ball end mill

Abstract

As a ball end mill with two blades, the cutting edge is formed on the intersecting ridge between the groove wall of the opening groove and the flank surface, and the flank surface has a first flank surface that forms a chisel edge and a second flank surface that extends from the first flank surface in the rotational direction at a larger flank angle. When viewed from the axial tip side, the intersection point between one of the two cutting edges and the chisel edge is set as the first intersection point, and a straight line passing through the axis line that is perpendicular to the tangent of the cutting edge at the first intersection point is set as the reference line, and the intersection point between the flank surface boundary line of the first flank surface and the second flank surface of the other cutting edge and the groove wall is set as the second intersection point, so that the second intersection point is located in the rotational direction forward side of the reference line, and the flank surface boundary line of the other cutting edge intersects the cutting edge tangent of one cutting edge.

Description

Technology Field

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

[0002] The present application claims priority based on Japanese patent application No. 2022-058902 filed in Japan on March 31, 2022, and incorporates the contents thereof herein by reference. Background Technology

[0003] Most of the cutting debris generated by the cutting edge of a ball end mill is smoothly discharged from the gash groove adjacent to the cutting edge. However, cutting debris generated near the axis of rotation where the chisel edge is formed tends to remain because a space is formed nearby that is blocked by the chisel edge, flank surface, and machined surface.

[0004] In Patent Document 1, when processing extremely hard materials such as cemented carbide, if cutting debris clogging occurs near the axis of rotation, it leads to a defect near the center of the tool. Therefore, as a study to improve the cutting debris evacuation of the inner end of the bottom edge, a configuration is disclosed in which the inner end of the bottom edge becomes the starting point of the groove wall of the opening groove.

[0005] In addition, Patent Documents 2 and 3 disclose that, in order to obtain good surface roughness, the cutting edge thickness angle, chisel width, chisel angle, etc. are set to a predetermined range, and a flank surface having a relatively small predetermined flank angle and flank surface width is formed as a flank surface adjacent to an arc-shaped cutting edge. Prior art literature

[0006] Japanese Published Patent Application No. 2018-83245 Japanese Published Patent Application No. 2005-342835 Japanese Published Patent Application No. 2006-088232 The problem to be solved

[0007] Even if research on the groove wall shape of a chisel groove is conducted as described in Patent Document 1, and even if cutting debris evacuation is obtained sufficient to suppress defects near the rotation axis caused by clogging of extremely hard cutting debris in the machining of extremely hard workpieces such as cemented carbide, there remains a problem that welding occurs on the machined surface in finishing processes where high machined surface quality is desired, and that this deteriorates the machined surface quality. Furthermore, even if the shape of the chisel edge, the flank angle of the flank surface, or the flank surface width is adjusted as described in Patent Documents 2 and 3, welding or tearing occurs on the machined surface.

[0008] The present invention was made against this background, and one of its objectives is to provide a ball end mill capable of improving the quality of the machined surface in a ball end mill in which a chisel edge is formed. means of solving the problem

[0009] According to one aspect of the present invention,

[0010] A ball end mill having two cutting edges having an end mill body that rotates around an axis,

[0011] The cutting edge is formed on the intersection ridge between the groove wall of the opening groove and a flank surface located rearward in the rotational direction of the opening groove, and the flank surface has a first flank surface forming a chisel edge and a second flank surface extending rearward in the rotational direction from the first flank surface at a larger flank angle.

[0012] When viewed from the axial tip side, the intersection point of one of the cutting edges and the chisel edge is set as the first intersection point, a straight line passing through the axis while being perpendicular to the tangent of the cutting edge at the first intersection point is set as the reference line, and the intersection point of the flank surface boundary line between the first flank surface and the second flank surface of the other cutting edge and the groove wall surface is set as the second intersection point,

[0013] The above second intersection point is located on the rotational front side of the above reference line, and

[0014] A ball end mill is provided, characterized in that the flank surface boundary line of the cutting edge of the other side intersects the cutting edge tangent of the cutting edge of the first side.

[0015] That is, the area enclosed by the chisel edge, the cutting edge located in front of the rotational direction of the chisel edge, and the reference line (chisel edge front area) consists only of the first flank surface and does not include the boundary between the first flank surface and the second flank surface (flank surface boundary line). According to this configuration, during cutting, an edge portion that is convex toward the processing surface is not formed in the chisel edge front area, which is a region prone to clogging and is near the area where cutting debris is generated. As a result, it becomes difficult for cutting debris near the rotational axis to be pressed against the processing surface, thereby suppressing the occurrence of welding.

[0016] At the same time, the cutting edge (axial cutting edge) that defines the original chisel edge front area is close to the axis of rotation, making it difficult to increase the cutting speed. However, by configuring the chisel edge front area with only the first flank surface, the tip angle of the axial cutting edge becomes relatively smaller compared to the case where a second flank surface exists in the chisel edge front area. As a result, the cutting performance of the axial cutting edge is improved, and the occurrence of tearing can also be suppressed.

[0017] In addition, since the cutting edge tangent line at the intersection point (first intersection point) of the flank surface boundary line of one cutting edge and the chisel edge of the other cutting edge intersects, the width of the first flank surface of the cutting edge located on the outer side can be narrowed in the direction perpendicular to the edge, thereby suppressing the cutting resistance from becoming excessively large and ensuring the cutting performance of the cutting edge that mainly performs cutting.

