CHIP FORMATION ANALYSIS IN HIGH-SPEED MACHINING OF A NICKEL-BASE SUPERALLOY WITH SILICON-CARBIDE WHISKER-REINFORCED ALUMINA

High speed turning tests were performed on a heat resistant alloy (Inc onel 718), using SiC (20%) whiskers reinforced ceramic tools. The main aims of these tests were the following: (1) mapping cutting speed-fee d and machined volume in order to find a region from tool breakage; (2 ) analysing tool wear and chip formation mechanisms; and (3) from the experimental results modelling analytically both chip formation proces ses and tool wear mechanism. Tool and chip were semiquantitative analy ses were carried out to evaluate micro-welds on the chip and areas of welded or scattered material over the tool. Micro-hardness mapping was carried out on the longitudinal cross-section of the chips to monitor its dependence by process parameters. Variable wear mechanisms along the the tool-chip contact length that were attributed to variations in plastic deformation energy were observed. There variations were analy tically modelled in orthogonal cutting conditions. Longitudinal and tr ansverse shear planes into the chip were also observed. The causes and the mechanisms of wear, chip formation and the hardening of work mate rial were deduced. The presence of whiskers pull out mechanisms due to temperature effects in the tool-chip interface were also observed.