| The chip segmentation phenomena significantly limits the material removal rates in machining of hard-to-machine material, with the uncut chip thickness, feeds, cutting speeds selected to provide adequate tool lives. Serious vibrations are often encountered that impose a limit on material removal rate and, consequently, productivity. In addition, chip mechanics significantly influences the behavior of workpiece/tool interface such as temperature over the tool rake face, which in turn affects tool life. In order to increase productivity and tool life it is necessary to understand the phenomenon of serrated chip formation during machining of hard-to-machine material and then control it if possible so as to improve the machinability as well as to increase the tool life.; In this research Ti-6Al-4V was employed as a model material to investigate the chip segmentation mechanism because serrated chip is commonly observed in machining of titanium alloys. The FEM software DEFORM_2D™ was applied in simulation of orthogonal cutting processes for cutting Ti-6Al-4V. A new interpretation of chip segmentation in cutting Ti-6Al-4V based on the FEM simulation is presented. The chip segmentation is found to arise as a result of crack initiation and propagation, which is closely related to the microstructure evolution during the cutting process. The effects of cutting speed and thermophysical properties on the temperature distribution over the cool rake face were also investigated. It is found that increasing cutting speed not only increases temperature in the tool, but also reduces the contact length between chip and cutting tool. A crater wear model was presented for calculating the rate of tool wear based on diffusion of tool material into the workpiece in this research. Experiment of turning Ti-6Al-4V was conducted and the experimental results from other researchers [Lee, 1985] [Gente, 2001] were also used to make a comparison with the present simulation result. It is shown that the present results are in good agreement with the experimental data. |
