Cutting inserts and rotary cutting tools

Abstract

In ramping processes, etc., it can improve the resistance to chipping around the cutting edge, achieving stable machining performance and extended tool life. [Solution] The cutting insert (10) comprises a first end face (10U) and a second end face (10L) and a side face (10S) connected thereto, a cutting edge (2A) provided on at least a part of the intersection ridge between the first end face (10U) and the side face (10S), a flank portion (F1) formed to connect with the cutting edge (2A) and forming an obtuse angle with the first end face (10U), a contact surface portion (R13) protruding outward from the flank portion (F1), and a step portion (B1) connected to the flank portion (F1) and the contact surface portion (R13) and forming a shape with a concave arc (C) and a convex arc (P) in a cross section perpendicular or approximately perpendicular to the first end face (10U).

Description

[Technical Field]

[0001] The present disclosure relates to a cutting insert and a rotary cutting tool including the cutting insert. [Background technology]

[0002] Recently, there has been an increasing demand for rotary cutting tools capable of high-feed machining in order to improve machining efficiency. For example, Patent Document 1 proposes a cutting insert intended to prevent chipping while ensuring cutting edge strength and preventing chipping of the cutting edge, which is recognized as being applicable to high-feed machining. Furthermore, Patent Document 2 describes a cutting insert for a milling cutter, although it is not intended for high-feed machining. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-119022 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-188595 Summary of the Invention [Problem to be solved by the invention]

[0004] However, even higher efficiency can be expected when using ramping or helical cutting, which involves cutting the workpiece while approaching it at an angle or in a spiral, using a rotary cutting tool capable of high-feed machining. In this type of cutting, unlike conventional side cutting, the inner cutting edge near the tip of the cutting insert directly penetrates the workpiece. As a result, the cutting load is not distributed throughout the tool, but tends to concentrate on a specific part of the inner cutting edge, which can cause chipping of the cutting edge. The impact of this load (stress) concentration is particularly pronounced when machining high-hardness workpieces, making the durability of the inner cutting edge a key issue.

[0005] In contrast, with the cutting insert shape described in Patent Document 1, the cutting load on the cutting edge tends to concentrate at the area where the flank and the constraint surface (the contact surface that contacts the flank) meet. Specifically, this area forms a bend with an apex, causing stress to concentrate at the apex. As a result, when performing ramping or helical machining, which actively utilizes the inner cutting edge, the area around the inner cutting edge is prone to chipping. To address this issue, it is conceivable to connect the flank of the cutting insert described in Patent Document 1 to the upper surface at an obtuse angle, but simply configuring it this way is hardly a sufficient solution. Particularly under conditions of high cutting load, such as high-feed machining of high-hardness workpieces, further measures are required. Regarding the shape of the flank and the contact surface that contacts it, the cutting insert described in Patent Document 2 is configured with a flank that has a concave groove extending along the cutting edge. However, even with this cross-sectional shape, it is difficult to adequately suppress stress concentration that can occur at the area where the flank and the contact surface meet during high-feed machining of high-hardness workpieces.

[0006] Therefore, the present disclosure has been made in consideration of the above circumstances, and aims to provide a cutting insert that can improve the chipping resistance around the cutting edge during ramping processing, etc., thereby achieving stable processing performance and extended tool life, and a rotary cutting tool equipped with the cutting insert. [Means for solving the problem]

[0007] [1] In order to solve the above problem, one example of a cutting insert according to the present disclosure includes a first end face and a second end face facing each other, a side face connected to the first end face and the second end face, a cutting edge provided on at least a part of the intersecting ridge between the first end face and the side face, a flank portion formed on at least a part of the side face so as to be connected to the cutting edge and having an obtuse interior angle with respect to the first end face, a contact surface portion formed on at least a part of the side face and protruding outward from the flank surface portion, and a step portion connected to a specific portion of the flank surface portion and a specific portion of the contact surface portion corresponding to the specific portion of the flank surface portion, and having a shape with a concave arc and a convex arc in a cross section perpendicular or substantially perpendicular to (with respect to) the first end face.

[0008] Here, the term "concave arc" refers to a cross-sectional shape of a concave curved surface that is recessed inward from the side surface of the cutting insert. The term "convex arc" refers to a cross-sectional shape of a convex curved surface that bulges outward from the side surface of the cutting insert. The term "convex arc" refers to a cross-sectional shape of a convex curved surface that is bulging outward from the side surface of the cutting insert. The term "convex arc" refers to a cross-sectional shape of a convex curved surface that is not limited to a circular arc with a constant curvature, but includes any arc with a continuously changing curvature. Since the abutment surface protrudes outward more than the flank surface, the portion of the step that connects to the flank surface is a concave curved surface, and the portion that connects to the abutment surface is a convex curved surface. The "abutment surface" functions as a part of a fixing portion that fixes the cutting insert by being pressed against the tip seat (pocket) of the tool body when the cutting insert is attached to the tip seat, and may be, for example, a flat surface.

