Figure 3 High-efficiency composite center drill
1. Twist drill 2. Stepped hole edge 3. Hole chamfering edge
(1) The center drill groove shape adopts two kinds of spiral grooves of 25°~30°, and the E groove and the F groove are favorable for discharging the chips to form a spiral curved surface. The cutting edges are distributed on the two chip pockets, which increases the sharpness of the spiral groove. 14. The 5mm drill face rake face B is on the F spiral groove, the 17mm stepped hole cutting edge C face and the 60° cone cutting edge A face are on the F spiral groove. In the initial trial production, the rake faces of the two places are on the F-slot (see the physical map 4), and the chips discharged from the two cutting parts are disturbed and cluttered at the 60° guard cone, burning the cutting. The edge greatly reduces the life of the tool. Through the trial production to improve the center drill structure, the E-slot and the F-slot form are adopted, and the chip removal is smooth, solving the problem of burning the knife.
(2) The center drill bit is designed in the form of a twist drill. In order to maintain the strength and rigidity of the drill bit, the two main cutting edges of the drill do not pass through the center of the drill but are parallel to each other and staggered to form a chisel edge. It not only improves the processing efficiency and reduces the process, but also greatly improves the sharpness of the center drill, reduces the friction between the drill bit and the workpiece during the machining process, and prolongs the service life of the tool.
Figure 4
(3) Grinding the secondary relief surface at the flank of the drill bit is very beneficial for chip breaking (see the D surface shown in Figure 3). The special groove shape can improve the rigidity of the cutter and improve the cutting condition. Conducive to the discharge of chips. In order to protect the main cutting edge, the chamfer is ground on the cutting edge, and another chamfer is added to protect the drill corner and the secondary cutting edge. The use of special structures and cutting edge geometry for bit machining facilitates the removal of shredded chips. If there is continuous chipping, the chip removal will be unfavorable. The long chips from the chip F chip pocket and the chip generated by the center drill cone will easily interfere, and will be cluttered around the center drill cone, which will easily burn the cone. The cutting edge reduces the service life of the tool and greatly reduces the machining accuracy.
(4) The center hole of the shaft end face is machined at one time, which simplifies the process, ensures the concentricity requirement of the center hole, improves the utilization rate of the machine tool, greatly reduces the processing cost and tool cost, and improves the production efficiency.
3. Efficient use of efficient center drills
During the use of the center drill, the geometric parameters and drilling amount of the drill bit should be reasonably selected according to the actual conditions of the workpiece material and hardness.
To control the overheating of the cutting edge during machining, the cutting speed should not be too high, to improve lubrication and adequate cooling. After processing a certain number of workpieces, it should be sharpened in time to ensure the sharpness of the drill bit, and the drill bit should not be excessively worn to prevent the cutting edge from being burnt and seriously affect the life of the drill bit and the surface roughness of the machined hole.
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