Modelling the laser fusion cutting process: I. Mathematical modelling of the cut kerf geometry for laser fusion cutting of thick metal

A model for calculating the three-dimensional stationary geometric shape of the cutting front for laser fusion cutting is presented in this paper. The model relates the cut kerf geometry with the cut-through depth, various laser parameters such as power, speed, focus position and material thickness. In this model, the energy absorbed by the workpiece includes not only the direct energy from the laser beam but also the energy from the multiple reflections generated by the beam impinging on the cutting front of the cut kerf. The effects of multiple reflections are functions of the inclined angle of the cutting front and the cutting depth. The effects of various laser processing parameters, multiple reflections and inert gas pressure on the geometric shape of the cutting front have been analysed systematically and in detail. The model allows accurate prediction of the cut-through depth and cut-edge quality for a given set of process parameters. It also helps to explain the effect of focal position, cut-assist pressure and other parameters upon the cut-edge quality.