Cutting insert and blade-tip-replaceable cutting tool

Abstract

This cutting edge has a convex curved edge that is a curve convex toward the outer circumference of the tip of a cutting insert. A rake angle (α) in a normal direction of a rake face of the convex curved edge is a negative angle over an entire length of the convex curved edge, and gradually increases to the negative angle side as an end point on a rear end side of the convex curved edge is approached at a radiation angle (θ) of 15°-90°. Where a change amount of the rake angle (α) in the normal direction per 15° of an angle range of the radiation angle (θ) is σ1, σ1 ≤ 3.0°. Where a change amount of the rake angle in an axial direction per 15° of the angle range of the radiation angle (θ) is σ2, σ2 ≤ 6.0° when the radiation angle (θ) is 60°-90°.

Description

Cutting insert and tip-exchangeable cutting tool

[0001] The present invention relates to a cutting insert and a tip-exchangeable cutting tool. This application claims priority based on Japanese Patent Application No. 2024-178904 filed in Japan on October 11, 2024, and incorporates its content herein.

[0002] Conventionally, when performing cutting operations such as semi-finishing and finishing on workpieces such as cast iron used in press dies, etc., a tip-exchangeable ball end mill (tip-exchangeable cutting tool) has been used (for example, Patent Documents 1 and 2).

[0003] The tip-exchangeable ball end mill includes a tool body (holder) that is rotated around a central axis, and a plate-shaped cutting insert that is detachably attached to a slit-shaped insert mounting seat disposed at the tip of the tool body. The cutting insert includes a pair of cutting edges that are spaced apart from each other around the central axis. Each cutting edge has an arc-shaped convex arc edge that protrudes toward the outer peripheral side of the tool tip.

[0004] Specifically, each convex arc edge of the pair of cutting edges is disposed at a position that is rotationally symmetric by 180° around the central axis. The rotational locus formed by the rotation of these convex arc edges around the central axis is in the shape of a hemispherical surface that protrudes toward the tool tip side.

[0005] Japanese Patent No. 5939208 Japanese Patent No. 6683261

[0006] In conventional cutting inserts and tip-exchangeable cutting tools, there has been room for improvement in reducing the surface roughness of cutting surfaces (machined surfaces) such as gently sloping curved surfaces (hereinafter sometimes referred to as gentle surfaces) and vertical walls formed on the workpiece by cutting operations and improving the cutting surface properties.

[0007] An object of the present invention is to provide a cutting insert and a tip-exchangeable cutting tool that can improve the cutting surface properties of gentle surfaces and vertical walls of a workpiece.

[0008] To solve the above problems, the present invention provides the following means.

[0009] [Aspect 1 of the present invention] A plate-shaped cutting insert that is detachably attached to the tip of a tool body that is rotatable around a central axis, comprising a pair of cutting blades spaced apart from each other around the central axis, each cutting blade having a curved convex curved blade that is convex toward the outer circumference of the tip of the cutting insert, defined as the radial angle when the virtual line passing through the center of the radius of curvature of the convex curved blade and a predetermined point on the convex curved blade is inclined with respect to the central axis in a plan view of the cutting insert as viewed from the thickness direction of the cutting insert, defined as the normal rake angle when the rake face of the convex curved blade is inclined with respect to a reference plane perpendicular to the thickness direction in a virtual plane that includes the virtual line and extends along the thickness direction, and the cutting insert A cutting insert in which, in a side view of the insert viewed from the left and right directions perpendicular to the thickness direction and axial direction, the angle at which the tangent line passing through a predetermined point on the convex curve blade is inclined with respect to the central axis is defined as the axial rake angle, the normal rake angle is a negative angle over the entire length of the convex curve blade, and when the radiation angle is 15° or more and 90° or less, it gradually increases towards the negative side as it approaches the rear end of the convex curve blade, and when the change in the normal rake angle per 15° of the angular range of the radiation angle is denoted as σ1, σ1 ≤ 3.0°, and when the change in the axial rake angle per 15° of the angular range of the radiation angle is denoted as σ2, σ2 ≤ 6.0° when the radiation angle is 60° or more and 90° or less.

[0010] [Aspect 2 of the present invention] A cutting insert according to aspect 1, comprising a chisel portion arranged on the ridge line portion to which the relief faces of the pair of cutting blades are connected, wherein, in a front view of the cutting insert viewed from the axial tip side, the chisel angle formed between the tip of the convex curved blade and the chisel edge of the chisel portion is 165° or more, and in a front view of the insert, when L1 is the chisel thickness along the width direction of the chisel portion perpendicular to the blade length direction in which the tip of the convex curved blade extends, and L2 is the length of the chisel edge, L2 / L1 is 3.9 or more and 5.0 or less.

[0011] [Aspect 3 of the present invention] A cutting insert according to aspect 1 or 2, comprising a pair of concave pockets arranged on the rake face side of each of the pair of cutting blades around the central axis, wherein, when the cutting insert is viewed from the tip side in the axial direction, the angle formed between the ridge portion where the relief surface of the cutting blade and the pocket are connected and the extension line of the tip of the convex curve blade is defined as the pocket opening angle ζ, and 95° ≤ ζ ≤ 105°.

