End mill

Abstract

A kind of end mill (1), with cutting edge portion (3) and shank (2) rotating around center axis (O), and with located on the front end surface of cutting edge portion (10) bottom blade (11) and located on the outer peripheral surface of cutting edge portion (10) peripheral blade (13), bottom blade (11) has bottom blade outer peripheral portion (11a), bottom blade outer peripheral portion (11a) is with the inclination angle (α) of 3 ° or less to the plane orthogonal to center axis (O) with the extension to the shank side as from the outer peripheral end of bottom blade towards the radial inside, the clearance angle of bottom blade outer peripheral portion first relief surface (14a) adjacent to bottom blade outer peripheral portion (11a) is greater than the clearance angle of peripheral blade first relief surface (14a) adjacent to peripheral blade (13), the width (W2) of bottom blade outer peripheral portion first relief surface is greater than the width (W1) of peripheral blade first relief surface.

Description

Technical Field

[0001] This invention relates to end mills.

[0002] This application claims priority based on Japanese Patent Application No. 2022-143470, filed on September 9, 2022, the contents of which are incorporated herein by reference. Background Technology

[0003] Previously, it was known that, in order to improve the tip strength of the peripheral cutting edge of an end mill, a flank face with a small clearance angle and a small flank face width was provided on the flank face of the peripheral cutting edge, as described in Patent Document 1.

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

[0005] However, even in end mills with a small flank face designed to improve tip strength, chipping or nicking near the tip of the peripheral cutting edge is sometimes not sufficiently suppressed, thus further extending tool life is desirable. In particular, end mills made of CBN, which lacks resistance to chipping, are prone to chipping or nicking near the tip of the peripheral cutting edge. Summary of the Invention

[0006] One object of the present invention is to provide an end mill that suppresses chipping or notching near the tip of its peripheral cutting edge and has a long service life.

[0007] (1) According to one aspect of the present invention, an end mill is provided, comprising a cutting edge portion and a shank that rotate about a central axis. It has a bottom cutting edge located on the front end face of the cutting edge portion and an outer peripheral cutting edge located on the outer peripheral face of the cutting edge portion. The bottom cutting edge has a bottom cutting edge outer peripheral portion, which extends towards the shank side at an inclination angle of less than 3° relative to a plane orthogonal to the central axis, from the outer peripheral end of the bottom cutting edge toward the radially inward side. The clearance angle of the first clearance face of the bottom cutting edge outer peripheral portion adjacent to the bottom cutting edge outer peripheral portion is greater than the clearance angle of the first clearance face of the outer peripheral cutting edge adjacent to the outer peripheral cutting edge. The width of the first clearance face of the bottom cutting edge outer peripheral portion is greater than the width of the first clearance face of the outer peripheral cutting edge.

[0008] According to the above structure, the bottom cutting edge has an outer periphery with a core-cutting angle of 3° or less. Therefore, the direction of the cutting resistance of the bottom cutting edge is made approximately parallel to the central axis, thereby reducing the load acting from the bottom cutting edge towards the outer periphery. Furthermore, not only is the clearance angle of the first flank face of the outer periphery of the bottom cutting edge greater than that of the first flank face of the outer periphery, but the width of the first flank face of the outer periphery of the bottom cutting edge is also greater than that of the first flank face of the outer periphery. Therefore, not only is the tip strength of the outer periphery improved, but even with the core-cutting angle of the outer periphery of the bottom cutting edge suppressed to below 3°, the cutting resistance of the bottom cutting edge is not excessive. This also ensures sufficient rigidity near the tip of the end mill and reduces the load acting from the bottom cutting edge towards the outer periphery near the tip of the outer periphery, effectively suppressing chipping or large notches occurring near the tip of the outer periphery.

[0009] (2) In the end mill of (1), the cutting edge can be configured to be constructed of CBN sintered body.

