JPH08294839A - Spindle head - Google Patents

Abstract

PURPOSE: To set off the elongations of a spindle and feed screw caused by thermal displacement with the elongations of a spindle head and a receptacle table by forming the receptacle table from a metal material having a greater coefficient of thermal expansion than the materials of the spindle and feed screw. CONSTITUTION: The direction in which a spindle head 4 and receptacle table 10 elongate is opposite to the direction in which a spindle 8 and ball screw elongate, so that the elongations are set off by each other, and the thermal displacement at the spindle nose 8a can be minimized when the thermal displacement 5A of the part with a total length A of the spindle 8 and ball screw is equal to the thermal displacement 3B of the spindle head 4 and receptacle table 10. Therefore, the receptacle table 10 should be made of a metal material such as aluminum having a greater coefficient of thermal expansion than that of iron material with which the spindle 8 and ball screw are formed. If the ratio of the coefficient of thermal expansion of the material of spindle 8 and ball screw to the material of receptacle table 10 is 1:2, the two are set off by each other, provided that the elongation of the spindle head 4 is ignored and a simplification as the temp. being uniform is introduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spindle head of a machine tool such as a boring machine or a machining center. In particular, a material having a large thermal expansion coefficient is used as a material of a pedestal of the spindle head, and the thermal displacement of the spindle and the spindle The present invention relates to a spindle head capable of canceling the thermal displacement of the head and the pedestal.

[0002]

2. Description of the Related Art In machine tools, various technical improvements have been made to improve the machining accuracy, and thermal displacement due to temperature rise of the machine has a great influence on the machining accuracy. In horizontal boring machines and machining centers, the change in positioning accuracy is mostly due to the thermal displacement of the machine. In addition, since the spindle position accuracy is also the relative relationship between the work and the tool, there is a problem that no matter how much the spindle feed accuracy is increased, as long as there is thermal displacement, it will not directly improve the spindle position accuracy. is there.

Various measures have conventionally been taken against thermal displacement. For example, various attempts have been made to cool the lubricating oil of the spindle head with a cooler in order to reduce the amount of heat generation, or to use a material having a small thermal expansion coefficient for the spindle.

[0004]

However, even if the cause of thermal displacement is the heat generated from the machine side or the heat generated by processing, they are intricately entangled in relation to the structure of the machine. The fact is that it is not easy to take preventive measures. In addition, among machine tools, in horizontal boring machines and machining centers, thermal displacement of the spindle head and the pedestal that houses the feed mechanism such as feed screws and nuts can also affect the spindle position accuracy. Regarding the pedestal, no measures against thermal displacement were taken.

Therefore, an object of the present invention is to solve the problems of the above-mentioned prior art and to make it possible to offset the elongation of the spindle and the feed screw due to thermal displacement and the elongation of the spindle head and the pedestal so that the spindle position accuracy is improved. It is to provide a spindle head that can achieve the improvement of.

[0006]

In order to achieve the above object, the present invention provides a machine tool having a pedestal for supporting a rear end portion of a spindle and accommodating a feed screw / nut mechanism for feeding the spindle. In the above spindle head, the pedestal is made of a metal material having a coefficient of thermal expansion larger than that of the material of the spindle and the feed screw.

As the material of the pedestal, it is preferable to use a metal material such as aluminum or aluminum alloy, which has a coefficient of thermal expansion about twice that of the iron-based metal material.

[0008]

According to the present invention, since the pedestal is made of a metal material having a coefficient of thermal expansion larger than that of the material of the main shaft and / or the feed screw, the extension of the pedestal is greater than that of the main spindle or the feed screw. It is large, and since the extending direction of the spindle head and the pedestal and the extending direction of the spindle are opposite directions, the elongation of both is canceled out as a whole, so the influence of thermal displacement on the spindle position accuracy can be reduced. .

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the spindle head according to the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a view showing a spindle head of a horizontal boring machine according to an embodiment of the present invention, and 2 is a column for holding a spindle head 4.

