Analysis of Residual Stresses in Spot Cooled Vibration Assisted Turning of Ti6Al4V Alloy using Computational Fluid Dynamics-Aided Finite Element Method

Residual stresses retained in the machined component are very crucial for the service and fatigue life of the component. Hence, it is very important to verify the residual stresses developed in the machined component while adopting any new machining or cooling technique. However, identification of residual stresses and its thorough investigation is quite cumbersome in machined component. In this work, the machining was carried out using a novel technique termed as Spot Cooled Vibration Assisted Turning (SCVAT) which is an integrated process that combines vortex tube-based spot cooling (VTSC) using CO 2 gas with Vibration Assisted Turning (VAT). The nature and magnitude of residual stress induced in the machined component on its surface and along its depth was investigated while machining Ti6Al4V alloy using CFD aided FE model. Initially experiments were conducted at constant machining, vibration and flow parameters. The residual stresses were measured using x-ray diffraction technique and the same are used to validate the CFD aided Finite Element model (FE), and it was observed that the model predicts the residual stresses with acceptable accuracy. This validated CFD aided FE model was used to carry out a thorough parametric study on the influence of machining, vibration and cooling parameters on residual stress and its nature, on the surface and along the depth from the surface. The thermomechanical loading responsible for residual stress formation was studied through CFD aided FE analysis. Surface level hardness and surface topography were observed for the samples to understand the surface integrity. The results are better than conventional turning, VAT and VTSC. SCVAT is able to develop compressive residual stresses of higher magnitude than its counterparts. Application of lower cutting speed, higher amplitude of vibration, less nozzle tool distance and nozzle diameter, high coolant pressure and cold fraction are able to induce compressive residual stresses.