[0009] In this configuration, the flank portion forms an obtuse angle with the first end face, and a specific portion of the flank portion and a specific portion of the abutment surface are connected via a stepped portion with smooth irregularities. This eliminates the corners that would be formed if the flank portion and the abutment surface were directly connected, preventing localized stress concentration. In particular, the stepped portion has a curved, uneven shape, which gently distributes stress and prevents high-stress points due to sudden cross-sectional changes. Furthermore, providing such a stepped portion distributes cutting loads over a wide area between the flank portion and the abutment surface, thereby reducing localized loads. Furthermore, the convex arc of the stepped portion increases the apparent cross-sectional area and volume of the flank portion, improving rigidity and enhancing fracture resistance around the cutting edge corresponding to the stepped portion. As a result, applying this configuration to the area around an inner cutting edge, which is actively used in ramping and other processes, can improve fracture resistance around the inner cutting edge, making it particularly suitable for high-hardness workpieces.

[0010] [2] In the above configuration, the cross-sectional portion of the side surface perpendicular or nearly perpendicular to the cutting edge may be smoothly formed so that the boundaries between the flank surface and the abutment surface and the step portion, and between the concave arc and the convex arc, do not form any sharp or obtuse angles, and the curvature change is not discontinuous (so that the latter boundary forms an inflection point without interruption of the curvature). This ensures a smooth transition from the flank surface and the abutment surface to the step portion in the portion of the side surface corresponding to the cutting edge, preventing abrupt changes in shape. Furthermore, in this portion of the side surface, there is no abrupt change in curvature, such as an edge or a sharp broken line, between the concave and convex portions of the step portion. This suppresses stress concentration, which is likely to occur when there are corners or abrupt changes in curvature, and reduces damage and wear around the cutting edge due to such stress concentration. Furthermore, the smooth change in shape around the cutting edge stabilizes the load during cutting, which is expected to improve machining accuracy.

[0011] [3] In the above configuration, cutting edges may be formed on both the first end face and the second end face, and the cutting edges on the first end face and the second end face may be arranged so as to be 180° (2-fold) rotationally symmetric about a virtual axis existing on a virtual horizontal plane that bisects the side face into the first end face side and the second end face side. This configuration allows the cutting insert to be used on both sides, which is economical, reduces the time required for tool replacement, and improves work efficiency. Furthermore, because the cutting edges are 180° rotationally symmetric, the same cutting characteristics can be obtained with the same cutting edges even if the cutting insert is installed upside down.

[0012] [4] When the cutting edges of the first and second end faces are arranged with 180° rotational symmetry so that the cutting insert can be used on both sides, and each cutting edge has a first cutting edge and a second cutting edge, the first cutting edges and the second cutting edges are arranged in a twisted positional relationship in a side view. In this case, for example, the first cutting edge of the first end face and the second cutting edge of the second end face may face each other in a predetermined cross section of the side. In this case, the flank surface portion and the abutment surface portion connected to the first cutting edge may be connected via a first step portion having only a convex arc (not having both a concave arc and a convex arc), while the flank surface portion and the abutment surface portion connected to the second cutting edge may be connected via a second step portion having both a concave arc and a convex arc (the step portion of [1]). This allows for a design that prioritizes increased rigidity around the first cutting edge while considering stress relaxation around the second cutting edge.

[0013] [5] Furthermore, multiple cutting edges may be formed on at least one of the first end face and the second end face, and the multiple cutting edges may be arranged to be rotationally symmetrical (by a predetermined angle) with respect to each other around the central axis of the end face on which they are provided. For example, when three sets of cutting edges are provided on one end face, the cutting edges may be rotationally symmetrical by 120°. This allows multiple replacement uses of one end face, further improving economy and further extending the life of the cutting insert. In addition, the replacement frequency and replacement time can be further reduced, further improving work efficiency. Furthermore, because the cutting edges are rotationally symmetrical with respect to the central axis of the through hole, a good shape balance is achieved, and stable machining accuracy can be obtained.

[0014] [6] More specifically, when the cutting insert has a through hole drilled so as to penetrate the first end face and the second end face, it may be configured to satisfy the relationship shown in the following formula (1), where Ts represents the minimum width of the side surface, and Th represents the maximum radius of the opening of the through hole. Ts <Th …(1)

[0015] By configuring it in this manner, the through hole that functions as an attachment hole when attaching the cutting insert to the tool body can be sufficiently large, and the overall width of the cutting insert can be made thinner, making it easier to increase the number of cutting edges for the same cutter diameter.

[0016] [7] The cutting edge may have a first cutting edge and a second cutting edge, and may be configured to satisfy the relationship shown in the following formula (2). In the formula, Hf1 indicates the height of a specific portion of the first flank portion connected to the first cutting edge in a predetermined cross section of the side surface, and Hr1 indicates the height of a specific portion of the first abutment surface portion corresponding to the specific portion of the first flank portion in the predetermined cross section. Here, "height" indicates the length in a direction parallel to the central axis of the cutting insert (a direction along or approximately along the central axis of the through hole), and may also be called "vertical width" (the same applies in [8] below). Hf1 <Hr1 / 2 …(2)

[0017] By configuring the cutting insert in this manner, it is possible to ensure sufficient area for the contact surface portion that functions as part of the fixing portion when attaching the cutting insert to the tool body, ensuring mounting rigidity and stability, while reducing the height of the relief surface portion that connects to the first cutting edge, thereby increasing the rigidity directly below the first cutting edge and making the cutting insert thinner, thereby promoting compactness.

