Kinematic fields measurement during Ti-6Al-4V chip formation using new high-speed imaging system

Abstract

Orthogonal cutting on Ti-6Al-4V produces segmented chips which results from localized deformation within the Primary Shear Zone (PSZ). For in situ visualization of the material flow during Ti-6Al-4V chip formation, a new high-speed optical system is proposed. Difficulties arise from the submillimetric size of the cutting zone. Therefore, a dedicated optical system with coaxial illumination is designed allowing for local scale analysis of chip formation. In this paper, the cutting forces were measured highlighting the unsteady nature of Ti-6Al-4V chip segmentation. For kinematic fields measurement, a novel method of Digital Image Correlation (DIC) technique is applied on the recorded images from the cutting zone. It allows for the identification of the localized deformation bands. Then, the level of the cumulative strain fields reached in the PSZ was presented and analyzed. The effect of the rake angle on the strain fields was studied. Using a 0∘ rake angle, the segment chip was found to be more subjected to deformation than in the case using 15∘. Accuracy of the measured strain fields was discussed function of the main source of errors. In addition, the chip morphology and microstructure were investigated with a scanning electron microscopy (SEM). It shows crack opening along the PSZ and high material failure near the tool-chip interface which explains the difficulties of DIC application in the context of kinematic fields measurement during orthogonal cutting. Finally, correlation between the measured strain fields and the mean value of the chip segment width was made.