors responsible for laser cutting process performance. In general, it is impractical to investigate all of the factors at one time. The identification of the dominant factors for which variation could lead to large effects on the cut quality is important. In this research, the gas-composition variation and the gas pressure were selected as the dominant factors. Their effects on the cut quality are investigated, with particular reference to small variations in gas composition. The gas mixtures used in this study are composed of oxygen, argon, nitrogen, helium. From the experimental results, it has been found that a high purity of oxygen is required for the high-performance CO₂ laser cutting of mild steel. Only a tiny oxygen impurity (1.25%) will reduce the maximum cutting speed by 50%. For 3 mm thick mild steel CO₂ laser cutting, a good cut was not found in the present study using low pressure - up to 6 bar - inert gas (nitrogen, argon, helium) cutting.