[0018] [8] Similarly, the cutting edge may have a first cutting edge and a second cutting edge, and may be configured to satisfy the relationship shown in the following formula (3): In the formula, Hf2 indicates the height of a specific portion of the second flank portion connected to the second cutting edge in a specific cross section of the side, and Hr2 indicates the height of a specific portion of the second abutment surface portion corresponding to the specific portion of the second flank portion in the specific cross section. Hf2 <Hr2 / 2 …(3) In this case too, by ensuring sufficient area for the contact surface that functions as part of the fixing part when attaching the cutting insert to the tool body and ensuring mounting rigidity and stability, and by reducing the height of the relief surface that connects to the second cutting edge, the rigidity directly below the second cutting edge can be increased and the cutting insert can be made thinner, promoting compactness.

[0019] [9] The cutting edge may have a first cutting edge and a second cutting edge, and a specific portion of the second flank surface connected to the second cutting edge and a second step portion (the boundary between the two specific portions) connected to a corresponding specific portion of the second abutment surface may be configured to approach the first end face as they move away from the first cutting edge. This improves the chipping resistance around the second cutting edge and widens the second abutment surface, thereby improving installation stability on the tool body. In this case, it is effective to position the second step portion as close as possible to the first end face (making the boundary as high as possible). However, due to the design of the cutting edge, it is difficult to narrow the entire second flank surface and maintain a uniform height at the boundary. Therefore, by focusing on increasing the height of the boundary portion at a position away from the first cutting edge, chipping resistance and installation stability can be improved.

[0020]

[10] Alternatively, in the configuration of [8] above, the ratio (Hf2 / Hr2) of the height Hf2 of the specific portion of the second flank surface to the height Hr2 of the specific portion of the second abutment surface may be configured to decrease with increasing distance from the first cutting edge, i.e., the ratio of Hr2 to Hf2 may be increased. This makes it easier to make the boundary portion at a position away from the first cutting edge relatively high, as in the configuration of [9] above, thereby improving fracture resistance and installation stability.

[0021]

[11] Furthermore, an example of a rotary cutting tool according to the present disclosure can be effectively configured with a tool body having a constraint surface, and a cutting insert according to the present disclosure attached to the tool body so that an abutment surface portion abuts against the constraint surface. That is, the cutting insert includes first and second end faces facing each other, side faces connected to the first and second end faces, a cutting edge provided on at least a part of an intersection ridge between the first end faces and the side faces, a flank portion formed on at least a part of the side face so as to be connected to the cutting edge and having an obtuse interior angle with respect to the first end face, an abutment surface portion formed on at least a part of the side face and protruding outward from the side face beyond the flank portion, and a step portion connected to a specific portion of the flank face and a specific portion of the abutment surface portion corresponding to the specific portion of the flank face, and having a shape including a concave arc and a convex arc in a cross section orthogonal or approximately orthogonal to the first end face. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a perspective view schematically showing the overall configuration of a cutting insert 10 provided in a cutting tool according to an embodiment of the present invention. [Figure 2] 2 is a plan view (top view) of the cutting insert 10 shown in FIG. 1. FIG. [Figure 3] FIG. 2 is a front view of the cutting insert 10 shown in FIG. [Figure 4] 4 is a diagram showing a part of the upper surface 10U side in a cross section taken along line IV-IV in FIG. 2. FIG. [Figure 5] 5 is an enlarged cross-sectional view showing a part (near a step B1) of FIG. 4. FIG. [Figure 6]6 is an enlarged cross-sectional view showing a step B3 corresponding to the step B1 in FIG. 5. FIG. [Figure 7] 1 is an enlarged perspective view showing the vicinity of the tip of a rotary cutting tool 100 according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0023] Hereinafter, this embodiment will be described with reference to the accompanying drawings. To facilitate understanding of the description, the same components in each drawing will be assigned the same reference numerals as much as possible, and redundant description will be omitted. Fig. 1 is a perspective view schematically showing the overall configuration of a cutting insert 10 provided in a cutting tool according to this embodiment, Fig. 2 is a plan view (top view) of the cutting insert 10 shown in Fig. 1, and Fig. 3 is a front view of the cutting insert 10 shown in Fig. 1.

[0024] <Cutting insert 10> As shown in FIGS. 1 to 3 , the cutting insert 10 has an upper surface 10U and a lower surface 10L (which correspond to examples of the “first end surface” and “second end surface” in the present disclosure, respectively) that face each other, and a side surface 10S that connects them. Furthermore, the cutting insert 10 has a through-hole H drilled through the upper surface 10U and the lower surface 10L. For convenience, the direction in which the upper surface 10U faces is referred to as “upward,” and the direction in which the lower surface 10L faces is referred to as “downward.” That is, the upper surface 10U and the lower surface 10L face in the vertical direction, and the side surface 10S faces in the horizontal direction. As will be described later, the upper surface 10U faces in the rotation direction of the cutting insert 10 when it is attached to the tool body 70, and the lower surface 10L is the opposite surface.

[0025] 1 and 2, the cutting insert 10 has a substantially polygonal (substantially hexagonal) shape in a plan view. Furthermore, cutting edges 2A, 2B, and 2C having the same structure are provided on a portion of the intersection ridge (the edge portion of the upper surface 10U) between the upper surface 10U and the side surface 10S. These three cutting edges 2A, 2B, and 2C are provided to be rotationally symmetrical with one another by 120° (three times) about the central axis Az (here, coinciding with the central axis of the through hole H) of the upper surface 10U and the lower surface 10D on which they are formed.

