End mill

Abstract

An end mill (1) extends in an axial direction along a central axis (C). The end mill (1) has a blade part (3) at the leading end of the end mill (1). The blade part (3) is provided with four or more sets of cutting blades (7) around the central axis (C). The rotation path of the cutting blades (7) around the central axis (C) has a diameter dimension (D) of 3 mm or less. The radial inner edge of a bottom blade (71) is disposed away from the central axis (C) in the radial direction. The rotation path of the bottom blade (71) around the central axis (C) makes a curved shape that is convex toward the leading end in a longitudinal sectional view along the central axis (C), and in this longitudinal sectional view, the radius of curvature (R) of the convex curve made by the rotation path of the bottom blade (71) is larger than the diameter dimension (D). A chip discharge groove (4) has a linearly extending groove transition part (10) located at the boundary between a trailing end part of the chip discharge groove (4) and the outer circumferential surface (3b) of the blade part (3). The ratio (L / D) between the diameter dimension (D) and the axial dimension (L) between the leading end of the bottom blade (71) and the trailing end of the chip discharge groove (4) is 2.0 or less.

Description

End mill

[0001] This application claims priority from Japanese Patent Application No. 2024-003342, filed on January 12, 2024, the contents of which are incorporated herein by reference.

[0002] Conventionally, end mills have been known that include a cutting edge portion and a shank disposed on the rear end side of the cutting edge portion, and extend in the axial direction along a central axis. Patent Document 1 discloses a small-diameter end mill in which the maximum outer diameter of the cutting edge portion (i.e., the cutting edge diameter dimension) is formed to, for example, 6 mm or less.

[0003] Japanese Patent Application Laid-Open No. 2018-192566

[0004] With conventional small-diameter end mills, it has been difficult to meet the demand for improved machining efficiency while maintaining rigidity, especially when the diameter of the cutting edge (blade diameter) is reduced to 3 mm or less. For example, when cutting a hard workpiece such as high-hardness steel, it has been difficult to achieve both improved machining efficiency and a high rigidity.

[0005] An object of the present invention is to provide an end mill that is small in diameter but has increased rigidity and can improve machining efficiency.

[0006] In order to solve the above problems, the present invention provides the following means.

[0007] [Aspect 1 of the present invention] An end mill extending in an axial direction along a central axis, the end mill having a cutting portion on the tip side of the end mill, the cutting portion having a chip discharge groove extending in a direction opposite to the end mill rotation direction around the central axis as it moves from the tip face of the cutting portion toward the rear end side, a bottom cutting edge disposed on a ridge line connecting a wall face of the chip discharge groove facing the end mill rotation direction to the tip face of the cutting portion, a peripheral cutting edge disposed on a ridge line connecting the wall face to the outer peripheral face of the cutting portion, and a convex curved corner cutting edge connecting the bottom cutting edge to the peripheral cutting edge, and four or more sets of cutting edges including the bottom cutting edge, the peripheral cutting edge and the corner cutting edge are provided at intervals around the central axis. an end mill in which a diameter dimension D of a rotation locus of the cutting blade about the central axis is 3 mm or less, a radially inner end of the bottom cutting edge is positioned radially away from the central axis, the rotation locus of the bottom cutting edge about the central axis forms a curve that is convex toward the tip side when viewed in vertical section along the central axis, and a radius of curvature R of the convex curve formed by the rotation locus of the bottom cutting edge when viewed in vertical section is larger than the diameter dimension D, the chip discharge groove has a groove cut-out portion that is located at the boundary between the rear end of the chip discharge groove and the outer peripheral surface of the cutting portion and extends linearly, and L / D, which is a ratio of the axial dimension L between the tip of the bottom cutting edge and the rear end of the chip discharge groove to the diameter dimension D, is 2.0 or less.

[0008] [Aspect 2 of the Present Invention] The end mill according to aspect 1, wherein the groove turning-up portion extends substantially parallel to the central axis.

[0009] [Aspect 3 of the present invention] The end mill according to Aspect 1 or 2, wherein the chip discharge groove has, in a cross section perpendicular to the central axis, a first concave curved surface portion that forms a concave curve extending radially inward from the peripheral cutting edge toward the end mill rotation direction, a convex curved surface portion that is connected to an end of the first concave curved surface portion in the end mill rotation direction and forms a convex curve extending in the end mill rotation direction, and a second concave curved surface portion that is connected to an end of the convex curved surface portion in the end mill rotation direction and forms a concave curve extending radially outward toward the end mill rotation direction.

[0010] [Aspect 4 of the present invention] The end mill according to aspect 3, wherein, in the cross-sectional view, the radius of curvature of the convex curved surface portion is larger than the radius of curvature of the first concave curved surface portion and is also larger than the radius of curvature of the second concave curved surface portion.

[0011] [Aspect 5 of the present invention] The end mill according to aspect 3 or 4, wherein, when viewed in the cross section, a maximum protrusion amount of the convex curved surface portion protruding from an imaginary line connecting radially inner ends of the first concave curved surface portion and the second concave curved surface portion in a direction perpendicular to the imaginary line is defined as h, a value of a ratio of the maximum protrusion amount h to the diameter dimension D (h / D) is 1% or more and 12% or less.

[0012] [Aspect 6 of the present invention] An end mill according to any one of aspects 1 to 5, wherein the chip discharge groove has a groove-shaped gash arranged adjacent to the bottom cutting edge in the direction of end mill rotation of the bottom cutting edge, and the number of gashes is four or more, the same as the number of bottom cutting edges, and the radially inner ends of each gash are connected to each other on the central axis.

[0013] [Aspect 7 of the present invention] The end mill according to any one of aspects 1 to 6, further comprising a shank arranged on the rear end side of the cutting portion, the diameter dimension of the shank being larger than the diameter dimension D, and the ratio M / D of the axial dimension M from the tip of the shank to the tip of the cutting portion and the diameter dimension D is 10 or less.

