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 path. The ball blade, with its appropriately designed rake angle and clearance angle, can be used to cut complex curved surfaces and draft slope surfaces (inclined flat surfaces) of molds, resulting in a good machined surface.

[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, which makes it difficult to obtain a good machined surface when machining flat surfaces 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 glossy, well-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] Japanese Patent Application Laid-Open No. 2000-233311 Summary of the Invention [Problem to be solved by the invention]

[0006] The ball end mill of Patent Document 1 has two ball cutting edges arranged in a center-up position, and the chisel angle of the chisel edge formed by the flanks of the two ball cutting edges is set to 155 degrees or more, or the ratio of the spacing between the inner edges of the rake faces of the two cutting edges formed by gash on the ball cutting edges 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 with chisel edges have been in widespread use for some time, and because this chisel edge is an intersecting ridge where the relief faces 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 of the chisel edge are adjusted to appropriate values ​​as disclosed in Patent Document 1, it is difficult to obtain a machined surface (flat surface) with such high gloss that the 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 machining, which can 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 can omit the polishing step or reduce the polishing processing labor. [Means for solving the problem]

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

[0010] A ball end mill is provided with a plurality of chip discharge grooves 2 on the outer periphery of a tool body 1, which are open at the tip and extend from the tool tip side to the tool base end side, and a ball-shaped cutting edge 5 is provided at each of the intersection ridges between the rake faces 3 of the chip discharge grooves 2 and the tip flank 4 of the tool body 1, and a convex tip face 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 the tip face 6 and the rake face 3 forms a center cutting edge 7 connected to the ball-shaped cutting edge 5. The tip surface 6 is configured to slide in contact with the cutting surface cut by the center cutting edge 7. The present invention relates to a ball end mill characterized by the above.

[0011] Furthermore, in the ball end mill described in claim 1, the tip surface 6 is characterized in that it is arranged between the tip flanks 4 of each of the pair of ball cutting edges 5 arranged 180 degrees rotationally symmetrically about the tool rotation axis a, so as to be continuous with the tip flanks 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 tip of the tool, the profile linearly connecting any point on one of the center cutting edges 7 connected to one of the pair of ball blades 5 passing near the tool rotation axis a and any point on the other center 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 surfaces 4, and the intersection of the other ridge line 10 formed by the other center cutting edge 7 connected to the other, the tip surface 6 and the other tip flank surface 4, is configured to be 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.

[0014] Furthermore, in the ball end mill described in any one of claims 1 to 4, the tip surface 6 is connected to the tip relief surface 4, and this tip surface 6 is arranged so that, when viewed from the tip of the tool, with respect to the center cutting edge 7 or a perpendicular line 9 of an extension line 8 of the center cutting edge 7 passing through the tool rotation axis a, the side of the ball blade 5 to which the center cutting edge 7 is connected is defined as the positive side and the opposite side is defined as the negative side, so that 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 center cutting edge 7 is 0% or more and 10% or less of the tool outer diameter. Note 1 Intersection point P1: In the tool tip view, 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 of the ridge line 10 formed by the tip face 6 and the tip flank 4, which is on the side farther from the ball-shaped cutting edge 5, and the edge of the tip of the chip discharge groove 2 having the ball-shaped cutting edge 5 and the center-side cutting edge 7 connected to the ball-shaped cutting edge 5.

[0015] In addition, in the ball end mill described in any one of claims 1 to 4, 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 ridgelines 10 formed by the tip surface 6 and each of the tip flank surfaces 4 of a pair of ball cutting edges 5 arranged 180 degrees rotationally symmetrically with respect to 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).

[0016] Also, claims 5In the ball end mill described above, 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 relief surfaces 4 of a pair of ball blades 5 arranged 180 degrees rotationally symmetrically with respect to the tool rotation axis a, when viewed from the tip of the tool, and the width W of the tip surface 6 is configured so that 0.005 mm≦W≦0.2D (D: tool outer diameter).

[0017] Also, claims 6 In the ball end mill described above, the width W of the tip surface 6 is set within the following range. When the tool outer diameter is greater than φ1.5 mm, 0.01 mm ≦ W ≦ 0.3 mm If tool outer diameter≦φ1.5mm, 0.01mm≦W≦0.2D (D: tool outer diameter)

[0018] Also, claims 7 In the ball end mill described above, the width W of the tip surface 6 is set within the following range. When the tool outer diameter is greater than φ1.5 mm, 0.01 mm ≦ W ≦ 0.3 mm If tool outer diameter≦φ1.5mm, 0.01mm≦W≦0.2D (D: tool outer diameter) [Effects of the Invention]

