End mill

Abstract

An end mill (1) is provided with a cutting edge section (3) that rotates about a central axis (O) and a shank (2), and has an end cutting edge (11) that is positioned on the tip surface of the cutting edge section (10) and an outer peripheral cutting edge (13) that is positioned on the outer peripheral surface of the cutting edge section (10), the end cutting edge (11) having an end cutting edge outer peripheral section (11a). The end edge outer peripheral section (11a) extends toward the shank side from the outer peripheral end of the end edge toward the inside in the radial direction at an inclination angle (alpha) of 3 DEG or less with respect to a plane orthogonal to the center axis (O), and the relief angle of an end edge outer peripheral section first flank surface (14a) adjacent to the end edge outer peripheral section (11a) is larger than the relief angle of an outer peripheral section first flank surface (14a) adjacent to the outer peripheral edge (13). The width (W2) of the first flank surface of the outer peripheral part of the end blade is larger than the width (W1) of the first flank surface of the outer peripheral blade.

Description

Technical Field

[0001] The present invention relates to end mills.

[0002] This application claims priority based on patent application No. 2022-143470 filed in Japan on September 9, 2022, and its contents are incorporated herein. Background Art

[0003] Conventionally, it is known to provide a flank having a small clearance angle and a small flank width on the flank face of the peripheral cutting edge in order to improve the cutting edge strength of the peripheral cutting edge of an end mill, as described in Patent Document 1, for example.

[0004] Patent Document 1: Japanese Patent Application Publication No. 2012-091306 (A)

[0005] However, even in end mills that have a micro-flank surface to increase the strength of the cutting edge, chipping or notching near the tip of the peripheral cutting edge cannot be fully suppressed, and therefore it is desirable to further extend the tool life. In particular, end mills whose substrate is CBN that lacks defect resistance have the problem of chipping or notching being easily generated near the tip of the peripheral cutting edge. Summary of the invention

[0006] An object of the present invention is to provide an end mill in which chipping or notching in the vicinity of the front end of a peripheral cutting edge is suppressed and which has a long life.

[0007] (1) According to one embodiment of the present invention, there is provided an end mill, which comprises a cutting edge portion and a shank that rotates around a central axis. The end mill comprises a bottom blade located on the front end surface of the cutting edge portion and a peripheral blade located on the outer peripheral surface of the cutting edge portion. The bottom blade comprises a bottom blade peripheral portion, and the bottom blade peripheral portion extends toward the shank side from the outer peripheral end of the bottom blade toward the radial inside at an inclination angle of less than 3° relative to a plane orthogonal to the central axis. The back angle of the first back blade surface of the bottom blade peripheral portion adjacent to the bottom blade peripheral portion is greater than the back angle of the first back blade surface of the peripheral blade adjacent to the peripheral blade. The width of the first back blade surface of the bottom blade peripheral portion is greater than the width of the first back blade surface of the peripheral blade.

[0008] According to the above structure, the bottom blade has a bottom blade peripheral portion with a core digging angle of 3° or less, so the direction of the cutting resistance of the bottom blade can be close to the direction parallel to the center axis, thereby reducing the load acting from the bottom blade toward the peripheral blade. In addition, not only the clearance angle of the first clearance face of the bottom blade peripheral portion is greater than the clearance angle of the first clearance face of the peripheral blade, but also the width of the first clearance face of the bottom blade peripheral portion is greater than the width of the first clearance face of the peripheral blade, so that not only the tip strength of the peripheral blade is improved, but also even if the core digging angle of the bottom blade peripheral portion is suppressed to 3° or less, the cutting resistance of the bottom blade will not be too large, and sufficient rigidity near the front end of the end mill can be ensured, and the load acting from the bottom blade toward the peripheral blade near the front end of the peripheral blade can be reduced, thereby effectively suppressing chipping or large notches generated near the front end of the peripheral blade.

[0009] (2) In the end mill of (1), the cutting edge portion may be formed of a CBN sintered body.

[0010] (3) In the end mill of (1) or (2), the following structure may be adopted: the peripheral portion of the bottom blade is connected to the peripheral blade via a cutter head arc blade, and when viewed from the side of the end mill, the width of the first back cutting surface of the cutter head arc blade adjacent to the cutter head arc blade gradually decreases from the front end side of the cutter head arc blade toward the rear end side, and the back angle of the first back cutting surface of the cutter head arc blade also gradually decreases from the bottom blade side toward the peripheral blade side.

