Numerical simulation of assisting gas flow for laser cutting process

Abstract

In laser cutting process, an assisting gas is used to improve the mass removal rate from the cutting kerf and protect the kerf surfaces from the high temperature exothermic reactions, such as oxidation reactions, during the cutting process. Numerical simulations are carried out using a commercial CFD code Fluent. In the first part of this work, the behavior of assisting gas flow is computed without heat transfer in laminar model which reveals a vortex structures in the flow at the inlet and exit of the kerf, which may directly affect the surface quality in real gas-laser cutting of metals. The largest vortex, which arises at the channel exit, collects and accumulates the liquid flowing down the channel walls. The study with increasing the angle of the kerf shows that the vortices disappear, and a stable vortex-free attached gas flow is formed. In other side, the heat transfer from the kerf wall to the flow of the assisting gas is important for quality cutting which is carried out in second part of this study including the RNG/κ-e model. The kerf wall temperature is kept at 1500K to resemble the laser cutting process. The distance between the nozzle exit and the kerf top surface to nozzle diameter is selected as H=0.7, where H is the stand-off-distance.