[0019] 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 tool tip, and the ball end mill is suitable for finishing processing, which can omit the polishing step or reduce the polishing processing labor. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 2 is an explanatory plan view showing the main part of the present embodiment as viewed from the tip of the tool. [Figure 2] 1A and 1B are explanatory left side and front views showing the main parts of the present embodiment. [Figure 3] FIG. 10 is an explanatory plan view showing a main part of a first modified example of the present embodiment, as viewed from the tip of the tool. [Figure 4] 1A and 1B are explanatory left side and front views showing the main parts of a first modified example of the present embodiment. [Figure 5] FIG. 10 is an explanatory plan view showing a main part of a second modified example of the present embodiment, as viewed from the tip of the tool. [Figure 6] 10A and 10B are explanatory left side and front views showing the main parts 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 of the present embodiment. [Figure 8] FIG. 2 is an explanatory diagram defining the amount of convexity of the convex outer shape (profile) of the tip surface of the present embodiment. [Figure 9] 10 is an example of profile data showing the convex outer shape (profile) of the 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 as viewed from the tip of the tool in this embodiment. FIG. [Figure 11] 10 is an image diagram of the tool tip when the intersection point P2 is on the positive side and the negative side in this embodiment. FIG. [Figure 12] 2A and 2B are an explanatory plan view and an explanatory front view showing a configuration example of a tip surface of the present embodiment. [Figure 13] 1 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] 1 is a photograph showing the observation results of the processed surface in Experimental Example 1. [Figure 16] 10 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] 10 is a graph showing the 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 at processing times of 20 minutes and 60 minutes in Experimental Example 4. [Figure 18]10 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 a processing time of 20 minutes in Experimental Example 4. DETAILED DESCRIPTION OF THE INVENTION

[0021] A preferred embodiment of the present invention will be briefly described below, illustrating the operation of the present invention with reference to the drawings.

[0022] In the present invention, the tool tip is provided with a convex tip surface 6 that intersects with the tool rotation axis a of the tool body 1, so there is no chisel edge with a large negative rake angle, and gouging due to the influence of the chisel edge is prevented as much as possible.

[0023] In addition, in the present invention, the intersecting ridge between the tip surface 6 and the cutting face 3 is configured as a center cutting edge 7 connected to the ball cutting edge 5, so that the center cutting edge 7 has the same rake angle as the ball cutting edge 5 and exhibits the same high cutting performance as the ball cutting edge 5.

[0024] 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 displaced 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.

[0025] In this way, in the present invention, when machining a plane surface that is perpendicular to or intersects with 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 surface 6 against the cutting surface reduce the occurrence 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 a ball cutting edge 5 is obtained. [Example]

[0026] Specific embodiments of the present invention will be described with reference to the drawings.

[0027] In this embodiment, a ball end mill is provided with a plurality of chip discharge grooves 2 formed on the outer periphery of a tool body 1, which are open at the tip and extend from the tool tip side to the tool base side, and a ball blade 5 is provided at each of the intersection ridges between the cutting faces 3 of these chip discharge grooves 2 and the tip relief faces 4 of the tool body 1, and a convex tip face 6 is provided at the tool tip which intersects with the tool rotation axis a of the tool body 1 and is convex towards the tip side in the direction of the tool rotation axis a, and the intersection ridge between this tip face 6 and the cutting face 3 is configured as a center cutting edge 7 connected to the ball blade 5.

[0028] 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, as shown in Figures 1 and 2, and having ball blades 5 on each of the ridges where two cutting faces 3 formed at the tip of these chip discharge grooves 2 intersect with the tip relief face 4 of the tool body 1.

[0029] This embodiment is not limited to the configuration of the two-blade ball end mill described above, but may be configured as a multi-blade ball end mill having three or more ball blades by providing ball blades in addition to the pair (two) of ball blades 5. In the drawing, the arrow with the symbol T indicates the tool rotation direction.

[0030] More specifically, in this embodiment, a gash 11, which is part of the chip discharge groove 2, is formed at the tip of the rake face 3 (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 rake face 3 at the tip of the tool.

[0031] In addition to the above configuration, this embodiment may also be configured as a so-called straight-blade ball end mill, in which a linear chip discharge groove 2 is provided and 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.

[0032] In addition, in this embodiment, when viewed from the tip of the tool, the center cutting edge 7 near the tool rotation axis a is arranged forward in the tool rotation direction relative to the tool rotation axis a, which is a so-called center-up shape.

[0033] 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 spaced outward 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 the 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).

[0034] 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.

[0035] Furthermore, this embodiment is not limited to the above-described configuration, i.e., the configuration of the center-upward shape shown in Figures 1 to 4, but may also be configured as a so-called center-downward shape, 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, as in Alternative Example 2 shown in Figures 5 and 6.

[0036] Each component of this embodiment will be described in detail below.

[0037] As shown in FIGS. 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 a different angle from 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 a different angle from the second flank 4b.

[0038] In addition, each ball blade 5 (pair of ball blades 5) is provided at the intersection ridge between the first flank 4a of each tip flank 4 and the cutting face 3 (gash face 12) facing forward in the tool rotation direction, and is provided 180 degrees rotationally symmetrically with respect to the tool rotation axis a, as shown in Figure 1.

