JPS6130846B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a center cut end mill.

Generally, when using an end mill to form a keyway on the outer periphery of a shaft, for example, the end mill is cut down in the direction of its axis and then transversely fed in a direction perpendicular to the axis. For this purpose, a center cut end mill is used which can perform down cutting and cross cutting.

As this type of center cut end mill,
For example, as shown in FIGS. 1 and 2, an inner tip 2 and an outer tip 3 are removably attached to the tip of an end mill body 1 using tightening bolts 4, 4, respectively. Are known.
In this case, a square throw-away tip is used for the inner tip 2 and the outer tip 3, and the nose portions 2a, 2b and straight portion 2c located on the tip side of the inner tip 2 are used as the inner tip 2 and the outer tip 3. While the center part of the bottom blade is formed, the outer tip 3
The outer peripheral part of the bottom blade is formed by the nose parts 3a, 3b and the straight part 3c located on the tip side of the tip 3, and the nose part 3 located on the outer peripheral side of the outer peripheral tip 3.
A peripheral blade is formed by b, 3d and the straight portion 3e.

By the way, when performing cross-feed cutting using such a center cut end mill, for example, in order to obtain the perpendicularity between the bottom and side surfaces of the keyway, as shown in FIG. Chip 3
Since the linear part 3e forming the outer circumferential cutting edge is parallel to the axis O of the end mill body 1, and since a square tip is used as the outer circumferential tip 3, the bottom cutting edge of the outer circumferential tip 3 is formed. The straight portion 3c is perpendicular to the axis O, and therefore the relief required for the straight portion 3c in lateral cutting, that is, the straight portion 3c is aligned with the axis O as it goes from the outer circumferential side to the axis O side.
There is no way to escape to the rear. For this reason, cutting is performed such that the straight portion 3c rubs, which deteriorates the machined surface and causes work hardening.This work hardening and scraping work together, resulting in down cutting compared to cross-feed cutting. Although the machining frequency is significantly low, the straight portion 3c wears out early. In this way, the outer peripheral edge tip 3 wears out the entire area of two of its four straight parts 3c and 3e due to the horizontal cutting process.
There was a problem in that the cutting blade could only be replaced once, and the economic effects of the throw-away type could not be fully obtained.

On the other hand, when down cutting is performed,
A large thrust load acts on the axis O side portion of the bottom cutter formed by the inner cutting edge tip 2, which causes the problem that the nose portion 2a, which has particularly low strength, is prone to breakage, and furthermore, the outer tip 3 straight part 3c
is perpendicular to the axis O, there was a problem in that the thrust load and cutting torque acted impulsively on the end mill body 1 during biting.

This invention was made in order to solve the above problem, and it is possible to prevent scraping of the straight part forming the bottom edge of the outer tip, and moreover, to effectively utilize the cutting edge of the tip, and to improve the cutting edge of the inner tip. It is an object of the present invention to provide a center cut end mill capable of preventing breakage of the nose part and mitigating the impact caused by biting during down cutting.

The feature of this invention is to use diamond-shaped or parallelogram-shaped chips of the same shape and size as the inner and outer tips, and to attach the obtuse nose of the inner tip to the center of the tip of the entomill body. At the same time, the sharp nose part of the outer tip is located further forward than all other cutting edge parts, and the leading edge and rear end of the straight part extending from this acute nose part to the rear in the axial direction of the end mill body. The edge is spaced approximately the same distance from the axis of the end mill body.

An embodiment of the present invention will be described below with reference to FIGS. 4 to 7. 4 is a front view of the center cut end mill according to the present invention, FIG. 5 is an enlarged front view of the main parts thereof, and FIG. 6 is a bottom view of FIG. 5.

Reference numeral 11 in the figure is an end mill main body, which is composed of a shank portion 12 on the rear end side and a blade portion 13 on the front end side. A chip discharge groove 14,1 extending in the direction of the axis O of the end mill body 11 is provided at the tip of the blade part 13.
5 are formed spaced apart from each other by approximately 180° in the circumferential direction. A chip seat 1 is provided at the tip of the wall surface facing the rotation direction of these chip discharge grooves 14 and 15, respectively.
6 and 17 are formed. These Chipus 1
6 and 17, an inner peripheral chip 18 and an outer peripheral chip 19 having the same shape and size as each other are tightened and fixed by tightening bolts 20 and 20, respectively.