[0011] (4) In the end mill described in any one of (1) to (3), the following structure may be adopted: the ratio of the width of the first flank surface of the first cutting edge to the width of the first flank surface of the second cutting edge is within a range of greater than 3 and less than 20.

[0012] (5) In the end mill described in any one of (1) to (4), a difference between a clearance angle of the first clearance face of the first cutting edge and a clearance angle of the first clearance face of the second cutting edge may be 4° or more.

[0013] (6) In the end mill of (5), the first clearance face of the first cutting edge may have a clearance angle of 15° or less, and the first clearance face of the second cutting edge may have a clearance angle of 5° or less.

[0014] According to one aspect of the present invention, there is provided a long-life end mill in which chipping or notching in the vicinity of the tip of a peripheral cutting edge is suppressed. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a side view showing the entire end mill according to the embodiment.

[0016] Figure 2 This is a perspective view showing an enlarged cutting edge portion of an end mill according to the embodiment.

[0017] Figure 3 This is a perspective view showing an enlarged arc portion of the cutting edge.

[0018] Figure 4 This is a schematic diagram of the cutting edge viewed from the front side in the tool rotation direction T.

[0019] Figure 5 This is a front end face view of the front end face of the end mill as viewed from the extending direction of the rotation axis (viewed from the front end face).

[0020] Figure 6 This is a side view (viewed from the side) of the first flank surface of the peripheral cutting edge as viewed from a direction perpendicular to the extending direction of the rotation axis.

[0021] Figure 7 This is a schematic diagram showing a machining method for cutting evaluation according to an embodiment. DETAILED DESCRIPTION

[0022] Figure 1 It is a side view showing the entire end mill according to the present embodiment. Figure 2 This is a perspective view showing an enlarged view of the cutting edge portion 3 of the end mill 1 according to the present embodiment. Figure 3 It is a perspective view showing an enlarged view of the arc portion of the cutting edge 3 .

[0023] The end mill 1 of this embodiment is a long-neck arc end mill with a tool diameter D of 2 mm, a cutter head arc radius of 0.02 mm, and a neck lower length L of 6 mm. The end mill 1 includes a shank 2 extending along a central axis O and a cutting edge portion 3 fixed to the end of the shank 2. The end mill 1 is used while rotating around the central axis O. Therefore, the central axis O is the rotation central axis of the end mill 1.

[0024] In the description of this embodiment, the direction in which the center axis O of the end mill 1 extends, that is, the direction along the center axis O is referred to as the axial direction. The direction from the cutting edge portion 3 toward the shank 2 in the axial direction is referred to as the rear end side. Figure 1 The direction from the shank 2 toward the cutting edge 3 in the axial direction is called the front end side. Figure 1 The left side of the center axis O. The direction perpendicular to the center axis O is called the radial direction. The direction close to the center axis O in the radial direction is called the radial inner side, and the direction away from the center axis O is called the radial outer side or the outer peripheral side. The direction of rotation around the center axis O is called the circumferential direction. The direction in the circumferential direction in which the end mill 1 rotates during cutting is called the tool rotation direction T (refer to Figure 2 ), and the rotation direction opposite to the tool rotation direction T is called the direction opposite to the tool rotation direction T or the counter tool rotation direction.

[0025] The tool holder 2 has a tool holder body 2a mounted on the main spindle of the machine tool and a neck 2b extending from the tool holder body 2a to the front end side along the center axis O. With respect to the tool holder body 2a, the rear end side is a cylindrical shape extending along the center axis O, and the front end side is a tapered shape that tapers toward the neck 2b. The neck 2b extends from the front end of the tapered portion of the tool holder body 2a to the front end side. The neck 2b is a cylindrical shape having a smaller diameter than the diameter of the tool holder body 2a. The cutting edge portion 3 is fixed to the front end of the neck 2b of the tool holder 2.

[0026] In the present embodiment, the cutting edge portion 3 is a CBN sintered body. The cutting edge portion 3 may also be configured as a structure that is entirely composed of cemented carbide. When the cutting edge portion 3 is configured as cemented carbide, the shank 2 and the cutting edge portion 3 may also be configured as a structure that is provided on a single cemented carbide component.

[0027] The cutting edge portion 3 has two cutting edges 10. The cutting edge portion 3 is a 180° rotationally symmetrical shape with the central axis O as the axis of symmetry. The two cutting edges 10 are arranged to be 180° rotationally symmetrical with the central axis O as the center. The two cutting edges 10 respectively have a bottom edge 11, a bottom edge flank 12, a peripheral edge 13, a peripheral edge flank 14, a tip circular edge 15, a tip circular edge first flank 16, a front edge 17 and a negative blade 18.

