Gear cutting – milling – or planing – Milling – Cutter spindle or spindle support
Reexamination Certificate
2000-02-25
2001-05-29
Briggs, William (Department: 3722)
Gear cutting, milling, or planing
Milling
Cutter spindle or spindle support
C408S23900A
Reexamination Certificate
active
06238152
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a main spindle structure of a machine tool, and more specifically, to a tool clamping mechanism of the ball-chuck type with high tool retaining stiffness, and a pull stud used for the tool clamping mechanism.
2. Description of the Prior Art
FIG. 7
is a view showing a main spindle structure that uses a conventional tool clamping mechanism of the ball-chuck type.
A housing
2
is fixed to the distal end of a spindle head
1
, and a main spindle
4
is rotatably held by means of a bearing
3
in the housing
2
. A draw bar
10
is disposed in a through hole that extends along the axis of the main spindle
4
. Balls
7
a
are embedded in the distal end of the draw bar
10
, thus forming a ball chuck portion for holding a pull stud
13
that is attached to a tool shank
5
. The pull stud
13
is held by means of the ball chuck portion and pulled into the main spindle
4
.
A spring
11
is provided coaxially surrounding the draw bar
10
. The draw bar
10
is moved upward as in
FIG. 7
by means of the repulsive force of the spring
11
, and the pull stud
13
held by means of the ball chuck portion is pulled into the through hole in the main spindle
4
.
As a roller
12
advances, the draw bar
10
that is coupled to a guide ring
10
b
is pushed downward as in FIG.
7
. As the draw bar
10
descends, a spread portion of the through hole in the main spindle
4
causes the ball chuck portion of the draw bar
10
to open, thereby allowing the pull stud
13
to be stored. When the pull stud
13
of the tool is inserted into the main spindle
4
through its distal end, the ball chuck portion of the draw bar
10
holds the stud
13
.
As the roller
12
retreats, the draw bar
10
is moved upward as in FIG.
7
and pulled in by means of the repulsive force of the spring
11
, and the ball chuck portion securely holds the pull stud
13
by means of a contracted portion of the through hole.
When the pull stud
13
is pulled into the through hole of the main spindle
4
by means of the draw bar
10
, a taper surface
5
a
of the tool shank
5
and a taper surface on the inner peripheral surface of the distal end of the spindle
4
are brought intimately into contact with each other. Thereupon, the tool is held integrally with the spindle
4
and clamped.
In general, a disk spring or coil spring is used as the spring
11
. The example shown in
FIG. 7
is a double coil spring that can generate a clamping force of about 270 kgf. This clamping force is a proper force for the size of the tool shank of the taper-crank type.
The coil spring, compared to the disk spring, is subject to less frictional hysteresis, so that it produces a stable load. Since it smoothly touches the draw bar
10
, moreover, the coil spring cannot easily mar the draw bar
10
. If it is designed with a stress amplitude not higher than a given value, furthermore, it can repeat the generation of its load substantially permanently, thus enjoying good durability.
As mentioned before, on the other hand, the clamping force is generated by the intimate contact between the taper portions. In order to enhance the tool retaining stiffness, therefore, cuttings or other foreign matter must be kept away from the taper surfaces.
The taper portions can be cleaned by taper cleaning such that foreign matter is discharged to the outside by means of a large quantity of compressed air that is delivered from a center through hole
10
c
of the draw bar
10
and flows between the taper portions when the taper surface
5
a
of the tool shank
5
is caused slightly to leave the taper portion of the main spindle
4
by tool changing operation. In attaching a new tool shank to the main spindle
4
, their taper portions are subjected to the taper cleaning with compressed air so that they come intimately into contact with each other.
A cutting fluid for cooling and lubricating the cutting edge of a tool can be delivered to the tool through the center through hole
10
c
of the draw bar
10
and a center through hole in the pull stud
13
.
As the productivity of modern machine tools is improved, the tool retaining force is expected to be increased by enhancing the fixation of the tool or tool holder to the spindle shaft, in order to ensure higher cutting performance. To attain this, two-side-restricted tool shanks have started to be generally used (See Japanese Patent Application Laid-Open No. 10-58260).
This two-side-restricted tool shank is designed so that both a taper portion and a cylindrical end face of an arbor are brought intimately into contact with a main spindle. Basically, the tool retaining stiffness of the tool shank of this type can be made higher than that of a tool shank that is designed for intimate contact between taper portions only.
The two-side-restricted tool shank requires cleaning of the contact portions between the respective end faces of the main spindle and the tool shank. If cuttings and the like adhere to the end contact portions, the tool shank is inevitably inclined when it is attached to the main spindle, so that the machining accuracy is lowered. Accordingly, it is necessary to provide means for supplying plenty of compressed air to the end contact portions to blow off the cuttings and other foreign matter, as well as the taper cleaning.
Recently, center-through cooling has been generalized such that cutting oil is supplied from the center of the main spindle to the tool end. In order to feed the cutting oil to the tool end under sufficient pressure according to this method, however, it is necessary to seal the tool shank and the clamping mechanism and provide only the tool end with a fluid channel. This requirement is not compatible with the requirement of the end face cleaning that involves the necessity to deliver air to the taper portions. In general, therefore, an expensive clamping mechanism is needed to reconcile the requirements of the center-through cooling and the end face cleaning.
In order to enhance the tool retaining stiffness for the main spindle, the adhesion between the respective contact surfaces of the main spindle and the tool shank should be enhanced, in ether case of ad hession between only taper portions or case of restriction by two-side ad hesion between a taper portion and end face. To attain this, the tool pulling force must be increased. The tool pulling force of a collet-type clamping mechanism is greater than that of a clamping mechanism of the ball-chuck type.
FIGS. 8A
to
8
C and
FIGS. 9A
to
9
C show a main spindle structure designed and studied in the process of development of the present invention using the collet-type clamping mechanism. The same reference numerals are used for elements and components which are identical with those in the clamping mechanism of the ball-chuck type shown in FIG.
7
.
In this collet-type clamping mechanism, the repulsive force of a spring
11
that acts on a draw bar
10
in a through hole in a main spindle
4
is transmitted to a pull stud
13
after it is amplified by means of a collet
16
.
FIG. 8A
shows a state in which the draw bar
10
is withdrawn in the main spindle. In this state, as shown in
FIG. 8C
, the collet
16
is closed so that it can clamp the pull stud
13
. When the draw bar
10
is pushed downward as in
FIG. 8A
, resisting the repulsive force of the spring
11
, on the other hand, the collet
16
is opened so that it can receive pull stud
13
.
A plunger
14
, which is incorporated in the draw bar
10
, is urged in the upward direction of
FIG. 8A
by means of a spring
15
in the draw bar
10
. When the draw bar
10
is pushed down, as shown in
FIG. 9A
, the distal end of the collet
16
opens, as shown in
FIG. 8B
, so that the passage of the pull stud
13
is allowed. When the draw bar
10
is caused to ascend by the repulsive force of the spring
11
, as shown in
FIG. 9B
, on the other hand, the distal end of the collet
16
is closed, as shown in
FIG. 8C
, and then holds and pulls up the pull stud
13
.
In replacing the tool, com
Fujimoto Akihiko
Kojima Kunio
Okamoto Shinya
Sato Naoki
Briggs William
Fanuc Ltd.
Staas & Halsey , LLP
LandOfFree
Tool clamping mechanism and pull stud does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Tool clamping mechanism and pull stud, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Tool clamping mechanism and pull stud will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2480804