JPH10113809A - Ball end mill for high speed - Google Patents

Abstract

PROBLEM TO BE SOLVED: To minimize local damage to a ball head end part by forming a ball edge of a CBN sintered body, distorting the ball edge all along from an outer peripheral cutting edge and gradually changing a rake of a ball cutting edge in the normal direction in a specified range. SOLUTION: It is a ball end mill manufactured by using a hard metal shank 1 and a edge body holding part 2 to head ends of which a CBN sintered body 3 is connected, a twist angle is about 15 deg., and a rake of a ball part is continuously changed from the maximum 10 deg. in the neighbourhood of an outer peripheral edge 4 to 0 deg. of a nose. The used CBN sintered body contains 50 to 95% of CBN, and its length is set more than a half of a edge diameter so as to make an overall ball edge part and a part of the outer peripheral edge the CBN sintered body.

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 used for processing steel, especially a tempered material.

[0002]

2. Description of the Related Art It is well known that a CBN sintered body is used in a ball end mill for cutting a hard material such as hardened steel using a machine tool such as a milling machine. The ball end mill shown in "Research" (Niigata Industrial Technology Center-Industrial Technology Research Report No. 24, pp. 9-13) is an example of cutting SKD11 and the like at a very high cutting speed of 1100 m / min. The conventional CBN tool suggests an application to ordinary cutting such as direct engraving rather than a concept for finishing. In addition, it is described that the actual machining time can be reduced to 1/7 or less in comparison with a tool coated with a carbide. Furthermore, the CBN sintered body has higher hardness and is suitable for use in cutting hard materials, compared to a general-purpose cemented carbide as a tool material, but has a very high hardness but is relatively brittle. This is particularly noticeable as the binder amount is smaller. In addition, the dimensions and shape of the material are limited, and the workability is poor and the tool shape cannot be freely obtained.
Since chipping is apt to occur during cutting, it can be used only for limited applications such as for finishing fine cutting.

[0003]

However, in the case of a ball end mill, it is impossible to impart rigidity to the tip of the ball due to its design, and a cutting speed cannot be obtained at the center of rotation, resulting in poor sharpness. Further, since the ball end mill cuts a curved surface, the entire surface of the ball blade is rarely involved in the cutting, and a part of the ball blade performs cutting according to a processing position. Therefore, damage concentrates near the center of the ball blade, and there is a problem that the life of the ball end mill using the CBN sintered body is not sufficient.

[0004]

SUMMARY OF THE INVENTION The object of the present invention is to solve the above-mentioned problems. In particular, by minimizing local damage at the tip of the ball, it is possible to cut a wide curved surface and obtain a long tool life. -End mills.

[0005]

In order to achieve the above object, the present invention has a plurality of cutting edges formed on the outer periphery of a tool body, one or more grooves, and a ball-shaped cross section at the tip of the grooves. In a ball end mill comprising at least one pair of cutting edge portions formed as described above, the ball blade is formed of a CBN sintered body, is twisted from the outer peripheral cutting edge to the ball cutting edge, and has a ball cutting edge method. The rake in the line direction is -20
From 0 ° to 0 °, and the CBN sintered body has an axial length from the tip of at least の of the blade diameter and contains 80 to 95% of CBN. Is what it is.

[0006]

According to the present invention, first, the cutting edge is twisted as a means for supplementing the toughness from the viewpoint of the tool shape, and second, the rake angle in the normal direction of the cutting edge is continuously from -20 ° to 0 °. It is set so that it changes dynamically. First, the torsion of the cutting edge is employed in end mills made of cemented carbide.
There is no example for a material having poor workability such as a BN sintered body. This can be realized by providing a plurality of cutting edges and making the edge grooves shallow, that is, by reducing the machining allowance.
Second, the rake angle in the normal direction of the cutting edge is -20 ° to 0 °.
The reason is that the CBN sintered body tool that can be used at a high speed needs to smoothly remove chips and the effect of increasing the edge angle to reinforce toughness. Therefore, if this angle is too large in the negative direction, the toughness will be further reinforced, but the cutting performance will be impaired and the performance will be reduced. If the rake angle in the normal direction exceeds 0 °, the chipping edge is likely to be too sharp and chipping is likely to occur, so the rake angle in the normal direction of the cutting edge is set to −20 ° to 0 °.

