Ball End Mill

Abstract

Provided is a ball end mill comprising a ball blade formed in a partially spherical shape. The ball blade includes a plurality of grooves, including grooves having a first twisted shape and grooves having a second twisted shape different from the first twisted shape, such grooves extending from the leading end side of the ball blade towards the outer-circumferential side, when viewed in the rotational axis direction from the leading end. The plurality of grooves are non-connected at the leading end.

Description

[Technical field]

[0001] The present invention relates to a ball end mill. [Background technology]

[0002] Patent Documents 1 and 2 disclose ball end mills in which the surface roughness of the ball cutting edge is reduced in order to achieve a mirror finish on the machined surface of a workpiece. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2018-122365 A [Patent Document 2] JP 2016-112678 A Summary of the Invention [Problem to be solved by the invention]

[0004] In ball end mills such as those described in Patent Documents 1 and 2, the contact area between the ball blade portion and the surface of the workpiece is large, which can result in large resistance during machining. Therefore, by forming multiple grooves in the ball blade portion and reducing the contact area between the ball blade portion and the surface of the workpiece, it is possible to reduce the resistance during machining.

[0005] However, if a groove is formed up to the tip of the ball cutting edge, the area of ​​the workpiece corresponding to the tip may be insufficiently machined.

[0006] Some embodiments of the present invention aim to achieve a burnishing effect at the tip of the ball cutting edge. [Means for solving the problem]

[0007] Some embodiments of the present invention are a ball end mill including a ball blade portion formed into a partially spherical shape, the ball blade portion having a plurality of grooves including a groove of a first twist pattern and a groove of a second twist pattern different from the first twist pattern, the grooves extending from the tip side of the ball blade portion toward the outer periphery when viewed in the direction of the rotation axis from the tip, and the plurality of grooves being unconnected at the tip.

[0008] Other features of the present invention will become apparent from the following specification and drawings. Effect of the Invention

[0009] According to some embodiments of the present invention, a burnishing effect can be obtained at the tip of the ball cutting edge. [Brief description of the drawings]

[0010] [Figure 1] 1A is a side view of the ball end mill 10, and FIG. 1B is a view seen from a tip 13 of a ball cutting portion 12 in the direction of the rotation axis. [Diagram 2] FIG. [Diagram 3] 3A is a diagram of a ball blade portion 12 in which only groove 20A is formed, FIG. 3B is a diagram of a ball blade portion 12 in which only groove 20B is formed, and FIG. 3C is a diagram of a ball blade portion 12 in which grooves 20A and 20B are formed. [Figure 4] 4A is an explanatory diagram of multiple intersections 21 in a ball blade portion 12X of a comparative example, FIG. 4B is an explanatory diagram of an enlarged portion of intersection 21, and FIG. 4C is an explanatory diagram of multiple intersections 21 in a ball blade portion 12 of the present embodiment. [Diagram 5] 5A and 5B are explanatory diagrams of examples in which the number of grooves 20 formed in the ball blade portion 12 is changed. FIG. 5A is an explanatory diagram of an example in which there are 16 grooves 20A and 13 grooves 20B, and FIG. 5B is an explanatory diagram of an example in which there are 16 grooves 20A and 11 grooves 20B. [Figure 6]6A is an explanatory diagram of an example in which the number of grooves 20 formed in the ball blade portion 12 is changed, FIG. 6A is an explanatory diagram of an example in which there are 17 grooves 20A and 15 grooves 20B, FIG. 6B is an explanatory diagram of an example in which there are 9 grooves 20A and 7 grooves 20B, and FIG. 6C is an explanatory diagram of an example in which there are 7 grooves 20A and 5 grooves 20B. [Figure 7] 7A and 7B are explanatory diagrams of examples in which the number of grooves 20 formed in the ball blade portion 12 is changed, where FIG. 7A is an explanatory diagram of an example in which there are 16 grooves 20A and 14 grooves 20B, and FIG. 7B is an explanatory diagram of an example in which there are 15 grooves 20A and 10 grooves 20B. [Figure 8] 8A is a diagram of the ball blade portion 32 in which only groove 20C is formed, FIG. 8B is a diagram of the ball blade portion 32 in which only groove 20B is formed, and FIG. 8C is a diagram of the ball blade portion 32 in which grooves 20C and 20B are formed. [Figure 9] 9A and 9B are explanatory diagrams of the configuration of grooves 20 formed in a ball blade portion 42 of a second modified example, where FIG. 9A is a diagram of a ball blade portion 42 in which only groove 20A is formed, FIG. 9B is a diagram of a ball blade portion 42 in which only groove 20D is formed, and FIG. 9C is a diagram of a ball blade portion 42 in which grooves 20A and 20D are formed. [Figure 10] 10A is a diagram of a ball end mill 50 having a ball blade portion 52, FIG. 10B is a diagram of a ball end mill 60 having a ball blade portion 62, and FIG. 10C is a diagram of a ball end mill 10 having a ball blade portion 12. [Figure 11] FIG. 11 is an explanatory diagram for explaining processing conditions in a processing test. [Figure 12] 12A and 12B are graphs showing an example of a comparison result of processing torque under processing condition 1, where FIG. 12A is a graph showing average torque values ​​and FIG. 12B is a graph showing maximum torque values. [Figure 13] 13A and 13B are graphs showing an example of a comparison result of processing torque under processing condition 2, where FIG. 13A is a graph showing an average torque value and FIG. 13B is a graph showing a maximum torque value. [Figure 14]14A and 14B are diagrams relating to processing errors under processing conditions 1 and 2, in which FIG. 14A is an explanatory diagram of processing errors, and FIG. 14B is a table showing an example of a comparison result of processing errors. [Figure 15] 15A is a view of the ball blade portions 72 and 82 of the second embodiment, where FIG. 15A is a view of the ball blade portion 72 of the first embodiment as viewed in the direction of the rotation axis from the tip 13, and FIG. 15B is a view of the ball blade portion 82 of the second embodiment as viewed in the direction of the rotation axis from the tip 13. [Figure 16] 13 is a view of a ball cutting edge portion 92 of a third embodiment as viewed in the direction of a rotation axis. FIG. [Figure 17] 17A shows a first example of the shape of the ball-shaped blade portion 12, and FIG. 17B shows a second example of the shape of the ball-shaped blade portion 12. FIG. [Figure 18] 11 is another example of the groove 20 of the ball cutting portion 12. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] At least the following points will become apparent from the description of this specification and the accompanying drawings.

[0012] Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. The same or equivalent components, members, etc. shown in each drawing are designated by the same reference numerals, and duplicated descriptions will be omitted as appropriate.

