JPS61270042A - Spindle mechanism of machine tool - Google Patents

Abstract

PURPOSE:To prevent the work surface of a workpiece and hearings from respective failure in accuracy and rigidity and seizure due to temperature rising by making the body section inside of both the ends of the bearing mechanism of a spindle out of lower thermal expansion coefficient glass and a spindle head and the bearing mechanism out of low thermal expansion coefficient cost iron. CONSTITUTION:Neoceram used as material for a spindle body section 31 being extremely small in comparison with conventionally used irony material in a thermal expansion coefficient, the thermal displacement of the lower end of the body section 31 in relation to thrust bearing sections 22b and 23a determining the axial directional position of the body section 31 becomes extremely small. And the LE cast irony used as material for a spindle head 12 and bearing metals 21 thru 23 supported by a bed through column 11 is so small in comparison with ordinary cost iron or gun metal in a thermal expansion coefficient that the thermal displacement of the thrust bearing sections 22b and 23a in relation to the bed is also small. Even if the temperature of a spindle 30 is raised due to the rotation, therefore, the thermal displacement in relation to the bed of the lower end of the body section 31 to which a grinding wheel G is attached becomes extremely small preventing a workpiece W from failling the accuracy of the work surface.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a spindle device of a machine tool suitable for an ultra-precision surface grinder or the like.

[Prior art]

In a spindle device for a machine tool, the spindle device includes a spindle head supported on a bed, and a spindle supported by the spindle head in an axially immovable manner via a bearing device having a radial bearing portion and a thrust bearing portion. Conventionally, a spindle made of hardened and ground iron-based material, a spindle head made of ordinary cast iron, and a bearing device made of gun metal have been used.

[Problem that the invention attempts to solve]

In this type of spindle device, when the spindle rotates, heat is generated near the bearing surface, the temperature of the spindle increases, the spindle, bearing device, and spindle head expand, and the end of the spindle is displaced in the longitudinal direction relative to the bed. . Therefore, in ultra-precision surface grinders, etc., in which a grinding wheel is attached to the end of the spindle and grinding is performed using a grinding surface perpendicular to the axis of the spindle, subtle changes in the grinding wheel relative to the workpiece may occur due to displacement in the longitudinal direction due to the expansion of each part. There is a problem in that the depth of cut cannot be made accurately and the precision of the machined surface of the workpiece decreases. The present invention attempts to solve this problem by using glass with a low coefficient of thermal expansion as the spindle and cast iron with a low coefficient of thermal expansion as the spindle head and bearing device.

[Means for solving problems]

For this purpose, the spindle device for a machine tool according to the present invention includes a spindle head 12 supported on a bed 1o and a radial bearing portion 21a, as shown in the accompanying drawings.

22a and thrust bearing portions 22b, 23a, and the main shaft l1J via this bearing device 20.
In a main spindle device for a machine tool comprising a main spindle 30 that is pivotally supported in an axially immovable manner by a bearing device 112, at least a main body portion 31 of the main spindle 30 located inside of both ends 20a and 20b of the bearing device 20 has low thermal expansion. It is characterized in that it is made of coefficient glass, and the spindle head 12 and bearing device 20 are made of cast iron with a low coefficient of thermal expansion.

[Effect]

When the main shaft 30 rotates, heat is generated between the main body 31 and the radial bearings 21a, 22a and thrust bearings 22b, 23a due to fluid friction of lubricating oil, etc. The temperatures of the bearing device 20 and the spindle head 12 rise.

However, since the low coefficient of thermal expansion glass that constitutes the main body 31 has an extremely small coefficient of thermal expansion compared to the iron-based material conventionally used for the main shaft, the expansion of the main body 31 and, by extension, the main shaft 30 is extremely small. The longitudinal displacement of the end of the main shaft 30 with respect to the bearing device 20 supporting the main shaft 30 is extremely small. Furthermore, the low thermal expansion coefficient cast iron that constitutes the main shaft tiJ112 and the bearing device 20 has a smaller thermal expansion coefficient than the normal cast iron or gunmetal that has been conventionally used for these components. 23
The longitudinal displacement of a with respect to the bed 10 is also small. As a result, the length of the end of the main shaft 30 relative to the bed 10 is also extremely reduced.

〔Effect of the invention〕

As described above (according to the present invention), the main body is damaged due to heat generation between the main body of the spindle and the bearing that supports the main shaft.

Even if the temperature of the bearing device and spindle head rises, the longitudinal displacement of the spindle end relative to the bed, which is a support member, is extremely small, so such a temperature rise will not reduce the accuracy of the machined surface of the workpiece. . ) Moreover, changes in bearing clearance due to temperature rise are also reduced, so changes in bearing rigidity and seizure can be prevented.

〔Example〕

An example of an ultra-precision surface grinder will be described below with reference to the accompanying drawings.

As shown in FIG. 2, a column 11 is erected on the bed 10, and a main shaft al12 is vertically slidably guided and supported on the column 11, and as shown in FIG.
A feed movement is provided by a motor 15 via 3 and a feed screw 14. The main shaft 30 is rotatably supported on the main shaft 812 (see Fig. 1), and the main shaft 30 is rotatably supported around the vertical axis.
A grindstone G is attached to the lower end of 0. On the bed 10 below the spindle head 12, a rotary table 17 for supporting a workpiece W is rotatably supported around a vertical axis.