[0018] Through the synergistic effects of suppressing welding, suppressing tearing, and providing good cutting performance on the cutting edge, the finish surface properties (roughness or quality) in the finishing process can be comprehensively improved.

[0019] When viewed from the axial end side, the tip surface may be configured such that the sum of the flank surface widths in the direction of extension of the reference line of the first flank surface of the cutting edge of one side and the first flank surface of the cutting edge of the other side, which are adjacent to each other at the chisel edge, decreases from the second intersection point toward the outer circumference in the diameter direction.

[0020] When viewed from the axial end side, the flank surface boundary line may be configured to have a portion extending from the second intersection point toward the outer circumference in the radial direction, in a direction approaching the chisel edge.

[0021] When viewed from the axial tip side, the angle of inclination in the direction perpendicular to the edge of the inclined surface of the axial cutting edge located on the radial outer circumference side relative to the reference line and on the radial axial side relative to the first intersection point may be configured to be negative.

[0022] The above inclination angle may be configured to be -30° or more and -15° or less, and the above first flank angle may be 5° or more and less than 10°. Effects of the invention

[0023] According to one aspect of the present invention, a ball end mill capable of improving the quality of the machined surface is provided. Brief explanation of the drawing

[0024] FIG. 1 is a side view showing a ball end mill of an embodiment. FIG. 2 is a partial side view showing the tip of a ball end mill of an embodiment. FIG. 3 is a plan view of the tip of a ball end mill viewed in the axial direction. FIG. 4 is a plan view showing an enlarged view of the chisel area of ​​the first embodiment. FIG. 5 is a plan view showing an enlarged view of the chisel area of ​​the second embodiment. FIG. 6 is a partial cross-sectional view of the chisel portion at a position along the reference line (L) of FIG. 4 and FIG. 5. Figure 7 is a reference diagram showing chisel edge areas of different configurations for comparison. Figure 8 is a reference diagram showing a cross-section along the reference line (L) shown in Figure 7. Figure 9 is a photograph of the processed surface in the example and comparative example. Specific details for implementing the invention

[0025] <First Embodiment>

[0026] FIG. 1 is a side view showing a ball end mill of an embodiment. FIG. 2 is a partial side view showing the tip portion of a ball end mill of an embodiment. FIG. 3 is a plan view of the tip portion of a ball end mill viewed in the axial direction. FIG. 4 is a plan view showing an enlarged view of the chisel area of ​​a first embodiment.

[0027] The ball end mill (1) of the present embodiment is integrally formed from a base material made of a hard material such as cemented carbide into a multi-stage, roughly cylindrical shape centered on the axis (O) as shown in FIG. 1. The rear end of the ball end mill (1) (the upper part in FIG. 1 and FIG. 2) is a large-diameter cylindrical shank (2). The front end of the ball end mill (1) (the lower part in FIG. 1 and FIG. 2) is an end mill body (3) that is roughly cylindrical in shape with a smaller diameter than the shank (2). In addition, the shank (2) and the end mill body (3) are connected by a tapered neck (4) that is tapered to the end of a truncated cone shape centered on the axis (O).

[0028] In this specification, the direction parallel to the axis (O) is simply referred to as the “axial direction,” the direction perpendicular to the axis (O) is simply referred to as the “diameter direction,” and the circumferential direction centered on the axis (O) is simply referred to as the “circumferential direction.” Additionally, when viewed in the axial direction, the outer side of the diameter direction is referred to as the outer circumferential side, and the inner side of the diameter direction is referred to as the inner circumferential side or the axis-centered side.

[0029] A ball end mill (1) performs cutting work on a workpiece by means of cutting edges (51, 52) formed on the end mill body (3) by being fed in a direction intersecting the axis (O) as the shank (2) is gripped by the main spindle of a machine tool and rotated around the axis (O) in the direction of end mill rotation (T). That is, the rotation axis of the ball end mill (1) coincides with the axis (O).

[0030] The ball end mill (1) is a two-blade ball end mill having two cutting blades (51, 52). The cutting blade (51) has a bottom blade (51a) and an outer blade (51b). The cutting blade (52) has a bottom blade (52a) and an outer blade (52b).

[0031] On the outer periphery of the end mill body (3), two cutting debris discharge grooves (71, 72) are formed rotationally symmetrically with respect to the axis (O), which are opened at the leading flank surface (61, 62) located at the leading end of the ball end mill (1) and extend toward the trailing end. The cutting debris discharge grooves (71, 72) are formed in a spiral shape, twisted to face the opposite direction to the end mill rotation direction (T) around the axis (O) as they face toward the trailing end of the ball end mill (1). Additionally, the ball end mill (1) is formed in a shape that is 180° rotationally symmetrical with respect to the axis (O).