[0013] ===First embodiment=== Fig. 1 is a diagram of a ball end mill 10 according to a first embodiment. Fig. 1A is a side view of the ball end mill 10, and Fig. 1B is a view seen in the direction of the rotation axis from a tip 13 of a ball cutting portion 12. Fig. 2 is a cross-sectional view of a groove 20.

[0014] <Definitions of directions and terms, etc.> First, with reference to FIG. 1, directions and terms used in the ball end mill 10 will be defined.

[0015] As shown in FIG. 1A, the direction along the rotation axis A of the ball end mill 10 is referred to as the "rotation axis direction" or simply the "axial direction." The "rotation axis direction" is also the longitudinal direction of the ball end mill 10. The rotation axis direction of the ball end mill 10 includes both the "tip direction" and the "base direction." As shown in FIG. 1A, the "tip direction" is the direction toward the tip side of the ball end mill 10, and the "base direction" is the direction toward the base side of the ball end mill 10. The "tip direction" and the "base direction" each have a fixed orientation.

[0016] As shown in FIG. 1B, the direction along the rotation direction of the ball end mill 10 may be referred to as the "circumferential direction." The "circumferential direction" is also the direction along the outer periphery 14 of the ball cutting portion 12, which will be described later. The circumferential direction of the ball end mill 10 includes both the "clockwise direction" and the "counterclockwise direction." Each of the "clockwise direction" and the "counterclockwise direction" has a fixed orientation. The "clockwise direction" may be referred to as the "right-handed direction," and the "counterclockwise direction" may be referred to as the "left-handed direction."

[0017] Here, the "axis of rotation" of the ball end mill 10 refers to the axis about which the ball end mill 10 rotates. The "axis of rotation" is sometimes called the "axis center." In this embodiment, the axis of rotation A of the ball end mill 10 is the central axis of the ball end mill 10, as shown in FIG. 1A.

[0018] Moreover, the "tip" of ball end mill 10 refers to the tip-most portion of the portion of ball end mill 10 that processes the workpiece (i.e., ball blade portion 12). In this embodiment, tip 13 of ball end mill 10 is located on the surface of ball blade portion 12 of ball end mill 10. As shown in FIG. 1B, when viewed from tip 13 in the direction of the rotation axis, tip 13 is located at the center of ball blade portion 12. Therefore, tip 13 is located on rotation axis A.

[0019] The above-mentioned definitions of directions, terms, etc. are common to other embodiments of this specification unless otherwise specified.

[0020] <Outline of Ball End Mill 10> Next, an overview of the ball end mill 10 according to this embodiment will be described with reference to FIGS.

[0021] The ball end mill 10 is a tool that processes a workpiece by using a cutting portion that is formed into a partially spherical shape.

[0022] Here, "partially spherical" refers to the shape of a portion of a sphere. In the ball end mill 10 of this embodiment, the blade portion is formed in a hemispherical shape as shown in FIG. 1A. However, the blade portion of the ball end mill 10 may be formed in a partially spherical shape other than a hemispherical shape, for example, in a shape shown in FIG. 17A described later. In addition, the "sphere" is not limited to a strict sphere, but also includes an elliptical sphere and the like. Therefore, the "partially spherical" includes not only a hemispherical shape, but also a semi-elliptical sphere and the like shown in FIG. 17B described later, for example.

[0023] Furthermore, the "partially spherical" shape may be a shape in which a part of the sphere is deformed, i.e., a part of the sphere may have a notch (concave) or a protrusion (convex). Specifically, as described below, a groove 20 that is a concave portion on the surface is formed in the part of the ball end mill 10 that is formed as a partially spherical shape (i.e., the ball cutting portion 12).

[0024] In a typical ball end mill, a curved surface is formed on a workpiece by machining the workpiece with a blade formed in a partially spherical shape. The ball end mill 10 of this embodiment is used to perform at least a burnishing process on the surface of the workpiece. Here, the "burnishing process" is a process for forming a smooth finished surface while causing plastic deformation and work hardening on the surface of the workpiece. Therefore, the ball end mill 10 of this embodiment is sometimes called a "burnishing end mill." In addition, the effect of forming a smooth finished surface on the surface of the workpiece by the burnishing process is sometimes called the "burnishing effect." In addition, the "burnishing process" and the "burnishing effect" are sometimes called the "vanishing process" and the "vanishing effect," respectively.

[0025] The ball end mill 10 of this embodiment is attached to a machine tool or the like via a holder (not shown), and the curved surface of the workpiece is burnished by the rotation of the cutting edge. By burnishing the workpiece, the machined surface of the workpiece can be mirror-finished.

[0026] As shown in FIG. 1A, the ball end mill 10 has a shank 11 and a ball cutting edge portion 12.

[0027] The shank 11 is a member that is supported by a holder (not shown) when the ball end mill 10 is attached to a machine tool, etc. The shank 11 is formed long in the direction of the rotation axis.

[0028] The ball end mill 10 has a tip end portion 12a and a tip end portion 12b, and the tip end portion 12b is a blade member that performs at least burnishing of a workpiece. ...b and is formed in a partially spherical shape.

[0029] The ball blade portion 12 is made of a sintered body formed to have a high hardness in order to perform burnishing of the workpiece. For example, PCD (Poly Crystalline Diamond), CBN (Cubic Boron Nitride), ceramics, cemented carbide, etc. can be used as the material of the ball blade portion 12. However, as long as the burnishing of the workpiece can be performed, materials other than the sintered body formed to have a high hardness may be used as the material of the ball blade portion 12.

[0030] The surface of the ball blade portion 12 is formed smoothly by grinding or laser processing. Specifically, the surface of the ball blade portion 12 is formed so that the surface roughness is Rz 1.6 μm or less. This can enhance the burnishing effect on the machined surface of the workpiece. However, the ball blade portion 12 may be formed so that the surface roughness is greater than Rz 1.6 μm, as long as the burnishing effect can be obtained on the machined surface of the workpiece. The surface of the ball blade portion 12 may be formed smoothly by coating it with a smooth coating.

[0031] As described later, grooves 20 (recesses) are formed in the ball-shaped cutting portion 12. In this embodiment, the smoothly formed "surface of the ball-shaped cutting portion 12" refers to an area of ​​the ball-shaped cutting portion 12 where no grooves 20 are formed.

[0032] However, in a ball end mill in which the surface of the ball blade portion is smoothly formed, the contact area between the surface of the ball blade portion and the surface of the workpiece is large, which may result in a large resistance during burnishing. For this reason, in the ball end mill 10 of this embodiment, a groove 20 is formed in the ball blade portion 12. The groove 20 is a recess formed in the ball blade portion 12, as shown in FIG. 2.

