Gear cutting – milling – or planing – Milling – With cutter holder
Reexamination Certificate
1999-11-15
2001-11-06
Briggs, William (Department: 3722)
Gear cutting, milling, or planing
Milling
With cutter holder
C279S103000, C082S158000, C407S046000, C407S101000, C403S273000, C403S341000, C403S030000, C029S447000
Reexamination Certificate
active
06312201
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an interference fit type cutting tool in which a tool is detachably and replaceably mounted in a tool holding section.
This specification is based on patent applications filed in Japan (Japanese Patent Applications Nos. 10-151753 and 10-350405), and the descriptions in the Japanese applications are incorporated as a part of this specification.
2. Background Art
A boring bar as an example of this type of conventional cutting tool is shown in
FIGS. 18 and 19
.
This boring bar
1
is formed by detachably fitting a head section
4
having a throwaway tip
3
on a shank section
2
held by a machining center or the like (not shown). In this case, the shank section
2
is made of, for example, expensive cemented carbide having high rigidity. Since the head section
4
is prone to wear and damage due to chip abrasion, it is made of inexpensive steel or the like, and it is detachable and replaceable.
By making the head section
4
replaceable, head sections having different types of cutting edges can be mounted.
Regarding the structure of a fitting section
5
between the head section
4
and the shank section
2
in such a boring bar
1
, for example, a projection
6
a
formed at the center of a leading end face
6
of the shank section
2
is prismatically shaped, and a hole portion
7
a
in a base end face
7
of the head section
4
is formed in the shape of a prismatic recess. The projection
6
a
is fitted into the hole portion
7
a
, so that the leading end face
6
and the base end face
7
are in contact with each other, and the peripheral portions thereof are brazed.
In another structure, the projection
6
a
is formed in a substantially cylindrical shape and is externally threaded, the hole portion
7
a
is shaped like a substantially cylindrical recess and is internally threaded to be screwed on the external thread of the projection
6
a
, and the projection
6
a
and the hole portion
7
a
are fitted together.
In a further structure, the projection
6
a
and the hole portion
7
a
are subjected to shrinkage fitting.
In such structures of the fitting section
5
, however, when a rotating work material is subjected to boring by a cutting edge of the throwaway tip
3
, the principal force of cutting resistance is applied in a direction nearly orthogonal to the cutting edge, and is received mainly by the projection
6
a
and the hole portion
7
a
, and therefore, a heavy load is imposed on the head section
4
made of steel having a substantially low rigidity. The corners of the prismatic hole portion
7
a
are apt to crack in the former case, and the screwed portion between the internal thread and the external thread is apt to be damaged in the latter case. Stiffness of the boring bar
1
is low, and tool life is short.
In the case of shrinkage fitting, when the hole portion
7
a
of the head section
4
is heated and fitted on the projection
6
a
, and then contracts due to the fall in temperature to ordinary temperature, the base end face
7
of the head section
4
sometimes separates from the leading end face
6
of the shank section
2
due to errors in shrinkage. For this reason, the holding strength and stiffness of the boring bar
1
are low, and tool life is short.
SUMMARY OF THE INVENTION
In view of such circumstances, an object of the present invention is to provide an interference fit type cutting tool that achieves high tool stiffness and increases tool life.
Another object of the present invention is to provide an interference fit type cutting tool that achieves high tool fixing strength and allows high-precision working.
A further object of the present invention is to provide an interference fit type cutting tool that reduces vibration and runout during cutting and allows high-precision working.
In order to achieve the above objects, an interference fit type cutting tool according to the present invention includes a shaft portion provided in one of a tool with a cutting edge and a tool holding section, and a hole portion provided in the other to be interference-fitted on the shaft portion, wherein the shaft portion and the hole portion have a taper portion and a tapered portion at least in a part thereof, and one of the taper portion and the tapered portion has an interference.
Since the tool and the tool holding section are interference-fitted by shrinkage fitting, expansion fitting, or by other means, the shaft portion and the hole portion are fixedly pressed by the interference pressure at the taper portion and the tapered portion. Therefore, mutual holding strength is high, and tool stiffness is improved. Furthermore, the feed force and the principal force are received thereat, and dynamic stiffness is also enhanced.
In a preferred embodiment of the present invention, the shaft portion has a taper portion at the base thereof, and the hole portion has a tapered portion at an opening thereof.
Since the taper portion of the shaft portion and the tapered portion of the hole portion are in contact with each other when the shaft portion and the hole portion are fitted, even if another contact face is uneven, rattling is prevented, reliable pressure contact is established, and fitting strength is improved. For this reason, it is possible to reduce vibration and runout during cutting, and to allow high-precision working.
In another preferred embodiment of the present invention, an interference is provided on one of the peripheral surface of the shaft portion and the inner peripheral surface of the hole portion.
By subjecting the peripheral surface of the shaft portion and the inner peripheral surface of the hole portion, and the tapered portion and the taper portion to interference fitting, two-surface restraint can be established by the interference pressure, and tool stiffness can be improved. Fitting is facilitated and reliably performed by simultaneously cooling the shaft portion and the taper portion thereof from ordinary temperature shrinkage fitting.
When the hole portion and the tapered portion are shrinkage-fitted on the shaft portion and the taper portion, the tapered portion may be fitted on the taper portion while shrinkage thereof is proceeding.
Although dimensional errors in shrinkage sometimes occur when the temperature has returned to ordinary temperature, as long as the offset between the tapered portion and the taper portion is within the interference, the tapered portion and the taper portion are in contact with each other, and the interference pressure acts. Therefore, surface restraint can be ensured without forming a gap therebetween.
In a further preferred embodiment of the present invention, one of the shaft portion and the hole portion has a key, and the other has a key groove to be fitted on the key.
Even when the principal force and the feed force of cutting resistance are applied from the cutting edge so as to twist the head section, they can be partly received by the key and the key groove fitted to each other, which makes it possible to enhance the turn-preventing function during cutting and dynamic stiffness of the tool, to combine the shank section and the head section more firmly by the restraint by interference fitting and the fitting of the key and the key groove, and to thereby improve tool stiffness.
In a further preferred embodiment of the present invention, the key and the key groove extend in a direction nearly orthogonal to the principal force of cutting resistance to be applied to the cutting edge of the head section.
Particularly in a turning tool such as a boring bar, a cutting edge of a tool can be positioned with respect to the mounting position of a tool holding section in a machine tool or the like by a key and a key groove. Furthermore, since the principal force of cutting resistance is received by the key and the key groove placed in a direction nearly orthogonal thereto, dynamic stiffness during cutting is further improved.
In a further preferred embodiment of the present invention, the inner peripheral surface of the hole por
Nagaya Hidehiko
Okawa Masayuki
Shimano Takamasa
Shimomura Hiroshi
Yamazaki Kazuya
Briggs William
Ergenbright Erica
Mitsubishi Materials Corporation
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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