[0032] At the respective tip portions of the two cutting debris discharge grooves (71, 72), a concave groove-shaped opening groove (81, 82) is formed so as to extend toward the inner circumference of the ball end mill (1) as it faces toward the tip portion. A bottom edge (51a, 52a) of the cutting edge (51, 52) is formed at the intersection ridge portion of the groove wall surface (81a, 82a) and the tip flank surface (61, 62) facing the end mill rotation direction (T) of the opening groove (81, 82). As shown in FIG. 2, the bottom edge (51a, 52a) forms a convex hemispherical shape in which the rotational trajectory around the axis (O) has a center on the axis (O). In this embodiment, the diameter (D) of the convex hemispherical surface formed by the rotational trajectory of the bottom blades (51a, 52a) is 2 mm or less. The lower limit of the diameter (D) is not particularly limited, but the diameter (D) is preferably 0.1 mm or more. If the diameter (D) is 0.1 mm or more, the width and shape of the chisel part (10) described later can be precisely controlled.

[0033] On the outer surface of the end mill body (3), an outer flank surface (91, 92) is formed that extends along the cutting debris discharge groove (71, 72). The outer flank surface (91, 92) is each adjacent to the side opposite to the end mill rotation direction (T) of the cutting debris discharge groove (71, 72). An outer edge (51b) of the cutting edge (51) is formed on the intersecting ridge of the wall surface facing the end mill rotation direction (T) of the cutting debris discharge groove (71), which is on the rear end side of the opening groove (81), between the outer flank surface (91). An outer edge (52b) of the cutting edge (52) is formed on the intersecting ridge of the wall surface facing the end mill rotation direction (T) of the cutting debris discharge groove (72), which is on the rear end side of the opening groove (82), between the outer flank surface (92).

[0034] The outer edge (51b, 52b) forms a cylindrical shape centered on the axis (O), with a diameter equal to the diameter (D) of the convex hemispherical surface formed by the rotational trajectory of the bottom edge (51a, 52a), such that the rotational trajectory around the axis (O) is equal to the diameter of the bottom edge (51a, 52a). The outer edge (51b, 52b) is formed as needed. That is, the cutting edge of the ball end mill (1) may be composed only of the bottom edge.

[0035] As shown in FIGS. 3 and 4, the two opening grooves (81, 82) are staggered toward opposite sides without overlapping each other with the axis (O) in between when viewed from the axial end side. As shown in FIG. 2, the inner circumference of the groove wall surface (81a) facing the end mill rotation direction (T) of the opening groove (81) extends along the axis (O) when viewed from the side view opposite the groove wall surface (81a). The same applies to the groove wall surface (82a) of the opening groove (82).

[0036] The leading flank surface (61) has a first flank surface (61a) adjacent to the rear side of the end mill rotation direction (T) of the bottom blade (51a), and a second flank surface (61b) adjacent to the rear side of the end mill rotation direction (T) of the first flank surface (61a). The leading flank surface (62) has a first flank surface (62a) adjacent to the rear side of the end mill rotation direction (T) of the bottom blade (52a), and a second flank surface (62b) adjacent to the rear side of the end mill rotation direction (T) of the first flank surface (62a). The rotational trajectory of the leading flank surfaces (61, 62) is offset inward from the rotational trajectory of the bottom blade (51a, 52a). The plank angle of the second plank plane (61b, 62b) is greater than the plank angle of the first plank plane (61a, 62a).

[0037] In the tip portion of the end mill body (3), a chisel portion (10) is formed between two intersecting open grooves (81, 82) that extend in opposite directions. In the chisel portion (10), a chisel edge (10a) is formed that intersects the axis (O) as an intersecting ridge formed by the intersection of two tip flank surfaces (61, 62) that extend in the opposite direction to the end mill rotation direction (T) of the two bottom blades (51a, 52a). In this embodiment, the chisel edge (10a) is formed on the intersecting ridge between the two first flank surfaces (61a, 62a).

[0038] In this embodiment, when viewed from the axial tip side, the bottom blades (51a, 52a) are arranged in a so-called core-raising configuration, positioned on the end mill rotation direction (T) side rather than the line passing through the axis (O) that is parallel to the bottom blades (51a, 52a). By having the bottom blades (51a, 52a) arranged in a core-raising configuration, the separation of cutting debris from the bottom blades (51a, 52a) is improved, which is desirable.

[0039] As shown in FIG. 4, the bottom blades (51a, 52a) each intersect with the chisel edge (10a) at the first intersection point (P11, P21). The bottom blade (51a) has a main cutting edge (51A) extending outward from the first intersection point (P11) and an axial cutting edge (51B) extending outward from the first intersection point (P11) toward the axis (O). The bottom blade (52a) has a main cutting edge (52A) extending outward from the first intersection point (P21) and an axial cutting edge (52B) extending outward from the first intersection point (P21) toward the axis (O).

[0040] In the present specification, the main cutting edge (51A) refers to the intersection ridge of the groove wall (81a) of the open groove (81), which is located in front of the end mill rotation direction (T) of the main cutting edge (51A) and functions as an inclined surface, and the first flank surface (61a), which is located behind the rotation direction of the main cutting edge (51A) and forms a rotation trajectory closer to the axis (O) than the rotation trajectory of the main cutting edge (51A). The axial cutting edge (51B) is connected to one main cutting edge (51A) but is formed on the intersection ridge of the first flank surface (62a) of a separate main cutting edge (52A) that is different from one main cutting edge (51A) and the groove wall surface (81a). The same applies to the main cutting edge (52A) and the axial cutting edge (52B) of the bottom edge (52a).