[0014] [Aspect 8 of the present invention] An end mill described in any one of aspects 1 to 7, wherein four or more peripheral blades are provided, and the four or more peripheral blades include a main peripheral blade that is located radially outermost among the peripheral blades, and a secondary peripheral blade that is located radially inner than the main peripheral blade, and the main peripheral blades and the secondary peripheral blades are arranged alternately around the central axis.

[0015] [Aspect 9 of the present invention] An end mill according to aspect 8, wherein the diameter dimension of the rotational locus of the main peripheral cutting edge around the central axis is the diameter dimension D, and the difference (D-d) between the diameter dimension D and the diameter dimension d of the rotational locus of the auxiliary peripheral cutting edge around the central axis is 0.04 times or less the diameter dimension D.

[0016] [Aspect 10 of the present invention] The end mill according to any one of aspects 1 to 9, wherein the rake angle of the peripheral cutting edge is a negative angle, and the rake angle of the end cutting edge is a negative angle.

[0017] [Aspect 11 of the present invention] The end mill according to aspect 10, wherein the rake angle of each of the peripheral cutting edge and the bottom cutting edge is −30° or more and −10° or less.

[0018] [Aspect 12 of the present invention] An end mill extending in an axial direction along a central axis, the end mill having a cutting portion on the tip side of the end mill, the cutting portion having a chip discharge groove extending in a direction opposite to the end mill rotation direction around the central axis as it moves from the tip face of the cutting portion toward the rear end side, a bottom cutting edge disposed on a ridge line connecting a wall face of the chip discharge groove facing the end mill rotation direction to the tip face of the cutting portion, a peripheral cutting edge disposed on a ridge line connecting the wall face to the outer peripheral face of the cutting portion, and a convex curved corner cutting edge connecting the bottom cutting edge to the peripheral cutting edge, and three sets of cutting edges each including the bottom cutting edge, the peripheral cutting edge, and the corner cutting edge are provided at intervals around the central axis, an end mill in which a diameter dimension D of a rotation locus of the cutting blade about the central axis is 3 mm or less, a radially inner end of the bottom cutting edge is positioned radially away from the central axis, the rotation locus of the bottom cutting edge about the central axis forms a curve that is convex toward the tip side when viewed in vertical section along the central axis, a radius of curvature R of the convex curve formed by the rotation locus of the bottom cutting edge when viewed in vertical section is larger than the diameter dimension D, the chip discharge groove has a groove cut-off portion that is located at the boundary between the rear end of the chip discharge groove and the outer peripheral surface of the cutting portion and extends linearly, and L / D, which is a ratio of the axial dimension L between the tip of the bottom cutting edge and the rear end of the chip discharge groove to the diameter dimension D, is 2.0 or less.

[0019] According to the above aspect of the present invention, an end mill is provided that is small in diameter but has increased rigidity and can improve machining efficiency.

[0020] FIG. 1 is a side view showing an end mill according to this embodiment, with a simplified representation of a portion thereof (the cutting edge). FIG. 2 is a side view showing the cutting edge of the end mill. FIG. 3 is a cross-sectional view (longitudinal cross-sectional view) showing a simplified cross section along the central axis of the rotation trajectory obtained by rotating the cutting edge around the central axis. For ease of explanation, the difference in the radial position of each peripheral cutting edge is emphasized for easy understanding. Also, corner cutting edges are not shown. FIG. 4 is a front view of the cutting edge as seen from the tip side. FIG. 5 is a cross-sectional view (transverse cross-sectional view) showing the cutting edge as a cross section perpendicular to the central axis. FIG. 6 is a cross-sectional view (transverse cross-sectional view) showing the cutting edge of a modified end mill according to this embodiment, with the cross section perpendicular to the central axis.

[0021] An end mill 1 according to one embodiment of the present invention will be described with reference to Figures 1 to 5. The end mill 1 according to this embodiment is a cutting tool (milling tool) that performs milling (milling) on ​​a workpiece such as a metal. Specifically, the end mill 1 according to this embodiment is a radius end mill that is suitable for milling a workpiece having high hardness, such as high-hardness steel.

[0022] 1 and 2, the end mill 1 has a columnar shape centered on a central axis C. The end mill 1 includes a shank 2 and a cutting portion 3. Note that the cutting portion 3 is shown in a simplified form in FIG.

[0023] 3 is a cross-sectional view (longitudinal cross-sectional view) showing, in simplified form, the rotation trajectory obtained by rotating the cutting portion 3 around the central axis C, as a cross section along the central axis C. In FIG. 3 , the diameter dimension (outer diameter dimension) D of the cutting portion 3, i.e., the blade diameter dimension D, is, for example, 3 mm or less. The diameter dimension D of the cutting portion 3 may be 2 mm or less, or may be 1 mm or less. In this embodiment, the diameter dimension D of the cutting portion 3 is set to a predetermined value, for example, in the range of 0.5 mm to 0.8 mm. Since the diameter dimension D of the cutting portion 3 is thus small, the end mill 1 of this embodiment may also be referred to as a small-diameter end mill.

[0024] 1, the shank 2 and the cutting portion 3 are arranged coaxially with each other, with the central axis C as a common axis. Furthermore, the shank 2 and the cutting portion 3 are arranged at different positions from each other in the direction in which the central axis C extends.

[0025] In this embodiment, the direction in which the central axis C of the end mill 1 extends is referred to as the axial direction. The end mill 1 extends in the axial direction along the central axis C. Within the axial direction, the direction from the shank 2 to the cutting portion 3 is referred to as the axial tip side or simply the tip side, and the direction from the cutting portion 3 to the shank 2 is referred to as the axial rear end side or simply the rear end side.

[0026] The direction perpendicular to the central axis C is called the radial direction. Within the radial direction, the direction approaching the central axis C is called the radially inner direction, and the direction away from the central axis C is called the radially outer direction. Additionally, the direction rotating around the central axis C is called the circumferential direction. Within the circumferential direction, the direction in which the end mill 1 is rotated during cutting is called the end mill rotation direction T, and the opposite rotation direction is called the side opposite to the end mill rotation direction T or the counter-end mill rotation direction (see FIGS. 4 and 5).

