Effects of inter-pulse and intra-pulse shaping during laser percussion drilling

An advent advocate of laser percussion drilling is the aerospace industry, where billions of holes have been laser drilled in turbine components, for the provision of effusion cooling holes, which consequently allowed higher combustion temperatures and engine efficiencies, However, in order for other industries to capitalise on the benefits of laser drilling, greater flexibility is required in producing the desired hole geometries. In this study, the effects of intra-pulse and inter-pulse shaping are investigated in terms of hole geometry control. While intra-pulse shaping involves temporally shaping within an individual laser pulse and repeatedly using the shaped pulse throughout the pulse train, inter-pulse shaping is carried out by temporal pulse shaping the overall delivery pattern of a pulse train required to percussion drill a hole. Experiments were performed using a fibre-optic delivered Nd:YAG laser for the drilling of through-holes in stainless steel 304. The fundamental effects of intra- and interpulse shaping are also compared with percussion drilling with unshaped rectangular pulses and the normal delivery pattern (NDP). The work has shown that inter-pulse shaping is effective in. reducing the hole taper during laser percussion drilling. This was chiefly attributed to the optimised laser pulse distribution as the beam propagates into the hole.