Flow Instability in the Orthogonal Machining of CP Titanium

Abstract

An experimental and analytical investigation of flow instability and shear localization in the orthogonal machining of grade 2 commercially pure titanium was made. A criterion for thermo-plastic instability was developed from torsion test results and applied to the analysis of the chip formation process. It was shown that flow instability followed by flow localization occurs when machining titanium at all cutting speeds and that a transition in the chip type from uniform to segmented does not occur. Orthogonal machining experiments were conducted in the speed range from 8.75 × 10−5 to 3.20 m/s for various depths of cut and the shear strain in the chip was calculated. It was shown that shear localization occurred in the chip formation process when the uniform shear strain involved in producing a chip segment reached a critical value and that this critical shear strain correlates fairly well with the instability shear strain predicted by the thermo-plastic instability criterion.