JPH06218611A - Ball end mill - Google Patents

Abstract

PURPOSE:To increase tool life and raise cutting efficiency in such machining as three-dimensional machining of a die by forming bottom edge in convex curvature as viewed from the tip of the tool and further setting a rake angle of the bottom edge at a negative angle. CONSTITUTION:A bottom edge 5B is formed in convex curvature, bulging on the forward side in tool rotation direction, as viewed from the tip of the tool 1 and the rake angle of the bottom edge 5B is set at a negative angle. Thereby the rake face 6 continuing from the bottom edge 5B thus gradually widens along the bottom edge toward depth of the bottom edge 5B. Accordingly, cutting chips formed by the bottom edge 5B and rubbing on the rake face 6 are subjected to stress such that the width is increased along the bottom edge 5B, as they flow into depth of the rake face. Consequently, the chips are broken into smaller pieces and thus the adhesion on the edge tips is prevented even at high speed cutting and the chipping is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ball end mill in which a bottom blade having a hemispherical rotational locus is formed at the tip of a tool body.

[0002]

2. Description of the Related Art In this type of ball end mill, cutting performance is improved by improving chip removability and cutting edge structure.
There is one described in Japanese Patent No. In the ball end mill described in this publication, two bottom blades are formed at the tip of the tool body, and one bottom blade is seen from the tip side of the tool body from the tool axis line, which is the center of rotation, to the tool outer peripheral side. The bottom blade is formed so as to extend in a convex curve shape, and the other bottom blade is formed so as to extend to the outer peripheral side from a position separated from the center of rotation via a notch.

In the cutout portion, auxiliary cutting edge ridges are formed in the horizontal direction, and upright ridges are formed in the axial direction. Further, an outer peripheral cutting edge having a positive helix angle is formed so as to be continuous with the bottom blade on the tool axial direction base end side of each bottom blade, and in the tool rotation direction front side of the bottom blade and the outer peripheral cutting edge. A chip discharge groove is formed. Then, the notch formed between the inner peripheral end of the other bottom blade and the center of rotation at the tip of the tool body improves the chip discharge property because the chip discharge groove is opened at the tip side. Further, the auxiliary cutting edge ridges and the upright ridges formed in the cutout portion also promote the removal of chips, so that the ball end mill having the above-mentioned configuration can improve the cutting performance.

[0004]

By the way, in cutting with such a ball end mill or a drill, the cutting speed gradually decreases from the outer peripheral side of the bottom blade toward the center of rotation, and becomes 0 at the center of rotation. Is known to be. Then, in accordance with this, the cutting resistance gradually increases, and at the center of rotation, rather than scraping off the work material, the cutting form becomes more like squeezing and crushing. For this reason, even with a ball end mill that improves the chip removability as described above, it becomes difficult to process the chips in the vicinity of the center of rotation, and chip adhesion occurs partially and the tool material However, there was a problem that the tool edge was chipped and the tool life was significantly shortened. This tendency is particularly remarkable when high-speed cutting is performed in order to improve the cutting efficiency of the steel material in the three-dimensional processing of the mold and the like.

The present invention has been made for the purpose of solving the above problems and improving the tool life and cutting efficiency particularly in three-dimensional machining of a die.

[0006]

In order to solve the above problems and to achieve the above object, the present invention provides a hemispherical rotation locus about the axis at the tip of a tool body rotated about the axis. In a ball end mill having a bottom blade formed, the bottom blade is formed so as to form a convex curve that bulges toward the front side in the tool rotation direction when viewed from the tip side of the tool body, and the rake angle of the bottom blade is negative. It is characterized by being set to a corner.

[0007]

In the ball end mill having the above construction, the bottom blade is formed in a convex curved shape when viewed from the tip side of the tool body, and the rake angle is set to a negative angle. The width in the direction along the bottom blade gradually widens from the blade side toward the back. As a result, the chips generated by the bottom blade and abraded on the rake face are subjected to stress such that the width thereof is widened in the direction along the bottom blade as it flows out toward the back of the rake face. As a result, chips can be finely divided. Therefore, according to the present invention, it is possible to further improve the chip discharge performance over the entire length of the bottom blade, prevent the chips from adhering to the cutting blade, extend the tool life, and reduce the cutting resistance. It becomes possible to do.