[0027] As shown in FIG. 1 , the shank 2 has a cylindrical shape extending in the axial direction about a central axis C. The shank 2 is disposed on the rear end side of the cutting portion 3. The diameter dimension of the shank 2 is larger than the diameter dimension (blade diameter dimension) D of the cutting portion 3. The tip portion of the shank 2 is tapered so that the diameter dimension decreases (contracts) toward the tip side. In this embodiment, M / D, which is the ratio of the axial dimension M from the tip of the shank 2 to the diameter dimension D, is, for example, 10 or less. Preferably, M / D is 8 or less, and more preferably 5 or less. The axial dimension M may also be referred to as the neck length, etc.

[0028] The shank 2 is detachably held by a spindle or the like of a machine tool (not shown, hereinafter sometimes abbreviated as the spindle or the like). The shank 2 is rotated by the spindle or the like in the end mill rotation direction T, while being moved radially and axially relative to a workpiece (not shown). As a result, the end mill 1 cuts into the workpiece with cutting edges 7 (bottom cutting edge 71, peripheral cutting edge 72, and corner cutting edge 73) of the cutting portion 3, which will be described later, to perform milling. The diameter dimension (blade diameter dimension) D of the cutting portion 3 described above corresponds to the diameter dimension of the rotational trajectory of the cutting edge 7 about the central axis C, and more specifically, corresponds to the diameter dimension of the rotational trajectory of the peripheral cutting edge 72 about the central axis C.

[0029] The cutting portion 3 is disposed on the tip side (tip portion) of the end mill 1. The cutting portion 3 has a generally cylindrical shape extending in the axial direction along the central axis C. As shown in Figures 2 to 5, the cutting portion 3 has a chip discharge flute 4, a rake face 5, a flank face 6, and a cutting edge 7.

[0030] The chip discharge grooves 4 are groove-shaped and open to the leading end surface 3a facing the axial leading end of the cutting portion 3 and to the outer circumferential surface 3b facing radially outward. The chip discharge grooves 4 extend in the opposite direction to the end mill rotation direction T around the central axis C as they move from the leading end surface 3a of the cutting portion 3 toward the rear end. A plurality of chip discharge grooves 4 are provided in the cutting portion 3 at intervals in the circumferential direction. In this embodiment, four or more chip discharge grooves 4 are provided at equal or unequal pitches in the circumferential direction.

[0031] The chip discharge groove 4 has a gash 9 disposed at the tip of the chip discharge groove 4. The gash 9 constitutes a part (tip) of the chip discharge groove 4. The gash 9 is a groove recessed from the tip surface 3a of the cutting portion 3 toward the rear end, and extends generally along the radial direction. The gash 9 is disposed adjacent to the bottom cutting edge 71 in the end mill rotation direction T of the bottom cutting edge 71, which will be described later. In this embodiment, as shown in Figure 4, the groove width dimension of the gash 9 increases as it extends radially outward.

[0032] As shown in FIG. 2 , the chip discharge groove 4 has a groove sweep 10 disposed at the rear end of the chip discharge groove 4. The groove sweep 10 is a ridge located at the boundary between the rear end of the chip discharge groove 4 and the outer peripheral surface 3b of the cutting portion 3, and extends linearly. More specifically, the groove sweep 10 corresponds to the ridge connecting the rear end of the first edge 4b, which is located in the end mill rotation direction T, and the rear end of the second edge 4c (corresponding to the peripheral cutting edge 72 described later), which is located in the opposite direction to the end mill rotation direction, of both end edges (a pair of edges) 4b, 4c of the chip discharge groove 4 in the groove width direction. The groove sweep 10 corresponds to the portion referred to as a "cutter sweep" by those skilled in the art.

[0033] In this embodiment, the groove starting portion 10 extends substantially parallel to the central axis C. That is, the groove starting portion 10 extends generally along the axial direction. In this embodiment, the phrase "substantially parallel to the central axis C" means that, when the cutting portion 3 is viewed from a radial direction perpendicular to the central axis C as shown in FIG. 2 , the angle at which the groove starting portion 10 is inclined with respect to the central axis C is within ±3°, and preferably ±2° or less.

[0034] The chip discharge groove 4 has a first concave curved surface portion 41, a convex curved surface portion 43, and a second concave curved surface portion 42. As shown in Fig. 5 , the first concave curved surface portion 41 has a concave curved shape extending radially inward from the peripheral cutting edge 72 (described later) toward the end mill rotation direction T. In this cross-sectional view, the convex curved surface portion 43 is connected to the end of the first concave curved surface portion 41 in the end mill rotation direction T, and has a convex curved shape extending in the end mill rotation direction T. In this cross-sectional view, the second concave curved surface portion 42 is connected to the end of the convex curved surface portion 43 in the end mill rotation direction T, and has a concave curved shape extending radially outward toward the end mill rotation direction T.

[0035] That is, the chip discharge groove 4 has a pair of concave curved surface portions (first concave curved surface portion and second concave curved surface portion) 41, 42 spaced apart from each other in the circumferential direction, and a convex curved surface portion 43 located between the pair of concave curved surface portions 41, 42 in the circumferential direction. In the cross-sectional view shown in Figure 5, the pair of concave curved surface portions 41, 42 each have a curved shape that is concave toward the inside in the radial direction, specifically, a concave arc shape. In addition, in this cross-sectional view, the convex curved surface portion 43 has a curved shape that is convex toward the outside in the radial direction, specifically, a convex arc shape (an arc shape centered on the central axis C).

