Indexable cutting tool

Abstract

Indexable cutting tool (10) comprising a body (30) rotatable about an axis of rotation (C0), an interchangeable cutting insert (20) attached to the body (30), and a fastening element (40) that secures the cutting insert (20) to the body (30), wherein the fastening element (40) has a distal end part which is formed with a radially reducing conical surface (41), wherein the cutting insert (20) has an upper surface (24) and a lower surface (22), each in a rectangular shape, with a pair of longer sides (241, 243) and a pair of shorter sides (242, 244), and a side surface (25) connecting the upper surface (24) and the lower surface (22), wherein a cutting edge (21) is formed in a cutting edge section (241, 242, 243, 244) where the upper surface (24) and the side surface (25) intersect along the longer side (241), wherein the upper surface (24) is formed with a depression (23) which has a bottom (231), wherein at least a part of an inner wall surface of the depression (23) is a curved surface (232) which is curved towards a central axis (C2) of the depression (23), provided that a plane which has the central axis (C2) of the depression (23) and is parallel to the axis of rotation (C0) of the body (30) is taken as a first imaginary reference plane (IS1), and a plane which has the central axis (C2) of the depression (23) and is perpendicular to the axis of rotation (C0) of the body (30), is taken as a second imaginary reference plane (IS2), in the depression (23), when it is subdivided into four areas, a first, a second, a third and a fourth area (51, 52, 53, 54) by the first imaginary reference plane (IS1) and the second imaginary reference plane (IS2), the second area (52) being located on a central side closer to the axis of rotation (C0) of the body (30) and on a proximal side of the body (30) in the depression (23), the conical surface (41) of the fastening element (40) makes contact (X) with the curved surface (232) in the second area (52), and the fastening element (40) has a central axis line (C1) which is inclined in such a direction that a head part (42) is arranged closer to the midline and proximal side of the body (30) than the distal end part.

Description

Background area

[0001] The present invention relates to an indexable cutting tool and in particular an indexable milling tool used with a thread cutting insert. Description of the state of the art

[0002] Milling tools with removable tips used for thread cutting are already known. For example, patent disclosure JP-A-2006-068898 discloses a thread milling tool with an interchangeable cutting insert. The cutting insert is essentially rectangular in shape, and cutting edges, configured to suit the shape of an internal or external thread to be cut, are provided in a side-edge section along one of the longer sides of the rectangle. The cutting tool is attached to the body of a milling tool, and this milling tool itself is rotated about a rotary axis to cut threads into a workpiece.

[0003] A means for firmly attaching a threading insert to a body, disclosed for example in patent disclosure JP-A-2006-068898, is the use of an axial force of a screw inserted into a recess formed in the upper surface of the threading insert to exert a force on the threading insert so that it is secured.

[0004] An indexable thread-cutting tool is known from JP 2013 - 56 396 A. The tool has a body with a mounting groove for receiving an indexable insert. When the tool's mounting screws are screwed into the body while the indexable insert is inserted into the mounting groove, a rear surface of the indexable insert is pressed against a bearing surface of the mounting groove by the interaction of conical contact sections of the mounting screws with corresponding conical recesses in the indexable insert.

[0005] From EP 0 037 554 A1, a cutting tool is known which consists of a tool body with a recess for receiving a center-hole indexable insert and with a bore for receiving a rotationally symmetrical clamping bolt for clamping the indexable insert. The bore has an upper section whose axis is perpendicular to the insert bearing surface, and a lower, threaded section whose axis is inclined by 2° to 7° to the axis of the upper section. One end of the clamping bolt engages in the center hole of the indexable insert. The other end can be screwed into the threaded section. The central part of the clamping bolt is supported against the tool body in the upper bore section. This bore section has two axially congruent cylindrical sections with different diameters. The upper cylindrical section tapers to the lower cylindrical section via a circularly curved shoulder.The clamping bolt has a cylindrical section in its central area that tapers via a circularly curved shoulder to a threaded shaft. By specifically selecting the radii of the two shoulders, which can be in a ratio of 1:1 to 1:2.3 to the radius of the cylindrical section, a degressive increase in the compressive forces from the clamping bolt to the central bore wall of the indexable insert is achieved when the clamping bolt (5) is screwed in through a constant angle. Summary

