ball end mill

Abstract

A ball end mill comprising an end mill body (1), a cutting debris discharge groove (5), a first opening (7), and a bottom blade (8). A second opening (9) is formed at least on the first wall surface (7a) of the first opening (7) at a distance from the bottom blade (8). The minimum radius of curvature in the axial cross-section of the second opening (9) is greater than the minimum radius of curvature in the axial cross-section of the groove bottom portion (7c) of the first opening (7).

Description

Technology Field

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

[0002] An embodiment of the present invention relates to a ball end mill in which a cutting debris discharge groove is formed on the outer circumference of the leading end of an end mill body that rotates in the direction of rotation of the end mill around an axis, the cutting debris discharge groove is formed in the leading end clearance surface of the end mill body and extends toward the rear end in the direction of rotation of the axis, and a recess in the shape of a concave groove is formed on the leading end of the cutting debris discharge groove so as to notch the bottom surface of the cutting debris discharge groove toward the inner circumference of the end mill body, and a bottom edge is formed on the outer circumference of the leading end of the wall surface facing the direction of rotation of the end mill, forming a hemispherical shape in which the rotational trajectory around the axis has its center on the axis and is convex toward the leading end. Background Technology

[0003] As such, for example, Patent Document 1 describes a ball end mill having a ball edge (bottom edge) made of a single tool material, wherein when the shape of the edge is projected in a direction perpendicular to a line segment connecting the cutting edge (the bottom edge) located at 45˚ relative to the end mill rotation axis (axis line) from the ball center of the ball edge portion within a plane including the end mill rotation axis (axis line), the angle of inclination at this position is 5˚ or more, and furthermore, the radius of roundness (R) of the end mill blade bottom (start) is described in the relationship R = (0.15 to 0.3) × D with respect to the end mill diameter (D). Prior art literature

[0004] Japanese Patent Publication No. Hei 5-042410 The problem to be solved

[0005] However, in the case of the ball end mill described in this patent document 1, where the radius of the bottom edge (R) of the bottom edge located at 45˚ relative to the end mill rotation axis from the ball center of the ball cutting portion is set to R = (0.15 to 0.3) × D relative to the end mill diameter (D) to enlarge the chip pocket and the rake angle is set to 5˚ or more to improve cutting performance, the cutting angle of the bottom edge becomes smaller, which causes a decrease in strength and may lead to chipping or defects on the bottom edge.

[0006] In addition, the radius of the blade base and the rake angle of the blade base remain unchanged, extending from the tip clearance of the end mill body to the vicinity of the end mill rotation center through which the axis passes. In this configuration, since the peripheral speed is close to zero, the strength of the blade base is reduced even in the vicinity of the end mill rotation center where a large cutting load is applied, making it prone to chipping or breakage.

[0007] Meanwhile, by reducing the rake angle of the bottom edge and also reducing the chip pocket to increase the cutting angle of the bottom edge, the strength of the bottom edge can be secured. However, in this configuration, particularly when cutting is performed by rotating the end mill body at high speed or when cutting is performed with a large depth of cut, the evacuation of cutting debris is impaired, causing cutting debris clogging and resulting in increased cutting resistance.

[0008] The present invention was made against this background and aims to provide a ball end mill with a long end mill life.

[0009] An embodiment of the present invention is a ball end mill capable of preventing chipping or defects on the bottom edge by ensuring good cutting debris discharge to suppress an increase in cutting resistance caused by cutting debris clogging, while suppressing a decrease in strength of the bottom edge. means of solving the problem

[0010] A ball end mill according to one embodiment of the present invention comprises: an end mill body that rotates in the end mill rotation direction around an axis; a cutting debris discharge groove located on the outer circumference of the leading end of the end mill body, which opens on the leading end clearance surface of the end mill body and extends toward the rear end in the axial direction; a first opening in the shape of a concave groove located at the leading end of the cutting debris discharge groove, which notches the bottom surface of the cutting debris discharge groove toward the inner circumference of the end mill body; and a bottom edge located on the outer circumference of the leading end of a first wall surface facing the end mill rotation direction of the first opening, which forms a hemispherical shape in which the rotational trajectory around the axis has a center on the axis and is convex toward the leading end. The first opening has the first wall surface, a bottom surface facing the outer circumference of the leading end of the end mill body, and a groove bottom portion extending between the bottom surface and the first wall surface. At least on the first wall surface of the first opening, a second opening in the shape of a concave groove is formed, which further notches the first wall surface at a distance from the bottom edge. The minimum radius of curvature in the cross-section perpendicular to the axis of the second opening is greater than the minimum radius of curvature in the cross-section perpendicular to the axis of the bottom portion of the groove of the first opening.

[0011] In a ball end mill configured in this manner, a second opening with a concave groove shape is formed on a first wall surface facing at least the end mill rotation direction of a first opening with a concave groove shape formed at the tip of a cutting debris discharge groove, and the second opening is further notched to this first wall surface. This second opening is spaced apart from a bottom edge formed on the outer edge of the tip of the first wall surface facing the end mill rotation direction.

[0012] Accordingly, the cutting angle of the bottom edge can be significantly secured by the first wall surface of the first opening, even near the end mill rotation center or on the outer circumference of the end mill body. Additionally, the size of the chip pocket can also be significantly secured by the second opening formed to notch at least the first wall surface of the first opening. As a result, it is possible to suppress chipping or defects caused by the reduction in strength of the bottom edge due to the reduced cutting angle, while simultaneously improving the evacuation of cutting debris and suppressing the increase in cutting resistance caused by debris clogging.

[0013] Furthermore, the minimum radius of curvature in the cross-section perpendicular to the axis of this second opening, that is, the radius of rounding of the blade base, is greater than the minimum radius of curvature in the cross-section perpendicular to the axis of the groove bottom portion of this first opening. By forming the second opening with this configuration, stress concentration on the blade base can be prevented, thereby ensuring the rigidity of the blade base. As a result, it becomes possible to extend the end mill life.

[0014] In the case where the second opening is formed extending from the first wall surface of the first opening, beyond the groove bottom portion, and across the bottom surface, the angle formed by the straight line passing through the intersection of the groove bottom portion and the second opening, which passes through the intersection of the groove bottom portion and the second opening and is perpendicular to the first wall surface and is viewed from a direction opposite to the first wall surface, with respect to the axis extending from the center of the bottom edge toward the tip side, is preferably within the range of 40° to 85°. The angle may be 45° or more, 50° or more, or 55° or more. The angle may be 80° or less, 75° or less, or 70° or less.

[0015] In the case where the second opening is formed extending from the first wall surface of the first opening, over the bottom portion of the groove, and across the bottom surface, the intersection of the bottom portion of the groove and the second opening becomes one of the boundary portions on the leading edge side in the axial direction of the first and second openings. If the angle formed by a straight line passing through this intersection from the center of the bottom edge with respect to the axis extending from the center of the bottom edge toward the leading edge is less than 40˚, there is a risk that the second opening will be too close to the end mill rotation center, making it prone to chipping or defects on the bottom edge.

