3D FE modelling of high-speed ball nose end milling

Abstract

The paper details research and development of a Lagrangian-based, 3D finite element (FE) model to simulate the high-speed ball nose end milling of Inconel 718 nickel-based superalloy using the commercial FE package ABAQUS Explicit. The workpiece material was modelled as elastic plastic with isotropic hardening and the flow stress defined as a function of strain, strain rate and temperature. Workpiece material data were obtained from uniaxial compression tests at elevated strain rates and temperatures (up to 100/s and 850°C, respectively) on a Gleeble 3500 thermo-mechanical simulator. The data were fitted to an overstress power law constitutive relationship in order to characterise flow behaviour of the material at the level of strain rates found in machining processes (typically up to 105/s). Evolution of the chip was initially seen to progress smoothly, with the predicted machined workpiece contour showing good correlation with an actual chip profile/shape. Cutting force predictions from the FE model were validated against corresponding experimental values measured using a piezoelectric dynamometer, while modelled shear zone/chip temperatures were compared with previously determined experimental data. The model was successful in predicting the forces in the feed and step-over direction to within 10% of corresponding experimental values but showed a very large discrepancy with the thrust force component (∼90%). Modelled shear-plane temperatures calculated at the point of maximum cutting force were found to demonstrate very good agreement with measured values, giving a discrepancy of ∼5%. The simulation required a computational time of approximately 167 h to complete one full revolution of the ball end mill at 90 m/min cutting speed.