[0039] 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.

[0040] Specifically, as shown in FIG. 1, the tip surface 6 is configured as a convex surface between the tip flanks 4 (first flanks 4a) of each of the ball-shaped blades 5, and is connected to the tip flanks 4 (first flanks 4a) and the cutting faces 3 of each of the ball-shaped blades 5. Furthermore, the intersecting ridge portions between this tip surface 6 and the cutting faces 3 of each of the ball-shaped blades 5 are connected to the ball-shaped blades 5, and these intersecting ridge portions are configured to form a center-side cutting edge 7 with the same rake angle as the ball-shaped blades 5.

[0041] In this embodiment, the center cutting edges 7 are provided in a pair, rotationally symmetrical by 180 degrees with respect to the tool rotation axis a.

[0042] Furthermore, the tip surface 6 includes the tool rotation axis a within the surface, and as shown in Figure 7, when viewed from the tip of the tool, it is configured as a convex surface with an outer shape (profile) that is a mountain-shaped line connecting an arbitrary point A on one of the center cutting edges 7 connected to one of the pair of ball blades 5, passing near the tool rotation axis a, and an arbitrary point B on the other center cutting edge 7 connected to the other ball blade 5.

[0043] 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.

[0044] In this embodiment, the line segment L connecting point A and point B as shown in Figure 8 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.

[0045] 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.

[0046] Specifically, the external shape (profile) of the tip surface 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 external shape (profile) of the tip surface 6 represents the shape of the tip surface 6 as seen from the side of the tool (perpendicular to the tool rotation axis a).

[0047] As a result, the outer shape (profile) of the tip surface 6 becomes a mountain-shaped shape that is convex from the center cutting edge 7 side toward the center of the tool (toward the tool rotation axis a), and it can be confirmed 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.

[0048] Furthermore, the tip surface 6 is configured so that the center cutting edge 7 is formed up to the vicinity of the tool rotation axis a, and as a result, this embodiment is configured to obtain a machined surface with excellent gloss and little ripping when machining a plane perpendicular to the tool rotation axis a.

[0049] Specifically, in this embodiment, as described above, the tip surface 6 is connected to the tip flank 4 (first flank 4a). Furthermore, as shown in FIG. 10, when viewed from the tip of the tool, with respect to the central cutting edge 7 or a perpendicular line 9 of the extension line 8 of the central cutting edge 7 passing through the tool rotation axis a, if the side of the ball-shaped cutting edge 5 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, the tip surface 6 is connected to the tip flank 4. The tool is configured so that intersection P1 (the intersection between the center-side cutting edge 7 or an extension line 8 of the center-side cutting edge 7 and a 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) and intersection P2 is on the negative side, or the separation distance X in the direction along the center-side cutting edge 7 between intersection P1 and intersection P2 is 0% to 10% of the tool outer diameter, and as a result, the center-side cutting edge 7 is configured to be extended up to the vicinity of the tool rotation axis a.

[0050] In this embodiment, as shown in FIGS. 10 and 11 , the center cutting edge 7 is formed linearly at the ridgeline where the tip surface 6 intersects with the rake face 3 (gash surface 12) facing forward in the tool rotation direction. The center cutting edge 7 may be formed linearly throughout, or partially linearly. For example, a portion of the center cutting edge 7 extending from an intersection Q between the center cutting edge 7 and the adjacent ball-shaped cutting edge 5 (the intersection Q between the tip surface 6 and the tip flank 4 (first flank 4a) and the ball-shaped cutting edge 5, the intersection point between the ball-shaped cutting edge 5 and the leading edge of the chip flute 2 having the center cutting edge 7 connected to the ball-shaped cutting edge 5) toward the inside of the tool (the opposite direction from the ball-shaped cutting edge 5, i.e., the negative side) may be linear. FIG. 11( b ), which will be described later, is an example of such a partially linear configuration. In this case, the linear portion is grasped, 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.

[0051] Figure 11 is an image diagram of the tool tip of this embodiment, in which the center cutting edge 7 is formed in a straight line, when the intersection point P2 is on the positive side and when it is on the negative side, with (a) and (b) being image diagrams of the intersection point P2 on the positive side, and (c) and (d) being image diagrams of the intersection point P2 on the negative side.

[0052] Specifically, Figures 11(a) and (b) show an example in which the intersection point P2 is located on the edge of the tip of the chip discharge groove 2 having the center cutting edge 7, 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 (in the opposite direction to the ball blade 5, i.e., the negative side), and a curved portion that connects to the edge of the wall surface facing backward in the tool rotation direction, and the intersection point P2 is located on this curved portion.