[0041] The reference line (L) shown in FIG. 4 is a straight line that passes through the axis (O) and is orthogonal to the tangent of the cutting edge (cutting edge tangent (L1, L2)) at the first intersection (P11, P21) when viewed from the axial end side. In the present embodiment, the reference line passing through the axis (O) and orthogonal to the tangent of the cutting edge at the first intersection (P11), and the reference line passing through the axis (O) and orthogonal to the tangent of the cutting edge at the first intersection (P21) coincide with each other when viewed from the axial end side, so they are shown as one reference line (L). [This is the case of the [un-severing], and the [un-severing], which is the case of

[0042] Next, the feature part of the present embodiment will be described. The second intersection point (P12), which is the intersection point between the first flank surface (62a) and the second flank surface (62b) and the groove wall surface (81a) of the opening groove (81), is located forward of the end mill rotation direction (T) from the reference line (L).

[0043] In other words, the area (chisel edge front area (A1)) enclosed by the chisel edge (10a), the reference line (L), and the axial cutting edge (51B) consists only of the first flank surface (62a) and does not include the second flank surface (62b). That is, the chisel edge front area (A1) does not include the boundary (flank surface boundary line (62c)) between the first flank surface (62a) and the second flank surface (62b). Likewise, the chisel edge front area (A2) also does not include the boundary (flank surface boundary line (61c)) between the first flank surface (61a) and the second flank surface (61b).

[0044] By configuring it in this way, the ball end mill (1) of the present embodiment has no boundary of flank surfaces with different flank angles in the chisel edge front region (A1, A2), and since no edge portion convex toward the processing surface is formed in the chisel edge front region (A1, A2), it is difficult for cutting debris to be pressed toward the processing surface near the axis (O), thereby suppressing the occurrence of welding.

[0045] At the same time, since the ball end mill (1) of the present embodiment does not include a second flank surface (62b, 61b) in the chisel edge front area (A1, A2), the cutting edge angle (α) of the axial cutting edge (51B, 52B) of the present embodiment can be made relatively smaller compared to the case where the second flank surface (62b, 61b) is included. As a result, in the present embodiment, the cutting performance of the axial cutting edge (51B, 52B) is improved and the occurrence of tearing can be suppressed.

[0046] Additionally, as shown in FIG. 4, the flank surface boundary line (61c) of one bottom edge (51a) intersects the cutting edge tangent (L2) at the intersection point (first intersection point (P21)) with the chisel edge (10a) of the other bottom edge (52a). Likewise, the flank surface boundary line (62c) of the other bottom edge (52a) intersects the cutting edge tangent (L1) at the intersection point (first intersection point (P11)) with the chisel edge (10a) of the one bottom edge (51a).

[0047] By configuring it in this way, the ball end mill (1) of the present embodiment can secure a large area occupied by the first flank surface on the axis side, while narrowing the width in the direction perpendicular to the blade of the first flank surface on the outer side, thereby suppressing the cutting resistance from becoming excessively large and securing the cutting performance of the cutting edge that contributes mainly to cutting.

[0048] Additionally, as shown in FIG. 4, in this embodiment, when viewed from the axial tip side, the total flank surface width (W) in the direction in which the reference line of the first flank surface (61a) of one bottom blade (51a) and the first flank surface (62a) of the other bottom blade (52a), which are adjacent to each other at the chisel edge, extends has a portion that decreases toward the outer circumference in the radial direction from the second intersection point.

[0049] By configuring it in this way, the ball end mill (1) of the present embodiment can secure a large area occupied by the first flank surface on the axis side, while narrowing the width in the direction perpendicular to the blade of the first flank surface on the outer side, thereby suppressing the cutting resistance from becoming excessively large and securing the cutting performance of the cutting edge that contributes mainly to cutting.

[0050] <Second Embodiment>

[0051] As a variation of the first embodiment, a second embodiment is shown in FIG. 5. In the first embodiment, there was no clear curve in the flank surface boundary line (61c, 62c), but in the second embodiment, there is a clear curve (connection position) (61C, 62C). The other shape is the same as in the first embodiment. The same reference numerals are used for points identical to those in the first embodiment.

[0052] In the leading flank surface (61), the flank surface boundary line (61c), which is the boundary line between the first flank surface (61a) and the second flank surface (61b), has a first part (61A) that extends along the bottom edge (51a) adjacent to the first flank surface (61a), as shown in FIG. 5, and a second part (61B) that is continuous with the inner circumferential end of the first part (61A) and extends in a direction away from the bottom edge (51a) to reach the end edge of the opening groove (82). In the leading flank surface (62), the flank surface boundary line (62c) of the first flank surface (62a) and the second flank surface (62b) has a first part (62A) and a second part (62B) in the same way as the flank surface boundary line (61c).

[0053] The first part (61A) of the flank surface boundary line (61c) extends nearly parallel to the main cutting edge (51A) of one bottom edge (51a). In this embodiment, the inner end of the first part (61A) extends slightly inward (toward the axis (O) side) from the first intersection point (P11), which is the inner end of the main cutting edge (51A). The flank surface boundary line (61c) bends at the connection position (61C) between the first part (61A) and the second part (61B). The second part (61B) extends from the connection position (61C) in a direction away from one bottom edge (51a). The second part (61B) extends toward the opening groove (82) adjacent to the bottom edge (52a) on the opposite side. The second part (61B) intersects the opening groove (82) (groove wall surface (82a)) on the opposite side at the second intersection point (P22), just like in the first embodiment.