[0033] As a result, in the region of the ball blade portion 12 where the groove 20 is formed, the surface of the workpiece 100 does not come into contact with the ball blade portion 12 as shown in FIG. 2. Therefore, in the ball end mill 10 of this embodiment where the groove 20 is formed, the contact area between the ball blade portion 12 and the surface of the workpiece 100 is reduced compared to a ball blade portion where the groove 20 is not formed. In other words, in the ball end mill 10 of this embodiment, the groove 20 is formed in the ball blade portion 12, so that the resistance during the burnishing process can be reduced. Note that the burnishing process is mainly performed in the portion of the ball blade portion 12 where the groove 20 is not formed, i.e., the portion that comes into contact with the surface of the workpiece 100.

[0034] In this embodiment, as shown in FIG. 1B, the groove 20 is composed of a groove 20A and a groove 20B. The groove 20A and the groove 20B have different twist patterns, as described later. Here, the "twist pattern" refers to the deformation pattern of the shape of the groove 20 when viewed from the tip 13 of the ball cutting portion 12 in the direction of the rotation axis, as shown in FIG. 1B. For example, in this embodiment, the groove 20A has a "right twist" twist pattern, which will be described later, and the groove 20B has a "left twist" twist pattern, which will be described later. Note that the "twist pattern" is not limited to "right twist" or "left twist", but includes a spiral shape and a meandering shape.

[0035] In the following, when the groove 20A and the groove 20B are commonly described, or when one of the grooves 20A and 20B is described as a representative, a subscript may not be added. For example, the grooves 20A and 20B may be simply referred to as "groove 20." Either the groove 20A or the groove 20B may be simply referred to as "groove 20."

[0036] In this embodiment, the groove 20 is formed in the ball blade portion 12, and the peripheral portion 22 of the groove 20 shown in FIG. 2 becomes a cutting edge, and micro-cutting of the workpiece can be performed. In other words, the ball blade portion 12 of this embodiment can perform not only burnishing but also micro-cutting of the workpiece. Hereinafter, micro-cutting may be simply referred to as "cutting". In the ball end mill 10 of this embodiment, the groove 20 is formed in the ball blade portion 12, and therefore the mirror finish of the curved surface of the workpiece 100 can be performed by both burnishing and cutting.

[0037] Depending on the rake angle of the peripheral portion 22, the peripheral portion 22 may bite into the workpiece 100 (biting phenomenon) during machining of the workpiece 100. This biting phenomenon may result in overcutting the workpiece 100, causing problems such as a deterioration in the machining dimensions of the workpiece 100 and a decrease in the burnishing effect. Furthermore, the movement of the peripheral portion 22 biting into the workpiece 100 and the movement of the peripheral portion 22 returning to its original state from the biting occur periodically in a short period of time, which may cause chatter vibration.

[0038] In the ball cutting portion 12 of this embodiment, in order to suppress problems caused by such a biting phenomenon, the groove 20 has a negative rake angle R as shown in Fig. 2. However, if it is acceptable to some extent that the peripheral portion 22 may be biting into the workpiece 100 during machining of the workpiece 100, the groove 20 may be formed to have a positive rake angle.

[0039] 1B, the groove 20 has an intersection 21. The intersection 21 is a portion where the groove 20A and the groove 20B intersect. The characteristics of the intersection 21 in this embodiment will be described later.

[0040] <Twisting Mode of Groove 20> The twisting aspect of the groove 20 will now be described with reference to FIG. 3 in conjunction with FIG. 1 described above.

[0041] FIG. 3 is an explanatory diagram of the form of the groove 20 formed in the ball blade portion 12. Note that FIG. 3A is a diagram of the ball blade portion 12 in which only the groove 20A is formed, FIG. 3B is a diagram of the ball blade portion 12 in which only the groove 20B is formed, and FIG. 3C is a diagram of the ball blade portion 12 in which the groove 20A and the groove 20B are formed. Note that FIG. 3A and FIG. 3B are diagrams of the ball blade portion 12 in which the groove 20A and the groove 20B are taken out, respectively, in order to explain the groove 20A and the groove 20B individually. Also, in FIG. 3A to FIG. 3C, one groove 20A of the multiple grooves 20A that is the subject of explanation is indicated by a thick line. Similarly, one groove 20B of the multiple grooves 20B that is the subject of explanation is indicated by a thick line.

[0042] As described above, the grooves 20A and 20B have different twist patterns.

[0043] Groove 20A is a right-handed twist groove. A right-handed twist groove is a groove that twists in a clockwise direction from tip 13 to outer periphery 14 of ball-shaped cutting portion 12. In other words, a right-handed twist groove is a groove that curves so as to be convex in the counterclockwise direction along outer periphery 14 of ball-shaped cutting portion 12.

[0044] In the ball cutting portion 12 of this embodiment, a plurality of grooves 20A are formed. Specifically, as shown in FIG. 3A, 16 grooves 20A are formed in the ball cutting portion 12. The plurality of grooves 20A are provided radially from the tip 13 to the outer periphery 14. As shown in FIG. 3A, the plurality of grooves 20A are formed in the ball cutting portion 12 so that adjacent grooves 20A in the circumferential direction are equally spaced. In other words, the plurality of grooves 20A are formed in the ball cutting portion 12 so as to be equally divided. In other words, the plurality of grooves 20A are positioned so as to be rotationally symmetrical about the tip 13.

[0045] Here, "rotational symmetry" means that when n grooves are positioned radially around a center, they overlap when a groove is rotated (360 / n) degrees around the center. Here, 16 grooves 20A are formed in the ball cutting portion 12. Therefore, the multiple grooves 20A are arranged to overlap when rotated 22.5 (360 / 16) degrees in the circumferential direction.

[0046] Groove 20B is a left-handed twist groove. A left-handed twist groove is a groove that twists in a counterclockwise direction from tip 13 to outer periphery 14 of ball-shaped cutting portion 12. In other words, a left-handed twist groove is a groove that curves so as to be convex in a clockwise direction along outer periphery 14 of ball-shaped cutting portion 12.

[0047] In the ball blade portion 12 of this embodiment, a plurality of grooves 20B are formed. Specifically, as shown in FIG. 3B, 15 grooves 20B are formed in the ball blade portion 12. The plurality of grooves 20B are provided radially from the tip 13 to the outer periphery 14. As shown in FIG. 3B, the plurality of grooves 20B are formed in the ball blade portion 12 such that adjacent grooves 20B in the circumferential direction are equally spaced. In other words, the plurality of grooves 20B are formed in the ball blade portion 12 so as to be equally divided. In other words, the plurality of grooves 20B are positioned so as to be rotationally symmetrical about the tip 13.