[0053] Also, Figure 11(c) shows an example in which the intersection point P2 is located on the edge of the tip of the chip discharge groove 2 having the center cutting edge 7, 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) shows an example in which the intersection point P2 is located on the edge of the tip of the chip discharge groove 2 having the center cutting edge 7, on the edge of the tip of the wall surface on the negative side facing backward in the tool rotation direction.

[0054] 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 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 11(d). In this case, X takes a negative value.

[0055] Furthermore, the center-side cutting edge 7 is not limited to being linear, but may also be curved. For example, as shown in Figures 10 and 11(a), when the intersection point P2 is on the positive side, these figures show the center-side cutting edge 7 formed as a straight line having its end points at the intersection points Q and P2. However, the center-side cutting edge 7 may be formed as a curved line curving forward or backward in the tool rotation direction, or as a wavy line. In this case, the virtual line connecting the intersection points Q and P2 is regarded as the center-side cutting edge 7, and 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.

[0056] Furthermore, as shown in FIG. 10, in view of the tip of the tool, the tip surface 6 in this embodiment is configured such that the width W of the tip surface 6 is the distance between the opposing two ridge lines 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 with respect to the tool rotation axis a, and the width W of the tip surface 6 is 0.005 mm≦W≦0.2D (D: tool outer diameter).

[0057] 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 φ1.5 mm or less.

[0058] The effects of the present embodiment configured as above will be described below.

[0059] In this embodiment, the tool tip is provided with a convex tip surface 6 that intersects with the tool rotation axis a of the tool body 1, so there is no chisel edge with a large negative rake angle, and gouging due to the influence of the chisel edge is prevented as much as possible.

[0060] In addition, in this embodiment, the intersection ridge between the tip surface 6 and the cutting face 3 is configured as a center cutting edge 7 connected to the ball cutting edge 5, so this center cutting edge 7 has the same rake angle as the ball cutting edge 5 and exhibits the same high cutting performance as the ball cutting edge 5.

[0061] 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 displaced during machining of 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.

[0062] In this way, in this embodiment, when machining a plane 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 surface 6 against the cutting surface reduce the occurrence of cutting marks during cutting with the center cutting edge 7, resulting in a machined surface with a glossiness equal to or greater than that obtained when cutting with the ball cutting edge 5.

[0063] 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 the center-side cutting edge 7 or a perpendicular line 9 of the extension line 8 of the center-side cutting edge 7 passing through the tool rotation axis a, the tip surface 6 is connected to the ball-shaped cutting edge 5 side of the ball-shaped cutting edge 5 when the side of the ball-shaped cutting edge 5 connected to the center-side cutting edge 7 is the positive side and the opposite side is the negative side. Since the center-side cutting edge 7 is extended up to the vicinity of the tool rotation axis a, a machined surface with minimal gouges can be obtained when machining a plane that is perpendicular to or intersects with the tool rotation axis a.

[0064] Furthermore, in this embodiment, the width W of the tip surface 6 is formed to satisfy the relationship 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 satisfy the relationship 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 satisfy the relationship 0.01 mm≦W≦0.2D (D: tool outer diameter). This suppresses the occurrence of ripping and welding of chips due to increased cutting resistance, as well as the progression of wear on the tip surface 6, and results in a machined surface with a glossiness equal to or greater than that achieved when finished with a ball cutting edge 5.

[0065] In this way, 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 tool tip, and which can omit the polishing process or reduce the polishing process labor.

[0066] 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 consisting of two faces as shown in Figure 12(c), or a truncated cone shape with a flat surface at the top of the convex face as shown in Figure 12(d).

[0067] The shape of the tip surface 6 (frustum cone shape) shown in Figure 12(d) is specifically an example in which it is configured as a truncated cone with 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 with a flat surface at the apex of a quadrangular pyramid-shaped convex surface as shown in Figure 12(b).

[0068] In the actual tool of this embodiment, the amount of convexity is small, so 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 ridges between the tip faces 6, as shown in the plan views (as viewed from the tip of the tool) in Figs. 12(b) to 12(d), may not be clearly visible.

[0069] In all cases of Figures 12(a) to (d), the outer shape (profile) of the tip surface 6 is a mountain-shaped shape that is convex from the center cutting edge 7 side toward the tool center side (toward the tool rotation axis a). Specifically, in Figures 12(a) to (c), it is a triangular mountain-shaped shape, and in Figure 12(d), it is a trapezoidal mountain-shaped shape.

[0070] Although not shown, the above-described effects can also be obtained when the shape of the tip surface 6 is a curved surface that is 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.

[0071] Next, an experimental example that supports the effect of this embodiment will be described.

[0072] <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. Multiple samples were produced in which the amount of convexity (maximum height of the profile shape of the tip face 6) in the outer shape of the tip face 6 connecting arbitrary points on the two center cutting edges 7 passing near the tool rotation axis a was changed, and the glossiness of the machined surface was evaluated when each sample was used to cut a workpiece under the following processing conditions.

