Cutters – for shaping – Rotary cutting tool – Face or end mill
Reexamination Certificate
2001-05-07
2003-07-08
Wellington, A. L. (Department: 3722)
Cutters, for shaping
Rotary cutting tool
Face or end mill
C407S061000
Reexamination Certificate
active
06588990
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a milling cutter such as an end mill.
2. Description of the Related Art
Heretofore, as a milling cutter having a plurality of peripheral cutting edges, such as an end mill, various forms are known. However of these, those where the shape of the transverse cross-section (the cross-section perpendicular to the axial direction) is a regular hexagon or a regular square are easy to manufacture due to the simple shape. Hence development of these has been actively promoted (refer for example to Japanese Unexamined Patent Application, First Publication Nos. Hei 3-26413 or 4-53615).
As one example of these, an end mill with a transverse cross-section of a regular hexagon is shown in FIG.
5
and
FIG. 6
, while an end mill with a transverse cross-section of a regular square is shown in FIG.
7
and FIG.
8
. The end mills in these figures have a shank
10
, and a cutting part at a tip end thereof. On this cutting part is formed a plurality of peripheral cutting edges
12
along a cylindrical peripheral face, and each peripheral cutting edge
12
is twisted in a helix.
Looking at the cutting part in the transverse cross-section shown in FIG.
6
A and
FIG. 8A
, the respective vertices of the polygons constituting the transverse cross-section constitute the peripheral cutting edge
12
, the vicinity of the front side in the tool rotation direction (the cutting direction) of the peripheral cutting edge
12
constitutes a rake face
14
of the peripheral cutting edge
12
, and the vicinity of the rearside in the tool rotation direction constitutes a relief face
16
. That is to say, the rake face
14
of one peripheral cutting edge
12
is also used a relief face of the adjacent peripheral cutting edge
12
on the front side in the tool rotation direction of that peripheral cutting edge
12
.
Consequently, with the end mill having the transverse cross-section of a regular hexagon shown in
FIG. 6A
, as shown in
FIG. 6C
, with a rake angle &agr; of each of the peripheral cutting edges
12
of −60°, a relief angle &egr; of 30°, the wedge angle &bgr; (the apex angle constituting the peripheral cutting edge
12
in transverse cross-section) becomes 120°, while with the end mill having the transverse cross-section of a regular square shown in
FIG. 8B
, as shown in
FIG. 8C
, with a rake angle &agr; of each of the peripheral cutting edges
12
of −45°, a relief angle &egr; of 45°, the wedge angle &bgr; (the apex angle constituting the peripheral cutting edge
12
in transverse cross-section) becomes 90°.
In the tip of the cutting part, as shown in FIG.
6
B and
FIG. 8B
, when viewed from the tool tip side, there is formed bottom edge rake faces
19
extending in the tool diameter direction so that the apex angles of the two peripheral cutting edges
12
are respectively evenly divided. These bottom edge rake faces
19
extend in approximately parallel directions to the tool axis, with the tips thereof constituting bottom edges
18
, and tool tip faces located on the rear side in the tool rotation direction of the bottom edges
18
become bottom edge relief faces
20
. Consequently, a wedge angle &ggr; of each bottom edge
18
(the apex angle subtending the bottom edge
18
viewed from the tool tip side) become approximately half of the wedge angle &bgr; of the peripheral cutting edge
12
, and with the end mill shown in
FIG. 6B
, &ggr;=60°, while with the end mill shown in
FIG. 8B
, &ggr;=45°.
Comparing the aforementioned regular hexagon section end mill and the regular square section end mill, for the regular hexagon section end mill, the size of the wedge angle &bgr; of the peripheral cutting edge is larger (&bgr;=120°) than for the regular square section end mill, and to that extent there is a strengthwise advantage. However on the other hand, the rake angle &agr; of the peripheral cutting edge is much smaller at −60°. Therefore there is the disadvantage of inferior sharpness. Conversely, with the regular square section end mill, the rake angle &agr; of the peripheral cutting edge is larger at −45°. Therefore, compared to the regular hexagon section end mill, sharpness is excellent. However since the relief angle &egr; is also large, the wedge angle &bgr; of the peripheral cutting edge is small (&bgr;=90°). Hence it is difficult to maintain sufficient cutting edge strength, and to that chipping is likely to occur.
That is to say, with the conventional end mill where the transverse cross-section is a regular polygon (the same for other end mills), there is the characteristic that, if the number of vertices, that is the number of peripheral cutting edges, is increased the strength of the peripheral cutting edges is increased, however the sharpness deteriorates, while on the other hand, if the number of peripheral cutting edges is reduced, the sharpness improves, however the strength of the peripheral cutting edges is reduced. Hence there is the problem that it is extremely difficult to improve the sharpness and at the same time to maintain the cutting edge strength.
In particular, as shown in FIG.
6
B and
FIG. 8B
, in an end mill where the bottom edge rake faces
19
are formed so as to equally divide the apex angles of the peripheral cutting edges
12
, and the bottom edges
18
are formed in the tips thereof, the wedge angle &ggr; of each bottom edge
18
further becomes approximately half the wedge angle &bgr; of the peripheral cutting edge
12
. Hence insufficiency of cutting edge strength at this bottom edge
18
is serious.
SUMMARY OF THE INVENTION
The present invention takes in to consideration such a situation, with the object of providing a milling cutter which can provide for both an improvement in sharpness and a retention of cutting edge strength, while making the transverse cross-section an easily manufactured polygon shape.
As a means for solving the above problems, the present invention, in a milling cutter having a plurality of peripheral cutting edges around a circumferential direction, and with a transverse cross-section shape of a polygon, is constructed such that the polygon is a convex polygon with one more apex point existing between apex point pairs constituting the peripheral cutting edges with an apex angle greater than that of the apex points, and a longer side of the sides on either side of each of the peripheral cutting edges constitutes a rake face, while a shorter side constitutes a relief face.
According to this construction, there is the easily manufactured transverse cross-section shape polygon. However instead of the conventional regular polygon, this is an irregular convex polygon with an apex point existing between apex point pairs constituting the peripheral cutting edge, with an apex angle greater than that of the apex points. Furthermore, the long side of these sides constitutes the rake face, while the short side constitutes the relief face. Therefore, due to the difference in length of these sides (in other words the difference in the apex angles), as the rake angle of each peripheral cutting edge is increased, the relief angle is reduced, and to that extent the wedge angle of the peripheral cutting edges can be kept large. That is to say, it is possible to simultaneously realize both an improvement in sharpness and a retention of cutting edge strength.
For example, in the case where the milling cutter according to the present invention has four peripheral cutting edges (that is, the transverse cross-section shape is an octagon), then with the rake angles of each of the peripheral cutting edges greater than −60° and less than −45° (−60° with the conventional regular hexagon milling cutter), the apex angle of each of the peripheral cutting edges in transverse cross-section can be an angle greater than 120° and less than 135° (120° with the conventional regular hexagon milling cutter). That is to say, while keeping the edge angle of the peripheral cutting edge the same as or greater than for th
Aoki Taiitsu
Ikeuchi Hiroshi
Kimura Yoshihiko
MMC Kobelco Tool Co., Ltd.
Rader & Fishman & Grauer, PLLC
Ross Dana
Wellington A. L.
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