Thermal Modeling for Finish Hard Turning Using a New Tool

Abstract

This study develops an analytical thermal model for temperature predictions in finish hard turning by a new tool. Tool life in finish hard turning is limited by part surface quality, e.g., white layer formations (microstructural alterations). Thermal damage due to temperature rise at machined surfaces is the primary source of such surface degradation. Thus, a thermal model capable of machined surface temperature predictions will enable part surface damage assessment as well as thermal management strategy for process optimization. A mechanistic model that accounts for nonuniform uncut chip thickness across the cutting edge is employed to estimate three-component machining forces. Machining forces and cutting characteristics, i.e., shear angle and chip-tool contact, approximate the heat intensity and geometry of shear plane and rake face heat sources. Due to tool nose radius, the two heat sources are three dimensional in nature and are further discretized into small segments, each treated as an individual rectangular heat source. Individual small heat-source segments are then used to study temperature rise in machining, using modified moving oblique heat source (shear plane) and modified moving and stationary heat sources (rake face) developed by Komanduri and Hou [1,2]. Temperature rise due to all small heat-source segments is superimposed, with proper coordinate transformation, to obtain final temperature distributions due to overall heat sources. The thermal model can be applied to study machining parameter effects on machining temperatures. It is indicated that maximum machined-surface temperatures are adversely affected by increasing feed rate and cutting speed, but favorably by increasing depth of cut. Tool rake face temperatures increase with cutting speed and feed rate as well. However, rake face temperatures decrease with increased depth of cut at high feed rates, but, reversely at low feed. The model has also been tested to evaluate white layer formations in finish hard turning. Tool nose radius effects have been analyzed and the results show that the smaller the tool nose radius, the deeper the white layer under identical machining conditions. Experimental results show good agreement with analytical predictions.