JP6057010B1 - Drilling tool - Google Patents

Abstract

An object of the present invention is to provide a drilling tool having improved chip fragmentation capability. Two cutting inserts 30 having the same shape as a two-blade center drill 20 are attached to the tip of a body 10, and the two cutting inserts 30 are rotation trajectories of respective cutting edges around the rotation axis of the body 10. The cutting insert 30 looks like a staircase when viewed from above, and the cutting regions of the two partial cutting edges 32a and 32b extending on both sides across the stepped portion 33 partially overlap. It has a blade 32, the side surface portion of the cutting insert 30 has an upper side surface portion 36a and a lower side surface portion 36b, the upper side surface portion 36a is accommodated in the relief portion 13a of the tip seat 12, and the lower side surface portion 36b is the tip seat. The drilling tool 100 which contacts 12 insert restraint parts 13b. [Selection] Figure 5

Description

The present invention relates to a drilling tool including a center drill having a plurality of cutting edges and a plurality of cutting inserts arranged around the center drill, and a drilling tool in which a center cutting edge and an outer peripheral cutting edge are integrated in a body.

Conventionally, a drill body as disclosed in Patent Document 1 is composed of a drill body and a drill head that is detachably attached to the tip thereof, and a drill insert having a plurality of cutting blades is detachably attached to the center of the drill head. There has been a drilling tool provided with a cutting insert that is detachably disposed on the drill head outside the drill insert.
A characteristic of such a drilling tool is high chip discharge performance. The reason for this is that chips having a relatively small width are generated from each of the cutting edge provided in the drill insert and the cutting edge provided in the cutting insert. Further, since the generated chips are fine, there is no need for a chip discharge groove having a large cross-sectional space, and the drilling tool shown in Patent Document 1 has a cutting edge in the form disclosed in Patent Document 2 when compared with the same tool diameter. Tool rigidity is higher than replaceable drills.

International Publication No. 2007/107294

JP 2004-330373 A

In recent years, there has been a demand for a drilling tool capable of more efficient machining. When the cutting speed and feed rate are increased to perform high-efficiency machining, the thickness of the chip becomes thick and the chip becomes difficult to deform. For this reason, the chips are likely to be clogged inside the chip discharge groove, or the chips frequently damage the inner wall surface of the processed hole.
The present invention has been made to solve the above problems. That is, an object of the present invention is to provide a drilling tool capable of further subdividing chips.

  A drilling tool according to a first aspect of the present invention includes a body having a rotation axis, a center drill having a plurality of cutting edges, and a plurality of cutting inserts, and the cutting insert is a tip portion of the body and from the center drill. Are also arranged in a plurality of tip seats formed at positions away from the rotation axis, each cutting insert has an end surface and a side surface portion intersecting the end surface, when viewed from the direction facing the end surface, The cross ridge line portion between the side surface portion facing the tip direction of the tool body and the end surface of the side surface portion has a step portion, and the first partial cross ridge line portion connected to one end of the step portion in the front end view of the body. The rotation locus around the rotation axis partly overlaps with the rotation locus around the rotation axis of the second partial crossing ridge line portion connected to the other end of the step portion.

In the drilling tool of the present invention, the intersecting ridge line portion of the cutting insert has a plurality of step portions, and when viewed from the direction facing the end surface, the step portion located further away from the rotation axis is closer to the body. It is preferable that it is located on the base end side.

In the drilling tool of the present invention, the cutting insert has a second end face facing the end face, and at least one of the side face parts of the side face part of the cutting insert facing the wall part constituting the tip seat. An upper side surface portion connected to the end surface, and a lower side surface portion positioned closer to the second end surface than the upper side surface portion and positioned closer to the center of the cutting insert than the upper side surface portion. A portion of the wall portion that opposes the side surface portion includes a concavely-curved thin portion, and a cutting insert restraining portion that is positioned closer to the bottom surface of the tip seat than the thin portion, It is preferable that the lower side surface portion abuts on the cutting insert restraining portion and the upper side surface portion is accommodated in the lightening portion (13a).