[0048] In the ball blade portion 12 of this embodiment, as shown in FIG. 3C, right-handed grooves 20A and left-handed grooves 20B are alternately arranged in the rotation direction of the ball end mill 10. As a result, when the workpiece is machined by the rotation of the ball end mill 10, the machining direction of the workpiece changes for each groove 20. In addition, when the workpiece is machined by the rotation of the ball end mill 10, an unequal twist effect is also achieved. Therefore, it is possible to suppress the generation of burrs on the workpiece after machining. In addition, it is possible to improve the vibration-proofing effect when the workpiece is machined.

[0049] 3C, in the ball cutting portion 12 of the present embodiment, the multiple grooves 20, each consisting of groove 20A and groove 20B, are not connected to each other at the tip 13. As described above, the burnishing process is performed in a portion where no groove 20 is formed. Therefore, by making the multiple grooves 20 not connected to each other at the tip 13, it is possible to prevent the grooves 20 (recesses) from being formed at the tip 13 and obtain a burnishing effect at the tip 13.

[0050] <Intersection 21> In the following, the characteristics of the intersection 21 of the ball cutting portion 12 of the present embodiment will be described using a comparative example.

[0051] Fig. 4 is an explanatory diagram of an intersection 21 of a groove 20. Fig. 4A is an explanatory diagram of a plurality of intersections 21 in a ball blade portion 12X of a comparative example, Fig. 4B is an explanatory diagram in which the intersections 21 are enlarged, and Fig. 4C is an explanatory diagram of a plurality of intersections 21 in the ball blade portion 12 of this embodiment. Figs. 4A to 4C show views (side views) of the ball blade portion 12X or the ball blade portion 12 as viewed in a direction perpendicular to the rotation axis direction.

[0052] In the comparative ball blade portion 12X shown in FIG. 4A, a plurality of right-handed grooves 20A and a plurality of left-handed grooves 20B, the same number as the grooves 20A, are formed. Specifically, the comparative ball blade portion 12X has 15 grooves 20A and 15 grooves 20B. In the comparative ball blade portion 12X, the plurality of grooves 20A and the plurality of grooves 20B are each positioned so as to be rotationally symmetrical about the tip 13. As a result, in a side view of the ball blade portion 12X, a plurality of intersections 21 formed by the grooves 20A and the grooves 20B are concentrated on a line along the rotation direction, as shown by the area surrounded by a line in FIG. 4A.

[0053] Here, when the ball end mill 10X of the comparative example machines a workpiece while rotating in the rotation direction shown in Fig. 4A, how a certain point on the workpiece passes through the groove 20 and the intersection 21 will be described with reference to Fig. 4B. Fig. 4B shows an enlarged view of a portion of the ball blade portion 12X including the intersection 21 where a certain groove 20A and a certain groove 20B intersect. Also, in Fig. 4B, the area of ​​the intersection 21 is shown by shading using dots.

[0054] In Fig. 4B, a trajectory through which a certain point of the workpiece passes in the ball-shaped blade portion 12X is indicated by a dashed line L1. Also, a trajectory through which another point of the workpiece passes in the ball-shaped blade portion 12X is indicated by L2. As shown in Fig. 4B, the trajectory L1 does not pass through the intersection 21, but the trajectory L2 passes through the intersection 21.

[0055] As described above, among the processes performed by the ball end mill 10, the burnishing process is mainly performed on the portion of the ball cutting portion 12 where the grooves 20 are not formed. For this reason, the burnishing process is not performed on the grooves 20 or the intersections 21 of the grooves 20.

[0056] The portion of the ball blade portion 12 where the burnishing process is performed will be described with reference to the diagram shown in FIG. 4B. The burnishing process is performed at the portions of the locus L1 and the locus L2 indicated by the arrows. Here, in the locus L1, the arrow portions where the burnishing process is performed appear regularly on either side of the groove 20B or the groove 20A. On the other hand, in the locus L2, the arrow portions where the burnishing process is performed do not appear from the time when the locus starts passing through the groove 20B until the time when the locus finishes passing through the groove 20A. In other words, in the locus L2, the portions where the burnishing process is not performed appear more than in the locus L1. Therefore, the locus L2 that passes through the intersection 21 is more disadvantageous in terms of the burnishing process than the locus L1 that does not pass through the intersection 21.

[0057] As described above, among the processes performed by the ball end mill 10, the cutting process is mainly performed on part C of the peripheral edge 22 of the groove 20 on the cutting edge side, as shown in Fig. 4B. The peripheral edge 22 has two parts, the side where the trajectory L1 and the trajectory L2 start passing and the side where the trajectory ends passing, and part C is the part of the peripheral edge 22 on the side where the trajectory ends passing.

[0058] Here, in the locus L1, the portion C where cutting is performed appears twice. On the other hand, in the locus L2, the portion C where cutting is performed appears only once. In other words, in the locus L2, the portion C where cutting is performed is smaller than in the locus L1. Therefore, in terms of cutting, the locus L2 that passes through the intersection 21 is more disadvantageous than the locus L1 that does not pass through the intersection 21.

[0059] As described above, the trajectory L2 that passes through the intersections 21 is less favorable in both burnishing and cutting than the trajectory L1 that does not pass through the intersections 21. Here, in the ball blade portion 12X of the comparative example, the intersections 21 that are disadvantageous in burnishing and cutting are concentrated on a line along the rotation direction. In the area of ​​the machined surface of the workpiece through which such a large number of intersections 21 pass, machining may be insufficient, and the quality of the machined surface of the workpiece may be reduced.

[0060] In the ball cutting section 12 of this embodiment, in order to improve the quality of the machined surface of the workpiece, the intersections 21 are prevented from concentrating on a line along the rotation direction. This improves the quality of the machined surface of the workpiece and also increases the accuracy. The arrangement of the intersections 21 of the ball cutting section 12 of this embodiment will be described below with reference to FIG. 3C described above.

[0061] When viewed in the rotation axis direction from the tip 13 of the ball blade portion 12 shown in Fig. 3C, in a certain groove 20B, an intersection 21 located at a predetermined position (e.g., the third position) from the tip 13 side is defined as a first intersection 21A. In addition, in another groove 20B adjacent in the circumferential direction, an intersection located at the same predetermined position (the third position) from the tip 13 side as described above is defined as a second intersection 21B. In this case, in the ball blade portion 12 of this embodiment, the length from the tip 13 to the first intersection 21A is different from the length from the tip 13 to the second intersection 21B.

[0062] Therefore, in the ball blade portion 12 of this embodiment, it is possible to prevent the intersections 21 from concentrating on a line along the rotation direction. That is, in the side view of the ball blade portion 12 shown in FIG. 4C, the line on which the multiple intersections 21 are located (i.e., the area surrounded by the line in FIG. 4C) is inclined with respect to the line along the rotation direction. In the ball blade portion 12 of this embodiment, only one intersection 21 is located on each line along the rotation direction. When viewed from the tip 13 of the ball blade portion 12 shown in FIG. 3C in the direction of the rotation axis, the multiple intersections 21 are located on a spiral curve centered on the tip 13 (i.e., the dashed line in FIG. 3C).

