JPH05228714A - Ball end mill - Google Patents

Abstract

PURPOSE:To provide a ball end mill which can highly effectively machine the free curved face of a metallic mold or the like into the state of a finished surface having fine roughness. CONSTITUTION:A CBN sintered body 7 where a cutting edge 8 is to be formed is provided with a rake angle of 5 deg.-15 deg. in a direction having an angle from 0 deg. to 45 deg. to the axial center C of a main body 1 to improve cutting quality on the side of the inside end 8a of the cutting edge 8, and moreover the cutting edge 8 is formed in a circular arc-shape being convex in the direction of rotation to facilitate reduction in cutting resistance, the control of tool vibration and the prevention of the damage of the tip of the cutting edge. In addition, the inside end 8a of the cutting edge 8 is displaced by DELTAt (0.05mm or less) from the axial center C backward in the drection of rotation to remove a domain where the cutting speed of the cutting edge becomes zero. Thus, a plucking phenomenon occurring in a cutting region near the center of rotation can be reduced, and even when a feed speed is increased, the roughness of a finished surface can be improved.

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 which is capable of processing a die or the like made of steel, cast iron or the like with high efficiency and good finished surface roughness.

[0002]

2. Description of the Related Art The processing of a free-form surface provided on a mold or the like is usually carried out by copying processing using a ball end mill or NC processing. Recently, as this ball end mill, the cutting edge is made of a CBN (high pressure phase cubic boron nitride) sintered body, or the cutting edge of the CBN sintered body is cut into an S-shaped cutting edge shape. Some products with reduced resistance are also available and are being used for finishing.

[0003]

In the conventional ball end mill described above, the radial inner end of the cutting edge (hereinafter referred to simply as the inner end) is on the axis of the main body, that is, on the center of rotation. On the other hand, the cutting speed of the cutting edge in the rotary cutting tool is
No matter how fast the tool is rotated, it becomes zero at the center of rotation,
Near that, the speed is close to zero. At such a low speed, as is well known, the working form approaches plastic working, and good cutting cannot be expected. In the die machining with a ball end mill, the cutting edge in the center of rotation, which rotates at a low speed, scrapes the flat bottom of the free-form surface. Therefore, use a CBN sintered body that is advantageous in terms of high precision and high efficiency machining. However, the peeling phenomenon occurs at the bottom, and the finished surface roughness tends to deteriorate.

The present invention is intended to provide a ball end mill which is effective in solving the above problems.

[0005]

In order to solve the above-mentioned problems, in the present invention, a high hardness sintered body such as CBN forming a cutting edge is provided at 0 ° or more and 45 ° or less with respect to the axis of the main body. Make a rake angle of 5 to 15 ° in the angled direction. Further, by providing the rake angle, the radial inner end of the cutting edge at the forefront is displaced from the center of rotation backward by 0.05 mm or less.

[0006]

[Function] When the cutting edge is provided with a positive rake angle, the sharpness is improved as is well known. In the present invention, since the direction in which the rake angle is applied is limited, the sharpness is remarkably improved on the inner end side of the cutting edge.

Further, it is known that a cutting edge having a convex arc in the rotational direction is effective for reducing cutting resistance, suppressing tool vibration, and preventing breakage of the cutting edge. Since a rake angle is added, the ridgeline of the cutting edge becomes such a convex arc shape.

Further, by displacing the inner end of the cutting edge from the center of rotation, a cutting speed is also generated at the inner end and the cutting condition on the inner end side is improved.

All of these are effective in preventing the peeling phenomenon. Therefore, according to the present invention, the flat bottom portion of the surface to be machined can be finished with high efficiency and excellent surface roughness.

[0010]

1 to 3 show an embodiment of the present invention. As shown in the figure, a cutting edge tip 3 is attached to a tip seat 2 at the tip of the main body 1. The cutting edge tip 3 is detachably attached using the set screw 4 and the presser foot 5, but it is not limited to be integrally fixed by brazing.
Also, as shown in the figure, if two cutting edge chips 3 are arranged at equal points in the circumferential direction and each half of the semi-circular work area is cut by half, the rotational balance will be stable. Vibration during cutting becomes smaller.