[0010] (3) In the end mill of (1) or (2), the following structure can also be provided: that is, the outer periphery of the bottom edge is connected to the outer periphery edge via the cutter tip arc edge. When viewed from the side of the end mill, the width of the first back face of the cutter tip arc edge adjacent to the cutter tip arc edge gradually decreases from the front end side of the cutter tip arc edge toward the rear end side, and the back angle of the first back face of the cutter tip arc edge also gradually decreases from the bottom edge side toward the outer periphery edge side.

[0011] (4) In any one of (1) to (3), the end mill may also be configured such that the ratio of the width of the first flank face of the first cutting edge to the width of the first flank face of the second cutting edge is in the range of 3 or more and 20 or less.

[0012] (5) In any one of (1) to (4) the end mill may also be configured such that the difference between the clearance angle of the first flank face of the first cutting edge and the clearance angle of the first flank face of the second cutting edge is 4° or more.

[0013] (6) In the end mill of (5), the following structure can also be provided: the clearance angle of the first flank face of the first cutting edge is 15° or less, and the clearance angle of the first flank face of the second cutting edge is 5° or less.

[0014] According to one aspect of the present invention, a long-life end mill is provided in which chipping or notching near the tip of the peripheral cutting edge is suppressed. Attached Figure Description

[0015] Figure 1 This is a side view of the end mill as described in the embodiment.

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

[0017] Figure 3 It is a three-dimensional view showing the arc portion of the cutting edge of the tool head magnified.

[0018] Figure 4 This is a schematic diagram of the cutting edge viewed from the front side of the tool's rotation direction T.

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

[0020] Figure 6 This is a side view (viewed from the side) of the first flank face of the outer peripheral cutting edge, viewed from a direction orthogonal to the extension direction of the rotation axis.

[0021] Figure 7 This is a schematic diagram illustrating a machining method for cutting evaluation according to an embodiment. Detailed Implementation

[0022] Figure 1 This is a side view showing the end mill as a whole according to this embodiment. Figure 2 This is a perspective view showing the cutting edge 3 of the end mill 1 in this embodiment, magnified. Figure 3 This is a perspective view showing the enlarged arc portion of the cutting edge 3.

[0023] The end mill 1 in this embodiment is a long-neck, round-arc end mill with a tool diameter D of 2 mm, a tip radius of 0.02 mm, and a neck length L of 6 mm. The end mill 1 includes a shank 2 extending along the central axis O and a cutting edge 3 fixed to the end of the shank 2. The end mill 1 is used by rotating about the central axis O. Therefore, the central axis O is the rotational axis of the end mill 1.

[0024] In this embodiment, the direction extending from the central axis O of the end mill 1, that is, the direction along the central axis O, is referred to as the axial direction. The direction in the axial direction from the cutting edge 3 toward the tool holder 2 is referred to as the rear end side. The rear end side is... Figure 1 The right side of the tool holder 2. The direction along the axial direction from the tool holder 2 towards the cutting edge 3 is called the front end side. The front end side is... Figure 1 The left side of the axis. The direction orthogonal to the central axis O is called the radial direction. The direction closer to the central axis O within the radial direction is called the inner radial direction, and the direction farther from the central axis O is called the outer radial direction or outer circumferential direction. The direction of rotation about the central axis O is called the circumferential direction. The direction within the circumferential direction that causes the end mill 1 to rotate during cutting is called the tool rotation direction T (refer to...). Figure 2 Furthermore, the direction of rotation opposite to the tool rotation direction T is called the direction opposite to the tool rotation direction T or the anti-tool rotation direction.

[0025] The tool holder 2 has a tool holder body 2a mounted on the spindle of a machine tool and a neck 2b extending from the tool holder body 2a along the central axis O toward the front end. Regarding the tool holder body 2a, the rear end is cylindrical extending along the central axis O, and the front end is tapered, tapering toward the neck 2b. The neck 2b extends from the front end of the tapered portion of the tool holder body 2a toward the front end. The neck 2b is cylindrical with a diameter smaller than that of the tool holder body 2a. The cutting edge 3 is fixed to the front end of the neck 2b of the tool holder 2.

