Ball end mill

Abstract

To provide a ball end mill suitable for finishing, with which a high-gloss machined surface is obtained in the cutting of a flat surface orthogonal to a tool rotation axis, such as a bottom surface of a die, using a tool tip portion, and with which it is possible to omit a polishing step or reduce the number of polishing man-hours.SOLUTION: There is provided a ball end mill in which a plurality of swarf discharge grooves 2 opened at a tip end and leading from a tool-tip-end side to a tool-base-end side are formed in an outer periphery of a tool body 1, and ball blades 5 are provided at intersection ridgelines between rake faces 3 of the swarf discharge grooves 2 and tip-end flanks 4 of the tool body 1. Therein: a convex tip surface 6 intersecting a tool rotation axis a of the tool body 1 is provided at a tool tip portion; and intersection ridgelines between the tip surface 6 and the rake faces 3 are configured as central cutting blades 7 continuous with the ball blades 5.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] Ball end mills are widely used in the fields of mold and part machining. They are equipped with an arc-shaped ball blade at the tip of the tool that creates a hemispherical rotation trajectory. The ball blade, with its appropriately designed rake angle and clearance angle, can be used to cut complex curved surfaces and mold draft surfaces (inclined flat surfaces), making it possible to obtain good machined surfaces.

[0003] However, the cutting ability of the tip portion of the ball end mill (the top of the arc-shaped ball blade and its vicinity) is inferior to that of the outer peripheral portion of the ball blade, and there was a problem in that it was difficult to obtain a good machined surface when machining a plane perpendicular to the tool rotation axis, such as the bottom surface of a mold.

[0004] Therefore, a finishing ball end mill has been proposed, as shown in Patent Document 1, with the aim of obtaining a high-gloss machined surface even when machining flat surfaces perpendicular to the tool rotation axis, such as the bottom surface of a mold. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2000-233311 A Summary of the Invention [Problem to be solved by the invention]

[0006] The ball end mill of Patent Document 1 mentioned above has two ball blades arranged at a center-up position, and the chisel angle of the chisel edge formed by the flank of the two ball blades is set to 155 degrees or more, or the ratio of the distance between the inner edges of the rake faces of the two blades formed by gash on the ball blade to the length of the chisel edge is set to 1 / 7 to 1 / 3, and the cutting action of the chisel edge is used to cut flat surfaces perpendicular to the tool rotation axis, such as the bottom surface of a mold.

[0007] However, ball end mills equipped with a chisel edge have long been in widespread use, and because this chisel edge is an intersecting ridge where the flanks of the ball cutting edges intersect at a large obtuse angle, the rake angle is large and negative, causing chipping on the machined surface. Therefore, even if the angle (chisel angle) and length at which the chisel edge is arranged are adjusted to appropriate values ​​as disclosed in Patent Document 1 above, it is difficult to obtain a machined surface (flat surface) with such excellent gloss that a polishing process (finishing treatment) can be omitted. For this reason, the current situation is that a polishing process (finishing treatment) must be performed after cutting.

[0008] The present invention has been made in consideration of the current situation, and aims to provide a ball end mill that is suitable for finishing processing, which can obtain a machined surface with excellent glossiness when cutting a plane perpendicular to the tool rotation axis, such as the bottom surface of a mold, using the tip of the tool, and can omit the polishing step or reduce the polishing processing labor. [Means for solving the problem]

[0009] The gist of the present invention will now be described with reference to the accompanying drawings.

[0010] This ball end mill has a plurality of chip discharge grooves 2 formed on the outer periphery of a tool body 1, which are open at the tip and run from the tool tip side to the tool base end side, and a ball blade 5 is provided on each of the intersection ridges between the cutting faces 3 of these chip discharge grooves 2 and the tip clearance face 4 of the tool body 1, and is characterized in that a convex tip surface 6 is provided at the tool tip which intersects with the tool rotation axis a of the tool body 1, and the intersection ridge between this tip surface 6 and the cutting face 3 is configured as a center cutting edge 7 connected to the ball blade 5.

[0011] In addition, in the ball end mill described in claim 1, the tip surface 6 is characterized in that it is arranged between the tip surface 4 of each of the pair of ball blades 5 arranged 180 degrees rotationally symmetrically about the tool rotation axis a, so as to be connected to the tip surface 4 and each of the cutting faces 3.

[0012] In addition, in the ball end mill described in claim 2, the tip surface 6 includes the tool rotation axis a, and is configured so that, when viewed from the tool tip, the profile linearly connecting an arbitrary point on one of the center side cutting edges 7 connected to one of the pair of ball blades 5 passing near the tool rotation axis a and an arbitrary point on the other center side cutting edge 7 connected to the other is in a mountain shape.

[0013] In addition, in the ball end mill described in claim 3, the tip surface 6 includes the tool rotation axis a, and when viewed from the tip of the tool, the profile linearly connecting the intersection of one of the center cutting edges 7 connected to one of the pair of ball blades 5 and one ridge line 10 formed by the tip surface 6 and one of the tip flank faces 4, and the intersection of the other of the center cutting edges 7 connected to the other of the pair of ball blades 5 and the other ridge line 10 formed by the tip surface 6 and the other tip flank face 4, is configured to be mountain-shaped, and further, the ball end mill is configured so that the maximum height of the mountain-shaped shape is 6 μm or less.

[0014] The present invention relates to a ball end mill according to any one of claims 1 to 4, characterized in that the center cutting edge 7 is provided up to the vicinity of the tool rotation axis a.

[0015] Moreover, in the ball end mill described in any one of claims 1 to 4, the tip surface 6 is connected to the tip clearance surface 4, and this tip surface 6 is arranged so that, when viewed from the tip of the tool, with respect to the central cutting edge 7 or a perpendicular line 9 of an extension line 8 of the central cutting edge 7 passing through the tool rotation axis a, when the side of the ball blade 5 to which the central cutting edge 7 is connected is defined as the positive side and the opposite side is defined as the negative side, the intersection P2 of 2 below is either on the negative side, or on the positive side where the separation distance X between the intersection P1 and the intersection P2 of 1 below in the direction along the central cutting edge 7 is 0% or more and 10% or less of the tool outer diameter. Note 1 Intersection P1: When viewed from the tip of the tool, the intersection point between the center side cutting edge 7 or the extension line 8 of the center side cutting edge 7 and the perpendicular line 9 of the center side cutting edge 7 or the extension line 8 of the center side cutting edge 7 passing through the tool rotation axis a Note 2 Intersection point P2: When viewed from the tip of the tool, the intersection point between the ridge line 10 formed by the tip face 6 and the tip flank face 4, which is on the side farther from the ball-shaped blade 5, and the edge of the tip of the chip discharge groove 2 having the ball-shaped blade 5 and the center-side cutting edge 7 connected to the ball-shaped blade 5.

[0016] In addition, in the ball end mill described in claim 5, the tip surface 6 is connected to the tip clearance surface 4, and this tip surface 6 is arranged so that, when viewed from the tip of the tool, with respect to the central cutting edge 7 or a perpendicular line 9 of an extension line 8 of the central cutting edge 7 passing through the tool rotation axis a, when the side of the ball blade 5 to which the central cutting edge 7 is connected is defined as the positive side and the opposite side is defined as the negative side, the intersection P2 of 2 below is either on the negative side, or on the positive side where the separation distance X between the intersection P1 and the intersection P2 of 1 below in the direction along the central cutting edge 7 is 0% or more and 10% or less of the tool outer diameter. Note 1 Intersection P1: When viewed from the tip of the tool, the intersection point between the center side cutting edge 7 or the extension line 8 of the center side cutting edge 7 and the perpendicular line 9 of the center side cutting edge 7 or the extension line 8 of the center side cutting edge 7 passing through the tool rotation axis a Note 2 Intersection point P2: When viewed from the tip of the tool, the intersection point between the ridge line 10 formed by the tip face 6 and the tip flank face 4, which is on the side farther from the ball-shaped blade 5, and the edge of the tip of the chip discharge groove 2 having the ball-shaped blade 5 and the center-side cutting edge 7 connected to the ball-shaped blade 5.

