Cutting by use of rotating axially moving tool – Tool or tool with support – Including detailed shank
Reexamination Certificate
2000-02-04
2001-03-13
Bishop, Steven C. (Department: 3722)
Cutting by use of rotating axially moving tool
Tool or tool with support
Including detailed shank
C029S432000, C029S525000, C403S280000, C403S282000, C076S108100, C076S108600
Reexamination Certificate
active
06200076
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to composite-type cutting tools, whose drill portion and shank portion are made of different materials, and a method for producing such tools, for example, miniature drills used for making small-diameter holes in a printed circuit board.
This application claims priority of Japanese Patent Application Nos. 9-19485, 9-161393, and 9-208101 which are hereby incorporated by reference.
2. Discussion of the Background
Generally, miniature drills are used for making holes having extremely small-diameters. Thus, miniature drills have: a cylindrical drill portion having a diameter of approximately 0.1 to 3.175 mm at the tip end of the drill body; and a larger-diameter shank portion at the rear end, which is used for holding the drill body in the axis of rotation of the machine tools. In general, the drill portion is formed from a cemented carbide.
Thus, to produce a solid-type miniature drill, the drill portion and the shank portion are integrally formed, for example, by grinding a cylindrical cemented carbide. Since such a cemented carbide is expensive and a large amount of the cemented carbide is ground for forming the drill portion, the cost inevitably increases.
Meanwhile, composite drills have been suggested which are produced as follows: a small-diameter drill portion is formed from a substantially cylindrical cemented carbide; a large-diameter shank portion is made from a low-cost material, such as steel or SUS, different from the material used for the drill portion; and the rear of the drill portion is allowed to fit into a hole made in the tip end of the shank portion.
FIGS.
12
(A) to
12
(E) show a method for producing such a conventional composite drill.
A shank portion
1
shown in FIG.
12
(A) has a tapered portion
1
a
at the tip end and a hole
1
b
made in the end face of the tapered portion
1
a.
According to shrinkage fitting, a substantially cylindrical drill portion
2
is pressed into the hole
1
b
while enlarging the diameter of the hole
1
b
by high-frequency heating (see FIG.
12
(B)). Since the outer diameter of the drill portion
2
is set to be slightly larger than the inner diameter of the hole
1
b
, the inner wall of the hole
1
b
is shaved to produce chips by the insertion. The chips are pushed into the bottom of the hole
1
b
by the drill portion
2
. The diameter of the hole
1
b
is then shrunk by cooling to achieve a tight fit.
The drill portion
2
can also be fitted to the hole
1
b
by brazing as follows: the drill portion
2
is pressed into the hole
1
b
having an inner diameter slightly larger than the outer diameter of the drill portion
2
, and then, brazed.
Both sides of a joint
3
, shown in FIG.
12
(C), formed between the tapered portion
1
a
of the shank portion
1
and the drill portion
2
are finely ground to form a tapered face
3
a
having a smooth linear taper from the shank portion
1
to the drill
2
(see FIG.
12
(D)), and the tip end of the drill portion
2
in succession to the tapered face
3
a
is ground to form a drill edge
2
a
(see FIGS.
12
(D) and
12
(E)).
However, since such methods for producing composite drills need a large number of steps, the process becomes complicated and laborious, disadvantageously increasing the cost. Furthermore, before pressing the drill portion
2
into the shank portion
1
, the shank portion
1
is annealed by high frequency heating in the case of shrinkage fitting and by a flux in the case of brazing. Thus, the hardness of the shank portion
1
decreases so that the fastening strength due to the fitting to the drill portion
2
is disadvantageously reduced.
Furthermore, the drill portion
2
heated by high frequency heating is undesirably deformed when it is pressed into the hole
1
b
. The fastening strength due to fitting is also lowered by shaving the inner wall of the hole
1
b
. Furthermore, since the length of the drill portion
2
exposed outside the shank portion
1
varies with the amount of the shaved chips, it is necessary to adjust the length of the shank portion
1
to achieve a constant total length of the miniature drills.
Moreover, disadvantageously, the inner wall of the hole
1
b
is readily corroded by the flux at the time of brazing.
In addition, since the shank portion
1
and the drill portion
2
are made of different materials, it is difficult to simultaneously grind both of them into the linearly tapered face
3
a
over both sides of the joint
3
between the shank portion
1
and the drill portion
2
.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a method for producing a cutting tool, by which method the drill portion is not deformed by fitting to the shank portion, and a cutting tool that can be easily produced having a high fastening strength.
Another object of the present invention is to provide a cutting tool whose drill portion and shank portion are joined by a joint having high fastening strength and which can be easily produced.
To achieve the above objects, a method for producing a cutting tool incorporated in the present invention is characterized in that where a cutting tool prepared by fitting a drill portion into a hole of a shank portion, the inner diameter of the hole of the shank portion is formed slightly smaller than the outer diameter of the drill portion, and the rear of the drill portion is pressed into the hole of the shank portion at normal temperature which is room temperature.
By forcibly pressing the drill portion into the hole of the shank portion at normal temperature, the drill portion shaves the inner wall of the hole while enlarging the hole, and is tightly fitted into the hole. Since the joint is achieved without brazing, the number of steps is low and the procedure is simplified, and furthermore, the drill portion, which is to be used for cutting, is not deformed because the procedure is carried out at normal temperature which is room temperature.
Moreover, according to one preferred embodiment of the present invention, the drill edge of the drill portion is formed by grinding after pressing the drill portion into the shank portion. Thus, only the drill portion is required to be ground to form the drill edge, resulting in easier grinding.
According to another preferred embodiment of the present invention, the shank portion is quenched before fitting. Therefore, the hardness of the resulting shank portion increases, and a cutting tool having a high joint strength can be formed with high accuracy because the inner diameter of the hole is enlarged by pressing the drill portion into the hole of the shank portion without being readily shaved. Thus, the shank portion is not damaged by shaved chips produced by processing. Furthermore, a less deformed shank portion having a smooth surface can be achieved by quenching under vacuum. Moreover, if the surface of the shank portion is hardened by nitriding before fitting, the shank portion becomes harder, the joint strength with the drill portion increases, and deformation does not occur because heat treatment such as quenching is not required.
The rear of the drill portion has a rounded or linearly chamfered edge, or the like. Thus, when the drill portion is pressed into the hole, the chamfered edge presses and enlarges the inner diameter of the hole without shaving the inner wall, resulting in a reliable fastening fit. If the rear of the drill portion has a sharp edge, the inner wall of the hole is shaved by pressing the drill portion into the hole.
A cutting tool incorporated into the present invention is characterized in that a small-diameter drill portion is fitted to a hole of a large-diameter shank portion, a step is formed at the joint between the shank portion and the drill portion, and the drill portion is formed into a drill edge.
The diameter of the shank portion is larger than that of the drill portion by the height of the step formed at the joint between the shank portion and the drill portion. Therefore, the strength of the cutting tool increase
Fujii Yasuyoshi
Kaneko Kazuhiro
Matsuura Seiji
Bishop Steven C.
Mitsubishi Materials Corporation
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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