[0073] Specifically, the tool specifications were: tool outer diameter: φ6 mm, shank diameter: φ6 mm, effective length: 30 mm; and tool 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 tool tip 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 visual inspection of the appearance as in the case of a tool outer diameter of φ6 mm, surface roughness was also evaluated and the machined surface was observed.

[0074] In detail, in the visual appearance evaluation, multiple clear circles were arranged repeatedly in the longitudinal direction on the back of the scale (metal ruler), and the scale was set on the processed surface so that the surface on which the circles were repeatedly arranged was perpendicular to each processed surface, and the appearance of the circles (reflected images) reflected on the processed surface was compared and evaluated.

[0075] In addition, in the evaluation of surface roughness, the arithmetic mean roughness Ra was measured, and in the observation evaluation of the processed surface, the processed surface was enlarged and the state of cutting marks or gouges on the processed surface was observed.

[0076] In producing samples with multiple desired convex amounts as shown in Table 1 below, for samples with 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. Furthermore, for samples with 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.

[0077] [Processing conditions when the tool outer diameter is φ6 mm] Work material: Pre-hardened steel (30HRC) Rotation speed: 13,000 min -1 Feed speed: 1,500 mm / min Axial cutting depth: 0.05 mm Radial cutting depth: 0.1 mm Coolant: Water-soluble cutting fluid

[0078] [Processing conditions when the tool outer diameter is φ3 mm] 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

[0079] [result] Table 1 below shows the evaluation results of the glossiness of samples with tool outer diameters of 6 mm and 3 mm.

[0080] Regarding the evaluation results of glossiness, a mark of ⊚ was used to denote a glossiness equal to or superior to that of the machined surface finished with the ball blade 5, a mark of ◯ was used to denote a glossiness better than that of the machined surface finished with the conventional chisel edge, and a mark of × was used to denote 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.

[0081] [Table 1]

[0082] As shown in Table 1, it was confirmed that when the tool outer diameter was φ6 mm or when the tool outer diameter was φ3 mm, those with a convexity of 6.00 μm or less achieved a better gloss than those machined surfaces finished with a conventional chisel edge. In particular, those with a convexity of 4.00 μm or less achieved a gloss equivalent to or better than that of those machined surfaces finished with a ball blade 5, as shown in Figure 13. Note that Figure 13 shows the results of visual appearance inspection (appearance of reflected image) when the tool outer diameter was φ3 mm (convexity: 0.30 μm to 1.00 μm), but the same applies when the tool outer diameter was φ6 mm.

[0083] 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 set to φ3 mm.

[0084] [Table 2]

[0085] As shown in Table 2, it was confirmed that the smaller the amount of protrusion, the smaller the surface roughness (arithmetic mean roughness Ra).

[0086] Furthermore, Fig. 15 shows the results of observation of the machined surface when the tool outer diameter was set to φ3 mm. As shown in Fig. 15, it was confirmed that the smaller the amount of convexity, the smaller the cutting marks or gouges on the machined surface, which corresponds to the surface roughness evaluation results shown in Table 2 and Fig. 14.

[0087] As described above, experimental example 1 has confirmed that a machined surface with good gloss can be obtained by configuring the tip surface 6 so that the convexity (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, and that 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.

[0088] <Experimental Example 2> Experimental Example 2 was intended to confirm the appropriate formation range of the tip face 6 based on the position of the center-side cutting edge 7 formed by providing the tip face 6. As shown in Figure 10, when viewed from the tip of the tool, the center-side cutting edge 7 or an extension line 8 of the center-side cutting edge 7 intersects with a 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, and the intersection point P2 of the ridge line 10 formed by the tip face 6 and the tip flank 4 (first flank 4a) that is farther from the ball blade 5 intersects with the edge of the tip of the chip discharge groove 2 having 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 prepared in which the position of the center-side cutting edge 7 was changed, and the gloss of the machined surface was evaluated when each sample was used to cut a workpiece under the following processing conditions.

[0089] Specifically, the tool specifications were: tool outer diameter: φ6 mm, shank diameter: φ6 mm, effective length: 30 mm; and tool outer diameter: φ3 mm, shank diameter: φ6 mm, effective length: 12 mm. The machining times were 20 minutes and 60 minutes, respectively, and the glossiness of the machined surface when a plane perpendicular to the tool rotation axis a was machined with the tool tip was evaluated by visual inspection.

[0090] 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 set to φ6 mm, the width W of the tip face 6 (the distance between the opposing two ridge lines 10 formed by the tip face 6 and each of the tip flank faces 4 (first flank faces 4 a) of the pair of ball-cutting edges 5 in FIG. 10) was set to 0.02 mm, and when the tool outer diameter was set to 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, that is, when the separation distance X = 0.00, W = 0.1 mm when the tool outer diameter was φ6 mm, and W = 0.05 mm when the tool outer diameter was φ3 mm. Furthermore, when the diameter ratio X / D = -0.01, W = 0.2 mm when the tool outer diameter was φ6 mm, and W = 0.1 mm when the tool outer diameter was φ3 mm.

