| An analytical thermal model has been developed to study machining temperatures in finish hard turning. Thermal damage due to temperature rise at machined surfaces is the primary source of surface degradation (e.g. microstructural alterations). Thus, a thermal model capable of machined-surface temperature predictions in finish hard turning will enable part surface damage assessment and process optimization.; Mechanistic force and wear-land force models with three-dimensional uncut chip geometry have been first constructed for cutting force predictions in finish hard turning. Shear plane, rake face, and wear-land heat sources, with intensity derived from cutting forces and parameters, were discretized into a number of small two-dimensional heat-source segments subsequently used for temperature calculations using moving and stationary heat source solutions. Through coordinate transformation, heat partitioning, and superposition, temperature rise in the tool, chip and workpiece can be evaluated.; The advantages of the developed thermal model are as follows. The model is able to analyze geometrically complex heat sources resulting from non-uniform uncut chip thickness. The model provides an integrated approach to systematically investigate parameter effects for process optimization. In addition, the model requires less computational time and memory than finite element and difference methods.; The model has been applied to parametric studies with following major findings concluded. In new tool cutting, 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. In worn tool cutting, wear-land size is the dominant factor to machined-surface temperatures. Moreover, machined-surface temperatures increase with increasing cutting speed, yet, with a slower rate at high cutting speeds. On the other hand, maximum machined-surface temperatures linearly increases with feed rate, but insensitive to depth of cut. Tool rake face temperatures monotonically increase with cutting speed, feed rate, and depth of cut, however, only slightly increase with flank wear.; Experimental investigations have also been conducted to validate the proposed model. Microstructural changes at machined surfaces were measured as an indication of the phase transformation temperature being reached. The experimental results show good agreement with analytical predictions. |
