JPH11129106A - Tool holder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simplify the structure of a tool holder and a spindle to reduce unstable elements during high-speed rotation and costs. SOLUTION: A tool holder 20 as a connecting jig to coaxially mount a tool T on a spindle 1 which is increased in heating value as increased in rotating speed has a protrusion 22s molded in shape to be fitted to a tapered recess 1e formed in the center at the end of the spindle 1. The thermal expansion coefficient and thermal conductivity of the protusion 22s are so set that the protrusion 22s can be thermally expanded to the radial direction after receiving heat from the spindle 1, enough to expansively open the recess 1e of the spindle 1 during rotation. In this way, such a system that the protrusion 22s of the tool holder 20 is expanded by heat caused during rotation of the spindle 1 to fill a clearance, which is about to occur between the recess 1e of the spindle 1 and the recess 22s of the tool holder 20 during high-speed rotation of the spindle 1, eliminates the need for a heater for the spindle and a cooling fin for the tool holder as conventional.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tool holder which is a connecting jig for attaching a tool coaxially to a main shaft of a machine tool.

[0002]

2. Description of the Related Art A technique related to this is disclosed in Japanese Patent Application No. 8-1024.
No. 17 disclosed by the applicant. The technique according to Japanese Patent Application No. 8-102417 relates to a spindle device, and FIG. 5 shows a tool holder 1 of the spindle device 10.
2 and main part sectional views of the main shaft 11 are shown. The tool holder 12 has a substantially frustoconical recess 12 in the center on the spindle side.
t is formed, and the main shaft 10 is formed at the center of the concave portion 12t.
The projection 12k connected to the draw bar 14 is formed. On the other hand, at the tip of the main shaft 11, a truncated cone-shaped projection 11t that can be fitted into the recess 12t is formed. Then, the concave portion 1 of the tool holder 12 is
2t is fitted, so that the tool holder 12 is attached to the spindle 1
It is held coaxial with 1.

The protruding portion 11t of the main shaft 11 is formed of a material which is easily thermally expanded, and a heater 11h is embedded near the protruding portion 11t. On the other hand, the tool holder 12 has cooling fins 12f for heat radiation on its outer peripheral surface.
Are provided, so that the temperature is hardly increased. For this reason, even if the concave portion 12t of the tool holder 12 expands in the radial direction due to centrifugal force due to the high speed rotation of the main shaft 11, the convex portion 11t of the main shaft 11 expands due to the heat of the heater 11h. 12t and spindle 11
The clearance to be generated between the convex portion 11t and the convex portion 11t is filled. Therefore, the support rigidity of the tool holder 12 in the radial direction can be maintained, and machining accuracy can be ensured even during high-speed rotation.

[0004]

However, according to the spindle device 10 described above, the convex portion 11t of the spindle 11 is heated by the heater 11h and thermally expanded, and conversely, the tool holder 12 is heated.
Is cooled to suppress the thermal expansion of the concave portion 12t, so that temperature control or the like is required, and there is a problem that the structure is complicated. Since the cooling fins 12f are provided on the tool holder 12, the diameter of the tool holder 12 is increased by the size of the cooling fins 12f. For this reason, the peripheral speed of the tool holder 12 increases, mechanical strength against centrifugal force is required, and rotation accuracy also deteriorates. Further, since the cooling fins 12f must be machined with high precision, the manufacturing cost of the tool holder 12 also increases.

Therefore, according to the first aspect of the present invention, while maintaining the rigidity of the support of the tool holder during high-speed rotation, the temperature control of the spindle and the cooling fins of the tool holder which are conventionally required are not required. Accordingly, the object of the present invention is to simplify the structure of the tool holder and the like, reduce unstable elements during high-speed rotation, and reduce costs. Another object of the present invention is to reduce the centrifugal force applied to the tool holder during high-speed rotation to improve rotation accuracy.

[0006]

The above object is achieved by a tool holder having the following features. That is,
The tool holder according to claim 1 is a tool holder that is a connection jig for attaching a tool coaxially to a main shaft whose amount of heat increases as the number of rotations increases, and is formed at the center of the front end of the main shaft. A convex portion formed into a shape that can be fitted to the tapered concave portion, and a thermal expansion coefficient and a thermal conductivity of the convex portion substantially correspond to an amount by which the concave portion of the main shaft expands during rotation. The value is set so that the convex portion receives heat from the main shaft and thermally expands in the radial direction.

According to the present invention, even when the concave portion of the main shaft expands due to centrifugal force or the like during high-speed rotation, the radius of the convex portion of the tool holder substantially corresponds to the amount by which the concave portion expands due to the heat of the main shaft. Due to the thermal expansion in the direction, the clearance between the concave portion of the main shaft and the convex portion of the tool holder is filled. For this reason, the rigidity of support of the tool holder in the radial direction can be maintained, and machining accuracy can be ensured even during high-speed rotation. That is, conventionally, it is required because the convex portion of the tool holder is expanded by utilizing the heat of the main shaft to fill a clearance between a concave portion of the main shaft and the convex portion of the tool holder. In addition, a heater or the like for the main shaft or a cooling fin for the tool holder becomes unnecessary.
For this reason, the structure of the tool holder, the main shaft, and the like is simplified, and unstable elements during high-speed rotation can be reduced, and the cost can be reduced. In particular, since cooling fins are not required for the tool holder, the diameter of the tool holder can be reduced, and the mechanical strength against centrifugal force can be reduced. Further, since the rotation accuracy is improved, the run-out of the tool tip can be reduced.

