Adjustment of the geometries of the cutting front and the kerf by means of beam shaping to maximize the speed of laser cutting

The shape of the laser beam used for fusion cutting significantly influences the geometry of both the cutting front and the cutting kerf. The angle of the cutting front in turn impacts the local absorptivity, while the width of the kerf defines the amount of material, which has to be molten. The kerf's geometry therefore determines the maximum possible cutting speed at which a successful cut is feasible with a given available laser power. The absorptivity, the width of the kerf, and the maximum possible cutting speed can be estimated from a simple model considering the conservation of energy and rough geometrical approximations. In order to verify the prediction of the model, the geometry of the cutting front and kerf resulting from different processing conditions was observed by means of online high-speed X-ray diagnostics. The geometry of the interaction zone was recorded with a framerate of 1000 Hz during fusion cutting of 10-mm-thick samples of stainless steel. Comparing the results obtained with different shapes of the laser beam, it was found that the absorptivity is increased when the beam's longitudinal cross-section (parallel to the feed) is enlarged. Reducing the width of the beam in the transversal direction normal to the feed reduces the cross-sectional area of the cutting kerf. The findings show a good agreement with the geometric model which enabled the prediction of the absorptivity and the cross-sectional area of the cutting kerf and hence allows to reliably estimate the maximum cutting speed for different shapes of the laser beam, laser power, and sheet thicknesses.