[0026] Each of the three cutting edges 2A, 2B, and 2C on the upper surface 10U has, in counterclockwise order in FIGS. 1 and 2 , an inner cutting edge 21, a bottom cutting edge 22 (finishing edge), a major cutting edge 23, and an arc portion 24 extending outward. Of these, the inner cutting edge 21 corresponds to an example of a “cutting edge” in the present disclosure. The major cutting edge 23 and the inner cutting edge 21 correspond to examples of a “first cutting edge” and a “second cutting edge,” respectively. The bottom cutting edge 22 is located on the end face of the rotary cutting tool 100 when the cutting insert 10 is attached to a tool body 70 (described later) and functions to improve the finished surface of the workpiece. In this embodiment, the inner cutting edge 21 and the major cutting edge 23 are linear in plan view, the bottom cutting edge 22 is substantially arc-shaped, and the arc portion 24 is also substantially arc-shaped. Thus, the bottom cutting edge 22 and the arc portion 24 are located at the corners of the cutting insert 10. In this case, the corner of the bottom cutting edge 22 is formed to have an apex angle of, for example, 140° to 160°, and the corner of the arc portion 24 is formed to have an apex angle of, for example, 80° to 100° (e.g., the corner of the bottom cutting edge 22 is 150° and the corner of the arc portion 24 is 90°).

[0027] FIG. 3 shows the position of a virtual horizontal plane S1 (a plane perpendicular to the central axis Az) that passes through the middle of the side surface 10S of the cutting insert 10, dividing it into the upper surface 10U and the lower surface 10L. In addition, FIGS. 1 and 2 show virtual axes Ax and Ay as an example of two-dimensional coordinate axes that exist (are included) on the virtual horizontal plane S1. The cutting insert 10 is formed so that the structures of the upper surface 10U and the lower surface 10L are rotationally symmetrical by 180° (two times) about the virtual axes Ax and Ay, so that both surfaces of the cutting insert 10 can be used. Thus, the upper surface 10U and the lower surface 10L have the same structure. That is, cutting edges 2A, 2B, and 2C with the same structure as those on the upper surface 10U are formed on a portion of the intersection ridge (the edge portion of the lower surface 10L) between the lower surface 10L and the side surface 10S.

[0028] On the outer edge sides of these upper surface 10U and lower surface 10L, the areas connecting to the cutting edges 2A, 2B, 2C function as cutting surfaces, and further, around the through hole H of the upper surface 10U and lower surface 10L, a flat portion is formed to fix the cutting insert 10 when it is pressed against the chip seat 71 when the cutting insert 10 is attached to the chip seat 71 of the tool body 70.

[0029] 2 and 3, the side surface 10S connecting the upper surface 10U and the lower surface 10L has flank portions F1, F2, F3, and F4 formed thereon, which are connected to the inner cutting edge 21, the bottom cutting edge 22, the main cutting edge 23, and the arc portion 24, respectively. Each of these flank portions F1, F2, F3, and F4 is formed so that the interior angle θ with respect to the upper surface 10U and the lower surface 10L is an obtuse angle (has a negative flank angle).

[0030] 1 and 3, on the side surface 10S, contact surface portions R13, R22, R31, R44, which are, for example, flat surfaces, are formed between the flank portions F1, F2, F3, F4 on one side of the upper surface 10U and the lower surface 10L and the flank portions F4, F3, F2, F1 on the other side of the upper surface 10U and the lower surface 10L. These contact surface portions R13, R22, R31, R44 protrude outward from the flank portions F1, F2, F3, F4 and, together with the flat portion of the rake face described above, function as part of a fixing portion that is fixed by being pressed against the tip seat 71 when the cutting insert 10 is attached to the tip seat 71 (pocket) of the tool body 70.

[0031] FIG. 4 is a diagram showing a portion of the upper surface 10U side in a cross section taken along line IV-IV in FIG. 2 (a cross section perpendicular or substantially perpendicular to the upper surface 10U and the lower surface 10L, and parallel to the central axis Az). FIG. 3 also shows the approximate position of the cross section. FIG. 5 is an enlarged cross-sectional view of a portion of FIG. 4 (near the step B1), and FIG. 6 is an enlarged cross-sectional view of the step B3 corresponding to the step B1 in FIG. 5. Thus, the flank portion F1 connected to the inner cutting edge 21 (which corresponds to an example of a "specific portion of the flank portion" in the present disclosure) and the corresponding abutment surface portion R13 (which corresponds to an example of a "specific portion of the abutment surface" in the present disclosure) are connected via the step B1, which has a shape including a concave arc C and a convex arc V. Meanwhile, the flank portion F3 connected to the major cutting edge 23 and the corresponding abutment surface portion R13 are connected via the step B3, which only has the convex arc V. As such, the step portion B3 on the side of the main cutting edge 23 and the step portion B1 on the side of the inner cutting edge 21 are examples of the "first step portion" and "second step portion" in the present disclosure, respectively.

[0032] 5, the concave arc C of the step portion B1 is recessed inward (to the left in the figure) from an imaginary line (broken line in the figure) connecting a boundary P1 between the flank portion F1 and the step portion B1 and a boundary P2 between the step portion B1 and the abutment surface R13, and its periphery is a concave curved surface. On the other hand, the convex arc V of the step portion B1 bulges outward (to the right in the figure) from the imaginary line, and its periphery is a convex curved surface. Furthermore, the boundaries P1 and P2 do not form any angle, whether acute or obtuse, and are formed smoothly so that the change in curvature is not discontinuous.

