JP2004136395A - Bed for machine tool - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide at a low cost a bed for a machine tool which realizes a low temperature displacement. <P>SOLUTION: The bed 1 for the machine tool comprises a molded article with draft holes 2 which has a hollow structure, and the draft holes 2 are closed with lids 3, 4, thus the inside of the bed 1 is formed into a closed space. In another way, the draft holes 2 of the bed 1 are closed with the lids 3, 4, and further the inside of the bed is filled with a liquid to increase thermal capacity of the whole bed. The liquid is preferably water or oil added with rust preventive agent. By these solving means, the bed 1 has a structure which is made insensitive to a variation in outside temperature. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a machine tool bed for realizing low thermal displacement.
[0002]
2. Description of the Related Art It is well known that a bed for a machine tool used in a grinding machine or the like is generally made of a casting. Usually, the cast bed is cast out so that the inside thereof has a hollow structure, and the cast-out bed has ribs integrally formed to form a lattice-like reinforced structure. Also, a plurality of cast-out holes are formed in the side and bottom surfaces of the bed. The reason why the inside of the bed has a hollow rib structure made of a casting is to reduce the weight of the bed body and to reduce the influence of distortion due to aging of the material. The cast-out hole cannot be eliminated because the inside of the bed must have a hollow rib structure.
[0003] On the other hand, among machine tools, particularly, beds used in ultra-precision machines which require high machining accuracy for optical parts and the like are made of stones such as granite in addition to castings. There is. Stone beds made of granite or the like are characterized by a material having less aging and a large heat capacity as compared with cast beds, and are usually used as a solid structure.
[0004]
However, in the conventional casting bed, the internal structure is exposed to the outside air through a cast hole, and the contact area with the outside air is large as compared with the solid structure. Susceptible to outside temperatures.
In general, the time required for an object having a temperature difference from the outside air temperature to adjust to the outside air temperature and become the same temperature becomes shorter as the ratio of the surface area S to the volume V, that is, S / V is larger. For example, FIG. 10 shows the results obtained by calculating the temperature changes of three types of objects having a constant volume and different surface areas having a temperature difference from the outside air temperature. These three types of objects are of the same material (grey cast iron), and are calculated at the initial temperature (25 ° C.) and the ambient temperature (20 ° C.). From FIG. 10, it can be seen that the time required for the sphere having the minimum S / V to reach the same temperature as the outside air temperature is long, and the longer the S / V is, the shorter the time is. That is, it can be said that the larger the S / V, the more easily the influence of the outside air temperature is.
A conventional cast bed has a large S / V compared to a solid structure because the inside of the bed has a hollow rib structure. Therefore, the bed temperature is likely to change due to the fluctuation of the outside air temperature, and as a result, the structure attached to the bed, specifically, the slide surface, the tool shaft, the work spindle, etc., are affected, and the work-tool Will cause an error in the positional relationship. As a result, there has been a problem that the processing accuracy varies during long-time processing.
[0007] The above problem arises in that the room temperature is controlled to, for example, ± 1 ° C or less with respect to a set temperature like a super-precision processing machine as well as a machine tool installed in a place where the outside air temperature fluctuates greatly, such as a factory. It also had a significant effect on machines that were installed in a constant temperature room and required extremely high processing accuracy.
On the other hand, a stone bed made of granite or the like has a larger heat capacity than a cast bed, and has a small contact area with the outside air because it is a solid rectangular solid. Therefore, there is an advantage that it is difficult to follow the fluctuation of the outside air temperature and high processing accuracy can be obtained. However, since granite is more expensive than a casting and is not easily machined, there is a problem that the degree of freedom in design is low.
The present invention has been made in view of the above circumstances, and has as its object to provide an inexpensive machine tool bed that realizes low thermal displacement.
[0010]
According to a first aspect of the present invention, there is provided a machine tool bed comprising a casting having a hollow structure and a cast hole. Wherein the cast hole is closed with a lid.
[0011] In the machine tool bed according to the second aspect of the present invention, the machine tool bed made of a casting having a hollow structure and a cast hole is closed with a cover, and the inside of the bed is further filled with liquid. It is characterized by the following.