[0012] [Aspect 4 of the present invention] A cutting insert according to any one of aspects 1 to 3, wherein the normal rake angle is -6° to -8° when the radiation angle is 0° or more and 15° or less.

[0013] [Aspect 5 of the present invention] An interchangeable cutting tool comprising a tool body that can be rotated around a central axis, and a cutting insert according to any one of aspects 1 to 4 that is detachably attached to the tip of the tool body.

[0014] According to the above-described aspect of the present invention, a cutting insert and an interchangeable cutting tool are provided that can improve the cutting surface properties of a workpiece, such as a gently curved surface or a vertical wall.

[0015] Figure 1 is a perspective view showing an indexable cutting tool according to one embodiment of the present invention. Figure 2 is a front view of the indexable cutting tool viewed from the axial tip side. Figure 3 is a plan view showing a part of the indexable cutting tool (near the cutting edge). Figure 4 is a front view of the tool body viewed from the axial tip side. Figure 5 is a plan view showing a part of the tool body (near the insert mounting seat). Figure 6 is a side view showing a part of the tool body (near the insert mounting seat). Figure 7 is a plan view of the cutting insert viewed from the thickness direction, and a diagram illustrating the radial angle and normal rake angle. Figure 8 is a side view of the cutting insert viewed from the left and right directions. Figure 9 is a front view of the cutting insert (enlarged view of the tip) of a part of the cutting insert (near the center of the tip) viewed from the axial tip side. Figure 10 is a graph showing the relationship between the radial angle and the normal rake angle. Figure 11 is a graph showing the relationship between the radial angle and the axial rake angle.

[0016] A cutting insert 5 and an indexable cutting tool 6 according to one embodiment of the present invention will be described with reference to the drawings. The indexable cutting tool 6 in this embodiment is, for example, an indexable ball end mill. The indexable cutting tool 6 is suitable for milling operations such as semi-finishing and finishing on high-hardness workpieces such as hardened cast iron. In this embodiment, the indexable cutting tool 6 may be simply referred to as a cutting tool or tool, etc. Also, the cutting insert 5 may be simply referred to as an insert, etc.

[0017] As shown in Figures 1 to 3, the replaceable-tip cutting tool 6 comprises a columnar tool body (holder) 1 that can be rotated around a central axis C, a plate-shaped cutting insert 5, and fixing screws 8 for fixing the cutting insert 5 to the tool body 1. The cutting insert 5 is detachably attached to one end (tip 2) of the tool body 1, which has two ends (one end and the other end) in the direction in which the tool body 1 extends.

[0018] Here, we will explain the definition of direction used in this embodiment. In this embodiment, the direction in which the central axis C of the replaceable-tip cutting tool 6 extends, that is, the direction along the central axis C, is called the axial direction. In this embodiment, the central axis C of the replaceable-tip cutting tool 6 is the central axis of the tool body 1 and is also the central axis of the cutting insert 5.

[0019] In the axial direction, the direction from one end of the tool body 1 where the cutting insert 5 is mounted to the other end is called the axial rear end or simply the rear end. Similarly, the direction from the other end of the tool body 1 to one end is called the axial front end or simply the front end. In the following explanation, one end of the tool is referred to as the front end 2, and the other end as the rear end. The front end 2 may also be referred to as the cutting edge, etc.

[0020] Furthermore, the direction perpendicular to the central axis C is called the radial direction. Within the radial direction, the direction approaching the central axis C is called the radially inward direction, and the direction moving away from the central axis C is called the radially outward direction. The direction of rotation around the central axis C is called the circumferential direction. Within the circumferential direction, the direction in which the tool is rotated during cutting is called the tool rotation direction T, and the opposite direction of rotation is called the opposite side of the tool rotation direction T or the anti-tool rotation direction.

[0021] In Figures 7 and 8, the direction along the thickness of the cutting insert 5 is called the thickness direction. The direction perpendicular to the thickness direction and axial direction of the cutting insert 5 is called the left-right direction. The direction approaching the central axis C along the left-right direction is called the central side of the left-right direction or the inside of the left-right direction. The direction moving away from the central axis C along the left-right direction is called the outside of the left-right direction. The thickness direction corresponds to a predetermined direction within the radial direction. The left-right direction corresponds to another predetermined direction within the radial direction that is different from the thickness direction.

[0022] Next, we will explain in detail each component of the replaceable-tip cutting tool 6. The tool body 1 is made of metal, such as steel. As shown in Figure 1, the tool body 1 is roughly cylindrical in shape and extends in the axial direction. As shown in Figures 1 to 6, the tool body 1 has an insert mounting seat 3 located at the tip 2 of the tool body 1, an insert fixing screw hole 2c located at the tip 2, and a shank portion which constitutes the part of the tool body 1 other than the tip 2. The shank portion is cylindrical in shape and extends in the axial direction.

