Milling tool

A milling tool includes: a body having an outer circumferential surface formed around a central axis; a cutting insert having a rake surface, a flank surface, and a cutting edge formed by a ridgeline of the rake surface and the flank surface; and a screw attaching the cutting insert to the body. The outer circumferential surface has an insert attachment portion. The insert attachment portion is defined by a first seat surface continuing to the outer circumferential surface and a second seat surface continuing to the first seat surface and having a flat portion provided with a screw hole in which the screw is inserted. The cutting edge is formed of a sintered material containing at least one of cubic boron nitride and polycrystalline diamond. In a cross section perpendicular to the central axis, a first angle formed by a first direction and a second direction is an acute angle.

TECHNICAL FIELD

The present disclosure relates to a milling tool. The present application claims priority of Japanese Patent Application No. 2017-059267 filed on Mar. 24, 2017. The disclosure of the above-identified Japanese application is herein incorporated by reference in its entirety.

BACKGROUND ART

A milling tool disclosed in Japanese Patent Laying-Open No. 2016-159388 (PTL 1) has been known. The milling tool disclosed in PTL 1 includes a body, a cutting insert, a locking piece, and a bolt. The body has an outer circumferential surface and an insert pocket. The insert pocket is defined by a first side surface, a second side surface, and a bottom surface. The first side surface and the second side surface continue to the outer circumferential surface of the body. The first side surface and the second side surface are arranged to face each other in the circumferential direction of the body. The bottom surface continues to the first side surface and the second side surface.

The cutting insert is positioned in the insert pocket such that the cutting insert is in contact with the first side surface. The bolt is tightened to press the locking piece toward the bottom surface of the insert pocket. The locking pin has a side surface inclined toward the location where the cutting insert is positioned. The locking piece is fastened with the bolt to be pressed toward the bottom surface of the insert pocket, and accordingly the inclined side surface of the locking piece presses the cutting insert against the first side surface. Thus, the cutting insert is attached to the body.

In addition, milling tools disclosed for example in Japanese Patent Laying-Open No. 7-195220 (PTL 2) and Japanese National Patent Publication Nos. 2010-535638 (PTL 3) and 2007-525334 (PTL 4) have also been known.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

A milling tool according to an aspect of the present disclosure includes: a body having an outer circumferential surface formed around a central axis; a cutting insert having a rake surface, a flank surface, and a cutting edge formed by a ridgeline of the rake surface and the flank surface; and a screw attaching the cutting insert to the body. The outer circumferential surface has an insert attachment portion which is recessed toward the central axis and to which the cutting insert is attached. The insert attachment portion is defined by a first seat surface and a second seat surface. The first seat surface continues to the outer circumferential surface. The second seat surface continues to the first seat surface. The second seat surface has a flat portion, and the flat portion has a screw hole in which the screw is inserted. The cutting edge is formed of a sintered material containing at least one of cubic boron nitride and polycrystalline diamond. In a cross section perpendicular to the central axis, a first angle formed by a first direction and a second direction is an acute angle, the first direction is a direction in which the screw hole extends, and the second direction is a direction perpendicular to the flat portion of the second seat surface and oriented inward of the body.

DETAILED DESCRIPTION

Problem to be Solved by the Present Disclosure

Regarding the milling tool disclosed in PTL 1, the clamping force applied for attaching the cutting insert to the body has room for improvement. If the clamping force is insufficient, the position at which the cutting insert is attached may be displaced during cutting, leading to deterioration of the cutting accuracy. If the clamping force is insufficient, the centrifugal force exerted on the cutting insert during cutting may cause the cutting insert to be detached to fly away from the body.

The present disclosure is given in view of the above-described problem with the conventional art. More specifically, the present disclosure provides a milling tool that enables improvement of the clamping force applied for attaching the cutting insert to the body.

Advantageous Effect of the Present Disclosure

A milling tool according to an aspect of the present disclosure enables improvement of the clamping force applied for attaching the cutting insert to the body.

Description of Embodiments of the Present Disclosure

First, characteristics of embodiments of the present disclosure are described one by one.

(1) A milling tool according to an aspect of the present disclosure includes: a body having an outer circumferential surface formed around a central axis; a cutting insert having a rake surface, a flank surface, and a cutting edge formed by a ridgeline of the rake surface and the flank surface; and a screw attaching the cutting insert to the body. The outer circumferential surface has an insert attachment portion which is recessed toward the central axis and to which the cutting insert is attached. The insert attachment portion is defined by a first seat surface and a second seat surface. The first seat surface continues to the outer circumferential surface. The second seat surface continues to the first seat surface. The second seat surface has a flat portion, and the flat portion has a screw hole in which the screw is inserted. The cutting edge is formed of a sintered material containing at least one of cubic boron nitride and polycrystalline diamond. In a cross section perpendicular to the central axis, a first angle formed by a first direction and a second direction is an acute angle, the first direction is a direction in which the screw hole extends, and the second direction is a direction perpendicular to the flat portion of the second seat surface and oriented inward of the body.

