ROLE OF TOOL FLANK WEAR AND MACHINING SPEED IN DEVELOPING OF RESIDUAL STRESS IN MACHINED SURFACE DURING HIGH SPEED MACHINING OF TITANIUM ALLOYS

摘要

Residual stresses generated from finish machining have a significant impact on the fatigue life of mechanical components by controlling crack initiation and propagation processes in their near subsurface. As governing variables, tool geometry, tool wear, machining parameter, work material property, and lubrication conditions have been widely studied to determine their effects on residual stress pattern in machined surface and subsurface. Among those parameters, tool flank wear was seldom fully investigated although tool flank wear, as well as machining speed, has been identified as the most important contributor to residual stress. Especially, tool flank wear becomes more significant due to the poor work thermal property during the high speed machining of titanium Ti-6Al-4V alloy. This study aims to investigate the combined role of tool flank wear and machining speed in developing residual stress in the machining of titanium alloy using finite element method. A microstructure sensitive material model based on Self Consistent Method (SCM) is adopted to incorporate the phase state and its transformations during machining cycle. Critical flank wear land and corresponding machining speeds are identified, beyond which compressive residual stresses are transferred into tensile residual stresses. High machining speeds demonstrate a distinct influence on residual stresses by means of promoting tool flank wear rate. The numerical simulation results are validated by empirical data provided in previous research.