The machining characteristics of a glassy thermoplastic\ud (Polyvinyl Chloride) and a semi-crystalline thermoplastic (High\ud Density Polyethylene) have been studied. Chip formation\ud mechanisms, cutting forces and surface integrity were found to\ud be dependent, on the cutting conditions and tool geometry.\ud Results were explained by considering the different nature of\ud the microstructure. Segmented and discontinuous chips were\ud produced with PVC, and continuous and segmented chips were\ud produced with HDPE. It was observed that surface damage was\ud closely related to the nature of chip formation in these\ud plastics.\ud Chip formation, surface damage and tool wear mechanisms when\ud machining Glass-Fibre-Reinforced-Plastic (GFRP) were also\ud studied. Cutting tools used were High-Speed-Steel (HSS),\ud cemented carbide (P type and K type) and coated carbide\ud (titanium carbide - and triple-coated). Discontinuous chips\ud were always produced when machining GFRP. Sliding contact is\ud present at the tool/chip and tool/work interface. The\ud principal aspects of surface damage include fibre breakage,\ud resin cracking, resin decomposition and fibre/resin interface\ud debonding. Cutting temperature is not high, but excessive heat\ud generates when the flank wear land develops. Coated carbide\ud tools showed the best performance and HSS tools the poorest.\ud The main wear mechanisms are abrasive wear with HSS tools,\ud attrition wear with cemented carbides, and discrete plastic\ud deformation followed by attrition wear with coated carbides
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