The milling tool of (1) described above enables improvement of the clamping force applied for attaching the cutting insert to the body.

(2) Regarding the milling tool of (1) described above, a second angle formed by the second direction and a third direction which is a direction from the cutting edge toward the central axis as seen in end view may be an acute angle.

The milling tool of (2) described above enables improvement of the machining accuracy.

(3) Regarding the milling tool of (2) described above, a sum of the first angle and the second angle may be more than or equal to 5° and less than or equal to 50°.

The milling tool of (3) described above enables suppression of interference between cutting inserts adjacent to each other when the cutting inserts are attached to the body.

(4) Regarding the milling tool of (1) to (3) described above, a third angle formed by the third direction and a fourth direction which is a direction parallel to a flat portion of the first seat surface and which is oriented inward of the body as seen in end view may be an acute angle.

The milling tool of (4) described above enables suppression of fly-away of the cutting insert from the body during cutting.

(5) Regarding the milling tool of (4) described above, the third angle may be more than 2° and less than or equal to 35°.

The milling tool of (5) described above enables suppression of stiffness degradation of the body.

(6) Regarding the milling tool of (1) to (5) described above, the insert attachment portion may be further defined by a fly-off prevention surface, the fly-off prevention surface faces the first seat surface with the cutting insert interposed between the fly-off prevention surface and the first seat surface, and a distance between the fly-off prevention surface and the first seat surface decreases gradually toward the outer circumferential surface.

The milling tool of (6) described above enables suppression of fly-away of the cutting insert from the body during cutting.

(7) Regarding the milling tool of (1) to (6) described above, a width of the second seat surface may be more than or equal to 0.8 times and less than or equal to 1 time as large as a width of the first seat surface as seen in end view.

The milling tool of (7) described above enables suppression of fly-away of the cutting insert from the body during cutting.

(8) Regarding the milling tool of (1) to (7) described above, the insert attachment portion may have an oil hole through which cutting oil to be supplied to the cutting edge flows. The cutting insert has an insert body, and the insert body may have an indentation extending upward from the rake surface.

The milling tool of (8) described above enables cooling of the cutting edge.

Details of the Embodiments of the Disclosure

Next, details of embodiments of the present disclosure are described with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference characters. Embodiments described below may at least partially be combined arbitrarily.

Structure of Milling Tool According to Embodiment

In the following, a structure of a milling tool according to an embodiment is described.

FIG. 1is a perspective view of a milling tool according to an embodiment.FIG. 2is a perspective view of a body of the milling tool according to an embodiment.FIG. 3is a front view of the milling tool according to an embodiment as seen from a first end1bside. As shown inFIGS. 1 to 3, the milling tool according to an embodiment includes a body1and a cutting insert2. Body1has a first end1band a second end1c. First end1band second end1care ends of body1in the direction of a central axis1a. Second end1cis an end of body1to be attached to a headstock of a machine tool. First end1bis an end opposite to second end1c. Body1is made of steel for example.

Body1has an outer circumferential surface11. Outer circumferential surface11is formed around central axis1aof body1. Outer circumferential surface11continues to first end1b. Outer circumferential surface11has an arc shape as seen in end view. “End view” is a view of body1as seen from the first end1bside in a direction parallel to central axis1a. Outer circumferential surface11has an insert attachment portion12. Outer circumferential surface11may have a plurality of insert attachment portions12. Four or more insert attachment portions12may be arranged substantially at a diameter of one inch (2.54 cm) of an envelope circle of cutting edges centered at central axis1aof body1. Insert attachment portion12is recessed from outer circumferential surface11toward central axis1a.

FIG. 4is an enlarged view of a region IV inFIG. 3. As shown inFIG. 4, insert attachment portion12is defined by a first seat surface13and a second seat surface14. Insert attachment portion12may further be defined by a fly-off prevention surface15. First seat surface13is located rearward with respect to the rotational direction (indicated by an arrow in the drawing) of the milling tool according to an embodiment. The rotational direction of the milling tool according to an embodiment is the direction in which the milling tool according to the embodiment rotates such that a cutting edge27moves in the direction from the flank surface (side surface26) side toward the rake surface24side. Fly-off prevention surface15is located forward with respect to the rotational direction of the milling tool according to an embodiment.