[0006] With the aforementioned method, in which a screw is inserted into the recess to secure the cutting insert, the axial force of the screw may not be sufficiently exerted on the cutting insert, depending on the precision of the distal end of the screw or the recess formed in the insert. Alternatively, the positional precision of the cutting insert may be adversely affected by a deviation in the contact point between the screw and the recess. In particular, with the method where the screw is inserted diagonally into the recess, a gap can easily form between the screw and the recess, in which case hardly any axial force can be exerted on the cutting insert.

[0007] Furthermore, since the recess is relatively shallow, the screw head can easily pop out of the recess compared to a fastening screw that passes through a through hole in the insert. Therefore, there is a possibility that the head of a popped-out screw could cross the rotational trajectory of the cutting edges and touch the material being cut (workpiece) during the cutting process.

[0008] In light of the problem described above, the present invention was developed to solve it. That is, it is an object of the present invention to provide an indexable cutting tool that enables stable clamping of cutting inserts and prevents contact between the heads of fasteners and workpieces.

[0009] The problem is solved by an indexable cutting tool with the features of claim 1.

[0010] An indexable cutting tool according to one aspect of the present invention comprises a body rotatable about an axis of rotation, a cutting insert interchangeably mounted on the body, and a fastening element that secures the cutting insert to the body. The fastening element has a distal end portion formed with a conical surface. The cutting insert has an upper surface and a lower surface, each rectangular in shape, with a pair of longer sides and a pair of shorter sides, and a side surface connecting the upper surface and the lower surface. A cutting edge is formed longitudinally in a cutting edge section where the upper surface and the side surface intersect along the longer side. The upper surface is formed with a recess having a bottom.At least part of an inner wall surface of the recess is a curved surface that arches towards a central axis of the recess. If the recess is divided into four regions, first through fourth, by a first imaginary reference plane containing the central axis of the recess and parallel to the axis of rotation of the body, and a second imaginary reference plane containing the central axis of the recess and perpendicular to the axis of rotation of the body, the second region is located on a central side closer to the axis of rotation of the body and on a proximal side of the body within the recess. The conical surface of the fastener contacts the curved surface in the second region. The central axis line of the fastener is inclined such that a head portion is located closer to the central side and to the proximal side of the body than the distal end portion.

[0011] In accordance with this design, the central axis of the fastener is inclined such that the fastener head is angled away from the cutting edge. Because the head and cutting edge are further apart, the likelihood of the head contacting the workpiece is reduced. The conical surface transfers the fastener's axial force to the cutting insert in oblique sliding contact with the curved surface, ensuring the cutting insert is firmly attached to the body. This allows for the creation of an indexable cutting tool that provides stable clamping of cutting inserts and prevents contact between fastener heads and workpieces.

[0012] In the above aspect, the indexable cutting tool has several recesses, wherein preferably a central axis line of a first fastening element that is inserted into the recess closest to a proximal end of the cutting insert and the first imaginary reference plane form an angle that is smaller than an angle formed by a central axis line of a second fastening element that is inserted into the recess closest to a distal end of the cutting insert and the first imaginary reference plane.

[0013] According to this aspect, the centerline of the fastening elements on the proximal and distal sides of the cutting insert are inclined in different directions. Since the direction in which the distal end of the fastening element presses against the recess of the cutting insert is slightly offset, the cutting insert can be pressed against the body from multiple directions, thus enabling a more stable clamping action. The angle between the centerline and the first imaginary reference plane is defined as the supplementary angle of the angle formed by the direction vector of the centerline and the normal vector of the first imaginary reference plane.Accordingly, the angle between the central axis line and the second imaginary reference plane is defined as a supplementary angle to the angle formed by the direction vector of the central axis line and the normal line vector of the second imaginary reference plane.

