Cutting insert and indexable insert cutting tool

Abstract

The cutting insert (1) is formed with two cutting edges (5, 6) on an intersection ridge portion of a rake face (2) and a flank face (4), the two cutting edges (5, 6) each having a circular-arc-shaped cutting edge portion (5a, 6a) extending in a circular-arc shape in plan view and a straight cutting edge portion (5b, 6b). In the cutting edges (5, 6), at least the circular-arc-shaped cutting edge portion (5a, 6a) has a convex curved portion (17) that approaches the seating face (3) after being away from the seating face (3) as it is away from the straight cutting edge portion (5b, 6b), and in side view, the circular-arc-shaped cutting edge portion (5a, 6a) has a curvature change point (Q1, Q2) between a most convex point (S1, S2) farthest from the seating face (3) and a nose tip end (2a, 2b) of the circular-arc-shaped cutting edge portion.

Description

Technical Field

[0001] This invention relates to cutting inserts and indexable insert cutting tools.

[0002] This application claims priority based on Japanese Patent Application No. 2021-030531, filed on February 26, 2021, the contents of which are incorporated herein by reference. Background Technology

[0003] As a cutting insert mounted on an indexable insert cutting tool, for example, Patent Document 1 discloses a cutting insert comprising: a rake face facing the rotational direction of the tool body; a seat face facing the side opposite to the rake face and seated on the bottom surface of the insert holder; and a flank face extending around the rake face and the seat face. Two cutting edges are formed on the intersection of the rake face and the flank face, each having an arc-shaped cutting edge portion and a straight cutting edge portion. The arc-shaped cutting edge portion extends in an arc shape when viewed from above in a direction opposite to the rake face, and the straight cutting edge portion extends tangentially to the arc-shaped cutting edge portion. The arc-shaped and straight cutting edge portions are alternately arranged in the circumferential direction of the rake face. Furthermore, the arc-shaped cutting edge portion of the main cutting edge and the arc-shaped cutting edge portion of the secondary cutting edge are formed into a convex curve that moves away from the seat surface side as it moves away from the straight cutting edge portion and then moves closer to the seat surface side. Therefore, Patent Document 1 describes that since the arc-shaped cutting edge portion gradually bites into and cuts into the workpiece from the most convex point that is furthest from the seat surface during cutting, cutting resistance can be reduced.

[0004] Patent Document 1: Japanese Patent No. 6540928

[0005] However, if the cutting insert described in Patent Document 1 is used for cutting with a depth of cut that is not suitable for the design position of the convex point, there is a problem that the life of the cutting insert is easily shortened due to insufficient strength of the cutting edge. Although prior art document 1 describes that the position of the convex point can be set within a wide range on the arc-shaped cutting edge using the first cross angle and the second cross angle, in reality, it is necessary to choose whether to set the convex point at a position corresponding to machining with a large depth of cut or at a position corresponding to machining with a small depth of cut.

[0006] For example, if the cutting insert is set at a position corresponding to a large depth of cut, and is used for a small depth of cut, a defect caused by stress concentration will occur at the tip of the cutting insert, resulting in a shorter lifespan.

[0007] On the other hand, when the maximum protrusion is set at a position corresponding to machining of materials with low cutting depth such as high hardness and difficult-to-cut materials, the cutting insert may also experience damage (cracks) due to stress concentration when machining with a cutting depth exceeding the maximum protrusion during machining where the cutting depth changes, thus resulting in a shorter lifespan.

[0008] For example, when using ball end mills to machine complex metal mold shapes, the depth of cut varies at each machining location. Applying a cutting tool locally that corresponds to the depth of cut is impractical.

[0009] Furthermore, although the depth of cut varies when machining weld overlays, it is impractical to change tools based on the depth of cut in this case. Weld overlays are used for the purpose of repairing metal molds and ensuring local strength. Since unevenness is generated on the machined surface at each machining location as described above, variations in the depth of cut due to these unevennesses are common. Summary of the Invention

[0010] The present invention was made in this context, and its object is to provide a cutting insert and an indexable insert type cutting tool that improves the strength of the tip side by dispersing stress during cutting at a cutting depth with a width wider than conventionally, thereby suppressing cracks generated on the cutting edge.

[0011] One aspect of the present invention provides a cutting insert detachably mounted on an insert holder at the front end of a tool body formed in an indexable insert cutting tool rotating about an axis. The cutting insert includes: a rake face facing the direction of rotation of the tool body; a seat face facing the side opposite to the rake face and seated on the bottom surface of the insert holder; and a flank face extending around the rake face and the seat face. Two cutting edges are formed at the intersection of the rake face and the flank face. Each cutting edge has an arc-shaped cutting edge portion and a straight cutting edge portion. When viewed from above in a direction opposite to the rake face, the arc-shaped cutting edge portion extends in an arc shape, and the straight cutting edge portion extends tangentially to the arc-shaped cutting edge portion. The two cutting edges are formed in a manner in which the arc-shaped cutting edge portion and the straight cutting edge portion are alternately arranged in the circumferential direction of the rake face. In the cutting edge, at least the arc-shaped cutting edge portion has a convex curve portion that moves away from the seat surface as it moves away from the straight cutting edge portion and then moves closer to the seat surface. When viewed from the side in a direction opposite to the flank face, with the point on the convex curve portion furthest from the seat surface as the most convex point, the arc-shaped cutting edge portion has a point of curvature change between the most convex point and the tip of the arc-shaped cutting edge portion.

[0012] According to this structure, when viewed from the side facing the flank of the cutting edge, the arc-shaped cutting edge has a curvature change point between the most convex point furthest from the seat surface on the convex curve portion and the tip of the arc-shaped cutting edge. This results in a shape with varying curvature along the boundary of the curvature change point. In cutting processes with a greater depth of cut than usual, the stress during cutting is dispersed over a wider range within the arc-shaped cutting edge. This prevents defects or breakage (cracks) in the cutting insert and improves the overall strength of the arc-shaped cutting edge, thereby suppressing cracks generated on the cutting edge. Furthermore, by setting a curvature change point between the most convex point and the tip of the cutting edge, the cutting edge shape is smoother in the initial stage of the cutting insert biting into the workpiece, thus reducing chip distortion. Therefore, it is possible to prevent distorted chips from exerting irregular forces on the cutting insert and the workpiece.

[0013] Regarding a cutting insert according to one aspect of the present invention, when viewed from the side view relative to the normal direction of the tangent of the arc-shaped cutting edge passing through the most convex point, the cutting edge includes at least two arcs with different curvatures. When the radius of the arc on the tip side is set as R1 and the radius of the arc on the most convex point side is set as R2, the relationship R1 < R2 can be satisfied.

[0014] According to this structure, among the two arc radii R1 and R2 with different curvatures that constitute part of the cutting edge, the arc radius R1 on the tip side is smaller than the arc radius R2 on the most convex point side. The arc on the tip side has a steep curve, so the cutting edge will make smooth contact with the workpiece, the impact on the cutting edge is reduced, and the effect of dispersing stress and reducing cutting resistance can be achieved.

[0015] Furthermore, according to this structure, the cutting edge from the tip side to the most convex point side can include two arcs with different curvatures. For example, the arcs with different curvatures or the arc on the most convex point side and the most convex point can be connected by a curve or a straight line. Alternatively, the arc on the most convex point side of the two arcs with different curvatures can be connected by a curve or a straight line. In this case, the straight line can be a tangent to the arc or not. On the other hand, the present invention is configured such that the arc-shaped cutting edge gradually contacts the workpiece during cutting to mitigate the impact acting on the tool tip during machining. Therefore, the straight line is formed parallel to the seat surface or moves away from the seat surface as it moves from the tip towards the most convex point. Similarly, the curve is also formed so that it always moves away from the seat surface as it moves from the tip towards the most convex point.

[0016] In one aspect of the present invention, the cutting blade may be a structure in which the arc radius R1 is less than 1 / 2 of the arc radius R2, preferably less than 1 / 3, and more preferably less than 1 / 4.

[0017] According to this structure, the arc radius R1 is formed to be at least half the size of the arc radius R2, thereby creating a steep curve on the cutting edge at the tip, which significantly reduces the impact on the cutting edge. Furthermore, by forming the arc radius R1 to be less than one-third to one-quarter the size of the arc radius R2, the curve becomes even steeper, further mitigating the impact on the tip. The lower limit of R1 / R2 is not limited, but in reality it is approximately 1 / 100.

[0018] One aspect of the cutting insert of the present invention can be structured as follows: when viewed from the side, the cutting edge is constructed with the curvature change point as the boundary, consisting of a first curved cutting edge that convexes upward relative to the seat surface on the tip side and a second cutting edge that convexes upward relative to the seat surface on the most convex point side, wherein the second cutting edge is formed by a curved second cutting edge or a straight second cutting edge with a curvature smaller than that of the first cutting edge, and the intersection of the first cutting edge and the second cutting edge is the curvature change point.