[0008]

1 to 8 show an embodiment of the present invention. In these drawings, the tool main body 1 is formed of a hard material such as cemented carbide of P type or M type in JIS standard, cermet, or the like, or a material obtained by coating various coatings on the tool body 1 to form an axial shape, The base end side is the shank portion 2 and the blade portion 3 is provided at the tip end portion. The blade portion 3 has a tool rotation direction T as it goes from the tip to the base end side in the axis O direction of the tool body 1.
Is formed so as to be twisted toward the rear side of the blade, and the wall surface of the chip discharge groove 4 that faces the tool rotation direction T and the outer peripheral surface and the tip side of the blade portion 3 are formed. Cutting edges 5 are respectively formed at the ridges intersecting with the facing surface.

Here, these cutting blades 5 ... Are respectively formed on the outer peripheral blade 5A formed at the ridge line portion where the wall surface of the chip discharge groove 4 and the outer peripheral surface of the blade portion 3 intersect, and at the tip of this outer peripheral blade 5A. The bottom blade 5B is continuous and extends from the outer peripheral side to the inner peripheral side of the tool body 1 when viewed from the tip side in the tool axis O direction at the tip of the blade portion 3. Therefore, as shown in FIGS. 1 and 4, the outer peripheral blade 5A is formed into a twisted blade shape in accordance with the twist of each chip discharge groove 4. On the other hand, the bottom blade 5
As shown in FIGS. 2 and 5, B ... Are formed in a convex curve shape that bulges toward the front side in the tool rotation direction T as viewed from the tip side. Further, a portion of the wall surface of the chip discharge groove 4 which is connected to the bottom blade 5B and becomes the rake face 6 of the bottom blade 5B is bulged forward in the tool rotation direction T as it goes away from the bottom blade 5B and goes deeper. The bottom blade 5B is provided with a negative rake angle γ as shown in FIGS. 6 to 8.

In the present embodiment, these bottom blades 5B ...
The convex curve formed by is viewed from the tip side is formed to have a ½ ellipse shape having a major axis on a radial line passing through the axis O as shown in FIG. Further, the ratio A: B between the length A of the major axis and the length B of the minor axis of the ellipse formed by this convex curve is 1: 0.65-
1: It is set to about 0.67. Further, the bottom blades 5B of the three cutting blades 5 are formed so that one of them reaches the vicinity of the tool axis O when viewed from the tip side of the tool body 1, while the other two are tools. Notch 6 from axis O
It is formed so as to draw an elliptical convex curve from a position slightly separated via the. Furthermore, in the present embodiment, the rake angle (radial rake angle) of the outer peripheral blade 5A of the cutting blade 5 is set to be a negative angle. Further, the cutting blades 5 ... Are arranged so as to be slightly unevenly spaced in the circumferential direction of the tool body 1.

In the ball end mill having such a structure,
As described above, the bottom blades 5B ... Are formed so as to draw an elliptical convex curve that bulges toward the front side in the tool rotation direction T as viewed from the tip end side of the tool body 1, and the rake of the bottom blade 5B. Since the angle γ is set to a negative angle, the rake face 6 that is continuous with the cutting edge 5B is separated from the bottom blade 5B side, and the width in the direction along the bottom blade 5B gradually increases toward the back side thereof. It will be formed into a curved surface. For this reason, the chips generated by the bottom blade 5B are subjected to tensile stress in a direction intersecting the outflow direction while being rubbed against the rake face 6 and flowing out toward the depth thereof, and are thus finely divided. Further, this promotes good discharge of chips and prevents adhesion to the cutting edge, so that the ball end mill having the above configuration can prevent chipping due to falling of the tool material. This makes it possible to prevent a situation in which the tool life is significantly shortened.