[0054] The flank surface boundary line (62c) has the same configuration as the flank surface boundary line (61c). That is, the first part (62A) extends along the main cutting edge (52A) of the bottom edge (52a). The flank surface boundary line (62c) bends at a connection position (62C) located near the first intersection point (P21). The second part (62B) extends toward the opening groove (81) on the opposite side and intersects the end edge (groove wall surface (81a)) of the opening groove (81) at the second intersection point (P12).

[0055] In this embodiment, even in the bottom blade (51a), the second intersection point (P12) is located on the side facing forward of the end mill rotation direction (T) relative to the reference line (L). In the bottom blade (52a), the second intersection point (P22) is located on the side facing forward of the end mill rotation direction (T) relative to the reference line (L).

[0056] According to this configuration, the chisel edge front area (A1), surrounded by the chisel edge (10a), the open groove (81) (in other words, the axial cutting edge (51B)), and the reference line (L), is composed solely of the first flank surface (62a). That is, the second flank surface (62b) does not intrude into the chisel edge front area (A1). Thus, as with the first embodiment, the occurrence of welding or tearing on the workpiece can be suppressed. The chisel edge front area (A2), surrounded by the chisel edge (10a), the open groove (82) (in other words, the axial cutting edge (52B)), and the reference line (L), is likewise composed solely of the first flank surface (61a).

[0057] Next, a configuration unique to the second embodiment will be described.

[0058] In this embodiment, as shown in FIG. 5, the connection position (61C) of the first part (61A) and the second part (61B) of the flank surface boundary line (61c) of one bottom edge (51a) is located between the third intersection point (P23), which is the intersection point of the other bottom edge (52a) and the reference line (L), and the axis line (O), in the direction in which the reference line (L) extends (up and down direction in the illustration). Also, the connection position (62C) of the first part (62A) and the second part (62B) of the flank surface boundary line (62c) of the other bottom edge is located between the third intersection point (P13), which is the intersection point of the one bottom edge (51a) and the reference line (L), and the axis line (O), in the direction in which the reference line (L) extends.

[0059] Thus, on the inner side, the flank surface boundary line is not included in the area in front of the chisel edge, thereby suppressing the occurrence of welding, and on the outer side, the width in the direction perpendicular to the blade of the first flank surface (61a, 62a) can be narrowed, thereby suppressing cutting resistance from becoming excessively large and ensuring the cutting performance of the main cutting edge (51A, 52A) that mainly performs cutting. Overall, the characteristics of the machined surface can be improved.

[0060] In the ball end mill (1) of the present embodiment, the width (W1) of the first flank surface (61a) in the direction along the reference line (L) at the position of the first intersection point (P11) is smaller than the width (W2) of the gap in the direction along the reference line (L) of the cutting edge tangent (L1) at the bottom edge (51a) and the cutting edge tangent (L2) at the bottom edge (52a). In the present embodiment, the width of the first flank surface (62a) in the direction along the reference line (L) at the position of the first intersection point (P21) is almost the same as the width (W1) of the first flank surface (61a) mentioned above, and is likewise smaller than the width (W2).

[0061] According to this configuration, the width of the first flank surface (61a, 62a) of the cutting edge located on the outer side can be narrowed in the direction perpendicular to the edge, thereby reducing cutting resistance and improving the cutting performance of the main cutting edge (51A, 52A).

[0062] Additionally, the width (W2) of the gap between the cutting edge tangents (L1, L2) in the direction along the reference line (L) is approximately equal to the width of the chisel portion (10). The width of the chisel portion (10) is the width of the thinnest part between the groove walls (81a, 82a) facing the end mill rotation direction (T) in the two intersecting open grooves (81, 82) when viewed from the axial tip side. Accordingly, the width (W1) of the first flank surface (61a, 62a) may be smaller than the width of the chisel portion (10).

[0063] In this embodiment, when viewed from the axial tip side, the second part (61B) extends in a direction away from the chisel edge (10a) as it approaches the opening groove (82). Additionally, the second part (62B) extends in a direction away from the chisel edge (10a) as it approaches the opening groove (81). According to this configuration, the first flank surface (61a) becomes wider as it approaches the chisel edge front area (A2), and the first flank surface (62a) becomes wider as it approaches the chisel edge front area (A1). This allows for securing a larger area of ​​the thicker part of the chisel portion (10). The strength of the axial cutting edge (51B, 52B) can be increased.

[0064] In this embodiment, when viewed from the axial end side, in the area on the inner side of the connection position (61C) of the first part (61A) and the second part (61B) of the flank surface boundary line (61c), the total flank surface width (W) in the direction in which the reference line (L) of the two first flank surfaces (61a, 62a) extends increases as it goes toward the inner side in the section from the connection position (61C) to the second intersection point (P22). Likewise, in the area on the inner side of the connection position (62C) between the first part (62A) and the second part (62B) of the flank surface boundary line (62c), the total flank surface width (W) in the direction in which the reference line (L) of the two first flank surfaces (61a, 62a) extends increases as it moves toward the inner side in the section from the connection position (62C) to the second intersection point (P12). This allows for securing a larger area of ​​the thicker part in the chisel portion (10). The strength of the axial cutting edge (51B, 52B) can be increased.

