Research On Graphite Cutting Mechanism

Graphite, owing to its lower electrode wear, quicker EDM speed, higher heat resistance and better machining accuracy, has gradually substituted for copper as the major electrode material in EDM. High-speed machining is the main method for graphite electrode to get higher surface finish and cutting accuracy. Because it's typical brittleness, graphite electrode can be easily cracked by cutting impact. At present, high-speed machining is widely adopted in graphite electrode machining industry. Graphite high-speed machining causes rapid tool wear and severe work edge chipping. It is valuable and important to research graphite cutting mechanism.Because of rapid cutting speed and hard observed of cutting process, low-speed orthogonal cutting experiments are adopted in the paper. The processes of chip formation can be observed clearly. The effect of the different cutting conditions to graphite chip formation, morphologies of graphite chips and cutting force is studied. In practical machining, milled dust concentration is high, thus diversified prevention measures are brought forward in this paper.The study result of the processes of chip formation indicates: (1) The effect of depth of cut to the processes of chip formation is distinct. Under small depth of cut in 0~0.06mm, the chip shape is spurious ribbon or floccule;with moderate depth of cut in 0.06-0.12mm, several small collapse chips appear;with large depth of cut in 0.12~0.24mm, the chips mostly are break-up. (2) Cutting speed influents chip dimension. The chip dimensions will increase correspondingly with the increase of cutting speed. (3) Tool angle will influence the chip detachment. Tool with negative rake will extrude the chips persistently and small crack chips will produce. When the chip uplifted by pressure is extruded continuously, positive rake angle is good for chip detachment.The study results of orthogonal test of cutting force indicate that: (1) The average value of cutting force changes little with the increase of depth of cut, the maximum value and scopevalue of cutting force gradually increase. (2) Cutting speed has inconspicuous influence on cutting force. (3)Cutting force increases linearly with cutting width increasing.Chip appears erose shape of piece, banding and globosity in orthogonal cutting experiment. The surface of chip is extraordinary rough, which surface consists of rupture craters, little craters and residual rupture squama .Those are similar to the chip in high speed milling. Diversified prevention and cure methods are as bellow: (l)High speed machining center for graphite shall be introduced, or existing machines should be reconstructed by using dust collection device;(2)The plant should be installed in hermetic space with dust absorption conduits, and it is recommended that plants should be periodic cleaned;(3)workers should wear respirator during working.