[0036] In the cross-sectional view of Figure 5, the first concave curved surface portion 41 and the convex curved surface portion 43 are connected without any steps so as to smoothly contact each other. Specifically, the first concave curved surface portion 41 and the convex curved surface portion 43 are continuously formed so as to have a common tangent at their connecting portion. In addition, in this cross-sectional view, the convex curved surface portion 43 and the second concave curved surface portion 42 are connected without any steps so as to smoothly contact each other. Specifically, the convex curved surface portion 43 and the second concave curved surface portion 42 are continuously formed so as to have a common tangent at their connecting portion. In addition, the second concave curved surface portion 42 is connected to an outer peripheral flank surface (flank surface 6) described later that is adjacent to the chip discharge groove 4 in the end mill rotation direction T.

[0037] 5 , the radius of curvature r3 of the convex curved surface portion 43 is larger than the radius of curvature r1 of the first concave curved surface portion 41 and is larger than the radius of curvature r2 of the second concave curved surface portion 42. In this cross-sectional view, h denotes the maximum amount of protrusion (maximum protrusion dimension) of the convex curved surface portion 43 protruding from an imaginary line VL connecting the radial inner ends (deepest points) of the first concave curved surface portion 41 and the second concave curved surface portion 42 in a direction perpendicular to the imaginary line VL. In this embodiment, the ratio (h / D) of the maximum protrusion amount h to the diameter dimension (blade diameter dimension) D of the cutting portion 3 is set to, for example, 1% or more and 12% or less.

[0038] As shown in Figures 2, 4, and 5, the rake face 5 is arranged on the wall surface 4a of the chip discharge groove 4 facing the end mill rotation direction T. The rake face 5 has a tip rake face, a peripheral rake face, and a corner rake face. The tip rake face is arranged at the tip portion of the wall surface 4a that connects to the tip surface 3a of the cutting portion 3. The peripheral rake face is arranged at the radially outer end portion of the wall surface 4a that connects to the outer peripheral surface 3b of the cutting portion 3. The corner rake face is arranged on the wall surface 4a between the radially outer end portion of the tip rake face and the tip portion of the peripheral rake face. Note that at least a portion of the tip rake face and the corner rake face is arranged on the wall surface (a portion constituting the wall surface 4a) that faces the end mill rotation direction T of the gash 9. For this reason, the tip rake face and the corner rake face may also be referred to as gash rake faces, etc.

[0039] The flank 6 has a tip flank arranged on the tip surface 3 a of the cutting portion 3, an outer circumferential flank arranged on the outer circumferential surface 3 b of the cutting portion 3, and a corner flank arranged between the radial outer end of the tip flank and the tip of the outer circumferential flank.

[0040] The tip flank is disposed between circumferentially adjacent chip discharge grooves 4 (gash 9) on the tip face 3a of the cutting portion 3. The tip flank is connected to a bottom cutting edge 71 (described later) of the cutting edge 7 and extends along the bottom cutting edge 71. The tip flank extends from the bottom cutting edge 71 toward the rear end in the axial direction as it moves away from the bottom cutting edge 71 toward the opposite side to the end mill rotation direction T. This provides the bottom cutting edge 71 with a clearance angle.

[0041] The peripheral flank is disposed between adjacent chip discharge grooves 4 in the circumferential direction on the outer peripheral surface 3b of the cutting portion 3. The peripheral flank is connected to the peripheral cutting edge 72 (described later) of the cutting edge 7, and extends along the peripheral cutting edge 72. The peripheral flank extends radially inward as it moves from the peripheral cutting edge 72 toward the opposite side of the end mill rotation direction T. This provides the peripheral cutting edge 72 with a clearance angle.

[0042] The corner flank is disposed at the corner where the tip surface 3a and outer peripheral surface 3b of the cutting portion 3 are connected. The corner flank has a curved shape that is convex toward the tip outer periphery. The corner flank is connected to a corner edge 73 (described later) of the cutting edge 7 and extends along the corner edge 73. As the corner flank moves from the corner edge 73 toward the opposite side of the end mill rotation direction T, it extends toward the rear end side in the axial direction and toward the radially inner side. This provides the corner edge 73 with a clearance angle.

[0043] The cutting edge 7 has a bottom cutting edge 71, a peripheral cutting edge 72, and a corner cutting edge 73. The bottom cutting edge 71 is located on a ridge line connecting a wall surface 4a (i.e., the rake face 5, and the same applies below) of the chip discharge groove 4 facing the end mill rotation direction T with the tip surface 3a of the cutting portion 3. The peripheral cutting edge 72 is located on a ridge line connecting the wall surface 4a with the peripheral surface 3b of the cutting portion 3. The corner cutting edge 73 connects the bottom cutting edge 71 and the peripheral cutting edge 72 and forms a convex curve. That is, the cutting portion 3 has the bottom cutting edge 71, the peripheral cutting edge 72, and the corner cutting edge 73.

[0044] A plurality of sets of cutting edges 7, each including a bottom cutting edge 71, a peripheral cutting edge 72, and a corner cutting edge 73, are provided at intervals around the central axis C. In this embodiment, four or more sets of cutting edges 7 are provided. In other words, this end mill 1 is a multi-blade end mill with four or more blades. The plurality of cutting edges 7 are arranged at equal or unequal pitches in the circumferential direction around the central axis C.

[0045] The bottom cutting edge 71 is disposed on the ridge where the tip rake face and the tip flank face are connected. The bottom cutting edge 71 extends in a substantially radial direction along the direction in which the gashes 9 extend. In this embodiment, the number of bottom cutting edges 71 is four or more, and the number of gashes 9 is the same as the number of bottom cutting edges 71, i.e., four or more. As shown in FIG. 4 , the radial inner ends of each gashes 9 are connected to each other on the central axis C. In other words, each gashes 9 is in communication with each other via the central axis C. The multiple gashes 9 extend radially around the central axis C.

[0046] Specifically, as shown in Figure 4, in a front view of the cutting portion 3 from the tip side, each bottom cutting edge 71 has a curved shape that is convex toward the end mill rotation direction T. Furthermore, the radially inner end of each bottom cutting edge 71 is disposed away from the central axis C in the radial direction. In other words, the radially inner end of the bottom cutting edge 71 is disposed radially outward of the central axis C.