[0008] The invention described in claim 2 is the first invention.
The tool holder described in (1) is characterized by being formed of a material having a lower specific gravity than the main shaft. According to the present invention, since the specific gravity of the tool holder is smaller than that of the main spindle, the centrifugal force applied to the tool holder is smaller than when a conventional tool holder having the same specific gravity as the main spindle is used. For this reason, as described above, the rotation accuracy of the tool holder is improved.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A tool holder according to an embodiment of the present invention will be described below with reference to FIGS.
The tool holder according to the present embodiment is a holder mounted on a main spindle for high-speed rotation using a magnetic bearing, and FIG. 1 is a longitudinal sectional view of a tip end of the main spindle on which the tool holder is mounted. I have. 2 is a view taken in the direction of arrows II-II in FIG. 1, and FIG. 3 is a perspective view of a collet which is a main part of the tool holder.

The spindle 1 is rotatably supported by a spindle head (not shown) via a magnetic bearing, and a built-in motor (not shown) is provided between the spindle head and the spindle 1. Is installed. And
The stator of the built-in motor is provided on the spindle head side, and the rotor is formed around the spindle 1. Therefore, when the built-in motor is driven, the spindle 1
Rotates at high speed around the axis. At this time, the spindle 1 receives heat due to losses (iron loss, mechanical loss, copper loss, etc.) from the built-in motor, and the temperature rises (increases to about 100 ° C.) as the rotation speed increases.

A collet holder 1h for coaxially supporting the collet 22 of the tool holder 20 is integrally formed at the tip of the main shaft 1. The collet holder 1h has a concave portion 1e formed coaxially with the main shaft 1. The concave portion 1e is provided with a taper so that the inner diameter increases on the distal end side, and a small-diameter cylindrical portion 1t is provided around the distal end side of the concave portion 1e. Further, a male screw 1w is formed on the outer peripheral surface of the cylindrical portion 1t.

The tool holder 20 includes a collet 22 for coaxially supporting a rod-shaped tool T, and a lock nut 2 for attaching the collet 22 to the collet holder 1h.
And 5. The collet 22 is shown in FIG.
As shown in FIG. 3, the concave portion 1 of the collet holder 1h
e and a protruding portion 22f protruding from the concave portion 1e to the distal end side.

The fitting projection 22s is provided with a taper equal to that of the concave portion 1e so that its outer peripheral surface is in surface contact with the inner peripheral surface of the concave portion 1e of the collet holder 1h.
A lock nut 25 described later is provided on the protruding portion 22f.
Convex surface 22t in surface contact with tapered concave surface 25f
Are formed. That is, the fitting convex portion 22s corresponds to the convex portion of the present invention, and the concave portion 1e of the collet holder 1h corresponds to a tapered concave portion formed at the center of the tip of the main shaft of the present invention.

A through hole 22k through which the tool T is passed is formed in the center axis direction of the collet 22, and slit-like cracks 22c are formed at equal intervals in the circumferential direction from the tip to the base of the collet 22. It is formed in four places. Further, also from the base end to the tip end of the collet 22, four slit-shaped splits 22d are formed at equal intervals in the circumferential direction.

Further, since the material of the collet 22 is a copper-beryllium alloy or an aluminum alloy, the thermal expansion coefficient and the thermal conductivity of the collet 22 are determined by the main shaft 1.
It becomes sufficiently larger than the thermal expansion coefficient and the thermal conductivity of (iron). Here, the thermal expansion coefficient and the thermal conductivity of the collet 22 are substantially equal to the amount by which the concave portion 1e of the main shaft expands due to centrifugal force or the like when the main shaft 1 rotates. The value is set so as to expand in the radial direction in response to this.

The collet 22 is mounted on the collet holder 1h.
As shown in FIG. 1, the lock nut 25 for attaching to the is a bag-shaped nut, and an opening 25 h through which the tool T is passed is formed at the center thereof. A tapered concave surface 25f, which is in surface contact with the tapered convex surface 22t of the collet 22, is formed in a ring shape around the opening 25h inside the lock nut 25. Further, the lock nut 2
A female screw 25w that is screwed with the male screw 1w of the collet holder 1h is formed on the inner side wall of the collet holder 1h.

Next, the operation of the tool holder 20 will be described. First, a tool T is inserted into the through hole 22k of the collet 22.
Is passed through the fitting projection 22s of the collet 22.
Is fitted into the concave portion 1e of the collet holder 1h of the main shaft 1. Next, as shown in FIG. 1, a lock nut 25 is put on the collet 22, and the lock nut 25 is
Female screw 25w is screwed into the male screw 1w of the collet holder 1h. Then, the lock nut 25 is tightened with a predetermined torque.

