Twist Drill Drillable Deep Hole under Continuous High Feed Rate(Mechanism of Particular Type Chip Formation of 0-Degree Rake Angle Twist Drill)

Abstract

This drill generates three particular type chips. It has narrow face of 0-degree rake angle. It has clearance between chip and drill flute (2nd rake face) near the narrow face. When the chip top comes in contact with the wall of drilled hole, the contact reaction twists chip due to the clearance. The twist causes “chip-lever effect” at outside of chip and decreases the frictional force at inside of chip. These effects make the shear angle large at both inside and outside of chip, and generate twist ribbon type chip. The twist ribbon type chip is gradually restrained by the flute. Then, the cross section of chip becomes U-shape (U-type chip). At deep hole stage, the chip is restrained by the flute and the drilled hole. The chip is compressed when its top reaches to drill chuck. U-shape cross section makes the compressive force strong. The strong compressive force progresses the bending of chip near the narrow face, and generates the wavy type chip. When the chip curl is restrained, the chip receives the forces at chip top and narrow rake face end. The chip acts as a lever. Then, strong force acts at the shear zone near the cutting edge. And the shear deformation zone is narrow. The narrow shear deformation zone is that the shear angle is large. The chip curl restraint makes the frictional force large. The large frictional force makes the shear angle small. Therefore, the chip becomes thin, when the chip lever effect is larger than the frictional effect.