Improve the service life of the drill with automatic reduction of the feed device

September 21 13:08:58, 2023

During the machining of the drilling process, the breaking of the drill bit often occurs, especially in castings with deep holes, small diameters and hard materials. After our analysis, the main reason is that the bit feed rate is constant from beginning to end during the drilling process, especially when the hole is drilled, the closer the bit is to the bottom of the workpiece, at which point the metal at the exit of the hole begins to bulge. It is easy to hold the drill bit, and at this time the temperature of the drill bit is high and easily broken. How to automatically reduce the amount of feed that the drill bit will drill through when machining the part is the most effective way to prevent the bit from breaking. After repeated trials, we designed the device shown in Figure 1 to achieve this goal.

The tail taper of the sleeve 2 is inserted into the spindle 1 of the drill. The side wall of the cylindrical portion of the sleeve has a through hole. A ball 4 is mounted in the hole, and the surface of the ball is in contact with the movable ring 3 having the inner surface of the cone. The lower end of the mandrel is provided with a drill chuck 6 and a drill bit 7, and the upper end of the mandrel is slidably engaged with the inner surface of the sleeve. The downward movement of the heart axial direction is limited by the removable shifting ring 9. The height of the baffle 10 can be adjusted as needed, with a thrust bearing mounted thereon.

working principle

When the drill spindle is rotated together with the sleeve 2, normal drilling is started with the axial feed amount S0. At this time, the axial component of the normal force and the drilling force of the contact surface of the movable ring 3 and the ball 4 are in an equilibrium state. During the cutting process, the sleeve 2 is moved downward, and the distance L1 between the end surface of the movable ring 3 and the thrust bearing 11 is gradually reduced. When the hole is drilled, the distance between the drill bit and the bottom surface of the workpiece is L (the metal starts to bulge at the exit of the hole), and the movable ring 3 comes into contact with the thrust bearing 11 and stops moving downward, while the sleeve 2 remains Continue to move downward with the feed amount S0. This produces a radial displacement of the ball which, when drilled through the workpiece, reduces its axial feed rate SCB compared to the normal feed rate S0, in which case the hole is drilled through.

The instantaneous feed amount SCB value of the bit drill through part depends on the ratio of the cone angle a of the inner surface of the movable ring 3 to the cone angle b of the outer surface of the mandrel s. As can be seen from Figure 2, the feed of the drill bit is also the same only when ab. Because the axial axial slip speed is faster than the drill spindle slowdown. In order to vary the feed rate according to different requirements, the conical surface should be made into an irregular shape, such as convex outward or concave inward.

Since the device has been used for more than a year, the effect is obvious, especially when the drill bit is broken when the small and deep holes are drilled. This device can also be used to prevent overloading of the machine during drilling, and the moving ring 3 will move upward as the drilling force increases. At the same time compress the spring. If a limit switch is installed in the bushing, the drive mechanism will automatically close when the cutting force reaches the specified limit.

razor wire

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