First seat surface13continues to outer circumferential surface11. First seat surface13has a flat portion13a. Flat portion13ais formed by a flat surface. Second seat surface14continues to first seat surface13. Second seat surface14has a flat portion14a. Flat portion14ais formed by a flat surface.

First seat surface13has a width W1as seen in end view. Second seat surface14has a width W2as seen in end view. Width W2is preferably more than or equal to 0.8 times and less than or equal to 1 time as large as width W1.

FIG. 5is a cross-sectional view along V-V inFIG. 1.FIG. 6is an enlarged view of a region VI inFIG. 5. As shown inFIGS. 5 and 6, second seat surface14has a screw hole16. In screw hole16, a screw3is inserted. A first direction D1in which screw hole16extends and a second direction D2which is perpendicular to flat portion14aof second seat surface14and oriented inward of body1form a first angle θ1. First angle θ1is an acute angle. The fact that first angle θ1is an acute angle means that first direction D1has been rotated from second direction D2by an angle of more than 0° and less than 90° along the rotational direction of the milling tool according to an embodiment. First angle θ1is preferably more than or equal to 5° and less than or equal to 45°. First angle θ1within this range enables cutting insert2to be fixed firmly to body1.

As shown inFIG. 4, second direction D2and a third direction D3which is the direction from cutting edge27toward central axis1aform a second angle θ2. Second angle θ2is preferably an acute angle. The fact that second angle θ2is an acute angle means that second direction D2has been rotated from third direction D3by an angle of more than 0° and less than 90° along the rotational direction of the milling tool according to an embodiment. Second angle θ2is preferably more than 0° and less than or equal to 35°. The sum of first angle θ1and second angle θ2is preferably more than or equal to 5° and less than or equal to 50°. The sum of first angle θ1and second angle θ2within this range enables increase of the region to which the cutting force is applied and enables cutting to be performed stably.

Third direction D3and a fourth direction D4which is parallel to flat portion13aof first seat surface13and directed inward of body1form a third angle θ3. Third angle θ3is preferably an acute angle. The fact that third angle θ3is an acute angle means that fourth direction D4has been rotated from third direction D3by an angle of more than 0° and less than 90° along the rotational direction of the milling tool according to an embodiment. Third angle θ3is preferably more than 2° and less than or equal to 35°. Preferably, third angle θ3is substantially equal to second angle θ2. Specifically, third angle θ3is preferably within a range of second angle θ2±5°. Accordingly, the process cost for forming insert attachment portion12can be reduced.

Fly-off prevention surface15is located to face first seat surface13with cutting insert2interposed between fly-off prevention surface15and first seat surface13. Fly-off prevention surface15extends toward outer circumferential surface11. The distance between fly-off prevention surface15and first seat surface13decreases gradually toward outer circumferential surface11.

Insert attachment portion12may have an oil hole17. Oil hole17is oriented toward cutting edge27. Oil hole17communicates with a flow path18(seeFIG. 5) provided in body1. Cutting oil flowing though flow path18provided in body1is supplied to cutting edge27through oil hole17.

As shown inFIGS. 1 and 3, cutting insert2is attached to insert attachment portion12.FIG. 7is a perspective view of the cutting insert for the milling tool according to an embodiment. As shown inFIG. 7, cutting insert2includes an insert body21and a cutting-edge insert22.

Insert body21has a columnar shape. Insert body21is made of cemented carbide, for example. Cutting insert2is attached to insert attachment portion12such that the direction in which insert body21extends is along the direction from second end1ctoward first end1bof the body. Cutting insert2is attached to insert attachment portion12such that insert body21is in contact with first seat surface13and second seat surface14.

Insert body21has a through hole23. Screw3inserted in through hole23is further inserted in screw hole16to thereby attach cutting insert2to insert attachment portion12.

Cutting-edge insert22is attached by brazing or the like to insert body21, for example. Cutting-edge insert22is formed of a sintered material containing at least one of cubic boron nitride (CBN) and polycrystalline diamond (PCD). Cutting-edge insert22has a flat plate shape.

Cutting-edge insert22has a rake surface24, an attachment surface25, a side surface26, and a cutting edge27. Attachment surface25is opposite to rake surface24. Attachment surface25of cutting-edge insert22is brazed for example to insert body21and accordingly cutting-edge insert22is attached to insert body21.

Cutting-edge insert22is attached to insert body21such that side surface26runs along the direction in which insert body21extends. Side surface26continues to rake surface24. Cutting edge27is formed by a ridgeline of rake surface24and side surface26. In other words, side surface26is a flank surface. Cutting edge27extends in the direction in which insert body21extends. In other words, cutting edge27extends in the direction from second end1ctoward first end1bof body1. Cutting insert2is attached to insert attachment portion12such that cutting edge27protrudes from outer circumferential surface11.

