JPH04315511A - Drill - Google Patents

Abstract

PURPOSE:To increase the tool strength of a drill. CONSTITUTION:A drill has a shank part and a cutting edge tip 1 removably secured to the shank part. A recessed part in which the cutting edge tip 1 is mounted is formed in the tip part of the shank part. The cutting edge tip 1 is formed approximately in the shape of a T-plate. A cutting edge part 15 of the cutting edge tip 1 has an outside diameter width responding to a hole diameter to be machined, and a part 16 to be nipped inserted in a shank is formed having width narrower than that of the cutting edge part 15. A curvature part to relax concentration of a stress is formed to a throat part between the cutting edge part 15 and the part 16 to be nipped.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to improving the tool strength of drills used primarily for drilling steel materials.

0002

2. Description of the Related Art A drill is one of the cutting tools used for drilling holes in steel materials. As an example, the structure of a twist drill is shown in FIG. twist drill 3
0 is composed of a cutting blade part 31 used for drilling, and a shank part 32 that does not participate in cutting and is mainly used for ejecting chips and for attaching to a chuck part of a cutting machine such as a ball plate. .

FIG. 20 shows the tip shape of the cutting edge of a twist drill. The pair of cutting edges 33, 33 are arranged at rotationally symmetrical positions with respect to the rotation axis of the drill. Further, the cutting edge portion 23 is formed to extend linearly from the end of the chisel edge 24 toward the outer diameter direction of the drill.

FIG. 21 shows another example of a conventional drill.
It shows the structure of a spade drill. spade drill 4
0 is composed of a shank portion 41 and a cutting edge portion 42 fixed to the shank portion by a mounting pin 43. FIG. 22 shows the shape of the cutting edge of the cutting edge portion 42. The cutting edge portion 42 of the spade drill 40 is formed into a flat plate shape. A pair of symmetrically arranged cutting edges 44, 44 are formed at the tip of the cutting edge portion 42, extending linearly from the center toward both ends. In addition, there is a cutting edge 4 on the side that becomes the flank of the drill.
An elongated groove-like nick portion 45 is formed in a direction substantially perpendicular to 4.

[0005]

A drill is a consumable material that has a certain lifespan due to wear and tear during cutting. Therefore, from an economic point of view, a drill in which only the cutting edge 42 is replaceable, such as the spade drill 40, is preferable. However, in the conventional spade drill 40, the cutting edge portion 42 is fixed by a mounting pin 43. Therefore, there have been problems such as reduced machining accuracy due to mounting play and damage to the drill due to insufficient mounting strength.

[0006] Therefore, the present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a drill that is highly economical and has sufficient tool strength.

[0007]

SUMMARY OF THE INVENTION A drill according to the present invention includes a cutting tip having a cutting edge for cutting a workpiece, and a shank for attaching to a predetermined position of a cutting machine. The shank portion has a recessed portion for receiving the cutting tip and a clamping portion for holding the cutting tip at its distal end. In addition, the cutting tip has a clamped part that is inserted into the recess of the shank part and an outer diameter width corresponding to the diameter of the hole to be machined, and has a tip surface that is centered around the rotation axis of the drill. It has a pair of cutting edges and a symmetrically formed cutting edge portion, and the whole is formed into a substantially T-shaped flat plate shape. The corner portion where the held portion of the cutting blade tip and the cutting edge portion are continuous is processed into an arc shape.

[0008]

[Operation] The cutting tip is fixed to the shank portion by press-fitting the held portion into the recess of the shank portion. Therefore, the mounting position of the shank portion and the cutting blade tip is automatically defined. Furthermore, by processing the corners between the held portion of the cutting tip and the cutting edge into an arc shape, stress caused by external force applied to the drill during cutting is prevented from concentrating on the corners and causing cracks.

[0009]

Embodiments Hereinafter, embodiments of the present invention will be explained in detail with reference to the drawings.