[0063] In the ball blade portion 12 of this embodiment, the number of grooves 20A and the number of grooves 20B different from the number of grooves 20A are formed. Specifically, as described above, 16 grooves 20A and 15 grooves 20B are formed. In addition, in the ball blade portion 12 of this embodiment, the multiple grooves 20A and the multiple grooves 20B are each positioned so as to be rotationally symmetrical about the tip 13. This makes it possible to make the length from the tip 13 of the ball blade portion 12 to the first intersection 21A and the length from the tip 13 of the ball blade portion 12 to the second intersection 21B different.

[0064] <Example of changing the number of grooves 20> In the following, examples in which the number of grooves 20A and the number of grooves 20B are changed will be described with reference to Figs. 5 to 7.

[0065] An example in which the number of grooves 20A and the number of grooves 20B are mutually prime Fig. 5 is an explanatory diagram of an example in which the number of grooves 20 formed in the ball cutting portion 12 is changed. Fig. 5A is an explanatory diagram of an example in which there are 16 grooves 20A and 13 grooves 20B, and Fig. 5B is an explanatory diagram of an example in which there are 16 grooves 20A and 11 grooves 20B.

[0066] 6A and 6B are explanatory diagrams of examples in which the number of grooves 20 formed in the ball blade portion 12 is changed. Fig. 6A is an explanatory diagram of an example in which there are 17 grooves 20A and 15 grooves 20B, Fig. 6B is an explanatory diagram of an example in which there are 9 grooves 20A and 7 grooves 20B, and Fig. 6C is an explanatory diagram of an example in which there are 7 grooves 20A and 5 grooves 20B.

[0067] In the ball blade portion 12 shown in Figures 5A, 5B, and 6A to 6C, the number of grooves 20A and the number of grooves 20B are in a prime relationship with each other. In this case, as shown in Figures 5A, 5B, and 6A to 6C, when viewed from the tip 13 of the ball blade portion 12 in the rotation axis direction, the length from the tip 13 to the intersection 21 is different for all of the intersections 21. In this case, the multiple intersections 21 are located on a spiral curve centered on the tip 13 (i.e., the dashed line in Figures 5A, 5B, and 6A to 6C).

[0068] An example in which the number of grooves 20A and the number of grooves 20B are not coprime Fig. 7 is an explanatory diagram of an example in which the number of grooves 20 formed in the ball blade portion 12 is changed. Fig. 7A is an explanatory diagram of an example in which there are 16 grooves 20A and 14 grooves 20B, and Fig. 7B is an explanatory diagram of an example in which there are 15 grooves 20A and 10 grooves 20B.

[0069] In the ball blade portion 12 shown in Fig. 7A and Fig. 7B, the number of grooves 20A and the number of grooves 20B are not coprime. In this case, for example, in the ball blade portion 12 shown in Fig. 7A, two intersections 21 appear at symmetric positions on a plane including the rotation axis. In other words, in the case of the ball blade portion 12 shown in Fig. 7A, two intersections 21 are located on a line along the rotation direction (i.e., the dashed line in Fig. 7A). Similarly, in the case of the ball blade portion 12 shown in Fig. 7B, five intersections 21 are located on a line along the rotation direction (i.e., the dashed line in Fig. 7B). Therefore, in the case of the ball blade portion 12 shown in Fig. 7A and Fig. 7B, when viewed from the tip 13 in the rotation axis direction, two or more intersections 21 appear that have the same length from the tip 13 to the intersections 21.

[0070] Therefore, in the ball blade portion 12 of the present embodiment, it is more preferable that the number of grooves 20A and the number of grooves 20B are different and are mutually prime.

[0071] In the above, it has been described that the length from the tip 13 of the ball blade portion 12 to the first intersection 21A and the length from the tip 13 of the ball blade portion 12 to the second intersection 21B are different due to the difference between the number of grooves 20A and the number of grooves 20B. However, the manner in which the length from the tip 13 of the ball blade portion 12 to the first intersection 21A and the length from the tip 13 of the ball blade portion 12 to the second intersection 21B are different is not limited to the above. Even in the case of the modified examples (first modified example and second modified example) shown below, the length from the tip 13 of the ball blade portion 12 to the first intersection 21A and the length from the tip 13 of the ball blade portion 12 to the second intersection 21B are different.

[0072] <First Modification> Fig. 8 is an explanatory diagram of an aspect of the groove 20 formed in the ball-shaped cutting portion 32 of the first modified example. Fig. 8A is a diagram of the ball-shaped cutting portion 32 in which only the groove 20C is formed, Fig. 8B is a diagram of the ball-shaped cutting portion 32 in which only the groove 20B is formed, and Fig. 8C is a diagram of the ball-shaped cutting portion 32 in which the grooves 20C and 20B are formed.

[0073] 3C described above, the plurality of grooves 20A and the plurality of grooves 20B are both positioned to be rotationally symmetrical about the tip 13. However, in the ball blade portion 32 of the first modified example, at least one of the plurality of grooves 20A and the plurality of grooves 20B does not have to be positioned to be rotationally symmetrical about the tip 13.

[0074] 8A, in the ball blade portion 32 of the first modified example, the division angle between circumferentially adjacent grooves 20C is set to gradually increase. In other words, when comparing the division angle α between certain grooves 20C and the division angle β between other grooves 20C, the division angle β is set to be larger than the division angle α (β>α).

[0075] On the other hand, in the ball blade portion 32 of the first modified example, the groove 20B having a different twist pattern from the groove 20C is positioned so as to be rotationally symmetric about the tip 13, similar to the above-mentioned ball blade portion 12, as shown in FIG. 8B.

[0076] The ball blade portion 32 of the first modification can also prevent the intersections 21 from concentrating on a line along the rotation direction. That is, the ball blade portion 32 of the first modification also has only one intersection 21 on a line along the rotation direction. When viewed in the direction of the rotation axis from the tip 13 of the ball blade portion 32 shown in FIG. 8C, the multiple intersections 21 are located on a spiral curve (i.e., the dashed line in FIG. 8C) centered on the tip 13 of the ball blade portion 32. Therefore, the quality of the machined surface of the workpiece can be improved in the ball blade portion 32 of the first modification.

