UBC Theses and Dissertations
A transient thermal model for machining Islam, Coskun
Prediction of temperature in the tool, chip and workpiece surface layer is essential for tool design and the selection of most productive cutting conditions which yield the desired tool life and acceptable residual stresses left on the machined part. This thesis presents a comprehensive, finite difference method based numerical model on simulating the temperature distribution in the chip, tool, and finished workpiece surface layer as a function of material properties, cutting speed, feed rate and tool-workpiece engagement period. The heat is generated in the primary shear zone where the chip is sheared from the metal, in the secondary zone where the chip sticks and slides on the rake face, and in the tertiary zone where cutting-edge ploughs the workpiece surface. The chip, layer of the workpiece surface and the tool edge are meshed into discrete elements. The heat is transferred to the stationary tool, and dynamically moving chip and workpiece surface by conforming heat balance equations within each element. A finite difference technique with implicit time discretization is used to solve heat balance equations of the temperature fields on the tool, workpiece, and chip. Anisotropic material properties can be considered in the model which allows the inclusion of a coating layer on the tool. The proposed model allows two and three-dimensional heat transfer, hence it can be used to predict the temperature distribution in turning, drilling and milling operations. The continuous machining processes such as turning generate constant heat, so the temperature reaches a steady state after a transient period. The intermittent operations such as milling generate time-varying and periodic heat, hence the temperature variation is always in a transient state. The proposed model is experimentally validated with the data found in the literature and experiments conducted by the author at the industrial partner’s (Sandvik Coromant AB, Sweden) research facility. Experimental validations cover uncoated, single and multi-layer coated tools to simulate continuous turning, interrupted turning and milling operations. The proposed model is able to predict the temperature with less than 20% error in most of the validated cases.
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