[0016] Conversely, if the angle formed by the straight line passing through this intersection from the center of the bottom edge with respect to the axis extending from the center of the bottom edge toward the tip is greater than 85˚, most of the inclined surface of the bottom edge is occupied by the first wall surface of the first opening, and thus there is a risk that it will be difficult to improve the discharge of cutting debris.

[0017] The minimum radius of curvature in the cross-section perpendicular to the axis of the second opening is preferably within the range of 0.03×R to 0.2×R with respect to the radius (R) of the hemisphere formed by the rotational trajectory around the axis of the bottom edge. If the minimum radius of curvature of the second opening is smaller than the above range, the second opening becomes smaller, and there is a risk that it will be difficult to improve the discharge of cutting debris. If the minimum radius of curvature of the second opening is larger than the above range, the first opening is notched excessively large, and there is a risk that it will be difficult to secure the strength of the bottom edge. The minimum radius of curvature may be 0.05×R or more or 0.07×R or more with respect to the radius (R). The minimum radius of curvature may be 0.15×R or less or 0.12×R or less with respect to the radius (R).

[0018] In addition, the minimum radius of curvature in a cross-section perpendicular to the axis of the bottom portion of the first opening is preferably within the range of 0.005×R to 0.15×R with respect to the radius (R) of the hemisphere formed by the rotational trajectory around the axis of the bottom edge. If the minimum radius of the bottom portion of the first opening is smaller than the above range, there is a risk that cutting debris may get caught in the bottom portion of the groove and cause clogging. If the minimum radius of the bottom portion of the first opening is larger than the above range, there is a risk that the strength of the bottom edge at the leading edge side in the axial direction of the second opening may be impaired. The minimum radius of curvature may be 0.01×R or more or 0.05×R or more with respect to the radius (R). The minimum radius of curvature may be 0.12×R or less or 0.1×R or less with respect to the radius (R).

[0019] The first wall surface between the intersection ridge of the first wall surface and the second opening on the outer circumference of the leading end of the end mill body and the bottom edge may be a chamfered surface. It is preferable that the radial width with respect to the center of the hemisphere formed by the rotational trajectory of the bottom edge around the axis of this chamfered surface be larger on the leading end side in the axial direction than on the trailing end side. By doing so, the strength of the bottom edge can be maintained on the leading end side in the axial direction where a large cutting load is applied. Since the radius of rotation around the axis is increased, the shedding of cutting debris generated by this bottom edge can be improved on the trailing end side in the axial direction of the bottom edge where a large amount of cutting debris is generated.

[0020] In the case of having the above chamfered surface, it is preferable to keep the radial width with respect to the center of the hemisphere formed by the rotational trajectory of the bottom edge around the axis of the chamfered surface constant at the rear end side in the axis direction. By doing so, it is possible to prevent the strength of the bottom edge from being reduced more than necessary at the rear end side in the axis direction of the bottom edge.

[0021] It is preferable that the radial width with respect to the center of the hemisphere formed by the rotational trajectory around the axis of the bottom edge of the chamfered surface, which is constant on the rear end side in the axial direction, be within the range of 0.03×R to 0.25×R with respect to the radius (R) of the hemisphere formed by the rotational trajectory around the axis of the bottom edge. If the width of the chamfered surface is small enough to be less than 0.03×R, there is a risk that the strength of the bottom edge will be compromised. If the width of the chamfered surface is large enough to be greater than 0.25×R, there is a risk that it will cause an increase in cutting resistance. The width may be 0.06×R or greater, or 0.09×R or greater. The width may be 0.2×R or less, or 0.15×R or less.

[0022] The configuration may be such that, when viewed from a direction opposite to the first wall surface along a straight line perpendicular to the first wall surface passing through the intersection of the bottom portion of the groove and the second opening, the intersection ridge of the first wall surface and the second opening at the tip side of the end mill body forms a convex curve shape that is convex toward the tip side in the direction of the axis. In this case, it is preferable that the angle formed by the tangent line tangent to the convex curve formed by the intersection ridge at the tip side of the end mill body from the center of the hemispherical surface formed by the rotational trajectory of the bottom edge around the axis is within the range of 35° to 75° with respect to the axis extending from the center of the bottom edge toward the tip side. The angle may be 40° or more, 45° or more, or 50° or more. The angle may be 70° or less, 65° or less, or 60° or less.

[0023] In this case, the above tangent represents the position around the center of the bottom edge from the axis on the leading edge side to the leading edge of the chamfered surface, rather than the center of the bottom edge. If the angle formed by this tangent is less than 35˚, the chamfered surface is too close to the center of rotation of the end mill, and there is a risk that the sharpness of the bottom edge will be reduced. In addition, if the angle formed by this tangent exceeds 75˚, the chamfered surface is formed from the rear end side in the direction of the axis, and there is a risk that the cutting debris falling off on the leading edge side cannot be improved.

[0024] Meanwhile, the above-mentioned first opener and the above-mentioned second opener may be configured to be twisted toward the side opposite to the end mill rotation direction as they face the rear end side in the axis direction. In this case, it is preferable that the twist angle with respect to the axis of the second opener twist line, which connects the groove bottom position where the distance from the axis of the arc that becomes the minimum radius of curvature in the cross-section perpendicular to the axis of the second opener is the shortest, is greater than the twist angle with respect to the axis of the first opener twist line, which connects the groove bottom position where the distance from the axis of the arc that becomes the minimum radius of curvature in the cross-section perpendicular to the axis of the first opener is the shortest, is greater.

[0025] Accordingly, the second opening is formed to be twisted toward the rear end side in the axial direction with a larger twist angle than the first opening, so as to be twisted toward the side opposite to the end mill rotation direction. As a result, the second opening can be formed deeper relative to the first wall surface of the first opening on the rear end side in the axial direction. Therefore, the efficiency of cutting debris evacuation can be further improved. Cutting debris fragmentation can also be improved by increasing the drop from the bottom edge to the second opening.

[0026] It is preferable that the difference between the twist angle of the second opening twist line with respect to the axis and the twist angle of the first opening twist line with respect to the axis be within the range of 2° to 15°. If this difference in twist angle is less than 2°, the second opening cannot be formed deeper relative to the first wall surface of the first opening, and there is a risk that the cutting debris evacuation or cutting debris fragmentation properties cannot be sufficiently improved. If the difference in twist angle exceeds 15°, the second opening becomes excessively deep at the rear end, and there is a risk that the strength of the bottom edge or the end mill body will decrease. The difference in twist angle may be 4° or more or 6° or more. The difference in twist angle β-α may be 12° or less or 9° or less.

[0027] Regarding the straight line connecting the axis and the groove bottom position of the first opener in a cross-section perpendicular to the axis when the first opener twist line is extended toward the rear end side in the direction of the axis in a state of twist angle with respect to the axis, it is preferable that the straight line connecting the axis and the groove bottom position of the second opener in the same cross-section is offset in the end mill rotation direction with respect to the axis.

[0028] That is, regarding the straight line connecting the axis and the groove bottom position of the first opener in the same cross-section orthogonal to the axis, the straight line connecting the axis and the groove bottom position of the second opener is offset in the end mill rotation direction with respect to the axis, thereby forming a phase difference between the groove bottom positions of the first and second openers. By doing so, especially when performing cutting with a large depth of cut, the groove bottom position of the second opener, where the thick cutting debris generated by the bottom edge on the rear end side in the axial direction curves, can be moved further away from the bottom edge.

