Characteristics and application of parabolic bit
Parabolic drill chip groove is parabolic, specially used for continuous drilling of deep holes with length-diameter ratio of 15:1 and material hardness of not more than 25 ~ 26HRC(including low carbon steel, various aluminum alloys, copper alloys, etc.). For example, a 12.7mm diameter parabolic bit can successfully drill holes up to 190mm deep. Because of the larger clearance space, common parabolic bit can be cutting edge in chip discharge, at the same time may allow more cutting fluid into the cutting zone, significantly reduce the cutting friction as well as the possibility of a chip welding death occur, in addition to processing when the power consumption can be reduced, torque load and cutting.
The trough curve of the so-called parabolic bit has an approximate mathematical parabolic shape. And the standard twist drill groove shape has a big difference, bit groove curve has an inflection point.
In terms of design parameters, the helix Angle is usually 36~38deg, the core thickness is (0.3~0.6) *D, and the drill point Angle is 130~140deg.
At present, in practical application, the main cutting edge of parabolic drill is passivated and then used to process cold hardening materials. It may be speculated that the front Angle of the groove drill formed at the main cutting edge is larger, resulting in poor edge strength.
Parabolic drill bits must be used to optimize the cutting speed and feed rate according to a specific aspect ratio. The price is two to three times that of a standard twist drill.
The research of parabolic bit focuses on the effect of groove curve on chip removal and rigidity and the condition of the main cutting edge after grinding the drill tip.
The helix Angle of parabolic drill is 36° ~ 38°, which is larger than that of standard twist drill (28° ~ 30°). The spiral Angle can indicate the degree of "torsion" of the bit. The larger the spiral Angle, the faster the bit & chip removal speed. Another characteristic of ordinary parabolic drill bits suitable for deep hole machining is the thick drill core (the drill core is the central part of the drill bit that has not been ground after forming the chip groove). The core of a standard twist drill makes up about 20% of the finished bit, while the core of a parabolic drill can make up about 40% of the bit. In deep hole drilling, a thicker core increases the rigidity of the bit and improves the stability of the drilling process. Parabolic bits have grooves at the drill tip, allowing for a larger core diameter and preventing the bit displacement that is common at the beginning of drilling.
Parabolic bits are made of high speed steel and can also be coated to enhance cutting performance.