[0014] In the aspect above, the cutting insert of the indexable cutting tool can have a cutting edge for cutting threads.

[0015] According to this aspect, the essentially rectangular cutting insert can be clamped stably and reliably, which is advantageous for cutting threads.

[0016] The indexable cutting tool according to the present invention enables a more stable clamping of the cutting insert than before. That is, the cutting insert can be secured more firmly. Furthermore, the indexable cutting tool according to the present invention enables stable cutting even when using a clamping method, whereby the cutting insert is secured by pressure exerted by a fastening element in the recess of the cutting insert, since the distal end part of the fastening element does not overlap with the rotational trajectory of the cutting edge. Brief description of the drawings Fig. Figure 1 is a perspective view of an indexable cutting tool according to an embodiment of the present invention; Fig. 2 is a perspective view of the in Fig. 1. Cutting tool shown from a different angle; Fig. 3 is a left side view of the in Fig. 1 cutting tool shown; Fig. 4 is a front view of the in Fig. 1 cutting tool shown; Fig. 5 is a top view of the in Fig. 1 cutting tool shown; Fig. 6 is a perspective view of the in Fig. 1 cutting tool shown in a state in which cutting inserts have been removed; Fig. Figure 7A is a perspective view of a cutting insert according to this embodiment; Fig. Figure 7B is a front view of the cutting insert according to this embodiment; Fig. Figure 7C is a top view of the cutting insert according to this embodiment; Fig. Figure 8A is a perspective view of a fastening element according to this embodiment; Fig. Figure 8B is a front view of the fastening element according to this embodiment; Fig. Figure 9 is a top view to illustrate the inclination direction of the center axis line of the fastening element; Fig. Figure 10 is a cross-sectional view along line XX in Fig. 9; and Fig. Figure 11 is a top view to illustrate the inclination direction of the central axis line of the fastening element in a variation example of the in Fig. 9 shown embodiment. Detailed description

[0017] An embodiment of the present invention is described below with reference to the drawings. Components that are given the same reference numerals in different drawings have the same or a similar configuration. In various embodiments of the present invention (hereinafter simply referred to as "cutting tool 10"), the indexable cutting tool 10 comprises a fastening screw 40 having a radially reducing conical surface 41 and a cutting insert 20 with a recess 23 having a curved surface 232 that is convex towards the center. The central axis line C1 of the fastening screw 40 is inclined such that a head portion 42 of the fastening screw 40 is arranged closer to the central side and to a proximal side of a body 30 than a distal end portion of the fastening screw 40.A contact point X between the conical surface 41 of the fastening screw 40 and the curved surface 232 of the cutting insert 20 is arranged within a second area 52 of the recess 23, which is arranged closer to the central side and to the proximal side of the body 30 than other areas 52, 53, and 54 of the recess 23 (see . Fig. 9 and Fig. 10).

[0018] Since the head 42 of the fastening screw 40 is oriented away from the cutting edges 21, it is less likely that the head 42 will come into contact with a workpiece. Because the conical surface 41 transmits the axial force of the fastening screw 40 to the cutting insert 20 in oblique sliding contact with the curved surface 232, the cutting insert 20 is firmly attached to the body 30. Each configuration is described in more detail below with reference to Fig. 1 to Fig. 11 described.

[0019] Fig. Figure 1 is a perspective view of the cutting tool 10 according to an embodiment of the present invention, and Fig. Figure 2 is a perspective view of the cutting tool 10 from a different angle than Fig. 1 seen. As in Fig. 1 and Fig. As shown in Figure 2, the indexable cutting tool 10 has two essentially rectangular cutting inserts 20, a body 30 for holding the cutting inserts 20, and fastening elements (e.g., fastening screws 40) for securing the cutting inserts 20 to the body 30. The number of cutting inserts 20 is not limited to that of the illustrated example and can be one, three, or more.