When the drilling tool of the present invention is viewed from a direction in which a curved outer peripheral corner is connected to an outer peripheral end of the intersecting ridge line portion of the cutting insert, and a linear ridge line portion is connected to the outer peripheral corner and facing the end surface. The linear ridge line portion preferably extends substantially parallel to the rotation axis of the body.

In the drilling tool of the present invention, it is preferable that the plurality of cutting edges of the center drill are arranged at equal intervals around the rotation axis of the body.

In the drilling tool of the present invention, it is preferable that the plurality of cutting inserts are arranged at equal intervals around the rotation axis of the body.

In the drilling tool of the present invention, it is preferable that the shape of the end face is n-fold rotationally symmetric and n is a natural number of 3 or more.

In the drilling tool of the present invention, the center drill has two cutting edges at a position rotationally symmetrical twice with respect to the rotation axis of the body, has two cutting inserts, and the cutting inserts are the body. Is arranged at a position rotationally symmetrical twice with respect to the rotation axis of the body, and in the front end view of the body, an extension line of the intersecting ridge line portion of the first cutting insert and an extension of the first cutting edge of the center drill The angle θ formed by the line is preferably greater than 0 ° and less than 180 °.

In the drilling tool of the present invention, a plurality of spiral chip discharge grooves are formed on the outer peripheral surface of the body, and the chip discharge grooves are formed in a strongly twisted spiral portion and the body more than the strongly twisted spiral portion. It is preferable that the torsion angle of the weakly twisted spiral portion is larger than the twist angle of the weakly twisted spiral portion.

In the drilling tool of the present invention, the working depth is preferably 6 times or more of the tool diameter, and the length of the weakly twisted spiral portion is preferably 2.5 times or more of the length of the strongly twisted spiral portion. .

The drilling tool of the present invention has a plurality of center cutting edges integrated with a body tip having a rotation axis, and a plurality of outer peripheral cutting edges, and each of the center cutting edges around the rotation axis of the body. When the rotation trajectory overlaps each other, the outer peripheral cutting edge is located farther from the rotation axis than the central cutting edge, and each outer peripheral cutting edge is viewed from the direction facing the rake face corresponding to each outer peripheral cutting edge. The outer peripheral cutting edge has a stepped portion, and when viewed from the front end of the body, the rotation locus of the first partial outer peripheral cutting edge connected to one end of the stepped portion around the rotation axis and the other of the stepped portion The rotation trajectory around the rotation axis of the second partial outer peripheral cutting edge connected to the end partly overlaps.

FIG. 1 is a perspective view of a drilling tool according to an embodiment of the present invention. FIG. 2 is an enlarged perspective view of the drilling tool of FIG. FIG. 3 is an enlarged perspective view of the drilling tool of FIG. 1 viewed from another angle. FIG. 4 is a front view of the drilling tool of FIG. FIG. 5 is an enlarged view of the drilling tool of FIG. 1 as viewed from the direction facing the upper surface of the cutting insert. FIG. 6 is a perspective view of the cutting insert of FIG. FIG. 7 is a perspective view of the insert of FIG. 5 viewed from another direction. FIG. 8 is a plan view of the cutting insert of FIG. FIG. 9 is a schematic view of the stepped cutting edge of the cutting insert of FIG. FIG. 10 is a bottom view of the cutting insert of FIG. FIG. 11 is a side view of the cutting insert of FIG. FIG. 12 is another side view of the cutting insert of FIG. FIG. 13 is a perspective view showing the chip seat. 14 is a cross-sectional view taken along the line XIV-XIV in FIG. FIG. 15 is a perspective view showing a cutting insert according to another embodiment. FIG. 16 is a schematic view showing a tip seat according to another embodiment. FIG. 17 is a plan view showing a cutting insert according to another embodiment.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In addition, for convenience of explanation, there may be used a word indicating the relative positional relationship between two objects such as “upper” and “lower”, but in that case, the positional relationship in each drawing is only described. However, it does not define the absolute positional relationship between the two objects. That is, even if it is described that “object A is above object B”, it is only drawn as such in a specific drawing, and object A is always absolutely above object B. It does not explain that it is placed.