[0065] The effects of operation common to the first and second embodiments will be explained in more detail.

[0066] FIG. 6 is a partial cross-sectional view of the chisel portion (10) at a position along the reference line (L) of FIG. 4 or FIG. 5. FIG. 7 is a reference diagram showing a chisel edge area of ​​a different configuration for comparison. FIG. 8 is a reference diagram showing a cross-section along the reference line (L) shown in FIG. 7.

[0067] In any embodiment of the present invention, since the chisel edge front region (A1, A2) is configured to consist only of the first flank surface (62a, 61a), as shown in FIG. 6, the chisel edge front region (A1, A2) becomes a region where the surface is a flat surface.

[0068] Meanwhile, in the comparative example, as shown in FIG. 7, when the boundary line between the first flank surface and the second flank surface is a flank surface boundary line (61v) extending along the bottom edge (51a) and a flank surface boundary line (62v) extending along the bottom edge (52a), the intersection point of the flank surface boundary line (61v) and the end edge of the opening groove (82) becomes a second intersection point (P22v) located on the rearward side of the rotational direction relative to the reference line (L). Also, the intersection point of the flank surface boundary line (62v) and the end edge of the opening groove (81) becomes a second intersection point (P12v) located on the rearward side of the rotational direction relative to the reference line (L).

[0069] In the configuration shown in FIG. 7, the chisel edge front region (A1) includes a portion formed by a first flank surface (62a) and a portion formed by a second flank surface (62b). The chisel edge front region (A2) includes a portion formed by a first flank surface (61a) and a portion formed by a second flank surface (61b). In other words, in the chisel edge front region, there exists a boundary of flank surfaces with different flank angles. In such a configuration, as shown in FIG. 7 and 8, an edge portion that is convex toward the processing surface, formed by flank surface boundary lines (62v, 61v), is formed within the chisel edge front region (A1, A2). The chisel edge front region (A1, A2) is a region that is prone to being blocked by the chisel edge (10a) and the processing surface, and is also a region where cutting debris is generated during cutting. Therefore, if the edge portion is inside the chisel edge front area (A1, A2), the cutting debris gets caught on the edge portion, and because the cutting debris is pressed against the machined surface near the axis (O), welding to the workpiece is likely to occur.

[0070] In the above, in the ball end mill (1) of the first and second embodiments, there is no boundary of flank surfaces with different flank angles in the chisel edge front region (A1, A2), and since the chisel edge front region (A1, A2) is a flat surface, it is difficult for cutting debris to be pressed onto the processing surface near the axis (O), and thus the occurrence of welding can be suppressed.

[0071] At the same time, although the original axial cutting edge (51B, 52B) is close to the axis of rotation (axis line (O)), making it difficult to increase the cutting speed, by configuring the chisel edge front area (A1, A2) with only the first flank surface (62a, 61a), the cutting edge angle (angle (α) in FIG. 6) of the axial cutting edge (51B, 52B) becomes relatively smaller compared to the case where the second flank surface (62b, 61b) exists in the chisel edge front area (A1, A2) (angle (β) in FIG. 8). Thus, in this embodiment, the cutting performance of the axial cutting edge (51B, 52B) is improved, and the occurrence of tearing can also be suppressed.

[0072] In addition, in the ball end mill (1) of the present embodiment, the cutting edge tangent line at the intersection point (first intersection point) of the flank surface boundary line of one cutting edge and the chisel edge of the other cutting edge intersects. Therefore, on the inner side, the chisel edge front area does not include the flank surface boundary line, thereby suppressing the occurrence of welding, while on the outer side, the width in the direction perpendicular to the first flank surface edge can be narrowed, thereby suppressing the cutting resistance from becoming excessively large and ensuring the cutting performance of the cutting edge that mainly performs cutting.

[0073] According to the ball end mill (1) of the present embodiment, the finishing surface properties (roughness or quality) in finishing processing can be improved through the synergistic effects of suppressing welding, suppressing tearing, and ensuring cutting performance.

[0074] In this embodiment, the width of each of the first flank surfaces (61a, 62a) of the main cutting blades (51A, 52A) in the direction perpendicular to the blade is not particularly limited, but, for example, it can be within the range of 1% or more and 15% or less of the diameter (D) of the arc-shaped rotational trajectory of the bottom blades (51a, 52a).

[0075] In the first and second embodiments, the groove wall surface (81a, 82a) facing the end mill rotation direction (T) of the opening groove (81, 82) is an inclined surface facing the end mill rotation direction (T) side as it moves away from the bottom edge (51a, 52a) and faces the center side of the convex hemispherical surface formed by the rotation trajectory of the bottom edge (51a, 52a). Thus, the axial cutting edge (51B) located between the first intersection point (P11) and the third intersection point (P13) of the bottom edge (51a), and the axial cutting edge (52B) located between the first intersection point (P21) and the third intersection point (P23) of the bottom edge (52a) both have an inclination angle perpendicular to the edge. The angle of inclination in the direction perpendicular to the blade of the axial cutting edge (51B, 52B) in the present specification is the angle formed by the inclined plane and a straight line passing through the axial cutting edge (51B, 52B) and parallel to the axis (O) in a cross section passing through the axial cutting edge (51B, 52B) and parallel to the reference line (L) and the axis (O).