A cylindrical housing 6 is attached to the spindle head 4, and a quill (not shown) is coaxially housed inside the housing 6, and a spindle 8 is rotatable via the quill. It is supported.

On the rear side of the spindle head 4, a cradle 1 incorporating a ball screw mechanism for feeding the spindle 8 concentrically with the spindle 8.
0 is attached.

FIG. 2 is a sectional view of the pedestal 10.
0 is fixed to the rear end of the housing 6, and the main shaft 8
The thrust load and the radial load are supported by the angular bearing 12 inside the pedestal 10.

In the feed mechanism inside the pedestal 10, the angular bearing 12, the hydraulic cylinder 14 for unclamping the tool holder inserted at the tip of the main shaft 8, and the feed nut held via the holding member 17 are provided. 16 is assembled integrally.

On the other hand, the ball screw 18 with which the feed nut 16 is screwed is coaxially incorporated into a draw bar 19 inside the main shaft 8, and its end portion is supported by a bearing 21. Motor 20 for driving this ball screw 18
Is transmitted via a gear train composed of gears 22, 23, 24. Therefore, with the rotation of the ball screw 18,
The main shaft 8 is supported by an angular bearing 12 and is rotated and fed integrally with the hydraulic cylinder 14 in the ± z direction. Reference numeral 26 denotes a rod that holds the holding member 17 slidably and guides the feed, and also serves as a rotation stopping function. Reference numeral 28 denotes a piston of the hydraulic cylinder 14. The piston 28 presses against the elastic force of a disc spring (not shown) which abuts on the end of the draw bar 19 and clamps the tool holder, so that the tool holder is pushed. It is supposed to be unclamped.

The cradle 1 containing the above-mentioned feeding mechanism
No. 0 is made of a material different from the materials of the main shaft 8 and the ball screw 18. In this example,
The main shaft 8 and the ball screw 18 are made of an iron-based metal material such as steel, which is generally used as a material for this type of component, while the pedestal 10 is made of aluminum or an aluminum alloy.

In FIG. 1, A shows the total length from the end face of the spindle tip 8a to the end of the ball screw 18 inside the pedestal 10, and B shows the length of the pedestal 10. Here, the displacement of the spindle tip 8a due to thermal displacement is considered with the front end face of the column 2 as the reference plane Z0.

During operation of the machine, heat is generated by machining, gears and bearings transmitting power to the main spindle 8 generate heat inside the spindle head 4, and the pedestal 10 causes ball movement due to feed movement. The screw 18 generates heat. Using these as heat sources, the temperature of each part of the machine rises and the main shaft 8 and ball screw 1
8. Thermal displacement occurs on the pedestal 10.

Since the main shaft 8 is connected to the ball screw 18 via the feed nut 16, the main shaft 8 and the ball screw 1
Thermal displacement can be considered by integrating 8 and 8. As for the direction of thermal displacement, the end portion of the ball screw 18 is axially fixed by the bearing 21, and therefore extends in the forward + z direction in FIG.

On the other hand, the pedestal 10 has a rear end portion which is a free end and extends rearward in the -z direction due to thermal displacement. In this case, strictly speaking, a portion having a length C from the reference surface Z0 including the spindle head 4 together with the pedestal 10 to the rear end portion of the pedestal 10 extends in the −z direction.

FIG. 3 shows the thermal displacement of the portion of the total length A of the main shaft 8 and the ball screw 18 due to the temperature rise, and the pedestal 10.
FIG. 6 is a diagram qualitatively showing thermal displacement of a portion having a length C in which the spindle head 4 is summed up. In this figure, the change in A is represented by the curve of δA, the change in B is represented by the curve of δB, and the total thermal displacement with reference to the reference plane Z0 is represented by δA + δB.

