JPS6157124B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a drill that has excellent cutting performance and is capable of machining holes with high dimensional accuracy.

When drill holes are formed close to each other, the walls between adjacent holes become very thin, and these thin walls are susceptible to tearing during drilling. When this hole is drilled with a conventional drill, the thin wall is broken by the force that pushes the chips out in the radial direction, and the chips get caught between the outer circumferential surface of the drill and the inner circumferential surface of the drilled hole. ,
This had the drawback of increasing the rotational resistance of the drill and damaging the inner wall of the drilled hole. In addition, when drilling holes that overlap each other, chips are pushed out into the openings of the overlapped parts, and the chips get caught between the outer periphery of the drill and the inner periphery of the drilled hole, preventing the rotation of the drill. There is also.

This invention was made to solve these conventional drawbacks, and it is made so that chips near the outer periphery of the cutting edge are continuously generated, a thin wall is formed in the overlapped part of the hole, and this is This prevents the chips from being pushed out in the radial direction, allowing smooth discharge and cutting of the chips. That is, in the present invention, the pair of first cutting blades have their starting ends near the center of rotation and are arranged approximately point-symmetrically with respect to each other when viewed from the tip in the axial direction, and each of the first cutting blades is arranged generally in the direction of rotation. form a convex curve, each first
A nearly straight second cutting edge continues at the end of the cutting edge, and the second cutting edge has a radial rake angle of -50° to -5° and an axial rake angle of -20° to +15°. Moreover, the blade width of the second cutting edge is set within the range of 1/6 to 1/2 of the radius of the drill.

Embodiments of the present invention will be described below with reference to the drawings. In Figures 1 to 3, 1 is the drill body, 2,
3 is a chip, and the chips 2 and 3 are each continuously formed with a first cutting edge 4 and a second cutting edge 50. The starting end 0 of the first cutting edge 4 is located approximately at the center of the drill, and the first cutting edge 4 is arranged approximately point symmetrically with respect to each other, and has a curved line that is convex in the rotation direction and has a large curvature at the center. The term "curve" as used herein is a concept that includes a connecting line between a curve and a straight line as shown in the figure. Further, a second cutting edge 50 is continuously formed at the terminal end of the first cutting edge 4. The second cutting edge 50 has a shape obtained by cutting off the corners of the chips 2 and 3, and its rake face 5 has a triangular side surface shape. The second cutting edge 50 has a rake angle in the radial direction, that is, an inclination angle α with respect to the radiation A of -
The rake angle in the axial direction, that is, the inclination angle θ with respect to a line B parallel to the axis of the drill is −8°. The α value may be set within the range of −50° to −5°, and the θ value may be set within the range of −20° to +15°. Further, the blade width l of the second cutting edge 50 is set within a range of 1/6 to 1/2 of the radius L of the drill. Note that the pair of first cutting edges 4, 4 do not need to be continuous at the center, and may have a slight gap.

When drilling with a drill having such a shape, the chips generated by the first cutting edge 4 curl, and the chips generated by the second cutting edge 50 extend in a straight line. Both chips are continuous with each other. That is, as shown in FIG. 4, the chips 8 are curled chips 82 generated by the first cutting edge 4 and chips 81 generated by the second cutting edge.
Continuous chips 8 are generated at regular intervals, and these chips ascend in the chip discharge groove 7. When the chips 8 reach a certain length, they protrude from the machined hole and break due to the centrifugal force generated thereby. In addition, when machining overlapping holes, as shown in Fig. 5, the hole 1 that is being machined overlaps the previously machined hole 13.
A thin film-like wall is formed on the outer circumferential trajectory 11a of the drill hole 11 to prevent chips from protruding, thereby preventing the chips from getting caught between the outer circumference of the drill, the inner circumference of the machined hole 11, and the inner circumference of the machined hole 11. This prevents chips from being washed away and allows chips to be smoothly discharged. Such a thin wall is formed because the second cutting edge 50 is negative in the radial direction, and because the outer periphery becomes high temperature and is machined at high speed, the machined surface of the machined hole 11 becomes plastic. It is thought that this is to deform the shape. In this way, chips are discharged sequentially as a continuous piece of a fixed length, and are not affected by thin walls or overlapping openings between adjacent holes, so it is useful when machining a large number of adjacent holes. It has an excellent effect on
For example, it is particularly effective when machining a general shape with a drill when a mold is not available.

