The Effect of Focal Distance and Type of Auxiliary Gas on Cut Width in CO۲ Laser Cutting of Stainless and Mild Steel Sheets

Lens focal distance and auxiliary gas type utilized in CO۲ laser cutting are two important parameters affecting process measures such as cuts width and quality at desired cutting speeds. This research work focuses on cuts width and quality in CO۲ laser cutting with a power of ۴۰۰۰W on two types of steel sheets at different focal distance values and using different types of auxiliary gas. The effect of focal distances of ۵” and ۷.۵” as well as utilizing oxygen and nitrogen as auxiliary gas on cut width and quality in ۳۰۴L stainless steel and St۳۷ steel sheets were investigated. The size of cut widths was measured using an optical microscopy. The results demonstrate that cuts performed at the focal distance of ۷.۵” are wider than those created at the focal distance of ۵”. It is also observed that with increased workpiece thickness, the use of focal distance of ۷.۵” is more feasible because cuts are faster; need lower laser power, and use less amount of auxiliary gas. When using oxygen as auxiliary gas, the main factor affecting the cutting efficiency is the oxidation reaction, whereby oxidation energy is added to laser power which results to an increased energy level in the cutting region. This means that using oxygen as auxiliary gas makes it possible to cut thicker sheets at higher cutting speeds as compared to that of nitrogen. However, when using oxygen as auxiliary gas, the quality of cuts appears to be lower and their width larger as compared to cuts performed by nitrogen auxiliary gas.