Investigating the recast layer formed during the laser trepan drilling of Inconel 718 using the Taguchi method

This paper presents an investigation into the recast layer formed during the laser trepan drilling of Inconel 718 by a Nd:YAG laser. Laser drilling has evolved into the method of choice for the drilling of cooling holes in aerospace components. However, holes drilled with this particular technique are liable to display a variety of defects, including spattering, tapering, microcracks, and a recast layer. In order to meet the standards specified by the original engine manufacturer, this paper investigates the effects of the various laser drilling parameters on the recast layer thickness in the trepan drilling mode. A total of eight laser drilling parameters are considered in a series of experiments arranged using a Taguchi L18 orthogonal array. Taguchi analytical techniques are employed to establish the optimum set of parameters which yields a minimum recast layer thickness. The results indicate that the assist gas pressure, the peak power, and the focal position exert the greatest influence on the recast layer thickness. Having performed a confirmation experiment based on the initial Taguchi design experiments, the recast layer thickness is reduced further by adjusting the values of the assist gas pressure and the trepanning speed.