[0076] In the case of the first and second embodiments, the inclination angle in the direction perpendicular to the cutting edge of the axial cutting edge (51B, 52B) is an angle within the range of -30° or more and -15° or less. According to this configuration, the cutting edge angle (α) of the axial cutting edge (51B, 52B) can be set to a cutting edge angle that has a good balance of cutting performance and cutting edge strength in the axial cutting edge (51B, 52B) located near the closed space and at a slow rotational speed, thereby suppressing chipping or defects on the axial cutting edge (51B, 52B) and further suppressing the occurrence of tearing or welding.

[0077] In the chisel portion (10), if the rake angle of the axial cutting edge (51B, 52B) is greater than -15° toward the positive angle, the tip angle of the bottom edge (51a, 52a) becomes smaller, and the tip strength becomes insufficient, making it prone to chipping or breakage. On the other hand, if the rake angle of the axial cutting edge (51B, 52B) is greater than -30° toward the negative angle, the cutting performance deteriorates, making it prone to tearing. The rake angle of the bottom edge (51a, 52a) may gradually change from the chisel portion (10) toward the outer edge (51b, 52b). In the part on the outer side of the first intersection point (P11, P21) of the bottom edge (51a, 52a), the angle of inclination of the bottom edge (51a, 52a) may be negative or positive.

[0078] In the present invention, the flank angle near the chisel of the first flank surface (61a, 62a) and the flank angle of the second flank surface (61b, 62b) are not particularly limited. For example, the flank angle of the first flank surface (61a, 62a) can be within the range of 5° or more and less than 10°. The flank angle of the second flank surface (61b, 62b) can be within the range of 10° or more and 30° or less.

[0079] According to this configuration, it becomes more difficult for cutting debris to be pressed onto the machined surface near the axis of rotation, thereby further suppressing the occurrence of welding near the axis of rotation, and at the same time, the balance between the cutting performance and edge strength of the cutting edge angle near the axis of rotation can be improved, and the occurrence of tearing can be further suppressed.

[0080] A hard film may be coated on the surface of at least the end mill body (3) of the tip portion of the ball end mill (1). The hard film may be coated on the entire surface of the ball end mill (1), including the shank (2) and the tapered neck (4). The hard film is coated, for example, using a physical vapor deposition method with a relatively low coating temperature. Among physical vapor deposition methods, it is preferable to coat the hard film using an arc ion plating method, which has excellent adhesion of the film.

[0081] As for the type of hard coating, nitrides or carbonitrides, which are types of coatings with excellent heat resistance and wear resistance, are preferred. Specifically, it is preferable to apply a hard coating composed of nitrides or carbonitrides, which have the highest content of Al, which is a type of coating with excellent heat resistance and wear resistance, and a total content of Al and Cr of 90 atomic% or more. In addition, among such hard coatings, it is preferable to apply a hard coating with a fine coating structure. Furthermore, this hard coating has a higher hardness than the base material forming the ball end mill (1).

[0082] As a hard coating, for example, the hard coating described in Japanese Patent Publication No. 6410797 may be suitably used. The hard coating described in the said patent publication is composed of a nitride or carbonitride in which, with respect to the total amount of metal (including metalloids) elements, the aluminum (Al) content ratio is 50 atomic% or more and 68 atomic% or less, the chromium (Cr) content ratio is 20 atomic% or more and 46 atomic% or less, and the silicon (Si) content ratio is 4 atomic% or more and 15 atomic% or less. When the sum of the metal (including metalloids) elements, nitrogen, oxygen, and carbon is 100 atomic%, the atomic ratio of the metal (including metalloids) elements (atomic%) A and the atomic ratio of nitrogen (atomic%) B satisfy the relationship 1.03 ≤ B / A ≤ 1.07. In the intensity profile obtained from the X-ray diffraction pattern or the limited field diffraction pattern of a transmission electron microscope, the peak intensity originating from the (200) plane or (111) plane of the face-centered cubic lattice structure represents the maximum intensity.

[0083] The film thickness of the hard film is preferably 1.0 μm or more, and more preferably 2.0 μm or more. The film thickness of the hard film is preferably 3.0 μm or less. In addition, as described in Japanese Patent Publication No. 6410797, a protective film may be formed on the hard film. The protective film described in the above patent publication is composed of a nitride or carbonitride having a Ti content of 50 atomic% or more and a Si content of 1 atomic% or more and 30 atomic% or less relative to the total amount of metal (including metalloids) elements. By applying such a protective film, wear resistance can be further increased even for high-hardness workpieces.