[0033] Furthermore, the boundary P3 between the concave arc C and the convex arc V is also formed smoothly, without forming a corner, so that the curvature is an inflection point without interruption. Meanwhile, as shown in FIG. 6 , the convex arc V of the step portion B3 bulges outward (to the right in the figure) from the imaginary line (the dashed line in the figure) connecting the boundary P4 between the abutment surface portion R13 and the step portion B3 and the boundary P5 between the step portion B3 and the flank surface portion F3, and the periphery thereof is a convex curved surface. The boundary P4 is also formed smoothly without forming a corner. Meanwhile, the boundary P5 may also be formed smoothly in consideration of stress concentration, but in this embodiment, a corner is formed due to design constraints that prioritize increasing rigidity by reducing the height below the main cutting edge 23.

[0034] The cutting insert 10 is configured to satisfy the relationship shown in the following formula (1), where Ts in the formula indicates the minimum width of the side surface 10S, and Th indicates the maximum opening radius of the through hole H (see FIG. 2). Ts <Th …(1)

[0035] Additionally, the cutting insert 10 is configured to satisfy the relationship shown in the following formula (2): where Hf1 in the formula indicates the height of the flank portion F3 (specific portion) connected to the major cutting edge 23 in a predetermined cross section of the side surface 10S, and Hr2 indicates the height of the abutment surface portion R31 (specific portion) corresponding to the flank portion F3 in the predetermined cross section (see FIG. 2). Hf <Hr / 2 …(2)

[0036] Similarly, the cutting insert 10 is configured to satisfy the relationship shown in the following formula (3): Here, Hf2 in the formula indicates the height of the flank portion F1 (specific portion) in a predetermined cross section of the side surface 10S, and Hr2 indicates the height of the abutment surface portion R13 (specific portion) corresponding to the flank portion F1 in the predetermined cross section (see FIG. 2). Hf2 <Hr2 / 2 …(3)

[0037] 3, the flank surface F1 connected to the inner cutting edge 21 and the step portion B1 (boundary portion) connected to the abutment surfaces R13 and R31 are configured to approach the upper surface 10U and the lower surface 10L as they move away from the major cutting edge 23. In other words, the edge of the step B1 on the upper surface 10U on the inner cutting edge 21 side is higher (i.e., closer to the upper surface 10U) at a position farther from the major cutting edge 23 than at a position closer to the major cutting edge 23 on the same upper surface 10U (although the opposite tendency may be observed in part). Similarly, the edge of the step B1 on the lower surface 10L on the inner cutting edge 21 side is lower (i.e., closer to the lower surface 10L) at a position farther from the major cutting edge 23 than at a position closer to the major cutting edge 23 (although the opposite tendency may be observed in part).

[0038] Furthermore, this configuration can also be expressed as follows when focusing on the ratio (Hf2 / Hr2) of the height Hf2 of the flank surface portion F1 to the height Hr2 of the abutment surface portion R13 shown in the above formula (3): That is, the cutting insert 10 is configured so that this ratio (Hf2 / Hr2) decreases with increasing distance from the main cutting edge 23 (the ratio of Hr2 becomes greater than Hf2). In other words, in the region of the abutment surface portions R13, R31, the upper and lower sides are not simply parallel and oblique, but one end of the side on the inner cutting edge 21 side has a shape that curves close to the upper surface 10U and the lower surface 10L, as shown in FIG.

[0039] <Rotary cutting tool 100> FIG. 7 is an enlarged perspective view of the vicinity of the end of the rotary cutting tool 100 according to this embodiment, showing three cutting inserts 10 attached to a tool body 70 that rotates around a rotation axis J, as viewed from the oblique tip side of the rotation axis J. As shown in the figure, the rotary cutting tool 100 includes a plurality of cutting inserts 10 and the tool body 70 to which the cutting inserts 10 are attached. Each cutting insert 10 is attached by threading a fixing member 72 having a male thread inserted into a through hole H with the female thread of a threaded hole formed in an insert seat 71 of the tool body 70, and pressing the cutting insert 10 against the tool body 70 with the fixing member 72. At this time, the upper surface 10U of the cutting insert 10 faces the rotation direction of the tool body 70, as shown in the figure. Furthermore, two of the contact surfaces R13, R22, R31, and R44 of the side surface 10S and the flat portion of the lower surface 10L are pressed against the tip seat 71 to define a fixed portion, thereby determining the fixed position of the cutting insert 10.

[0040] <Effects of the embodiment> According to the cutting insert 10 configured as described above and the rotary cutting tool 100 to which it is attached, the flank portions F1, F2, F3, F4 form obtuse angles with the upper surface 10U and the lower surface 10L, and in addition, the flank portion F1 and the abutment surface portion R13 are connected via a step portion B1 having smooth unevenness (concave arc C and convex arc V). Therefore, no angle is formed as would be formed if the flank portion F1 and the abutment surface portion R13 were directly connected, and therefore it is possible to prevent stress from concentrating locally.

[0041] In particular, the stepped portion B1 has a concave-convex curved shape, which results in a gentle stress distribution and prevents high-stress points due to sudden cross-sectional changes. Furthermore, the provision of such a stepped portion B1 distributes the cutting load over a wide area between the flank portion F1 and the abutment surface R13, reducing localized loads. Furthermore, the convex curve of the stepped portion B1 increases the apparent cross-sectional area and volume on the flank portion F1 side, improving rigidity and enhancing fracture resistance around the inner cutting edge 21 corresponding to the stepped portion B1. As a result, fracture resistance around the inner cutting edge 21, which is actively used in ramping and other processes, can be improved, enabling stable machining performance and extended tool life.