[0017] Furthermore, in the ball end mill described in any one of claims 1 to 4, the tip surface 6 is characterized in that the width W of the tip surface 6 is defined as the distance between two ridge lines 10 formed by the tip surface 6 and each of the tip clearance faces 4 of a pair of the ball blades 5 arranged 180 degrees rotationally symmetrically about the tool rotation axis a, when viewed from the tip of the tool, and the tip surface 6 is configured such that the width W satisfies 0.005 mm≦W≦0.2D (D: tool outer diameter).

[0018] In addition, in the ball end mill described in claim 5, the tip surface 6 is characterized in that, when viewed from the tip of the tool, the width W of the tip surface 6 is the distance between two ridges 10 formed by the tip surface 6 and each of the tip clearance faces 4 of a pair of the ball blades 5 arranged 180 degrees rotationally symmetrically about the tool rotation axis a, and the tip surface 6 is configured so that the width W is 0.005 mm≦W≦0.2D (D: tool outer diameter).

[0019] In addition, in the ball end mill described in claim 6, the tip surface 6 is characterized in that the width W of the tip surface 6 is the distance between two ridges 10 formed by the tip surface 6 and each of the tip clearance faces 4 of a pair of the ball blades 5 arranged 180 degrees rotationally symmetrically about the tool rotation axis a, when viewed from the tip of the tool, and the tip surface 6 is configured so that the width W is 0.005 mm≦W≦0.2D (D: tool outer diameter).

[0020] In addition, in the ball end mill described in claim 7, the tip surface 6 is characterized in that, when viewed from the tip of the tool, the width W of the tip surface 6 is the distance between two ridges 10 formed by the tip surface 6 and each of the tip clearance faces 4 of a pair of the ball blades 5 arranged 180 degrees rotationally symmetrically about the tool rotation axis a, and the tip surface 6 is configured so that the width W is 0.005 mm≦W≦0.2D (D: tool outer diameter).

[0021] The present invention relates to a ball end mill as recited in claim 8, characterized in that the width W of the tip surface 6 is set within the following range. When the tool outer diameter is greater than φ1.5mm, 0.01mm≦W≦0.3mm If tool outer diameter≦φ1.5mm, 0.01mm≦W≦0.2D (D: tool outer diameter)

[0022] The present invention relates to a ball end mill as recited in claim 9, characterized in that the width W of the tip surface 6 is set within the following range. When the tool outer diameter is greater than φ1.5mm, 0.01mm≦W≦0.3mm If tool outer diameter≦φ1.5mm, 0.01mm≦W≦0.2D (D: tool outer diameter)

[0023] The present invention relates to a ball end mill as set forth in claim 10, wherein the width W of the tip surface 6 is set within the following range. When the tool outer diameter is greater than φ1.5mm, 0.01mm≦W≦0.3mm If tool outer diameter≦φ1.5mm, 0.01mm≦W≦0.2D (D: tool outer diameter)

[0024] The ball end mill according to claim 11 is characterized in that the width W of the tip surface 6 is set within the following range. When the tool outer diameter is greater than φ1.5mm, 0.01mm≦W≦0.3mm If tool outer diameter≦φ1.5mm, 0.01mm≦W≦0.2D (D: tool outer diameter) Effect of the Invention

[0025] Since the present invention is configured as described above, it is possible to obtain a machined surface with excellent gloss when cutting a plane perpendicular to the tool rotation axis, such as the bottom surface of a mold, using the tip of the tool, and it becomes a ball end mill that is suitable for finishing processing, which can omit the polishing step or reduce the polishing processing labor hours. [Brief description of the drawings]

[0026] [Figure 1] FIG. 2 is an explanatory plan view showing a main part of the present embodiment, as viewed from the tip of the tool. [Diagram 2] 1A is an explanatory left side view and FIG. 1B is an explanatory front view showing a main portion of the present embodiment. [Diagram 3] FIG. 11 is an explanatory plan view showing a main part of a first modified example of the present embodiment, as viewed from a tip of a tool. [Figure 4] 1A and 1B are explanatory left side view and explanatory front view showing a main part of a first modified example of the present embodiment. [Diagram 5] FIG. 11 is an explanatory plan view showing a main part of a second modified example of the present embodiment, as viewed from the tip of a tool. [Figure 6] 13A and 13B are explanatory left side view and explanatory front view showing a main part of a second modified example of the present embodiment. [Figure 7] FIG. 2 is an explanatory diagram defining the convex outer shape (profile) of the tip surface in this embodiment. [Figure 8] FIG. 2 is an explanatory diagram defining the amount of convexity of the convex outer shape (profile) of the tip surface in this embodiment. [Figure 9] 1 is an example of profile data showing a convex outer shape (profile) of a tip surface of the present embodiment. [Figure 10] 1 is an explanatory diagram showing the positive side, negative side, separation distance X, and tip face width W in the present embodiment as viewed from the tip of the tool. [Figure 11] 13 is an image diagram of the tool tip when the intersection point P2 in this embodiment is on the positive side and the negative side. FIG. [Figure 12]3A and 3B are an explanatory plan view and an explanatory front view showing a configuration example of a tip surface of the present embodiment. [Figure 13] 4 is a photograph showing an example of the evaluation results of glossiness in Experimental Example 1. [Figure 14] 1 is a graph showing the evaluation results of surface roughness (measurement results of arithmetic mean roughness Ra) in Experimental Example 1. [Figure 15] 4 is a photograph showing the observation result of a processed surface in Experimental Example 1. [Figure 16] 11 is a photograph showing the evaluation results of the glossiness of the 0° surface of each of the present embodiment and a conventional product in Experimental Example 4. [Figure 17] 13 is a graph showing evaluation results (measurement results of arithmetic mean roughness Ra) of the surface roughness of the 0° surface of the present embodiment and a conventional product in Experimental Example 4, processed for 20 minutes and 60 minutes, respectively. [Figure 18] 13 is a graph showing the evaluation results (measurement results of arithmetic mean roughness Ra) of the surface roughness of the 0° surface and the 45° surface of the present embodiment and the conventional product after machining for 20 minutes in Experimental Example 4. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] A preferred embodiment of the present invention will be briefly described below with reference to the drawings to illustrate the operation of the present invention.

[0028] In the present invention, since the tip of the tool is provided with a convex tip surface 6 that intersects with the tool rotation axis a of the tool body 1, there is no chisel edge with a large negative rake angle, and the occurrence of ripping due to the effect of the chisel edge is prevented as much as possible.

[0029] In addition, in the present invention, the intersecting ridge portion between the tip surface 6 and the cutting face 3 is configured as a center cutting edge 7 connected to the ball-shaped blade 5, so that the center cutting edge 7 has the same rake angle as the ball-shaped blade 5 and exhibits the same high cutting performance as the ball-shaped blade 5.

[0030] Moreover, in the present invention, since the tip surface 6 is formed in a convex shape, even if the perpendicularity of the tool rotation axis a to the plane is shifted in machining a plane perpendicular to the tool rotation axis a (for example, even if the tool bends due to cutting resistance and the tool rotation axis a becomes slightly inclined relative to the plane), the tip surface 6 comes into contact with the plane, and a burnishing effect is achieved by the sliding action of the tip surface 6 against the cutting surface.

[0031] In this way, in the present invention, when machining planes perpendicular to or intersecting the tool rotation axis a, the high cutting ability of the center cutting edge 7 and the burnishing effect caused by the sliding action of the tip face 6 against the cutting surface reduce the generation of cutting marks during cutting with the center cutting edge 7, and a machined surface with a glossiness equal to or greater than that obtained when cutting with the ball blade 5 is obtained. EXAMPLES

[0032] A specific embodiment of the present invention will now be described with reference to the drawings.

[0033] In this embodiment, a ball end mill is formed on the outer periphery of a tool body 1, with multiple chip discharge grooves 2 that open at the tip and run from the tool tip side to the tool base end side, and a ball blade 5 is provided on each of the intersecting ridges between the cutting faces 3 of these chip discharge grooves 2 and the tip clearance face 4 of the tool body 1, and a convex tip surface 6 is provided at the tool tip which intersects with the tool rotation axis a of the tool body 1 and is convex on the tip side in the direction of the tool rotation axis a, and the intersecting ridge between this tip surface 6 and the cutting face 3 is configured as a center side cutting edge 7 connected to the ball blade 5.

