Chip Exhaust Mechanism of Twist Drill Drillable Deep Hole under Continuously High Feed Rate.

Abstract

This paper describes the mechanisms of chip formation, chip removal from cutting edge and chip exhaust out of drilling hole of the twist drill drillable deep hole under continuously high feed rate. The web of this drill is three times thicker than that of the conventional one. Then the flute is nallow. The chip is a conical helix type at first, succesively changes to segment type, and then to a long pitch helix type. The segment type chip lines up in the flute and the long pitch helix type chip is along the flute. So, the segment type chip and the long pitch helix type chip are exhausted out of the drilling hole very well. While the depth of hole is still shallow at the beginning of deep hole drilling, the conical helix type chip is scarcely constrained by the flute. The hole becomes deeper, the chip requires larger area to grow and are constrained by the flute. Then, both moment and frictional force are applied on the chip by the flute and the drilling hole, and the cutting ratio changes. When the workmaterial has enogh plasticity, the chip changes to the long pitch helix type chip due to large oblique angle of the first main cutting edge. When its plasticity is poor, the chip becomes the segment type chip. The segment type chip is same as the head of the long pitch helix type chip.