Effects of plasma on CO₂ laser cutting quality

In CO₂ laser cutting, the measurement of plasma size and transmittance is necessary since the plasma appearing on the surface of the workpiece absorbs a fraction of the incident energy and acts as a heat source, enhancing the cutting process. Consequently, when the plasma size increases, the energy distributed across the plasma becomes lower and the energy losses due to heat transfer increase. This increases the heat-affected zone and reduces the cutting quality. In the present study, CO₂ laser cutting of sheets of mild steel and titanium is examined while varying the cutting speed. Oxygen (as a reactive gas) and an argon/oxygen mixture are introduced through a nozzle in the cutting section. In order to examine the effect of the plasma on the cutting performance and quality, O₂ and gas mixture pressures are varied and the absorption of the He-Ne beam passing through the plasma in the direction normal to the CO₂ beam axis measured. It is found that the cutting quality improves at a particular O₂ pressure for the mild steel workpiece. The absorption of plasma increases as the cutting speed reduces.