[0028] The bottom cutting edge 11 is located at the front end portion (front end surface) in the axial direction of the end mill 1 . Figure 4 This is a schematic diagram of the cutting edge 10 viewed from the front side in the tool rotation direction T. Figure 4 As shown, when observing the reference plane including the center axis O and the outer peripheral end A of the bottom blade 11 from the front, the bottom blade 11 has a bottom blade outer peripheral portion 11a, and the bottom blade outer peripheral portion 11a extends toward the axial rear end side at an inclination angle (core angle) of 3° or less relative to a plane C orthogonal to the center axis O as it moves from the outer peripheral end A of the bottom blade 11 toward the radial inner side. In the present invention, the core angle α of at least the bottom blade outer peripheral portion 11a including the outer peripheral end A of the bottom blade 11 can be set to 3° or less. In other words, the core angle of the bottom blade 11 as a whole can be 3° or less, or the core angle of the bottom blade outer peripheral portion 11a can be 3° or less, and the core angle of the portion closer to the center axis side than the bottom blade outer peripheral portion 11a, that is, the bottom blade inner peripheral portion, is greater than 3°. The core angle α is an angle greater than 0° and less than 3°. In the present embodiment, the core-cutting angle α of the bottom blade outer peripheral portion 11 a is 1°, and the core-cutting angle β of the bottom blade inner peripheral portion 11 b extending radially inward from the radially inner end of the bottom blade outer peripheral portion 11 a is 6°.

[0029] In the present invention, there may or may not be a cutter head arc edge 15 between the bottom edge 11 and the peripheral edge 13. In the end mill 1 of the present embodiment, there is a cutter head arc edge 15, and the peripheral end A of the bottom edge 11 is connected to one end of the cutter head arc edge 15. In other words, the peripheral end A of the bottom edge peripheral portion 11a is connected to one end of the cutter head arc edge 15. In the case of the present embodiment, the radial length of the bottom edge peripheral portion 11a is 0.25 mm (0.125D), and the radial length of the bottom edge inner portion 11b is 0.75 mm (0.375D).

[0030] The inclination angle β of the bottom blade inner circumference 11b is not limited as long as it is an angle greater than the inclination angle α of the bottom blade outer circumference 11a, but the difference between the inclination angle β and the inclination angle α is preferably 3° or more. In other words, the inclination angle β is preferably an angle greater than 3°. The difference between the inclination angle β and the inclination angle α is more preferably 4° or more or 5° or more. In the present embodiment, the inclination angle β of the bottom blade inner circumference 11b is 6°.

[0031] like Figure 3 and Figure 5 As shown, the portion of the back cutting surface of the cutting edge 10 that extends along the bottom cutting edge 11 and in the direction opposite to the tool rotation direction T of the bottom cutting edge 11 is the bottom cutting edge back cutting surface 12. The bottom cutting edge back cutting surface 12 is located on the front end surface of the cutting edge portion 3. The bottom cutting edge back cutting surface 12 has a first back cutting surface 12a of the bottom cutting edge outer peripheral portion adjacent to the bottom cutting edge outer peripheral portion 11a and a first back cutting surface 12b of the bottom cutting edge inner peripheral portion adjacent to the bottom cutting edge inner peripheral portion 11b. It should be noted that in this specification, the back cutting surface adjacent to the cutting edge behind the cutting edge in the rotation direction is named "first back cutting surface", and the back cutting surface adjacent to the first back cutting surface behind the rotation direction is named "second back cutting surface".

[0032] The bottom blade flank 12 extends from the bottom blade 11 toward the rear end side in the direction opposite to the tool rotation direction T. Thus, the bottom blade flank 12 is given a back angle. In the case of the present embodiment, the back angle γ of the first back blade 12a at the outer peripheral portion of the bottom blade and the back angle of the first back blade 12b at the inner peripheral portion of the bottom blade are both 10°.

[0033] Figure 5 This is a front face view of the front face of the end mill (viewed from the front face) as viewed from the extension direction of the rotation axis. Figure 5 As shown, in this specification, the width W1 of the first flank surface 12a of the bottom blade periphery refers to the maximum length of the first flank surface 12a of the bottom blade periphery in a direction perpendicular to the extending direction of the bottom blade 11 when viewed from the front end surface. In this embodiment, the width W1 of the first flank surface 12a of the bottom blade periphery is 0.12D.