[0029] For this reason, thick cutting debris can be guided into the large chip pocket formed by the second opening and efficiently divided by bending it along the bottom portion of the groove. Therefore, by configuring it in this way, the chip pocket formed by the second opening can be effectively utilized, thereby enabling stable processing of cutting debris even when the depth of cut is large.

[0030] In the above cross-section, it is preferable that the intersection angle between the straight line connecting the axis line and the position of the bottom of the groove of the first opening, and the straight line connecting the axis line and the position of the bottom of the groove of the second opening, be within the range of 5° to 30°. If this intersection angle is less than 5°, the position of the bottom of the groove of the second opening cannot be sufficiently far from the bottom edge, and there is a risk that effective utilization of the chip pocket cannot be achieved. Conversely, if the intersection angle exceeds 30°, the position of the bottom of the groove of the second opening becomes excessively far from the bottom edge, and there is a risk that this will lead to an increase in cutting resistance. The intersection angle may be 7° or more, 10° or more, or 12° or more. The intersection angle may be 25° or less, or 20° or less. Effects of the invention

[0031] As described above, according to one aspect of the present invention, a ball end mill with a long end mill life is provided.

[0032] According to the ball end mill of the embodiment of the present invention, by forming a second opening at a distance from the bottom edge, the efficiency of cutting debris evacuation can be improved even when cutting with a large depth of cut, thereby suppressing the increase in cutting resistance caused by cutting debris clogging. According to the ball end mill of the embodiment of the present invention, by securing the cutting angle of the bottom edge, it is possible to suppress the reduction in strength of the bottom edge and to suppress the occurrence of chipping or defects. Brief explanation of the drawing

[0033] FIG. 1 is a perspective view of the tip portion of an end mill body showing one embodiment of the present invention. FIG. 2 is a front view of the embodiment shown in FIG. 1 seen from the leading edge in the axial direction. Figure 3 is a side view of the arrow line X direction in Figure 2. FIG. 4 is an enlarged side view of the tip portion of the end mill body in FIG. 3. Figure 5 is a cross-sectional view of VV in Figure 4. Figure 6 is a cross-sectional view of WW in Figure 4. Fig. 7 is a cross-sectional view of XX in Fig. 4. Figure 8 is a YY cross-sectional view in Figure 4. Fig. 9 is a cross-sectional view of ZZ in Fig. 4. Specific details for implementing the invention

[0034] FIGS. 1 to 9 illustrate an embodiment of the present invention. In this embodiment, the end mill body (1) is formed in a roughly cylindrical shape centered on an axis (O) by a hard material such as a cemented carbide alloy. The rear end of the end mill body (1) (upper right portion in FIG. 1; right portion in FIG. 3) is formed as a shank portion (2) in a cylindrical shape, and the front end (lower left portion in FIG. 1; left portion in FIG. 3) is formed as a cutting edge portion (3).

[0035] In this specification and drawings, a numerical range indicated by "~" refers to a range that includes the values ​​described before and after "~" as lower and upper limits. Furthermore, in the detailed description of the invention, redundant descriptions are omitted by assigning the same reference numeral to components having substantially the same functional configuration.

[0036] In the ball end mill of the present embodiment, the shank portion (2) is gripped by the main spindle of a machine tool and the end mill body (1) is rotated around the axis (O) in the end mill rotation direction (T), and is fed obliquely in a direction perpendicular to the axis (O) or in a direction perpendicular to the axis (O) and the axis (O), thereby performing groove machining or shoulder cutting machining on the workpiece by the cutting edge formed on the cutting edge portion (3).

[0037] On the outer circumference of the cutting edge portion (3), a cutting debris discharge groove (5) is formed that opens at the leading edge clearance surface (4), which is the leading edge surface of the cutting edge portion (3), and extends toward the rear end in the direction of the axis (O) while being twisted in the opposite direction to the end mill rotation direction (T) around the axis (O). In this embodiment, four sets of cutting debris discharge grooves (5) are formed at intervals in the circumferential direction. These cutting debris discharge grooves (5) are cut upward from the leading edge of the shank portion (2) toward the outer circumference.

[0038] On the outer edge of the wall facing the end mill rotation direction (T) of the cutting debris discharge groove (5), an outer edge (6) of the cutting edge is formed with the wall facing the end mill rotation direction (T). In this embodiment, the outer edge (6) is formed such that the rotational trajectory around the axis (O) forms a cylindrical shape centered on the axis (O). The outer edge (6) is twisted in the opposite direction to the end mill rotation direction (T) around the axis (O) as it faces the rear end side in the direction of the axis (O), just like the cutting debris discharge groove (5).

[0039] Meanwhile, at the leading edge of the cutting debris discharge groove (5), a wall surface facing the end mill rotation direction (T) of each cutting debris discharge groove (5) and a wall surface facing the opposite side of the end mill rotation direction (T) are notched toward the inner circumference of the end mill body (1), thereby forming a first opening (7) in the shape of a concave groove. This first opening (7) is provided with a first wall surface (7a) facing the end mill rotation direction (T), a bottom surface (7b) facing the outer circumference of the end mill body (1), a groove bottom portion (7c) extending between the first wall surface (7a) and the bottom surface (7b), and, in this embodiment, a second wall surface (7d) facing the opposite side of the end mill rotation direction (T). The first opening (7) is formed such that the width between the first and second wall surfaces (7a, 7d) gradually widens as it faces the outer circumference of the end mill body (1).

[0040] Additionally, a bottom blade (8) is formed on the outer edge portion of the first wall surface (7a) where the first wall surface (7a) of the first opening (7) and the front edge clearance surface (4) of the end mill body (1) intersect. The bottom blade (8) has a hemispherical shape in which the rotational trajectory around the axis (O) has a center (P) on the axis (O) and becomes convex toward the front edge. The end mill body (1) has a plurality of bottom blades (8). The outer edge of each bottom blade (8) is smoothly connected to the front edge of the outer edge blade (6) formed on the outer edge portion of the cutting debris discharge groove (5).

[0041] Here, in this embodiment, as shown in FIG. 2, among the four sets of bottom blades (8) formed, two bottom blades (8) that are spaced one apart in the circumferential direction (bottom blades extending in the up-down direction in FIG. 2) (8) are long bottom blades (8a) that extend to the vicinity of the end mill rotation center (C) through which the axis (O) passes in the tip clearance surface (4). The remaining two bottom blades (8) that are spaced one apart in the circumferential direction (bottom blades extending in the left-right direction in FIG. 2) (8) are short bottom blades (8b) that extend from the outer edge of the tip clearance surface (4) to a position spaced further from the end mill rotation center (C) than the long bottom blades (8a).

[0042] Meanwhile, in this embodiment, the first opening (7) is formed such that the first and second wall surfaces (7a, 7d) and the bottom surface (7b) extend approximately in a straight line in a cross-section perpendicular to the axis (O), as shown in FIG. 6. The groove bottom portion (7c) is formed in a concave curve shape, such as a concave arc with a very small radius of curvature, which contacts the first wall surface (7a) and the bottom surface (7b). The minimum radius of curvature (R1) in the cross-section perpendicular to the axis (O) of the groove bottom portion (7c) is preferably within the range of 0.005×R to 0.15×R with respect to the radius (R) of the hemisphere formed by the rotational trajectory around the axis (O) of the bottom edge (8). The minimum radius of curvature (R1) may be 0.01×R or more or 0.05×R or more with respect to the radius (R). The minimum radius of curvature (R1) may be 0.12×R or less or 0.1×R or less with respect to the radius (R).