[0026] In this embodiment, the cutting edge 3 is a CBN sintered body. The cutting edge 3 may also be a structure made entirely of cemented carbide. When the cutting edge 3 is made of cemented carbide, it may also be a structure in which the tool holder 2 and the cutting edge 3 are provided on a single cemented carbide component.

[0027] The cutting edge portion 3 has two cutting edges 10. The cutting edge portion 3 is 180° rotationally symmetrical about the central axis O. The two cutting edges 10 are arranged in a 180° rotationally symmetrical configuration about the central axis O. The two cutting edges 10 each have a bottom cutting edge 11, a bottom cutting edge flank face 12, an outer peripheral cutting edge 13, an outer peripheral cutting edge flank face 14, a cutting edge arc cutting edge 15, a cutting edge arc cutting edge first flank face 16, a rake face 17, and a negative cutting edge 18.

[0028] The bottom cutting edge 11 is located at the front end (front face) of the end mill 1 in the axial direction. Figure 4 This is a schematic diagram of the cutting edge 10 viewed from the front side of the tool's rotation direction T. (See diagram below.) Figure 4 As shown, when viewed from the front along a reference plane including the central axis O and the outer peripheral end A of the bottom edge 11, the bottom edge 11 has a bottom edge outer peripheral portion 11a. This bottom edge outer peripheral portion 11a extends radially inward from the outer peripheral end A of the bottom edge 11, relative to a plane C orthogonal to the central axis O, towards the axial rear end side at an angle of inclination (cut-out angle) of 3° or less. In this invention, the cut-out angle α of at least the bottom edge outer peripheral portion 11a, including the outer peripheral end A, in the bottom edge 11 can be set to 3° or less. That is, the cut-out angle of the bottom edge 11 as a whole can be 3° or less, or the cut-out angle of the bottom edge outer peripheral portion 11a can be 3° or less, and the cut-out angle of the portion closer to the central axis than the bottom edge outer peripheral portion 11a, i.e., the inner peripheral portion of the bottom edge, can be greater than 3°. The cut-out angle α is an angle greater than 0° and less than 3°. In this embodiment, the core-cutting angle α of the outer peripheral portion 11a of the bottom edge is 1°, and the core-cutting angle β of the inner peripheral portion 11b of the bottom edge, which extends further radially inward from the radially inner end of the outer peripheral portion 11a of the bottom edge, is 6°.

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

[0030] The inclination angle β of the inner periphery 11b of the bottom edge is not limited as long as it is greater than the inclination angle α of the outer periphery 11a of the bottom edge, but it is preferable that the difference between the inclination angle β and the inclination angle α is 3° or more. That is, 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 this embodiment, the inclination angle β of the inner periphery 11b of the bottom edge is 6°.

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

[0032] The bottom edge relief face 12 extends toward the rear end from the bottom edge 11 in a direction opposite to the tool rotation direction T. Thus, the bottom edge relief face 12 is endowed with a clearance angle. In this embodiment, the clearance angle γ of the first relief face 12a on the outer periphery of the bottom edge and the clearance angle of the first relief face 12b on the inner periphery of the bottom edge are both 10°.

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

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

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

[0036] In this embodiment, the outer peripheral cutting edge flank 14 is composed of a slightly narrow first outer peripheral cutting edge flank 14a adjacent to the outer peripheral cutting edge 13, and a wider second outer peripheral cutting edge flank 14b adjacent to the rear side of the first outer peripheral cutting edge flank 14a in the tool rotation direction T. In this embodiment, the clearance angle ε of the first outer peripheral cutting edge flank 14a is 4°. The clearance angle of the second outer peripheral cutting edge flank 14b is greater than the clearance angle ε of the first outer peripheral cutting edge flank 14a. In this embodiment, the clearance angle of the second outer peripheral cutting edge flank 14b is 14°.