[0023] The rear end of the shank portion of the tool body 1 is detachably attached to the spindle of a machine tool (not shown). The replaceable-tip cutting tool 6 is rotated by the spindle of the machine tool in the tool rotation direction T around the central axis C, and is also moved radially and axially, thereby performing cutting operations such as milling and contouring on the cutting surface (machined surface) of a workpiece, such as the surface of a mold.

[0024] As shown in Figures 4 to 6, the insert mounting seat 3 is concave, recessed into the tool from the tip surface and outer circumferential surface of the tip portion 2 of the tool body 1. A cutting insert 5 is detachably mounted on the insert mounting seat 3. The insert mounting seat 3 has a slit-shaped fitting groove 7.

[0025] The fitting groove 7 opens to the tip surface and outer circumference of the tool body 1 and penetrates the tool body 1 radially (left-right direction). The fitting groove 7 has a pair of planar inner walls 7a and 7b that are arranged parallel to each other with respect to the central axis C and face each other in the radial direction (thickness direction), and a bottom wall 7c that is located at the rear end of the fitting groove 7 and connected to the rear ends of the pair of inner walls 7a and 7b. The bottom wall 7c has a concave V-shape in cross-section that is recessed toward the rear end and faces toward the tip side in the axial direction.

[0026] Furthermore, the tool body 1 has a slit-shaped fitting groove 7 (insert mounting seat 3) at its tip 2, and has a pair of tip halves 2a and 2b that are spaced apart from each other in the radial direction (thickness direction) at the tip 2. The pair of tip halves 2a and 2b are each in the shape of a roughly semicircular plate.

[0027] The insert fixing screw hole 2c extends radially inward from the outer surface of one of the pair of tip halves 2a and 2b, through the fitting groove 7, and reaches into the other tip half 2b. The central axis of the screw hole 2c for insert fixing extends radially in the tip portion 2, specifically in a direction perpendicular to the direction in which the fitting groove 7 extends radially (left-right direction) (thickness direction).

[0028] Of the insert fixing screw holes 2c, the inner diameter of the hole formed in one end half 2a is larger than the inner diameter of the hole formed in the other end half 2b. Furthermore, the inner circumferential surface of the hole formed in the other end half 2b is provided with a female screw portion that engages with the male screw portion of the fixing screw 8. Of the insert fixing screw holes 2c, at least the hole formed in one end half 2a is a through hole. In this embodiment, each hole in one end half 2a and the other end half 2b are through holes.

[0029] The cutting insert 5 is made of a hard sintered body, such as cemented carbide. As shown in Figures 7 and 8, the cutting insert 5 is substantially flat. The cutting insert 5 has a concave pocket 9 recessed from the outer surface of the cutting insert 5, a rake face 10 positioned on the wall surface of the pocket 9 facing the tool rotation direction T, a relief face 11 positioned on the outer surface of the cutting insert 5, a cutting edge 4 positioned on the ridge where the rake face 10 and the relief face 11 are connected, a screw insertion hole 18 that penetrates the cutting insert 5 in the thickness direction, and a chisel portion 20 (see Figures 2 and 9) positioned at the center of the tip of the cutting insert 5.

[0030] The cutting insert 5 has a pair of sets consisting of a pocket 9, a rake face 10, a relief face 11, and a cutting edge 4. In other words, the cutting insert 5 has a pair of pockets 9, a pair of rake faces 10, a pair of relief faces 11, and a pair of cutting edges 4. That is, this cutting insert 5 is a two-blade cutting insert.

[0031] Each component of the pair of sets (a pair of pockets 9, a pair of rake faces 10, a pair of relief faces 11, and a pair of cutting edges 4) is arranged at intervals from each other around the central axis C. Specifically, the cutting insert 5 of this embodiment has a front-to-back inverted symmetrical shape (180° rotational symmetrical shape) with the central axis C as the center (axis of symmetry). Therefore, when the cutting insert 5 is rotated 180° around the central axis C, one of the cutting edges 4 coincides with the other cutting edge 4.

[0032] Of the cutting insert 5, the portion located towards the tip of the center O of the screw insertion hole 18 is roughly semicircular in shape. Of the cutting insert 5, the portion located towards the rear end of the center O of the screw insertion hole 18 is roughly polygonal in shape (roughly pentagonal in this embodiment).

[0033] On the pair of plate surfaces (front and back) of the cutting insert 5 facing the thickness direction, a pair of planar flat portions 16 and 17 are formed that extend in a direction perpendicular to the thickness direction (surface direction). In addition, on the surface facing the rear end side in the axial direction of the cutting insert 5, a top surface 19 with a convex V-shaped cross-section that protrudes toward the rear end side is formed.

[0034] When the cutting insert 5 is placed in the fitting groove 7 of the insert mounting seat 3, the pair of flat surfaces 16 and 17 come into contact with the pair of inner walls 7a and 7b of the fitting groove 7. The top surface 19 also comes into contact with the bottom wall 7c of the fitting groove 7. This positions the cutting insert 5 relative to the fitting groove 7 (insert mounting seat 3).