[0020] Fig. 3 is a left side view of the in Fig. 1 cutting tool shown 10, and Fig. 4 is a front view of the in Fig. 1 cutting tool shown 10. As in Fig. 3 and Fig. As shown in Figure 4, for the sake of simplicity, in the following description an axial line parallel to the axis of rotation C0 of the body 30 is defined as the X-axis, an axis perpendicular to the X-axis and to a base surface 311a of a tip seat 311, which will be described later, is defined as the Y-axis, and an axis perpendicular to the X-axis and parallel to the base surface 311a of the tip seat 311 is defined as the Z-axis.

[0021] If an object is positioned closer to the arrowhead of the X-axis than another object, it is described as being "closer to the distal side," while if it is positioned closer to the side opposite the arrowhead, it is described as being "closer to the back." If an object is positioned closer to the arrowhead of the Y-axis than another object, it is described as being "above," while if it is positioned closer to the side opposite the arrowhead, it is described as being "below." If an object is positioned closer to an origin point (e.g., the rotation axis C0 of body 30) than another object in the YZ plane, it is described as being "on the mid-side," while if it is positioned farther from the origin point, it is described as being "on the circumferential side."

[0022] The body 30 comprises a first cylindrical part 31 in a cylindrical shape and a second cylindrical part 32, which has a larger diameter than the first cylindrical part 31 and is connected to the rear end of the first cylindrical part 31. The first cylindrical part 31 is provided with two pointed seats 311 and 312 for fitting the cutting inserts 20. The pointed seats 311 and 312 are slots with a substantially U-shaped cross-section and generally extend over the entire length of the first cylindrical part 31. One end of the tip seats 311 and 312 extends to the end face of the first cylindrical part 31 and to the outer circumferential surface of the body 30. That is, the two tip seats 311 and 312 open into the distal end face and the outer circumferential surface of the body 30. The cutting tool 10 exhibits 180° rotational symmetry in all its features, including the two tip seats 311 and 312.Therefore, the configuration of one of the top seats is described in detail as a proxy for both, and a repeated description of the configuration of the other top seat is omitted.

[0023] The configuration of the tip seat 311 will now be described in detail. The tip seat 311 consists of a base surface 311a, which forms a part that abuts the cutting insert 20; a circumferential boundary wall 311b, which is arranged on the central side of the body 30 and extends perpendicular to the base surface 311a, with a normal line of its wall surface oriented along the Z-axis; an axial boundary wall 311c, which is arranged on the rear side of the body 30 and extends perpendicular to the base surface 311a, with a normal line of its wall surface oriented along the X-axis; and an upper wall 311d, which is arranged above the base surface 311a and is connected to the circumferential boundary wall 311b and the axial boundary wall 311c.

[0024] A recess (indentation) is formed at the junction between the base surface 311a and the axial boundary wall 311c to prevent part of a side edge section of the cutting insert 20 (shorter side 222 and its surroundings on a lower surface 22, which will be described later) from interfering with the junction when the cutting insert 20 is attached. Similarly, a recess is formed at the junction between the upper surface 311d and the axial boundary wall 311c to prevent part of a side edge section of the cutting insert 20 (shorter side 242 and its surroundings on an upper surface 24, which will be described later) from interfering with the junction.

[0025] A cavity 35 is formed in a central part of the circumferential boundary wall 311b. By forming the cavity 35, the contact point between the cutting insert 20 and the circumferential boundary wall 311b can be restricted to the distal side or rear side instead of to the center of the circumferential boundary wall 311b, where it is difficult to achieve a stable clamping force.

