DEFORM- AND EXHAUST-CONTROL OF CHIP IN DRILLING WITH A CONTINUOUS HIGH FEED RATE TWIST DRILL

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S-type drill has good performance in deep hole drilling of middle carbon steel. It produces long pitch chip in drilling SUS304 and the pure aluminium. However, the chip exhaust becomes bad at high cutting speed or high feed rate. In case of pure aluminium, chip becomes thick and can not be exhausted due to increase of adhesivity between chip and drill. In case of SUS304, the drill wear increases suddenly and then drilling is stopped. The cause is as follows : Increase of adhesivity makes chip thick, then it increses work hardening. It increases damage to cutting edge. It increases the adhesivity and the resistace against chip exhaust. Then, it increses the work hardening much more. By this chain reacting mechanism and cutting temperature, cutting edge wears rapidly and vanishes. It is desirable that drill flute is coated with low affinity material aganst these work materials. TiN-coating is not good. It is difficult that chip of aluminium alloys of A2011 and A2024 becomes the long pitch type. When cutting temperature becomes about 300℃, the long pitch chip occurs. In case of aluminium alloy of A5056, the long pitch chip occurs at about 160℃. However, chip becomes thick at higher cutting temperature than 160℃, then drilling becomes stop. The drilling mechanism of SCM440 is almost equal to that of S50C.In contrast with conventional drill, S-type drill is long tool life in drilling much carbon content SUS304 . In case of little carbon content SUS304, adhesivity affects the tool life of S-type drill. In drilling S50C, tool wear of conventional drill is affected by oscillation of drill. So, the flank wear of outside edge of main cutting edge becomes maximum. S-type drill hardly oscillate, so the flank wear becomes maximum at a little inside from outside edge.The long pitch chip does not occur in drilling 50mm S50C with S-type sintered drill under 5000rpm, 0.3mm/rev, in spite of high cutting temperature.