[0019] According to this structure, with the curvature change point at the intersection of the two first cutting edges with different curvatures as the boundary, the first cutting edge located on the tip side of the tool tip has a steep curve shape compared with the second cutting edge located on the most convex side. Therefore, the cutting edge will make smooth contact with the workpiece, and the impact on the tool tip will be reduced, thereby achieving the effect of dispersing stress and reducing cutting resistance.

[0020] Furthermore, the curvature of the straight line is "0". Therefore, since the curvature of the second cutting edge is also less than that of the first cutting edge when the second cutting edge is a straight line, the same effect can be obtained as when the second cutting edge is formed by a curve with a curvature smaller than that of the first cutting edge.

[0021] In one aspect of the present invention, the cutting insert may have a structure in which the curvature of the first cutting edge is more than twice that of the curvature of the second cutting edge, preferably more than three times, and more preferably more than four times.

[0022] According to this structure, when the curvature of the second cutting edge is more than twice that of the first cutting edge, the impact acting on the tool tip becomes sufficiently small. On the other hand, if the curvature of the second cutting edge is less than twice that of the first cutting edge, then the curvature of the first cutting edge cannot be considered sufficiently large, which would cause stress to easily concentrate on the cutting edge during machining.

[0023] In one aspect of the cutting blade of the present invention, in the arc-shaped cutting edge portion viewed from the side, the portion in which the ratio of the height from the tip of the blade to any cutting edge ridge in the direction perpendicular to the seat surface to the height from the tip of the blade to the most convex point is 90% or more may be the second cutting edge.

[0024] According to this structure, in the direction perpendicular to the seating surface, the height from the tip of the cutting tool to the point of curvature change is more than 90% of the height from the point of curvature change to the most convex point. Furthermore, with the point of curvature change as the boundary, the tip side forms a steeper curve than the most convex point side. Therefore, the cutting edge makes smooth contact with the workpiece, reducing the impact on the cutting tip. The upper limit of the height from the tip of the cutting tool to the point of curvature change is not limited relative to the height from the point of curvature change to the most convex point, but in reality it is around 98%.

[0025] One aspect of the cutting insert of the present invention may have the following structure: a groove having a wall surface that can abut against a protrusion protruding from the bottom surface of the insert mount, the groove being formed as two, separated by a mounting hole for mounting the cutting insert, the curvature change point being formed at a point closer to the tip of the insert than one of the two grooves that is closer to the arcuate cutting edge.

[0026] According to this structure, a curvature change point is formed at the tip of the tool, which is closer to the front end of the tool tip than the groove near the arc-shaped cutting edge. This ensures the wall thickness at the curvature change point and improves the strength of the tool tip.

[0027] In one aspect of the cutting insert of the present invention, the arc-shaped cutting edge portion may be constructed from at least two arc-shaped first cutting edges, second cutting edges to Nth cutting edges (N is an integer greater than or equal to 2) with different arc radii, starting from a position corresponding to the tool tip side. The arc radius of the first cutting edge on the tool tip side is smaller than the arc radii of the second to Nth cutting edges other than the first cutting edge. In the first cutting edge, the wedge angle formed by the flank face and the rake face gradually decreases from the second cutting edge side toward the tool tip side.

[0028] According to this structure, the wedge angle of the cutting edge is set to gradually decrease from the rear end of the first cutting edge of the arc-shaped cutting edge toward the front end. This increases the clearance angle of the cutting edge when cutting with the tip tip and suppresses the aggravation of the wear on the flank face of the tip tip.

[0029] Furthermore, in such tools, the tip of the arc-shaped cutting edge is typically subjected to an ejection force from the Z-axis direction during cutting, thus increasing the likelihood of damage. Additionally, while a larger wedge angle generally corresponds to a thicker wall and higher cutting strength, when machining workpieces made of high-hardness steel, a small clearance angle can lead to variations in cutting edge life even with a large wall thickness. In contrast, in the method described above, by gradually increasing the clearance angle of the tool tip from the rear end to the front end of the first cutting edge, the clearance angle at the tip of the arc-shaped cutting edge is ensured to a certain extent during cutting, thereby stabilizing the life of the tip of the arc-shaped cutting edge.

[0030] One aspect of the indexable insert cutting tool of the present invention can be structured as follows: when the center point of the arc-shaped cutting edge located on the axis is defined as P, and the angle formed by the line connecting the center point and the most convex point and the axis is set as θ1, and the angle formed by the line connecting the center point and the curvature change point and the axis is set as θ2, θ2 < θ1, 30° ≤ θ1 ≤ 50°, 15° ≤ θ2 ≤ 40°, preferably in the range of 40° ≤ θ1 ≤ 50°, 17° ≤ θ2 ≤ 37°.

[0031] According to this structure, a point of curvature change is formed on the tip side closer to the convex point than the most prominent point, which can distribute cutting stress over a wider area of ​​the cutting edge. Therefore, it can avoid defects or breakage (cracks) caused by stress concentration. This improves the strength of the tip side and suppresses cracks on the cutting edge. Furthermore, it reduces cutting resistance.

[0032] One aspect of the indexable insert cutting tool of the present invention can be structured as follows: when the distance from the tip of the cutting edge on the cutting insert to the point of curvature change is set as H in the direction along the axis, and the diameter of the tool body is set as D, the relationship D / 30≤H≤D / 10 is satisfied.

[0033] According to this structure, regardless of the depth of cut which varies with the tool diameter, it is possible to avoid stress concentration on the cutting edge and to mitigate the impact on the cutting edge tip during cutting.

[0034] Furthermore, regarding an indexable insert cutting tool according to one aspect of the present invention, the arc-shaped cutting edge is constructed sequentially from a position corresponding to the tool tip side by at least two arc-shaped first cutting edges, second cutting edges to Nth cutting edges (N being an integer greater than or equal to 2) with different arc radii. The arc radius of the first cutting edge on the tool tip side is smaller than the arc radii of the second to Nth cutting edges other than the first cutting edge. In the first cutting edge, from the second cutting edge side to the tool tip side, the clearance angle formed by the flank face of the cutting insert and the workpiece face gradually increases.

[0035] According to this structure, in the first cutting edge of the arc-shaped cutting edge, the clearance angle of the cutting blade gradually increases from the second cutting edge side to the tool tip side. This allows for a relatively larger clearance angle of the cutting edge when cutting with the tip tip, and also suppresses the aggravation of wear on the flank face of the tip tip.

[0036] Furthermore, from the second cutting edge side to the tool tip side, the clearance angle of the first cutting edge of the cutting insert gradually increases, thereby ensuring the clearance angle to a certain extent during cutting and stabilizing the lifespan of the front end of the arc-shaped cutting edge.

[0037] Regarding one aspect of the indexable insert cutting tool of the present invention, when a plurality of cutting inserts are mounted on the tool body, and when the difference between the lowest point of any one cutting insert and the lowest point of the other cutting inserts is set as H, the relationship between H and the diameter D of the tool body can be H / D equal to or less than 0.025.

[0038] In this structure, H / D is equal to or less than 0.025, which allows the cutting edge step of the cutting insert relative to the tool diameter D to be sufficiently small. As a result, the range of cutting operations using only the cutting insert on the lower side of the lowest point (cutting insert 1A in the following embodiment, i.e., the mother cutting edge) is reduced, wear at the tip of the cutting insert (mother cutting edge) on the lower side of the lowest point is suppressed, and the cutting insert life can be extended. H / D is preferably 0.020 or less, more preferably 0.017 or less. Although the lower limit of H / D is not limited, it is around 0.010 in practice.

[0039] In one aspect of the indexable insert cutting tool of the present invention, two insert mounting seats are formed at 180° intervals on the front end of the tool body, and each of the two insert mounting seats can be detachably mounted with any of the aforementioned cutting inserts. However, in the present invention, three insert mounting seats are formed at 120° intervals on the front end of the tool body, and similarly, four or more insert mounting seats can be formed at equal intervals along the circumferential direction.

[0040] According to the present invention, it is possible to provide a cutting insert and an indexable insert type cutting tool that suppresses cracks generated on the cutting edge by dispersing the stress generated on the arc-shaped cutting edge. Attached Figure Description

[0041] Figure 1 This is a diagram showing the front end side of an embodiment of the indexable insert ball end mill of the present invention (from...). Figure 9 (See arrow I in the diagram) is a diagram showing the structure in which multiple cutting blades of one embodiment of the present invention can be detachably mounted on the tool body.

[0042] Figure 2 This is a front view showing the structure of a cutting blade according to an embodiment of the present invention.