[0026] Fig. 5 is a top view of the in Fig. 1 cutting tool shown 10, and Fig. 6 is a perspective view of the in Fig. 1 of the cutting tool 10 shown, which represents a state where the cutting inserts have been removed. As in Fig. 5 and Fig. As shown in Figure 6, two through holes 33 are formed in the upper wall 311d. Fastening screws 40 are inserted through these through holes 33, so that the fastening screws 40 press and fix the cutting insert 20, which is inserted into the tip seat 311, against the base surface 311a.

[0027] A jet opening 34 for a coolant to cool the cutting insert 20 is formed near the rearmost of the through holes 33 formed in the first cylindrical part 31. The second cylindrical part 32 is a section that is gripped by a machine tool (not shown).

[0028] The cutting insert 20 has cutting edges 21 where several tooth tips and tooth roots corresponding to a desired internal or external thread shape are formed alternately in a side edge section along a longer side 241, i.e. only along the longer side 241, among the side edge sections (241, 242, 243, and 244) which essentially form a rectangle. Fig. 7A is a perspective view of the cutting insert 20, Fig. 7B is a front view of the cutting insert 20, and Fig. 7C is a top view of the cutting insert 20. As in Fig. As shown in Figure 7B, the rake face connected to the cutting edge 21 has a positive rake angle. The cutting insert 20 rests against the circumferential limiting wall 311b and the axial limiting wall 311c when it is mounted on the tip seat 311.

[0029] The cutting insert 20 has an upper surface 24, a lower surface 22 opposite the upper surface 24, and side surfaces 25 connecting the upper surface 24 and the lower surface 22. The upper surface 24 is essentially rectangular with a pair of longer sides 241 and 243 and a pair of shorter sides 242 and 244. Similarly, the lower surface 22 is essentially rectangular with a pair of longer sides 241 and 223 and a pair of shorter sides 242 and 224.

[0030] In the following description, the four sides 241, 242, 243, and 244 of the upper surface 24 are collectively referred to as the side edge sections of the upper surface 24, and the four sides 221, 222, 223, and 224 of the lower surface 22 can collectively be referred to as the side edge sections of the lower surface 22. The longer sides 241 and 243 are the longer side edge sections of the upper surface 24, and the shorter sides 242 and 244 are the shorter side edge sections of the upper surface 24. Similarly, the longer sides 221 and 223 are the longer side edge sections of the lower surface 22, and the shorter sides 222 and 224 are the shorter side edge sections of the lower surface 22.

[0031] The lower surface 22 is the contact surface that rests against the base surface 311a of the tip seat 311. The upper surface 24 is formed with recesses 23 for contact with the fastening screws 40, which are inserted through the through holes 33 in the body 30. In the illustrated example, the inner wall surface of the recess 23 is essentially in a truncated cone shape, consisting of an inclined surface 232 that tapers away from the upper surface 24 and a base surface 231 that is parallel to the upper surface 24. In particular, the inclined surface 232 is formed as a curved surface that is curved such that it arches towards the central axis of the recess 23. In the following description, the inclined surface 232 can be referred to as the curved surface 232.

[0032] Next, the relationship between the recess 23 of the cutting insert 20 and the fastening screw 40 will be explained. Fig. Figure 9 is a top view of the cutting insert 20 in the XZ plane, i.e., viewed from opposite the upper surface 24, where each of the recesses 23 is divided into four areas by an imaginary reference line IL1 parallel to the X-axis and an imaginary reference line IL2 parallel to the Z-axis. For the sake of simplicity, in the following description, the positional relationship "viewed from opposite the upper surface 24" can be referred to as the positional relationship "in top view".

[0033] The four regions subdivided by the two imaginary reference lines IL1 and IL2 shall be designated, starting from the top right of the drawing and proceeding counterclockwise, as a first region 51, a second region 52, a third region 53, and a fourth region 54. That is, of the four separate regions, the one located comparatively on the circumferential side and comparatively on the posterior side shall be designated as a first region 51, the one located closer to the center than the first region 51 shall be designated as a second region 52, the one located closer to the distal side than the second region 52 shall be designated as a third region 53, and the one located closer to the circumferential side than the third region 53 shall be designated as a fourth region 54.