[0043] Additionally, as shown in FIG. 4, at least the first wall surface (7a) of the first opening (7) has a second opening (9) formed in the shape of a concave groove to further notch the first wall surface (7a) at a distance from the bottom edge (8) in the circumferential direction. As shown in FIG. 8, in the present embodiment, the second opening (9) is formed such that in a cross section perpendicular to the axis (O), it extends from the first wall surface (7a) of the first opening (7) to the bottom surface (7b) beyond the groove bottom portion (7c) of the first opening (7) which extends between the first wall surface (7a) and the bottom surface (7b), and further extends to the second wall surface (7d) and connects to the tip clearance surface (4) adjacent to the end mill rotation direction (T).

[0044] Here, the bottom surface (9a) facing the outer circumference of the end mill body (1) of the second opening (9) is formed such that its entire shape forms a concave curve in a cross-section perpendicular to the axis (O), as shown in FIG. 6 to 9. The concave curve formed by the bottom surface (9a) of the second opening (9) in a cross-section perpendicular to the axis (O) becomes the minimum radius of curvature (R2) at the position of the approximate point of contact between the bottom surface (9a) and the circle inscribed within the bottom surface (9a) with the axis (O) as the center, as shown in FIG. 9. It is preferable that this minimum radius of curvature (R2) be within the range of 0.03×R to 0.2×R with respect to the radius (R) of the hemisphere formed by the rotational trajectory around the axis (O) of the bottom blade (8). The minimum radius of curvature (R2) may be 0.05×R or more or 0.07×R or more with respect to the radius (R). The minimum radius of curvature (R2) may be 0.15×R or less or 0.12×R or less with respect to the radius (R).

[0045] And, the minimum radius of curvature (R2) in the cross-section perpendicular to the axis (O) of the second opening (9) is greater than the minimum radius of curvature (R1) in the cross-section perpendicular to the axis (O) of the groove bottom part (7c) of the first opening (7).

[0046] In addition, a second opening (9) that forms a concave curve shape in a cross-section perpendicular to the axis (O) is formed extending from the first wall surface (7a) of the first opening (7) to the bottom surface (7b) beyond the groove bottom portion (7c), and intersects the first wall surface (7a) and the bottom surface (7b) that form a straight line in the cross-section. With this configuration, as shown in FIGS. 3 and 4, when viewed from a direction opposite to the first wall surface (7a), the intersection ridge (L1) between the first wall surface (7a) and the second opening (9) on the tip side of the end mill body (1) and the intersection ridge between the bottom surface (7b) and the second opening (9) form a convex curve shape that becomes convex toward the tip side in the direction of the axis (O). The intersection (Q) between the bottom part (7c) of the home and the second opening (9) is formed as a valley sandwiched between the mountain-shaped ridge (L1) formed by the intersection of the first wall surface (7a) and the bottom surface (7b).

[0047] In this embodiment, it is preferable that the angle (θ1) and angle (θ2) shown in FIG. 4 are within a predetermined angle range. FIG. 4 is a view taken from a direction facing the first wall surface (7a) along a straight line that passes through the intersection (Q) of the groove bottom portion (7c) and the second opening (9) and is perpendicular to the first wall surface (7a). The angle (θ1) is the angle formed by the tangent line (M1) that touches the convex curve formed by the intersection ridge (L1) of the first wall surface (7a) and the second opening (9) in the region of the tip side of the end mill body (1) from the center (P) of the bottom blade (8) with respect to the axis line (O) that extends from the center (P) of the bottom blade (8) toward the tip side. It is preferable that the angle (θ1) be within the range of 35˚ to 75˚. The angle (θ1) may be 40˚ or more, 45˚ or more, or 50˚ or more. The angle (θ1) may be 70˚ ​​or less, 65˚ or less, or 60˚ or less.

[0048] The angle (θ2) is the angle formed by the straight line (M2) passing through the intersection (Q) of the groove bottom part (7c) and the second opening (9) from the center (P) of the bottom blade (8), when viewed from the direction opposite to the first wall surface (7a), with respect to the axis (O) extending from the center (P) of the bottom blade (8) toward the tip. It is preferable that the angle (θ2) be within the range of 40˚ to 85˚. The angle (θ2) may be 45˚ or more, 50˚ or more, or 55˚ or more. The angle (θ2) may be 80˚ or less, 75˚ or less, or 70˚ or less.

[0049] Among the first wall surface (7a) of the first opener (7), the area that is fitted in the diameter direction by the second opener (9) and the bottom blade (8) is formed as a chamfered surface (7e). More specifically, the first wall surface (7a) of the first opener (7) and the second opener (9) are formed as a chamfered surface (7e) that is formed by chamfering the ridge portion that becomes the bottom blade (8) when the second opener (9) and the first wall surface (7a) of the first opener (7) and the second opener (9) are spaced apart from the protruding end on the front side in the direction of the axis (O) of the first wall surface (7a) and the second opener (9) are extended toward the rear side of the outer circumference of the end mill body (1) and the second opener (9) are spaced apart. Accordingly, the rear end portion of the first wall surface (7a) in the direction of the axis (O) rather than the tangent (M1) becomes this chamfer surface (7e).

[0050] The radial width (H) of the bottom edge (8) of the chamfered surface (7e) is larger at the front end side in the direction of the axis (O) than at the rear end side. In this embodiment, the width (H) of the chamfered surface (7e) is widest on the tangent (M1), gradually narrows as it moves toward the rear end side, and is of a constant size with a narrow width at the rear end side in the direction of the axis (O).

[0051] The intersection ridge between the first wall surface (7a) on the outer side of the end mill body (1) and the second opening (9) forms a convex curve that becomes convex toward the bottom blade (8). The width (H) of the chamfer surface (7e) decreases at a rate of narrowing from the front end side in the direction of the axis (O) toward the rear end side, and becomes a constant width at the rear end side in the direction of the axis (O) as described above. The radial width (H) of the chamfer surface (7e) at the rear end side of the bottom blade (8), which has become constant in this way, relative to the center (P) of the bottom blade (8), is preferably within the range of 0.03×R to 0.25×R with respect to the radius (R) of the hemisphere formed by the rotational trajectory around the axis (O) of the bottom blade (8). The width (H) may be 0.06×R or more, or 0.09×R or more. The width (H) may be 0.2×R or less, or 0.15×R or less.

[0052] In addition, in this embodiment, the first and second openings (7, 9) are formed to be twisted toward the rear end side in the direction of the axis (O) in accordance with the twisting of the cutting debris discharge groove (5), so as to be twisted toward the side opposite to the end mill rotation direction (T). Accordingly, the first and second wall surfaces (7a, 7d) and bottom surface (7b) of the first opening (7), which form a roughly straight line in a cross-section perpendicular to the axis (O), are formed in the shape of a twisted surface in the direction of the axis (O).