[0047] 3, the rotation path of the bottom cutting edge 71 around the central axis C forms a curve that is convex toward the tip side in a vertical cross-sectional view along the central axis C. In this embodiment, in this vertical cross-sectional view, the radius of curvature R of the convex curve formed by the rotation path of the bottom cutting edge 71 is larger than the diameter dimension (blade diameter dimension) D of the cutting portion 3. The radius of curvature R of the bottom cutting edge 71 is, for example, 1.05 to 3 times the diameter dimension D of the cutting portion 3, and preferably 1.07 to 2.0 times.

[0048] 2, in this embodiment, the ratio L / D, which is the ratio of the axial dimension L between the tip of the bottom cutting edge 71 and the rear end of the chip discharge groove 4 to the diameter dimension D, is, for example, 2.0 or less. Here, the "tip of the bottom cutting edge 71" refers to the most distal end point of the bottom cutting edge 71. Furthermore, the "rear end of the chip discharge groove 4" refers to the connection point where the rear end of the first edge 4b ​​of the chip discharge groove 4 and the rear end of the groove cutting portion 10 are connected.

[0049] The peripheral cutting edge 72 is disposed on the ridge where the peripheral rake face and the peripheral flank face are connected. The peripheral cutting edge 72 extends along the chip discharge groove 4. Specifically, the peripheral cutting edge 72 extends in the direction opposite to the end mill rotation as it moves toward the rear end in the axial direction. The peripheral cutting edge 72 is the cutting edge 7 that is disposed radially outermost. Therefore, the diameter dimension D of the cutting edge 3 described above can also be rephrased as the diameter dimension D of the rotational trajectory of the peripheral cutting edge 72 around the central axis C.

[0050] In this embodiment, a plurality of peripheral blades 72 are provided at intervals from one another in the circumferential direction, specifically, four or more are provided. As shown in Figure 3, the four or more peripheral blades 72 include a major peripheral blade 72a that is located radially outermost among the peripheral blades 72, and a minor peripheral blade 72b that is located radially inward of the major peripheral blade 72a. A plurality of major peripheral blades 72a are provided, specifically, two or more are provided. A plurality of minor peripheral blades 72b are provided, specifically, two or more are provided. The major peripheral blades 72a and the minor peripheral blades 72b are arranged alternately around the central axis C.

[0051] 3, the diameter of the rotational locus of the main peripheral cutting edge 72a around the central axis C is the above-mentioned diameter D. In this embodiment, the difference (D-d) between this diameter D and the diameter d of the rotational locus of the auxiliary peripheral cutting edge 72b around the central axis C is set to 0.04 times or less the diameter D.

[0052] As shown in Figure 2, the corner cutting edge 73 is located on the ridge where the corner rake face and the corner relief face are connected. The corner cutting edge 73 has a curved shape that is convex toward the outer periphery of the tip of the cutting portion 3. The radially inner end of the corner cutting edge 73 is connected to smoothly contact the radially outer end of the bottom cutting edge 71. The rear end of the corner cutting edge 73 is connected to smoothly contact the front end of the peripheral cutting edge 72.

[0053] In this embodiment, the rake angles of the bottom cutting edge 71, the peripheral cutting edge 72, and the corner cutting edge 73 are each negative angles. The rake angles of the bottom cutting edge 71, the peripheral cutting edge 72, and the corner cutting edge 73 are, for example, between -30° and -10°. Specifically, the rake angle of the bottom cutting edge 71 is, for example, an axial rake angle. Furthermore, the rake angle of the peripheral cutting edge 72 is, for example, a radial rake angle.

[0054] The end mill 1 of this embodiment described above is a small-diameter end mill in which the diameter dimension D of the rotational trajectory of the cutting blade 7, i.e., the diameter dimension (blade diameter dimension) D of the cutting portion 3, is 3 mm or less, and the cutting portion 3 is particularly thin.

[0055] Furthermore, the end mill 1 of this embodiment has four or more sets of cutting edges 7, including the bottom cutting edges 71, peripheral cutting edges 72, and corner cutting edges 73. In other words, this end mill 1 is a multi-blade end mill with four or more blades. Furthermore, the convex curve obtained by cutting the rotational trajectory of the bottom cutting edges 71 with a vertical cross section along the central axis C (an imaginary plane including the central axis C) has a radius of curvature R that is larger than the diameter dimension D of the cutting portion 3. This reduces the thickness of the chips produced by cutting with each bottom cutting edge 71, thereby reducing cutting resistance.

[0056] As described above, since the end mill 1 has multiple cutting edges and the cutting resistance of each bottom cutting edge 71 is reduced, it is possible to perform cutting processing by setting cutting conditions with high efficiency. Therefore, the end mill 1 of this embodiment can improve processing efficiency.

[0057] Furthermore, in this end mill 1, the ratio L / D, which is the ratio of the axial dimension L between the tip of the bottom cutting edge 71 and the rear end of the chip discharge groove 4 (corresponding to the overall axial dimension of the chip discharge groove 4) to the diameter dimension D, is kept small at 2.0 or less. While ensuring the chip discharge performance of the chip discharge groove 4, the amount of thinning of the end mill 1 due to the provision of the chip discharge groove 4 can be kept small, thereby suppressing a decrease in rigidity.

[0058] Furthermore, as shown in FIG. 1 of the aforementioned Patent Document 1 (JP 2018-192566 A), in conventional end mills, the groove upturning portion located at the rear end of the chip discharge flute 4 and cutting up to the outer peripheral surface 3b of the cutting portion 3 is concavely curved. In contrast, in the end mill 1 of this embodiment, the groove upturning portion 10 located at the rear end of the chip discharge flute 4 and cutting up to the outer peripheral surface 3b of the cutting portion 3 is linear. This configuration also minimizes the amount of thinning of the end mill 1. Therefore, the end mill 1 of this embodiment ensures stable rigidity.

