Dynamic Behavior and High Speed Machining of Ti-6246 and Alloy 625 Superalloys: Experimental and Modeling Approaches

Abstract

Titanium alloys and nickel based superalloys are used in various demanding applications because of their excellent high temperature properties, especially high strength and good corrosion and fatigue resistance. However, the high strength and hardness at high temperatures combined with strong strain hardening can lead to difficulties in machining of these alloys. Finite element simulations can be used to optimize the cutting conditions and to reduce the machining costs. However, simulations of machining operations require accurate material models that can only be built on reliable experimental data. Also, the mechanical properties of materials can only be measured in a limited range of strain and strain rate at the laboratory scale, from which the material behavior has to be extrapolated to the actual machining range. In this work, the mechanical behavior of Titanium-6246 and a nickel based superalloy, similar to Inconel 625, has been studied in details. The Johnson-Cook material model parameters were obtained from the experimental data and the model was used to describe the plastic behavior of the studied alloys in simulations of orthogonal cutting of the material. The model for the Ni- based superalloy was improved by introducing an additional strain softening term that allows decreasing of the strain hardening rate at large deformations. The preliminary simulation results have also been verified experimentally by comparing the simulation results with machining experiments, and the results of the simulations are briefly presented and discussed. The material models are able to reproduce the serrated chips with split shear bands, but the cutting stresses obtained from the simulations are somewhat higher than those obtained from the cutting experiments. Also, some differences were observed in the chip shape, and further development of the material model and simulations is needed.