In the case of the drawing, the cutting edge tip 3 is a CBN sintered body 7 of the minimum size necessary for the base metal 6 for cost reduction.
Are joined to form cutting edges 8. The CBN sintered body 7 of the cutting edge tip 3 is attached so as to be inclined in a direction having an angle of θ with respect to the axis C of the main body so that the rake angle of α shown in FIG. As seen from FIG. 2, the shape of the cutting edge 8 as viewed from the end is a circular arc that is convex in the rotational direction.

Further, in this state, the inner end 8a of the cutting edge 8 is displaced by Δt rearward in the rotational direction from the axis C of the main body, which is the center of rotation, as shown in FIG.

If the rake angle α is 5 ° or less, the effect of improving the sharpness is small. On the other hand, if the rake angle α exceeds 15 °, the wedge angle of the cutting edge becomes too small and the cutting edge is liable to be chipped.
It is suitable to be 15 ° or less and 15 ° or less.

Regarding the direction of rake angle,
In order to improve the sharpness on the rotation center side where the cutting speed becomes small, it is preferable to set θ in the direction of 0 ° or more and 45 ° or less.

Further, at the center of rotation where the cutting speed becomes zero, shifting the cutting edge from the center of rotation to increase the cutting speed leads to prevention of peeling, but the centering amount of the inner end of the cutting edge (the above-mentioned Δt). Is excessively large, the amount of axial retreat of the inner end 8a becomes large and the surface roughness is lowered due to the uncut portion in the center of rotation.

In addition, the corner on the inner end 8a side of the cutting edge is preferably rounded and reinforced as shown in FIG. 1, but if the corner R becomes too large, the center down amount Δt is set as described above. Since it becomes difficult to set the radius to 0.05 mm or less, it is preferable to set the radius R of the corner R to about 0.4 to 2 mm.

Below, the results of a comparative test of finished surface roughness by plane feed processing will be described.

In this test, the processing radius is 25 mm, θ = 30
°, α = 10 °, Δt <0.05 mm of the prototype ball end mill of the present invention having the illustrated shape, and the machining radius is 25 mm.
However, the cutting edge was formed by using a conventional ball end mill whose end face has a straight shape and whose inner end is the center of rotation.
Both end mills use a CBN sintered body for the cutting edge.

The cutting conditions are as follows: Work material: FC25 Spindle speed N = 5000 rpm Table feed F = 3000 mm / min Pick feed Pf = 0.5 mm Cut Ad = 0.5 mm Processing was performed to measure the finished surface roughness.

As a result, the finished surface of the conventional product had a finished surface roughness of Rmax 25 μm, whereas the finished surface roughness of the present invention product was Rmax of 10 μm, and the finished surface had very good properties.

[0021]

As described above, in the ball end mill of the present invention, the cutting edge is provided with a rake angle for particularly improving the sharpness on the rotation center side, and the cutting edge is formed into a convex arc in the rotation direction. By eliminating the area where the cutting speed is zero by displacing the inner edge of the cutting edge from the center of rotation, peeling of the part to be cut by the blade in the center of rotation is reduced and the finished surface roughness is very good. Become. Further, since the cutting edge has a convex arc shape, the tool life is extended.

[Brief description of drawings]

FIG. 1 is a side view of an embodiment.

FIG. 2 is a front view of the above.

FIG. 3 is a sectional view taken along line III-III in FIG.

[Explanation of symbols]

 1 main body 2 tip seat 3 cutting edge tip 4 set screw 5 presser foot 6 base metal 7 CBN sintered body 8 cutting edge 8a inner edge C body axis α rake angle θ angle indicating the direction of rake Δt inside cutting edge Amount of core down

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Takashi Kanda 1-1-1 Kunyo-kita, Itami-shi Itami Works, Sumitomo Electric Industries, Ltd. (72) Masafumi Hideshima 1-1-1 Kunyo-kita, Itami-shi Sumitomo Electric Industries, Ltd. Itami Works

Claims (1)

[Claims] 1. A ball end mill having a cutting edge of a high-hardness sintered body having a semicircular rotation locus at the tip of the main body, wherein the high-hardness sintered body has 0 ° or more with respect to the axis of the main body. A rake angle of 5 to 15 ° is provided in a direction having an angle of 45 ° or less, and the radial inner end of the cutting edge at the forefront is displaced from the center of rotation by 0.05 mm or less rearward in the rotational direction Ball end mill.