As shown in FIG. 1, the main shaft 30 consists of a main body part 31 and a protruding part 32 provided on the upper part.
Main shaft i! via a bearing device 20 equipped with a! It is pivotally supported on J112 so as not to be movable in the vertical axial direction. Bearing device 20
consists of bearing metals 21 and 22 that are fitted and fixed into openings provided above and below the spindle head 12, and a bearing metal 23 that is fixed to the inner end of the lower bearing metal 22.
The radial bearing parts 21a and 22a are formed on the inner periphery of the bearing metal 22, and the inner periphery sides of the bearing metals 22 and 23 face each other in the axial direction with a gap in between, and the thrust bearing parts 22b and 23a are formed in this part. is formed. Each bearing part 21
a, 22a, 22b, and 23a are all hydrostatic bearings,
Pressurized lubricating oil from a lubricating oil pump (not shown) is supplied to each bearing portion 21a, 22a, 22b, 23 via an annular groove 25, an oil passage, and a throttle 26 provided on the outer periphery of bearing metals 21, 22.
It is supplied to a.

Each bearing metal 21, 22, 23 that constitutes the bearing device 20
and the spindle head 12 are each integrally formed of LE cast iron (trade name). Linear expansion coefficient of LE cast iron b (10xlO/'c and 18.3, respectively)
x10/'C).

The main body part 31 of the main shaft 30 has a flange 31a in the middle part, and the whole body part 31 is integrally formed of Neoceram (trade name). Neoceram has a low thermal expansion coefficient b which is extremely small compared to the expansion coefficient (approximately 12X10/''C). At the same time, the flange portion 31a is held between the thrust bearing portions 22b and 23a with a small gap therebetween, so that the main body portion 31 is pivotally supported by the spindle head 12 so as not to be able to move in the axial direction, and its upper and lower ends are respectively supported by the bearing device 20. upper and lower ends 20a of
, 20b. Coaxial fitting holes 31b are formed at the upper and lower ends of the main body portion 31, and the fitting holes 31b are formed coaxially with each other.
A plurality of pieces 33 having internal threads are fixed in a plurality of holes surrounding 1b by adhesive or the like.

As shown in FIG. 1, at the upper end of the main body 31 of the main shaft 30,
A protruding portion 32 made of an iron-based material is provided coaxially through the fitting hole 31b, and is fixed to the main body portion 31 by a plurality of bolts that are screwed into the female threads of the piece 33. A spindle drive motor 16 is provided above the spindle head 12, and the stator 1
6b is fixed to the spindle head 12 together with the casing 16a,
The rotor 16c is fixed to the tapered portion of the protrusion 32 of the main shaft 30 with a ring nut. A grindstone mounting plate 34 made of permanent steel (umber) is fixed coaxially to the main body 31 by the same means as the protrusion 32 at the lower end of the main body 31. Grinding wheel G is bolted. The main body of the grinding wheel G is made of permanent steel, and diamond abrasive grains are coated and fixed together with an adhesive on the lower surface of the grinding surface G1 and near its inner and outer peripheries.

In the ultra-precision surface grinder of this embodiment, a grindstone G for surface grinding attached to the lower end of the main body 31 of the main shaft 30 is rotationally driven by the main shaft drive motor 16 together with the main shaft 30, and is vertically driven by the feed motor 15. A cutting feed is given in the direction, and the rotary table 17 is
The upper surface of the workpiece W supported above is ground. Each bearing part 21a, 22a, 22b, which is a static pressure bearing,
The calorific value per unit time of the column 23a increases in proportion to the square of the rotational speed of the spindle 30, and the temperatures of the main body 31, bearing metals 21, 22, 23, and spindle head 12 increase accordingly. The temperature of No. 11 does not rise that much. Neoceram, which was used as the material for the main body 31 in this embodiment, has a much smaller coefficient of thermal expansion than conventionally used iron-based materials, so the thrust bearing that determines the axial position of the main body 31 is Thermal displacement of the lower end of the main body part 31 with respect to the parts 22b and 23a becomes extremely small. Also, a spindle head 12 and a bearing metal 2 supported by the bed 10 via a column 11 are provided.
The LE cast iron used as the material for 1, 22.23 has a smaller coefficient of thermal expansion than normal cast iron or gunmetal, so bed 1
Thermal displacement of the thrust bearing portions 22b and 23a relative to zero is also small. As a result, even if the temperature rises due to the rotation of the main shaft 30, the bed 10 at the lower end of the main body 31 on which the grindstone G is attached
The thermal displacement relative to the workpiece W is extremely small, and the accuracy of the machined surface of the workpiece W does not deteriorate.

In addition, as described above, the main body portion 31 and the bearing metal 21, 22
．． 23 have small coefficients of thermal expansion, so changes in the gap between the thrust bearing parts g2b, 23a and the flange 31a due to temperature changes are also reduced. Therefore, changes in the support rigidity of the thrust bearings 22b and 23a due to temperature changes are reduced.
Further, the gap can be reduced and the support rigidity can be increased without fear of seizure, and the accuracy of the machined surface of the workpiece W can also be improved by this.

[Brief explanation of the drawing]

The drawings show an embodiment of an ultra-precision surface grinder of a spindle device of a machine tool according to the present invention, and FIG. 1 is a cross-sectional view of the main part, and FIG. 2 is a side view of the whole. Explanation of symbols 10...Bed, 12...Spindle head, 20...Bearing device, 20a, 20b...-Both ends, 21a, 2.2a-
- Radial bearing part, 22b, 23a... Thrust bearing part, 30... Main shaft, 31... Main body part.

Claims (1)

[Claims] A main shaft of a machine tool comprising: a main spindle head supported by a column; a bearing device having a radial bearing section and a thrust bearing section; In the apparatus, at least a main body portion of the main shaft located inside both ends of the bearing device is formed of glass with a low coefficient of thermal expansion, and the head of the spindle and the bearing device are formed of cast iron with a low coefficient of thermal expansion. Machine spindle device.