Utilizing the drill cutting lip to extract Johnson Cook flow stress parameters for Al6061-T6

Abstract

Owing to the chisel drill lip's complex geometric configuration, the material being cut witnesses great variations in strain, strain rate, and temperature along the cutting edge. This characteristic is explored in this work so that the drill point utilized as a material characterization tool to extract the flow stress parameters of the material cut. Specifically, the methodology, dubbed the Drill Lip Cutting Force Prediction Methodology (DLCFPM), utilizes a small number of pre-cored drilling experiments to extract the Johnson–Cook (JC) parameters for Aluminum Al6061-T6. Few drilling experiments are run to cover a wide range of drilling conditions: spindle speeds ranging from 1592 rpm rotational speed to 9868 rpm and drilling feed rates ranging from 0.08 mm/rev to 0.64 mm/rev. For calculating the cutting forces numerically, DLCFPM employs a combination of (1) Oxley's predictive machining theory (extended thick shear zone analysis) and (2) analytical formulation for lip force generation. A custom optimization code is developed for numerically converging on an optimum set of JC parameters by matching simulated drilling torque values at the lip with those measured experimentally. For further corroboration, finite element (FEM) simulations are run using DLCFPM-found JC parameters. Numerically-simulated torque and thrust values are found to agree with those generated from the drilling experiments and with FEM results giving validity to the developed methodology for determining the JC parameters of Al6061-T6 from few drilling tests. © 2019 CIRP