[0035] The pocket 9 is concave, recessed from the plate surface facing the thickness direction of the cutting insert 5, the tip surface facing the axial tip side, and the outer surface facing outward in the left-right direction. The rake face 10 is formed on the wall surface of the pocket 9 facing the tool rotation direction T, and in this embodiment, it is a convex curved surface that bulges in the tool rotation direction T. The relief face 11 is arranged across the tip surface facing the axial tip side and the outer surface facing outward in the left-right direction of the cutting insert 5, and is a curved surface that is convex toward the outer circumference of the tip of the tool.

[0036] The screw insertion hole 18 is circular in shape and penetrates the cutting insert 5 in the thickness direction, opening in one flat portion 16 and the other flat portion 17. A fixing screw 8 for fixing the cutting insert 5 to the insert mounting seat 3 is inserted through the screw insertion hole 18.

[0037] In detail, as shown in Figures 1 to 3, with the cutting insert 5 inserted into the fitting groove 7 of the insert mounting seat 3, a fixing screw 8 is inserted through the insert fixing screw hole 2c of one end half 2a. This fixing screw 8 is then inserted into the screw insertion hole 18 of the cutting insert 5 and screwed into the insert fixing screw hole 2c of the other end half 2b. This fastens and fixes the cutting insert 5 to the insert mounting seat 3.

[0038] As shown in Figure 7, each pair of cutting edges 4 extends from the axial tip to the radially outer end of the cutting insert 5. Each cutting edge 4 has a curved convex blade 41 that is convex toward the outer circumference of the tip of the cutting insert 5, and a substantially straight side blade 42 that is smoothly connected to the axial rear end S of the convex blade 41.

[0039] The convex curved blade 41 and the side blade 42 are smoothly connected such that they have a common tangent at their connection point. In this embodiment, the connection point between the convex curved blade 41 and the side blade 42 (i.e., the rear end of the convex curved blade 41, or endpoint S) corresponds to the outermost point of the cutting edge 4, which is radially outermost.

[0040] Specifically, in this embodiment, as shown in Figure 7, in a plan view of the cutting insert 5 viewed from the thickness direction of the cutting insert 5, the convex curved blade 41 has an arc shape that is convex toward the outer circumference of the tip of the cutting insert 5. The center O of the radius of curvature of the convex curved blade 41 and the center O of the screw insertion hole 18 coincide with each other. In this embodiment, the radius of curvature R of the convex curved blade 41 satisfies the relationship R = D / 2 when the diameter dimension (maximum dimension) of the rotational trajectory around the central axis C of the cutting edge 4 is the blade diameter dimension D.

[0041] As shown in Figure 8, in a side view of the cutting insert 5 viewed from the left and right directions, the convex curved blade 41 has a curved shape that is convex in the direction of tool rotation T. Also, as shown in Figure 2, in a front view of the cutting insert 5 viewed from the axial tip side (insert tip view), the convex curved blade 41 has a curved shape that is convex in the direction of tool rotation T.

[0042] In this embodiment, in the insert plan view shown in Figure 7, the angle θ at which a virtual straight line VL passing through the center O of the radius of curvature of the convex curve blade 41 and a predetermined point F on the convex curve blade 41 inclins with respect to the central axis C is defined as the "radiation angle θ". The radiation angle θ is set to a predetermined value between 0° and 90°. Furthermore, in a virtual plane VS that includes the virtual straight line VL and extends along the thickness direction, the angle α at which the rake face 10 of the convex curve blade 41 inclins with respect to a reference plane Pr perpendicular to the thickness direction is defined as the "normal direction rake angle α".

[0043] Figure 10 is a graph showing the relationship between the radiation angle θ and the rake angle α in the normal direction. In the graph of Figure 10, this embodiment is represented as an "example". As shown in Figure 10, in this embodiment (example), the rake angle α in the normal direction is a negative angle (negative angle) over the entire length of the convex curve blade 41. Further, the rake angle α in the normal direction of this embodiment (example) gradually increases toward the negative angle side as it approaches the end point S on the rear end side of the convex curve blade 41 (that is, as the radiation angle θ approaches 90°).

[0044] More specifically, the rake angle α in the normal direction of this embodiment (example) gradually increases toward the negative angle side as it approaches the end point S on the rear end side of the convex curve blade 41 (that is, as the radiation angle θ increases) at least in the region where the radiation angle θ is 15° or more and 90° or less. In the region where the radiation angle θ is 0° or more and 15° or less, the rake angle α in the normal direction of this embodiment (example) may gradually increase toward the negative angle side as the radiation angle θ increases, may gradually increase toward the positive angle (positive angle) side, or may be constant.

[0045] As shown in Figure 10, when the radiation angle θ is 0° or more and 15° or less, the rake angle α in the normal direction of this embodiment (example) is, for example, -6° to -8°, specifically about -7°. Also, when the radiation angle θ is 0° or more and 90° or less, the rake angle α in the normal direction of this embodiment (example) is, for example, -6° to -12°.