As a result, the collet 22 is fixed to the tapered concave surface 25f of the lock nut 25 and the collet holder 1.
The recess 1e is pressed from both sides in the axial direction. Further, the collet 22 has a tapered convex surface 22 on the distal end side.
Due to the action of t and the tapered concave surface 25f, and the taper action of the fitting convex portion 22s and the concave portion 1e at other portions, the pressing force is applied inward in the radial direction. For this reason, the collet 22 is attached to the collet holder 1h of the main shaft 1 while being restrained in the axial and radial directions.

Since the collet 22 is provided with longitudinal cracks 22c and 22d at equal intervals in the circumferential direction, the collet 22 receives a radially inner pressing force by the lock nut 25 and the collet holder 1h. Then, the tool T is deformed inward in the radial direction, and the tool T is tightened from the periphery.
Thereby, the tool T is coaxially mounted on the main shaft 1 via the tool holder 20.

When the tool T and the tool holder 20 are attached to the main shaft 1 in this way, the built-in motor is driven to rotate the main shaft 1, and the work is processed by the tool T. At this time, when the main shaft 1 rotates at a high speed, the opening of the concave portion 1e of the collet holder 1h expands due to centrifugal force, thermal expansion, or the like. Because it expands in the radial direction approximately equivalent to the amount of expansion,
The clearance between the recess 1e of the collet holder 1h and the collet 22 is filled. Thereby, the support rigidity in the radial direction of the tool holder 20 can be maintained, and the processing accuracy can be ensured even at the time of high-speed rotation.

As described above, according to the tool holder 20, there is no need to provide cooling fins or a heater on the main shaft unlike the conventional tool holder. And cost can be reduced. In particular, since cooling fins are not required for the tool holder 20, the diameter of the tool holder 20 can be reduced, and the mechanical strength against centrifugal force can be reduced. Further, since the rotation accuracy is improved, the run-out of the tool tip can be reduced. Further, by using an aluminum alloy or the like having a lower specific gravity than the main spindle 1 for the tool holder 20, the centrifugal force can be reduced, and the rotation accuracy of the tool holder can be further improved.

Here, in the present embodiment, an example in which a copper-beryllium alloy or an aluminum alloy is used as the material of the collet 22 has been described, but the present invention is not limited to this.
For example, a copper / beryllium alloy or an aluminum alloy can be used in combination with a resin or a carbon fiber material. In addition, in order to fix the tool T to the collet 22, the splits 22c and 22d are provided in the collet 22, but the radial expansion amount of the collet 22 is adjusted by the length and the number of the splits 22c and 22d. Is also possible. That is, when the number of the cracks 22c and 22d increases, the collet 22 easily spreads due to centrifugal force. Therefore, the clearance between the collet 22 and the recess 1e of the collet holder 1h can be satisfactorily filled by the synergistic effect of the thermal expansion of the collet 22 and the centrifugal force.

Further, in the present embodiment, the main shaft 1 in which the collet holder 1h is integrally formed has been described as an example, but the collet holder 30h is formed separately from the main shaft 30 as shown in FIG. , A bolt or the like (not shown). This makes it possible to select an appropriate material for the collet holder 30h in accordance with the material of the collet 22.

[0024]

According to the present invention, the convex portion of the tool holder is expanded by the heat of the main shaft to fill the clearance between the concave portion of the main shaft and the convex portion of the tool holder during high-speed rotation. This eliminates the need for cooling fins and the like for the tool holder, which are conventionally required. For this reason, the structure of the tool holder is simplified, unstable elements during high-speed rotation can be reduced, and costs can be reduced.

[Brief description of the drawings]

FIG. 1 is a detailed view of a distal end portion of a spindle on which a tool holder according to an embodiment of the present invention is mounted.

FIG. 2 is a view taken in the direction of arrows II-II in FIG. 1, in which a lock nut is omitted.

FIG. 3 is a perspective view of a collet of a tool holder according to one embodiment of the present invention.

FIG. 4 is a detailed view of the tip of another type of spindle on which a tool holder according to one embodiment of the present invention is mounted.

FIG. 5 is a detailed view of a distal end portion of a spindle on which a conventional tool holder is mounted.

[Explanation of symbols]

T tool 1 spindle 1h collet holder (tip of spindle) 1e recess (tapered recess formed at the center of tip of spindle) 20 tool holder 22 collet 22s fitting projection (projection) 25 lock nut

Claims (2)

[Claims] 1. A tool holder, which is a connecting jig for attaching a tool coaxially to a spindle whose amount of heat increases as the number of revolutions increases, comprising: a tapered recess formed at the center of the tip of the spindle; A protrusion formed into a shape that can be fitted, wherein the coefficient of thermal expansion and the thermal conductivity of the protrusion are approximately equivalent to the amount by which the recess of the main shaft expands during rotation. As it receives heat from the main shaft and thermally expands in the radial direction,
A tool holder, the value of which is set. 2. The tool holder according to claim 1, wherein the tool holder is formed of a material having a specific gravity smaller than that of the main shaft.