Cutting by use of rotating axially moving tool – Tool of specific diverse material
Reexamination Certificate
1999-10-27
2001-11-13
Tsai, Henry (Department: 3722)
Cutting by use of rotating axially moving tool
Tool of specific diverse material
C408S229000, C408S230000, C407S063000
Reexamination Certificate
active
06315504
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to a twist drill suitable for use in a boring of a hole without using cutting oil or in that while spraying a very small quantity of cutting oil onto frank faces of a tip end portion of the twist drill. More particularly, the present invention relates to a twist drill which is made of a high-speed steel or a cemented carbide. Further, the present invention relates to a twist drill in that at least on the tip end portion of the twist drill is coated with a Ti-based hard material film comprising at least one layer of TiN, TiC, TiCN, TiAlN or TiAlNC.
(2) Description of the Related Art
One example of a conventional twist drill is shown in FIGS.
3
(
a
) to (
d
) and FIG.
4
. As seen in FIG.
3
(
a
), the prior art twist drill has a drill body
30
rotatable about an axis in a drill rotation direction (arrow A), a pair of chip discharge flutes
16
formed in the outer peripheral surface of the drill body
30
, a pair of chisel edges
11
formed on a tip end of the drill body
30
, a pair of inner cutting edges
12
extending from each outer end of the chisel edges
11
and a pair of major cutting edges
13
extending from each outer end of the inner cutting edges
12
forming substantially straight lines. Also from FIGS.
3
(
c
) and (
d
), a pair of the major cutting edges
13
are configured as ridge lines formed by both the flutes
16
and flank faces or flanks
20
having an angle &agr;
11
and a relief angle of &agr;
12
. As seen in the cross-sectional view shown in
FIG. 4
, each flute
16
exhibits a configuration formed by one curve or a combination of a plurality of curves having a point angle &agr;
11
. Since each major cutting edge
13
is formed as a substantially straight line, the leading edge
17
of the land
19
formed by both the land
19
and the flute
16
has a positive rake angle of &agr;
13
. Further, each leading edge
17
forms an acute angle of &agr;
14
.
Generally, in a boring of a hole using cutting oil, wear or chippings of the cutting edges are reduced by a cooling effect caused by the cutting oil. However, in a boring of a hole without using cutting oil or in that while spraying a very small quantity of cutting oil onto frank faces of a tip end portion of a twist drill, since no cooling effect is caused by the cutting oil, the wear or the chipping of each cutting edge occurs. As seen in the cross-sectional view shown in
FIG. 4
, when each leading edge
17
of the land
19
has an acute angle of &agr;
14
, the outer comer
15
formed by the flute
16
, flank
20
and the land
19
has a sharp configuration and especially the wear or the chipping rapidly occurs at the outer corner
15
of the major cutting edge
13
where the cutting speed is maximum. When using cutting oil, chips or machined material generated by the boring of the hole are transferred and smoothly discharged out through the spaces formed between the bored hole and the chip discharge flutes by the aid of the lubricant effect of the cutting oil. However, in a boring of a hole without using cutting oil, no such lubricant effect is effected. Thereby, a large frictional resistance occurs, resulting in chippings of the leading edge
17
of the land
19
occurring. That is, when the leading edge
17
of the land
19
has a sharp configuration or a positive angle, the leading edge
17
is prone to chipping.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an improved twist drill which overcomes the above-described problems. The twist drill results in reduced wear or chippings of the major cutting edges and those of the leading edges of the lands, has a long service life and stays sharp, and is suitable for use in a boring of a hole without the use cutting oil or spraying a very small quantity of cutting oil onto the frank faces of the tip end portion of the twist drill.
Another object of the present invention is to provide an improved twist drill which is made of a high-speed steel or a cemented carbide suitable for use in such boring of the hole.
Another object of the present invention is to provide an improved twist drill wherein at least on the tip end portion of the twist drill is coated with a Ti-based hard material film comprising at least one layer of TiN, TiC, TiCN, TiAlN or TiAlNC suitable for use in such boring of the hole.
In order to achieve the above-mentioned objects, a twist drill according to the present invention comprises a drill body rotatable about an axis in a drill rotation direction and a pair of chip discharge flutes formed in the outer peripheral surface of the drill body. A pair of chisel edges are formed on a tip end of the drill body, and a pair of inner cutting edges extend from each outer end of the chisel edges. A pair of major cutting edges extend from each outer end of the inner cutting edges. Further, a pair of outer cutting edges are formed each receding relative to the drill rotation midway back from each of the major cutting edges at an angle &agr;
1
in a counter-direction of the drill rotation, and a pair of leading edges of the lands each are formed by the flute and the outer cutting edge and has a linear or curved rake face. Wherein, an angle &agr;
4
of the leading edge of the land between the land and the linear or curved rake face of the leading edge is made to form an obtuse angle.
By such an arrangement, since the leading edge of the land of the twist drill of the present invention has an obtuse angle, the toughness in the outer cutting edges and the leading edge of the land is strengthened thereby reducing wear or chippings of the major cutting edges. Wear of the outer cutting edges and of the leading edges of the lands are reduced, thereby enabling the twist drill according to the present invention to have a long service life and stay sharp. Also, the twist drill according to the present invention is suitable for use in a boring of a hole without using cutting oil or, in that while spraying a very small quantity of cutting oil onto the frank faces of the tip end portion of the twist drill, reducing wear or chippings of the major cutting edges, of the outer cutting edges and of the leading edges of the lands.
Preferably, the length of one of the outer cutting edges ranges from 0.05 to 0.20 of the diameter of the twist drill. By this arrangement, while the major cutting edges keep a good cutting action, the outer cutting edges and the leading edges of the lands enable the reduction of wear or chippings thereof.
Preferably, the angle &agr;
1
between the major cutting edge and the outer cutting edge ranges from 150 to 175°, in order to secure an adequate obtuse angle &agr;
4
of the leading edge of the land.
More preferably, the twist drill is made of a high-speed steel, or made of a cemented carbide to secure high wear resistance.
Preferably, the twist drill, at least on the tip end portion of the twist drill, is coated with a Ti-based hard material film comprising at least one layer of TiN, TiC, TiCN, TiAlN or TiAlNC to further reduce wear or chippings on its major cutting edges and on its leading edges of the lands.
REFERENCES:
patent: 750537 (1904-01-01), Hanson
patent: 3387511 (1968-06-01), Ackart, Sr. et al.
patent: 4756650 (1988-07-01), Wakihira et al.
patent: 5078554 (1992-01-01), Kubota
patent: 5186739 (1993-02-01), Isobe et al.
patent: 5431072 (1995-07-01), Christoffel
patent: 5597272 (1997-01-01), Moriguchi et al.
patent: 5622462 (1997-04-01), Gakhar et al.
Sekiguchi Toru
Suzuku Yoshiro
Kinberg Robert
Nachi-Fujikoshi Corporation
Spencer George H.
Tsai Henry
Venable
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