Insert body21has a first end21a(front end) and a second end21b(rear end). First end21ais an end of insert body21located on the first end1bside of body1when cutting insert2is attached to insert attachment portion12. Second end21bis an end of insert body21located opposite to first end21a.

Insert body21has an indentation28. Indentation21is located at first end21aof insert body21. Indentation28is provided to extend upward from rake surface24. In other words, a part of insert body21located higher than rake surface24has been removed. The direction “upward” is herein the direction from attachment surface25toward rake surface24. In another point of view, indentation28is located forward of rake surface24with respect to the rotational direction as seen in end view. As seen in side view, indentation width W3which is the distance from cutting edge27is preferably more than or equal to 0.1 time and less than or equal to 0.4 times as large as the length (distance between first end21aand second end21b) of insert body21.

Advantageous Effects of Milling Tool According to Embodiment

In the following, advantageous effects of the milling tool according to an embodiment are described.

FIG. 8is a schematic diagram illustrating advantageous effects of the milling tool according to an embodiment. As shown inFIG. 8, as screw3is inserted and tightened in screw hole16, a clamping force F that clamps cutting insert2against insert attachment portion12is generated. Since first direction D1is inclined such that first angle θ1is an acute angle as described above, clamping force F consists of a component F1perpendicular to flat portion14aof second seat surface14and a component F2perpendicular to flat portion13aof first seat surface13.

The milling tool according to an embodiment rotates about central axis1a. This rotation causes a centrifugal force to be applied to cutting insert2in the direction of separating cutting insert2away from body1. In the milling tool according to an embodiment, cutting insert2can be secured to body1by component F2of clamping force F applied to cutting insert2.

Thus, the milling tool according to an embodiment enables cutting insert2to be clamped more firmly against body1. Accordingly, the milling tool according to an embodiment can suppress fly-away of cutting insert2caused by rotation during cutting. Further, the milling tool according to an embodiment can suppress deterioration of the machining accuracy due to positional displacement of cutting insert2caused by rotation during cutting.

In the case where second direction D2is inclined with respect to third direction D3such that second angle θ2is an acute angle, a principal cutting force f applied from a workpiece to cutting insert2during cutting can be divided into a component f1perpendicular to flat portion13aof first seat surface13and a component f2perpendicular to flat portion14aof second seat surface14. Therefore, in this case, both first seat surface13and second seat surface14can be subjected to principal cutting force f, and thus positional displacement of cutting insert2caused by the principal cutting force is less likely to occur and the machining accuracy can be improved.

If first angle θ1and second angle θ2are larger, a tool such as wrench used for tightening screw3may interfere with attached cutting insert2adjacent to screw3. In the case where the sum of first angle θ1and second angle θ2is less than or equal to 50°, such interference can be suppressed.

In the case where fourth direction D4is inclined with respect to third direction D3such that third angle θ3is an acute angle, fly-away of cutting insert2can be suppressed more effectively.

As third angle θ3increases, the thickness of a portion of body1located between first seat surface13and outer circumferential surface11decreases. As a result of this, the stiffness of this portion may be decreased. In the case where third angle θ3is less than or equal to 35°, such decrease of the stiffness can be suppressed.

In the case where insert attachment portion12is further defined by fly-off prevention surface15, cutting insert2which may be caused to fly away during rotation is brought into contact with fly-off prevention surface15, since fly-off prevention surface15faces first seat surface13such that the distance between fly-off prevention surface15and first seat surface13decreases gradually toward outer circumferential surface11. Therefore, in this case, fly-away of cutting insert2can be suppressed more effectively.

In the case where width W2of second seat surface14is more than or equal to 0.8 times and less than or equal to 1 time as large as width W1of first seat surface13, component F2of clamping force F can be ensured more easily. Therefore, in this case, fly-away of cutting insert2can be suppressed still more effectively.

In the case where insert attachment portion12has oil hole17, cutting edge27can be cooled by cutting oil during cutting. In the case where insert body21has indentation28, supply of cutting oil from oil hole17to cutting edge27is less likely to be hindered by insert body21. Therefore, in this case, cutting edge27can be cooled more efficiently.

It should be construed that the embodiments disclosed herein are given by way of illustration in all respects, not by way of limitation. It is intended that the scope of the present invention is defined by claims, not by the description above, and encompasses all modifications and variations equivalent in meaning and scope to the claims.

REFERENCE SIGNS LIST