[0007] Third, a boa in which damage is likely to occur locally.
Utilizing the characteristics of LENDMILL, the cutting speed of super high speed is utilized and the cutting speed is increased near the center of rotation, so that a CBN sintered body with excellent wear resistance can be used for the cutting edge, and the damage can be reduced. It is. Here, in the present invention, since there are a plurality of cutting edges, superior effects in terms of machinability and tool life are obtained as compared with an end mill made of a single chip, and it is particularly suitable for small-diameter end mills. Further, the CBN sintered body may be applied to a ball blade that is liable to cause local damage, and may be longer than that. Especially after re-grinding after use,
When used also for side cutting, it is desirable to make it longer. Fourth, a CBN sintered body for a milling tool such as a ball end mill has a relatively low CBN content of about 50% because hardness, that is, toughness is prioritized over wear resistance. I have been. However, a ball end mill having a plurality of cutting edges and used for ultra-high-speed cutting, such as the present invention, has a greater emphasis on wear resistance.
% Of CBN is preferable, and it is preferable to extend the tool life as much as possible. Hereinafter, examples will be described in detail.

[0008]

1 and 2 show an embodiment of the present invention, in which a CBN sintered body 3 is provided at a tip end of a cemented carbide shank 1 and a blade body holding portion 2.
This is a ball end mill manufactured by using a combination of the following. The radius of the ball blade is 0.6 mm, the blade diameter is 1.2 mm, the blade length is 1.5 mm, the shank diameter is 6 mm, the total length is 60 mm, and the number of blades is 2. The torsion angle is 15 °, and the rake angle of the ball portion is continuously changed from a maximum of 10 ° in the vicinity of the outer peripheral edge to 0 ° of the nose. The CBN sintered body used contained 88% of CBN, and the length was 1.2 mm so that the entire ball blade portion and a part of the outer peripheral blade were formed as a CBN sintered body. Further, the blade holder 2 may be fixed to the shank 3 by welding or the like in terms of its strength and life, but the blade holder 2 is slightly smaller than the blade diameter.
It is preferable that the shank is manufactured in the shape of a pipe, and a part of the blade holder is inserted and fixed to the pipe in the shank.

This tool is rotated at a rotational speed of 20,000 rpm using an aerostatic spindle (cutting speed 75 m / mi).
n), depth of cut 0.1 mm, feed rate 1 m / mi
n, when hot tool steel quenched to hardness HRC40 was cut, stable cutting could be performed for a long time without any damage, and compared to the conventional ball end mill by 8 mm.
Twice as long cutting time was possible.

[0009]

As described above, according to the present invention, a ball end mill having a long tool life and capable of cutting a wide curved surface can be realized by minimizing local damage particularly at the tip of the ball.

[Brief description of the drawings]

FIG. 1 shows a front view of one embodiment of the present invention.

FIG. 2 shows a left side view of FIG. 1;

FIG. 3 shows a front view of an example of a conventional product.

[Explanation of symbols]

 Reference Signs List 1 shank made of cemented carbide 2 blade holder 3 CBN sintered body 4 outer peripheral blade α helix angle β rake angle

Claims (2)

[Claims] 1. A ball comprising a plurality of cutting edges formed on an outer periphery of a tool body, one or more pairs of grooves, and one or more pairs of cutting edges having a ball-shaped cross section at the tip of the grooves. In the end mill, the ball blade is formed of a CBN sintered body, is twisted from the outer peripheral cutting edge to the ball blade, and has a rake angle in the normal direction of the ball cutting edge of −20.
A high-speed ball end mill characterized by gradually changing the angle from 0 ° to 0 °. 2. The end mill according to claim 1, wherein a length of at least １ ／ of the blade diameter in the axial direction from the tip is a CBN sintered body containing 50 to 95% of CBN. High speed ball end mill.