[0059] Specifically, in conventional end mills, the rear end of the first edge 4b ​​of the chip discharge flute 4 is connected to the rear end of the second edge 4c by a groove chamfering portion in a concave curved line, resulting in a greater amount of thinning of the end mill 1 in the conventional end mill (see FIG. 2) compared to the present embodiment, in which the rear ends are connected by a linear groove chamfering portion 10.

[0060] As described above, according to this embodiment, even though it is a small-diameter end mill, it is possible to increase rigidity and improve machining efficiency. For example, even when cutting a hard workpiece such as high-hardness steel, it is possible to ensure both rigidity and improved machining efficiency. In particular, according to this embodiment, the above-mentioned effects are stably achieved even when the diameter dimension D of the cutting portion 3 is narrowed to, for example, 1 mm or less.

[0061] In this embodiment, the groove turning-up portion 10 extends substantially parallel to the central axis C. In this case, the amount of thinning of the end mill 1 due to the provision of the chip discharge grooves 4 can be reduced, thereby improving rigidity.

[0062] In the end mill 1 of this embodiment, the chip discharge groove 4 has, in a cross-sectional view perpendicular to the central axis C, a first concave curved surface portion 41 which forms a concave curve extending radially inward from the outer cutting edge 72 toward the end mill rotation direction T, a convex curved surface portion 43 which, in this cross-sectional view, is connected to the end of the first concave curved surface portion 41 in the end mill rotation direction T and forms a convex curve extending in the end mill rotation direction T, and a second concave curved surface portion 42 which, in this cross-sectional view, is connected to the end of the convex curved surface portion 43 in the end mill rotation direction T and forms a concave curve extending radially outward as it approaches the end mill rotation direction T.

[0063] That is, in this embodiment, the chip discharge flute 4 has a pair of concave curved surface portions (first and second concave curved surface portions) 41, 42 spaced apart from each other in the end mill rotation direction T, and a convex curved surface portion 43 disposed between the pair of concave curved surface portions 41, 42. Therefore, the radially inner ends of the pair of concave curved surface portions 41, 42 and the convex curved surface portion 43 can be arranged close to a single imaginary circle VC (a circle corresponding to the core thickness of the cutting portion 3) centered on the central axis C, as shown in FIG. 5 , in a cross-sectional view perpendicular to the central axis C. Unlike conventional end mills, this embodiment prevents a portion (deepest portion) of the chip discharge flute from being formed to dig more deeply into the radially inner side of the cutting portion than other portions. Therefore, according to this embodiment, even with the chip discharge flute 4, it is possible to ensure a large core thickness dimension W (the diameter dimension of the imaginary circle VC), thereby achieving both good chip discharge performance and stable increased rigidity.

[0064] Specifically, when the diameter dimension D of the cutting portion 3 is taken as the reference (100%), in this embodiment, the core thickness dimension W of the cutting portion 3 is set to 70% or more and 90% or less, and preferably 72% or more and 85% or less.

[0065] In this embodiment, in a cross-sectional view perpendicular to the central axis C, the radius of curvature r3 of the convex curved surface portion 43 is larger than the radius of curvature r1 of the first concave curved surface portion 41 and larger than the radius of curvature r2 of the second concave curved surface portion 42. In this case, it is easy to arrange the convex curved surface portion 43 along the circumference of the imaginary circle VC. This allows a large core thickness dimension W of the cutting portion 3 to be ensured, thereby stably improving rigidity. In this embodiment, in the cross-sectional view shown in FIG. 5, the convex curved surface portion 43 is arranged to coincide with the circumference of the imaginary circle VC, which corresponds to the core thickness of the cutting portion 3.

[0066] In addition, in this embodiment, when viewed in a cross section perpendicular to the central axis C, when the maximum protrusion amount of the convex curved surface portion 43 from the imaginary line VL connecting the radial inner ends (deepest points) of the first concave curved surface portion 41 and the second concave curved surface portion 42 in a direction perpendicular to this imaginary line VL is defined as h, the ratio of the maximum protrusion amount h to the diameter dimension D (h / D) is 1% or more and 12% or less.

[0067] When the value of the ratio (h / D) is 1% or more, a sufficient maximum protrusion amount h of the convex curved surface portion 43 is ensured. By providing the chip discharge groove 4 with the pair of concave curved surface portions (first concave curved surface portion and second concave curved surface portion) 41, 42 and the convex curved surface portion 43, the above-mentioned effect of ensuring a large core thickness of the cutting portion 3 is more stably achieved.

[0068] Furthermore, when the value of the ratio (h / D) is 12% or less, it is possible to prevent the maximum protrusion amount h of the convex curved surface portion 43 from becoming too large. This makes it possible to prevent the convex curved surface portion 43 from protruding too far outward in the radial direction within the chip discharge groove 4, thereby preventing an effect on chip discharge performance. The value of the ratio (h / D) is preferably 1.5% or more and 9% or less, and more preferably 2% or more and 6% or less.

[0069] Furthermore, in this embodiment, the chip discharge groove 4 has a groove-shaped gash 9 arranged adjacent to the bottom cutting edge 71 in the end mill rotation direction T of the bottom cutting edge 71. Four or more gashes 9 are provided, the same number as the bottom cutting edges 71, and the radial inner ends of each gash 9 are connected to each other on the central axis C. In this case, each gash 9 arranged adjacent to each bottom cutting edge 71 in the end mill rotation direction T communicates with each other via the central axis C. This increases the degree of freedom of flow of chips and coolant within the gash 9, thereby improving chip discharge performance.