[0091] [Processing conditions when the tool outer diameter is φ6 mm] Work material: Pre-hardened steel (30HRC) Rotation speed: 13,000 min -1 Feed speed: 1,500 mm / min Axial cutting depth: 0.05 mm Radial cutting depth: 0.1 mm Coolant: Water-soluble cutting fluid

[0092] [Processing conditions when the tool outer diameter is φ3 mm] 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

[0093] [result] Table 3 below shows the specifications (separation distance X, diameter ratio X / D) and gloss evaluation results for each sample when the tool outer diameter is φ6 mm, and Table 4 below shows the specifications (separation distance X, diameter ratio X / D) and gloss evaluation results for each sample when the tool outer diameter is φ3 mm.

[0094] Note that with regard to the separation distance X in Tables 3 and 4 below, when the intersection point P2 is on the negative side of the center cutting edge 7 passing through the tool rotation axis a or the perpendicular line 9 to the extension line 8 of the center cutting edge 7, it is expressed as a negative value. Also, when the intersection point P2 and the intersection point P1 are coincident, the separation distance X is expressed as 0.00.

[0095] Regarding the evaluation results of glossiness, a mark of ⊚ was used to denote a surface that had a glossiness equal to or greater than that of the surface finished with the ball blade 5, a mark of ◯ to denote a surface that had a glossiness better than that of the surface finished with the conventional chisel edge, and a mark of × to denote a surface that had a glossiness equal to that of 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.

[0096] [Table 3]

[0097] [Table 4]

[0098] As shown in Tables 3 and 4, for both a 6 mm and a 3 mm tool outer diameter, when the diameter ratio X / D was greater than 0.1 (i.e., when the separation distance X was greater than 10% of the tool outer diameter), the glossiness was equivalent to that achieved with a conventional chisel edge for both 20 and 60 minutes of machining. This is thought to be because, when the separation distance X was greater than 10% of the tool outer diameter, the center cutting edge 7, which has high cutting ability, was located farther from the tool rotation axis a. 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 gouges on the machined surface. The subsequent sliding contact of the tip face 6 with the cutting surface did not achieve a sufficient burnishing effect.

[0099] Furthermore, it was confirmed that when the diameter ratio X / D was 0.1 or less, i.e., when the separation distance X was 10% or less of the tool outer diameter, the machined surface had better gloss than that finished with a conventional chisel edge, for both 20-minute and 60-minute machining times. In particular, when the diameter ratio X / D was 0.08 or less, i.e., when the separation distance X was 8% or less of the tool outer diameter, it was confirmed that the machined surface had a gloss equivalent to or better than that finished with a ball blade 5.

[0100] As described above, experimental example 2 confirmed that by providing the tip surface 6 so that the center cutting edge 7 is provided up to the vicinity of the tool rotation axis a, a machined surface with excellent gloss can be obtained.

[0101] Specifically, when viewed from the tip of the tool, with respect to the central cutting edge 7 or the perpendicular 9 to 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. It has been confirmed that by arranging the tip surface 6 so that the intersection point P2 is either on the negative side, or on the positive side where the separation distance X between the intersection points P1 and P2 in the direction along the central cutting edge 7 is 0% to 10% of the tool outer diameter (0.1D or less (D: tool outer diameter)), preferably 0% to 8% (0.08D or less (D: tool outer diameter)), a machined surface with excellent gloss can be obtained.

[0102] <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 width W of the tip face 6 was defined as the opposing distance between two ridge lines 10 formed by the tip face 6 and each of the tip flanks 4 (first flanks 4 a) of a pair of ball-cutting blades 5. Samples were produced with different widths W of the tip face 6, and each sample was used to evaluate the glossiness of the machined surface when cutting a workpiece under the following machining conditions.

[0103] Specifically, the tool specifications were as follows: tool outer diameter: φ6 mm, shank diameter: φ6 mm, effective length: 30 mm; tool outer diameter: φ3 mm, shank diameter: φ6 mm, effective length: 12 mm; and tool outer diameter: φ1.5 mm, shank diameter: φ4 mm, effective length: 6 mm. The machining times were 20 minutes and 60 minutes, respectively, and the glossiness of the machined surface when a plane perpendicular to the tool rotation axis a was machined with the tool tip was evaluated by visual inspection of the appearance.

[0104] Regarding tool specifications, the amount of protrusion of the tip surface 6 of each sample was set to 0.30 μm, the same as in Experimental Example 2. The separation distance X was set to an appropriate value for each sample, as shown in Tables 5 to 7 below.