[0034] The peripheral edge 13 is located at the radial outer end of the cutting edge 10. The peripheral edge 13 extends axially and is connected to the end (connection point B) on the rear end side of the cutter head arc edge 15. The axial length of the peripheral edge 13 is 0.5 mm in this embodiment. When the end mill 1 is rotated around the central axis O, the rotation trajectory of the peripheral edge 13 is cylindrical with the central axis O as the center.

[0035] In the flank surface of the cutting edge 10, the portion extending along the peripheral edge 13 and rearward in the rotation direction of the peripheral edge 13 is the peripheral edge flank surface 14. The peripheral edge flank surface 14 is arranged on the outer peripheral surface of the cutting edge portion 3. The peripheral edge flank surface 14 extends radially inward as it moves from the peripheral edge 13 in the direction opposite to the tool rotation direction T. Thus, the peripheral edge flank surface 14 is given a clearance angle.

[0036] In the present embodiment, the peripheral blade flank surface 14 is composed of a peripheral blade first flank surface 14a of a small width adjacent to the peripheral blade 13, and a peripheral blade second flank surface 14b of a wider width adjacent to the rear side of the tool rotation direction T of the peripheral blade first flank surface 14a. In the present embodiment, the flank angle ε of the peripheral blade first flank surface 14a is 4°. The flank angle of the peripheral blade second flank surface 14b is greater than the flank angle ε of the peripheral blade first flank surface 14a. In the present embodiment, the flank angle of the peripheral blade second flank surface 14b is 14°.

[0037] Figure 6 This is a side view (when viewed from the side) of the first flank face 14a of the peripheral edge of the end mill as viewed from a direction perpendicular to the extending direction of the central axis. Figure 6 As shown, in this specification, the width W2 of the peripheral cutting edge first flank 14a refers to the maximum length of the peripheral cutting edge first flank 14a in a direction perpendicular to the extending direction of the peripheral cutting edge 13 when viewed from the side.

[0038] In this embodiment, if Figure 3 As shown, the front end side portion 14c of the peripheral blade first flank face 14a is a shape in which the width gradually narrows toward the front end side, but the peripheral blade first flank face 14a adjacent to the peripheral blade 13 has a predetermined width throughout the entire area of ​​the peripheral blade 13. In other words, the peripheral blade first flank face 14a is also formed as a flank face with a predetermined width at the connection point B between the peripheral blade 13 and the cutter head circular arc edge 15. In this embodiment, the width W2 of the peripheral blade first flank face 14a is 0.01D, and the width of the peripheral blade second flank face 14b adjacent to the peripheral blade first flank face 14a on the rear side in the rotation direction is 0.15D.

[0039] In the present invention, as long as the back angle γ of the first back cutting surface 12a of the peripheral portion of the bottom blade is greater than the back angle ε of the first back cutting surface 14a of the peripheral blade, and the width W1 of the first back cutting surface 12a of the peripheral portion of the bottom blade is greater than the width W2 of the first back cutting surface 14a of the peripheral blade, the back angle γ of the first back cutting surface 12a of the peripheral portion of the bottom blade and the width W1 of the back cutting surface can be constant along the bottom blade or vary. In addition, the back angle ε and the width W2 of the first back cutting surface 14a of the peripheral blade can be constant along the peripheral blade 13 or vary.

[0040] The cutter head arc edge 15 connects the radial peripheral end A of the bottom blade peripheral portion 11a with the front end (connection point B) of the peripheral edge 13, and is formed into an arc shape convex to the front peripheral side of the cutting edge portion 3. If the end mill 1 is rotated around the central axis O, the rotation trajectory of the pair of cutter head arc edges 15 is approximately 1 / 4 arc shape. In the present embodiment, the radius of the cutter head arc edge is 0.02 mm.

[0041] A first clearance face 16 of the cutter head circular edge is disposed adjacent to the cutter head circular edge 15 on the side opposite to the tool rotation direction T. The first clearance face 16 of the cutter head circular edge is in the shape of a curved surface convex toward the outer peripheral side of the front end of the cutting edge portion 3, and is formed toward the radial outer side and the front end side. The first clearance face 16 of the cutter head circular edge is inclined toward the radial inner side and the rear end side as it moves from the cutter head circular edge 15 toward the side opposite to the tool rotation direction T, and is given a clearance angle. Figure 6 As shown, when viewed from the radial side, the width of the first flank face 16 of the cutter head circular arc edge gradually changes (decreases) from the front end side toward the rear end side. In addition, the back angle of the first flank face 16 of the cutter head circular arc edge also gradually changes (decreases) from the bottom edge 11 side toward the peripheral edge 13 side. Thus, in the present invention in which the back angle and width of the first flank face of the bottom edge peripheral portion 11a and the peripheral edge 13 are different, the rapid change of the cutting resistance between the two cutting edges can be alleviated, and the chipping or notching of the front end portion of the bottom edge 11 can be further suppressed.

