The main geometric parameters of twist drill include the choice of cutting lip angle, the choice of land angle of cutting edge and lip clearance angle of cutting edge, the analysis of the influence of helix angle on the life of drill bit and the treatment of cutting edge.
Cutting lip angle determines chip width and bit front angle. When the diameter and feed of the bit remain unchanged, increasing the top angle will narrow the iron filings and reduce the load per unit cutting lip. Cutting lip angle has a great influence on the land angle. Increasing cutting lip angle correspondingly can improve the cutting conditions at the core. Cutting lip angle affects the direction of chip outflow. According to the relevant tool design data and the characteristics of low hardness but high viscidity of the processed product, the cutting lip angle of the bit is selected to be 140°.
The land angle of a twist drill is determined by other geometric parameters of the drill. In high-speed cutting, the rake angle has little influence on cutting deformation and cutting force, and the strength of tool tip can be enhanced with a smaller land angle. When the land angle is determined, the bigger the lip clearance angle is, the sharper the edge is, but the wedge angle will decrease correspondingly, which will affect the strength and heat dissipation area of the tool. For this purpose, the lip clearance angle of the drill bit is selected as a smaller one, which is 8°.
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