[0053] In addition, in this embodiment, the angle of twist (β) of the second opening twist line (N2) is larger than the angle of twist (α) of the first opening twist line (N1) shown in FIG. 4.

[0054] The first opening twist line (N1) is a twist line connecting the groove bottom position (7f) of the first opening (7) in the direction of the axis (O). As shown in FIG. 6, the groove bottom position (7f) is the position where the distance from the axis (O) of the arc that becomes the minimum radius of curvature (R1) in the cross section perpendicular to the axis (O) of the groove bottom part (7c) of the first opening (7) is the shortest. The twist angle (α) is the twist angle with respect to the axis (O) of the first opening twist line (N1).

[0055] The second opening twist line (N2) is a twist line connecting the groove bottom position (9b) of the second opening (9) in the direction of the axis (O). As shown in FIG. 9, the groove bottom position (9b) is the position where the distance from the axis (O) of the arc that becomes the minimum radius of curvature (R2) in the cross section perpendicular to the axis (O) of the second opening (9) is the shortest. The twist angle (β) is the twist angle with respect to the axis (O) of the second opening twist line (N2).

[0056] In the present embodiment, the difference β-α between the twist angle (β) with respect to the axis (O) of the second opening twist line (N2) and the twist angle (α) with respect to the axis (O) of the first opening twist line (N1) is preferably within the range of 2° to 15°. The difference β-α may be 4° or more or 6° or more. The difference β-α may be 12° or less or 9° or less.

[0057] In addition, in this embodiment, as shown in FIG. 9, a straight line (F1) and a straight line (F2) defining the position of the bottom of the opening groove in the same axial cross section are offset in the end mill rotation direction (T) with respect to the axis (O). The straight line (F1) and the straight line (F2) are defined in a cross section that intersects the second opening (9) and is orthogonal to the axis (O), as shown in FIG. 9.

[0058] The straight line (F1) is a straight line connecting the first groove bottom position (7f) in the cross section and the axis (O) in the cross section when the first opening twist line (N1) is extended toward the rear end in the direction of the axis (O) in a state of twist angle (α) with respect to the axis (O).

[0059] The straight line (F2) is a straight line connecting the axis line (O) in the same cross-section as the straight line (F1) and the groove bottom position (9b) of the second opening (9).

[0060] In this embodiment, as shown in FIG. 9, the intersection angle (γ) of the line (F1) connecting the axis (O) in the cross-section, which is the phase difference of these straight lines (F1, F2), and the line (F2) connecting the axis (O) and the groove bottom position (9b) of the first opening (7), and the line (F2) connecting the axis (O) and the groove bottom position (9b) of the second opening (9) is preferably within the range of 5˚ to 30˚. The intersection angle (γ) may be 7˚ or more, 10˚ or more, or 12˚ or more. The intersection angle (γ) may be 25˚ or less or 20˚ or less.

[0061] In a ball end mill configured in this manner, a second opening (9) with a concave groove shape is formed by additionally notching the first wall surface (7a) of the first opening (7) with a concave groove shape, at least on the first wall surface (7a) facing the end mill rotation direction (T) of the first opening (7) with a gap from the bottom edge (8) formed on the outer circumference of the front end of the first wall surface (7a).

[0062] Accordingly, the size of the chip pocket accommodating cutting debris can be significantly increased by the second opening (9) formed to notch the first wall surface (7a) of the first opening (7). Meanwhile, the cutting angle of the bottom blade (8) can also be significantly increased by the first wall surface (7a) of the first opening (7) near the end mill rotation center (C) or on the outer side of the end mill body (1). Because of this, it is possible to prevent a decrease in strength of the bottom blade (8) caused by the cutting angle of the bottom blade (8) becoming smaller, while improving the discharge of cutting debris and suppressing the increase in cutting resistance caused by cutting debris clogging.

[0063] Furthermore, in this embodiment, the second opening (9) extends beyond the groove bottom portion (7c) between the first wall surface (7a) facing the end mill rotation direction (T) of the first opening (7) and the bottom surface (7b) facing the outer circumference of the end mill body (1), and further extends to the bottom surface (7b), and additionally reaches the second wall surface (7d) facing the opposite side to the end mill rotation direction (T). Therefore, the capacity of the chip pocket created by the second opening (9) can be secured more significantly, so good cutting debris discharge can be obtained.

[0064] In addition, the minimum radius of curvature (R2) in the cross-section perpendicular to the axis (O) of the second opening (9) is greater than the minimum radius of curvature (R1) in the cross-section perpendicular to the axis (O) of the groove bottom portion (7c), which is the minimum radius of the first opening (7). Therefore, even if the second opening (9) is formed with a large radius of curvature of the groove bottom portion, the cutting edge strength of the bottom edge (8) can be secured because the radius of curvature of the groove bottom portion (7c) at the tool tip portion is small. Thus, by forming the second opening (9), the rigidity of the bottom edge (8) can be secured while preventing stress concentration in the groove bottom portion. As a result, it becomes possible to extend the end mill life.

[0065] In addition, in this embodiment, as described above, when the second opening (9) is formed extending from the first wall surface (7a) of the first opening (7) to the bottom surface (7b) facing the outer circumference of the end mill body (1) beyond the bottom portion (7c), a straight line (M2) is defined passing through the intersection (Q) of the bottom portion (7c) and the second opening (9) from the center (P) of the bottom blade (8). In this case, it is preferable that the angle (θ2) formed by the straight line (M2) with respect to the axis line (O) extending from the center (P) of the bottom blade (8) toward the tip is within the range of 40˚ to 85˚. If the angle (θ2) is within the above range, it is possible to ensure better cutting debris discharge while reliably preventing chipping or defects of the bottom blade (8).

[0066] That is, if the angle (θ2) formed by the straight line (M2) passing through the intersection (Q) from the center (C) of the bottom blade (8) with respect to the axis line (O) extending from the center (P) of the bottom blade (8) toward the tip side is less than 40˚, the second opening (9) approaches the end mill rotation center (C), and the thickness of the end mill tip side decreases. There is a risk that chipping or defects may easily occur on the bottom blade (8).

[0067] Meanwhile, if the angle (θ2) formed by the straight line (M2) passing through this intersection (Q) from the center (P) of the bottom blade (8) with respect to the axis (O) extending from the center (P) of the bottom blade (8) toward the tip is greater than 85˚, most of the inclined surface of the bottom blade (8) is occupied by the first wall surface (7a) of the first opening (7), and thus it may be difficult to improve the discharge of cutting debris.

[0068] In addition, in this embodiment, it is preferable that the minimum radius of curvature (R2) in the cross-section perpendicular to the axis (O) of the second opening (9) is within the range of 0.03×R to 0.2×R with respect to the radius (R) of the hemisphere formed by the rotational trajectory around the axis (O) of the bottom blade (8). By doing so, it becomes possible to secure even better cutting debris discharge. Furthermore, chipping or defects of the bottom blade (8) are further suppressed.