[0042] Furthermore, the cross-sectional portion of the inner cutting edge 21 on the side surface 10S does not form any sharp or obtuse angles at the boundaries P1 and P2 between the flank surface F1 and the abutment surface R13 and the step portion B1, and at the boundary P3 between the concave arc C and the convex arc V. The transition from the flank surface F1 and the abutment surface R13 to the step portion B1 is smooth, preventing abrupt changes in shape. Furthermore, the step portion B1 does not experience any abrupt changes in curvature, such as edges or sharp bends. This suppresses stress concentration, which is likely to occur when there are corners or abrupt changes in curvature, thereby reducing damage and wear around the inner cutting edge 21. Furthermore, the smooth shape change around the inner cutting edge 21 stabilizes the load during cutting, which is expected to improve machining accuracy.

[0043] Furthermore, the cutting edges 2A, 2B, and 2C are formed on both the upper surface 10U and the lower surface 10L, and are arranged so as to be 180° rotationally symmetrical about the imaginary axes Ax and Ay that exist on the imaginary horizontal plane S1. This allows the cutting insert 10 to be used on both sides. This improves economy, reduces the time required for tool replacement, and improves work efficiency. Furthermore, because the cutting edges 2A, 2B, and 2C are 180° rotationally symmetrical, the same cutting characteristics can be obtained with the same cutting edges even if the cutting insert 10 is installed upside down.

[0044] In this case, the inner cutting edges 21 of the cutting edges 2A, 2B, 2C and the main cutting edges 23 are arranged in a twisted positional relationship in a side view. In the case shown in FIG. 3, for example, the inner cutting edge 21 on the upper surface 10U and the main cutting edge 23 on the lower surface 10L are arranged to face each other in the same cross-section of the side surface 10S. Under such conditions, the relief surface portion F3 and the contact surface portions R13, R31 connected to the main cutting edge 23 are connected via a step portion B3 having only a convex arc V (FIG. 5). On the other hand, the relief surface portion F1 and the contact surface portions R13, R31 connected to the inner cutting edge 23 are connected via a step portion B1 having a concave arc C and a convex arc V (FIG. 6). Thereby, the relief surface F3 directly below the main cutting edge 23 is made as short (narrow) as possible, and is bulged outward at the step portion B3 to increase the cross-sectional area, so that a configuration considering stress relaxation around the inner cutting edge 21 can be realized while prioritizing a design with enhanced rigidity.

[0045] Furthermore, a plurality of cutting edges 2A, 2B, 2C are formed on both the upper surface 10U and the lower surface 10L, and the plurality of cutting edges 2A, 2B, 2C are configured to be rotationally symmetric with each other at 120° about the central axis Az of the upper surface 10U and the lower surface 10L. Therefore, since it is possible to exchange and use each of the upper surface 10U and the lower surface 10L a plurality of times, the economy is further improved, and the life of the cutting insert 10 can be further extended. In addition, the replacement frequency and replacement time can be further reduced, and the working efficiency can be further improved. Furthermore, since the cutting edges 2A, 2B, 2C are rotationally symmetric with respect to the central axis Az, they have excellent shape balance and stable machining accuracy can be obtained.

[0046] Moreover, when the relationship (Ts < Th) shown in the above formula (1) is satisfied, the size of the through-hole H that functions as a mounting hole when the cutting insert 10 is attached to the tool body 70 is sufficiently ensured, and by making the overall width of the cutting insert 10 thin, it is advantageous in that the number of cutting edges can be increased even with the same cutter diameter.

[0047] In addition, when the relationship (Hf1 < Hr1 / 2) shown in the above formula (2) is satisfied, a sufficient area of a part of the contact surfaces R13, R22, R31, and R44 that function as a part of the fixing portion when the cutting insert 10 is attached to the tool body 70 can be ensured, and the mounting rigidity and stability can be ensured. Further, by suppressing the height of the flank surface F3 connected to the main cutting edge 23, the rigidity directly below the main cutting edge 23 can be increased, and the cutting insert 10 can be made thinner to promote compactification. Similarly, when the relationship (Hf2 < Hr2 / 2) shown in the above formula (3) is satisfied, a sufficient area of a part of the contact surfaces R13, R22, R31, and R44 can be ensured, and the mounting rigidity and stability can be ensured. Further, by suppressing the height of the flank surface F1 connected to the inner cutting edge 21, the rigidity directly below the inner cutting edge 21 can be increased, and the cutting insert 10 can be made thinner to further promote compactification. In this case, even if the height of the side surface 10S is reduced more than before due to miniaturization, the notch resistance (durability) around the inner cutting edge 23 can be increased by providing the stepped portion B1 having smooth irregularities.

[0048] Also, the stepped portion B1 on the inner cutting edge 21 side (the boundary portion between the flank surface F1 and the contact surfaces R13 and R31) is configured to approach the upper surface 10U and the lower surface 10L as it moves away from the main cutting edge 23. Thereby, the notch resistance around the inner cutting edge 21 can be improved, and the contact surfaces R13 and R31 can be widened, which can also enhance the installation stability on the tool body 70. In this case, it is effective to bring the stepped portion B1 as close as possible to the upper surface 10U and the lower surface 10L sides. However, due to the cutting edge design, it is difficult to narrow the entire flank surface F1 and keep the height of the boundary portion constantly above a certain level. Therefore, by focusing on increasing the boundary portion at a position away from the main cutting edge 23, the notch resistance and the installation stability can be improved. Further, the ratio (Hf2 / Hr2) of the height Hf2 of the flank surface F1 to the height Hr2 of the contact surface R13 is configured to decrease as it moves away from the main cutting edge 23. Also in this regard, it becomes easier to relatively increase the boundary portion at a position away from the main cutting edge 23, and as a result, the notch resistance and the installation stability can be further improved.