[0043] Figure 3 This is a rear view showing the structure of a cutting blade according to an embodiment of the present invention.

[0044] Figure 4 From Figure 2 The side view viewed in the direction of arrow IV.

[0045] Figure 5 From Figure 2 The side view is viewed in the direction of arrow V.

[0046] Figure 6 From Figure 2 The side view is viewed in the direction of arrow VI.

[0047] Figure 7 From Figure 2 The side view viewed in the direction of arrow VII.

[0048] Figure 8 This is a perspective view of a cutting blade according to one embodiment of the present invention.

[0049] Figure 9 This is a front view of an indexable insert ball end mill according to an embodiment of the present invention.

[0050] Figure 10 It is the first cutting insert used for cutting with the main cutting edge. Figure 10 A top view of two cutting inserts (the right cutting insert in the middle) with their rake faces facing each other, arranged in their positional relationship when mounted on the tool body.

[0051] Figure 11A It is a graph showing the relationship between the distance and height from the tip 2b of the tool at any position on the arc-shaped cutting edge 5a.

[0052] Figure 11BIt is a graph showing the relationship between the distance from the tip 2b of the tool to any position on the arc-shaped cutting edge 5a in the direction parallel to the sitting surface, and the ratio of the height of any point on the arc-shaped cutting edge from the tip to the height of the most convex point in the direction perpendicular to the sitting surface.

[0053] Figure 12A This is a diagram showing the chip shape and the maximum principal stress applied to the cutting tool and chip under a simulation analysis when cutting with a conventional cutting tool with an angle of 16.5° from the axis to the convex point.

[0054] Figure 12B This is a graph showing the maximum principal stress applied to the cutting tool under a simulation analysis of cutting with a conventional cutting tool having an angle of 16.5° from the axis to the convex point.

[0055] Figure 13A This is a diagram showing the chip shape and the maximum principal stress applied to the cutting tool and chip under a simulation analysis of cutting with a conventional cutting tool at an angle of 22.5° from the axis to the convex point.

[0056] Figure 13B This is a graph showing the maximum principal stress applied to the cutting tool under a simulation analysis of cutting with a conventional cutting tool having an angle of 22.5° from the axis to the convex point.

[0057] Figure 14A This is a graph showing the chip shape and the maximum principal stress applied to the cutting blade and the chip under a simulation analysis of a cutting blade 1 according to an embodiment of the present invention, which has an angle of 45° from the axis O to the most convex point S1 and an angle of 22.5° from the axis to the point of curvature change.

[0058] Figure 14B This is a graph showing the maximum principal stress applied to the cutting insert during a simulation analysis of a cutting insert according to an embodiment of the present invention, where the angle from the axis to the most convex point is 45° and the angle from the axis to the point of curvature change is 22.5°.

[0059] Figure 15 This is a graph showing the minimum principal stress applied to the cutting tool under a simulation analysis of cutting with a conventional cutting tool having an angle θ1 of 16.5° from the axis to the most convex point.

[0060] Figure 16 This is a graph showing the minimum principal stress applied to the cutting insert under a simulation analysis of a cutting insert of an embodiment of the present invention, where the angle θ1 from the axis to the most convex point is 45° and the angle θ2 from the axis to the cutting edge change point is 22.5°. Detailed Implementation

[0061] Next, use Figures 1 to 11B The structure of a cutting insert and an indexable insert type cutting tool according to one embodiment of the present invention will be described.

[0062] Figure 1 This is a diagram showing the front end side of an embodiment of the indexable insert ball end mill of the present invention (from...). Figure 9 The diagram (observed in the direction of arrow I) shows the structure of a plurality of (two in this embodiment) cutting blades of an embodiment of the present invention that can be detachably mounted on the tool body 11. Figure 9 This is a front view of an indexable insert ball end mill according to an embodiment of the present invention.

[0063] <Indexable insert cutting tools>

[0064] like Figure 1 and Figure 9 As shown, an indexable insert ball end mill (indexable insert cutting tool) 100 according to one embodiment of the present invention includes a plurality of cutting inserts 1 and a tool body 11 for holding the plurality of cutting inserts 1. The tool body 11 rotates about axis O.

[0065] Multiple cutting inserts 1 are detachably mounted on multiple (two in this embodiment) insert mounts 12 formed on the front end side of the tool body 11. In this embodiment, two cutting inserts 1 (1A, 1B) are mounted on two insert mounts 12 (12A, 12B) provided on the end mill body. These two cutting inserts 1 (1A, 1B) are identical in shape and size. In this invention, the number of cutting inserts 1 and insert mounts 12 is not limited to two; three or more insert mounts 12 can be provided at equal intervals along the circumferential direction around axis O. In this embodiment, cutting insert 1A is located below cutting insert 1B; in this case, cutting insert 1A is referred to as the mother cutting edge, and cutting insert 1B is referred to as the daughter cutting edge.

[0066] (End mill body)

[0067] The tool body 11 is made of metal materials such as steel. Its rear end is a cylindrical handle centered on axis O, and its front end is a convex hemisphere centered on axis O.

[0068] Regarding the indexable insert ball end mill 100 of this embodiment, the tool body 11 rotates around axis O in the rotation direction of the tool body 11 while being fed out in a direction intersecting axis O, thereby using the cutting insert 1 mounted on the insert mounting seat 12 to perform cutting machining on the workpiece.

[0069] Furthermore, in this embodiment, the direction extending along axis O is referred to as the front end side (from the shank portion of the tool body 11 to the blade mounting base 12). Figure 1 The lower end side), the direction from the blade mount 12 toward the tool holder is called the rear end side ( Figure 1 (The upper side). Furthermore, the direction orthogonal to axis O is called the radial direction. Within the radial direction, the direction closer to axis O is called the inner circumferential side, and the direction farther from axis O is called the outer circumferential side.

[0070] In this embodiment, two chip grooves 13 are formed on the outer periphery of the front end of the cutting tool body 11. On the bottom surface 12a of the two chip grooves 13 facing the rotation direction T of the end mill, insert mounting seats 12 are formed on opposite sides of each other in a circumferential direction.

[0071] In this embodiment, two cutting blades 1 (1A, 1B) of the same type and identical shape and size can be detachably mounted on the two blade mounting seats 12 (12A, 12B) of the tool body 11. By mounting two cutting blades 1 (1A, 1B) of the same type on the tool body 11, cutting from near the axis O at the front end of the tool body 11 to the outer periphery and cutting from a position away from the axis O to the outer periphery can be performed. As a result, the cutting blades 1 can be easily managed, and only one type of mold is needed for manufacturing the cutting blades 1 (1A, 1B).

[0072] The cutting inserts 1 (1A, 1B) have a main cutting edge 5 and a secondary cutting edge 6, each having an arc-shaped cutting edge and a straight cutting edge, respectively. In the positional relationship when the cutting inserts 1 (1A, 1B) are respectively mounted on the tool body 11, as follows... Figure 10 As shown, there is an axial step H3 between the tip of the main cutting edge 5 of one cutting insert 1A and the tip of the secondary cutting edge 6 of another cutting insert 1B. Specifically, as... Figure 10 As shown, the tip 2b of one cutting insert 1A is located further forward than the tip 2a of the other cutting insert 1B. Furthermore, the main cutting edge 5 of one cutting insert 1A and the secondary cutting edge 6 of the other cutting insert 1B are mounted such that their rotational trajectories overlap during cutting, except for the area corresponding to the step H3.

[0073] When cutting inserts 1 (1A, 1B) are mounted on insert mounts 12 (12A, 12B), the first cutting insert 1A is configured such that the arc-shaped cutting edge portion 5a of the main cutting edge 5 extends from near the axis O on the front end side of the tool body 11 toward the rear end side. The second cutting insert 1B is configured such that the arc-shaped cutting edge portion 6a of the secondary cutting edge 6 extends from a position on the axis O on the front end side of the tool body 11 away from the outer periphery toward the rear end side.

[0074] Along with this, in Figure 1 In the indexable insert ball end mill 100 of this embodiment shown, the first insert mounting seat 12A is also formed such that the front end side of the tool body 11 is cut open to the extent including the axis O at the front end side, while the second insert mounting seat 12B is formed from a position slightly away from the axis O on the outer periphery side.

[0075] The two cutting inserts 1 (1A, 1B) are located on the same convex hemisphere on the front end side of the tool body 11.

[0076] In the event of wear or other damage to the main cutting edge 5 of the first cutting insert 1A and the secondary cutting edge 6 of the second cutting insert 1B due to cutting, these cutting inserts 1 can be reinstalled on the insert mounting base 12 on the opposite side, and the first cutting insert 1A can be reused as the second cutting insert 1B, and the second cutting insert 1B can be reused as the first cutting insert 1A, which is very economical.