[0070] In this embodiment, the diameter of the shank 2 is larger than the diameter of the cutting portion 3, and the ratio M / D, which is the ratio of the axial dimension M from the tip of the shank 2 to the tip of the cutting portion 3 to the diameter D, is 10 or less. In this embodiment, as described above, the axial dimension L between the tip of the bottom cutting edge 71 and the rear end of the chip discharge groove 4, i.e., the ratio L / D, which is the ratio of the axial overall length L of the chip discharge groove 4 to the diameter D, is kept small, at 2.0 or less. This makes it easy to keep the axial dimension M between the tip of the shank 2 and the tip of the cutting portion 3, i.e., the ratio M / D, which is the ratio of the so-called neck length M to the diameter D, small, at 10 or less. Since the ratio of the overall length of the shank 2, which has a larger (thicker) outer diameter than the cutting portion 3 (the ratio of the axial length of the shank 2 to the overall axial length of the end mill 1), can be secured to a large value, thereby stably increasing rigidity. M / D is preferably 8 or less, and more preferably 5 or less.

[0071] In this embodiment, the four or more (plural) peripheral cutting edges 72 include a main peripheral cutting edge 72a that is located radially outermost among these peripheral cutting edges 72, and a sub peripheral cutting edge 72b that is located radially inward of the main peripheral cutting edge 72a. The main peripheral cutting edges 72a and the sub peripheral cutting edges 72b are arranged alternately around the central axis C. In this case, the multiple peripheral cutting edges 72 include main peripheral cutting edges 72a and sub peripheral cutting edges 72b that are located at different radial positions from each other. This suppresses resonance during cutting, thereby suppressing chatter vibrations. The end mill 1 of this embodiment enables stable, high-precision cutting.

[0072] In this embodiment, the difference (D-d) between the diameter dimension D of the rotational locus around the central axis C of the main peripheral cutting edge 72a and the diameter dimension d of the rotational locus around the central axis C of the auxiliary peripheral cutting edge 72b is 0.04 times or less than the diameter dimension D. When the difference (D-d) is 0.04 times or less than the diameter dimension D, chatter vibrations during cutting can be stably suppressed while ensuring rigidity, as described above.

[0073] In this embodiment, the rake angle of the peripheral cutting edge 72 is a negative angle, the rake angle of the bottom cutting edge 71 is a negative angle, and the rake angle of the corner cutting edge 73 is a negative angle. In this case, the cutting angles of the peripheral cutting edge 72, bottom cutting edge 71, and corner cutting edge 73 are each ensured to be large, thereby suppressing chipping and damage to the cutting edge 7. In particular, the cutting performance of the end mill 1 is maintained excellent even when cutting a hard workpiece such as high-hardness steel.

[0074] In this embodiment, the rake angles of the peripheral cutting edge 72, bottom cutting edge 71, and corner cutting edge 73 are between -30° and -10°. When the rake angles of the peripheral cutting edge 72, bottom cutting edge 71, and corner cutting edge 73 are between -30° and -10°, chipping and breakage of the cutting edge 7 can be stably suppressed while maintaining good sharpness.

[0075] The present invention is not limited to the above-described embodiment, and the configuration may be modified within the scope of the present invention, as described below. In the illustrations of the modified examples, the same components as those in the above-described embodiment are denoted by the same reference numerals, and the following mainly describes the differences.

[0076] In the above embodiment, the rake angles of the peripheral cutting edge 72, the bottom cutting edge 71, and the corner cutting edge 73 are each between -30° and -10°, but this is not limitative. At least one of the rake angles of the peripheral cutting edge 72, the bottom cutting edge 71, and the corner cutting edge 73 may be outside the above numerical range.

[0077] Fig. 6 is a cross-sectional view (transverse cross-sectional view) showing the cutting portion 3 of an end mill 1A according to a modified example of the above-described embodiment, taken along a cross section perpendicular to the central axis C. As shown in Fig. 6, the end mill 1A according to this modified example has three sets of cutting edges 7, each set including a bottom cutting edge 71, a peripheral cutting edge 72, and a corner cutting edge 73, spaced apart from one another around the central axis C. The three sets of cutting edges 7 are arranged at equal intervals in the circumferential direction around the central axis C. However, the three sets of cutting edges 7 may also be arranged at unequal intervals in the circumferential direction.

[0078] Although not specifically shown, three gashes 9 are provided, the same number as the bottom cutting edges 71. The radially inner ends of each gashes 9 are connected to each other on the central axis C (see Figure 4). The three peripheral cutting edges 72 include a major peripheral cutting edge 72a and a minor peripheral cutting edge 72b (see Figure 3). One of the major peripheral cutting edge 72a and the minor peripheral cutting edge 72b is provided in one piece, and two of the other are provided in two pieces. The major peripheral cutting edge 72a and the minor peripheral cutting edge 72b are arranged alternately from a predetermined position around the central axis C toward the end mill rotation direction T.

[0079] The end mill 1A of the above modified example also provides the same excellent effects as the end mill 1 described in the above embodiment.

[0080] The present invention may be combined with the various configurations described in the above-described embodiments and modifications, and may also include additions, omissions, substitutions, and other modifications of configurations, without departing from the spirit of the present invention. Furthermore, the present invention is not limited to the above-described embodiments, but is limited only by the scope of the claims.

[0081] According to the present invention, an end mill that can improve the rigidity and machining efficiency even though it is a small diameter end mill is provided, and therefore has industrial applicability.

[0082] 1, 1A…End mill, 2…Shank, 3…Cutting edge, 3a…Tip face, 3b…Peripheral surface, 4…Chip discharge groove, 4a…Wall surface, 7…Cutting edge, 9…Gash, 10…Groove cut upper portion, 41…1st concave curved portion, 42…2nd concave curved portion, 43…Convex curved portion, 71…Bottom edge, 72…Peripheral cutting edge, 72a…Main peripheral cutting edge, 72b…Sub peripheral cutting edge, 73…Corner edge, C…Center axis, D, d…Diameter dimensions, h…Maximum protrusion, L, M…Axial dimensions, R, r1, r2, r3…Radius of curvature, T…End mill rotation direction, VL…Imaginary straight line