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

[0038] In this embodiment, such as Figure 3 As shown, the front end portion 14c of the first flank face 14a of the outer peripheral cutting edge has a shape that gradually narrows towards the front end. However, the first flank face 14a of the outer peripheral cutting edge adjacent to the outer peripheral cutting edge 13 covers the entire area of ​​the outer peripheral cutting edge 13 and has a predetermined width. That is, the first flank face 14a of the outer peripheral cutting edge is also formed as a flank face with a predetermined width at the connection point B between the outer peripheral cutting edge 13 and the circular arc cutting edge 15 of the cutting head. In this embodiment, the width W2 of the first flank face 14a of the outer peripheral cutting edge is 0.01D, and the width of the second flank face 14b of the outer peripheral cutting edge adjacent to the first flank face 14a of the outer peripheral cutting edge on the rear side in the rotation direction is 0.15D.

[0039] In this invention, as long as the clearance angle γ of the first clearance face 12a of the outer periphery of the bottom edge is greater than the clearance angle ε of the first clearance face 14a of the outer periphery of the bottom edge, and the width W1 of the first clearance face 12a of the outer periphery of the bottom edge is greater than the width W2 of the first clearance face 14a of the outer periphery of the bottom edge, the clearance angle γ and the width W1 of the clearance face 12a of the outer periphery of the bottom edge can be constant or variable along the bottom edge. In addition, the clearance angle ε and the width W2 of the first clearance face 14a of the outer periphery of the bottom edge can be constant or variable along the outer periphery of the bottom edge.

[0040] The circular arc cutting edge 15 connects the radially outer peripheral end A of the bottom cutting edge 11a to the front end (connection point B) of the outer peripheral cutting edge 13, and is formed into a circular arc shape protruding towards the outer peripheral side of the front end of the cutting edge 3. If the end mill 1 is rotated about the central axis O, the rotation trajectory of the pair of circular arc cutting edges 15 is approximately a 1 / 4 arc. In this embodiment, the radius of the circular arc cutting edge is 0.02 mm.

[0041] A first flank face 16 of the cutting edge 15 is disposed adjacent to the side opposite to the tool rotation direction T. The first flank face 16 is a curved surface convex towards the outer periphery of the front end of the cutting edge 3, and is formed radially outward and towards the front end. The first flank face 16 is inclined radially inward and towards the rear end as it moves from the cutting 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 a radial side view, the width of the first flank face 16 of the cutter tip's arc-shaped cutting edge gradually changes (decreases) from the front end side towards the rear end side. Furthermore, the clearance angle of the first flank face 16 of the cutter tip's arc-shaped cutting edge also gradually changes (decreases) from the bottom cutting edge 11 side towards the outer peripheral cutting edge 13 side. Therefore, in this invention, where the clearance angle and width of the first flank face of the outer peripheral portion 11a of the bottom cutting edge and the outer peripheral cutting edge 13 are different, the abrupt change in cutting resistance between the two cutting edges can be mitigated, and chipping or nicking at the front end of the bottom cutting edge 11 can be further suppressed.

[0042] The negative cutting edge 18 is formed along the periphery of the rake face 17. The negative cutting edge 18 is L-shaped when viewed from the front side in the tool rotation direction T. The negative cutting edge 18 is arranged along the entire area of ​​the L-shaped cutting edge 10. The negative cutting edge 18 is an inclined surface located behind the tool rotation direction T, facing the periphery of the rake face 17. The bottom cutting edge 11, the outer peripheral cutting edge 13, and the tip arc cutting edge 15 are given a negative rake angle by the negative cutting edge 18. In this embodiment, the rake angle of the bottom cutting edge 11, the outer peripheral cutting edge 13, and the tip arc cutting edge 15 is -30°.