[0084] In addition, a hard film can be formed using the method described in Japanese Patent Publication No. 6410797. In the film formation method described in the said patent publication, an alloy target is installed at the cathode in which, with respect to the total amount of metal (including metalloid) elements, the aluminum (Al) content ratio is 55 atomic% or more and 70 atomic% or less, the chromium (Cr) content ratio is 20 atomic% or more and 35 atomic% or less, and the silicon (Si) content ratio is 7 atomic% or more and 20 atomic% or less, and the film is formed by an arc ion plating method. The film formation conditions are such that the bias voltage applied to the substrate is -220 V or more and -60 V or less, and the cathode voltage is 22 V or more and 27 V or less, or the bias voltage applied to the substrate is -120 V or more and -60 V or less, and the cathode voltage is 28 V or more and 32 V or less.

[0085] Examples

[0086] Next, the present invention will be explained in more detail by way of examples.

[0087] In this embodiment, a ball end mill based on the embodiment described above and a ball end mill based on the comparative example explained with reference to FIGS. 7 and 8 were manufactured. That is, in the ball end mill of the embodiment, the second flank surface does not penetrate to the area in front of the chisel edge. In the ball end mill of the embodiment, the flank surface boundary line of the first flank surface and the second flank surface changes its direction of extension near the axis line (O), and the intersection point between the flank surface boundary line and the wall of the opening groove is located on the rotational direction forward side relative to the reference line (L). In addition, the cutting edge tangent at the intersection point of one bottom edge and the chisel edge intersects the flank surface boundary line of the other bottom edge. On the other hand, in the ball end mill of the comparative example, the second flank surface penetrates to the inner side of the area in front of the chisel edge. Common tool specifications are shown below.

[0088] (Tool Specifications)

[0089] · Blade diameter: 0.6 mm

[0090] · 1st plank angle: 9°

[0091] · Second plank angle: 17°

[0092] For the ball end mills of the example and comparative example, contour machining of the bottom surface was performed under the following cutting conditions, and the condition of the machined surface was observed. Figure 9 shows a photograph of the observation results. As shown in Figure 9, welding was observed in various places on the machined surface of the workpiece cut with the ball end mill of the comparative example. In addition, tearing occurred at points where the direction changed during contour machining. On the other hand, neither welding nor tearing occurred on the machined surface of the workpiece cut with the ball end mill of the example. Furthermore, the surface roughness of the machined surface was lower on the machined surface cut with the ball end mill of the example.

[0093] (Cutting conditions)

[0094] · Rotation speed n : 40000 min -1

[0095] · Rotational speed Vc: 75 m / min

[0096] · Cutting speed Vf: 800 mm / min

[0097] · Feed rate per tooth fz: 0.01 mm / t

[0098] · Axial depth of cut ap: 0.005 mm

[0099] · Diameter depth of cut ae: 0.01 mm

[0100] · Workpiece: VANADIS23 (64HRC)

[0101] · Machining point: Bottom surface machining

[0102] · Coolant: Mist Blow Explanation of the symbols

[0103] 1 … Ball end mill, 3 … End mill body, 10a … Chisel edge, 51, 52 … Cutting edge, 52A, 52B … Axial cutting edge, 61a, 62a … First flank face, 61b, 62b … Second flank face, 61c, 61v, 62c, 62v … Flank face boundary line, 81, 82 … Opening groove, 81a, 82a … Groove wall, L … Reference line, L1, L2 … Cutting edge tangent, O … Axis line, P11, P21 … First intersection point, P12, P22, P12v, P22v … Second intersection point, W … Total flank face width, W1, W2 … Width

Claims

Claim 1 A ball end mill having two cutting edges having an end mill body that rotates around an axis, wherein the cutting edges are formed on an intersection ridge between a groove wall of an opening groove and a flank surface located rearward in the rotational direction of the opening groove, and the flank surface has a first flank surface forming a chisel edge and a second flank surface extending rearward in the rotational direction from the first flank surface at a larger flank angle, wherein, when viewed from the axial tip side, the intersection point between one of the cutting edges and the chisel edge is set as the first intersection point, and a straight line passing through the axis while being perpendicular to the tangent of the cutting edge at the first intersection point is set as the reference line, and the intersection point between the flank surface boundary line of the first flank surface and the second flank surface of the other cutting edge and the groove wall is set as the second intersection point, wherein the second intersection point is located forward in the rotational direction from the reference line, and the flank surface of the other cutting edge A ball end mill characterized in that the boundary line intersects the tangent of the cutting edge of the one cutting edge, and when viewed from the axial tip side, the tip surface of the ball end mill has a portion in the direction of extension of the reference line of the first flank surface of the one cutting edge and the first flank surface of the other cutting edge, which are adjacent to each other at the chisel edge, that decreases from the second intersection point toward the radial outer circumference. Claim 2 A ball end mill according to claim 1, characterized in that, when viewed from the axial tip side, the flank surface boundary line has a portion extending from the second intersection point toward the radial outer circumference side in a direction approaching the chisel edge. Claim 3 A ball end mill according to claim 1 or 2, characterized in that, when viewed from the axial tip side, the angle of inclination in the direction perpendicular to the cutting edge of the inclined surface of the axial cutting edge located on the radial outer circumference side relative to the reference line and on the radial axial side relative to the first intersection point is a negative angle. Claim 4 A ball end mill according to claim 3, characterized in that the inclination angle is -30° or more and -15° or less, and the flank angle of the first flank surface is 5° or more and less than 10°. Claim 5 delete

Images