Further, since the chip discharging property is improved in this way, it is possible to prevent an increase in cutting resistance due to clogging of chips and further reduce mechanical vibration such as chattering. Therefore, it is possible to further extend the tool life. Furthermore, the rake angle γ
Since it is set to a negative angle side, it is possible to set the cutting edge angle of the bottom blade 5B to a relatively large value, and thereby the cutting edge strength of the cutting blade 5 can be improved. With the ball end mill, it is possible to further improve the tool life. For example, the ball end mill of this embodiment and the ball end mill of the conventional example described above are SKD11 which are work materials in which adhesion is particularly likely to occur.
When the high speed cutting test of was conducted under the same cutting conditions,
In the present embodiment, the tool life is exhausted only by normal wear, whereas in the conventional example, chipping occurs at the cutting edge during cutting, and the tool life is exhausted at a fraction of 1 to 1/10 of the embodiment. Oops. Further, when the chips produced by the bottom blade and discharged were compared, the chips were finely divided in the ball end mill of the example as compared with the conventional example.

By the way, in this embodiment, the convex curve formed by the bottom blades 5B ... Seen from the tip side of the tool body 1 has a ratio of the length A to B of the major axis to the minor axis of 1: 0.65-1. However, when the convex curve formed by the bottom blade 5B is formed into an elliptical shape, the length ratio A: B is 1:
It is desirable to set within the range of 1 to 2: 1. This is because when the ratio A: B is less than 1: 1, that is, when the bottom blade 5B has a flattened shape in the radial direction of the tool body 1 as compared with a state in which the bottom blade 5B is formed so as to draw a semicircle. ,
This is because the swelling of the bottom blade 5B in the tool rotation direction T becomes too large, which may make it difficult to secure the chip discharge groove 4 having a sufficient size. Conversely, the ratio A: B is 2:
If the bottom blade 5B is flattened more than 1 in the tool rotation direction T, the rake face 6 may not spread sufficiently from the bottom blade 5B side to the back, and a sufficient chip cutting effect may not be obtained. Because it will occur.

Further, in the present embodiment, the case where the present invention is used in the ball end mill having the three-blade cutting blades 5 has been described, but the ball end mill having one blade, two blades, or four or more blades. The present invention may be used for further,
In this embodiment, only one bottom blade 5B of the three cutting blades 5 ... Has a configuration in which it almost reaches the tool axis O, but such a configuration may not be adopted.

[0015]

As described above, according to the present invention, the chips generated by the bottom blade can be finely divided and quickly discharged, and even when high-speed cutting is performed, the adhesion to the cutting edge portion is achieved. It is possible to prevent chipping. As a result, the tool life can be improved while improving the cutting efficiency even in the three-dimensional processing of the mold.

[Brief description of drawings]

FIG. 1 is a side view showing an embodiment of the present invention.

FIG. 2 is a front view of the embodiment shown in FIG. 1 viewed from the front end side in the direction of the axis O.

FIG. 3 is a WW sectional view of the embodiment shown in FIG.

FIG. 4 is a rake face 6 of a bottom blade 5B portion of the embodiment shown in FIG.
It is an expanded side view from the side.

FIG. 5 is an enlarged front view of the bottom blade 5B ... Part of the embodiment shown in FIG.

6 is a sectional view taken along line XX in FIG.

7 is a sectional view taken along line YY in FIG.

8 is a cross-sectional view in the Z direction in FIG.

[Explanation of symbols]

1 Tool Main Body 2 Shank Part 3 Blade Part 4 Chip Discharge Groove 5 Cutting Edge 5A Peripheral Edge Blade 5B Bottom Blade 6 Rake Surface of Bottom Blade 5B O Axis of Tool Body T Tool Rotation Direction γ Bottom Blade 5B Rake Angle A Bottom Blade 5B Is the length of the major axis of the ellipse when viewed from the tip side of the tool body 1 B The length of the minor axis of the ellipse that the bottom blade 5B is viewed from the tip side of the tool body 1

Claims (3)

[Claims] 1. A ball end mill in which a bottom blade forming a hemispherical rotation locus around the axis is formed at the tip of the tool body rotated about the axis, wherein the bottom blade is the tip of the tool body. A ball end mill characterized by being formed so as to form a convex curve that bulges forward in the tool rotation direction when viewed from the side, and the rake angle of the bottom blade is set to a negative angle. 2. The ball end mill according to claim 1, wherein the bottom blade is formed to have an arc shape or an elliptical shape when viewed from the tip side of the tool body. 3. The ratio of the lengths of the major axis and the minor axis of the arc or ellipse exhibited by the bottom blade is set within the range of 1: 1 to 2: 1. Ball end mill described.