[0034] The first to fourth areas 51, 52, 53, and 54 mentioned above are further described from a different perspective. A plane containing the central axis C2 of the recess 23 and parallel to the axis of rotation C0 of the body 30 is defined as a first imaginary reference plane IS1. A plane containing the central axis C2 of the recess 23 and perpendicular to the axis of rotation C0 of the body 30 is defined as a second imaginary reference plane IS2. The first imaginary reference line IL1 mentioned above is a line of intersection between the first imaginary reference plane IS1 and an imaginary plane IS0 (see Fig. 10), which is coplanar with the upper surface 24. The second imaginary reference line IL2 mentioned above is a line of intersection between the second imaginary reference plane IS2 and the imaginary plane IS0.

[0035] If each of the recesses 23 is subdivided by the first and second imaginary reference planes IS1 and IS2 into four, first to fourth, regions 51, 52, 53, and 54, the region located on the central side closer to the axis of rotation C0 of the body 30 and on the proximal side of the body 30 is the second region 52. Similarly, the region located on the circumferential side furthest from the axis of rotation C0 of the body 30 and on the proximal side of the body 30 is the first region 51. The region located on the central side closer to the axis of rotation C0 of the body 30 and on the distal side of the body 30 is the third region 53. The region located on the circumferential side furthest from the axis of rotation C0 of the body 30 and on the distal side of the body 30 is the fourth region 54.

[0036] When the cutting insert 20 is placed on the tip seat 311, all fastening screws 40 are in contact with the recesses 23 of the cutting insert 20 in the second region 52. The central axis line of the fastening screw 40 is inclined to the Y-axis in one direction from the second region 52 to the fourth region 54, which is diagonally opposite to the second region 52, and downwards from the second region 52 to the fourth region 54. In other words, the central axis line C1 of the fastening screw 40 is inclined such that a head portion 42, which is opposite a distal end portion (e.g., the conical surface 41), is positioned closer to the midline and to the proximal side of the body 30 than the distal end portion.

[0037] Fig. Figure 9 is a top view to illustrate the orientation of the center axis line C1 of the fastening screw 40, and Fig. Figure 10 is a cross-sectional view along line XX of the Fig. 9. As in Fig. As shown in Figure 9, the center axis line C1 of the fastening screw 40 is inclined such that, viewed in the XZ plane, it extends over both the second region 52 and the fourth region 54. The center axis line C1 is, as shown in Fig. 10 shown, inclined so that the part contained in the second area 52 is arranged above the part contained in the fourth area 54.

[0038] Fig. 8A is a perspective view of the fastening screw 40, and Fig. Figure 8B is a front view of fastening screw 40. As shown in Fig. 8A and Fig. As shown in Figure 8B, the fastening screw 40 has a distal end portion formed as a conical surface 41 that tapers radially towards the distal end. The conical surface 41 rests against the inner wall of the recess 23 of the cutting insert 20 when the cutting insert 20 is attached to the body 30.

[0039] In other words, the indexable cutting tool 10 comprises the cutting inserts 20, the body 30 for holding the cutting inserts 20, and the fastening elements (e.g., fastening screws 40) for securing the cutting inserts 20 to the body 30. Cutting edges 21 are formed in a cutting edge section where a longer of the side edge sections (i.e., longer side 241) of the upper surface 24 of the cutting insert 20 intersects the side surface 25 of the cutting insert 20. The cutting inserts 20 are inserted into the tip seats 311 and 312 with a U-shaped cross-section formed in the body 30. Recesses 23 with a bottom are formed in the upper surface 24 of the cutting insert 20. At least a portion of the inner wall surface (231, 232) of the recess 23 is a curved surface 232 that is convex to the central axis C2 of the recess 23. A contact point X between the fastening element 40 and the recess 23 is located on the conical surface 41.Viewed from an imaginary plane IS0 (which is coplanar with, for example, the upper surface 24) containing the edges of the recess 23, the recess 23 is divided into four regions (51, 52, 53, and 54) by a first imaginary reference line IL1, parallel to an imaginary line obtained by projecting the axis of rotation C0 of the body 30 onto the imaginary plane IS0, and a second imaginary reference line IL2 perpendicular to the first imaginary reference line IL1. The contact point X between the recess 23 and the fastening element 40 is located in the second region 52, which is closer to the axis of rotation C0 of the body 30 and to the proximal side of the body 30. The center axis C1 of the fastening element 40 is inclined downwards from the second region 52 to the fourth region 54, which is diagonally opposite to the second region 52.