Here, in FIG. 7, one obtuse nose portion of the inner circumferential tip 18 is labeled 18a, and the other three nose portions are labeled counterclockwise from there with symbols 18b, 18c, and 18d, respectively. Further, a symbol 18e is attached to the straight part between the nose parts 18a and 18b,
When reference numbers 18f, 18g, and 18h are attached to the other three straight parts in a counterclockwise direction from there, the obtuse nose part 18a of the inner tip 18 is located at the center of the tip of the end mill body 11, and As shown in FIG. 7, a virtual intersection S formed by extending two straight portions 18e and 18h adjacent to the nose portion 18a is spaced apart from the axis O by a distance l ₁ . This distance l ₁ is desirably such that the core to be generated at the center is threaded by the nose portion 18a, specifically 0.1
It is desirable to set it as mm - 1.25mm. Further, the straight part 18e adjacent to the nose part 18a and forming the center part of the bottom blade has an angle of α with respect to the axis O, the angle from the straight part 18e toward the inner tip 18 side. has been done. If this angle α is too small, the nose portion 18d of the inner chip 18 will come into contact with the outer chip 19 when the inner and outer chips 18, 19 are arranged, and the chips 18, 19
In reality, it becomes impossible to attach the end mill body 11 to the end mill body 11. As long as such a situation does not occur, the angle α can be set arbitrarily, but it is generally desirable to set it to 65° or more. It is desirable that it be less than ゜. Note that in this case, the angle α is an acute angle.

On the other hand, reference numeral 19a is attached to one acute-angled nose portion of the outer peripheral side chip 19, and reference numerals 19b, 19c, and 1 are attached to the other three nose portions counterclockwise from there.
Add 9d. Further, the straight line portion between the nose portions 19a and 19d is designated by the symbol 19e, and the other three straight portions are designated by the symbol 19f and 19 in the counterclockwise direction from there, respectively.
g, 19h, this outer peripheral chip 19
In this case, an acute-angled nose portion 19a is located on the outer periphery of the tip of the end mill body 11. Moreover, the acute-angled nose portion 19a is located further forward in the direction of the axis O than all other cutting edge portions, that is, not only other cutting edge portions of the outer tip 19 but also further forward than the cutting edge portion of the inner tip 18. It is located. Further, a straight part 19f adjacent to the nose part 19a and extending in the axial direction, that is, a straight part 19f forming an outer peripheral blade.
has its leading edge 19i and trailing edge 19j aligned with the axis O.
Therefore, in a rotation locus on a plane including the axis O, this straight portion 19f is substantially parallel to the axis O. When the outer peripheral chip 19 is arranged in this way, the nose portion 1
Since the nose angle of the blade 9a is acute, the straight part 19e adjacent to the nose part 19a and forming the outer peripheral part of the bottom blade becomes oriented toward the rear of the axis O as it goes from the outer peripheral side to the axis O side. Among the angles formed between this straight part 19e and the axis O, the straight part 19e
The angle β of the angle toward the outer peripheral chip 19 side is an obtuse angle. Since the angle β becomes an obtuse angle, a clearance angle γ is provided between the straight portion 19e and the workpiece during lateral cutting. Note that the angle β can be changed as appropriate by changing the nose angle, radial rake angle, axial rake angle, center upward arrangement, or center downward arrangement of the outer peripheral chip 19, but if it is too small, the relief angle γ becomes small. On the other hand, if it becomes too large, the nose angle of the nose portion 19a becomes too small. Therefore, it is desirable that the angle β be 94° to 101°.

In addition, the inner tip 18 and the outer tip 19 are arranged so that their linear portions 18e and 19e intersect at a point P located approximately in the center of the inner tip 18 and the outer tip 19 in a rotation locus on a plane including the axis O. . The distance l ₂ of this point P from the axis O is approximately 1/4 of the diameter of the end mill, and therefore the ratio of the cutting lengths of the straight parts 18e and 19e during down cutting is 1:1. This enables balanced cutting, prevents the end mill from wobbling, and allows stable down-cutting.
In addition, in order to keep this distance l ₂ constant, it is desirable that the angle formed by the straight portions 18e and 19e be 2° or more.From this point, the maximum angle α mentioned above is set to 99° (101°). -2°=99°) is desirable.

Therefore, when cross-feed cutting is performed with such a center-cut end mill, the nose portion 19a of the outer peripheral tip 19 is located further ahead of the axis O than all other cutting edge portions, Since the relief angle γ is given to the straight part 19e, the straight part 19e does not undergo scraping and cutting, which prevents deterioration of the machined surface and also prevents work hardening. Early wear of the straight portion 19e can be prevented by preventing work hardening and scraping.

