Controlling nozzle and kerf gas dynamics to manage hazardous laser cutting fume

Abstract

Conventional laser cutting is optimized for cut speed and quality but does not consider process fume. When processing hazardous materials in environments where global extraction is not practical, such as during in situ nuclear decommissioning, consideration of process fume is critically important. Fume generation in laser cutting is governed by forces applied to the molten cut front; dynamic interactions between the assist-gas and the cut front control these forces. This paper investigates the causal links between key gas-dynamic features and fume generation mechanisms in laser cutting. Its aim is to provide the preliminary understanding required to design process setups targeted at reducing the fine particle fraction. During laser cutting, the assist-gas boundary layer separates (BLS) from the molten cut front and, therefore, downstream forces applied on the melt are significantly changed. In this work, the BLS point is analyzed, captured via schlieren imaging, in an idealized environment. This separation point is related to features on the cut wall of laser-cut samples, validating the gas-dynamic interactions. The samples were cut from 3 mm thick 304 stainless steel, using a 1 kW Nd:Yb fiber laser. Control of the surface stagnation pressure and gas flow boundary conditions were used to relocate the point of BLS within the cut front, and the relationship of these parameters was analyzed. The results demonstrate that shifting the point of BLS along the cut front can be used to control fume generation mechanisms. This study successfully provided the preliminary understanding necessary to manage fume generation during the laser cutting process.