[0040] Next, the effects achieved by the cutting tool 10 of this embodiment will be explained. The cutting insert 20 has cutting edges 21 in a shape corresponding to the characteristics of internal threads or the like, so that internal threads and the like can be formed by a milling process. Since the cutting tool 10 has two cutting inserts 20, the machining can be carried out with good efficiency.

[0041] Since the contact point X between the fastening screw 40 and the recess 23 of the cutting insert 20 is located in the second region 52 of the recess 23, the fastening screw 40 can exert a force on the cutting insert 20 in one direction towards the circumferential limiting wall 311b and the axial limiting wall 311c. As a result, the force is efficiently exerted on the cutting insert 20, and it is clamped securely because its movement in two directions is restricted. Furthermore, the fastening screw 40 and the recess 23 are brought into contact with each other on the conical surface 41 of the fastening screw 40 and on the curved inner wall of the recess 23, thus ensuring reliable contact.

[0042] Since the center axis line C1 of the fastening screw 40 is inclined downwards from the second region 52 to the fourth region 54, the head 42 of the fastening screw 40 can hardly intersect the rotational trajectory of the cutting edges. Generally, the head 42 of a fastening screw inserted into a dead-end hole (a recess with a bottom) cannot be fully inserted into the hole, so that, depending on the shape of the cutting insert 20 or how it is arranged, the protruding head 42 of the fastening screw can sometimes overlap with the rotational trajectory of the cutting edges 21. However, since the center axis line C1 of the fastening screw 40 is inclined to the Y-axis in the cutting tool 10, the head 42 of the fastening screw 40 can reliably avoid the rotational trajectory of the cutting edges 21.

[0043] The means to displace the head part 42 of the fastening screw 40 from the rotational trajectory of the cutting edges 21 are not based on the in Fig. The example shown in 9 is limited. In another embodiment, for example, as shown in Fig.As shown in Figure 11, the mid-axis line of a fastening screw 40a, located on the rear side, can be inclined in a direction closer to the parallel with the imaginary line IL1, while the mid-axis line of a fastening screw 40b, located on the distal side, can be inclined in a direction closer to the parallel with the imaginary line IL2. In other words, the angle formed by the mid-axis line of fastening screw 40a and the imaginary line IL1 can be made smaller than the angle formed by the mid-axis line of fastening screw 40b and the imaginary line IL1. By making the inclination directions of the mid-axis lines of fastening screws 40a and 40b different from each other in order to shift the contact points within the second region, the cutting insert 20 can be clamped more stably.

[0044] Optionally, three or more fastening screws 40 can be used. In this case, the center axis line of a rearmost fastening element 40 can be inclined in a different direction than the center axis line of a frontmost fastening element 40, as described above.

[0045] The distal end face of the fastening screw 40 should preferably not be in contact with the bottom of the recess 23 of the cutting insert 20. A force exerted on the bottom of the recess 23 can cause the cutting insert 20 to rotate about this section as a pivot point, which will lift the lower surface 22 from the bottom surface 311a or 312a of the tip seat and reduce the clamping force.