[0105] [Processing conditions when the tool outer diameter is φ6 mm] Work material: Pre-hardened steel (30HRC) Rotation speed: 13,000 min -1 Feed speed: 1,500 mm / min Axial cutting depth: 0.05 mm Radial cutting depth: 0.1 mm Coolant: Water-soluble cutting fluid

[0106] [Processing conditions when the tool outer diameter is φ3 mm] 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

[0107] [Processing conditions when the tool outer diameter is φ1.5 mm] Work material: Pre-hardened steel (30HRC) Rotation speed: 20,000 min -1 Feed speed: 400mm / min Axial cutting depth: 0.015 mm Radial cutting depth: 0.03 mm Coolant: Water-soluble cutting fluid

[0108] [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; hereinafter simply referred to as "diameter ratio W / D"), separation distance X) and gloss evaluation results of each sample when the tool outer diameter was 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 was 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 was φ1.5 mm.

[0109] Regarding the separation distance X in Tables 5 to 7 below, cases where the intersection point P2 is on the negative side of the center cutting edge 7 or the perpendicular 9 to the extension line 8 of the center cutting edge 7 passing through the tool rotation axis a are indicated by a negative symbol. Regarding the gloss evaluation results, a symbol ⊚ indicates that the gloss was equal to or better than that of the machined surface finished with the ball cutting edge 5, a symbol ◯ indicates that the gloss was better than that of the machined surface finished with the conventional chisel edge, and a symbol × indicates that the gloss was equal to that of the machined surface finished with the conventional chisel edge. In Experimental Example 4, the machined surface finished with the ball cutting edge 5 was a flat surface inclined at 45° with respect to the tool rotation axis a.

[0110] [Table 5]

[0111] [Table 6]

[0112] [Table 7]

[0113] As shown in Tables 5 to 7, when the tool outer diameter was φ6 mm, φ3 mm, or φ1.5 mm, it was confirmed that when the width W of the tip surface 6 was 0.002 mm, gouging occurred and the surface finished with a gloss equivalent to that of a conventional chisel edge for both 20-minute and 60-minute machining times, but when the width W of the tip surface 6 was 0.005 mm, it was confirmed that the surface finished with a gloss superior to that of a 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 of the tip surface 6 is reduced.

[0114] 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 when 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 the above-mentioned width W specification at the beginning of machining (machining time of 20 minutes) and the specification where the width W of the tip surface 6 was 0.01 mm or more and 0.3 mm or less when the machining time was 60 minutes resulted in a machined surface with a gloss equivalent to or better than that of a machined surface finished with a ball edge 5.

[0115] Furthermore, as shown in Table 7, when the tool outer diameter is φ1.5 mm, in specifications 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, resulting in a glossiness equivalent to or superior to that of the machined surface finished with a ball blade 5.

[0116] Furthermore, in all cases where the tool outer diameter was 6 mm, 3 mm, or 1.5 mm, when the diameter ratio W / D was greater than 0.2, that is, when the width W of the tip face 6 was greater than 20% of the tool outer diameter, it was confirmed that the machined surface had a better gloss than that finished with a conventional chisel edge in the early stages of machining (machining time 20 minutes), but after machining time 60 minutes, the gloss decreased and it was confirmed to have the same gloss as that finished with a conventional chisel edge. This is thought to be because when the width W of the tip face 6 was greater than 20% of the tool outer diameter, the cutting resistance increased, causing ripping and chip welding from the early stages of machining, and therefore a sufficient burnishing effect could not be obtained even with the subsequent sliding action of the tip face 6 against the cutting surface.

[0117] As described above, experimental example 3 confirmed that by forming the tip surface 6 so that the width W of the tip surface 6 is 0.005 mm≦W≦0.2D (D: tool outer diameter), a machined surface with excellent gloss can be obtained.

[0118] 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 φ1.5 mm or less, 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.

[0119] Although not shown in Tables 5 to 7, in the process of carrying out the above-mentioned experimental example 3, even if the width W of the tip surface 6 was confirmed to have a specification that would result in a glossiness (rating of ◎) equivalent to or superior to 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, it was confirmed that this does not necessarily result in a glossiness (rating of ◎) equivalent to or superior to that of a machined surface finished with a ball blade 5, and that there may be cases in which the glossiness is better than that of a machined surface finished with a conventional chisel edge.

[0120] This is thought 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.

[0121] For these reasons, it is preferable to form the tip surface 6 so that, when viewed from the tip of the tool, the diameter of the circle that forms the rotation locus of the tip surface 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 surface 6, which is the radius of the largest circle that forms the rotation locus of the tip surface 6, is 17.5% or less of the outer diameter of the tool.

[0122] <Experimental Example 4> Experimental Example 4 is a comparative evaluation of this example and a conventional product (a ball end mill with a tip shape having a chisel edge at the tool tip). In this example, the convexity 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 example and the conventional product is whether the tip surface 6 or the chisel edge is present at the tool tip; in other words, the ball cutting edge 5 and other parts have the same specifications. Using this example and the conventional product with these specifications, the gloss and surface roughness of the machined surface when cutting a workpiece under the following machining conditions were evaluated.