According to a third aspect of the present invention, in the machine tool bed, the liquid is water or oil to which a rust inhibitor has been added.
[0013]
According to the present invention, since the inside of the bed of the machine tool bed made of a casting having a hollow structure and having a cast hole is closed by closing the cast hole with a lid, the bed is exposed to the outside air. The surface area is reduced, and thermal displacement of the entire bed can be suppressed.
In addition, the heat capacity of the entire bed is increased by closing the cast hole of a machine tool bed made of a casting having a hollow structure and having a cast hole with a lid and further filling the inside of the bed with a liquid. The bed can suppress thermal displacement more than a case where the cast hole is simply closed with a lid. In this case, the liquid used is preferably water or oil to which a rust inhibitor has been added.
[0015]
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a machine tool bed according to a first embodiment of the present invention. 1 and 2 schematically show a machine tool 100 using the bed 1 of the present invention. FIG. 1 is a plan view of the machine tool 100, and FIG. 2 is a front view of the machine tool 100. 3 and 4 are cross-sectional views of the bed 1. FIG. 3 is a cross-sectional view of the bed 1 taken along line AA in FIG. 1, and FIG. 4 is a cross-sectional view of the bed 1 taken along line BB of FIG. Represents. FIGS. 5 and 6 are enlarged views showing a state in which the cast hole 2 is closed by the lids 3 and 4. FIG. 5 shows a state in which the cast hole 2 on the side surface of the bed 1 is closed by the lid 3. FIG. 6 shows a state in which the cast hole 2 on the bottom surface of the bed 1 is closed by the lid 4.
The machine tool 100 processes a work W attached to the tip of the main shaft 140 by a tool (not shown) provided on a table 170 in a constant temperature room set at, for example, 20 ° C. Denotes an optical component such as a lens or a mold thereof.
A fixed base 110 is provided on the upper surface of the bed 1 of the machine tool 100 as shown in FIGS. Note that no cast hole is provided on the upper surface of the bed 1. The fixed base 110 guides and supports the intermediate base 120 so as to be able to reciprocate in the X-axis direction by a linear motor 111 fixed to an upper part thereof. The intermediate base 120 reciprocates in the X-axis direction by a guide mechanism provided on the fixed base 110, and engages the moving body 130 with a pair of guide surfaces formed on both sides of the inner surface, so that the intermediate base 120 The moving body 130 is guided and supported by a fixed linear motor (not shown) so as to be able to reciprocate in the Z-axis direction. The moving body 130 has a main shaft 140 attached to its tip, and reciprocates in the Z-axis direction together with the main shaft 140 by a guide mechanism provided on the intermediate base 120. The main shaft 140 clamps the cylindrical work W and rotates around the Z axis (C axis).
On the other hand, a base 150 is provided directly below the tip of the main shaft 140 on the side surface of the bed 1. It should be noted that no casting hole is provided on the side surface of the bed 1, which is the mounting surface of the base 150. The base 150 engages the moving body 160 with a pair of guide surfaces formed on both sides of the inner surface, and guides and supports the movable body 160 in a Y-axis direction by a linear motor (not shown) supported by the base 150. The moving body 160 has a table 170 attached to its tip, and reciprocates in the Z-axis direction together with the table 170 by a guide mechanism provided on the base 150. A tool (not shown) for processing the work W (for example, a cutting tool or a grindstone) is arranged on the table 170 at a position separated by a predetermined distance from a B-axis parallel to the Y-axis which is the rotation axis of the table 170. I have. The table 170 is rotated by a driving device (not shown), and the tool is turned around the Y axis (B axis).
As described above, the machine tool 100 is provided with a mechanism for moving the workpiece W in the X and Z axes and a mechanism for rotating the workpiece W around the Z axis on the upper surface of the bed 1 and at the side of the bed 1 directly below the main shaft 140. By providing a mechanism for moving the tool in the Y-axis direction and a mechanism for rotating the tool around the Y-axis on the side, free-form surface machining of the workpiece W can be realized.