The structure of an indexable drill according to the present invention is shown in FIGS. 1 to 3. FIG. 1 is a plan view of the indexable drill according to the present invention, and FIG.
is its left side view. The indexable drill includes a cutting tip 1 for cutting a workpiece such as steel, and a shank portion 20 for holding the cutting tip 1 and attaching the drill to a cutting tool. FIG. 3 is an exploded perspective view showing a method of joining the cutting blade tip 1 and the shank portion 20. Referring to FIG. 3, the cutting edge tip 1 is fixed to the shank portion 20 by the frictional force generated when the clamped surface 2 of the tip contacts the inner end surfaces of the clamping portions 21, 21 of the shank portion 20. Such a method of joining the cutting blade tip 1 and the shank portion 20 is referred to as a self-grip method.

Next, the structure of the cutting tip 1 will be explained using FIGS. 4 to 8(a) to 8(d). FIG. 4 is a front structural view of the cutting tip 1, FIG. 5 is a plan view thereof, FIG. 6 is a bottom view, and FIG. 7 is a left side view thereof. Furthermore, Fig. 8 (a
), (b), (c), and (d) are respectively cut along the cutting line A- in FIG.
It is a cross-sectional structure diagram taken from directions along A, BB, CC, and DD. Referring to these figures, the cutting blade tip 1 is
It consists of a cutting edge part 15 where a cutting edge is formed and a held part 16 which is held by a holding part 21 of a shank part 20, and is formed into a substantially T-shaped flat plate shape. Drill flank surfaces 6, 6 are formed on the tip surface of the cutting edge portion 15. Moreover, rake faces 7, 7 of the drill are formed on the side surfaces. Cutting edges 4, 4 of the drill are formed along the line of intersection between the flank face 6 and the rake face 7. The pair of cutting edges 4, 4 are arranged at rotationally symmetrical positions with respect to the rotation axis of the drill passing through the center of the chisel edge 3. The shape of the cutting edge 4 is shown in FIG. FIG. 9 is a plan structural diagram showing the shape of the cutting edge portion 4. As shown in FIG. The cutting edge part 4 has a first straight cutting edge area 4a and a curved cutting edge area 4 from the center point of the chisel edge 3 toward the outer diameter area of the drill.
c, the second straight cutting edge region 4b. Also,
A central cutting edge region 4d is formed between the first straight cutting edge region 4a and the chisel edge 3 by thinning. The first linear cutting edge region 4a and the second linear cutting edge region 4b are formed aligned on the same straight line. A pair of first straight cutting edge regions 4a, 4a and a second straight cutting edge region 4
b and 4b are formed parallel to each other. The curved cutting edge regions 4c, 4c have third straight cutting edge regions 4e, 4f, respectively. The third linear cutting edge regions 4e and 4f are formed to intersect with the second linear cutting edge region 4b at an intersection angle θ. Both ends of the third straight cutting edge regions 4e, 4f are connected to the first and second straight cutting edge regions 4a, 4b by smooth curved regions. Further, the curved cutting edge regions 4c, 4c of the pair of cutting edge portions 4, 4 are formed in mutually different shapes, for example, different widths. That is, in FIG. 9, a pair of curved cutting edge regions 4c, 4
The widths L2 and L3 of c are formed to have different sizes.

As shown in FIG. 9, by providing the pair of cutting edges 4 with curved cutting edge regions 4c, 4c, chips are formed in a shape that follows the shape of the cutting edges 4. Such chips are easily broken when they come into contact with the drill or the inner wall of the hole being machined. Therefore, the chips are crushed into chips, and the processing characteristics of the chips are improved.

FIG. 10 is a plan view showing a modified example of the cutting blade portion 4. As shown in FIG. Curved cutting edge region 4c of the cutting edge portion 4 shown in FIG.
, instead of the third straight cutting edge regions 4e and 4f shown in FIG. 9, curved regions 4g and 4h consisting of a part of a circular arc with radius
is formed.

Furthermore, FIG. 11 is a plan structural view showing another modification of the cutting blade 4. As shown in FIG. The cutting edge portion 4 shown in FIG. 11 has two curved cutting edge regions and three straight cutting edge regions. The shapes shown in FIGS. 9 and 10 above can be applied to the shapes of each of the plurality of curved cutting edge regions.

