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Surface Layer States of Worn Uncoated and TiN-Coated WC/Co-Cemented Carbide Cutting Tools after Dry Plain Turning of Carbon Steel

DOI: 10.1155/2013/519686

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Abstract:

Analyzing wear mechanisms and developments of surface layers in WC/Co-cemented carbide cutting inserts is of great importance for metal-cutting manufacturing. By knowing relevant processes within the surface layers of cutting tools during machining the choice of machining parameters can be influenced to get less wear and high tool life of the cutting tool. Tool wear obviously influences tool life and surface integrity of the workpiece (residual stresses, surface quality, work hardening, etc.), so the choice of optimised process parameters is of great relevance. Vapour-deposited coatings on WC/Co-cemented carbide cutting inserts are known to improve machining performance and tool life, but the mechanisms behind these improvements are not fully understood. The interaction between commercial TiN-coated and uncoated WC/Co-cemented carbide cutting inserts and a normalised SAE 1045 steel workpiece was investigated during a dry plain turning operation with constant material removal under varied machining parameters. Tool wear was assessed by light-optical microscopy, scanning electron microscopy (SEM), and EDX analysis. The state of surface layer was investigated by metallographic sectioning. Microstructural changes and material transfer due to tribological processes in the cutting zone were examined by SEM and EDX analyses. 1. Introduction At machining metals it is important to know about the wear behaviour of the cutting tool. This importance arises due to the fact that the surface integrity of the machined workpiece is influenced by tool wear [1, 2]. In this case surface integrity is described by three main parameters: the surface roughness, the residual stress state, and the work hardening in the surface zone [1]. For further improvement in the knowledge of wear behaviour of cutting tools the surface layer states of the worn tools are important to distinguish between different wear mechanisms acting in the cutting zone. One possibility at investigating wear with respect to the applied cutting parameters (e.g., cutting speed, feed rate, and depth of cut) is the idea proposed by Lim and Ashby with the wear mechanism maps [3]. Here the most important aspects of wear (seizure, delamination wear, mild wear, severe wear, etc.) are displayed with respect to the parameters varied in the wear tests (sliding velocity, pressure, etc.). The wear map approach is also applied to metal machining, and therefore the wear is displayed as a function of cutting speed and feed rate [4, 5]. In this work the aim is to develop a better understanding of the wear characteristics

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