Claims

1. An end mill extending axially along a central axis, the end mill having a cutting edge portion on the tip side of the end mill, the cutting edge portion including a chip discharge groove extending from the tip surface of the cutting edge portion toward the rear end side in a direction opposite to the end mill rotation direction around the central axis, a bottom cutting edge disposed at a ridge line portion where a wall surface of the chip discharge groove facing the end mill rotation direction and the tip surface of the cutting edge portion are connected, an outer peripheral cutting edge disposed at a ridge line portion where the wall surface and the outer peripheral surface of the cutting edge portion are connected, and a convex curve-shaped corner cutting edge connecting the bottom cutting edge and the outer peripheral cutting edge, wherein a set of cutting edges including the bottom cutting edge, the outer peripheral cutting edge, and the corner cutting edge are provided in four or more sets spaced apart from each other around the central axis, a diameter dimension D of a rotation locus of the cutting edge around the central axis is 3 mm or less, an inner end in the radial direction of the bottom cutting edge is disposed away from the central axis in the radial direction, a rotation locus of the bottom cutting edge around the central axis is in a curved shape convex toward the tip side in a longitudinal sectional view along the central axis, a curvature radius R of a convex curve formed by the rotation locus of the bottom cutting edge in the longitudinal sectional view is larger than the diameter dimension D, the chip discharge groove has a groove finishing portion located at a boundary between a rear end portion of the chip discharge groove and the outer peripheral surface of the cutting edge portion and extending linearly, and an L / D which is a ratio of an axial dimension L between the tip of the bottom cutting edge and the rear end of the chip discharge groove to the diameter dimension D is 2.0 or less. End mill.

2. The groove finishing portion extends substantially parallel to the central axis. The end mill according to claim 1.

3. The chip discharge groove has a first concave curved surface portion formed in a concave curve shape extending in the end mill rotation direction from the outer peripheral cutting edge toward the inner side in the radial direction in a cross-sectional view perpendicular to the central axis, a convex curved surface portion formed in a convex curve shape connected to an end of the first concave curved surface portion in the end mill rotation direction and extending in the end mill rotation direction, and a second concave curved surface portion formed in a concave curve shape connected to an end of the convex curved surface portion in the end mill rotation direction and extending toward the outer side in the radial direction as it goes in the end mill rotation direction in the cross-sectional view. The end mill according to claim 1 or 2.

4. In the cross-sectional view, the curvature radius of the convex curved surface portion is larger than the curvature radius of the first concave curved surface portion and larger than the curvature radius of the second concave curved surface portion. The end mill according to claim 3.

5. In the cross-sectional view, when the maximum protrusion amount h of the convex curved surface portion protruding in a direction orthogonal to the virtual straight line connecting the radially inner ends of the first concave curved surface portion and the second concave curved surface portion is defined, the ratio value (h / D) of the maximum protrusion amount h to the diameter dimension D is 1% or more and 12% or less. The end mill according to claim 3.

6. The chip discharge groove has a groove-shaped gullet arranged adjacent to the bottom edge in the end mill rotation direction of the bottom edge. The gullets are provided in the same number as the bottom edges and four or more are provided. The radially inner end portions of the respective gullets are connected to each other on the central axis. The end mill according to claim 1 or 2.

7. Further comprising a shank arranged on the rear end side of the cutting edge portion, the diameter dimension of the shank is larger than the diameter dimension D, and the ratio M / D, which is the ratio of the axial dimension M from the tip of the shank to the tip of the cutting edge portion to the diameter dimension D, is 10 or less. The end mill according to claim 1 or 2.

8. Four or more outer peripheral cutting edges are provided. The four or more outer peripheral cutting edges include a main outer peripheral cutting edge located on the outermost side in the radial direction among these outer peripheral cutting edges and a sub-outer peripheral cutting edge arranged on the inner side in the radial direction with respect to the main outer peripheral cutting edge. The main outer peripheral cutting edge and the sub-outer peripheral cutting edge are alternately arranged around the central axis. The end mill according to claim 1 or 2.

9. The diameter dimension of the rotation locus of the main outer peripheral cutting edge around the central axis is the diameter dimension D, and the difference (D - d) between the diameter dimension D and the diameter dimension d of the rotation locus of the sub-outer peripheral cutting edge around the central axis is 0.04 times or less with respect to the diameter dimension D. The end mill according to claim 8.

10. The rake angle of the outer peripheral cutting edge is a negative angle, and the rake angle of the bottom edge is a negative angle. The end mill according to claim 1 or 2.

11. The rake angles of the outer peripheral cutting edge and the bottom edge are each -30° or more and -10° or less. The end mill according to claim 10.

12. An end mill extending axially along a central axis, the end mill having a cutting edge portion on the tip side of the end mill, the cutting edge portion including: a chip discharge groove extending from the tip surface of the cutting edge portion toward the rear end side in a direction opposite to the end mill rotation direction about the central axis; a bottom cutting edge disposed at a ridge line portion where a wall surface facing the end mill rotation direction of the chip discharge groove and the tip surface of the cutting edge portion are connected; an outer peripheral cutting edge disposed at a ridge line portion where the wall surface and the outer peripheral surface of the cutting edge portion are connected; and a convex curved corner cutting edge connecting the bottom cutting edge and the outer peripheral cutting edge. A set of three cutting edges including the bottom cutting edge, the outer peripheral cutting edge, and the corner cutting edge are provided at intervals from each other about the central axis. The diameter dimension D of the rotational locus of the cutting edge about the central axis is 3 mm or less. The radially inner end of the bottom cutting edge is disposed radially away from the central axis. The rotational locus of the bottom cutting edge about the central axis is curved convex toward the tip side in a longitudinal sectional view along the central axis. In the longitudinal sectional view, the radius of curvature R of the convex curve formed by the rotational locus of the bottom cutting edge is larger than the diameter dimension D. The chip discharge groove has a groove finishing portion located at the boundary between the rear end portion of the chip discharge groove and the outer peripheral surface of the cutting edge portion and extending linearly. The ratio L / D, which is the ratio of the axial dimension L between the tip of the bottom cutting edge and the rear end of the chip discharge groove to the diameter dimension D, is 2.0 or less. End mill.

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