OPTIMIZATION OF LASER DEEP-HOLE DRILLING OF INCONEL 718 USING THE TAGUCHI METHOD

The use of a Nd:YAG laser to drill deep cooling holes in aerospace components is a stringent operation. Various characteristics pertaining to the input beam, focussing lens, and assist gas have to be optimized in order to produce a hole economically and of sufficiently good quality. This paper reports the use of the Taguchi technique of experimental design in optimizing the process parameters for drilling deep-holes in nickel-based superalloy, Inconel 718. The thickness of the material is 25.0 mm. Oxygen is the assist gas and the focal length of the focussing lens is 300 mm. The effects of five process parameters - pulse energy, pulse duration, pulse shape, focal position, and assist gas pressure - have been explored. The various parameters are assigned to an L18 orthogonal array. The primary response under study is the drilling time. It is predicted that a minimum drilling time of 31.51 s is needed to drill a hole with a pulse energy of 30.0 J, a pulse duration of 1.8 ms, a ''treble'' pulse shape, a focal position of 0.0 mm into the material, and an oxygen pressure of 0.35 MPa. Confirmatory experiments have produced results that lay within the 95% confidence interval.