[0042] The negative blade flap 18 is formed along the peripheral portion of the front cutting edge 17. The negative blade flap 18 is formed into an L-shape when viewed from the front side in the tool rotation direction T. The negative blade flap 18 is arranged along the entire area of ​​the L-shaped cutting edge 10. The negative blade flap 18 is an inclined surface located on the rear side in the tool rotation direction T as it approaches the peripheral edge of the front cutting edge 17. The bottom edge 11, the peripheral edge 13 and the cutter head arc edge 15 are given a negative front angle by the negative blade flap 18. In the case of the present embodiment, the front angles of the bottom edge 11, the peripheral edge 13 and the cutter head arc edge 15 are -30°.

[0043] Regarding the end mill 1 of the present embodiment described above, the core digging angle α of the bottom blade peripheral portion 11a extending radially inward from the peripheral end A of the bottom blade 11 is 3° or less, and the clearance angle γ and width W1 of the bottom blade peripheral portion first clearance face 12a adjacent to the bottom blade peripheral portion 11a are respectively larger than the clearance angle ε and width W2 of the peripheral blade first clearance face 14a adjacent to the peripheral blade 13. The effects thereof are described below.

[0044] As a comparative example Figure 4 The imaginary bottom blade 11v indicated by the double-dotted chain line has a core angle α of 6° at the peripheral portion of the bottom blade including the peripheral end A of the bottom blade 11. In the cutting process of the bottom blade 11 of the present embodiment using the core angle of 1° at the peripheral portion 11a of the bottom blade and the cutting process using the imaginary bottom blade 11v having a core angle of 6° at the peripheral portion of the bottom blade, the directions of the cutting resistance of the bottom blade are different. That is, the direction d1 of the cutting resistance of the peripheral portion 11a of the bottom blade having a smaller core angle (inclination angle α) is closer to a direction parallel to the axial direction than the direction d2 of the cutting resistance of the imaginary bottom blade 11v having a larger core angle. As a result, the load acting from the bottom blade 11 toward the peripheral blade 13 near the front end of the peripheral blade is reduced.

[0045] Furthermore, in the present invention, not only is the back angle γ of the first back cutting surface 12a of the peripheral portion of the bottom blade greater than the back angle ε of the first back cutting surface 14a of the peripheral blade, but the width W1 of the first back cutting surface 12a of the peripheral portion of the bottom blade is also greater than the width W2 of the first back cutting surface 14a of the peripheral blade. Therefore, not only the tip strength of the peripheral blade is improved, but also even if the core digging angle of the peripheral portion of the bottom blade is suppressed to below 3°, the cutting resistance of the bottom blade will not be too large, and sufficient rigidity near the front end of the end mill can be ensured, and the load acting from the bottom blade 11 toward the peripheral blade 13 near the front end of the peripheral blade can be reduced, thereby effectively suppressing chipping or large notches generated near the front end of the peripheral blade.

[0046] In particular, when a CBN sintered body with poor defect resistance is used as the base material of the cutting edge portion 3, or when the radius of the cutter head arc is set to 0.1 mm or less, this problem is particularly significant, and even if the clearance angle of the peripheral edge or the bottom edge is reduced and the wedge angle of the cutting edge is increased, a large-sized notch that reaches about 20% of the tool diameter in the axial direction may be generated near the front end of the peripheral edge. However, by setting the structure of the present invention as described above, even when a CBN sintered body with poor or excellent defect resistance is used as the base material of the cutting edge portion 3, or even when the radius of the cutter head arc is set to 0.1 mm or less, it is possible to fully suppress notches or chipping near the front end of the peripheral edge.

[0047] In the above-mentioned embodiment, although the dimensions of each part are specifically exemplified and described, the dimensions of each part of the end mill 1 can be changed within a range that does not impair the function.