[0043] Regarding the end mill 1 of this embodiment described above, the core-cutting angle α of the outer peripheral portion 11a of the bottom cutting edge 11 extending radially inward from the outer peripheral end A of the bottom cutting edge 11 is 3° or less, and the clearance angle γ and width W1 of the first clearance face 12a of the outer peripheral portion of the bottom cutting edge adjacent to the outer peripheral portion 11a are greater than the clearance angle ε and width W2 of the first clearance face 14a of the outer peripheral cutting edge adjacent to the outer peripheral cutting edge 13, respectively. Its effects will be explained below.

[0044] Regarding the comparative example Figure 4 The imaginary bottom cutting edge 11v, indicated by the double-dotted line, has a core-cutting angle α of 6° for the outer peripheral portion of the bottom cutting edge 11, including the outer peripheral end A. In cutting operations using the bottom cutting edge 11 of this embodiment with a core-cutting angle of 1° for the outer peripheral portion 11a, and in cutting operations using the imaginary bottom cutting edge 11v with a core-cutting angle of 6° for the outer peripheral portion of the bottom cutting edge, the directions of the cutting resistance of the bottom cutting edge are different. That is, the direction d1 of the cutting resistance of the outer peripheral portion 11a with a smaller core-cutting angle (tilt angle α) is closer to the direction parallel to the axial direction than the direction d2 of the cutting resistance of the imaginary bottom cutting edge 11v with a larger core-cutting angle. Therefore, the load acting on the end mill 1 from the bottom cutting edge 11 toward the outer peripheral cutting edge 13 near the tip of the outer peripheral cutting edge is reduced.

[0045] Furthermore, in this invention, not only is the clearance angle γ of the first clearance face 12a of the outer periphery of the bottom cutting edge greater than the clearance angle ε of the first clearance face 14a of the outer periphery of the bottom cutting edge, but the width W1 of the first clearance face 12a of the outer periphery of the bottom cutting edge is also greater than the width W2 of the first clearance face 14a of the outer periphery of the outer periphery. Therefore, not only is the tip strength of the outer periphery of the cutting edge improved, but even if the core-cutting angle of the outer periphery of the bottom cutting edge is suppressed to below 3°, the cutting resistance of the bottom cutting edge will not be too large. It can also ensure sufficient rigidity near the front end of the end mill and reduce the load acting from the bottom cutting edge 11 toward the outer periphery cutting edge 13 near the front end of the outer periphery of the cutting edge, thereby effectively suppressing chipping or large notches generated near the front end of the outer periphery of the cutting edge.

[0046] In particular, this problem is especially pronounced when using CBN sintered body with poor chipping resistance as the base material for the cutting edge 3, or when the tip radius is set to 0.1 mm or less. Even when the clearance angle of the outer peripheral edge or bottom edge is reduced and the wedge angle of the cutting edge is increased, a relatively large notch, approximately 20% of the tool diameter in the axial direction, may sometimes occur near the tip of the outer peripheral edge. However, with the structure of the present invention as described above, chipping or breakage near the tip of the outer peripheral edge can be sufficiently suppressed even when using CBN sintered body with poor or excellent chipping resistance as the base material for the cutting edge 3, or even when the tip radius is set to 0.1 mm or less.

[0047] In the above embodiments, although the dimensions of each part have been specifically illustrated, the dimensions of each part in the end mill 1 can be changed without impairing its function.

[0048] In the above embodiment, although the length of the outer peripheral portion 11a of the bottom cutting edge is set to 0.25 mm (0.125D), when the tool diameter D is 1 mm or more, the length of the outer peripheral portion 11a of the bottom cutting edge is preferably 0.05D or more, more preferably 0.1D or more. The length of the outer peripheral portion 11a of the bottom cutting edge is preferably 0.8D or less, more preferably 0.5D or less. If the outer peripheral portion 11a of the bottom cutting edge is too long, the cutting resistance of the bottom cutting edge 11 increases. If the outer peripheral portion 11a of the bottom cutting edge is too short, the effect of making the cutting resistance closer to the axial side is reduced, thereby reducing the effect of suppressing the notch near the front end of the outer peripheral cutting edge 13.