Next, the bed 1 will be described in detail with reference to the drawings. The bed 1 of the machine tool 100 is made of a casting, and the inside is cast out as shown in FIGS. 3 and 4, and the inside of the bed 1 is provided with ribs 10 integrally formed with the bed 1 at regular intervals in a grid pattern. Is provided. The ribs 10 are provided at regular intervals in a lattice pattern inside the bed 1 to reinforce the bed 1, and the inside of the bed 1 is 2 (length) × 3 (width) × 2 (height) = 12 in total. Are provided so as to partition into spaces having the same volume. In addition, the rib 10 is provided with a through-hole 11 that penetrates and connects adjacent spaces.
A cast hole 2 is opened through the side and bottom of the bed 1. The casting hole 2 is provided for removing the casting sand filling each space inside the bed 1 at the time of casting, and each space inside the bed 1 is easily removed from the casting sand. At least one or more are provided. The cast-out hole 2 on the side surface of the bed 1 is closed by a lid 3, and the cast-out hole 2 on the bottom surface of the bed 1 is closed by a lid 4, so that the inside of the bed 1 is configured as a closed space.
The lid 3 for closing the cast hole 2 on the side surface of the bed 1 has a larger shape than the cast hole 2 so as to cover the entire cast hole 2, and the center portion thereof will be described later. A hole for passing the bolt 7 is provided. Further, a groove for inserting an O-ring 5 for sealing the inside of the bed 1 is provided over the entire periphery of the portion of the lid 3 which is in close contact with the bed 1, as shown in FIG. The O-ring 5 is inserted into the. Then, the lid 3 is closed by the clamper 6 and the bolt 7 so as to be in close contact with the bed 1. Specifically, the clamper 6 has a cross-shaped shape, and its center is threaded. The bolt 7 is passed through the screw part of the clamper 6 through the lid 3, and the clamper 6 and the bed 1 come into close contact with each other by tightening the bolt 7. As a result, the lid 3 is closed so as to be in close contact with the bed 1, and it is possible to prevent leakage of air inside the bed 1 and entry of outside air into the inside of the bed 1.
On the other hand, the cover 4 for closing the cast hole 2 on the bottom surface of the bed 1 has a shape larger than the cast hole 2 so as to cover the entire cast hole 2, and a cover is provided on the outer periphery thereof. A plurality of holes for passing bolts 8 for tightening 4 are formed. Further, a groove for inserting an O-ring 9 is provided over the entire periphery of the portion of the lid 4 which is in close contact with the bed 1 as shown in FIG. 6, and the O-ring 9 is inserted into the groove. . Then, the lid 4 is passed through a bolt 8 through a through hole and a screw portion (not shown) provided on the outer periphery of the cast hole 2 of the bed 1, and is closed so as to be in close contact with the bed 1 by tightening. As a result, it is possible to prevent leakage of air inside the bed 1 and entry of outside air into the bed 1.
As described above, by closing the cast holes 2 on the side and bottom surfaces of the bed 1 with the lids 3 and 4, the inside of the bed 1 becomes a closed space, and the surface area exposed to the outside air is reduced. Thermal displacement can be suppressed. As a result, accuracy in long-time processing can be stabilized. In addition, what is indicated by 12 on the upper surface of the bed 1 is a liquid injection port used in the second embodiment, which is not required in the first embodiment and is plugged.
Next, a second embodiment will be described. In the second embodiment, the cast hole of the bed is closed with a lid, and the inside of the bed is further filled with liquid. Note that the configurations of the machine tool and the bed of the second embodiment are the same as those of the first embodiment. In other words, the process until the cast hole 2 of the bed 1 of the machine tool 100 is closed by the lids 3 and 4 is the same as that of the first embodiment, and thereafter, the inside of the bed that has become a closed space is filled with liquid. Since the O-rings 5 and 9 are inserted into the lids 3 and 4, there is no fear that the liquid leaks from the portion where the bed 1 and the lids 3 and 4 are in close contact.