[0077] In the ball blade portion 32 of the first modified example described above, the right-handed groove 20C is provided so that the angle between adjacent grooves 20 in the circumferential direction gradually increases. However, instead of the right-handed groove 20C, the left-handed groove 20B may be provided so that the angle between adjacent grooves 20B in the circumferential direction gradually increases. Also, for both the right-handed groove 20C and the left-handed groove 20B, the angle between adjacent grooves 20C in the circumferential direction and adjacent grooves 20B in the circumferential direction may be set so that the angle between adjacent grooves 20C in the circumferential direction and adjacent grooves 20B in the circumferential direction gradually increases. They may also be provided so as to gradually increase in size.

[0078] Furthermore, the angle between adjacent grooves 20 in the circumferential direction may be gradually decreased. However, the present invention is not limited thereto, and as long as it is possible to prevent the intersections 21 from being concentrated on a line along the rotation direction, it is sufficient that the angle between adjacent grooves 20 in one circumferential direction is different from the angle between adjacent grooves 20 in another circumferential direction. In the ball blade portion 32 of the first modified example, the number of grooves 20C and the number of grooves 20B may be the same.

[0079] <Second Modification> Fig. 9 is an explanatory diagram of an aspect of the groove 20 formed in the ball blade portion 42 of the second modified example. Fig. 9A is a diagram of the ball blade portion 42 in which only the groove 20A is formed, Fig. 9B is a diagram of the ball blade portion 42 in which only the groove 20D is formed, and Fig. 9C is a diagram of the ball blade portion 42 in which the grooves 20A and 20D are formed.

[0080] In the ball blade portion 12 shown in Fig. 3C described above, a plurality of grooves 20A and a plurality of grooves 20B are formed. However, in the ball blade portion 42 of the second modified example, only one of the grooves 20A and 20B may be formed. The twist pattern of the only groove formed may be a pattern other than the right twist and left twist shown in Fig. 3C.

[0081] A plurality of grooves 20A are formed in the ball blade portion 42 of the second modified example. As shown in Fig. 9A, the plurality of grooves 20A are positioned to be rotationally symmetrical about the tip 13, similar to the ball blade portion 12 described above.

[0082] On the other hand, in the ball blade portion 42 of the second modified example, one groove 20D is formed as shown in Fig. 9B. The groove 20D is a groove formed by a spiral curve centered on the tip 13.

[0083] The ball blade portion 42 of the second modification can also prevent the intersections 21 from concentrating on a line along the rotation direction. That is, the ball blade portion 42 of the second modification also has only one intersection 21 on a line along the rotation direction. When viewed in the rotation axis direction from the tip 13 of the ball blade portion 42 shown in FIG. 9C, the multiple intersections 21 are located on a spiral curve (i.e., groove 20D in FIG. 9C) centered on the tip 13 of the ball blade portion 42. Therefore, the quality of the machined surface of the workpiece can be improved in the ball blade portion 42 of the second modification.

[0084] <Processing test> Three types of ball end mills were prepared, with and without grooves on the ball cutting edge and the shape of the grooves, and machining tests were conducted on the workpiece. First, an overview of the three types of ball end mills will be described below.

[0085] Fig. 10 is an explanatory diagram of a ball end mill used in a machining test using a ball end mill. Fig. 10A is a diagram of a ball end mill 50 having a ball end mill 52, Fig. 10B is a diagram of a ball end mill 60 having a ball end mill 62, and Fig. 10C is a diagram of a ball end mill 10 having a ball end mill 12.

[0086] As shown in Fig. 10A, the grooves 20 are not formed in the ball blade portion 52 of the ball end mill 50. That is, the entire surface of the ball blade portion 52 comes into contact with the surface of the workpiece, and the burnishing process is performed on the workpiece. Since the ball blade portion 52 has no grooves, the above-mentioned cutting process is not performed.

[0087] As shown in Fig. 10B, the grooves 20 are formed in the ball cutting edge portion 62 of the ball end mill 60. The grooves 20 are composed of only 16 right-handed grooves 20A. A cross-sectional view of the grooves 20 is shown on the right side of Fig. 10B. The grooves 20 have a negative rake angle, similar to the grooves 20 shown in Fig. 2 described above.

[0088] As shown in FIG. 10C, the ball blade portion 12 of the ball end mill 10 has grooves 20 formed therein. The grooves 20 are composed of 16 right-handed grooves 20A and 15 left-handed grooves 20B. That is, the ball blade portion 12 is similar to the ball blade portion 12 of the ball end mill 10 of this embodiment shown in FIG. 3C and the like. A cross-sectional view of the grooves 20 is shown on the right side of FIG. 10C. The grooves 20 have a negative rake angle, similar to the grooves 20 shown in FIG. 2.

[0089] Next, two types of processing conditions (processing condition 1 and processing condition 2) in this processing test will be described.

[0090] Fig. 11 is an explanatory diagram for explaining the machining conditions in the machining test. Note that Fig. 11 shows the machining conditions for the ball blade portion 12 (ball end mill 10) as a representative, but the same applies to the ball blade portion 52 (ball end mill 50) and the ball blade portion 62 (ball end mill 60).

[0091] As shown in Fig. 11, the ball end mill 10 performs up-cutting on the workpiece 100 by moving in the direction of the arrow shown in Fig. 11 while rotating the ball blade portion 12. Here, the area to be machined of the workpiece 100 has already been cut into a recess formed of a curved surface as shown in Fig. 11. The ball blade portion 12 of the ball end mill 10 is scheduled to cut in a direction perpendicular to the axial direction during machining.

[0092] Here, under the processing condition 1, the rotation speed of the ball blade portion 12 is 800 min -1(Cutting speed: 20 m / min), table feed speed is 320 mm / min, axial cutting depth is 4 mm, and planned cutting depth is 0.005 mm. In addition, in machining condition 2, the rotation speed of the ball blade portion 12 is 800 min -1 (Cutting speed: 20 m / min), the table feed speed is set to 32 mm / min, the axial cutting depth is set to 4 mm, and the planned cutting depth is set to 0.010 mm.

[0093] <Comparison of machining torque> Fig. 12 is a graph showing an example of a comparison result of processing torque under processing condition 1. Fig. 12A is a graph showing the average torque value, and Fig. 12B is a graph showing the maximum torque value. Fig. 13 is a graph showing an example of a comparison result of processing torque under processing condition 2. Fig. 13A is a graph showing the average torque value, and Fig. 13B is a graph showing the maximum torque value.

[0094] Under machining condition 1, the machining torque is highest in the ball blade portion 52 where no grooves 20 are formed, for both the average torque value shown in Fig. 12A and the maximum torque value shown in Fig. 12B. The machining torque in the ball blade portion 62 formed only with right-handed grooves 20A is the second highest after the machining torque in the ball blade portion 52. The machining torque in the ball blade portion 12 formed with right-handed grooves 20A and left-handed grooves 20B is the lowest.