[0049] In end mills 1 with a tool diameter D less than 1 mm, it is difficult to machine the bottom cutting edge 11 into two cutting edges with different core-cutting angles. Therefore, in end mills 1 with a tool diameter D less than 1 mm, the overall core-cutting angle of the bottom cutting edge 11 can also be set to 3° or less. That is to say, it can also be set to a structure in which the overall core-cutting angle of the bottom cutting edge 11 is the same as the core-cutting angle of the outer periphery 11a of the bottom cutting edge, which is 3° or less.

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

[0051] The ratio W1 / W2 of the width W1 of the first flank face 12a of the bottom edge outer periphery 11a to the width W2 of the first flank face 14a of the outer periphery of the bottom edge 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 flank face 12a of the outer periphery of the bottom cutting edge 11a is preferably in the range of 0.11D or more and 0.19D or less relative to the tool diameter D. More preferably, the width W1 is 0.12D or more or 0.13D or more. Even more preferably, the width W1 is 0.18D or less or 0.17D or less. In the above embodiment where the tool diameter D is 2 mm, the width W1 is preferably in the range of 0.22 mm or more and 0.38 mm or less.

[0053] The width W2 of the first flank face 14a of the outer peripheral cutting edge is preferably in the range of 0.01D or more and 0.04D or less relative to the tool diameter D. More preferably, the width W2 is 0.15D or more or 0.02D or more. Even more preferably, the width W2 is 0.035D or less or 0.03D or less. In the above embodiment where the tool diameter D is 2 mm, the width W2 is preferably in the range of 0.02 mm or more and 0.08 mm or less.

[0054] The clearance angle of the first clearance face 12b on the inner periphery of the bottom edge is preferably in the range of 15° or less. In the above embodiment, although the clearance angle γ of the first clearance face 12a on the outer periphery of the bottom edge and the clearance angle of the first clearance face 12b on the inner periphery of the bottom edge are both set to 10°, the clearance angle γ of the first clearance face 12a on the outer periphery of the bottom edge and the clearance angle of the first clearance face 12b on the inner periphery of the bottom edge can also be different angles.

[0055] The radius of the cutting edge 15 (cutter tip radius) is not particularly limited. When the tool diameter D of the end mill is 3 mm or less, if the cutting edge radius is 0.1 mm or less, a notch near the tip of the outer peripheral cutting edge is easily generated. Therefore, the structure of this embodiment is suitable for circular arc end mills or square end mills with a tool diameter D of 3 mm and a cutting edge radius of 0.1 mm or less.

[0056] The rake angles of the bottom cutting edge 11, the outer peripheral cutting edge 13, and the tip arc cutting edge 15 are preferably in the range of -50° to -20°. More preferably, the rake angles are -45° or higher or -35° or higher. More preferably, the rake angles are -25° or lower. The rake angles of the bottom cutting edge 11, the outer peripheral cutting edge 13, and the tip arc cutting edge 15 can be different angles.

[0057] Example

[0058] The present invention will now be specifically described through embodiments. However, the present invention is not limited to these embodiments.

[0059] (End mill fabrication and cutting tests)

[0060] As Example 1, an end mill of the aforementioned embodiment is manufactured. The elements are shown below.

[0061] Cutting edge: CBN, two cutting edges

[0062] Handle: Carbide

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

[0064] Cutter tip radius: 0.02mm

[0065] Neck length: 6mm

[0066] Bottom edge outer perimeter: Core-cutting angle is 1°

[0067] The first flank face on the outer periphery of the bottom cutting edge: flank angle is 10°, width is 0.24mm.

[0068] Bottom edge inner circumference: Core-cutting angle is 6°

[0069] The first back face of the inner circumference of the bottom edge has a back angle of 10°.