[0069] That is, if the minimum radius of curvature (R2) of this second opening (9) is smaller than the above range, the space of the groove bottom portion of the second opening (9) becomes smaller, and there is a concern that it will be difficult to improve the discharge of cutting debris. On the other hand, conversely, if the minimum radius of curvature (R2) of this second opening (9) is larger than the above range, the first opening (7) is notched significantly. If the thickness of the tool tip side becomes excessively thin, there is a concern that the strength of the bottom edge (8) cannot be secured.

[0070] In addition, in this embodiment, the minimum radius of curvature (R1) in the cross-section perpendicular to the axis (O) of the groove bottom portion (7c) of the first opening (7) is preferably within the range of 0.005×R to 0.15×R with respect to the radius (R) of the hemisphere formed by the rotational trajectory around the axis (O) of the bottom blade (8). By doing so, good cutting debris discharge can be secured. In addition, chipping or defects of the bottom blade (8) are further suppressed.

[0071] That is, if the minimum radius (R1) of the groove bottom portion (7c) of the first opening (7) is smaller than the above range, there is a risk that cutting debris will get caught in the groove bottom portion (7c) and cause blockage. On the other hand, conversely, if the minimum radius (R1) of the groove bottom portion (7c) of the first opening (7) is larger than the above range, the thickness at the leading edge in the direction of the axis (O) becomes thinner than that of the second opening (9). If the thickness at the leading edge of the tool becomes excessively thin, the strength of the bottom edge (8) is compromised, and there is a risk of chipping or defects occurring.

[0072] Additionally, the first wall surface (7a) remaining between the first wall surface (7a) of the first opening (7) and the bottom surface (9a) of the second opening (9) on the outer side of the front end of the end mill body (1) and the bottom blade (8) becomes a chamfered surface (7e) that is formed by beveling the ridge portion that becomes the bottom blade (8) when the second opening (9) and the front clearance surface (4) are extended and intersected in the end mill rotation direction (T) as described above. In this embodiment, the radial width (H) of this chamfered surface (7e) with respect to the center (P) of the bottom blade (8) is greater on the front side in the axis direction (O) than on the rear side.

[0073] Accordingly, according to the present embodiment, the strength of the bottom blade (8) can be maintained at the leading edge in the direction of the axis (O) where a large cutting load is applied. In addition, since the radius of rotation around the axis (O) increases, it is possible to promote good cutting debris shedding at the trailing edge of the bottom blade (8), where a large amount of cutting debris is generated.

[0074] In addition, in this embodiment, when the radial width (H) with respect to the center (P) of the bottom blade (8) of the chamfered surface (7e) is larger at the front end side in the direction of the axis (O) than at the rear end side, the radial width (H) with respect to the center (P) of the bottom blade (8) of the chamfered surface (7e) is constant at the rear end side portion in the direction of the axis (O) of the chamfered surface (7e). Because of this, the width (H) at the rear end side portion in the direction of the axis (O) of the chamfered surface (7e) does not become excessively narrow, and the strength of the bottom blade (8) is prevented from being inhibited more than necessary.

[0075] In addition, in this embodiment, it is preferable that the radial width (H) of the chamfered surface (7e) at the rear end of the bottom blade (8) relative to the center (P) of the bottom blade (8) is within the range of 0.03×R to 0.25×R relative to the radius (R) of the hemisphere formed by the rotational trajectory around the axis (O) of the bottom blade (8). By doing so, the cutting resistance can be avoided while maintaining the strength of the bottom blade (8).

[0076] That is, if the radial width (H) of the chamfered surface (7e) at the rear end of the bottom blade (8) relative to the center (P) of the bottom blade (8) is smaller than 0.03 × R, the chamfered surface (7e) becomes excessively small, and there is a risk that the strength of the bottom blade (8) will be compromised. On the other hand, if this width (H) is larger than 0.25 × R, the chamfered surface (7e) becomes excessively large, and there is a risk that it will cause an increase in cutting resistance.

[0077] In addition, in this embodiment, it is preferable that a tangent line (M1) that is in contact with an intersecting ridge (L1) forming a convex curve shape that is convex toward the front end side of the first wall surface (7a) of the first opening (7) and the front end side of the bottom surface (9a) of the second opening (9), passing through the intersection (Q) of the bottom part (7c) of the groove and the second opening (9) and perpendicular to the first wall surface (7a) when viewed from a direction opposite to the first wall surface (7a) of the first opening (7), intersects the axis line (O) extending from the center (P) of the bottom blade (8) toward the front end side at an angle (θ1) within the range of 35˚ to 75˚. By setting the angle (θ1) to the above range, it becomes possible to achieve good cutting debris removal while maintaining the sharpness of the bottom blade (8).

[0078] That is, if the angle (θ1) formed by this tangent (M1) with respect to the axis (O) extending from the center (P) of the bottom blade (8) toward the tip side is less than 35˚, the chamfered surface (7e) is extended to near the end mill rotation center (C), and there is a risk that the sharpness of the bottom blade (8) will be reduced. On the other hand, if the angle (θ1) formed by this tangent (M1) with respect to the axis (O) extending from the center (P) of the bottom blade (8) toward the tip side is greater than 75˚, the chamfered surface (7e) is formed excessively from the rear end side in the direction of the axis (O), and there is a risk that the cutting debris falling off at the tip side cannot be improved.

[0079] Meanwhile, in this embodiment, the first and second openings (7, 9) are formed to be twisted toward the opposite side of the end mill rotation direction (T) as they face toward the rear end side in the direction of the axis (O), the same as the cutting debris discharge groove (5). Because of this, as the end mill body (1) rotates during cutting, the cutting debris generated by the bottom blade (8) is fed into the cutting debris discharge groove (5) on the rear end side and discharged, so good cutting debris discharge performance can be obtained.

[0080] In addition, in this embodiment, the first opening (7) and the second opening (9) are formed with different twist angles such that the twist angle (β) with respect to the axis (O) of the second opening twist line (N2), which connects the groove bottom position (9b) in the direction of the axis (O) where the distance from the axis (O) of the arc that becomes the minimum radius of curvature (R2) in the cross section perpendicular to the axis (O) of the second opening (9) is the shortest, is greater than the twist angle (α) with respect to the axis (O) of the first opening twist line (N1), which connects the groove bottom position (7f) in the direction of the axis (O) where the distance from the axis (O) of the arc that becomes the minimum radius of curvature (R1) in the cross section perpendicular to the axis (O) of the groove bottom part (7c) of the first opening (7) is the shortest, is greater.

[0081] For this reason, the second opening (9) is formed to face the opposite side to the end mill rotation direction (T) as it faces the rear end side in the direction of the axis (O), while being twisted by a twist angle (β) greater than the twist angle (α) of the first opening (7). By doing so, the second opening (9) can be formed to be deeper with respect to the first wall surface (7a) of the first opening (7) at the rear end side in the direction of the axis (O).

[0082] Accordingly, according to the present embodiment, the capacity of the chip pocket created by the second opening (9) can be further increased to further improve the discharge of cutting debris. In addition, by increasing the drop from the bottom blade (8) to the bottom surface (9a) of the second opening (9), it becomes possible to improve the fragmentation of cutting debris.