[0048] In the above-mentioned embodiment, although the length of the bottom blade peripheral portion 11a is set to 0.25 mm (0.125D), when the tool diameter D is greater than 1 mm, the length of the bottom blade peripheral portion 11a is preferably greater than 0.05D. More preferably, it is greater than 0.1D. The length of the bottom blade peripheral portion 11a is preferably less than 0.8D, and more preferably less than 0.5D. If the bottom blade peripheral portion 11a is too long, the cutting resistance of the bottom blade 11 increases. If the bottom blade peripheral portion 11a is too short, the effect of bringing the direction of the cutting resistance closer to the axial side becomes smaller, thereby reducing the effect of suppressing the notch near the front end of the peripheral blade 13.

[0049] In the end mill 1 with a tool diameter D of less than 1 mm, it is difficult to process the bottom blade 11 into two cutting edges with different core digging angles. Therefore, in the end mill 1 with a tool diameter D of less than 1 mm, the core digging angle of the bottom blade 11 as a whole may be set to 3° or less. In other words, the core digging angle of the bottom blade 11 as a whole may be set to be the same as the core digging angle of the bottom blade outer peripheral portion 11a, which is less than 3°.

[0050] The clearance angle γ of the first clearance face 12a of the bottom blade peripheral portion 11a and the clearance angle ε of the first clearance face 14a of the peripheral blade are preferably an angle whose difference is 4° or more, and more preferably 5° or more. In the above embodiment, the angle difference γ-ε of the clearance angles is 6°. The clearance angle γ of the first clearance face 12a of the bottom blade peripheral portion is preferably within a range of 15° or less, and the clearance angle ε of the first clearance face 14a of the peripheral blade is preferably within a range of 5° or less.

[0051] The ratio W1 / W2 of the width W1 of the bottom edge peripheral portion first flank surface 12a of the bottom edge peripheral portion 11a to the width W2 of the peripheral edge first flank surface 14a is preferably in the range of 3 or more and 20 or less. The lower limit of the ratio W1 / W2 is preferably 5 or more, more preferably 8 or more. The upper limit of the ratio W1 / W2 is preferably 18 or less, more preferably 15 or less.

[0052] The width W1 of the first back cutting surface 12a of the bottom cutting edge peripheral portion 11a is preferably within a range of 0.11D to 0.19D relative to the tool diameter D. The width W1 is more preferably 0.12D to 0.13D. The width W1 is more preferably 0.18D to 0.17D. In the above embodiment where the tool diameter D is 2 mm, the width W1 is preferably within a range of 0.22 mm to 0.38 mm.

[0053] The width W2 of the first flank surface 14a of the peripheral blade is preferably within a range of 0.01D to 0.04D relative to the tool diameter D. The width W2 is more preferably 0.15D to 0.02D. The width W2 is more preferably 0.035D to 0.03D. In the above embodiment where the tool diameter D is 2 mm, the width W2 is preferably within a range of 0.02 mm to 0.08 mm.

[0054] The clearance angle of the first clearance face 12b at the inner peripheral portion of the bottom blade is preferably within a range of 15° or less. In the above embodiment, although the clearance angle γ of the first clearance face 12a at the outer peripheral portion of the bottom blade and the clearance angle of the first clearance face 12b at the inner peripheral portion of the bottom blade are both set to 10°, the clearance angle γ of the first clearance face 12a at the outer peripheral portion of the bottom blade and the clearance angle of the first clearance face 12b at the inner peripheral portion of the bottom blade may be different angles.

[0055] The radius of the cutter head arc edge 15 (cutter head arc radius) is not particularly limited. When the tool diameter D of the end mill is less than 3 mm, if the cutter head arc radius is less than 0.1 mm, a notch is likely to occur near the front end of the peripheral edge. Therefore, the structure of this embodiment is suitable for a circular end mill or a square end mill with a tool diameter D of 3 mm and a cutter head arc radius of less than 0.1 mm.

[0056] The rake angles of the bottom edge 11, the peripheral edge 13 and the cutter head arc edge 15 are preferably within a range of -50° to -20°. The rake angle is more preferably -45° or -35°. The rake angle is more preferably -25° or less. The rake angles of the bottom edge 11, the peripheral edge 13 and the cutter head arc edge 15 may be different angles.

[0057] Example

[0058] Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited to these examples.

[0059] (Manufacturing and cutting test of end mills)

[0060] An end mill of the above-described embodiment was produced as Example 1. Each element is shown below.