[0070] Outer peripheral cutting edge: twist angle is 0°

[0071] The first flank face of the outer peripheral cutting edge has a clearance angle of 4° and a width of 0.02mm.

[0072] The second flank face of the outer peripheral cutting edge has a clearance angle of 14° and a width of 0.30mm.

[0073] Negative blade flap: Front angle is -30°

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

[0075] Regarding the end mill in Comparative Example 1, as a typical conventional CBN circular arc end mill, the clearance angle of the first flank face of the outer peripheral cutting edge is set to 14°, the clearance angle of the first flank face of the outer peripheral cutting edge is set to 10°, the width of the first flank face of the outer peripheral cutting edge is set to 0.16D, the width of the first flank face of the outer peripheral cutting edge is set to 0.12D, and the core-cutting angle of the outer peripheral cutting edge is set to 6°. Other structures are the same as in Example 1.

[0076] Comparative Example 2 is an end mill with a larger wedge angle on the outer peripheral edge than that in Comparative Example 1.

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

[0078] Comparative Example 4 has a wedge angle greater than that of the outer peripheral cutting edge and the outer peripheral part of the bottom cutting edge than that of Comparative Example 1. Furthermore, the inclination of the outer peripheral part of the bottom cutting edge relative to the right-angle plane of the axis is gentler than that of the end mill in Comparative Example 1.

[0079] It should be noted that in Embodiment 1 described above, only the wedge angle of the outer peripheral cutting edge is larger than that of Comparative Example 1, and the inclination of the outer periphery of the bottom cutting edge relative to the right-angle plane of the axis is gentler than that of Comparative Example 1. Moreover, not only the back angle of the bottom cutting edge, but also the width of the back face of the bottom cutting edge is larger than the back angle and the width of the back face of the outer peripheral cutting edge, respectively.

[0080] The circular arc end mills of Example 1, Comparative Examples 1 to 4, which were manufactured in this way, were mounted on a machine tool and their cutting performance was evaluated. Figure 7The machining method during cutting evaluation is shown in general. STAVAX material was used as the material for workpiece W, with dimensions of 60×60×30 (mm). Under conditions of 1° taper, no tool tip radius, and an entry tilt angle of 0.5°, contour grooves of 10mm×10mm×0.6mm were repeatedly machined on workpiece W.

[0081] After each specified machining cycle, the cutting edge of the end mill is examined under a microscope to check for chipping, nicks, and wear.

[0082] <Cutting Conditions>

[0083] Workpiece: STAVAX (52HRC)

[0084] Coolant: Spray

[0085] Spindle speed (n): 24,000 rpm (Vc = 150 m / min)

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

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

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

[0089] [Table 1]

[0090]

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

[0092] Comparative Example 2 increases the wedge angle of the outer peripheral cutting edge by making the clearance angle of the first flank face of the outer peripheral cutting edge smaller than that of Comparative Example 1. However, although no large notch is produced on the outer peripheral cutting edge, chipping occurs on the outer peripheral cutting edge after four hours of cutting.

[0093] In Comparative Example 3, not only was the clearance angle of the first flank face of the outer peripheral cutting edge smaller than that of Comparative Example 1, but the clearance angle of the outer peripheral flank face of the bottom cutting edge was also smaller than that of Comparative Example 1, thereby increasing the wedge angles of both the outer peripheral cutting edge and the outer peripheral portion of the bottom cutting edge. However, similar to Comparative Example 2, Comparative Example 3 also experienced chipping on the outer peripheral cutting edge after four hours of cutting. This shows that simply increasing the wedge angle of the cutting edges such as the bottom or outer peripheral cutting edge (increasing the tool tip strength) is insufficient to adequately suppress chipping near the tip of the outer peripheral cutting edge.

