Control of melt dynamics in laser cutting based on a resonant nozzle cavity

Instabilities of the melt flow dynamics on the laser cutting front lead to quality losses, due to the formation of striations and burr at the cut flank, especially when using cost-efficient 1 μm laser radiation. This paper summarizes fundamental studies utilizing the concept of a resonant cavity as basis for the nozzle design in a novel approach to improve the quality of cut flanks. The nozzle is designed to excite acoustic waves for promoting gas flow oscillations in the interaction zone and to ideally match the acoustic resonance of the gas column in the kerf. The influence of the cavity length on the oscillation frequency is analyzed using schlieren and acoustic techniques. Further, it is experimentally demonstrated that the average surface roughness of the resulting cut flanks is reduced up to 50 % in the upper third section, where the coupling of the gas flow oscillation to the melt is most pronounced, while the assist gas consumption is significantly decreased compared to a standard 3 mm diameter conical nozzle.