[0034] Specifically, in this embodiment, the ball end mill of the present invention is configured as a two-blade ball end mill (a ball end mill having a pair of ball blades 5) having two spiral chip discharge grooves 2 and a ball blade 5 on each of the intersecting ridges between two cutting faces 3 formed at the tip of the chip discharge grooves 2 and the tip clearance face 4 of the tool body 1, as shown in Figures 1 and 2.

[0035] In addition, this embodiment is not limited to the above-mentioned double-edged ball end mill configuration, and may be configured as a multi-edged ball end mill having three or more ball blades by providing ball blades in addition to the pair (two) of ball blades 5. In addition, in the figure, the arrow with the symbol T indicates the tool rotation direction.

[0036] More specifically, in this embodiment, a gash 11, which is part of the chip discharge groove 2, is formed at the tip of the cutting face 3 (the wall surface facing forward in the tool rotation direction) of the chip discharge groove 2 to provide a gash surface 12 facing forward in the tool rotation direction, and this gash surface 12 is used as the cutting face 3 at the tip of the tool.

[0037] In addition to the above configuration, this embodiment may also be configured as a so-called straight-edged ball end mill, in which a linear chip discharge groove 2 is provided, no gash 11 is provided, i.e., no gash surface 12 is provided, and the wall surface of the chip discharge groove 2 facing forward in the tool rotation direction is configured as the cutting face 3 at the tip of the tool, as in Example 1 shown in Figures 3 and 4.

[0038] In addition, in this embodiment, when viewed from the tip of the tool, the center side cutting edge 7 near the tool rotation axis a is arranged on the front side in the tool rotation direction with respect to the tool rotation axis a, that is, configured to have a so-called center-up shape.

[0039] Specifically, in this embodiment, when viewed from the tip of the tool, the chip discharge groove 2 (gash 11) that opens at the tip is provided away from the outer periphery of the tool relative to the tool rotation axis a so as to leave a core around the tool rotation axis a, and is configured in a center-upward shape in which a center side cutting edge 7 is provided near the tool rotation axis a on the edge of the tip of this chip discharge groove 2 (gash 11).

[0040] In addition, the chip discharge groove 2 (gash 11) that forms this center-up shape may be provided from the outer periphery of the tool beyond the tool rotation axis a, when viewed from the tip of the tool, or may be provided without extending beyond the tool rotation axis a.

[0041] Furthermore, this embodiment is not limited to the above-mentioned configuration, i.e., the center-upward shape configuration shown in Figures 1 to 4, but may be configured, for example, as in Alternative Example 2 shown in Figures 5 and 6, in which, when viewed from the tip of the tool, the center side cutting edge 7 near the tool rotation axis a is positioned rearward in the tool rotation direction relative to the tool rotation axis a, thus forming a so-called center-downward shape.

[0042] Each component of this embodiment will be described in detail below.

[0043] As shown in Figures 1 and 2, the tip flank 4 in this embodiment is composed of a first flank 4a that is inclined at a predetermined angle with respect to the tool rotation axis a, a second flank 4b that is provided on the rear side of the first flank 4a in the tool rotation direction and is inclined at an angle different from that of the first flank 4a, and a third flank 4c that is provided on the rear side of the second flank 4b in the tool rotation direction and is inclined at an angle different from that of the second flank 4b.

[0044] In addition, each ball blade 5 (a pair of ball blades 5) is provided at the intersection ridge between the first clearance 4a of each tip clearance 4 and the cutting face 3 (gash face 12) facing forward in the tool rotation direction, and is provided 180 degrees rotationally symmetrical with respect to the tool rotation axis a, as shown in Figure 1.

[0045] As described above, the tip surface 6 is configured as a convex surface that intersects with the tool rotation axis a at the tip of the tool and is convex toward the tip side in the direction of the tool rotation axis a.

[0046] Specifically, as shown in FIG. 1, the tip surface 6 is configured as a convex surface between the tip surface 4 (first surface 4a) of each ball-shaped blade 5 and connected to the tip surface 4 (first surface 4a) and the cutting surface 3 of each ball-shaped blade 5, and further, the intersecting ridge portion between this tip surface 6 and the cutting surface 3 of each ball-shaped blade 5 is connected to the ball-shaped blade 5, and this intersecting ridge portion is configured to become a central cutting edge 7 having the same rake angle as the ball-shaped blade 5.

[0047] In this embodiment, the central cutting edges 7 are provided in a pair, rotationally symmetrical at 180 degrees with respect to the tool rotation axis a.

[0048] In addition, the tip surface 6 includes the tool rotation axis a within the surface, and is configured as a convex surface in which, as shown in Figure 7, when viewed from the tip of the tool, the outer shape (profile) that linearly connects from an arbitrary point A on one of the central cutting edges 7 connected to one of the pair of ball blades 5, through the vicinity of the tool rotation axis a, to an arbitrary point B on the other central cutting edge 7 connected to the other ball blade 5, forms a mountain-shaped outer shape.

[0049] Specifically, the tip surface 6 is configured so that the outer shape (profile) is a mountain shape, and the maximum height of this mountain shape is 6 μm or less.

[0050] In this embodiment, as shown in Figure 8, the line segment L connecting point A and point B is used as a reference, and the difference between this line segment L and the highest point in the outer shape (profile) is defined as the maximum height (amount of convexity) of the mountain-shaped shape.

[0051] In this embodiment, the outer shape (profile) of the tip surface 6 is measured using a laser microscope to obtain profile data as shown in FIG.

[0052] Specifically, the outer shape (profile) of the tip face 6 as shown in Figure 9 is measured with a laser microscope in a direction linearly connecting point A on one center cutting edge 7 and point B on the other center cutting edge 7 when viewed from the tip of the tool, and the difference in distance from any appropriate position in the direction of the tool rotation axis a is plotted as data. In other words, the outer shape (profile) of the tip face 6 represents the shape of the tip face 6 viewed from the lateral direction of the tool (perpendicular to the tool rotation axis a).

[0053] As a result, it can be confirmed that the outer shape (profile) of the tip surface 6 has a mountain-like shape that is convex from the center cutting edge 7 side toward the center of the tool (the side of the tool rotation axis a), and that the tip surface 6 is a convex surface that is convex toward the tip side in the direction of the tool rotation axis a.

[0054] In addition, the tip surface 6 is configured so that the central cutting edge 7 is formed up to the vicinity of the tool rotation axis a. As a result, in this embodiment, when machining a plane perpendicular to the tool rotation axis a, a machined surface with excellent gloss and little rips can be obtained.

[0055] Specifically, in this embodiment, as described above, the tip surface 6 is connected to the tip flank 4 (first flank 4a). Also, as shown in FIG. 10, when viewed from the tip of the tool, with respect to the central cutting edge 7 or the perpendicular line 9 of the extension line 8 of the central cutting edge 7 passing through the tool rotation axis a, if the ball-shaped blade 5 side to which the central cutting edge 7 is connected is taken as the positive side and the opposite side is taken as the negative side, then the tip surface 6 is located at an intersection P2 (when viewed from the tip of the tool, the intersection P2 is the intersection between the ridge line 10 farther from the ball-shaped blade 5 out of the ridge lines 10 formed by the tip surface 6 and the tip flank 4 and the ridge line 10 farther from the ball-shaped blade 5 and the ball-shaped blade 5 and the ball-shaped blade 5). The central cutting edge 7 is provided so that the intersection point P1 (the intersection point between the central cutting edge 7 or an extension line 8 of the central cutting edge 7, when viewed from the tip of the tool, and a perpendicular line 9 to the extension line 8 of the central cutting edge 7 or the central cutting edge 7 passing through the tool rotation axis a) and the intersection point P2 is on the positive side such that the separation distance X in the direction along the central cutting edge 7 is 0% or more and 10% or less of the tool outer diameter, thereby enabling the central cutting edge 7 to be provided up to the vicinity of the tool rotation axis a.