[0046] In this embodiment (example), when the change amount of the rake angle α in the normal direction per 15° of the radiation angle θ (per unit angle of 15°) is defined as σ1, σ1 ≤ 3.0°. The change amount σ1 of the rake angle α in the normal direction is more preferably σ1 ≤ 2.0°, and more desirably σ1 ≤ 1.0°.

[0047] Here, in this embodiment, as shown in Figure 8, in the side view of the insert seen from the left-right direction perpendicular to the thickness direction and the axial direction of the cutting insert 5, the angle β of the tangent TL passing through a predetermined point F on the convex curve blade 41 with respect to the central axis C is defined as the "axial rake angle β".

[0048] Figure 11 is a graph showing the relationship between the radiation angle θ and the axial rake angle β. In the graph of Figure 11, this embodiment is represented as "Example". As shown in Figure 11, the axial rake angle β of this embodiment (Example) gradually increases toward the positive angle as it approaches the endpoint S on the rear end side of the convex curve blade 41 (i.e., as the radiation angle θ increases toward 90°). Furthermore, in the process of the radiation angle θ increasing, the axial rake angle β of this embodiment (Example) changes from the negative angle side to the positive angle side when the radiation angle θ exceeds 60° and is 75° or less (70° or less in the illustrated example).

[0049] Furthermore, in this embodiment (example), when the change in the axial rake angle β per 15° angle range of the radiation angle θ (per unit angle of 15°) is defined as σ2, the change in σ2 in the region of radiation angle θ between 60° and 90° is smaller than the change in σ2 in the region of radiation angle θ between 0° and 60°.

[0050] More specifically, when the radiation angle θ is between 60° and 90°, the above change amount σ2 is set to σ2 ≤ 6.0°. When the radiation angle θ is between 60° and 90°, the above change amount σ2 is more preferably set to σ2 ≤ 5.0°, and even more preferably to σ2 ≤ 4.0°.

[0051] As shown in Figures 7 and 8, the side blade 42 is connected to the convex curve blade 41 via the rear end endpoint (the outermost point of the cutting edge 4) S of the convex curve blade 41. The side blade 42 extends in a substantially straight line. Specifically, as shown in Figure 7, the side blade 42 extends radially inward (inward in the left-right direction) as it moves from the outermost point S toward the rear end in the axial direction. Also, as shown in Figure 8, the side blade 42 extends in the direction opposite to the tool rotation as it moves toward the rear end in the axial direction.

[0052] Figure 9 is a front view of the cutting insert 5, seen from the axial tip side near the center of the tip, and shows an enlarged view of the area near the center of the tip of the cutting insert 5. As shown in Figure 9, the chisel portion 20 is positioned on the ridge where the relief faces 11 of the pair of cutting edges 4 are connected. In this embodiment, this ridge portion is sometimes called the chisel edge 21. The chisel portion 20 has a straight chisel edge 21. The central axis C is located on the chisel edge 21.

[0053] As shown in Figure 9, in a front view of the cutting insert 5 viewed from the axial tip side, the tip of the convex curved blade 41 (the radially inward end) extends in a straight line. In this front view of the insert, the very tip (radially inward endpoint) 41a of the convex curved blade 41 does not reach the central axis C. That is, the very tip 41a of the convex curved blade 41 is positioned away from the central axis C.

[0054] The chisel portion 20 is positioned between the leading edges 41a of each convex curved blade 41 of the pair of cutting blades 4. The leading edges 41a of each convex curved blade 41 of the pair of cutting blades 4 are connected to both ends of the chisel edge 21. In this embodiment, in the insert front view shown in Figure 9, the chisel angle γ formed between the leading edge of the convex curved blade 41 and the chisel edge 21 of the chisel portion 20 is, for example, 165° or more, specifically about 167°.

[0055] Here, in the front view of the insert in Figure 9, the dimension along the width direction of the chisel portion 20 perpendicular to the blade length direction in which the tip of the convex curved blade 41 extends is defined as the chisel thickness L1, and the length dimension of the chisel edge 21 is defined as the chisel edge length L2. In this embodiment, the chisel thickness L1 is, for example, 0.175 mm or less, specifically about 0.168 mm. The chisel edge length L2 is, for example, 0.7 mm or more, specifically about 0.73 mm. The ratio of the chisel edge length L2 to the chisel thickness L1 (L2 / L1) is, for example, 3.9 or more and 5.0 or less, specifically about 4.32.

[0056] As shown in Figure 9, the pair of concave pockets 9 are arranged on the rake face 10 side (tool rotation direction T) of each of the pair of cutting edges 4 around the central axis C. The pocket 9 provided on the rake face 10 side of one of the pair of cutting edges 4 is positioned adjacent to the relief face 11 of the other cutting edge 4 in the direction opposite to the tool rotation.

[0057] In the front view of the insert shown in Figure 9, the angle ζ formed between the ridge portion 23 where the relief surface 11 of the cutting edge 4 and the pocket 9 are connected, and the extension line 22 of the tip of the convex curved blade 41, is defined as the "pocket opening angle ζ". In this embodiment, the pocket opening angle ζ is, for example, 95° or more and 105° or less, and specifically about 104°.