[0083] In this embodiment, it is preferable that the difference β-α between the twist angle (β) with respect to the axis (O) of the second opening twist line (N2) and the twist angle (α) with respect to the axis (O) of the first opening twist line (N1) be within the range of 2˚ to 15˚. By setting the difference β-α to the above range, the cutting debris discharge and cutting debris fragmentation properties can be further improved, while preventing a decrease in strength of the bottom blade (8) or the end mill body (1).

[0084] That is, if the difference between the twist angles (β, α) β-α is small enough to be less than 2˚, the second opening (9) cannot be formed deeply relative to the first wall surface (7a) of the first opening (7), and there is a concern that the cutting debris discharge or cutting debris fragmentation cannot be sufficiently improved. On the other hand, if the difference between the twist angles (β, α) β-α is large enough to be greater than 15˚, the second opening (9) is engraved too deeply at the rear end side in the direction of the axis (O), and there is a concern that the strength of the bottom edge (8) or the cutting edge portion (3) of the end mill body (1) will be reduced.

[0085] Meanwhile, in this embodiment, regarding the straight line (F1) connecting the axis (O) and the groove bottom position (7f) of the first opening (7) in a cross-section orthogonal to the axis (O) that intersects the second opening (9) when the first opening twist line (N1) is extended toward the rear end side in the direction of the axis (O) at a twist angle (α) with respect to the axis (O), the straight line (F2) connecting the axis (O) and the groove bottom position (9b) of the second opening (9) in the same cross-section is offset in the end mill rotation direction (T) with respect to the axis (O).

[0086] For this reason, according to the present embodiment, a straight line (F2) connecting the axis (O) and the groove bottom position (9b) of the second opening (9) is offset in the end mill rotation direction (T) from the straight line (F1) connecting the axis (O) and the groove bottom position (7f) of the first opening (7), with the axis (O) as the center, that is, a phase difference is formed between the groove bottom positions (7f, 9b) of the first and second openings (7, 9). In particular, when performing cutting processing with a large amount of cutting, the thick cutting debris generated by the bottom edge (8) on the rear end side in the direction of the axis (O) is bent at the groove bottom position (9b) of the second opening (9). According to the above configuration, it is possible to move the groove bottom position (9b), where the cutting debris bends, far away from the bottom edge (8).

[0087] Accordingly, by inducing the thick cutting debris generated by the large cut into the large chip pocket formed by the second cut (9) and bending it by the portion of the groove bottom position (9b), it can be efficiently divided. For this reason, in this embodiment, the chip pocket formed by the second cut (9) can be effectively utilized. As described above, even when the amount of cut is large, it becomes possible to promote stable processing of thick cutting debris.

[0088] Meanwhile, in this case, in the present embodiment, it is preferable that the intersection angle (γ) of the straight line (F1) connecting the axis line (O) in the cross-section and the groove bottom position (7f) of the first opening (7) and the straight line (F2) connecting the axis line (O) and the groove bottom position (9b) of the second opening (9) be within the range of 5˚ to 30˚. By having the intersection angle (γ) within the above range, effective utilization of the chip pocket by the second opening (9) as described above can be ensured, while preventing the cutting resistance from increasing more than necessary due to clogging of cutting debris, etc.

[0089] That is, if this intersection angle (γ) is less than 5˚, the groove bottom position (9b) of the second opening (9) cannot be sufficiently far from the bottom edge (8), and there is a risk that the chip pocket cannot be effectively utilized by the second opening (9). On the other hand, conversely, if this intersection angle (γ) exceeds 30˚, the groove bottom position (9b) of the second opening (9) is too far from the bottom edge (8), and the cutting debris will abrade the bottom surface (9a) of the second opening (9) for a long time, causing cutting debris clogging, etc., and there is a risk of causing an increase in cutting resistance.

[0090] According to the above embodiments, the following aspects are also understood.

[0091] (1) A ball end mill having an end mill body that rotates in the direction of end mill rotation around an axis, a cutting debris discharge groove located on the outer circumference of the leading edge of the end mill body that opens on the leading edge clearance surface of the end mill body and extends toward the rear end in the direction of the axis, a first opening in the shape of a concave groove located on the leading edge of the cutting debris discharge groove that notches the bottom surface of the cutting debris discharge groove toward the inner circumference of the end mill body, and a bottom edge located on the edge of the leading edge of the first wall surface facing the direction of end mill rotation of the first opening, forming a hemispherical shape in which the rotational trajectory around the axis has a center on the axis and becomes convex toward the leading edge.

[0092] At least on the first wall surface of the first opening, a second opening in the shape of a concave groove is formed, which additionally notches the first wall surface at a distance from the bottom edge.

[0093] The first wall surface between the intersection ridge of the first wall surface and the second opening on the outer circumference of the tip of the end mill body and the bottom edge is a chamfered surface, and

[0094] A ball end mill in which the radial width with respect to the center of the hemisphere formed by the rotational trajectory of the bottom edge of the chamfered surface is larger at the leading end in the axial direction than at the trailing end.

[0095] (2) A ball end mill having an end mill body that rotates in the direction of end mill rotation around an axis, a cutting debris discharge groove located on the outer circumference of the leading edge of the end mill body that opens on the leading edge clearance surface of the end mill body and extends toward the rear end in the direction of the axis, a first opening in the shape of a concave groove located at the leading edge of the cutting debris discharge groove that notches the bottom surface of the cutting debris discharge groove toward the inner circumference of the end mill body, and a bottom edge located on the outer circumference of the leading edge of the first wall surface facing the direction of end mill rotation of the first opening, forming a hemispherical shape in which the rotational trajectory around the axis has a center on the axis and is convex toward the leading edge.

[0096] The first opening has the first wall surface, a bottom surface facing the outer circumference of the tip of the end mill body, and a groove bottom portion extending between the bottom surface and the first wall surface.

[0097] At least on the first wall surface of the first opening, a second opening in the shape of a concave groove is formed, which additionally notches the first wall surface at a distance from the bottom edge.

[0098] The first opening and the second opening are formed to be twisted toward the side opposite to the end mill rotation direction as they face toward the rear end side in the axial direction, and

[0099] The twist angle with respect to the axis of the second opening twist line, which connects the groove bottom position in the axial direction where the distance from the axis of the arc that becomes the minimum radius of curvature in a cross-section orthogonal to the axis of the second opening is the shortest,

[0100] A ball end mill having a twist angle greater than the axis of a first opening twist line connecting the groove bottom position, where the distance from the axis of the arc that becomes the minimum radius of curvature in a cross-section perpendicular to the axis of the first opening groove bottom part is the shortest, in the axial direction. Explanation of the symbols