The liquid filling the inside of the bed 1 is injected from a liquid inlet 12 provided on the upper surface of the bed 1. The liquid inlet 12 is usually filled with a plug to prevent outside air from entering, and the liquid is injected by removing the plug when injecting the liquid. After the liquid has been injected, the liquid injection port 12 is plugged again to seal the inside of the bed 1 in order to prevent the intrusion of outside air and the evaporation of the liquid to reduce the amount.
As the liquid to be filled in the bed 1, water having a large specific heat is most preferable. Furthermore, it is preferable to add a rust preventive to water in order to prevent the cast iron bed 1 from rusting. Further, ethylene glycol or the like may be added as an antifreeze so that water does not freeze. Further, as the liquid to be filled into the inside of the bed 1, oil may be filled from the viewpoint of rust prevention and antifreezing in addition to water.
As described above, the inside of the bed 1 is made a closed space by providing the lids 3 and 4 for closing the cast hole 2 of the bed 1, and the inside of the bed 1 is filled with liquid. The heat capacity of the bed becomes larger, and the thermal displacement of the entire bed can be further suppressed as compared with the case where the casting hole is merely covered.
FIG. 7 shows the relationship between the volume V, the surface area S, the ratio S / V of the volume V and the surface area S, the weight, and the total heat capacity for the modeled conventional and present bed structures. The bed structure shown in FIG. 7 includes a solid cast bed (A) having a cube of 1 m on a side and a cube having a solid structure of 1 m on a side and having a rib thickness of 50 mm and 3 (length) × 3 (width). ) × 3 (height) = Casting bed of hollow rib structure (B) divided into a total of 27 spaces, bed of solid granite structure (C) having a cube of 1 m on a side, casting of hollow rib structure bed closes the hole punching cast against manufacturing bed (B) a lid (B _0), bed was filled with mineral oil to the internal bed cast punching holes relative to the bed that closed by a lid (B ₀₎ (B ₁ ) And a bed (B ₂ ) in which the inside of the bed is filled with water with respect to a bed (B ₀ ) in which the cast hole is closed with a lid.
First, the cast bed (A) having a solid structure has advantages such as a small surface area and a large heat capacity. However, as described above, it is preferable in view of the effects of distortion due to weight reduction and aging as described above. Absent. Therefore, in a conventional cast iron bed, about 70% is cast as a hollow rib structure as shown in (B). When the cast iron bed (B) cast in this way is compared with the granite bed (C) having a solid structure, the heat capacity of the cast iron bed (C) is larger and the ratio of the surface area S to the volume V (S / V). (C) is also smaller. Therefore, it can be said that the granite bed (C) is a structure that is less adaptable to changes in the outside air temperature.
However, the bed (B ₀ ) in which the cast hole is closed by the lid with respect to the cast bed (B) having the rib structure has a reduced surface area in contact with the outside air by closing the cast hole with the lid. / V is reduced, and a structure that is less adaptable to outside temperature fluctuations than (B) can be obtained. Further, in the case of the bed (B ₁ ) in which the bed is filled with mineral oil with respect to the cast iron bed (B ₀ ) with the cast-hole closed, a heat capacity equivalent to that of the granite bed (C) is obtained, In the case of water (B ₂ ), about twice the heat capacity of (C) is obtained. With these, it is possible to make the structure insensitive to external temperature fluctuations.
FIG. 8 shows a constant temperature chamber when the cast holes 2 on the side and bottom surfaces of the bed 1 of the machine tool 100 shown in FIGS. 2 shows the measurement results of the room temperature and the temperature inside the bed. Here, the set temperature in the constant temperature room is 20 ° C. The room temperature in the thermostatic chamber and the temperature inside the bed were measured with a platinum resistance thermometer. The temperature inside the bed was measured by inserting the platinum resistance temperature sensor through the liquid inlet 12 of the bed 1. As shown in FIG. 8, when the machine is started ((1) in FIG. 8), the room temperature rises due to the heat generated by the machine main body. I have. When the machine is stopped ((2) in FIG. 8), the room temperature has dropped to near the set temperature because there is no heat generation in the machine body.