[0058] In the cutting insert 5 and replaceable cutting tool 6 of this embodiment described above, the normal rake angle α of the rake face 10 of the convex curved blade 41 is a negative angle along the entire length of the convex curved blade 41, and gradually increases towards the negative angle as it approaches the rear end S of the convex curved blade 41. Furthermore, the amount of change σ1 of the normal rake angle α per 15° angle range of the radial angle θ is kept small, at 3.0° or less. By using such a normal rake angle α profile, the surface roughness of the cutting surface (machined surface) such as gently curved surfaces and vertical walls formed on the workpiece by cutting can be kept small, thereby improving the characteristics of the cutting surface.

[0059] Furthermore, the rake angle α in the normal direction gradually increases towards the negative angle as it approaches the rear end, and the amount of change σ1 is kept small at 3.0° or less, thereby reducing the overall cutting load on the convex curve blade 41. In addition, near the rear end point S of the convex curve blade 41 (around the radiation angle θ = 90°), the rake angle α in the normal direction is maximized towards the negative angle, ensuring a large cross-sectional thickness (tool angle) near the rear end of the convex curve blade 41, as well as ensuring cutting edge strength. The amount of change σ1 of the rake angle α in the normal direction is more preferably 2.0° or less, and even more preferably 1.0° or less.

[0060] Here, the vicinity of the rear end endpoint S of the convex curved blade 41 corresponds to the radially outer end of the convex curved blade 41, and therefore the rotational speed (circumferential speed) is maximum at this point. For this reason, as described above, if the normal rake angle α is maximized on the negative side near the rear end endpoint S of the convex curved blade 41, the cutting load near this endpoint S tends to be greater.

[0061] Therefore, in this embodiment, in the region where the radiation angle θ is 60° to 90°, corresponding to the vicinity of the rear end endpoint S of the convex curve blade 41, the change in the axial rake angle β σ2 is reduced to 6.0° or less. This makes it possible to secure a larger wall thickness dimension for the portion corresponding to the back metal of the convex curve blade 41 (the portion adjacent to the convex curve blade 41 in the anti-tool rotation direction) near the rear end endpoint S of the convex curve blade 41, thereby increasing the insert strength. Furthermore, in the region where the radiation angle θ is 60° to 90°, the change in the axial rake angle β σ2 is more preferably 5.0° or less, and even more preferably 4.0° or less.

[0062] In this embodiment, when the cutting insert 5 is viewed from the axial tip side, the chisel angle γ formed between the tip of the convex curved blade 41 and the chisel edge 21 of the chisel portion 20 is 165° or more. Also, in this front view of the insert, when L1 is the chisel thickness along the width direction of the chisel portion 20 perpendicular to the blade length direction in which the tip of the convex curved blade 41 extends, and L2 is the length of the chisel edge 21, L2 / L1 is 3.9 or more and 5.0 or less.

[0063] In the above configuration, the chisel angle γ is set to a large value of 165° or more, which suppresses excessive bending (abrupt bending) of the connection portion between the tip of the convex curved blade 41 and the chisel edge 21. As a result, stress concentration at the connection portion during cutting is suppressed, and chipping from the vicinity of the chisel portion 20 is suppressed.

[0064] Furthermore, since L2 / L1 is large, at 3.9 or more, the chisel edge length L2 is large, or (and) the chisel thickness L1 is small. When the chisel edge length L2 is large, a large volume is secured in the inner circumferential portion of the concave pocket 9 adjacent to the chisel portion 20. This suppresses chip jamming near the chisel portion 20 and improves chip evacuation. Also, when the chisel thickness L1 is small, the contact area (ground contact area) between the chisel portion 20 and the cutting surface (machined surface) can be kept small on the chisel portion 20, which is the tool rotation center where the rotational speed (circumferential speed) is approximately zero, thereby improving the cutting surface properties.

[0065] Furthermore, if L2 / L1 is 5.0 or less, good cutting surface properties can be obtained. In other words, it is suppressed that the chisel edge length L2 does not become too large, which increases the contact resistance between the chisel portion 20 and the cutting surface. Also, it is suppressed that the chisel thickness L1 does not become too small, which makes the chisel portion 20 prone to chipping.

[0066] In this embodiment, the pocket opening angle ζ is defined as the angle ζ formed between the ridge portion 23, where the relief surface 11 of the cutting edge 4 and the pocket 9 are connected, and the extension line 22 of the tip of the convex curved blade 41, when the cutting insert 5 is viewed from the axial tip side of the insert. The pocket opening angle ζ is an obtuse angle, and 95° ≤ ζ ≤ 105°.

[0067] As described above, when the pocket opening angle ζ is obtuse, specifically 95° or more, a large volume is secured in the inner circumferential portion of the concave pocket 9 adjacent to the chisel portion 20. This suppresses chip jamming near the chisel portion 20 and improves chip evacuation.

[0068] Furthermore, if the pocket opening angle ζ is 105° or less, the thickness of the relief surface 11 of the cutting insert 5 can be ensured, and the cutting insert 5 can be given appropriate strength.