[0095] Also, under machining condition 2, the machining torque is highest in the ball blade portion 52 where no grooves 20 are formed, for both the average torque value shown in Fig. 13A and the maximum torque value shown in Fig. 13B. The machining torque in the ball blade portion 62 formed only with right-handed grooves 20A is the second highest after the machining torque in the ball blade portion 52. The machining torque in the ball blade portion 12 formed with right-handed grooves 20A and left-handed grooves 20B is the lowest.

[0096] From the comparison results of this machining test, a significant difference due to the formation of the groove 20 in the ball cutting edge portion is clear. As described above, in the ball end mill 10 of this embodiment, the groove 20 is formed in the ball cutting edge portion, so that the resistance during the burnishing process can be reduced. However, the groove 20 is formed in the ball cutting edge portion, so that resistance due to the cutting process on the workpiece may occur. In other words, this machining test showed that even if resistance due to the cutting process occurs, the effect of reducing resistance due to the burnishing process is greater.

[0097] <Comparison of processing errors> Next, we verify the machining errors for three types of ball end mills.

[0098] Fig. 14 is a table regarding machining errors under machining conditions 1 and 2. Fig. 14A is an explanatory diagram of machining errors, and Fig. 14B is a table showing an example of a comparison result of machining errors. Fig. 14A shows a cross-sectional view of a workpiece as seen in the moving direction of a ball end mill.

[0099] Here, as shown in Fig. 14A, the machining error is represented by the difference between the planned cutting position of the workpiece (i.e., the position of the dashed line shown in Fig. 14A) and the actual cutting position (i.e., the position of the solid line shown in Fig. 14A). The side opposite the ball blade portion side is a positive value, and the ball blade portion side is a negative value. In other words, when the machining error is a positive value, it means that the cutting was actually too deep compared to the planned cutting position. On the other hand, when the machining error is a negative value, it means that the cutting was actually insufficient compared to the planned cutting position.

[0100] 14B, under machining condition 1, the machining error is the largest in the ball blade portion 52 where no grooves 20 are formed. The machining error in the ball blade portion 62 formed only of the right-handed grooves 20A is the second largest after the machining error in the ball blade portion 52. The machining error in the ball blade portion 12 formed of the right-handed grooves 20A and the left-handed grooves 20B is the smallest.

[0101] 14B, under machining condition 2, the machining error is the largest in the ball blade portion 52 where no groove 20 is formed. The machining error in the ball blade portion 62 formed only of the right-handed groove 20A is the second largest after the machining error in the ball blade portion 52. The machining error in the ball blade portion 12 formed of the right-handed groove 20A and the left-handed groove 20B is the smallest.

[0102] From the above, the verification results of the processing error also clearly show a significant difference due to the formation of the groove 20 in the ball-shaped cutting portion. Furthermore, it was found that the ball-shaped cutting portion 12 composed of the right-handed groove 20A and the left-handed groove 20B is more advantageous in terms of processing error than the ball-shaped cutting portion 62 composed of only the right-handed groove 20A.

[0103] ===Second embodiment=== In the ball end mill 10 of the first embodiment described above, the multiple grooves 20 formed in the ball cutting edge portion 12 are not connected at the tip 13. This prevents the grooves 20 (recesses) from being formed at the tip 13, and allows the burnishing effect at the tip 13 to be obtained.

[0104] Moreover, the multiple grooves 20 are provided radially from the tip 13 to the outer periphery 14. For this reason, in the ball cutting portion 12 of the first embodiment, the multiple grooves 20 are concentrated closer to the tip 13. As described above, since burnishing is not performed on the portion of the ball cutting portion 12 where the grooves 20 are formed, the burnishing effect may be weakened around the tip 13.

[0105] Therefore, the following describes a ball end mill that improves the burnishing effect around the tip of the ball cutting edge.

[0106] Fig. 15 is a diagram of the ball blade portions 72 and 82 of the second embodiment. Fig. 15A is a diagram of the ball blade portion 72 of the first embodiment as viewed from the tip 13 in the direction of the rotation axis, and Fig. 15B is a diagram of the ball blade portion 82 of the second embodiment as viewed from the tip 13 in the direction of the rotation axis. Fig. 16 is a diagram of the ball blade portion 92 of the third embodiment as viewed from the tip 13 in the direction of the rotation axis.

[0107] 15A, the ball-shaped cutting portion 72 of the first example of this embodiment has a region 15 that includes the tip 13 and is wider than the tip 13. The end of each of the plurality of grooves 20 on the tip 13 side is located outside the region 15. In other words, no grooves 20 are formed on the ball-shaped cutting portion 72 inside the region 15. This makes it possible to enhance the burnishing effect around the tip 13 of the ball-shaped cutting portion where the grooves 20 are concentrated.

[0108] However, it is not necessary that all ends of the grooves 20 on the tip 13 side are located outside the region 15. As shown in Fig. 15B, among the multiple grooves 20 formed in the ball cutting edge portion, the ends of the tip 13 side of each of some of the grooves may be located inside the region 15.

[0109] 15B, the ball blade portion 82 of the second example of this embodiment has groove 20A whose end on the tip 13 side extends to the tip 13, and grooves 20E and 20F whose ends on the tip 13 side are located outside the region 15. That is, the multiple grooves 20 of the ball blade portion 82 have grooves 20 whose ends on the tip 13 side are located outside the region 15 (i.e., grooves 20E and 20F) and grooves 20 whose ends on the tip 13 side are located inside the region 15 (i.e., groove 20A). This makes it possible to improve the burnishing effect and the cutting effect around the tip 13 of the ball blade portion where the grooves 20 are concentrated.

[0110] The position of the end of groove 20 on the tip 13 side may be stepped. As shown in Fig. 16, ball cutting section 92 of a third example of this embodiment has region 16 that includes tip 13 and is narrower than region 15. As shown in Fig. 16, groove 20 may be composed of groove 20G whose end on the tip 13 side is located inside region 15 and outside region 16, and groove 20A whose end on the tip 13 side is located inside region 16. This makes it possible to improve the burnishing effect and the cutting effect around tip 13 of the ball cutting section where grooves 20 are concentrated.

[0111] ===Other embodiments=== <Another Example of the Shape of the Ball-Blade Section 12> 17A and 17B show another example of the shape of the ball-shaped blade portion 12, with FIG. 17A showing a first example of the shape of the ball-shaped blade portion 12 and FIG. 17B showing a second example of the shape of the ball-shaped blade portion 12.

[0112] The shape of the ball cutting portion 12 is not limited to the hemispherical shape shown in Fig. 1A. For example, the ball cutting portion 12 may have a shape closer to a sphere than a hemispherical shape, as shown in Fig. 17A. Also, the ball cutting portion 12 may have an elliptical spherical shape, as shown in Fig. 17B.