[0077] (Cutting blade)

[0078] Next, the structure of the cutting blade 1 according to one embodiment of the present invention will be described in detail.

[0079] Figure 2 This is a front view showing the structure of a cutting blade 1 according to an embodiment of the present invention. Figure 3 This is a rear view showing the structure of a cutting blade 1 according to an embodiment of the present invention. Figure 4 From Figure 2 The side view viewed in the direction of arrow IV. Figure 5 From Figure 2 The side view is viewed in the direction of arrow V. Figure 6 From Figure 2 The side view is viewed in the direction of arrow VI. Figure 7 From Figure 2 The side view viewed in the direction of arrow VII. Figure 8 This is a perspective view showing the structure of a cutting blade 1 according to an embodiment of the present invention. Figure 10 The first cutting insert 1A (used for cutting with the main cutting edge 5) Figure 10 A top view of two cutting inserts 1 (1A, 1B) positioned in the tool body 11, with their rake faces facing each other.

[0080] like Figures 2-8 As shown, by mounting the cutting blade 1 (1A, 1B) according to an embodiment of the present invention onto... Figure 1 The tool body 11 shown is used to construct one embodiment of the indexable insert ball end mill 100 of the present invention.

[0081] like Figure 2 As shown, the cutting blade 1 (1A, 1B) of this embodiment includes: facing... Figure 1 The tool body 11 shown has a front cutting face 2 in the direction of rotation T; a sitting surface 3 on the bottom surface 12a of the blade mounting seat 12 facing the opposite side to the front cutting face 2; and a rear cutting face 4 extending around the front cutting face 2 and the sitting surface 3.

[0082] At the intersection of the rake face 2 and the flank face 4, two main cutting edges (cutting edges) 5 and two secondary cutting edges (cutting edges) 6 are formed on the ridge line (hereinafter referred to as the intersecting ridge line portion) formed by them.

[0083] like Figure 2 As shown, in the front view of the cutting insert 1 viewed axially opposite to the rake face 2, the main cutting edge 5 and the secondary cutting edge 6 respectively have arc-shaped cutting edge portions 5a and 6a extending in an arc shape, and straight cutting edge portions 5b and 6b extending tangentially to each arc-shaped cutting edge portion 5a and 6a. These two main cutting edges 5 and secondary cutting edges 6 are formed in a manner in which the arc-shaped cutting edge portions 5a and 6a and the straight cutting edge portions 5b and 6b are arranged alternately in the circumferential direction of the rake face 2.

[0084] like Figure 4 , Figure 5 and Figure 6 As shown, in the main cutting edge 5 and the secondary cutting edge 6 of this embodiment, at least the arc-shaped cutting edge portions 5a and 6a each have a convex curve portion 17. This convex curve portion 17 moves away from the straight cutting edge portions 5b and 6b and then moves closer to the seat surface 3. The points where the convex curve portions 17 formed by these arc-shaped cutting edge portions 5a and 6a protrude furthest from the seat surface 3 (the most prominent points from the seat surface 3) are the most prominent point S1 of the main cutting edge and the most prominent point S2 of the secondary cutting edge, respectively.

[0085] like Figure 4 and Figure 5 As shown, when viewed from the side from a direction opposite to the flank face 4, the arc-shaped cutting edge 5a has a main cutting edge curvature change point Q1 between the most convex point S1 of the main cutting edge furthest from the seat surface 3 on the convex curve portion 17 and the tip 2b of the arc-shaped cutting edge 5a. Additionally, as... Figure 6 As shown, in the arc-shaped cutting edge portion 6a of the secondary cutting edge 6, there is also a curvature change point Q2 between the most convex point S2 of the secondary cutting edge furthest from the sitting surface 3 on the convex curve portion 17 and the tip 2a of the arc-shaped cutting edge portion 6a.

[0086] When the arc-shaped cutting edge portion 5a (6a) from the tip 2b (2a) to the most convex point S1 of the main cutting edge (the most convex point S2 of the secondary cutting edge) is constructed from two arcs or curves with different curvatures, the curvature change point Q1 (Q2) can be determined at the point where the curvatures of the two arcs or curves are different. Furthermore, when there is a straight line or curve between the two different arcs, the curvature change point Q1 (Q2) can be determined at the endpoint of the arc closest to the most convex point S1 (S2) on the tip 2b (2a) side. Moreover, when the tip 2b (2a) side is constructed with a curve and the most convex point S1 (S2) side is constructed with a straight line, the curvature change point Q1 (Q2) can be determined at the point where the curve and the straight line intersect.

[0087] Furthermore, it is preferable that the curvature change point Q1 (Q2) is the boundary, and the curvature on the side of the most convex point S1 (S2) is more than twice the curvature on the side of the tip 2b (2a). That is, the curvature change point Q1 (Q2) can be determined by measuring the curvature from the tip 2b (2a) to the most convex point S1 (S2).

[0088] The normal direction of the tangent N1 passing through the most convex point S1 of the main cutting edge, in the direction opposite to the back face 4, i.e. relative to the arc-shaped cutting edge 5a. Figure 2 When viewed from the side (in the direction of arrow VII), the arc-shaped cutting edge 5a comprises at least two arcs with different curvatures. Specifically, the arc-shaped cutting edge 5a is formed by a curved first cutting edge 51 located on the tip 2b side with the curvature change point Q1 of the main cutting edge as the boundary, and a curved (or straight) second cutting edge 52 located on the side of the most convex point S1 of the main cutting edge with a curvature smaller than that of the first cutting edge 51. Thus, in this embodiment, the arc-shaped cutting edge 5a is constructed with the curvature change point Q1 of the main cutting edge as the boundary, consisting of a curved first cutting edge 51 convex upward relative to the seat surface 3 on the tip 2b side and a second cutting edge 52 convex upward relative to the seat surface 3 on the side of the most convex point S1 of the main cutting edge. The intersection of these first cutting edges 51 and second cutting edges 52 is the curvature change point Q1 of the main cutting edge.

[0089] Furthermore, regarding the arc-shaped cutting edge portion 6a, when viewed from the side in a direction opposite to the flank face 4, i.e., in the normal direction of the tangent N2 passing through the most convex point S2 of the secondary cutting edge, the arc-shaped cutting edge portion 6a also includes at least two arcs with different curvatures. Specifically, the arc-shaped cutting edge portion 6a is formed by a curved first cutting edge 61 located on the tip 2a side with the curvature change point Q2 of the secondary cutting edge as the boundary, and a curved (or straight) second cutting edge 62 located on the side of the most convex point S2 of the secondary cutting edge with a curvature smaller than that of the first cutting edge 61. Thus, in this embodiment, the arc-shaped cutting edge portion 6a is constructed with the curvature change point Q2 of the secondary cutting edge as the boundary, consisting of a curved first cutting edge 61 convex upward relative to the seat surface 3 on the tip 2a side and a second cutting edge 62 convex upward relative to the seat surface 3 on the side of the most convex point S2 of the secondary cutting edge. The intersection of the first cutting edge 61 and the second cutting edge 62 is the point Q2 where the curvature of the secondary cutting edge changes.

[0090] The arc-shaped cutting edge 5a is formed by the first cutting edge 51 and the second cutting edge 52, which have two arcs with different curvatures. In the arc-shaped cutting edge 5a, when the radius of the arc of the first cutting edge 51 on the tip 2b side is set as the arc radius R1, and the radius of the arc of the second cutting edge 52 on the side of the most convex point S1 of the main cutting edge is set as the arc radius R2, the relationship R1 < R2 is formed. The arc radius R1 is formed to be less than half the arc radius R2. In this embodiment, specifically, the sizes of these two arc radii R1 and R2 are R1 = 6.8 mm and R2 = 56.4 mm, satisfying the relationship that the arc radius R2 is more than twice the arc radius R1.

[0091] Alternatively, the arc-shaped cutting edge 6a can also be formed from the first cutting edge 61 and the second cutting edge 62, which have two arcs with different curvatures, as described above. In this case, the arc radius R2 of the second cutting edge 62 is larger than the arc radius R1 of the first cutting edge 61. That is, in the arc-shaped cutting edge 6a, the relationship R1 < R2 is also formed, and the arc radius R1 is formed to be less than half the arc radius R2. In this embodiment, specifically, the sizes of these two arc radii R1 and R2 are R1 = 2.7 mm and R2 = 56.4 mm, satisfying the relationship that the arc radius R2 is more than twice the arc radius R1.