[0056] Here, in this embodiment, as shown in Figs. 10 and 11, the center cutting edge 7 is formed in a straight line at the intersection ridge between the tip surface 6 and the rake face 3 (gash face 12) facing forward in the tool rotation direction. The center cutting edge 7 may be formed in a straight line throughout its entirety, or may be formed in a straight line partially. For example, a part of the center cutting edge 7 may be formed in a straight line from the intersection Q between the center cutting edge 7 and the ball blade 5 connected thereto (the intersection between the ball blade 5 and the edge of the tip of the chip discharge groove 2 having the center cutting edge 7 connected to the ball blade 5, among the ridges 10 formed by the tip surface 6 and the tip flank 4 (first flank 4a)) toward the inside of the tool (the opposite direction to the ball blade 5, i.e., the negative side). Fig. 11(b) described later is an example of such a mode in which a part of the center cutting edge 7 is formed in a straight line. In this case, the straight line portion is captured, the extension line 8 of the center side cutting edge 7 and the direction along the center side cutting edge 7 are determined, and the separation distance X is confirmed.

[0057] In addition, Figure 11 is an image diagram of the case where intersection point P2 is on the positive side and the case where intersection point P2 is on the negative side when viewed from the tip of the tool in this embodiment in which the center cutting edge 7 is formed in a straight line, (a) and (b) are image diagrams when intersection point P2 is on the positive side, and (c) and (d) are image diagrams when intersection point P2 is on the negative side.

[0058] Specifically, Figures 11(a) and (b) show an example in which intersection point P2 is located on the edge of the tip of the chip discharge groove 2 having the center cutting edge 7, and on the positive edge of the tip of the wall surface (cutting face 3) facing forward in the tool rotation direction, and Figure 11(b) shows an example in which the center cutting edge 7 is formed from a straight portion that extends from the intersection point Q with the ball blade 5 connected to this center cutting edge 7 toward the inside of the tool (the opposite direction to the ball blade 5, i.e., the negative side), and a curved portion that is connected to the edge of the wall surface facing backward in the tool rotation direction, and intersection point P2 is located on this curved portion.

[0059] Moreover, Figure 11(c) is an example where the intersection point P2 is located on the edge of the tip of the chip discharge groove 2 having the center cutting edge 7, and on the negative edge of the tip of the same surface as the wall surface (cutting face 3) facing forward in the tool rotation direction, and Figure 11(d) is an example where the intersection point P2 is located on the edge of the tip of the chip discharge groove 2 having the center cutting edge 7, and on the edge of the tip of the wall surface on the negative side facing rearward in the tool rotation direction.

[0060] As described above, the separation distance X in this embodiment is one of the invention elements (indexes) used when the intersection point P2 is on the positive side, but in order to facilitate understanding of the contents of Experimental Examples 2 and 3 described below, the part corresponding to the separation distance X is shown in parentheses in Figures 11(c) and (d). In this case, X takes a negative value.

[0061] Furthermore, the center cutting edge 7 is not limited to being linear, but may be curved. For example, as shown in Fig. 10 and Fig. 11(a), when the intersection point P2 is on the positive side, the center cutting edge 7 is formed in a straight line having end points at the intersection points Q and P2 in these figures, but the center cutting edge 7 may be formed in a curved line curved toward the front side or rear side in the tool rotation direction, or may be formed in a wavy line. In this case, the virtual line connecting the intersection points Q and P2 is regarded as the center cutting edge 7, and the extension line 8 of the center cutting edge 7 and the direction along the center cutting edge 7 are determined, and the separation distance X is confirmed.

[0062] Furthermore, as shown in FIG. 10, in view of the tip of the tool, the tip surface 6 in this embodiment has a width W defined as the distance between two ridges 10 formed by the tip surface 6 and each tip flank 4 (first flank 4a) of a pair of ball blades 5 arranged 180 degrees rotationally symmetrically about the tool rotation axis a, and the tip surface 6 is configured so that this width W satisfies 0.005 mm≦W≦0.2D (D: outer diameter of the tool).

[0063] Specifically, as a more preferred specification, the tip surface 6 of this embodiment is configured so that the width W is 0.01 mm≦W≦0.3 mm when the tool outer diameter is larger than φ1.5 mm, and is configured so that the width W is 0.01 mm≦W≦0.2D (D: tool outer diameter) when the tool outer diameter is equal to or smaller than φ1.5 mm.

[0064] The effects of the present embodiment configured as above will be described below.

[0065] In this embodiment, the tip of the tool is provided with a convex tip surface 6 that intersects with the tool rotation axis a of the tool body 1, so that there is no chisel edge with a large negative rake angle, and the occurrence of chipping due to the effect of the chisel edge is prevented as much as possible.

[0066] In addition, in this embodiment, the intersecting ridge portion between the tip surface 6 and the cutting face 3 is configured as a center cutting edge 7 connected to the ball-shaped blade 5, so that this center cutting edge 7 has the same rake angle as the ball-shaped blade 5 and exhibits the same high cutting performance as the ball-shaped blade 5.

[0067] Moreover, since the tip surface 6 in this embodiment is formed in a convex shape, even if the perpendicularity of the tool rotation axis a to the plane is shifted in machining a plane perpendicular to the tool rotation axis a (for example, even if the tool bends due to cutting resistance and the tool rotation axis a becomes slightly inclined relative to the plane), the tip surface 6 comes into contact with the plane, and a burnishing effect is achieved by the sliding action of the tip surface 6 against the cutting surface.

[0068] In this way, in this embodiment, when machining planes perpendicular to or intersecting the tool rotation axis a, the high cutting ability of the center cutting edge 7 and the burnishing effect caused by the sliding action of the tip face 6 against the cutting surface reduce the generation of cutting marks during cutting with the center cutting edge 7, and a machined surface with a glossiness equal to or greater than that achieved when cutting with the ball blade 5 is obtained.

[0069] In this embodiment, the tip surface 6 is connected to the tip flank 4 (first flank 4a). Furthermore, when viewed from the tip of the tool, with respect to a perpendicular line 9 of the center cutting edge 7 or an extension line 8 of the center cutting edge 7 passing through the tool rotation axis a, the tip surface 6 is located at an intersection P2 (the intersection P3 of the ridge line 10 formed by the tip surface 6 and the tip flank 4 (first flank 4a) on the side farther from the ball blade 5, and the intersection P4 of the chip discharge groove 2 having the ball blade 5 and the center cutting edge 7 connected to the ball blade 5, when the opposite side is taken as the positive side and the negative side, respectively. Since the center side cutting edge 7 is provided up to the vicinity of the tool rotation axis a, a machined surface with less burrs can be obtained when machining planes perpendicular to or intersecting the tool rotation axis a.

[0070] Furthermore, in this embodiment, the width W of the tip surface 6 is formed to be 0.005 mm≦W≦0.2D (D: tool outer diameter). Furthermore, as a more preferable specification, when the tool outer diameter is larger than φ1.5 mm, the width W is configured to be 0.01 mm≦W≦0.3 mm, and when the tool outer diameter is φ1.5 mm or less, the width W is configured to be 0.01 mm≦W≦0.2D (D: tool outer diameter). Therefore, the occurrence of ripping and welding of chips due to an increase in cutting resistance is suppressed, and the progress of wear of the tip surface 6 is suppressed, and a machined surface with a glossiness equal to or superior to that obtained when finished with the ball blade 5 is obtained.

[0071] In this manner, this embodiment is a ball end mill that is suitable for finishing machining in which a machined surface with excellent gloss can be obtained when cutting a plane perpendicular to the tool rotation axis a, such as the bottom surface of a mold using the tip of the tool, and the polishing step can be omitted or the polishing process labor can be reduced.

[0072] In this embodiment, the shape of the tip surface 6 is configured to be a cone shape as shown in Figure 12(a). However, the above-mentioned effects can also be obtained when the tip surface 6 is configured to be a square pyramid shape as shown in Figure 12(b), a gable roof shape composed of two sides as shown in Figure 12(c), or even a truncated cone shape having a flat surface at the top of the convex surface as shown in Figure 12(d).

[0073] The shape of the tip surface 6 shown in Figure 12(d) (frustum-shaped) is specifically an example in which it is configured as a truncated cone having a flat surface at the apex of a cone-shaped convex surface as shown in Figure 12(a) , but although not shown, it may also be a truncated pyramid having a flat surface at the apex of a quadrangular pyramid-shaped convex surface as shown in Figure 12(b) .