As shown in FIG. 1 to FIG. 3, the drilling tool 100 is a substantially cylindrical body 10, a center drill 20 that is detachably attached to the center of the tip of the body 10, and a tool that is detachably attached to the outer periphery of the tip of the body 10. Two cutting inserts 30 having the same shape. The drilling tool 100 rotates with the rotation axis C of the body 10 as the rotation axis.

There are two chip discharge grooves 11 on the outer peripheral surface of the body 10. Chips generated by the cutting edges of the center drill 20 and the cutting insert 30 pass through the inside of the chip discharge groove 11 and are discharged out of the processed hole.

The chip discharge groove 11 includes a strongly twisted spiral portion 11a and a weakly twisted spiral portion 11b. Each of the strongly twisted spiral portion 11a and the weakly twisted spiral portion 11b is spirally formed on the outer peripheral surface of the body 10, and the twist angle of the strongly twisted spiral portion 11a is the twist angle of the weakly twisted spiral portion 11b. Bigger than. The “twist angle” in the present embodiment is synonymous with the definition of “the angle formed by the leading edge and a straight line parallel to the axis of the drill that passes through that point” described in JIS B0171 4004. The strongly twisted spiral portion 11 a and the weakly twisted spiral portion 11 b are continuous, and the strongly twisted spiral portion 11 a is located on the front end side of the body 10. By changing the twist angle of the chip discharge groove 11 on the way, chip discharge performance and tool rigidity can be realized at a sufficient level. When the machining depth of the drilling tool 100 is 6 times or more and 20 times or less of the tool diameter, the weakly twisted spiral portion 11b is within the range of 2.5 times or more and 4 times the length of the strongly twisted spiral portion 11a. It is preferable to set as appropriate. By setting the weakly twisted spiral portion 11b within such a range, it is possible to realize a sufficient level of tool rigidity and chip dischargeability for deep hole machining.

As shown in FIG. 3, the center drill 20 has two surfaces 21 at the tip, and each surface 21 is connected to a rake surface 22. The intersecting ridge line portion 23 between the surface 21 and the rake surface 22 acts as a cutting edge, and the surface 21 acts as a flank. In the following description, this intersecting ridge line portion is referred to as “cutting edge 23” for convenience. The surface 21 is arranged twice rotationally symmetrically with respect to the rotational axis C of the body 10, and therefore the cutting edge 23 is also arranged twice rotationally symmetrically with respect to the rotational axis C. Therefore, the rotation trajectories of the two cutting edges 23 around the rotation axis C of the body 10 coincide. The “match” in this case is not only completely matched, but also within a range in which the center drill 20 functions as a two-blade drilling tool, there is a state in which it is slightly shifted or distorted due to a manufacturing error or the like. It is a concept that includes it.
As shown in FIG. 2, the thinning surface 24 is located adjacent to the rake surface 22 on the rotation axis C side of the body 10. That is, the thinning surface 24 is located closer to the rotation axis C of the body 10 than the rake surface 22. As shown in FIG. 4, the thinning surface 24 is connected to the rake face 22 at an obtuse angle, so that the intersecting ridge line portion 25 between the surface 21 and the thinning surface 24 also forms an obtuse angle with the cutting edge 23. Further, this intersecting ridge line portion 25 also acts as a cutting edge.

As shown in FIGS. 4 and 5, the two cutting inserts 30 a and 30 b are disposed at positions farther from the rotation axis C of the body 10 than the center drill 20. Further, the two cutting inserts 30 are arranged at a position rotationally symmetrical twice with respect to the rotation axis C of the body 10.
As shown in FIG. 4 in which the drilling tool 100 is viewed from the tip, an angle θ formed by a stepped ridge line portion 32 of a cutting insert 30a described later and one cutting edge 23a of the center drill 20 is greater than 0 ° and less than 180 °, Specifically, it is about 80 °.