[0092] [Table 1]

[0093]

[0094] Table 1 shows the normal direction of the tangent N1 passing through the most convex point S1 of the main cutting edge relative to the arc-shaped cutting edge 5a in this embodiment. Figure 2The profile of the cutting edge when viewed from the side (arrow VII in the image). When the cutting edge position is measured by 1 mm in a direction parallel to the seat surface 3 and with the cutting edge tip 2b as the origin, the height [mm] from the seat surface 3 in the direction perpendicular to the seat surface 3 changes as in (1), and the height [mm] from the cutting edge tip 2b in the direction perpendicular to the seat surface 3 changes as in (2). In addition, the percentage [%) of the height from the cutting edge tip 2b to the cutting edge tip S1 in the direction perpendicular to the seat surface 3 is set to 100% (the height of the cutting edge at each measurement point) changes as in (3).

[0095] Figure 11A This is a graph showing the relationship between the distance from the tip 2b in a direction parallel to the seat surface 3 [mm] in Table 1 and the above (1) as the vertical axis, representing the distance from the tip 2b in a direction parallel to the seat surface 3 and the height from the seat surface 3 in a direction perpendicular to the seat surface 3 at any position on the arc-shaped cutting edge 5a. Here, the height from the seat surface 3 to the arc-shaped cutting edge 5a refers to the so-called "wall thickness".

[0096] Viewed from the normal direction relative to the tangent N1 of the arc-shaped cutting edge 5a Figure 7 When viewed from the side, for example, as shown... Figure 11A As shown, the height from the seat surface 3 to the tip 2b is 4.571 mm, the height from the seat surface 3 to the point Q1 where the curvature of the main cutting edge changes is 7.250 mm, and the height from the seat surface 3 to the most convex point S1 of the main cutting edge is 7.498 mm.

[0097] In this embodiment, when viewed from the normal direction relative to the tangent N1 of the arc-shaped cutting edge 5a... Figure 7 When viewed from the side, the height T1 from the tip 2b to the point Q1 where the curvature of the main cutting edge changes in the direction perpendicular to the sitting surface 3 is more than 10 times the height T2 from the point Q1 where the curvature of the main cutting edge changes in the direction perpendicular to the sitting surface 3 to the point S1 where the curvature of the main cutting edge changes most prominently.

[0098] As a specific example, the height T1 from the tip 2b of the tool to the point Q1 where the curvature of the main cutting edge changes in the direction perpendicular to the sitting surface 3 is 2.679 mm, and the height T2 from the point Q1 where the curvature of the main cutting edge changes in the direction perpendicular to the sitting surface 3 to the most convex point S1 of the main cutting edge is 0.248 mm. The height T1 is more than 10 times the height T2.

[0099] Figure 11BThe graph shows the distance from the tip of the blade 2b in the direction parallel to the seat surface 3 [mm] on the horizontal axis and the percentage from the tip of the blade 2b to the most prominent point S1 as 100% [%) on the vertical axis.

[0100] like Figure 11B As shown, when the height from the tip 2b to the most convex point S1 of the main cutting edge is set as the reference (100%), the height from the tip 2b to the curvature change point Q1 of the main cutting edge is approximately 92% of the reference. In this embodiment, the height at any number of points from the curvature change point Q1 of the main cutting edge to the most convex point S1 of the main cutting edge satisfies more than 90% of the reference, and the height difference from the curvature change point Q1 of the main cutting edge to the most convex point S1 of the main cutting edge is small. On the other hand, the height at any number of points from the curvature change point Q1 of the main cutting edge to the tip 2b varies significantly between adjacent points, ranging from 90% to 0% of the reference. Therefore, a curved shape is formed with the curvature change point Q1 of the main cutting edge as the boundary, where the height difference is larger on the side closer to the tip 2b than on the side of the most convex point S1 of the main cutting edge, and the height difference from the tip 2b to the curvature change point Q1 of the main cutting edge is sharply closer to the landing surface 3.

[0101] In this embodiment, in the arc-shaped cutting edge portion 5a including the first cutting edge 51 and the second cutting edge 52, the first cutting edge 51 located on the tip 2b side has a shape with a steeper arc curve compared to the second cutting edge 52 located on the side of the most convex point S1 of the main cutting edge. Furthermore, it can be said that the same applies to the arc-shaped cutting edge portion 6a.

[0102] Thus, in this embodiment, in the arc-shaped cutting edges 5a and 6a, durability can be ensured on the side of the most convex point S1 of the main cutting edge, including the point of curvature change Q1 of the main cutting edge, by ensuring a wall thickness of more than 90% of the most convex point S1 of the main cutting edge. Furthermore, by making the arc curve closer to the tip 2b and 2a of the tool tip than the point of curvature change Q1 of the main cutting edge steeper, the arc-shaped cutting edges 5a and 6a can make smooth contact with the workpiece, thereby reducing the impact acting on the tool tip and lowering cutting resistance.

[0103] In the rake face 2 of this embodiment, as Figure 2 and Figure 8As shown, chip breaker grooves 21 are formed in a convex curve shape near each of the intersecting ridge portions (arc-shaped cutting edges 5a and 6a) in a direction away from the seating surface 3. In a cross-section orthogonal to the main cutting edge 5 and the secondary cutting edge 6, the distance (height) of the apex (ridge) 21a of each chip breaker groove 21 from the seating surface 3 is greater than the distance of the arc-shaped cutting edges 5a and 6a from the seating surface 3. Preferably, the chip breaker grooves 21 are formed with the center point P of the arc-shaped cutting edges 5a and 6a located on the axis O as the center, within the range of 0° < θ3 < 50° from the axis O.

[0104] On the side of the seat surface 3 of the cutting insert 1, such as Figure 3 As shown, a groove 8 is formed that engages with a protrusion protruding from the bottom surface 12a of the first insert mounting base 12A. Two grooves 8 are formed on both radial sides of the mounting hole 7 for mounting the cutting insert 1. In these two grooves 8A and 8B, the main cutting edge curvature change point Q1 is formed closer to the tip 2b side than the groove 8A which is closer to the arc-shaped cutting edge 5a. The secondary cutting edge curvature change point Q2 is formed closer to the tip 2a side than the other groove 8B which is closer to the arc-shaped cutting edge 6a.

[0105] The groove 8B near the tip 2a is an opening on one side of the secondary cutting edge 6 and the other side of the primary cutting edge 5 along its length. The width of the groove 8B on the secondary cutting edge 6 side is narrower than the width on the primary cutting edge 5 side. The convex point S2 and the curvature change point Q2 of the secondary cutting edge 6 are formed at positions unaffected by the reduction in wall thickness of the groove 8B, thereby ensuring sufficient wall thickness at the convex point S2 and the curvature change point Q2. Therefore, the strength of the cutting insert 1 can be improved, and damage to the cutting insert 1 caused by the load during cutting can be prevented.

[0106] On the other hand, the groove 8A near the tip 2b has a stop groove shape with one end opening on the side of the secondary cutting edge 6 along its length, but the other end not opening on the side of the main cutting edge 5. Therefore, the most prominent point S1 and the point of curvature change Q1 of the main cutting edge 5 are formed at positions unaffected by the reduction in wall thickness of the groove 8A, thus ensuring sufficient wall thickness at the most prominent point S1 and the point of curvature change Q1. Therefore, the strength of the arc-shaped cutting edge portion 5a on the main cutting edge 5 can also be increased to prevent damage.

[0107] In addition, such as Figure 10As shown, when the cutting insert 1 is installed on the tool body 11, the center point of the hemisphere of the tool body 11 (cutting insert 1) located on the axis O is defined as P, the angle formed by the line L1 connecting the center point P and the most convex point S1 of the main cutting edge and the axis O is defined as θ1, and the angle formed by the line L2 connecting the center point P and the curvature change point Q1 of the main cutting edge and the axis O is defined as θ2. Thus, the angle θ2 is less than the angle θ1 (θ2 < θ1).

[0108] Here, the angle θ1 formed by the line L1 connecting the center point P and the most convex point S1 of the main cutting edge and the axis O is in the range of 30°≤θ1≤50°, preferably in the range of 40°≤θ1≤50°. In this embodiment, the angle θ1 from the axis O to the most convex point S1 of the main cutting edge is 45°.

[0109] When the main cutting edge's convex point S1 exists at an angle θ1 less than 30°, a tensile stress concentration may occur on the cutting insert during roughing operations or when the depth of cut is increased. On the other hand, when the main cutting edge's convex point S1 exists at an angle θ1 greater than 50°, the convex point S1 will be located away from the workpiece and the cutting insert on the tool's rear end side, thus reducing the effect of dispersing stress concentration. Therefore, it is preferable that the angle θ1 from the axis O to the main cutting edge's convex point S1 is within the aforementioned range.

[0110] Furthermore, the angle θ2 formed by the line L2 connecting the center point P and the curvature change point Q1 of the main cutting edge and the axis O is in the range of 15°≤θ2≤40°, preferably in the range of 17°≤θ2≤37°. In this embodiment, the angle θ2 from the axis O to the curvature change point is 22.5°.