[0074] In the actual embodiment, since the amount of convexity is small, the apex of the cone shape in Fig. 12(a) may not be clearly visible when viewed from the tip of the tool. Similarly, the intersecting ridge between the tip faces 6 as shown in the plan views (as viewed from the tip of the tool) in Figs. 12(b) to (d) may not be clearly visible.

[0075] In any case of Figures 12(a) to (d), the outer shape (profile) of the tip surface 6 has a mountain shape that is convex from the central cutting edge 7 side toward the tool center side (the tool rotation axis a side). Specifically, in Figures 12(a) to (c), it has a triangular mountain shape, and in Figure 12(d), it has a trapezoidal mountain shape.

[0076] In addition, although not shown, the above-mentioned effects can also be obtained when the shape of the tip surface 6 is curved so as to be convex toward the tip side in the direction of the tool rotation axis a, or when the flat surface at the top of a truncated cone as shown in Figure 12(d) is replaced with a curved surface that is convex toward the tip side in the direction of the tool rotation axis a.

[0077] Next, an experimental example that supports the effect of this embodiment will be described.

[0078] <Experimental Example 1> Experimental Example 1 was intended to confirm the state of the finished machined surface relative to the amount of convexity of the tip face 6. A number of samples were produced in which the amount of convexity (maximum height of the profile shape of the tip face 6) in the external shape of the tip face 6 connecting arbitrary points on the two central cutting edges 7 passing near the tool rotation axis a was changed, and the gloss of the machined surface was evaluated when each sample was used to cut a workpiece under the following machining conditions.

[0079] Specifically, the tool specifications were as follows: outer diameter: φ6 mm, shank diameter: φ6 mm, effective length: 30 mm; and outer diameter: φ3 mm, shank diameter: φ6 mm, effective length: 12 mm. The machining time was 20 minutes for each case. When the tool outer diameter was φ6 mm, the glossiness of the machined surface when a plane perpendicular to the tool rotation axis a was machined with the tip of the tool was evaluated by visual inspection of the appearance (appearance of the reflected image). When the tool outer diameter was φ3 mm, in addition to the above visual inspection of the appearance as when the tool outer diameter was φ6 mm, the surface roughness was also evaluated and the machined surface was observed.

[0080] In detail, in the visual appearance evaluation, multiple clear circles were repeatedly arranged in the longitudinal direction on the reverse side of a scale (a metal ruler), and the scale was set on the machined surfaces so that the surface on which the circles were repeatedly arranged was perpendicular to each machined surface, and the appearance of the circles (reflected images) reflected on the machined surfaces was comparatively evaluated.

[0081] In addition, in the evaluation of surface roughness, the arithmetic mean roughness Ra was measured, and in the observation evaluation of the machined surface, the machined surface was enlarged and the state of cutting marks or tearing on the machined surface was observed.

[0082] In producing samples having a plurality of desired convex amounts as shown in Table 1 below, for samples having a tool outer diameter of φ6 mm, the width W of the tip surface 6 was appropriately set in the range of 0.01 mm to 0.100 mm, and the separation distance X was appropriately set in the range of -0.038 mm to 0.055 mm, respectively. For samples having a tool outer diameter of φ3 mm, the width W of the tip surface 6 was appropriately set in the range of 0.01 mm to 0.100 mm, and the separation distance X was appropriately set in the range of -0.029 mm to 0.028 mm, respectively.

[0083] [Processing conditions when the tool outer diameter is φ6mm] Work material: Pre-hardened steel (30HRC) Rotation speed: 13,000 min -1 Feed speed: 1,500mm / min Axial cutting depth: 0.05 mm Radial depth of cut: 0.1 mm Coolant: Water-soluble cutting fluid

[0084] [Machining conditions when the tool outer diameter is φ3mm] Work material: Pre-hardened steel (30HRC) Rotation speed: 19,000 min -1 Feed speed: 950mm / min Axial cutting depth: 0.05 mm Radial cutting depth: 0.05 mm Coolant: Water-soluble cutting fluid

[0085] [result] Table 1 below shows the evaluation results of the glossiness of each sample with a tool outer diameter of φ6 mm and a tool outer diameter of φ3 mm.

[0086] Regarding the evaluation results of glossiness, a mark of ⊚ was used for a surface with a glossiness equal to or greater than that of the machined surface finished with the ball blade 5, a mark of ◯ for a surface with a glossiness better than that of the machined surface finished with the conventional chisel edge, and a mark of × for a surface with a glossiness equal to that of the machined surface finished with the conventional chisel edge. The machined surface finished with the ball blade 5 was a flat surface inclined at 45° to the tool rotation axis a.

[0087] [Table 1]

[0088] As shown in Table 1, it was confirmed that in both cases where the tool outer diameter was φ6 mm and where the tool outer diameter was φ3 mm, when the amount of protrusion was 6.00 μm or less, a better gloss was obtained than that of the machined surface finished with the conventional chisel edge. In particular, when the amount of protrusion was 4.00 μm or less, it was confirmed that an excellent gloss equivalent to or greater than that of the machined surface finished with the ball blade 5 was obtained, as shown in FIG. 13. Note that FIG. 13 shows the results of visual appearance inspection (appearance of reflected image) when the tool outer diameter was φ3 mm (amount of protrusion: 0.30 μm to 1.00 μm), but the same is true when the tool outer diameter was φ6 mm.

[0089] Table 2 below and FIG. 14 show the evaluation results of surface roughness (measurement results of arithmetic mean roughness Ra) when the tool outer diameter is φ3 mm.

[0090] [Table 2]

[0091] As shown in Table 2, it was confirmed that the smaller the amount of protrusion, the smaller the surface roughness (arithmetic mean roughness Ra).

[0092] In addition, Fig. 15 shows the observation results of the machined surface when the tool outer diameter is φ3 mm. As shown in Fig. 15, it was confirmed that the smaller the amount of convexity, the smaller the cutting marks or ripping on the machined surface, which corresponds to the surface roughness evaluation results shown in Table 2 and Fig. 14.

[0093] As described above, experimental example 1 has confirmed that by configuring the tip surface 6 so that the convexity amount (maximum height of the profile shape of the tip surface 6) in the outer shape of the tip surface 6 connecting any points on the two center cutting edges 7 passing near the tool rotation axis a is 6.00 μm or less, a machined surface with good gloss can be obtained, and by configuring it preferably to be 4.00 μm or less, a machined surface with gloss equal to or better than that of a machined surface finished with a ball blade 5 can be obtained.

[0094] <Experimental Example 2> Experimental Example 2 is for confirming the appropriate formation range of the tip surface 6 based on the position of the center side cutting edge 7 formed by providing the tip surface 6. As shown in FIG. 10, in the view of the tip of the tool, the center side cutting edge 7 or the extension line 8 of the center side cutting edge 7 and the intersection point P1 of the center side cutting edge 7 or the extension line 8 of the center side cutting edge 7 passing through the tool rotation axis a, and the intersection point P2 of the ridge line 10 formed by the tip surface 6 and the tip flank 4 (first flank 4a) farther from the ball blade 5 and the tip edge of the chip discharge groove 2 having the ball blade 5 and the center side cutting edge 7 connected to the ball blade 5. By changing the separation distance X in the direction along the center side cutting edge 7, samples were produced in which the position of the center side cutting edge 7 was changed, and the gloss of the machined surface was evaluated when the workpiece was cut using each sample under the following machining conditions.

[0095] Specifically, the tool specifications were as follows: outer diameter: φ6 mm, shank diameter: φ6 mm, effective length: 30 mm, and outer diameter: φ3 mm, shank diameter: φ6 mm, effective length: 12 mm. The machining times were 20 minutes and 60 minutes, respectively. The gloss of the machined surface when a plane perpendicular to the tool rotation axis a was machined with the tip of the tool was evaluated by visual inspection.