On the other hand, the temperature inside the bed is increased by starting the machine, but is not interlocked with the room temperature and is gradually rising with respect to the room temperature. Further, it can be seen that the temperature inside the bed is hardly affected by the fluctuation of the room temperature.
That is, since the inside of the bed is made a closed space by closing the cast holes 2 on the side and bottom surfaces of the bed 1 with the lids 3 and 4, the temperature inside the bed is hardly adapted to the fluctuation of room temperature and is insensitive. It can be said that it has become. As a result, the outer surface of the bed 1 is affected by the fluctuation of the room temperature, but the inner surface of the bed 1 is hardly affected by the fluctuation of the room temperature. Displacement can be suppressed.
FIG. 9 shows the measurement results of the room temperature and the liquid temperature in the constant temperature chamber when the liquid is filled in the bed 1 described in the second embodiment. Here, the set temperature in the constant temperature room is 20 ° C. The liquid filled in the bed 1 was obtained by adding a rust inhibitor to water. The room temperature and the liquid temperature in the thermostatic chamber were measured with a platinum resistance thermometer, and the measurement of the liquid temperature was performed by inserting the platinum resistance temperature detector through the liquid inlet 12 of the bed 1. As shown in FIG. 9, the room temperature rises due to the heat generated by the machine body when the machine is started ((1) in FIG. 9), as in the case of FIG. Room temperature fluctuates due to disturbances such as going in and out. Then, when the machine is stopped ((2) in FIG. 9), the room temperature has dropped to near the set temperature because there is no heat generation in the machine body.
On the other hand, the temperature of the liquid water in the bed is increased by starting the machine, but is not synchronized with the room temperature and is gradually increased with respect to the room temperature. Further, it can be seen that the liquid water temperature inside the bed is hardly affected by the fluctuation of the room temperature.
Compared to the case where the cast holes 2 on the side and bottom surfaces of the bed 1 in FIG. It is less familiar with and less sensitive. In other words, since the heat capacity of the entire bed was increased by filling the interior of the bed 1 with water to which a rust preventive was added, the temperature inside the bed was higher than when the cast hole was simply closed with a lid. It can be said that it became less familiar and less sensitive to temperature fluctuations. As a result, the thermal displacement of the entire bed can be suppressed as compared with a case where the cast hole of the bed is simply closed with the lid.
[Brief description of the drawings]
FIG. 1 is a plan view of a machine tool 100. FIG.
FIG. 2 is a front view of the machine tool 100.
FIG. 3 is a sectional view of the bed 1 of the machine tool 100 in FIG.
FIG. 4 is a sectional view of the bed 1 of the machine tool 100 in FIG.
FIG. 5 is an enlarged view showing a state in which a casting hole 2 on a side surface of the bed 1 of the machine tool 100 is closed by a lid 3.
FIG. 6 is an enlarged view showing a state in which a casting hole 2 on the bottom surface of the bed 1 of the machine tool 100 is closed by a lid 4.
FIG. 7 shows the relationship between the volume V, the surface area S, the ratio S / V of the volume V to the surface area S, the weight, and the total heat capacity for the modeled conventional and present bed structures. 3 shows the measurement results of the room temperature in the thermostatic chamber and the temperature inside the bed when the cast holes 2 on the side and bottom surfaces of the bed 1 of the machine tool 100 in FIG.
FIG. 9 shows the room temperature and the liquid in the constant temperature chamber when the cast holes 2 on the side and bottom surfaces of the bed 1 of the machine tool 100 in FIGS. It shows the measurement results of the temperature.
FIG. 10 shows the results of calculating the temperature changes of three types of objects having a constant volume and different surface areas having a temperature difference from the outside air temperature.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Bed 2 Cast-out holes 3 and 4 Lid 12 Liquid inlet 100 Machine tool

Claims (3)

A machine tool bed made of a casting having a hollow structure and having a cast hole, wherein the cast hole is closed with a lid. A machine tool bed comprising a casting having a hollow structure and a cast hole, wherein the cast hole is closed with a lid, and the inside of the bed is further filled with a liquid. 3. The machine tool bed according to claim 2, wherein the liquid is water or oil to which a rust inhibitor has been added.

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