[0111] If the main cutting edge curvature change point Q1 is set at an angle position where the aforementioned angle θ2 is less than 15°, stress concentration and defects will occur at the interface between the main cutting edge 5 and the workpiece when the cutting depth is greater than the main cutting edge curvature change point Q1, thus prematurely reaching the end of its service life. On the other hand, when the main cutting edge curvature change point Q1 exists at an angle position where the aforementioned angle θ2 is greater than 40°, a problem will arise where a stress concentration occurs at the tip of the arc-shaped cutting edge portion 5a. Therefore, it is preferable to set the angle θ2 from the axis O to the main cutting edge curvature change point Q1 within the aforementioned range.

[0112] Figures 12A to 16 The results are from simulation analysis of cutting workpieces using existing cutting inserts or the cutting inserts of this invention.

[0113] Figures 12A to 14BThe simulation analysis condition is that the spindle speed n = 2122 [min] -1 The following parameters were used for evaluation: feed rate per cutting edge fz = 0.4 mm / edge, depth of cut ap × cut width ae = 3 × 3 mm, tool diameter 30 mm, workpiece SKD61 (44 HRC), and maximum principal stress.

[0114] on the other hand, Figure 15 and Figure 16 The simulation analysis is based on the spindle speed n = 2122 [min] -1 The following parameters were used for evaluation: feed rate per cutting edge fz = 0.4 mm / edge, depth of cut ap × cut width ae = 3 × 3 mm, tool diameter 30 mm, workpiece SKD61 (44 HRC), and minimum principal stress.

[0115] Figure 12A This is a graph showing the cutting stress under simulated analysis when cutting with an existing cutting insert 90 at an angle θ1 of 16.5° from axis O to the most convex point S1 of the main cutting edge. It represents the maximum principal stress applied to the cutting insert 90 and the workpiece 91 (including the chip 91a) through cutting. Figure 12B This is a graph showing the maximum principal stress applied to the cutting insert 90 under simulation analysis when cutting using an existing cutting insert 90 with an angle of 16.5° from axis O to the most convex point S1 of the main cutting edge.

[0116] Figure 13A This is a graph showing the cutting stress under simulation analysis when cutting with an existing cutting insert 92 with an angle θ1 of 22.5° from axis O to the most convex point S1 of the main cutting edge. It represents the maximum principal stress applied to the cutting insert 92 and the workpiece 91 (including the chip 91a) through cutting. Figure 13B This is a graph showing the maximum principal stress applied to the cutting insert 92 under a simulation analysis when cutting with an existing cutting insert 92 having an angle θ1 of 22.5° from axis O to the most convex point S1 of the main cutting edge. Figure 13B From Figure 13A The diagram only shows the cutting blade 92.

[0117] Figure 14A This is a graph showing the cutting stress under simulation analysis when cutting with a cutting insert 1 according to an embodiment of the present invention, where the angle θ1 from the axis O to the most convex point S1 of the main cutting edge is 45° and the angle θ2 from the axis O to the curvature change point Q1 of the main cutting edge is 22.5°. It shows the maximum principal stress applied to the cutting insert 1 and the workpiece 91 (including the chip 91a) by cutting. Figure 14BThis is a graph showing the maximum principal stress applied to the cutting insert 1 under a simulation analysis when cutting with a cutting insert 1 according to an embodiment of the present invention, where the angle θ1 from axis O to the most convex point S1 of the main cutting edge is 45° and the angle θ2 from axis O to the curvature change point Q1 of the main cutting edge is 22.5°. Figure 14B From Figure 14A The diagram only shows cutting blade 1.

[0118] Figure 15 This is a graph showing the cutting stress under simulation analysis when cutting with an existing cutting insert 94 with an angle θ1 of 16.5° from axis O to the most convex point S1 of the main cutting edge. It represents the minimum principal stress applied to the cutting insert 94 by cutting.

[0119] Figure 16 This is a graph showing the cutting stress under simulation analysis when cutting with a cutting insert 1 of an embodiment of the present invention, where the angle θ1 from axis O to the most convex point S1 of the main cutting edge is 45° and the angle θ2 from axis O to the curvature change point Q1 of the main cutting edge is 22.5°. It shows the minimum principal stress applied to the cutting insert 1 by cutting.

[0120] from Figure 12B It can be seen that when the most prominent point S1 of the main cutting edge is located at an angle θ1 of 16.5° from the axis O, the maximum principal stress, i.e., the tensile stress, during cutting is concentrated near the most prominent point S1 of the main cutting edge. Furthermore, from... Figure 15 It can be seen that when in relation to Figure 12B When the most prominent point S1 of the main cutting edge is located at the same position, there are areas of minimum principal stress concentration, i.e., compressive stress concentration, before and after the most prominent point S1 of the main cutting edge. According to... Figure 12B and Figure 15 Under the existing arc-shaped cutting edge shape, during cutting, both tensile stress concentration areas and compressive stress concentration areas are generated on the arc-shaped cutting edge 5a, which easily leads to defects or breakage (cracks) of the cutting tool.

[0121] Furthermore, if the convex point S1 is set at the same position as the curvature change point Q1 in this embodiment (angle θ1 from axis O is 16.5°), and there is no cutting edge shape with curvature change point Q1 between the convex point S1 of the main cutting edge and the tip 2b, it can also be understood that... Figure 13A and Figure 13B As shown, a tensile stress concentration point is generated near the most convex point S1 of the main cutting edge during cutting.

[0122] In contrast, if the cutting edge shape is such that the most prominent point S1 of the main cutting edge 5 in this embodiment is located at a position 45° from the axis O, and there is a point Q1 where the curvature of the main cutting edge changes between the most prominent point S1 and the tip 2b (at a position where the angle θ2 from the axis O is 22.5°), then, as in this embodiment... Figure 14B As shown, the stress during cutting is dispersed over a wide range within the arc-shaped cutting edge 5a. Similarly, as Figure 16 As shown, compressive stress is also dispersed over a wider area of ​​the arc-shaped cutting edge 5a. That is, since the main cutting edge gradually cuts into the workpiece from the side of the most convex point S1 to the point of curvature change Q1 of the main cutting edge, stress concentration can be avoided, thereby improving the strength of the main cutting edge 5.

[0123] In addition, Figure 12A and Figure 13A The image shows that the chip 91a is significantly distorted. On the other hand, in this embodiment... Figure 14A The distortion of chip 91a shown is less than that of conventional examples. Chip 91a is formed along the arc-shaped cutting edge 5a. That is, by setting the curvature change point Q1 of the main cutting edge between the most convex point S1 of the main cutting edge and the tip 2b of the tool tip, it is possible to form chip 91a with less distortion.

[0124] In this embodiment, the cutting inserts 1 (1A, 1B) are respectively mounted on a substrate formed in... Figure 1 In the state of the blade mounting seats 12 (12A, 12B) at the front end of the tool body 11 shown, as Figure 10 As shown, the angle θ1 from axis O to the highest point S1 of the main cutting edge of the first cutting insert 1A and the angle θ3 from axis O to the highest point S2 of the secondary cutting edge of the second cutting insert 1B are equal. Therefore, in this embodiment, the angle θ3 is 45°, just like the angle θ1.

[0125] In this embodiment, the primary cutting edge 5 and secondary cutting edge 6 of the cutting inserts 1 (1A, 1B) are asymmetrical in shape. Consequently, in the two insert mounts 12A and 12B, the first insert mount 12A is configured to cut the front end of the tool body 11 at the front end side to a range including the axis O. On the other hand, as... Figure 1 As shown, a second blade mounting seat 12B is formed on the front end side of the tool body 11, starting from a position slightly away from the axis O on the outer periphery.

[0126] like Figure 1 As shown, the first cutting blade 1A and the second cutting blade 1B are inserted into their respective mounting holes 7. Figure 10 The fastening screws 9 are respectively installed on the first blade mounting seat 12A or the second blade mounting seat 12B.

[0127] Regarding the first cutting insert 1A, relative to the first insert mounting base 12A, the arc-shaped cutting edge portion 5a of the main cutting edge 5 is positioned on a convex hemisphere extending near the axis O and having a center on the axis O. Furthermore, the first cutting insert 1A is mounted such that the straight cutting edge portion 5b of the main cutting edge 5 is positioned on a cylindrical surface that contacts the convex hemisphere and is centered on the axis O.