[0096] Regarding the tool specifications, the amount of convexity of the tip face 6 of each sample was set to 0.30 μm based on the results of Experimental Example 1. When the tool outer diameter was φ6 mm, the width W of the tip face 6 (the opposing distance between two ridge lines 10 formed by the tip face 6 and each tip flank 4 (first flank 4a) of the pair of ball-shaped blades 5 in FIG. 10) was set to 0.02 mm, and when the tool outer diameter was φ3 mm, the width W of the tip face 6 was set to 0.01 mm. However, in manufacturing the tools, the diameter ratio X / D of the separation distance X to the tool outer diameter (D: tool outer diameter, hereinafter simply referred to as "diameter ratio X / D") = 0, i.e., when the separation distance X = 0.00, when the tool outer diameter is φ6 mm, W = 0.1 mm, and when the tool outer diameter is φ3 mm, W = 0.05 mm. Also, when the diameter ratio X / D = -0.01, when the tool outer diameter is φ6 mm, W = 0.2 mm, and when the tool outer diameter is φ3 mm, W = 0.1 mm.

[0097] [Processing conditions when the tool outer diameter is φ6mm] Work material: Pre-hardened steel (30HRC) Rotation speed: 13,000 min -1 Feed speed: 1,500mm / min Axial cutting depth: 0.05 mm Radial depth of cut: 0.1 mm Coolant: Water-soluble cutting fluid

[0098] [Machining conditions when the tool outer diameter is φ3mm] Work material: Pre-hardened steel (30HRC) Rotation speed: 19,000 min -1 Feed speed: 950mm / min Axial cutting depth: 0.05 mm Radial cutting depth: 0.05 mm Coolant: Water-soluble cutting fluid

[0099] [result] Table 3 below shows the specifications (separation distance X, diameter ratio X / D) and gloss evaluation results of each sample when the tool outer diameter is φ6mm, and Table 4 below shows the specifications (separation distance X, diameter ratio X / D) and gloss evaluation results of each sample when the tool outer diameter is φ3mm.

[0100] With regard to the separation distance X in Tables 3 and 4 below, the case where the intersection point P2 is on the negative side with respect to the central cutting edge 7 passing through the tool rotation axis a or the perpendicular line 9 to the extension line 8 of the central cutting edge 7 is expressed as a negative value. Also, the separation distance X when the intersection point P2 and the intersection point P1 are the same is expressed as 0.00.

[0101] Regarding the evaluation results of glossiness, a mark of ⊚ was used for a surface that was equal to or better than the surface finished with the ball blade 5, a mark of ◯ was used for a surface that was better than the surface finished with the conventional chisel edge, and a mark of × was used for a surface that was equal to the surface finished with the conventional chisel edge. In this experimental example, the surface finished with the ball blade 5 was a flat surface inclined at 45° to the tool rotation axis a.

[0102] [Table 3]

[0103] [Table 4]

[0104] As shown in Tables 3 and 4, in both cases where the tool outer diameter was φ6 mm and where the tool outer diameter was φ3 mm, it was confirmed that in the case where the diameter ratio X / D was greater than 0.1, that is, the separation distance X was greater than 10% of the tool outer diameter, the glossiness was equivalent to that of the conventional chisel edge for both the 20-minute and 60-minute machining times. This is because, when the separation distance X was greater than 10% of the tool outer diameter, the center cutting edge 7 with high cutting performance was located away from the tool rotation axis a, and in the area closer to the tool rotation axis a, the ridge 10 between the tip face 6 and the tip flank 4 (first flank 4a) acted as a cutting edge with a large negative rake angle, causing gouging on the machined surface, and the subsequent sliding action of the tip face 6 against the cutting surface did not provide a sufficient burnishing effect.

[0105] In addition, it was confirmed that in the case where the diameter ratio X / D is 0.1 or less, i.e., the separation distance X is 10% or less of the tool outer diameter, the machined surface finished with the conventional chisel edge had a better gloss than that of the conventional chisel edge in both the case where the machining time was 20 minutes and 60 minutes. In particular, it was confirmed that in the case where the diameter ratio X / D is 0.08 or less, i.e., the separation distance X is 8% or less of the tool outer diameter, the machined surface finished with the ball blade 5 had a gloss equivalent to or better than that of the ball blade 5.

[0106] As described above, from Experimental Example 2, it was confirmed that by providing the tip surface 6 so that the central cutting edge 7 is provided up to the vicinity of the tool rotation axis a, a machined surface with excellent gloss can be obtained.

[0107] Specifically, when viewed from the tip of the tool, with respect to the central cutting edge 7 or the perpendicular line 9 of the extension line 8 of the central cutting edge 7 passing through the tool rotation axis a, the side of the ball blade 5 to which the central cutting edge 7 is connected is defined as the positive side, and the opposite side is defined as the negative side, the intersection P2 is either on the negative side, or on the positive side where the separation distance X between the intersection P1 and the intersection P2 in the direction along the central cutting edge 7 is 0% or more and 10% or less of the tool outer diameter (0.1D or less (D: tool outer diameter)), preferably 0% or more and 8% or less (0.08D or less (D: tool outer diameter)), it has been confirmed that a machined surface with excellent gloss can be obtained by arranging the tip surface 6 so that

[0108] <Experimental Example 3> Experimental Example 3 was intended to confirm the appropriate formation range of the tip face 6 based on the width W of the tip face 6. As shown in FIG. 10, when viewed from the tip of the tool, the opposing distance between two ridge lines 10 formed by the tip face 6 and each of the tip flanks 4 (first flanks 4a) of a pair of ball-shaped blades 5 was defined as the width W of the tip face 6. Samples were produced in which the width W of the tip face 6 was changed, and each sample was used to evaluate the gloss of the machined surface when cutting a workpiece under the following machining conditions.

[0109] Specifically, the tool specifications were as follows: outer diameter: φ6 mm, shank diameter: φ6 mm, effective length: 30 mm; outer diameter: φ3 mm, shank diameter: φ6 mm, effective length: 12 mm; and outer diameter: φ1.5 mm, shank diameter: φ4 mm, effective length: 6 mm. The machining times were 20 minutes and 60 minutes, respectively. The gloss of the machined surface when a plane perpendicular to the tool rotation axis a was machined with the tip of the tool was evaluated by visual inspection of the appearance.

[0110] Regarding the tool specifications, the amount of protrusion of the tip surface 6 of each sample was set to 0.30 μm, similar to Experimental Example 2. Also, the separation distance X was set to an appropriate value for each sample, as shown in Tables 5 to 7 below.

[0111] [Processing conditions when the tool outer diameter is φ6mm] Work material: Pre-hardened steel (30HRC) Rotation speed: 13,000 min -1 Feed speed: 1,500mm / min Axial cutting depth: 0.05 mm Radial depth of cut: 0.1 mm Coolant: Water-soluble cutting fluid

[0112] [Machining conditions when the tool outer diameter is φ3mm] Work material: Pre-hardened steel (30HRC) Rotation speed: 19,000 min -1 Feed speed: 950mm / min Axial cutting depth: 0.05 mm Radial cutting depth: 0.05 mm Coolant: Water-soluble cutting fluid

[0113] [Processing conditions when the tool outer diameter is φ1.5mm] Work material: Pre-hardened steel (30HRC) Rotation speed: 20,000 min -1 Feed speed: 400mm / min Axial cutting depth: 0.015mm Radial cutting depth: 0.03 mm Coolant: Water-soluble cutting fluid

[0114] [result] Table 5 below shows the specifications (width W of tip surface 6, diameter ratio W / D of width W of tip surface 6 to tool outer diameter (D: tool outer diameter, hereafter simply referred to as "diameter ratio W / D"), separation distance X) and gloss evaluation results of each sample when the tool outer diameter is φ6 mm, Table 6 below shows the specifications (width W of tip surface 6, diameter ratio W / D, separation distance X) and gloss evaluation results of each sample when the tool outer diameter is φ3 mm, and Table 7 below shows the specifications (width W of tip surface 6, diameter ratio W / D, separation distance X) and gloss evaluation results of each sample when the tool outer diameter is φ1.5 mm.

[0115] In addition, with respect to the separation distance X in Tables 5 to 7 below, the intersection point P2 on the negative side of the center cutting edge 7 passing through the tool rotation axis a or the perpendicular line 9 of the extension line 8 of the center cutting edge 7 is indicated by a negative value. In addition, with respect to the evaluation results of glossiness, a mark of ◎ indicates that the glossiness was equal to or better than that of the machined surface finished with the ball cutting edge 5, a mark of ○ indicates that the glossiness was better than that of the machined surface finished with the conventional chisel edge, and a mark of × indicates that the glossiness was equal to that of the machined surface finished with the conventional chisel edge. In addition, in this experimental example 4, the machined surface finished with the ball cutting edge 5 was a flat surface inclined at 45° to the tool rotation axis a.