In addition, as shown in Fig. 8, when performing down cutting, the strong obtuse nose part 18a is placed in the center of the end mill where a large thrust load acts, so that the chipping can be avoided. It can be prevented. Moreover, in this case, since the nose portion 18a is separated from the axis O by a distance l ₁ ,
The nose portion 18a has a cutting speed,
In comparison with the case where the nose portion 18a is disposed so as to intersect with the axis O, breakage of the nose portion 18a can be further prevented. In this case, some protrusions remaining at the center are scraped off during the cross-feed cutting process, so there is no practical problem. Further, since the nose portion 19a of the outer peripheral tip 19 is located further forward in the direction of the axis O than other cutting edge portions, the workpiece 2 is moved from the nose portion 19a to the inner peripheral side of the straight portion 19e.
1, and thereby the impact load at the time of biting can be reduced. Further, in this case, since the straight portions 18e and 19e intersect each other gently, the cutting thickness thereof gradually decreases toward the point P, thereby preventing abnormal wear due to boundary wear. . In other words, if the amount of cutting changes rapidly after a point in the middle of a continuous cutting edge, for example, cutting the normal amount on one side from that point, and changing the amount of cutting on the other side. If is zero, the amount of wear at that point and the portions very close to it will be much greater than the amount of wear at other cutting edge portions that perform cutting, and so-called boundary wear may occur. In this regard, in the end mill described above, since the straight parts 18e and 19e intersect at a small angle, the amount of cutting in the vicinity of point P of each straight part 18e and 19e gradually decreases as it goes toward point P. becomes zero, and the point P
In this case, the cutting amount of each straight portion 18e, 19e does not suddenly change. Therefore, the straight portion 18e,1
It is possible to prevent boundary wear from occurring at 9e.

Next, effective use of the cutting edge portions of the inner tip 18 and the outer tip 19 will be explained with reference to FIGS. 9 to 12. FIGS. 9 and 10 show the respective wear conditions of the inner circumferential tip 18 and the outer circumferential tip 19 due to down cutting. Further, FIG. 11 shows the state of wear of the outer peripheral chip 19 due to the lateral cutting process. In addition, the wear shown in Fig. 10 and the
The wear shown in the figure is separated for convenience of explanation, and in reality, the wear occurs during the same set, so they occur simultaneously. FIG. 12 shows a throw-away tip whose entire cutting edge has been worn due to all of these cutting operations. As is clear from the above wear conditions, the inner tip 18 uses the obtuse nose portions 18a and 18c among its four nose portions, while the outer tip 19 uses the acute angle nose portions 19a and 19c. It is used for cutting. In this way, the inner tip 18 and the outer tip 19 have different nose portions for cutting, so the inner tip 18 can be exchanged and used as the outer tip 19, and the outer tip 19 can be used as the outer tip 19. The tip 19 can be used as the inner tip 18. Therefore, the cutting blade can be used effectively.

Note that when replacing the position, wear will overlap at the point P portion and the acute angle nose portion, but this does not pose any practical problem. In other words, the amount of wear on the straight parts 18e and 19e due to the down cutting process is such that the processing ratio between the down cutting process and the lateral cutting process is 1:9 to 3:7, and the wear amount of the straight line part 19f due to the lateral cutting process is This is because the amount of wear is significantly smaller than the amount of wear.
In this regard, in the conventional center-cut end mill mentioned above, the straight part that forms the bottom edge of the outer tip is greatly worn due to cross-feed cutting.
It is not possible to exchange the arrangement between the inner chip and the outer chip. On the other hand, when the tip 19 is used as the outer tip 19, the repeated wear of the acute angle nose portions 19a and 19c is not a problem at all because the same wear actually occurs simultaneously in the same set.

Further, FIGS. 13 to 16 respectively show other embodiments of the present invention, and it goes without saying that the same effects as the above-mentioned embodiments can be obtained in these embodiments.

The one shown in FIG. 13 is similar to the above embodiment in that the distance from point P to axis O is 1/4 of the diameter of the end mill, but the inner circumference side step 1
8 and the outer peripheral chip 19, the point P is located not in the center but at the end thereof.

In the case shown in FIG. 14, the obtuse nose portion 18a of the inner tip 18 extends beyond the axis O and is overcentered.

In addition, the one shown in FIG. 15 has an inner tip 18.
The straight part 18e of the straight part 18e is orthogonal to the axis O, and in the case shown in FIG. 16, the angle between the straight part 18e and the axis O is an obtuse angle.