Next, the nick portion will be explained. Figure 4,
With reference to FIG. 5 and FIGS. 9 to 11, the cutting blade tip 1
An elongated groove-shaped nick 5 extending from the curved cutting edge region 4c to the surface of the flank 6 is formed on the flank 6. For example, with reference to FIG. 9, by providing a nick 5 in the curved cutting edge region 4c, the first straight cutting edge portion 4a and the second straight cutting edge portion 4
The chips generated by b are divided in the generation direction at the nick 5 as a boundary and are discharged. This allows the width of the chips to be reduced.

Next, the chip breaker of the cutting tip 1 of the drill shown in FIG. 4 will be explained. A chip break surface 8 is formed on the side surface of the cutting edge chip 1 so as to be continuous with the rake surface 7. As shown in FIG. 8(d), the chip break surface 8 is formed with a constant inclination with respect to the rake surface 7. Furthermore, first chip breakers 9a, 9a each having two spherical protrusions are formed on the rake face 7, and a second chip breaker 9b having a spherical protrusion larger than the first chip breaker 9a is formed on the chip breaking surface 8. There is.

Furthermore, the thinning shape of the cutting blade tip 1 will be explained. Referring to FIG. 4, a thinning surface 10 is formed on the rake surface side of the pair of cutting blade central regions 4d, 4d centered on the center point of the chisel edge 3. The thinning surface 10 is formed to have a conical side surface shape with its tip pointing toward the center of the chisel edge. Such a thinning shape that utilizes a part of the side surface of the cone improves the sharpness of the drill by reducing the curvature of the central region 4d of the cutting edge on the chisel side and reducing the width of the chisel edge. Furthermore, the strength of the tip is increased by increasing the curvature on the rear side of the cutting edge.

Furthermore, the characteristics of the outer diameter shape of the cutting blade tip 1 will be explained. Referring to FIGS. 3 and 4, in the cutting edge 1, the clamped part 16 is held by the clamping parts 21 and 2 of the shank part 20.
1 by the wedge effect, and is fixed to the shank portion 20. In a state where it is fixed to the shank portion 20, the upper and lower surfaces 13, 13 of the cutting blade tip 1 are supported by the support surfaces 21a, 21a of the clamping portion of the shank portion 20. The thrust force applied from the tip of the cutting edge tip 1 to the center of the rotating shaft during cutting is supported by the support surfaces 21a, 21a of the shank portion. That is, a thrust is applied to the cutting tip 1 in the vicinity of the center of the rotating shaft passing approximately through the center of the chisel edge 3, and a supporting reaction force is applied to the upper and lower surfaces 13, 13 as a reaction force to the thrust. In such a loaded state, there is a concern that cracks may occur in the throat 11 between the cutting edge portion 15 and the clamped portion 16 due to stress concentration. Therefore, this throat portion 11 is provided with a curved surface having a radius R1. Further, the clamping portion 21 of the shank portion 20 is also provided with a curvature portion at a position corresponding to the throat portion 11. Figure 1
2 is a stress diagram showing the result of analyzing the degree of stress concentration occurring in the throat 11 using the finite element method using the radius R1 of the throat 11 as a parameter. An analytical model diagram is shown at the right end of FIG. From the analysis results shown in FIG. 12, when the radius of curvature R1 of the throat becomes 0.5 mm or more, the throat
It can be seen that the stress concentration at , is relaxed, resulting in a relatively flat stress distribution along the analysis position A. Furthermore, the radius of curvature R
It can also be seen that when 1 becomes, for example, 1 mm or more, the relaxation state of stress concentration does not change significantly.

Next, a description will be given of the results of cutting tests conducted on drills in which the radius of curvature of the throat portion 11 of the cutting edge portion 11 is different. Table 1 shows the shapes of the drills used in the cutting tests. Moreover, Table 2 shows the conditions of the cutting test.