[0116] [Table 5]

[0117] [Table 6]

[0118] [Table 7]

[0119] As shown in Tables 5 to 7, in all cases where the tool outer diameter was φ6 mm, φ3 mm, and φ1.5 mm, it was confirmed that in the case where the width W of the tip surface 6 was 0.002 mm, scraping occurred and the surface finished with the conventional chisel edge had the same glossiness as that of the surface finished with the conventional chisel edge for both 20 and 60 minutes of machining time, but in the case where the width W of the tip surface 6 was 0.005 mm, it was confirmed that the surface finished with the conventional chisel edge had a better glossiness than that of the surface finished with the conventional chisel edge. This is thought to be because when the width W of the tip surface 6 is less than 0.005 mm, the burnishing effect due to the sliding contact action of the tip surface 6 becomes smaller.

[0120] Furthermore, as shown in Tables 5 and 6, when the tool outer diameter was φ6 mm and when the tool outer diameter was φ3 mm, it was confirmed that in the specifications where the width W of the tip surface 6 was 0.01 mm or more and the diameter ratio W / D was 0.2 or less (i.e., the width W of the tip surface 6 was 20% or less of the tool outer diameter), the machined surface had better gloss than that finished with a conventional chisel edge. In particular, it was confirmed that in the above-mentioned width W specification in the early stage of machining (machining time 20 minutes) and in the specification where the width W of the tip surface 6 was 0.01 mm or more and 0.3 mm or less in the case where the machining time was 60 minutes, the machined surface had a gloss equivalent to or better than that finished with a ball blade 5.

[0121] Furthermore, as shown in Table 7, when the tool outer diameter is φ1.5 mm, in the case where the width W of the tip surface 6 is 0.01 mm or more and the diameter ratio W / D is 0.2 or less (i.e., the width W of the tip surface 6 is 20% or less of the tool outer diameter, and therefore the width W of the tip surface 6 is 0.3 mm or less), it was confirmed that the machining time was either 20 minutes or 60 minutes, and the machining surface had a glossiness equal to or better than that of a surface finished with a ball blade 5.

[0122] In addition, in all cases where the tool outer diameter was φ6 mm, φ3 mm, and φ1.5 mm, it was confirmed that in the case where the diameter ratio W / D was greater than 0.2, that is, the width W of the tip face 6 was greater than 20% of the tool outer diameter, the machined surface had a better gloss than that finished with the conventional chisel edge at the beginning of machining (machining time 20 minutes), but at the machining time of 60 minutes, the gloss decreased and it was confirmed that the gloss was equivalent to that of the machined surface finished with the conventional chisel edge. This is thought to be because the width W of the tip face 6 was greater than 20% of the tool outer diameter, which increased the cutting resistance, causing chipping and welding from the beginning of machining, and the subsequent sliding action of the tip face 6 against the cutting surface did not provide a sufficient burnishing effect.

[0123] As described above, experimental example 3 confirmed that by forming the tip surface 6 so that the width W of the tip surface 6 satisfies 0.005 mm≦W≦0.2D (D: outer diameter of the tool), a machined surface with excellent gloss can be obtained.

[0124] Furthermore, it has been confirmed that, preferably, when the tool outer diameter is greater than φ1.5 mm, the tip surface 6 is formed so that the width W of the tip surface 6 satisfies 0.01 mm≦W≦0.3 mm, and, when the tool outer diameter is equal to or less than φ1.5 mm, the tip surface 6 is formed so that the width W of the tip surface 6 satisfies 0.01 mm≦W≦0.2D (D: tool outer diameter), thereby obtaining a machined surface with superior gloss.

[0125] Although not shown in Tables 5 to 7, in the process of carrying out the above-mentioned experimental example 3, even if it was confirmed that the width W of the tip surface 6 is a specification that results in a glossiness (rating of ◎) equivalent to or greater than that of a machined surface finished with the above-mentioned ball blade 5, when viewed from the tip of the tool, the diameter of the circle that forms the rotational trajectory of the tip surface 6 is greater than 35% of the outer diameter of the tool, so that the glossiness does not necessarily result in a glossiness (rating of ◎) equivalent to or greater than that of a machined surface finished with a ball blade 5, and it was confirmed that there may be cases in which the glossiness is better than that of a machined surface finished with a conventional chisel edge (rating of ○).

[0126] This is believed to be because the diameter of the circle that forms the rotational trajectory of the tip surface 6 is larger than 35% of the outer diameter of the tool, which increases the cutting resistance and prevents a good cut surface from being obtained, and therefore the subsequent sliding action of the tip surface 6 against the cut surface does not provide a sufficient burnishing effect to obtain a machined surface with excellent gloss.

[0127] In view of the above, it is preferable to form the tip face 6 so that, when viewed from the tip of the tool, the diameter of the circle which forms the rotation locus of the tip face 6 is 35% or less of the outer diameter of the tool, in other words, so that the longest distance between the tool rotation axis a and the outer edge of the tip face 6, which is the radius of the largest circle which forms the rotation locus of the tip face 6, is 17.5% or less of the outer diameter of the tool.

[0128] <Experimental Example 4> Experimental Example 4 is a comparative evaluation of this embodiment and a conventional product (a ball end mill with a tip shape having a chisel edge at the tool tip). In this embodiment, the amount of protrusion of the tip surface 6 was 1.00 μm, the width W of the tip surface 6 was 0.025 mm, and the separation distance X was 0.005 mm. The only difference between this embodiment and the conventional product is whether the tip surface 6 or the chisel edge is present at the tool tip, that is, the ball blade 5 and other parts have the same specifications. Using this embodiment and the conventional product with these specifications, the glossiness and surface roughness of the machined surface when cutting a workpiece under the following processing conditions were evaluated.

[0129] Specifically, for both the present embodiment and the conventional product, the tool specifications were outer diameter: φ3 mm, shank diameter: φ6 mm, and effective length: 12 mm. The plane perpendicular to the tool rotation axis a (hereinafter referred to as the "0° surface") was used with the tool tip, and the plane inclined at 45° to the tool rotation axis a (hereinafter referred to as the "45° surface") was used with a ball blade 5. The gloss of the machined surfaces after 20 minutes and 60 minutes of machining was evaluated by visual appearance (appearance of the reflected image), and the surface roughness was evaluated by measuring the arithmetic mean roughness Ra.

[0130] [Processing conditions] Work material: Pre-hardened steel (30HRC) Rotation speed: 19,000 min -1 Feed speed: 950mm / min Axial cutting depth: 0.05 mm Radial cutting depth: 0.05 mm Coolant: Water-soluble cutting fluid

[0131] [result] FIG. 16 shows the evaluation results of the glossiness of the 0° surface of the present embodiment and the conventional product. Specifically, on the back side of the scale (gold ruler) at the top of the figure, multiple clear circles are repeatedly arranged in the longitudinal direction of the scale (gold ruler), and the surface on which the circles are repeatedly arranged is held over each processed surface (0° surface), and the appearance of the circles (reflected image) reflected on the processed surface (0° surface) is compared and evaluated. As shown in FIG. 16, for the 0° surface, the present embodiment obtained a processed surface with such excellent gloss that a clear reflected image (circle) was visually confirmed in both the 20-minute and 60-minute processing times, whereas the conventional product had a processed surface without gloss, where the reflected image (circle) could not be confirmed.

[0132] Regarding the 45° surface (surface machined with the ball blade 5), a comparison was made between this embodiment and the conventional product with a machining time of 20 minutes. As the ball blade 5 had the same specifications, no difference was observed between the two, and although not shown, it was confirmed that both produced machined surfaces with such excellent gloss that a clear reflected image could be visually confirmed.

[0133] FIG. 17 is a graph showing the measurement results of the arithmetic mean roughness Ra of the 0° surface for this embodiment and the conventional product after machining times of 20 minutes and 60 minutes, and FIG. 18 is a graph showing the measurement results of the arithmetic mean roughness Ra of the 0° surface and the 45° surface for this embodiment and the conventional product after machining times of 20 minutes.

