The formation mechanism of discontinuously segmented chip in high-speed cutting of Ti-6Al-4V

Abstract

The chip transition from continuously serrated to discontinuously segmented is one of the most fundamental and challenging problems in metal cutting. In this work, a reliable finite element model for high speed cutting of Ti-6Al-4V was developed based on the high speed cutting experiments. The Johnson-Cook (J-C) constitutive parameters of the Ti-6Al-4V were optimized using the response surface method (RSM) and multi-objective genetic algorithm to accurately describe the plastic behavior of Ti-6Al-4V alloy in high speed cutting. With using the optimized constitutive parameters, the simulated chip morphologies and cutting forces match well with the experimental results in a wide range of cutting speed from 0.05 m/s to 86.5 m/s. The formation mechanism of the discontinuously segmented chip was further studied based on the validated finite element model. The results reveal that three distinct cracks form successively in the segmented chip formation process: the crack I forms at chip root, the cracks II and III initiate at the primary shear zone center and chip free surface respectively and propagate along the direction of maximum stress triaxiality to seperate the chip and workpiece. The crack I, which forms at the chip root due to the maturely evolved shear banding, is the key reason for the transition of chip formation from continuously serrated to discontinuously segmented.