Research on removal characteristics of recast layer of laser-electrolytic machining on small holes

Abstract

To address defects in the recast layer and microcracks in laser drilling, this study adopted laser-electrolytic composite machining technology to conduct a boring test on nickel-based superalloy In718 through flushing outside the ring electrode and hydrostatic machining. This method obtained the characteristics of recast layer removal via composite machining and identified the influence rule of the residual rate of the recast layer via composite machining parameters. Results show that the recast layer exhibits a random distribution and gathers together at the exit when adopting the laser to rotationally cut and make the hole. Electrolytic post-processing for laser prefabricated small holes with a diameter larger than 1 mm by flushing outside the ring electrode proceeded as follows: using an electrolytic voltage of 20 V, NaNO3 electrolyte of 7.5 g/L, and electrolytic machining time of 20s, the reaming amount can reach 70–100 μm and steadily achieve recast layer removal. Electrolytic post-processing for prefabricated small holes with a diameter smaller than 1 mm can be carried out using hydrostatic machining under different flushing methods (continuous static electrolyte machining, free flushing, and forced flushing), indicating that forced flushing can remove the recast layers of the holes and achieve a better hole shape to create holes with good inwall quality.