[0128] Regarding the second cutting insert 1B, the second cutting insert 1B is mounted on the second insert mounting base 12B such that the arcuate cutting edge portion 6a of the secondary cutting edge 6 is positioned on the convex hemisphere of the arcuate cutting edge portion 5a of the main cutting edge 5 where the first cutting insert 1A is located, starting from a position away from the axis O. Alternatively, the second cutting insert 1B is mounted such that the straight cutting edge portion 6b of the secondary cutting edge 6 is located on the cylindrical surface of the straight cutting edge portion 5b of the main cutting edge 5 where the first cutting insert 1A is located.

[0129] With the first cutting insert 1A and the second cutting insert 1B respectively mounted on the tool body 11, as follows: Figure 10 As shown, when the diameter of the tool body 11 is set as D, and the distance from the tip 2b of the main cutting edge 5 to the curvature change point Q1 of the main cutting edge in the direction along the axis O is set as H, the relationship D / 30≤H≤D / 10 is satisfied, for example, H≥D / 20 is preferred.

[0130] Along the axis O, the lower limit position of the main cutting edge curvature change point Q1 and the upper limit position of the most convex point S1 of the main cutting edge are related to the maximum cutting depth (maximum depth of cut). Furthermore, generally, the larger the tool diameter D, the greater the maximum cutting depth. For example, when the tool diameter D is 30 mm, even if there are multiple arcs with different curvatures between the main cutting edge curvature change point Q1 and the tool tip 2b, the portion with a maximum cutting depth of less than 1.0 mm will not become the main cutting edge curvature change point Q1 in this embodiment. That is, when the tool diameter D is 30 mm, the distance H (the lower limit position of the main cutting edge curvature change point Q1) from the tool tip 2b to the main cutting edge curvature change point Q1 along the axis O is preferably 1.0 mm or more.

[0131] For example, when the tool diameter D is 30 mm, the distance H from the tip 2b to the point Q1 where the curvature of the main cutting edge changes is less than the maximum depth of cut of 3.0 mm. Specifically, in this embodiment, the distance H from the tip 2b to the point Q1 where the curvature of the main cutting edge changes is approximately 1.4 mm.

[0132] Furthermore, along the axis O, the upper limit position of the most prominent point S1 of the main cutting edge is preferably above the maximum cutting depth. When the tool diameter D is 30 mm, the distance H1 from the tip 2b to the most prominent point S1 of the main cutting edge is greater than the maximum cutting depth of 3.0 mm. Specifically, in this embodiment, the distance H1 from the tip 2b to the most prominent point S1 of the main cutting edge is approximately 4.6 mm.

[0133] By setting the arc-shaped cutting edge 5a of the main cutting edge 5 to a shape where the distance H1 from the tip 2b to the most convex point S1 of the main cutting edge is greater than the maximum cutting depth, the main cutting edge gradually cuts into the workpiece from the side of the most convex point S1 to the point Q1 where the curvature of the main cutting edge changes. This avoids stress concentration and reduces cutting resistance, thereby improving the strength of the main cutting edge 5.

[0134] When the tool is shaped such that the distance H1 from the tip 2b to the most prominent point S1 of the main cutting edge is less than the maximum depth of cut, the workpiece is initially cut from the most prominent point S1 of the main cutting edge. Therefore, cutting stress tends to concentrate on the most prominent point S1, making it easier for cracks to form on the side of the tool closer to the rear end than the most prominent point S1. Therefore, it is preferable to shaped the tool so that the distance H1 from the tip 2b to the most prominent point S1 of the main cutting edge is greater than the maximum depth of cut.

[0135] As described above, in this embodiment, the arc-shaped cutting edge portion 5a of the main cutting edge 5 and the arc-shaped cutting edge portion 6a of the secondary cutting edge 6 are formed as convex curves that move away from the side of the seat surface 3 after moving away from the straight cutting edge portions 5b and 6b, and then move closer to the side of the seat surface 3 again. Between the most convex points S1 and S2 of the arc-shaped cutting edge portions 5a and 6a that are most convex relative to the seat surface 3 and the tool tip tips 2b and 2a, there are curvature change points Q1 and Q2. By providing not only the most convex points S1 and S2, but also the curvature change points Q1 and Q2, during cutting, the arc-shaped cutting edge portions 5a and 6a gradually bite into and cut into the workpiece from the side furthest from the seat surface 3 and convex at the most convex points S1 and S2 to the curvature change points Q1 and Q2. Therefore, the stress during cutting can be distributed over a wider range, including the area from the most convex points S1 and S2 to the curvature change points Q1 and Q2.

[0136] Thus, by setting the most prominent points S1 and S2, the wall thickness of the cutting insert 1 is ensured and its strength is improved. Furthermore, by setting curvature change points Q1 and Q2 between the most prominent points S1 and S2 and the cutting tip 2b and 2a, the cutting resistance can be reduced. Therefore, damage to the cutting insert 1 caused by the load during cutting can be prevented.

[0137] Furthermore, although chips are generated during the cutting process, in the arc-shaped cutting edge 5a, the existing shape of the chip is such that there is no curvature change point Q between the most convex point S and the tip 2b, causing the chip to be twisted and pulled.

[0138] In contrast, in this embodiment, since there is a curvature change point Q between the most convex point S and the tip 2b, the chips generated during cutting are less likely to twist, and the stress during cutting is dispersed. As a result, chip removal is improved to prevent defects or breakage (cracks) from occurring on the arc-shaped cutting edge 5a, and consequently, the life of the cutting insert 1 can be extended.

[0139] In addition, such as Figure 3 As shown, since the most prominent points S1 and S2 and the curvature change points Q1 and Q2 are arranged in positions that do not overlap with the opening of the groove 8 facing the back face 4, the wall thickness from the seat surface 3 to the most prominent points S1 and S2 and the curvature change points Q1 and Q2 can be fully ensured. Even if a large cutting load is applied to the cutting insert 1, damage can be prevented on the main cutting edge 5 and the secondary cutting edge 6.

[0140] Thus, the cutting insert 1 of this embodiment improves the strength of the tip side by dispersing the stress during cutting at a cutting depth with a width wider than conventional ones, thereby suppressing cracks generated on the cutting edge.

[0141] The preferred embodiments of the present invention have been described above with reference to the accompanying drawings, but the present invention is not limited to these examples. Those skilled in the art can conceive of various modifications or alterations within the scope of the technical concept described in the claims. These modifications or alterations also fall within the technical scope of the present invention. The structures of the above embodiments can be appropriately combined.

[0142] Furthermore, the cutting insert of the present invention is preferably made of a cemented carbide with tungsten carbide-cobalt-based (WC-Co-based) as the main raw material. However, in addition to tungsten carbide-cobalt-based inserts and cemented carbide including carbonitridinium-based cermets, ceramics composed of high-speed steel, titanium carbide, silicon carbide, silicon nitride, aluminum nitride, alumina, and mixtures thereof, cubic boron nitride sintered bodies, diamond sintered bodies, and ultra-high pressure sintered bodies formed by sintering a hard phase composed of polycrystalline diamond or cubic boron nitride and a ceramic or iron group metal bonded phase under ultra-high pressure are also acceptable.

[0143] Furthermore, in the cutting insert of the above embodiment, the arc-shaped cutting edges 5a and 6a can be constructed from at least two arc-shaped first cutting edges 51 and 61, second cutting edges 52 and 62 to the Nth cutting edge (N is an integer of 2 or more, and in the above embodiment N=2) with different arc radii, starting from the position corresponding to the tool tip side. In addition, the arc radius of the first cutting edges 51 and 61 on the tool tip side can be set to be smaller than the arc radius of the other second cutting edges 52 and 62 to the Nth cutting edge, and in the first cutting edges 51 and 61, the wedge angle, which is the angle formed by the flank face 4 and the rake face 2, can gradually decrease from the second cutting edge 52 and 62 side toward the tool tip side.

[0144] In this case, in the first cutting edges 51 and 61 of the arc-shaped cutting edge portions 5a and 6a, the wedge angle of the cutting edge portion gradually decreases from the side of the second cutting edge 52 and 62 toward the front end, thereby increasing the clearance angle of the cutting edge when cutting from the front end of the tool tip, and suppressing the aggravation of the wear of the back face of the tool tip tip.

[0145] Furthermore, the tip of a circularly curved cutting edge is typically subjected to an ejection force from the Z-axis during cutting, making it more prone to damage. Additionally, while a larger wedge angle generally corresponds to greater thickness and cutting edge strength, when machining workpieces such as high-hardness steel, a smaller clearance angle can lead to variations in tool life even with a thicker wall. In contrast, in the above structure, by gradually decreasing the clearance angle of the tool tip from the rear end to the front end of the first cutting edges 51 and 61, the clearance angle at the tip of the circularly curved cutting edge can be maintained to a certain extent during cutting, thereby stabilizing the tool life of the front end of the circularly curved cutting edge. The clearance angle of the first cutting edges 51 and 61 is approximately 10–25° on the tool front end side and approximately 5–20° on the second cutting edges 52 and 62 side, with the difference preferably being approximately 5–15°. More preferably, the wedge angle of the first cutting edges 51 and 61 is about 15 to 25° on the front end side of the tool and about 8 to 18° on the side of the second cutting edges 52 and 62, with a difference of about 10 to 15°.