[0113] <Another Example of the Groove 20 of the Ball-Blade Section 12> FIG. 18 shows another example of the groove 20 of the ball cutting portion 12.

[0114] The grooves 20 formed in the above-described ball cutting portion 12 are formed to have the same width. However, as in the ball cutting portion 12 shown in Fig. 18, in each of the multiple grooves 20, the width of the groove 20 on the outer periphery 14 side may be greater than the width of the groove 20 on the tip 13 side. This makes it possible to suppress resistance on the outer periphery 14 side during burnishing.

[0115] ===Summary=== The ball end mill according to the embodiment of the present invention has been described above.

[0116] The ball end mill 10 of the first embodiment includes a ball blade portion 12 formed in a partially spherical shape, as shown in Fig. 1 for example. When viewed from the tip 13 in the direction of the rotation axis, the ball blade portion 12 has a plurality of grooves 20 including a right-handed groove 20A and a left-handed groove 20B that is different from the right-handed groove, which extend from the tip 13 side of the ball blade portion 12 to the outer periphery 14 side. The plurality of grooves 20 are not connected at the tip 13. This makes it possible to obtain a burnishing effect at the tip 13 of the ball blade portion 12.

[0117] Here, a right twist corresponds to a "first twist mode", and a left twist corresponds to a "second twist mode".

[0118] 15A, the ball-shaped cutting portion 72 of the first example of the second embodiment has a first region 15 that includes the tip 13 and is wider than the tip 13. The end of each of the multiple grooves 20 on the tip 13 side is located outside the first region 15. This makes it possible to enhance the burnishing effect around the tip 13 of the ball-shaped cutting portion where the grooves 20 are concentrated.

[0119] 15B, the ball blade portion 82 of the second example of the second embodiment has a first region 15 that includes the tip 13 and is wider than the tip 13. The multiple grooves 20 have grooves 20E and 20F whose ends on the tip 13 side are located outside the first region 15, and groove 20A whose end on the tip 13 side is located inside the first region 15. This makes it possible to improve the burnishing effect and the cutting effect around the tip 13 of the ball blade portion where the grooves 20 are concentrated.

[0120] Here, the grooves 20E and 20F correspond to a "first groove", and the groove 20A corresponds to a "second groove".

[0121] 16, the ball blade portion 92 of the third example of the second embodiment includes the tip 13 and has a second region 16 narrower than the first region 15. The grooves 20 include grooves 20 located inside the first region 15, and the grooves 20 include groove 20G whose end on the tip 13 side is located outside the second region 16 and groove 20A whose end on the tip 13 side is located inside the second region 16. This makes it possible to improve the burnishing effect and the cutting effect around the tip 13 of the ball blade portion where the grooves 20 are concentrated.

[0122] Here, the groove 20G corresponds to the "outer second groove", and the groove 20A corresponds to the "inner second groove".

[0123] 15B, when viewed in the rotation axis direction from the tip 13 of the ball-shaped blade portion 82 of the second example of the second embodiment, the first twist pattern is a left-handed twist pattern curved so as to be convex in a first direction along the outer periphery 14 of the ball-shaped blade portion 82, and the second twist pattern is a right-handed twist pattern curved so as to be convex in a second direction opposite to the first direction along the outer periphery 14 of the ball-shaped blade portion 82, the groove 20F is in the first twist pattern and the groove 20A is in the second twist pattern. This makes it possible to improve the burnishing effect and the cutting effect around the tip 13 of the ball-shaped blade portion where the grooves 20 are concentrated.

[0124] 15B, the plurality of grooves 20 formed in the ball cutting portion 82 of the second example of the second embodiment includes a plurality of grooves 20A located inside the first region 15, and the plurality of grooves 20A are located so as to be rotationally symmetrical about the tip 13. This makes it possible to improve the burnishing effect and the cutting effect around the tip 13 of the ball cutting portion where the grooves 20 are concentrated.

[0125] 18, in another example of the ball cutting edge portion 12, the width of each of the grooves 20 on the outer periphery 14 side is greater than the width of the groove 20 on the tip 13 side. This makes it possible to suppress resistance on the outer periphery 14 side during burnishing.

[0126] ===Other=== The above-described embodiment is for the purpose of facilitating understanding of the present invention, and is not intended to limit the present invention. The present invention may be modified or improved without departing from the spirit thereof, and it goes without saying that the present invention includes equivalents thereof. [Explanation of symbols]

[0127] 10,10X,30,40,50,60,70,80,90 Ball End Mill 11 Shank 12,12X,32,42,52,62,72,82,92 Ball-shaped cutting edge 13 Tip 14 Outer circumference 15,16 areas 20,20A~20G groove 21, 21A, 21B intersection 22 Periphery 100 Work material

Claims

1. The blade is provided with a ball cutting edge having a surface formed in a partially spherical shape for burnishing a workpiece, The ball cutting portion has a plurality of grooves which are recessed into the surface, and when viewed from the tip in the direction of the rotation axis, the plurality of grooves include a groove having a first twist pattern extending from a tip side of the ball cutting edge portion to an outer periphery side, and a groove having a second twist pattern different from the first twist pattern, and the grooves are not connected to each other at the tip. Ball end mill.

2. The ball cutting edge portion has a first region that includes the tip and is wider than the tip, The tip end of each of the plurality of grooves is located outside the first region. The ball end mill according to claim 1 .

3. The ball cutting edge portion has a first region that includes the tip and is wider than the tip, The plurality of grooves include a first groove, the tip end of which is located outside the first region; a second groove, the tip end of which is located inside the first region; having The ball end mill according to claim 1 .

4. the ball cutting edge portion has a second region that includes the tip and is narrower than the first region; The plurality of grooves include a plurality of the second grooves, The plurality of second grooves are an outer second groove, the tip end of which is located outside the second region; an inner second groove, the tip end of which is located inside the second region; having The ball end mill according to claim 3.

5. When viewed from the tip of the ball cutting edge in the direction of the rotation axis, the first twist pattern is a left-handed twist pattern curved so as to be convex in a first direction along an outer periphery of the ball-shaped cutting edge portion, the second twist pattern is a right-handed twist pattern curved so as to be convex in a second direction opposite to the first direction along an outer periphery of the ball-shaped cutting edge portion, The first groove is in the first twist configuration, and the second groove is in the second twist configuration. The ball end mill according to claim 3 or 4.

6. The plurality of grooves include a plurality of the second grooves, The plurality of second grooves are positioned so as to be rotationally symmetrical about the tip. The ball end mill according to any one of claims 3 to 5.

7. In each of the plurality of grooves, a width of the groove on the outer circumferential side is larger than a width of the groove on the tip side. The ball end mill according to any one of claims 1 to 6.

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