[0020]

[Table 1]

[0021]

[Table 2]

The results of the cutting test are shown in Table 3.

[0023]

[Table 3]

As can be seen from the results in Table 3, it is found that by increasing the radius of curvature of the throat portion 11 of the cutting blade tip 1, a large thrust force can be withstood. According to the test results, the preferred range of the width W of the approximately T-shaped cutting edge tip and the radius of curvature R of the throat is as follows.

0.15D≦W≦0.5D (D is the outer diameter of the drill) 0.3mm≦R≦5mm

[0026]

[Effects of the Invention] As described above, in the drill according to the present invention, the shank portion and the cutting tip are joined by a self-grip method, and the throat portion of the cutting tip is machined into an arc shape.
Stress concentration due to axial thrust during machining can be alleviated and tool strength can be increased.

[Brief explanation of the drawing]

FIG. 1 is a plan structural view of an indexable drill according to the present invention.

FIG. 2 is a left side view of the indexable drill shown in FIG. 1.

3 is an exploded perspective view showing a joining structure between a cutting tip and a shank portion of the drill shown in FIG. 1. FIG.

FIG. 4 is a front structural view of the cutting tip of the indexable drill of the present invention.

FIG. 5 is a plan view of the structure of the cutting tip shown in FIG. 4;

FIG. 6 is a bottom view of the cutting tip shown in FIG. 4;

7 is a left side view of the cutting tip shown in FIG. 4. FIG.

FIG. 8 is a cross-sectional structural diagram of the cutting edge tip shown in FIG.
a) is cut line A-A in Figure 4, (b) is also cut line B
-B, (c) is the same cutting line C-C, (d) is the same D
It is a sectional view from the direction along -D.

9 is a plan view showing the shape of the cutting edge portion of the cutting tip shown in FIG. 4. FIG.

FIG. 10 is a plan view showing the shape of another cutting edge portion of the cutting edge tip.

FIG. 11 is a plan view showing the shape of the cutting edge portion according to still another embodiment of the cutting edge tip.

FIG. 12 is a stress diagram of the cutting edge tip using the finite element method.

FIG. 13 is a plan view of a conventional twist drill.

14 is a diagram showing the shape of the cutting edge of the twist drill shown in FIG. 13. FIG.

FIG. 15 is a plan view of a conventional spade drill.

16 is a diagram showing the shape of the cutting edge of the spade drill shown in FIG. 15. FIG.

[Explanation of symbols]

1 Cutting blade tip 4 Cutting blade part 6 Relief surface 7 Rake face 11 Throat 15　Blade tip part 16 Clamped part 20 Shank part 21 Clamping part

Claims (2)

[Claims] 1. A cutting blade tip having a cutting edge part for cutting a workpiece, and a shank part for attaching to a predetermined position of a cutting machine, the cutting blade tip and the shank part being removable. In the drill joined to the shank, the shank portion has a recessed portion for receiving the cutting tip at its distal end and a clamping portion for holding the cutting tip, and the cutting tip is attached to the shank. a held part that is inserted into and held in the recess of the part; and a held part having an outer diameter width corresponding to the diameter of the hole to be machined, and a pair of cutting blades centered on the rotation axis of the drill on its tip surface. is formed into a substantially T-shaped flat plate shape consisting of a symmetrically formed cutting edge portion, and furthermore, a corner portion where the clamped portion of the cutting edge tip faces the cutting edge portion is machined into an arc shape. A drill characterized by: 2. The thickness of the flat plate-shaped cutting blade tip is 0.15 times or more and 0.5 times or less the outer diameter width of the cutting blade portion, and the thickness of the flat plate-shaped cutting blade tip is 0.15 times or more and 0.5 times or less the outer diameter width of the cutting blade portion, and the thickness of the flat plate-shaped cutting blade tip is 0.15 times or more and 0.5 times or less the outer diameter width of the cutting blade portion, and 2. The drill according to claim 1, wherein the radius of the arcuate surface of the portion is 0.3 mm or more and 5 mm or less.