[0146] Furthermore, in the aforementioned embodiment, the relationship between the difference H3 between the lowest point of the cutting insert 1A and the lowest point of the other cutting inserts 1B, and the diameter D of the tool body 11, can be H3 / D of 0.025 or less. In this case, since H3 / D is 0.025 or less, the cutting edge step of the cutting insert relative to the tool diameter D can be sufficiently reduced. As a result, the range of cutting operations using only the cutting insert 1A on the lower side of the lowest point (i.e., the mother cutting edge) is smaller, wear on the tip of the cutting insert 1A on the lower side of the lowest point is suppressed, and the life of the cutting insert 1A can be extended. H3 / D is preferably 0.020 or less, more preferably 0.017 or less. The lower limit of H3 / D is not limited, but in practice it is around 0.010.

[0147] Industrial availability

[0148] The cutting insert and indexable insert cutting tool according to the present invention can suppress the generation of cracks on the cutting edge by dispersing the stress generated on the arc-shaped cutting edge, thus enabling the present invention to be used in industry.

[0149] Explanation of reference numerals in the attached figures

[0150] 1. Cutting insert

[0151] 2. Rake face

[0152] 2a, 2b Cutting tip tip

[0153] 3. Seating surface

[0154] 4. Back face

[0155] 5. Main cutting edge (cutting edge)

[0156] 5a, 6a Arc-shaped cutting edge

[0157] 5b, 6b Straight cutting edge

[0158] 6. Secondary cutting edges (cutting edges)

[0159] 7 mounting holes

[0160] 8 (8A, 8B) groove

[0161] 11. Tool Body

[0162] 12, 12A Blade Mount

[0163] 12a Bottom surface

[0164] 17. Convex curve portion

[0165] 21 Chip Breaker Groove

[0166] 21a Vertex (Edge)

[0167] 51, 61 First cutting edge

[0168] 52, 62 Second cutting edge

[0169] 100 Indexable Insert Ball End Mill (Indexable Insert Cutting Tool)

[0170] Distances of H, H1, and H3

[0171] L1, L2 lines

[0172] N1, N2 tangents

[0173] O axis

[0174] P center point

[0175] Q(Q1, Q2) Curvature change points

[0176] R1 and R2 arc radii

[0177] S(S1, S2) most convex point

[0178] T-shaped end mill body rotation direction

[0179] T1 is the height (wall thickness) from the tip of the tool to the point of curvature change in a direction perpendicular to the seating surface.

[0180] T2 is the height (wall thickness) from the point of curvature change to the point of maximum convexity in a direction perpendicular to the seating surface.

[0181] Angles θ1, θ2, θ3

Claims

1. A cutting insert, detachably mounted on an insert mount at the front end of a tool body formed in a rotatable indexable insert cutting tool about an axis, the cutting insert comprising: The front cutting face faces the direction of rotation of the tool body; The seat surface faces the side opposite to the front cutting face and sits on the bottom surface of the blade mounting seat; as well as The flank face extends around the front face and the seat face. Two cutting edges are formed on the intersection of the rake face and the flank face. Each cutting edge has an arc-shaped cutting edge portion and a straight cutting edge portion. When viewed from above in a direction opposite to the rake face, the arc-shaped cutting edge portion extends in an arc shape, and the straight cutting edge portion extends tangentially to the arc-shaped cutting edge portion. The two cutting edges are formed in a manner where the arc-shaped cutting edge portion and the straight cutting edge portion are alternately arranged in the circumferential direction of the rake face. In each of the cutting edges, at least the arc-shaped cutting edge portion is constructed with a convex curve portion that moves away from the seat surface as it moves away from the straight cutting edge portion. Furthermore, when the point on the convex curve portion furthest from the seat surface is designated as the most convex point, in a side view relative to the normal direction of the tangent of the arc-shaped cutting edge portion passing through the most convex point, the arc-shaped cutting edge portion has a point of curvature change between the most convex point and the tip of the arc-shaped cutting edge portion.

2. The cutting insert according to claim 1, wherein, In the side view, viewed from the normal direction relative to the tangent of the arc-shaped cutting edge passing through the most convex point... Each of the aforementioned cutting edges comprises at least two circular arcs with different curvatures. When the radius of the arc on the tip side of the blade is set to R1 and the radius of the arc on the most convex point side is set to R2, the relationship R1 < R2 is satisfied.

3. The cutting insert according to claim 2, wherein, The radius of the arc R1 is less than 1 / 2 of the radius of the arc R2.

4. The cutting insert according to claim 1 or 2, wherein, During the side view observation, The cutting edge is defined by the point of curvature change, and consists of a first cutting edge, which is curved and convex upward relative to the seat surface on the tip side, and a second cutting edge, which is convex upward relative to the seat surface on the most convex point side. The second cutting edge is formed by either a curved or straight second cutting edge with a curvature smaller than that of the first cutting edge. The intersection of the first cutting edge and the second cutting edge is the curvature change point.

5. The cutting insert according to claim 4, wherein, The curvature of the first cutting edge is more than twice that of the second cutting edge.

6. The cutting insert according to claim 5, wherein, In the arc-shaped cutting edge portion as viewed from the side. The portion of the second cutting edge in a direction perpendicular to the sitting surface, where the ratio of the height from the tip of the blade to any cutting edge line to the height from the tip of the blade to the most convex point is 90% or more, is the second cutting edge.

7. The cutting insert according to any one of claims 1 to 3, 5 and 6, wherein, A groove with a wall is formed in the cutting blade, the wall being able to abut against a protrusion projecting from the bottom surface of the blade mount. The groove is formed in two parts, separated by mounting holes for mounting the cutting blade. The curvature change point is formed closer to the tip of the tool than one of the two grooves that is near the arc-shaped cutting edge.

8. The cutting insert according to any one of claims 1 to 3, 5 and 6, wherein, The arc-shaped cutting edge is constructed sequentially from the position corresponding to the tool tip side, consisting of at least two arc-shaped cutting edges of different radii: a first cutting edge, a second cutting edge, and so on up to the Nth cutting edge, where N is an integer greater than or equal to 2. The radius of the arc of the first cutting edge on the tip side of the blade is smaller than the radius of the arc of the second to Nth cutting edges, excluding the first cutting edge. In the first cutting edge, from the second cutting edge side toward the tool tip side, the wedge angle, which is the angle formed by the flank face and the rake face, gradually decreases.

9. An indexable insert cutting tool, comprising: The cutting blade according to any one of claims 1 to 8; and A tool body capable of mounting multiple cutting blades. When P is defined as the center point of the arc-shaped cutting edge located on the axis of the tool body, Let θ1 be the angle formed by the line connecting the center point P and the most convex point and the axis. And when the angle formed by the line connecting the center point and the point of curvature change and the axis is set as θ2, θ2<θ1, 30°≤θ1≤50°, 15°≤θ2≤40°.

10. The indexable insert cutting tool according to claim 9, wherein, When the distance from the tip of the cutting edge on the cutting insert to the point of curvature change is defined as H in the direction along the axis, and the diameter of the tool body is defined as D, the relationship D / 30≤H≤D / 10 is satisfied.

11. The indexable insert cutting tool according to claim 9 or 10, wherein, With the cutting insert of any one of claims 1 to 8 mounted on the tool body, The arc-shaped cutting edge is constructed sequentially from the position corresponding to the tool tip side, consisting of at least two arc-shaped cutting edges of different radii: a first cutting edge, a second cutting edge, and so on up to the Nth cutting edge, where N is an integer greater than or equal to 2. The radius of the arc of the first cutting edge on the tip side of the blade is smaller than the radius of the arc of the second to Nth cutting edges, excluding the first cutting edge. In the first cutting edge, from the second cutting edge side to the tool tip side, the clearance angle formed by the flank face of the cutting insert and the workpiece face gradually increases.

12. The indexable insert cutting tool according to claim 9 or 10, wherein, With the cutting inserts of any one of claims 1 to 8 mounted on the tool body, When the difference between the lowest point of any cutting insert and the lowest point of other cutting inserts is set as H, The relationship between H and the diameter D of the tool body is that H / D is equal to or less than 0.

025.

13. The indexable insert cutting tool according to claim 9 or 10, wherein, Two blade mounting seats are formed at a distance of 180° between each other at the front end of the tool body. Each of the two blade mounts is detachably mounted with a cutting blade as described in any one of claims 1 to 8.

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