As shown in FIGS. 6 to 12, the cutting insert 30 has a through hole 38 penetrating in the thickness direction, and the first end surface 31 (hereinafter referred to as “upper surface 31” for convenience) of the cutting insert 30 is a through hole. A shape that is rotationally symmetrical three times around the central axis of 38 is formed. Specifically, the upper surface 31 has a stepped ridgeline portion 32 (hereinafter referred to as “stepped cutting edge 32” for convenience) having two stepped portions 33 and a curved shape connected to one end of the stepped ridgeline portion 32. The outer peripheral corner 34 and the straight linear ridge line portion 35 connected to the outer peripheral corner 34 are combined into three sets to form a combined shape. As described above, since the two cutting inserts 30 are arranged in a rotationally symmetrical position twice with respect to the rotation axis C of the body 10, the stepped cutting edge 32 of each cutting insert around the rotation axis C of the body 10. The rotation trajectories coincide. The concept of “match” in this case is the same as that of the center drill 20 described above.

The side surface of the cutting insert 30 has two types of side surface portions having different shapes, one being a first side surface portion 36 corresponding to the stepped cutting edge 32, and the other being a first side portion corresponding to the linear ridge line portion 35. Two side surface portions 37. The first side surface portion 36 has an upper side surface portion 36a connected to the stepped cutting edge 32, and a second end surface 40 below the upper side surface portion 36a, that is, opposite to the upper surface 31 (hereinafter referred to as “lower surface 40” for convenience). And a lower side surface portion 36b positioned closer to the center of the cutting insert 30 than the upper side surface portion 36a. The upper side surface portion 36 a has a stepped surface corresponding to the stepped cutting edge 32. The angle formed between the upper side surface portion 36a and the upper surface 31 is an acute angle, and the upper side surface portion 36a is provided with a clearance angle.
The lower side surface portion 36b is a flat surface and has a clearance angle. There is a small inclined surface between the lower side surface portion 36b and the lower surface 40 as compared with the upper side surface portion 36a and the lower side surface portion 36b.
As shown in FIG. 5, when the drilling tool 100 is viewed from the direction facing the upper surface 31 of the cutting insert 30, the stepped portion 33 of the stepped cutting edge 32 is located at a location away from the rotation axis C of the body 10. The closer one is located on the base end side of the drilling tool 100. On the other hand, the straight ridge line portion 35 extends substantially parallel to the rotation axis C of the body 10.

As shown in FIG. 9, in each stepped cutting edge 32, a portion extending from one end of the stepped portion 33 toward the rotation axis C side of the body 10 is defined as a first partial intersecting ridge line portion 32 a (hereinafter, “first partial cutting edge” for convenience). 32a ”), and a portion extending from the other end of the stepped portion 33 to the outer peripheral side of the body 10 is a second partial crossing ridgeline portion 32b (hereinafter, referred to as“ second partial cutting edge 32b ”for convenience), and drilling is performed. When the tool 100 is viewed from the tip, the rotation locus of the first partial cutting edge 32a around the rotation axis C of the body 10 and the rotation locus of the second partial cutting edge 32b partially overlap in the vicinity of the step portion 33. That is, when the rotation trajectory of the first partial cutting edge 32a and the rotation trajectory of the second partial cutting edge 32b are projected onto a plane perpendicular to the rotation axis C of the body 10, a part of each rotation trajectory overlaps. In other words, there is an overlapping portion between the machining area of the first partial cutting edge 32a and the machining area of the second partial cutting edge 32b. In other words, rather than the length from the rotation axis C of the body 10 to the intersection of the first partial cutting edge 32 a and the step portion 33, the second partial cutting edge 32 b and the step portion 33 from the rotation axis C of the body 10. The length to the intersection with is shorter. These also apply to the second partial cutting edge 32b and the third partial cutting edge 32c extending from both ends of the other stepped portion 33b. Therefore, the stepped cutting edge 32 of one cutting insert 30 cuts the entire outer peripheral region of the hole bottom that the center drill 20 does not cut.

As shown in FIGS. 6 and 7, the second side surface portion 37 corresponding to the linear ridge line portion 35 is configured by two planes unlike the first side surface portion 36, and an upper portion 37 a substantially perpendicular to the lower surface 40, The lower portion 37 b has a tapered portion from the upper surface 31 to the lower surface 40.

