Effect of ambient pressure and gas on penetration depth and laser‐induced plasma behaviour ‐ Study on CO2laser welding phenomena

Abstract

The effect of ambient gas and pressure on the penetration and plasma behavior for AISI 304 stainless steel in CW CO2 laser welding with 4 kW output power was investigated. The major results are summarized as follows ;(1) The penetration depth significantly increased by reducing the ambient pressure. At the same time, the quantity of the laser-induced plasma also decreased as the ambient pressure decreased.The plasma in He and N2 ambient completely disappeared under the pressure of less than 100 torr, resulting in the significant increase in the penetration depth. The penetration depth reached more than 12 mm under the pressure of less than 100 torr at the traveling speed of 25 cm/min, which was around twice as deep as that under the atmospheric pressure. It was mainly because the formation of plasma which blocked the laser beam entering to the workpiece was greatly suppressed under the low pressure.(2) The plasma generation was dependent upon the physical properties of gas element as well as the ambient pressure. The higher the ionization potential and heat conductivity of the gas element was, the larger the plasma became.