[0049] The present embodiment has been described above with reference to specific examples. However, this is for the purpose of facilitating understanding of the present disclosure and is not intended to limit the present disclosure. In other words, the present disclosure is not limited to these specific examples. Design modifications to these specific examples made by a person skilled in the art are also encompassed within the technical scope of the present disclosure as long as they comprise the features of the present disclosure. Furthermore, unless otherwise specified, the elements, arrangements, materials, conditions, shapes, dimensions, sizes, scales, etc. of the above-described specific examples are not limited to those exemplified and can be modified as appropriate. Furthermore, the elements of the above-described specific examples can be combined as appropriate as long as no technical contradictions arise.

[0050] That is, for example, the cutting insert according to the present disclosure may have one, two, or four or more cutting edges equivalent to the cutting edges 2A, 2B, and 2C on each of the upper surface 10U and the lower surface 10L. Cutting edges may also be formed on the entire edges of the upper surface 10U and the lower surface 10L (note that in this case, some portions may not actually function as cutting edges). Furthermore, the shapes of the inner cutting edge 21 and the major cutting edge 23 are not limited to being linear in plan view, but may be curved, such as an arc having a larger radius of curvature than the arc portion 24 in plan view. Furthermore, the bottom cutting edge 22 may be linear rather than arc-shaped, thereby improving sharpness. The flank surface portion F3 and the abutment surfaces R13 and R31 connected to the major cutting edge 23 may be directly connected without a step. Additionally, the upper surface 10U and the lower surface 10L may be appropriately provided with an uneven shape such as a chip breaker on the rake faces that connect to the cutting edges 2A, 2B, and 2C. [Explanation of symbols]

[0051] 2A, 2B, 2C...Cutting edge, 10...Cutting insert, 10S...Side surface, 10U...Top surface (first end surface), 10L...Bottom surface (second end surface), 21...Inner cutting edge (second cutting edge), 22...Bottom cutting edge, 23...Main cutting edge (first cutting edge), 70...Tool body, 71...Insert seat, 72...Fixing member, 100...Rotary cutting tool, Ax, Ay...Virtual axis, Az...Central axis, B1...Step portion (second step portion), B3...Step portion (first step portion), C...Concave arc, F1, F2, F3, F4...Flank surface, H...Through hole, J...Rotation axis, P1, P2, P3, P4, P5...Boundary, R13, R22, R31, R44...Abutment surface, S1...Virtual horizontal plane, V...Convex arc, θ...Interior angle

Claims

1. A metal plate having a first end face and a second end face facing each other, and side faces connected to the first end face and the second end face; a cutting edge provided on at least a part of an intersection ridge line between the first end surface and the side surface; a flank portion formed on at least a part of the side surface so as to be connected to the cutting edge and having an interior angle with respect to the first end surface that is an obtuse angle; an abutment surface portion formed on at least a part of the side surface and protruding outward from the relief surface portion; a step portion that is connected to a specific portion of the relief surface portion and a specific portion of the contact surface portion that corresponds to the specific portion of the relief surface portion, and that has a shape that includes a concave arc and a convex arc in a cross section that is orthogonal or substantially orthogonal to the first end face; Equipped with The side surface has a cross-sectional portion that is perpendicular or substantially perpendicular to the cutting edge, and is formed smoothly so that no corners are formed at the boundaries between the relief surface portion and the step portion and between the abutment surface portion and the concave arc and the convex arc, and so that the change in curvature is not discontinuous. Cutting insert.

2. A first end face and a second end face facing each other, and side faces connected to the first end face and the second end face; a cutting edge provided on at least a part of an intersection ridge line between the first end surface and the side surface; a flank portion formed on at least a part of the side surface so as to be connected to the cutting edge and having an interior angle with respect to the first end surface that is an obtuse angle; an abutment surface portion formed on at least a part of the side surface and protruding outward from the relief surface portion; a step portion that is connected to a specific portion of the relief surface portion and a specific portion of the contact surface portion that corresponds to the specific portion of the relief surface portion, and that has a shape that includes a concave arc and a convex arc in a cross section that is orthogonal or substantially orthogonal to the first end face; Equipped with The cutting edges of the first end surface and the second end surface have first cutting edges and second cutting edges, respectively; The flank surface portion connected to the first cutting edge and the abutment surface portion are connected via a first step portion having only a convex arc, The flank surface portion connected to the second cutting edge and the abutment surface portion are connected via a second step portion having the concave arc and the convex arc. Cutting insert.

3. A first end face and a second end face that face each other, and side faces that connect to the first end face and the second end face; a cutting edge provided on at least a part of an intersection ridge line between the first end surface and the side surface; a flank portion formed on at least a part of the side surface so as to be connected to the cutting edge and having an interior angle with respect to the first end surface that is an obtuse angle; an abutment surface portion formed on at least a part of the side surface and protruding outward from the relief surface portion; a step portion that is connected to a specific portion of the relief surface portion and a specific portion of the contact surface portion that corresponds to the specific portion of the relief surface portion, and that has a shape that includes a concave arc and a convex arc in a cross section that is orthogonal or substantially orthogonal to the first end face; a through hole formed so as to penetrate the first end surface and the second end surface; Equipped with The following formula (1): Ts<Th ... (1) Ts: the minimum width of the side surface, Th: maximum opening radius of the through hole, The relationship shown in Cutting insert.