[0069] Furthermore, in this embodiment, the normal rake angle α gradually increases towards the negative angle as it approaches the rear end point S of the convex curve blade 41, when the radiation angle θ is between 15° and 90°.

[0070] In this case, over a wide range where the radiation angle θ is between 15° and 90°, the normal rake angle α is gradually increased towards the negative angle as it approaches the rear end endpoint S of the convex curve blade 41. Therefore, the cutting edge strength of the convex curve blade 41 can be more stably ensured.

[0071] In this embodiment, when the radiation angle θ is between 0° and 15°, the normal rake angle α is set to -6° to -8°.

[0072] As described above, when the normal rake angle α is set to a negative angle of -6° to -8° in the tip-side region of the convex curve blade 41 with a radiation angle θ of 0° to 15°, chip evacuation is improved and the cutting surface properties can be improved.

[0073] The present invention is not limited to the embodiments described above, and modifications to the configuration, etc., are possible without departing from the spirit of the invention, as described below, for example.

[0074] In the embodiments described above, the base material of the cutting insert 5 can be a cemented carbide containing tungsten carbide (WC) and cobalt (Co), or, for example, a ceramic made from cermet, high-speed steel, titanium carbide, silicon carbide, silicon nitride, aluminum nitride, aluminum oxide, and mixtures thereof, a cubic boron nitride sintered body, a diamond sintered body, polycrystalline diamond, or a hard phase made from cubic boron nitride, and a bonding phase such as ceramics or iron group metals fired under ultra-high pressure. Furthermore, the tool body 1 can be made from alloy tool steel such as SKD61, or it can be made by joining alloy tool steel such as SKD61 with cemented carbide.

[0075] The present invention may be combined in any way that does not depart from the spirit of the invention, as described in the above embodiments and modifications, and the configurations may be added, omitted, substituted, or otherwise modified. Furthermore, the present invention is not limited by the above embodiments, but is limited only by the claims.

[0076] The present invention will be described in detail below with reference to examples. However, the present invention is not limited to these examples.

[0077] [Machining Confirmation Test] Machining was performed using the cutting inserts in the embodiment of the present invention and in the conventional comparative examples 1 to 3, and the properties of the cut surface (machined surface) were confirmed.

[0078] In each cutting test, the feed direction refers to the direction in which the tool is advanced by the machine's movement to cut the workpiece, and the opposite direction. The pitch direction refers to the direction perpendicular to the feed direction.

[0079] As an embodiment of the present invention, a cutting insert 5 described in the above-described embodiment was prepared. In addition, as comparative examples 1 to 3, cutting inserts were prepared that differed from the cutting insert 5 of the embodiment in the configuration of the convex curved blade 41 and the vicinity of the chisel portion 20.

[0080] Specifically, the cutting inserts in Comparative Examples 1 to 3 differ from the cutting insert 5 of the embodiment in the relationship between the radiation angle θ of the convex curved blade 41 shown in Figure 10 and the normal rake angle α, and in the relationship between the radiation angle θ of the convex curved blade 41 shown in Figure 11 and the axial rake angle β.

[0081] Furthermore, as shown in Table 1 below, the cutting inserts of Comparative Examples 1 to 3 differ from the cutting insert 5 of the embodiment in the configuration near the chisel portion 20. In Table 1, the values ​​in parentheses shown alongside the values ​​of "Chisel Angle γ" represent the angle (180°-γ) formed between the extension line 22 of the tip of the convex curved blade 41 and the chisel edge 21 in the front view of the insert shown in Figure 9.

[0082]

[0083] Using an indexable cutting tool with the cutting inserts described above in the Examples and Comparative Examples 1 to 3 mounted on the tool body (holder), cutting of gently curved surfaces and vertical walls were performed under the following cutting conditions.

[0084] <Cutting conditions for gently curved surfaces> • Machine tool used: MAKINO (registered trademark) V77 • Workpiece material: FCD700 (equivalent to GGG70L) • Spindle speed: n = 7000 min －１- Feed rate: Vf = 6600 mm / min - Axial depth of cut: ap = 0.07 mm - Radial depth of cut: ae = 0.5 mm - Cutting time: 2 hours - Cutting surface: Cutting a gently curved surface with an inclination angle that changes gradually between 5° and 14° relative to the horizontal plane.

[0085] The surface roughness Ra of the cut surface was measured in both the pitch direction and the feed direction under the above cutting conditions. The results are shown in Table 2 below. The criteria for evaluating the surface roughness Ra of the cut surface were as follows: ・A…Ra ≤ 0.7 μm, indicating particularly excellent cut surface properties. ・B…0.7 μm < Ra < 1.0 μm, indicating good cut surface properties. ・C…Ra ≥ 1.0 μm, indicating poor cut surface properties.

[0086]

[0087] As shown in Table 2, the embodiment of the present invention received a B rating in the pitch direction and an A rating in the feed direction, confirming that the cutting surface properties of gently curved surfaces were superior to those of Comparative Examples 1 to 3 in both the pitch and feed directions.