Furthermore, the one shown in FIG. 17 has an intermediate chip 22 between the inner chip 18 and the outer chip 19.
are placed. In this case, the shape of the intermediate chip 22 is not limited to a diamond shape or a parallelogram shape, but may be a simple polygon shape.

In addition, in the above embodiment, the inner circumference side chip 1
Although the shape of the tip 8 and the outer peripheral side tip is rhombic, it may be parallelogram shaped.

Further, the chips used for the inner chip 18 and the outer chip 19 may be either positive chips or negative chips. In addition, in order to provide relief to the outer circumferential cutter during cutting down, the rear edge 19i of the straight portion 19e forming the outer circumferential cutter is positioned slightly closer to the axis O than the tip edge 19i, and the straight portion 19e is slightly It is also possible to provide a back taper of a certain amount.

As explained above, according to the center cut end mill of the present invention, rhombus-shaped chips or parallelogram-shaped chips having the same shape and the same size are used as the inner peripheral chip and the outer peripheral chip, and one part of the inner peripheral chip is The obtuse nose part of the tip is located at the center of the tip of the end mill body, while the acute nose part of the outer tip is located further forward in the axial direction than all other cutting edge parts, and the axis of the end mill body is The tip and the rear end of the straight part extending rearward in the direction are separated from the end mill body by an equal distance, and the straight parts forming the bottom cutting edge of the inner tip and the outer tip intersect with each other. Because of this, it is possible to prevent scraping of the straight part that forms the bottom edge of the outer tip, and moreover, it is possible to effectively utilize the cutting edge tip, prevent damage to the nose of the inner tip, and prevent bite during down cutting. In addition, the cutting amount of the bottom edge of each tip gradually decreases toward the intersection point in the rotation locus of the bottom edge of the inner tip and the bottom edge of the outer tip, and thus It is possible to prevent the occurrence of abnormal wear due to boundary wear at and near the intersection point, and even if the respective noses of the inner and outer chips are damaged, the chips can be connected to each other. Effects such as being able to be used by changing the arrangement can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a partially omitted front view showing an example of a conventional center cut end mill, Fig. 2 is a bottom view thereof, Fig. 3 is a view showing the state of down cutting by the end mill, and Figs. 4 to 8 The figures show one embodiment of the present invention, FIG. 4 is a front view thereof, FIG. 5 is an enlarged front view of main parts, FIG. 6 is a bottom view of FIG. 5, and FIG. 7 is an inner peripheral chip. FIG. 8 is a diagram showing the state of down-cutting, FIG. 9 and FIG. 10 are diagrams showing the state of wear due to down-cutting, and FIG. The figure shows the wear situation due to cross-feed cutting, Fig. 12 shows the wear situation after the cutting edge of the throw-away tip has been replaced and the arrangement has been changed, and Fig. 13 is another embodiment of the present invention. FIGS. 14 to 17 are views similar to FIG. 7 showing still other embodiments of the present invention. 11...End mill body, 18...Inner peripheral tip, 18a...Nose part, 18e...Straight line part, 1
9... Outer circumferential tip, 19a... Nose part, 19
e, 19f...straight portion, 19i...tip edge, 19
j... Trailing edge, S... Virtual intersection.

Claims (1)

[Claims] 1 A plurality of polygonal cutting blade tips having a nose part and a straight part are detachably attached to the tip of the end mill body, and the plurality of cutting blade tips have an inner part that forms the center part of the bottom blade. In a center cut end mill having a circumferential tip and an outer circumferential tip forming an outer circumferential portion of a bottom cutter and at least a tip portion of an outer circumferential cutter, the inner circumferential tip and the outer circumferential tip have the same shape and the same shape. The tip is a large diamond-shaped tip or a parallelogram-shaped tip, and one obtuse-angled nose of the inner tip is located at the center of the tip of the end mill body, and the outer tip is located at the outer periphery of the end mill body. An acute-angled nose portion on the outer peripheral side of the side is positioned further in the axial direction of the end mill body than all other cutting edge portions, and the tip of a straight portion extends from the acute-angled nose portion to the rear in the axial direction of the end mill body. The edge and the rear edge are spaced apart from the axis of the end mill main body by a substantially equal distance, and the inner tip and the outer tip have linear portions forming a bottom blade,
A center cut end mill characterized in that the end mills are arranged so as to intersect with each other in rotation loci on a plane including the axis of the end mill body.