Direct calculation of Johnson-Cook constitutive material parameters for oblique cutting operations

Characteristics and behaviors of materials during manufacturing processes highly depend on their mechanical properties and microstructures. However, these characteristics and behaviors can be greatly influenced by other factors such as strain, strain rate, and temperature during the process. The Johnson-Cook (J-C) constitutive material model has been extensively used to describe the material behavior under such circumstances. The J-C parameters are usually determined using the Split Hopkinson Pressure Bar (SHPB) test which is time consuming and costly. Other methods that have been introduced to numerically determine the J-C parameters are inverse methods that minimize the difference between the experimentally measured and theoretically calculated data. These numerical methods still require a combination of experimentally measured cutting forces and chip thickness. These two items are easy to obtain for simple machining processes like turning in which chip thickness and thus cutting force have almost steady state constant values. Nevertheless, majority of these numerical methods are not applicable to more complex machining processes, e.g., milling, in which tool-workpiece engagement is complex and the chip thickness and consequently cutting forces are varying during the process. To address this limitation, this paper presents a model to identify the J-C strain rate hardening and temperature softening parameters for complex oblique machining processes. The proposed model searches for an optimum set of J-C parameters by matching the calculated cutting forces using Oxley model with those obtained from experimental measurements. In addition, simulation and experiments were performed to compare the results and to validate the proposed model. The results proved the validity of the proposed model in estimating the J-C parameters directly from milling tests as an oblique cutting operation.