The cutting insert 30 is disposed on the chip seat 12 formed on the body 10 and is fixed by a screw inserted through the through hole 38. The wall portion surrounding the tip seat 12 has a concavely curved thin portion 13 a and a cutting insert restraining portion 13 b that abuts on the lower side surface portion 36 b of the cutting insert 30. As shown in FIGS. 13 and 14, the insert restraint portion 13b is located closer to the bottom surface 14 of the chip seat than the thin portion 13a. When the cutting insert 30 is disposed on the chip seat 12, the upper side surface portion 36a of the cutting insert 30 is accommodated in the sag portion 13a, and the sag portion 13a and the upper side surface portion 36a do not contact each other. Since the cutting insert restraint portion 13b is a flat surface inclined at substantially the same angle as the lower side surface portion 36b, the insert restraint portion 13b is in surface contact or line contact with the lower side surface portion 36b.

  Next, the effect produced by the drilling tool 100 will be described. The drilling tool 100 has a two-blade center drill 20 in which the rotation trajectories of the two cutting edges coincide with each other, and the two cutting inserts 30 are arranged so that the rotation trajectories of the stepped cutting edges 32 of the two cutting inserts 30 coincide with each other. Therefore, highly efficient processing is possible. Moreover, since the cutting insert 30 has the step-like cutting edge 32, it can produce | generate the finely divided chip which is narrower. For this reason, it is possible to suppress the occurrence of clogging of chips inside the chip discharge groove 11. Since the chips are subdivided, the cross-sectional area of the chip discharge groove 11 can be reduced.

  Since the cutting insert 30 is arranged so that the stepped cutting edge 32 is inclined with respect to the rotation axis C of the body 10, when inserting the drilling tool 100 into the workpiece, the center side of the stepped cutting edge 32 is located. Eat gradually from the outer part to the outer part. That is, it gradually participates in cutting from the center side of the stepped cutting edge 32 toward the outer peripheral side. This makes it possible for the drilling tool 100 to be inserted straight without bending with respect to the workpiece as compared with a case where cutting resistance is applied to the entire cutting edge at once.

When the cutting insert 30 is fixed to the chip seat 12, the lower side surface portion 36b of the cutting insert 30 and the cutting insert restraining portion 13b of the chip seat 12 come into contact with each other. As described above, the flat lower side surface portion 36b instead of the stepped upper side surface portion 36a serves as a contact portion with the wall portion of the chip seat 12, so that the cutting insert 30 is more firmly configured. Fixed to.
The upper side surface portion 36a is accommodated in the concavely-curved thin portion 13a, and a gap is formed between the portion protruding outward from the lower side surface portion 36b including the upper side surface portion 36a and the thin portion 13a. ing. When machining is performed by injecting coolant from the drilling tool 100, a part of the coolant that bounces back to the hole bottom and is discharged from the machining hole returns to the hole bottom again through this gap. Therefore, a certain amount of coolant accumulates at the bottom of the hole, and the cutting blade is effectively cooled.

  The upper portion 37a connected to the linear ridge line portion 35 extending substantially parallel to the rotational axis C of the body 10 functions as a margin, and this makes contact with the hole wall to stabilize the behavior of the drilling tool 100.

  Since the cutting insert 30 has a three-fold rotational symmetry, it can be used three times and is economical.

  As shown in FIG. 4, the cutting edge 23 of the center drill 20 and the stepped cutting edge 32 of the cutting insert 30 are not arranged in parallel or on the same straight line when the drilling tool 100 is viewed from the tip. A predetermined angle is formed. In other words, the angle θ formed by the extension line of the stepped cutting edge 32 of the cutting insert 30a and the extension line of one cutting edge 23a of the center drill 20 is larger than 0 ° and smaller than 180 °. By arranging the cutting edge in this way, chatter vibration during processing can be suppressed. Further, with such an arrangement of cutting edges, the lengths of the four cutting edges can be made substantially uniform. That is, when the cutting edge 23 of the center drill 20 and the stepped cutting edge 32 of the cutting insert 30 are arranged so as to be placed on the same straight line, the wall portion of the chip seat 12 is secured in order to ensure the strength of the chip seat 12. Needs to be moved to the outer peripheral side of the body 10 as compared with the above-described embodiment, and the chip seat 12 becomes smaller accordingly. When the chip seat 12 becomes smaller, the cutting insert 30 becomes smaller accordingly, and the stepped cutting edge 32 becomes shorter. In the above embodiment, since the lengths of the four cutting edges are substantially the same, the difference between the resistance applied to the center portion of the drilling tool 100 and the resistance applied to the outer peripheral portion is small, and the behavior of the drilling tool 100 is stabilized.

