Characteristics of high-power CO₂ laser welding and porosity suppression mechanism with nitrogen shielding. Study of high-power laser welding phenomena

Abstract

In its role as a welding heat source providing high energy density in ambient air, the laser can be used to perform high-precision, deep penetration welding under low-strain conditions. In the wake of the substantial high-power and high-beam quality enhancements of laser oscillators, the laser has most recently seen growing applications in a wide variety of industrial fields.^{1, 2} Available applications, however, are largely focused on high-precision welding of thin sheet metal in the automotive industry.^{3, 4} Deep penetration welding applications as another viable application avenue have been reported in shipbuilding and nuclear power generation, but remain relatively little documented.⁵ This is reportedly due to the fact that, with the increasing penetration depth of laser welding, welding defects such as porosity and solidification cracking more readily occur. Particularly in partial penetration welding of carbon steel, development of porosity prevention methods intended to allow laser welding to proceed at a depth of more than 10 mm has gone entirely unstudied. In this context, the authors have mounted an intensive research programme with the goal of developing a laser welding technology to prevent defects in welds at a penetration depth of more than 20 mm. In these circumstances, the oscillators used even now are high-power CO₂ lasers suitable for deep penetration applications.