[0134] As shown in FIG. 17, it was confirmed that the arithmetic mean roughness Ra of the machined surface of this embodiment was smaller than that of the conventional product.

[0135] Furthermore, as shown in Figure 18, in general, as in conventional products, the 0° surface machined with the chisel edge at the tip of the tool has a greater surface roughness than the 45° surface machined with a ball blade. However, in this embodiment, as shown in Figure 18, both the 45° surface and the 0° surface have good surface roughness, and it was confirmed that the 0° surface machined with the tool tip having tip surface 6 has a better surface roughness than the 45° surface machined with ball blade 5.

[0136] As described above, from Experimental Example 4, it has been confirmed that in this embodiment, by providing the tip surface 6 at the tool tip so that the center cutting edge 7 is provided up to the vicinity of the tool rotation axis a, even in flat surface machining perpendicular to the tool rotation axis a using this tool tip, a machined surface having a glossiness equal to or greater than that of a machined surface using a ball blade 5 can be obtained.

[0137] It should be noted that the present invention is not limited to the present embodiment, and the specific configuration of each component can be designed as appropriate. [Explanation of symbols]

[0138] 1 Tool body 2 Chip discharge groove 3. Scooping surface 4 Tip flank 5 Ball Blade 6 Tip surface 7 Center cutting edge 8 Extension line 9 Perpendicular 10 Ridgeline a Tool rotation axis X Separation distance

Claims

1. A ball end mill having a plurality of chip discharge grooves formed on the outer periphery of a tool body, the grooves opening at the tip and running from the tool tip side to the tool base end side, and a ball blade provided on each of the intersecting ridges between the cutting faces of the chip discharge grooves and the tip relief surface of the tool body, characterized in that the tool tip is provided with a convex tip surface that intersects with the tool rotation axis of the tool body, and the intersecting ridge between the tip surface and the cutting face is configured as a center cutting edge connected to the ball blade.

2. 2. The ball end mill according to claim 1, wherein the tip surface is disposed between the tip flanks of a pair of ball blades arranged 180 degrees rotationally symmetrically about the tool rotation axis, and is connected to the tip flanks and each of the cutting faces.

3. In the ball end mill described in claim 2, the tip surface includes the tool rotation axis, and is configured so that, when viewed from the tool tip, a profile linearly connecting an arbitrary point on one of the center cutting edges connected to one of the pair of ball blades passing near the tool rotation axis and an arbitrary point on the other center cutting edge connected to the other is in a mountain shape.

4. In the ball end mill described in claim 3, the tip surface includes the tool rotation axis, and is configured so that, when viewed from the tip of the tool, a profile linearly connecting an intersection point between one of the center cutting edges connected to one of the pair of ball blades and one ridge line formed by the tip surface and one of the tip flank faces, and an intersection point between the other of the center cutting edges connected to the other of the pair of ball blades and the other ridge line formed by the tip surface and the other tip flank face, is in a mountain shape, and further, the ball end mill is configured so that the maximum height of the mountain shape is 6 μm or less.

5. 5. The ball end mill according to claim 1, wherein the center cutting edge is provided up to the vicinity of the tool rotation axis.

6. A ball end mill as described in any one of claims 1 to 4, wherein the tip surface is connected to the tip relief surface, and the tip surface is arranged so that, when viewed from the tip of the tool, when the ball blade side to which the center side cutting edge is connected is defined as the positive side and the opposite side is defined as the negative side with respect to a perpendicular line to the center side cutting edge or an extension line of the center side cutting edge passing through the tool rotation axis, the intersection P2 of 2 below is either on the negative side, or on the positive side where the distance between intersection P1 and intersection P2 of 1 below in the direction along the center side cutting edge is 0% or more and 10% or less of the tool outer diameter. Note 1 Intersection P1: When viewed from the tip of the tool, an intersection point between the center side cutting edge or an extension line of the center side cutting edge and a perpendicular line of the center side cutting edge or the extension line of the center side cutting edge passing through the tool rotation axis Note 2 Intersection point P2: When viewed from the tip of the tool, the intersection point between the ridgeline formed by the tip face and the tip flank face that is farther from the ball-shaped blade and the edge of the tip of the chip discharge groove having the ball-shaped blade and the center cutting edge connected to the ball-shaped blade.

7. In the ball end mill described in claim 5, the tip surface is connected to the tip relief surface, and this tip surface is arranged so that, when viewed from the tip of the tool, when the ball blade side to which the center side cutting edge is connected is defined as the positive side and the opposite side is defined as the negative side with respect to a perpendicular line to the center side cutting edge or an extension line of the center side cutting edge passing through the tool rotation axis, the intersection P2 of 2 below is either on the negative side, or on the positive side where the distance between intersection P1 and intersection P2 of 1 below in the direction along the center side cutting edge is 0% or more and 10% or less of the tool outer diameter. Note 1 Intersection P1: When viewed from the tip of the tool, an intersection point between the center side cutting edge or an extension line of the center side cutting edge and a perpendicular line of the center side cutting edge or the extension line of the center side cutting edge passing through the tool rotation axis Note 2 Intersection point P2: When viewed from the tip of the tool, the intersection point between the ridgeline formed by the tip face and the tip flank face that is farther from the ball-shaped blade and the edge of the tip of the chip discharge groove having the ball-shaped blade and the center cutting edge connected to the ball-shaped blade.

8. 5. The ball end mill according to claim 1, wherein the tip surface is configured such that, when viewed from the tip of the tool, the width W of the tip surface is the distance between two ridgelines formed by the tip surface and each of the tip relief faces of a pair of the ball blades arranged 180 degrees rotationally symmetrically about the tool rotation axis, and the width W of the tip surface is 0.005 mm≦W≦0.2D (D: tool outer diameter).

9. 6. The ball end mill according to claim 5, wherein the tip surface is configured such that, when viewed from the tip of the tool, the width W of the tip surface is the distance between two ridgelines formed by the tip surface and each of the tip relief faces of a pair of the ball blades arranged 180 degrees rotationally symmetrically about the tool rotation axis, and the width W of the tip surface is 0.005 mm≦W≦0.2D (D: tool outer diameter).

10. 7. The ball end mill according to claim 6, wherein the tip surface is configured such that, when viewed from the tip of the tool, the width W of the tip surface is the distance between two ridgelines formed by the tip surface and each of the tip relief faces of a pair of the ball blades arranged 180 degrees rotationally symmetrically about the tool rotation axis, and the width W of the tip surface is 0.005 mm≦W≦0.2D (D: tool outer diameter).

11. 8. The ball end mill according to claim 7, wherein the tip surface is configured such that, when viewed from the tip of the tool, the width W of the tip surface is the distance between two ridgelines formed by the tip surface and each of the tip relief faces of a pair of the ball blades arranged 180 degrees rotationally symmetrically about the tool rotation axis, and the width W of the tip surface is 0.005 mm≦W≦0.2D (D: tool outer diameter).

12. 9. The ball end mill according to claim 8, wherein the width W of the tip surface is set within the following range: When the tool outer diameter is greater than φ1.5 mm, 0.01 mm ≦ W ≦ 0.3 mm When tool outer diameter≦φ1.5mm, 0.01mm≦W≦0.2D (D: tool outer diameter)

13. 10. The ball end mill according to claim 9, wherein the width W of the tip surface is set within the following range: When the tool outer diameter is greater than φ1.5 mm, 0.01 mm ≦ W ≦ 0.3 mm When tool outer diameter≦φ1.5mm, 0.01mm≦W≦0.2D (D: tool outer diameter)

14. 11. The ball end mill according to claim 10, wherein the width W of the tip surface is set within the following range: When the tool outer diameter is greater than φ1.5 mm, 0.01 mm ≦ W ≦ 0.3 mm When tool outer diameter≦φ1.5mm, 0.01mm≦W≦0.2D (D: tool outer diameter)

15. 12. The ball end mill according to claim 11, wherein the width W of the tip surface is set within the following range: When the tool outer diameter is greater than φ1.5 mm, 0.01 mm ≦ W ≦ 0.3 mm When tool outer diameter≦φ1.5mm, 0.01mm≦W≦0.2D (D: tool outer diameter)

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