Shallow Angle Drilling of Inconel 718 Using a Helical Laser Drilling Technique

Abstract

This study reports an experimental investigation for the shallow angle laser drilling of Inconel 718. In this study, a helical laser drilling technique was used to effectively produce holes with a diameter of several hundred microns. The design of experiment (DOE) using the Taguchi method was employed to examine the influence of various process parameters on the geometrical and metallurgical features of drilled holes. A higher laser power, lower speed, and closer focal position to the workpiece surface contributed to the further removal of material by the absorption of more laser energy and larger beam intensity. This resulted in a larger exit hole diameter and less hole taper. The increase in laser power reduced a thickness of the recast layer due to material removal by vaporization. From the DOE result, a regression model to estimate a correlation between experimental factors and hole quality was also suggested. In the second stage of this study, trials to improve drilling performance were made. Using the O2 assist gas of 50 kPa significantly enhanced the drilling performance owing to the delivery of more energy to the workpiece by an exothermic reaction. However, the further increase of O2 gas caused rapid cooling of the workpiece, which lowered the drilling performance. The drilling performance was greatly improved as well using the high laser duty cycle to provide more laser energy. The moving focal position was only beneficial to the drilling performance when a focusing of the beam was moderately maintained on the interaction region of the laser–workpiece.