[0088] <Cutting conditions for vertical walls> • Machine tool used: MAKINO (registered trademark) V77 • Workpiece material: FCD700 (equivalent to GGG70L) • Spindle speed: n = 7000 min －１ • Feed rate: Vf = 6600 mm / min • Axial depth of cut: ap = 0.5 mm • Radial depth of cut width: ae = 0.07 mm • Tool overhang: 120 mm • Cutting time: Down cut only, 1 hour • Cutting surface: Cutting a vertical wall with an 80° inclination to the horizontal plane

[0089] The vertical wall was machined under the above cutting conditions, and the surface roughness Ra of the machined surface was measured in both the pitch direction and the feed direction. The results are shown in Table 3 below. The criteria for evaluating the surface roughness Ra of the vertical wall were as follows: ・A…Ra ≤ 0.47 μm, indicating particularly excellent machined surface properties. ・B…0.47 μm < Ra < 0.49 μm, indicating good machined surface properties. ・C…Ra ≥ 0.49 μm, indicating poor machined surface properties.

[0090]

[0091] As shown in Table 3, the embodiments of the present invention achieved an evaluation of B or higher (A or B) in both the pitch direction and the feed direction, demonstrating that the quality of the cut surface properties of vertical walls can be stably improved compared to Comparative Examples 1 to 3.

[0092] The cutting insert and replaceable cutting tool of the present invention can improve the surface properties of cut materials, such as gently curved surfaces and vertical walls. Therefore, it has industrial applicability.

[0093] 1...Tool body, 2...Tip, 4...Cutting edge, 5...Cutting insert, 6...Interchangeable cutting tool, 9...Pocket, 10...Rake face, 11...Flap face, 20...Chisel part, 21...Chisel edge, 22...Extension of the tip of the convex curved blade, 23...Ridge where the flank face and pocket are connected, 41...Convex curved blade, C...Central axis, F...A predetermined point on the convex curved blade, L1...Chisel thickness, L2...Chisel edge length, O...Center of the radius of curvature of the convex curved blade, Pr...Reference plane, S...Endpoint on the rear end of the convex curved blade, TL...Tangency, VL...Virtual straight line, VS...Virtual plane, α...Normal rake angle, β...Axial rake angle, γ...Chisel angle, ζ...Pocket opening angle, θ...Radiation angle, σ1...Change in normal rake angle, σ2...Change in axial rake angle

Claims

1. A plate-shaped cutting insert detachably attached to the tip of a tool body that can be rotated around a central axis, comprising a pair of cutting edges spaced apart from each other around the central axis, each cutting edge having a curved convex curved blade that is convex toward the outer circumference of the tip of the cutting insert, defined as the radial angle, in a plan view of the cutting insert viewed from the thickness direction of the cutting insert, the angle at which a virtual line passing through the center of the radius of curvature of the convex curved blade and a predetermined point on the convex curved blade is inclined with respect to the central axis, defined as the normal rake angle, in a virtual plane that includes the virtual line and extends along the thickness direction, the angle at which the rake face of the convex curved blade is inclined with respect to a reference plane perpendicular to the thickness direction, defined as the axial rake angle, in a side view of the cutting insert viewed from the left and right directions perpendicular to the thickness direction and axial direction, the angle at which a tangent line passing through a predetermined point on the convex curved blade is inclined with respect to the central axis, A cutting insert wherein the normal rake angle is a negative angle over the entire length of the convex curved blade, and when the radiation angle is 15° or more and 90° or less, it gradually increases towards the negative side as it approaches the rear end of the convex curved blade, and when the change in the normal rake angle per 15° of the angular range of the radiation angle is denoted as σ1, σ1 ≤ 3.0°, and when the change in the axial rake angle per 15° of the angular range of the radiation angle is denoted as σ2, when the radiation angle is 60° or more and 90° or less, σ2 ≤ 6.0°.

2. The cutting insert according to claim 1, comprising a chisel portion positioned on the ridge where the relief faces of the pair of cutting blades are connected, wherein, in a front view of the cutting insert viewed from the axial tip side, the chisel angle formed between the tip of the convex curved blade and the chisel edge of the chisel portion is 165° or more, and in a front view of the insert, when L1 is the chisel thickness along the width direction of the chisel portion perpendicular to the blade length direction in which the tip of the convex curved blade extends, and L2 is the length of the chisel edge, L2 / L1 is 3.9 or more and 5.0 or less.

3. A cutting insert according to claim 1 or 2, comprising a pair of concave pockets arranged on the rake face side of each of the pair of cutting edges around the central axis, wherein, when the cutting insert is viewed from the axial tip side, the angle formed between the ridge portion where the relief surface of the cutting edge and the pocket are connected and the extension line of the tip of the convex curved blade is defined as the pocket opening angle ζ, and the angle is 95° ≤ ζ ≤ 105°.

4. The cutting insert according to claim 1 or 2, wherein, when the radiation angle is 0° or more and 15° or less, the normal rake angle is -6° to -8°.

5. An interchangeable cutting tool comprising a tool body that can be rotated around a central axis, and a cutting insert according to claim 1 or 2 that is detachably attached to the tip of the tool body.

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