[0061] Cutting edge: CBN, two blades

[0062] Shank: Carbide

[0063] Tool diameter (blade diameter) D: 2mm

[0064] Cutting head arc radius: 0.02mm

[0065] Neck length: 6mm

[0066] Bottom blade periphery: core digging angle is 1°

[0067] The first flank surface of the bottom edge: the flank angle is 10° and the width is 0.24mm

[0068] Bottom blade inner periphery: core digging angle is 6°

[0069] The first back surface of the inner periphery of the bottom blade: the back angle is 10°

[0070] Peripheral cutting edge: twist angle 0°

[0071] The first flank of the peripheral blade: the flank angle is 4° and the width is 0.02mm

[0072] The second flank of the peripheral blade: the flank angle is 14° and the width is 0.30mm

[0073] Negative blade: front angle is -30°

[0074] In addition, end mills of Comparative Examples 1 to 4 described in Table 1 were produced.

[0075] Regarding the end mill of Comparative Example 1, as an example of a conventional general CBN arc end mill, the clearance angle of the first clearance face of the peripheral blade is set to 14°, the clearance angle of the first clearance face of the peripheral portion of the bottom blade is set to 10°, the width of the first clearance face of the peripheral blade is set to 0.16D, the width of the first clearance face of the peripheral portion of the bottom blade is set to 0.12D, and the core digging angle of the peripheral portion of the bottom blade is set to 6°. The other structures are the same as those of Example 1.

[0076] Comparative Example 2 is an end mill having a larger wedge angle of the peripheral cutting edge than that of Comparative Example 1.

[0077] Comparative Example 3 is an end mill in which the wedge angles of both the peripheral cutting edge and the peripheral portion of the bottom cutting edge are larger than those of Comparative Example 1.

[0078] Comparative Example 4 is an end mill in which the wedge angles of both the peripheral cutting edge and the bottom cutting edge peripheral portion are larger than those of Comparative Example 1, and the inclination of the bottom cutting edge peripheral portion relative to the axial perpendicular plane is gentler than that of Comparative Example 1.

[0079] It should be noted that in the above-described embodiment 1, only the wedge angle of the peripheral cutting edge is larger than that of the comparative example 1, and the inclination of the peripheral portion of the bottom cutting edge relative to the plane perpendicular to the axis is gentler than that of the comparative example 1, and not only the back angle of the bottom cutting edge but also the back cutting edge width of the bottom cutting edge are larger than the back angle and the back cutting edge width of the peripheral cutting edge, respectively.

[0080] The arc end mills of Example 1 and Comparative Examples 1 to 4 manufactured in this manner were attached to a machine tool and cutting evaluation was performed. Figure 7The following is an overview of the processing method for cutting evaluation. The material of the workpiece W is STAVAX material with a size of 60×60×30 (mm). The workpiece W is repeatedly processed with a 10 mm×10 mm×0.6 mm contour groove under the conditions of a 1° slope, no cutter arc, and an entry inclination angle of 0.5°.

[0081] After each machining operation for a predetermined period of time, the cutting edge of the end mill was observed under a microscope to check for chipping or notching, as well as the wear condition.

[0082] <Cutting conditions>

[0083] Workpiece: STAVAX (52HRC)

[0084] Coolant: Spray

[0085] Spindle speed (n): 24000 rpm (Vc = 150 m / min)

[0086] Table feed (Vf): 1200mm / min (fz=0.025mm / t)

[0087] Axial cutting depth (ap): 0.005mm (constant)

[0088] Radial cutting depth (ae): 0.2mm (constant)

[0089] [Table 1]

[0090]

[0091] As shown in Table 1, the end mill of Comparative Example 1 had a large chip on the peripheral cutting edge after four hours of cutting.

[0092] In Comparative Example 2, the wedge angle of the peripheral cutting edge was increased by making the clearance angle of the first clearance surface of the peripheral cutting edge smaller than that of Comparative Example 1. However, although no large chip was generated on the peripheral cutting edge, chipping occurred on the peripheral cutting edge after four hours of cutting.

[0093] In Comparative Example 3, not only the clearance angle of the first clearance face of the peripheral cutting edge is smaller than that of Comparative Example 1, but also the clearance angle of the clearance face of the peripheral portion of the bottom cutting edge is smaller than that of Comparative Example 1, thereby increasing the wedge angles of both the peripheral cutting edge and the peripheral portion of the bottom cutting edge. However, in Comparative Example 3, similar to Comparative Example 2, chipping occurred on the peripheral cutting edge after four hours of cutting. It can be seen from this that chipping near the front end of the peripheral cutting edge cannot be fully suppressed by simply increasing the wedge angle of the cutting edges such as the bottom cutting edge or the peripheral cutting edge (increasing the blade edge strength).