As mentioned above, although one embodiment was described as an example about the present invention, the present invention is not limited to the above-mentioned embodiment. For example, like the cutting insert 300 in FIG. 15, the entire side surface portion corresponding to the stepped cutting edge 32 can be formed in a step shape. In this case, as shown in the schematic diagram of FIG. 16, when the tip seat 312 has a wall portion that follows the shape of the stepped side portion, the contact area with the cutting insert 300 increases, and the cutting insert 300 is inserted into the tip. The seat 312 is firmly fixed.

In the above embodiment, the number of the stepped portions 33 of the stepped cutting blade 32 is two, but it may be one or three or more. Further, the stepped cutting edge 32 is not a complete stepped shape as in the above embodiment, and the direction in which the first stepped portion 331 and the adjacent stepped portion 332 are formed stepwise as shown in FIG. The opposite shape is also possible.

The upper portion 37a connected to the linear ridge line portion 35 of the cutting insert 30 may be inclined with respect to the rotation axis C of the body 10 within a range that appropriately functions as a margin as described above. For example, when viewed from the direction facing the upper surface 31, the upper portion 37a functions as a sufficient margin even when the linear ridge line portion 35 is inclined with respect to the rotation axis C within a range of 0.75 ° or less. To do.

The number of cutting edges 23 that the center drill 20 has is not limited, and may be three or more. At that time, the cutting blades 23 do not necessarily have to be rotationally symmetrical with respect to the rotational axis of the body 10, but are preferably rotationally symmetrical. Similarly, the number of cutting inserts 30 to be arranged is not limited, and three or more cutting inserts 30 can be used. When three or more cutting inserts 30 are used, it is preferable to arrange each of them in rotational symmetry with respect to the rotation axis of the body 10.

In the present invention, the shape that can be adopted as the center drill 20 is not limited to the above-described embodiment as long as it has a plurality of cutting edges and is integrated into a shape in which the cutting areas of the respective cutting edges coincide. . For example, a drilling tool called a spade drill or a head replaceable drill can be used as the center drill of the present invention.

The shape of the upper surface 31 of the cutting insert 30 is not limited to the above embodiment, and other substantially polygonal shapes such as a quadrangular shape and a pentagonal shape can be employed. If the shape of the upper surface at this time is a rotationally symmetric shape, it is economical because it can be used while changing the cutting edge.

In the above embodiment, the cutting insert 30 is detachably fixed to the chip seat 12 with screws. However, the cutting insert 30 can be completely fixed using brazing, an adhesive, or the like.

The drilling tool of the present invention is not limited to a center drill and a cutting insert that can be exchanged as in the above-described embodiment. For example, a cutting blade and a body are integrated as in a solid drill. May be.

DESCRIPTION OF SYMBOLS 10 ... Body 11 ... Chip discharge | emission groove | channel 11a ... Strong torsion spiral part 11b ... Weak torsion spiral part 12 ... Tip seat 13a ... Nuts part 13b ... Insert restraint part 20 ... Center drill 21 ... Surface 22 ... Rake face 23 ... Intersection Ridge line (cutting edge)
24 ... Thinning surface 25 ... Intersecting ridge line portion 30 between tip surface and thinning surface ... Cutting insert 31 ... First end surface (upper surface)
32 ... Staircase ridge (stepped cutting edge)
32a: In the stepped cutting blade, the portion extending from the one end of the stepped portion to the rotation axis side of the body (first partial cutting blade)
32b: In the stepped cutting edge, the part extending from the other end of the stepped portion to the outer peripheral side of the body (second partial cutting edge)
33 ... Step 34 ... Outer corner 35 ... Linear ridge 36 ... First side part 36a ... Upper side part 36b ... Lower side part 37 ... Second side part 37a ... Upper part 37b ... Lower part 40 ... Second end face (Bottom)
100 ... Drilling tool