In addition, in conventional drilling, chips are divided and generated, and while the chips are rising in the chip discharge groove, the centrifugal force caused by the rotation of the drill applies force to the inner wall of the drilled hole in the radial direction, causing the adjacent holes 11 and 13 to The thin wall between the holes 11 and 11 was to be destroyed, and chips were to be caught between the inner wall of the hole 11 and the outer periphery of the drill, increasing the rotational resistance of the drill and damaging the inner wall of the drilled hole 11. .

In the above configuration, the chips 82 that are curled and generated intermittently are connected by the straight and continuous chips 81 to generate continuous chips as a whole. In order to
It is necessary to set θ to -20° to +15° and l to 1/6 to 1/2 of L. To explain this in more detail, the best cutting is achieved when α is set around -25°, and the further the distance from the above value, the weaker the effect becomes, and when α exceeds -50°, the best cutting results. The angle formed by the cutting edge 4 and the second cutting edge 50 is too large, so that curled chips 82 and straight chips 81 are not continuously generated. On the other hand, when α is -5° or less, the first cutting edge 4 and the second cutting edge 50 become almost straight cutting edges, so the chips are curled as a whole, as shown in FIG. No more chips are generated.

Regarding the rake angle in the axial direction, the best cutting is achieved when θ is set around -8°.
If θ exceeds -20°, machinability will deteriorate;
When the angle exceeds +15°, chips from the second cutting edge 50 are no longer generated in a straight line. Furthermore, a second cutting blade 50
Regarding the formation area, when the length l of the second cutting edge 50 in FIG. If it exceeds 1/2L, the linear chips 81 will become too large, and the curled chips 82 will become smaller, resulting in poor cutting performance.
In addition, the chips become difficult to break and the evacuation performance is impaired. That is, chips as shown in Fig. 4 are generated only in the ranges of α -50 to -5°, θ -20° to +15°, and l 1/6L to 1/2L, which results in the above-mentioned The following effects are achieved.

As explained above, the present invention continuously forms the second cutting edge on the outer periphery of the first cutting edge, thereby exhibiting good cutting performance and continuously forming chips in a straight line. Since the chips are smoothly discharged without being pressed against the inner wall of the machined hole, it is particularly effective when forming adjacent drill holes or overlapping holes. Furthermore, wear on the outer circumferential surface of the drill is reduced, the life of the tool is increased, and the inner surface roughness of the machined hole can also be improved.

[Brief explanation of the drawing]

FIG. 1 is a side view of a drill showing an embodiment of the present invention, FIG. 2 is a left side view thereof, FIG. 3 is a bottom view thereof, and FIG. 4 is a perspective view of chips generated by this drill. FIG. 5 is a sectional view of a hole for explaining overlapping hole machining. 1... Drill body, 2, 3... Chip, 4...
First cutting edge, 50...Second cutting edge, θ...Rake angle in the axial direction, α...Rake angle in the radial direction.

Claims (1)

[Claims] 1 The pair of first cutting edges have their starting ends near the center of rotation and are arranged approximately point symmetrically to each other when viewed from the axial tip, and each first cutting edge has a curve that is convex as a whole with respect to the direction of rotation. , a substantially straight second cutting edge continues at the end of each first cutting edge, and the second cutting edge has a radial rake angle of -50° to -5° and an axial rake angle of -20° to -5°. A drill characterized in that the width of the second cutting edge is set at +15° and the width of the second cutting edge is set in the range of 1/6 to 1/2 of the radius of the drill.