[0094] In Example 1, the clearance angle of the first clearance face of the peripheral blade is made smaller than that of Comparative Example 1. In other words, the clearance angle of the first clearance face of the peripheral blade is made smaller than that of the first clearance face of the peripheral portion of the bottom blade, and the inclination angle of the bottom blade relative to the perpendicular plane of the axis is made smaller than that of Comparative Example 1 in view of the direction and magnitude of the cutting resistance of the bottom blade, and the width of the first clearance face of the peripheral portion of the bottom blade is also made larger than that of the first clearance face of the peripheral blade. Such Example 1 can perform cutting for 10 hours, and the life is 2.5 times that of Comparative Example 1. In addition, Comparative Example 4 is based on Example 1, and the only difference from Example 1 is that in order to increase not only the wedge angle of the peripheral blade but also the wedge angle of the bottom blade, the clearance angle γ of the first clearance face of the peripheral portion of the bottom blade is made smaller than that of Example 1, and is equal to the clearance angle ε of the first clearance face of the peripheral blade of Example 1. However, after four hours of cutting, Comparative Example 4 had chipping on the peripheral blade and ended its life. It can be seen from this that it is important not only to shift the direction of the cutting resistance of the bottom cutting edge further toward the center axis to reduce the load on the peripheral cutting edge near the tip of the peripheral cutting edge, but also to avoid the cutting resistance of the bottom cutting edge from being too large.

[0095] Industrial Applicability

[0096] A long-life end mill can be provided in which chipping or notching near the front end of a peripheral cutting edge is suppressed.

[0097] Description of Reference Numerals

[0098] 1 End mill

[0099] 2. Knife handle

[0100] 3 Cutting edge

[0101] 10 cutting edges

[0102] 11 bottom edge

[0103] 11a Outer periphery of bottom blade

[0104] 12a First flank surface at the outer periphery of the bottom cutting edge

[0105] 13 Peripheral blade

[0106] 14a The first flank surface of the peripheral cutting edge

[0107] 15 blade arc edge

[0108] 16-blade arc blade first flank

[0109] A The outer edge of the bottom blade

[0110] B The tip of the peripheral blade (connection point)

[0111] C is a plane perpendicular to the central axis O.

[0112] D Tool diameter

[0113] W1 The width of the first flank surface at the outer periphery of the bottom edge

[0114] W2 Width of the first flank of the peripheral cutting edge

[0115] α, β inclination angle (core digging angle)

[0116] OCenter Axis

Claims

1. An end mill having a cutting edge portion rotating around a central axis and a tool holder, the end mill comprising: a bottom edge located on the front end surface of the cutting edge portion and a peripheral edge located on the outer peripheral surface of the cutting edge portion, The bottom blade has a bottom blade outer peripheral portion, and the bottom blade outer peripheral portion extends toward the shank side from the outer peripheral end of the bottom blade toward the radial inner side at an inclination angle of 3° or less relative to a plane perpendicular to the central axis. The clearance angle of the first clearance surface of the bottom edge peripheral portion adjacent to the bottom edge peripheral portion is greater than the clearance angle of the first clearance surface of the peripheral edge adjacent to the peripheral edge, and the width of the first clearance surface of the bottom edge peripheral portion is greater than the width of the first clearance surface of the peripheral edge.

2. The end mill according to claim 1, wherein: The cutting edge portion is configured from a CBN sintered body.

3. The end mill according to claim 1 or 2, wherein: The outer peripheral portion of the bottom blade is connected to the outer peripheral blade via the blade head circular arc blade. When the end mill is viewed from the side, the width of the first relief surface of the cutter head circular arc edge adjacent to the cutter head circular arc edge gradually decreases from the front end side toward the rear end side of the cutter head circular arc edge. The back angle of the first back cutting surface of the circular arc blade of the cutter head also gradually decreases from the bottom cutting edge side toward the peripheral cutting edge side.

4. The end mill according to claim 1 or 2, wherein: The ratio of the width of the first flank surface of the bottom cutting edge outer peripheral portion to the width of the first flank surface of the peripheral cutting edge is within a range of 3 or more and 20 or less.

5. The end mill according to claim 1 or 2, wherein: The difference between the clearance angle of the first clearance surface of the bottom cutting edge outer peripheral portion and the clearance angle of the first clearance surface of the peripheral cutting edge is 4° or more.

6. The end mill according to claim 5, wherein: The back angle of the first back cutting surface of the bottom blade outer periphery is less than 15°, and The clearance angle of the first clearance surface of the peripheral cutting edge is less than 5°.

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