4. A metal plate having a first end face and a second end face facing each other, and side faces connected to the first end face and the second end face; a cutting edge provided on at least a part of an intersection ridge line between the first end surface and the side surface; a flank portion formed on at least a part of the side surface so as to be connected to the cutting edge and having an interior angle with respect to the first end surface that is an obtuse angle; an abutment surface portion formed on at least a part of the side surface and protruding outward from the relief surface portion; a step portion that is connected to a specific portion of the relief surface portion and a specific portion of the contact surface portion that corresponds to the specific portion of the relief surface portion, and that has a shape that includes a concave arc and a convex arc in a cross section that is orthogonal or substantially orthogonal to the first end face; Equipped with The cutting edge has a first cutting edge and a second cutting edge, The following formula (2): Hf1<Hr1 / 2...(2), Hf1: the height of a specific portion of the first flank surface portion connected to the first cutting edge in a predetermined cross section of the side surface, Hr1: the height of a specific portion of the first contact surface portion corresponding to the specific portion of the first relief surface portion in the predetermined cross section of the side surface, The relationship shown in Cutting insert.

5. A first end face and a second end face facing each other, and side faces connected to the first end face and the second end face; a cutting edge provided on at least a part of an intersection ridge line between the first end surface and the side surface; a flank portion formed on at least a part of the side surface so as to be connected to the cutting edge and having an interior angle with respect to the first end surface that is an obtuse angle; an abutment surface portion formed on at least a part of the side surface and protruding outward from the relief surface portion; a step portion that is connected to a specific portion of the relief surface portion and a specific portion of the contact surface portion that corresponds to the specific portion of the relief surface portion, and that has a shape that includes a concave arc and a convex arc in a cross section that is orthogonal or substantially orthogonal to the first end face; Equipped with The cutting edge has a first cutting edge and a second cutting edge, The following formula (3): Hf2<Hr2 / 2...(3), Hf2: the height of a specific portion of the second flank surface portion connected to the second cutting edge in a predetermined cross section of the side surface, Hr2: the height of a specific portion of the second contact surface portion corresponding to the specific portion of the second relief surface portion in the predetermined cross section of the side surface, The relationship shown in Cutting insert.

6. A metal plate having a first end face and a second end face facing each other, and side faces connected to the first end face and the second end face; a cutting edge provided on at least a part of an intersection ridge line between the first end surface and the side surface; a flank portion formed on at least a part of the side surface so as to be connected to the cutting edge and having an interior angle with respect to the first end surface that is an obtuse angle; an abutment surface portion formed on at least a part of the side surface and protruding outward from the relief surface portion; a step portion that is connected to a specific portion of the relief surface portion and a specific portion of the contact surface portion that corresponds to the specific portion of the relief surface portion, and that has a shape that includes a concave arc and a convex arc in a cross section that is orthogonal or substantially orthogonal to the first end face; Equipped with The cutting edge has a first cutting edge and a second cutting edge, a second step portion connected to a specific portion of the second flank surface portion connected to the second cutting edge and a specific portion of the second abutment surface portion corresponding to the specific portion of the second flank surface portion approach the first end surface as they move away from the first cutting edge; Cutting insert.

7. The cutting insert according to claim 5, wherein a ratio Hf2 / Hr2 of a height Hf2 of a specific portion of the second flank surface portion to a height Hr2 of a specific portion of the second abutment surface portion decreases with increasing distance from the first cutting edge.

8. a first end surface and a second end surface facing each other, and side surfaces connected to the first end surface and the second end surface; a cutting edge provided on at least a part of an intersection ridge line between the first end surface and the side surface; a flank portion formed on at least a part of the side surface so as to be connected to the cutting edge and having an interior angle with respect to the first end surface that is an obtuse angle; an abutment surface portion formed on at least a part of the side surface and protruding outward from the relief surface portion; a step portion that is connected to a specific portion of the relief surface portion and a specific portion of the contact surface portion that corresponds to the specific portion of the relief surface portion, and that has a shape that includes a concave arc and a convex arc in a cross section that is orthogonal or substantially orthogonal to the first end face; Equipped with an edge line of the step portion has only one inflection point in a cross section perpendicular or substantially perpendicular to the first end surface and the second end surface; Cutting insert.

9. The cutting edge is formed on both the first end surface and the second end surface, The cutting edges of the first end surface and the second end surface are provided rotationally symmetrically by 180° around a virtual axis existing on a virtual horizontal plane that divides the side surface into two halves, the first end surface side and the second end surface side. The cutting insert according to claim 8.

10. The cutting insert according to claim 8, wherein a plurality of cutting edges are formed on at least one of the first end face and the second end face, and the plurality of cutting edges are arranged so as to be rotationally symmetrical about a central axis of the end face on which the plurality of cutting edges are formed.

11. a tool body having a constraint surface; The cutting insert according to any one of claims 1 to 10, which is attached to the tool body so that the abutment surface portion abuts against the constraint surface; A rotary cutting tool comprising:

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