Claims (8)

A body (10) having an axis of rotation;
A center drill (20) having a plurality of cutting edges;
A plurality of cutting inserts (30) having the same shape ,
The cutting insert (30) has a rotational trajectory around each rotation axis at the tip of the body (10) and at a position farther from the rotation axis than the center drill (20). Arranged,
The cutting insert (30) has a three-fold symmetrical shape, and has three stepped ridge lines (32), three corners (34), and three linear ridge lines (35). The corner portion (34) is connected to one side of the stepped ridge line portion (32), and the linear ridge line portion (35) is connected to the other side of the stepped ridge line portion (32). 1 end surface (31), a second end surface (40) facing the first end surface (31), and side surface portions (36, 37) intersecting the first end surface (31). ,
The stepped ridge portion (32) in the intersection ridge line of the side portion facing the distal direction (36) and said first end surface (31) of said body (10) of said side portions (36, 37) Formed,
The stepped ridge line part (32) has a step part (33),
In the front view of the body (10), the rotation trajectory around the rotation axis of the first partially intersecting ridge line part (32a) connected to one end of the step part (33) and the other end of the step part (33) And the rotation trajectory around the rotation axis of the second partial intersecting ridge line portion (32b) connected to
The side surface portion (37) corresponding to the linear ridge line portion (35) has an upper portion (37a) connected to the linear ridge line portion (35) and substantially perpendicular to the second end surface (40),
When the cutting insert (30) is viewed from the direction facing the first end surface (31), the linear ridge line portion (35) extends substantially parallel to the rotation axis. . The stepped ridge line part (32) of the cutting insert (30) has a plurality of the step parts (33),
The step portion (33) located further away from the rotational axis when viewed from the direction facing the first end face (31) is located closer to the base end side of the body (10). The drilling tool described. Of the side surface portions (36, 37) of the cutting insert (30), at least one of the side surface portions (36) facing the wall portion constituting the tip seat (12) is the first end surface (31). An upper side surface portion (36a) connected to the upper side surface portion (36a) and closer to the second end surface (40), and the cutting insert (30) than the upper side surface portion (36a). A lower side surface portion (36b) located on the center side,
Of the wall portion, a portion facing the side surface portion (36) is a concavely-curved thin portion (13a) and a cutting located closer to the bottom surface of the tip seat (12) than the thin portion (13a). An insert restraint portion (13b),
The drilling tool according to claim 1 or 2, wherein the lower side surface portion (36b) abuts on the cutting insert restraining portion (13b), and the upper side surface portion (36a) is accommodated in the lightening portion (13a). The drilling tool according to any one of claims 1 to 3, wherein the plurality of cutting edges of the center drill (20) are arranged at equal intervals around the rotation axis of the body (10). The said cutting insert (30) is a drilling tool as described in any one of Claim 1 to 4 arrange | positioned at equal intervals around the rotating shaft line of the said body (10). The center drill (20) has two cutting edges at a position twice symmetrical with respect to the rotational axis of the body (10);
Two cutting inserts (30), and the cutting inserts (30) are arranged at a position twice symmetrical with respect to the rotation axis of the body (10);
In the front view of the body (10), an extension line of the stepped ridge line portion (32) of the first cutting insert (30), an extension line of the first cutting edge of the center drill (20), The drilling tool according to any one of claims 1 to 5, wherein an angle θ formed by is greater than 0 ° and less than 180 °. A plurality of spiral chip discharge grooves (11) are formed on the outer peripheral surface of the body (10),
The chip discharge groove (11) includes a strongly twisted spiral portion (11a) and a weakly twisted spiral portion (11b) located on the base end side of the body (10) with respect to the strongly twisted spiral portion (11a). And
The drilling tool according to any one of claims 1 to 6, wherein a twist angle of the strong twist spiral portion (11a) is larger than a twist angle of the weak twist spiral portion (11b). The machining depth is more than 6 times the tool diameter,
The drilling tool according to claim 7, wherein the length of the weakly twisted spiral portion (11b) is 2.5 times or more of the length of the strongly twisted spiral portion (11a).

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