[0101] 1 End mill body 2 Sanctuary 3 cutting edges 4 tip clearance 5 Cutting debris discharge groove 6 Outsourcing Day 7 1st Gash 7a The first wall surface of the first opening (7) 7b Bottom surface of the first opening (7) 7c The bottom of the groove of the first gash (7) 7d The second wall of the first gash (7) 7e Champagne 7f Home bottom position of the first opening (7) 8 bottom day 8a Long bottom edge 8b short bottom edge 9 2nd Gash 9a Bottom surface of the second opening (9) 9b The bottom position of the second gash (9) O Axis of the end mill body (1) T-end mill rotation direction C end mill rotation center The center of the hemisphere formed by the rotational trajectory around the axis (O) of the bottom blade (8) P Q The intersection of the bottom part (7c) of the first opening (7) and the second opening (9) R Radius of the hemisphere formed by the rotational trajectory around the axis (O) of the bottom blade (8) R1 Minimum radius of curvature in a cross section perpendicular to the axis (O) of the bottom part (7c) of the first opening (7) R2 Minimum radius of curvature in a cross section perpendicular to the axis (O) of the bottom surface (9a) of the second opening (9) Radial width with respect to the center (P) of the bottom edge (8) of the H chamfer surface (7e) The intersection ridge of the first wall surface (7a) and bottom surface (7b) on the tip side of the L1 end mill body (1) and the second opening (9) A tangent line tangent to the convex curve formed by the intersection ridge (L1) of the first wall surface (7a) and the second opening (9) from the center (P) of the M1 bottom blade (8). The angle that the tangent (M1) of θ1 makes with respect to the axis (O) on the tip side relative to the center (P) of the bottom blade (8). A straight line passing through the intersection (Q) of the groove bottom part (7c) and the second opening (9) from the center (P) of the M2 bottom blade (8). The angle that the straight line (M2) θ2 makes with respect to the axis (O) on the tip side relative to the center (P) of the bottom blade (8). N1 First opening twist line N2 Second opening twist line α The twist angle with respect to the axis (O) of the first opening twist line (N1) β The twist angle with respect to the axis (O) of the second opening twist line (N2) F1 A straight line connecting the axis (O) in a cross-section that intersects the second opening (9) and is orthogonal to the axis (O) and the groove bottom position (7f) of the first opening (7). A straight line connecting the axis line (O) in the same cross-section as the F2 straight line (F1) and the groove bottom position (9b) of the second opening (9). γ, the intersection angle of the line (F1, F2)

Claims

Claim 1 A ball end mill comprising: an end mill body rotating in the end mill rotation direction around an axis; a cutting debris discharge groove located on the outer circumference of the leading end of the end mill body, opening into the leading end clearance surface of the end mill body and extending toward the rear end in the axial direction; a first opening in the shape of a concave groove located at the leading end of the cutting debris discharge groove, notching the bottom surface of the cutting debris discharge groove toward the inner circumference of the end mill body; and a bottom blade located on the edge of the leading end outer circumference of a first wall surface facing the end mill rotation direction of the first opening, forming a hemispherical shape in which the rotational trajectory around the axis has its center on the axis and is convex toward the leading end, wherein the first opening has the first wall surface, a bottom surface facing the leading end outer circumference of the end mill body, and a groove bottom portion extending between the bottom surface and the first wall surface, and at least the first wall surface of the first opening has a space from the bottom blade, and the first A ball end mill having a second opening in the shape of a concave groove that additionally notches the wall surface, wherein the minimum radius of curvature in a cross-section perpendicular to the axis of the second opening is greater than the minimum radius of curvature in the cross-section of the groove bottom portion of the first opening. Claim 2 A ball end mill according to claim 1, wherein the second opening is formed extending from the first wall surface of the first opening, beyond the groove bottom portion, and extending across the bottom surface, and wherein, when viewed from a direction opposite to the first wall surface along a straight line passing through the intersection portion of the groove bottom portion of the first opening and perpendicular to the first wall surface, the angle formed by a straight line passing through the intersection portion from the center of the hemisphere formed by the rotational trajectory around the axis of the bottom edge with respect to the axis extending from the center of the bottom edge toward the tip is within the range of 40˚ to 85˚. Claim 3 A ball end mill according to claim 1 or 2, wherein the minimum radius of curvature in the cross-section perpendicular to the axis of the second opening is within the range of 0.03×R to 0.2×R with respect to the radius (R) of the hemisphere formed by the rotational trajectory around the axis of the bottom edge. Claim 4 A ball end mill according to claim 1 or 2, wherein the minimum radius of curvature in a cross-section perpendicular to the axis of the bottom portion of the groove of the first opening is within the range of 0.005×R to 0.15×R with respect to the radius (R) of the hemisphere formed by the rotational trajectory around the axis of the bottom edge. Claim 5 A ball end mill according to claim 1 or 2, wherein the first wall surface between the intersection ridge of the first wall surface and the second opening on the outer circumference of the leading edge of the end mill body and the bottom edge is a chamfered surface, and the radial width with respect to the center of the hemisphere formed by the rotational trajectory of the chamfered surface around the axis of the bottom edge is greater on the leading edge side in the axial direction than on the trailing edge side. Claim 6 A ball end mill according to claim 5, wherein the radial width with respect to the center of the hemisphere formed by the rotational trajectory of the bottom edge of the chamfered surface around the axis is constant at the rear end in the axial direction. Claim 7 A ball end mill according to claim 6, wherein the radial width with respect to the center of the hemisphere formed by the rotational trajectory around the axis of the bottom edge of the chamfered surface, which is constant on the rear end side in the axial direction, is within the range of 0.03×R to 0.25×R with respect to the radius (R) of the hemisphere formed by the rotational trajectory around the axis of the bottom edge. Claim 8 A ball end mill according to claim 5, wherein, when viewed from a direction opposite to the first wall surface along a straight line passing through the intersection of the bottom portion of the groove and the second opening and perpendicular to the first wall surface, the intersection ridge of the first wall surface and the second opening at the tip side of the end mill body forms a convex curve shape that is convex toward the tip side in the axial direction, and the angle formed by the tangent line tangent to the convex curve formed by the intersection ridge at the tip side of the end mill body from the center of the hemisphere formed by the rotational trajectory around the axis of the bottom edge with respect to the axis extending toward the tip side from the center of the hemisphere formed by the rotational trajectory around the axis of the bottom edge is within the range of 35˚ to 75˚. Claim 9 A ball end mill according to claim 1 or 2, wherein the first opening and the second opening are formed to be twisted toward the side opposite to the end mill rotation direction as they face the rear end side in the axial direction, and the twist angle with respect to the axis of the second opening twist line connecting the groove bottom position in the axial direction, where the distance from the axis of the arc that becomes the minimum radius of curvature in the cross-section perpendicular to the axis of the second opening is shortest, is greater than the twist angle with respect to the axis of the first opening twist line connecting the groove bottom position in the axial direction, where the distance from the axis of the arc that becomes the minimum radius of curvature in the cross-section perpendicular to the axis of the first opening groove bottom part is shortest. Claim 10 A ball end mill according to claim 9, wherein the difference between the twist angle with respect to the axis of the second opening twist line and the twist angle with respect to the axis of the first opening twist line is within the range of 2° to 15°. Claim 11 A ball end mill according to claim 9, wherein, when the first opening twist line is extended toward the rear end side in the direction of the axis, the second opening intersects the first opening and, in a cross-section perpendicular to the axis, the straight line connecting the axis and the groove bottom position of the first opening is offset in the direction of end mill rotation with respect to the axis, with respect to the straight line connecting the axis and the groove bottom position of the second opening in the same cross-section. Claim 12 A ball end mill according to claim 11, wherein the angle of intersection between the straight line connecting the axis line in the cross-section and the position of the bottom of the groove of the first opening and the straight line connecting the axis line and the position of the bottom of the groove of the second opening is within the range of 5˚ to 30˚.

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