[0123] Specifically, the tool specifications for both the present embodiment and the conventional product were: tool outer diameter: φ3 mm, shank diameter: φ6 mm, effective length: 12 mm, and 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 glossiness of the machined surfaces after 20 minutes of machining and after 60 minutes of machining was evaluated by visual inspection of the appearance (appearance of the reflected image), and the surface roughness was evaluated by measuring the arithmetic mean roughness Ra.

[0124] [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

[0125] [result] Figure 16 shows the evaluation results of the glossiness of the 0° surface of each of the present example and the conventional product. Specifically, the backside of the scale (ruler) at the top of the figure has multiple clear circles repeatedly arranged in the longitudinal direction of the scale (ruler). The surface with these circles repeatedly arranged was held over each of the processed surfaces (0° surface), and the appearance of the circles (reflected images) reflected on the processed surface (0° surface) was compared and evaluated. As shown in Figure 16, with regard to the 0° surface, the present example produced a processed surface with such excellent gloss that clear reflected images (circles) were visually confirmed, regardless of whether the processing time was 20 minutes or 60 minutes. In contrast, the conventional product produced a processed surface with no visible reflected images (circles), resulting in a lackluster surface.

[0126] 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 has 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.

[0127] FIG. 17 is a graph showing the measurement results of the arithmetic mean roughness Ra of the 0° surface for the present embodiment and the conventional product after processing times of 20 minutes and 60 minutes, respectively, 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 the present embodiment and the conventional product after processing times of 20 minutes, respectively.

[0128] As shown in FIG. 17, it was confirmed that the arithmetic mean roughness Ra of the machined surface of this example was smaller than that of the conventional product.

[0129] Furthermore, as shown in Figure 18, in general, as with 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 the tip surface 6 has a better surface roughness than the 45° surface machined with the ball blade 5.

[0130] From the above, experimental example 4, it was 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, it is possible to obtain a machined surface with a glossiness equal to or superior to that of a machined surface using a ball blade 5, even when machining a plane perpendicular to the tool rotation axis a using this tool tip.

[0131] 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]

[0132] 1 Tool body 2 Chip discharge groove 3. Rake face 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 side, and a ball blade provided at each of the ridges where the rake faces of the chip discharge grooves intersect with the tip relief face of the tool body, wherein the tool tip has a convex tip surface that intersects with the tool rotation axis of the tool body, the ridge where this tip surface and the rake face intersect constitutes a center cutting edge connected to the ball blade, and the tip surface is configured to slide against the cutting surface cut by the center cutting edge.

2. 2. The ball end mill according to claim 1, wherein the tip surface is arranged between the tip flanks of a pair of ball cutting edges arranged 180 degrees rotationally symmetrically about the tool rotation axis, so as to be continuous with the tip flanks and the respective 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 tip of the tool, the profile linearly connecting any point on one of the center cutting edges connected to one of the pair of ball blades passing near the tool rotation axis and any point on the other center cutting edge connected to the other is in the shape of a mountain.

4. 4. The ball end mill according to claim 3, wherein the tip surface includes the tool rotation axis, and when viewed from the tip of the tool, a profile linearly connecting the intersection of 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 surfaces, and the intersection of 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 surface, forms a mountain-shaped profile, and further wherein the maximum height of the mountain-shaped profile is 6 μm or less.

5. In the ball end mill described in any one of claims 1 to 4, 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, with respect to a line perpendicular to the center cutting edge or an extension line of the center cutting edge passing through the tool rotation axis, the ball blade side to which the center cutting edge is connected is defined as the positive side and the opposite side is defined as the negative side, so that 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 cutting edge is 0% to 10% of the tool outer diameter. Note 1 Intersection point P1: In the view of the tip of the tool, the intersection point between the center side cutting edge or an extension line of the center side cutting edge and the center side cutting edge or a perpendicular line to 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 cutting edge and the edge of the tip of the chip discharge flute that has this ball-shaped cutting edge and a center-side cutting edge connected to the ball-shaped cutting edge

6. 5. The ball end mill according to claim 1, wherein the tip surface has a width W defined by the distance between two ridgelines formed by the tip surface and the tip flanks of a pair of ball cutting edges that are provided rotationally symmetrically at 180 degrees with respect to the tool rotation axis, and the width W of the tip surface is in the range of 0.005 mm≦W≦0.2D (D: tool outer diameter).

7. 6. The ball end mill according to claim 5, wherein the width W of the tip surface is defined as the distance between two ridgelines formed by the tip surface and the tip flanks of a pair of the ball cutting edges provided at 180 degrees rotational symmetry with respect to the tool rotation axis, as viewed from the tip of the tool, and the width W of the tip surface is configured so that 0.005 mm≦W≦0.2D (D: tool outer diameter).

8. 7. The ball end mill according to claim 6, 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)

9. 8. The ball end mill according to claim 7, 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)

Images