[0046] While one embodiment of the present invention has been described above as an example, the present invention is not limited to the embodiment described above. For example, while the cutting edges 21 of the cutting insert 20 of the embodiment described above have a shape corresponding to the features of internal threads or the like for cutting internal or external threads, the cutting edge of the cutting insert in the present invention is not limited to thread cutting purposes. For example, the cutting insert may have a straight cutting edge such as that used for shoulder milling.

[0047] While the upper surface 24 of the cutting insert 20 is parallel to the XZ plane in this embodiment, these planes need not necessarily be parallel to each other. In this case, the recess can be divided into four areas by a line obtained by projecting the axis of rotation of the body onto a plane containing the edges of the recess of the cutting insert, and a line perpendicular to this line. Again, in this case, the fastening screw 40 and the recess 23 come into contact with each other in the second area.

[0048] While the cutting insert 20 in the embodiment described above is configured such that only the upper surface 24 does not serve as a rake face, the cutting tool 10 of the present invention is not limited to this configuration. The cutting tool can be configured to use a cutting insert in which both the upper surface 24 and the lower surface 22 serve as rake faces, so that two surfaces can be cut simultaneously.

Claims

[1] Indexable cutting tool (10) comprising a body (30) rotatable about an axis of rotation (C0), an interchangeable cutting insert (20) attached to the body (30), and a fastening element (40) that secures the cutting insert (20) to the body (30), wherein the fastening element (40) has a distal end part which is formed with a radially reducing conical surface (41), wherein the cutting insert (20) has an upper surface (24) and a lower surface (22), each in a rectangular shape, with a pair of longer sides (241, 243) and a pair of shorter sides (242, 244), and a side surface (25) connecting the upper surface (24) and the lower surface (22), wherein a cutting edge (21) is formed in a cutting edge section (241, 242, 243, 244) where the upper surface (24) and the side surface (25) intersect along the longer side (241), wherein the upper surface (24) is formed with a depression (23) which has a bottom (231), wherein at least a part of an inner wall surface of the depression (23) is a curved surface (232) which is curved towards a central axis (C2) of the depression (23), provided that a plane which has the central axis (C2) of the depression (23) and is parallel to the axis of rotation (C0) of the body (30) is taken as a first imaginary reference plane (IS1), and a plane which has the central axis (C2) of the depression (23) and is perpendicular to the axis of rotation (C0) of the body (30), is taken as a second imaginary reference plane (IS2), in the depression (23), when it is subdivided into four areas, a first, a second, a third and a fourth area (51, 52, 53, 54) by the first imaginary reference plane (IS1) and the second imaginary reference plane (IS2), the second area (52) being located on a central side closer to the axis of rotation (C0) of the body (30) and on a proximal side of the body (30) in the depression (23), the conical surface (41) of the fastening element (40) makes contact (X) with the curved surface (232) in the second area (52), and the fastening element (40) has a central axis line (C1) which is inclined in such a direction that a head part (42) is arranged closer to the midline and proximal side of the body (30) than the distal end part. [2] Indexable cutting tool (10) according to claim 1, wherein several recesses (23), each being the recess (23) having a bottom (231), are formed on the upper surface (24) of the cutting insert (20), a central axis line (C1) of a first fastening element (40a) that is inserted into the recess (23) closest to a proximal end of the cutting insert (20), and the first imaginary reference plane (IS1) form an angle that is smaller than an angle formed by a central axis line (C1) of a second fastening element (40b) that is inserted into the recess (23) closest to a distal end of the cutting insert (20), and the first imaginary reference plane (IS1). [3] Indexable cutting tool (10) according to claim 1 or 2, wherein the cutting edge (21) is a cutting edge for cutting threads. [4] Indexable cutting tool (10) according to one of the preceding claims, wherein the distal end part of the fastening element (40) does not overlap with a rotational trajectory of the cutting edge (21), wherein the fastening element (40) has an external threaded section between the head part (42) and the distal end part, wherein the core diameter of the external thread section is larger than the diameter of the radially reducing conical surface (41).

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