Investigating the effect of different axial oscillation waveforms in laser fusion cutting

Laser processing systems provide elevated flexibility in dynamically shaping the laser beam in both space and time. Scientific literature indicates that such techniques represent promising solutions for improving both part quality and process productivity. However, methodological investigations for the processing of high thickness metal sheets have not been extensively reported. The wide range of possibilities enabled by novel beam-shaping approaches has yet to be systematically explored. The present work aims to study the effect of axial oscillations (i.e. along the beam propagation axis) in laser fusion cutting. By leveraging an analytical model, the power density distribution generated by different oscillation waveforms was explored. An experimental set up was developed to include a deformable mirror with the capability of generating high frequency modifications of the beam focal position, thus enabling experiments with axial oscillations in the 100-1500 Hz range. Successively, experiments were performed to demonstrate the improvements achievable in terms of part quality and productivity. While existing literature has primarily focused on dynamic beam shaping employing harmonic oscillations, this study explores the impact of various oscillation waveforms, including sinusoidal, triangular, square, ramp-up, and ramp-down patterns. Hence, the analytical model predicted the time-averaged laser power distribution within the process zone for the different oscillation waveforms. The use of axial oscillations, superimposed to the cutting-direction, was investigated during the processing of 20 mm thick AISI304. Experimental results demonstrate notable improvements in process performance, either by reducing burr defects in iso-productivity conditions or by increasing the speed whilst maintaining equivalent part quality.