[0094] In Example 1, the clearance angle of the first flank face of the outer peripheral cutting edge is smaller than that of Comparative Example 1. In other words, the clearance angle of the first flank face of the outer peripheral cutting edge is smaller than that of the clearance angle of the first flank face of the outer peripheral portion of the bottom cutting edge. Furthermore, considering the direction and magnitude of the cutting resistance of the bottom cutting edge, the inclination angle of the bottom cutting edge relative to the right-angle plane of the axis is smaller than that of Comparative Example 1, and the width of the first flank face of the outer peripheral portion of the bottom cutting edge is also larger than the width of the first flank face of the outer peripheral cutting edge. This Example 1 can perform 10 hours of cutting, with a lifespan 2.5 times that of Comparative Example 1. Comparative Example 4 is based on Example 1, but differs from Example 1 only in that, in order to increase not only the wedge angle of the outer peripheral cutting edge but also the wedge angle of the bottom cutting edge, the clearance angle γ of the first flank face of the outer peripheral portion of the bottom cutting edge is smaller than that of Example 1, and equal to the clearance angle ε of the first flank face of the outer peripheral cutting edge of Example 1. However, after four hours of cutting, Comparative Example 4 experiences chipping on the outer peripheral cutting edge, ending its lifespan. Therefore, it is important not only to move the direction of the cutting resistance of the bottom edge further toward the central axis to reduce the load on the outer peripheral edge near the front end, but also to avoid the cutting resistance of the bottom edge being too large.

[0095] Industrial applicability

[0096] A long-life end mill that can suppress chipping or notching near the tip of the peripheral cutting edge.

[0097] Explanation of reference numerals in the attached figures

[0098] 1 End mill

[0099] 2 knife handles

[0100] 3 Cutting edge

[0101] 10 cutting edges

[0102] 11 Bottom Edge

[0103] 11a Outer periphery of the bottom cutting edge

[0104] 12a First back face of the outer periphery of the bottom cutting edge

[0105] 13 peripheral blades

[0106] 14a peripheral cutting edge first flank face

[0107] 15-point rounded blade

[0108] 16-point cutter head with arc-shaped first back face

[0109] A. Outer periphery of the bottom edge

[0110] B. Front end (connection point) of the outer peripheral cutting edge

[0111] plane C is orthogonal to the central axis O

[0112] D tool diameter

[0113] The width of the first back face on the outer periphery of the W1 bottom edge

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

[0115] α and β tilt angles (core-digging angles)

[0116] O Central axis

Claims

1. An end mill comprising a cutting edge and a tool holder that rotate about a central axis, the end mill including: The bottom cutting edge located on the front end face of the cutting edge and the outer peripheral cutting edge located on the outer peripheral face of the cutting edge. The bottom cutting edge has an outer peripheral portion, which extends towards the handle side at an angle of less than 3° relative to a plane orthogonal to the central axis. The clearance angle of the first clearance face of the outer peripheral portion of the bottom edge adjacent to the outer peripheral portion of the bottom edge is greater than the clearance angle of the first clearance face of the outer peripheral edge adjacent to the outer peripheral edge, and the width of the first clearance face of the outer peripheral portion of the bottom edge is greater than the width of the first clearance face of the outer peripheral edge.

2. The end mill according to claim 1, wherein, The cutting edge is constructed from CBN sintered material.

3. The end mill according to claim 1 or 2, wherein, The outer periphery of the bottom cutting edge is connected to the outer peripheral cutting edge via a circular arc cutting edge. When viewed from the side of the end mill, the width of the first flank face of the arc-shaped cutting edge adjacent to the cutting edge gradually decreases from the front end to the rear end of the arc-shaped cutting edge. The rear angle of the first rear cutting face of the circular arc blade of the cutter head also gradually decreases from the bottom cutting side toward the outer peripheral cutting side.

4. The end mill according to claim 1 or 2, wherein, The ratio of the width of the first rear cutting surface of the outer periphery of the bottom cutting edge to the width of the first rear cutting surface of the outer peripheral cutting edge is in the range of 3 or more and 20 or less.

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

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

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