As described above, since the extending directions of the spindle head 4 and the pedestal 10 and the extending directions of the spindle 8 and the ball screw 18 are opposite to each other, the elongations of the both are offset, and therefore, the spindle 8 and the ball If the thermal displacement δA of the total length A of the screws 18 and the thermal displacement δB of the spindle head 4 and the pedestal 10 become the same amount, the thermal displacement at the spindle end 8a can be minimized.

Therefore, in the embodiment, the pedestal 10 is made of an aluminum-based material, and is made of a metal material having a larger thermal expansion coefficient than the iron-based metal that is the material of the main shaft 8 and the ball screw 18. ing.

If the ratio of the total length A of the spindle 8 and the ball screw 18 to the length B of the pedestal 10 is A: B = 2: 1, the material of the spindle 8 and the ball screw 18 and Stand 1
If the ratio of the coefficient of thermal expansion of the material of 0 is 1: 2, the elongation of the spindle head 4 is not taken into consideration, and if the temperature is considered to be uniform, the elongation of both is canceled out. become.

However, in reality, since the spindle head 4 also extends in the −z direction, the length C of the pedestal 10 can be considerably shortened, but on the other hand, the spindle 8 inside the spindle head 4 and the pedestal 10 and the ball screw. Considering that the temperature rise and the elongation of 18 are larger than those of the pedestal 10 that can radiate heat to the outside air, the displacement at the tip of the spindle can be set by setting A: B = 2.5: 1. It is possible to make it smaller.

In the case of aluminum, the coefficient of thermal expansion at 20 ° C. is 23.9 × 10 ⁻⁶ / ° C., the coefficient of thermal expansion of iron is 11.7 × 10 ⁻⁶ / ° C., and that of high carbon steel is 9.58 to. 10.
Since it is 87 × 10 ⁻⁶ / ° C., it has a coefficient of thermal expansion approximately twice, aluminum is used as the material of the pedestal 10, and the main shaft 8 and the ball screw 18 are conventionally formed. The generally used steel material may be used.

In addition to the above, the pedestal 10 may be made of, for example, silmine (19.8 to 21.2 × 10 ^-6 / ° C) or duralumin (22.6 × 10 ^-6 / ° C). Is applicable as. Further, the ratio between the length B of the pedestal 10 and the length A of the main shaft 8 and the ball screw 18 is not limited to the above-mentioned example, and is appropriate according to the ratio of the values of the coefficient of thermal expansion of the material. The length of the pedestal 10 may be set.

[0027]

As is apparent from the above description, according to the present invention, the spindle head and the pedestal are extended by using a metal material having a thermal expansion coefficient larger than that of the material of the spindle and the feed screw. The direction is opposite to the direction in which the main shaft and the feed screw extend, and the pedestal elongation is larger than that of the main shaft and the feed screw. Therefore, as a whole, the elongations of the both are canceled out, the influence of thermal displacement on the spindle position accuracy can be reduced, and the processing accuracy can be improved. Moreover, the pedestal is smaller than the spindle head and the material can be changed easily and at low cost, which is effective as a measure against thermal displacement.

[Brief description of drawings]

FIG. 1 is a side view of a spindle head of a horizontal boring machine according to an embodiment of the present invention.

FIG. 2 is a sectional view of a pedestal attached to a spindle head.

FIG. 3 is a graph qualitatively showing the thermal displacement of the spindle and the thermal displacement of the spindle head and the pedestal.

[Explanation of symbols]

 2 Column 4 Spindle head 8 Spindle 10 Cradle 16 Feed nut 18 Ball screw 19 Drawbar 20 Motor

Claims (2)

[Claims] 1. A spindle head of a machine tool having a pedestal for supporting a rear end portion of a spindle and for accommodating a feed screw / nut mechanism for feeding the spindle in an axial direction. A spindle head characterized by being made of a metal material having a coefficient of thermal expansion larger than that of the material. 2. The spindle according to claim 1, wherein the material used for the pedestal is a metallic material having a coefficient of thermal expansion about twice that of an iron-based metallic material of the spindle material. Head.