Tool Wear Mechanisms In High Speed Machining Nickel-based Alloy Inconel 718

High speed cutting (HSC) and high performance machining technology has been applied in steel, aluminum and high-temperature alloys cutting successfully because its particular advantages. Our research focused on the tool friction and tool wear process, the thermal-mechanical coupling in the rake face and flank of cutting tool and tool life prediction model under thermal-mechanical coupling action. The analysis of HSC process of Nickel-based superalloys Inconel 718 provided theoretical foundation and technical support for cutting tool material selection on Nickel-based superalloys machining, cutting tool structure design and cutting parameters optimization.During HSC Inconel718 process with coated carbide tools, by the calculation of thermodynamic entropy production on three wear sub-processes (viscosity flow, diffusion and oxidation), the entropy production of system was investigated with the changes of cutting speed and flank wear VB. The self-organization process of cutting tool was analyzed according to the changing of the entropy got from the system, the cutting process was divided into three (one) wear stages. When the values of the cutting parameters on HSC friction and wear system were with in a certain range, the friction films of self-organization kept friction and wear system in a stable stage. When these values exceeded a certain rage, the friction film of self-organization was difficult to be generated, which led cutting tool only has one wear stage and a short tool life. Mechanisms of 4 self-organization friction films (BUE, chip flow zone, oxide layer and the bonding layer) were considered in the high speed cutting process.The thermal-mechanical coupling 3D analytical model in the rake face and flank of cutting tool was created consedering nose radius and tool wear. The changes of shear angle, shear strain and tool-chip contact length for each differential cutting element were analyzed under different cutting parameters and different tool geometries. The temperature rised on each cutting element on the tool-chip contact surface was caused by shear and friction heat which was calculated by the heat distribution coefficient of HSC friction and wear system. By assuming that flow velocity of chip as uniform motion, the force vector sum was zero, and then three direction components and composition of forces on the tool could be calculated. The calculation of model show that the increased of cutting force on the rake face of cutting tool was not significant and cutting temperature decreased a little when the cutting tool is worn. The cutting force and temperature on the flank of cutting tool increased significantly with the tool wear. The influence of chip shapes, chip formation mechanism, cutting speed, feed rate and cutting tool wear on workpiece surface quality were analyzed based on the thermal-mechanical coupling on Incone1718.The proportion of each wear mechanisms on different wear stage was very different. In a beginning wear stage, general diffusion wear increased caused by frequent spalling and generation of bonding layer, so the most important influence factor in this stage for tool life was diffusion wear. And small diffusion concentration and low cutting temperature result the proportion of oxidized wear was so small to happen. In the stable wear stage, relatively stable bonding layer reduced spalling frequency, decreased concentration gradient of element and decreased diffusion speed, which provided suitable conditions for oxidation wear. Oxidation wear rate continued to rise, in the end of wear stage, it became the biggest influence factor on tool life at the failure stage. Considering the characteristics of the three wear stage and the thermal-mechanical coupling, tool life prediction model was established with diffusion wear, adhesive wear and oxidation wear were considered as the main wear mechanism.The tool wear and wear mechanisms in different cutting tool wear stages and a variety of cutting tools changed when the nickel-based superalloys Inconel 718 was cutting with coated carbide tools and Sialon ceramic tools.This research is supported by the National Natural Science Foundation of China (50575126) and the National Basic Research Program of China (2009CB724402).