Residual stresses (RS) induced by machining control a component's resistance to progressive failure. It is crucial to identify favorable cutting conditions that promote fatigue-inhibiting compressive RS while preserving other aspects of surface integrity. An extensive investigation was performed in the finish turning regime for two aerospace grade Ti-alloys, Ti-6Al-4V (Ti-64) and Ti-6Al-2Sn-4Zr-6Mo (Ti-6246). A comprehensive evaluation of surface integrity was carried out including RS, surface roughness, the near-surface microstructure, and hardness distribution. The behavior of RS and surface roughness was correlated to the cutting parameters. Within the investigated parameter range, RS were compressive in nature. High MRR conditions and small corner radii were found to promote larger compressive RS for both Ti-alloys. A conflict between RS and surface roughness was observed. While machining at high feed rates enhanced compressive RS, it was detrimental to surface finish. Guidelines were developed for the optimal selection of cutting parameters to achieve desired levels of RS and surface finish

A hybrid modeling approach based on computational fluid dynamics (CFD) and finite element method (FEM) is presented to simulate and study cryogenic machining (CM) of Ti–6Al–4V alloy. CFD analysis was carried out to study the characteristics of the fluid flow and heat transfer process of liquid nitrogen (LN2) jet used as a coolant in turning operation. The velocity, turbulence, gas volume fraction, and temperature of the impingement jet were investigated. Based on the analysis results, the coefficient of heat transfer (CHT) between the LN2 and cutting tool/insert was obtained and used in the FEM analysis to model the heat transfer process between the LN2 and the tool/chip/workpiece. A three-dimensional (3D) finite element (FE) model was developed to simulate a real CM operation. CM tests were carried out to validate the 3D FE model by comparing cutting forces and chip temperature. To evaluate LN2 cooling effect on tool temperature and tool wear, a two-dimensional (2D) FE model was developed for steady-state thermal analysis of cryogenic and dry machining. Based on the predicted temperatures, the tool wear was estimated, showing that LN2 cooling can significantly improve tool life.