JPH10277886A - Machine tool - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a machine tool in which the temperature relation between the spindle and the part to be measured is stabilized so that the thermal displacement of the spindle can be presumed accurately. SOLUTION: A coolant nozzle 6 is fixed to a spindle head 9 so that the blowout hole is directed so as to cool the tip of the spindle 1 and the tool shank part of a tool holder, and the first temperature sensor 3 is attached to near the bearing 2 of the spindle 1 while the second temperature sensor 4 is mounted on a bed 5, and the temperature there are sensed by a temperature sensor 11, while the thermal displacement amount of the spindle is calculated by a computing device 12, and on the basis of the result from computation, the command value to a Z-axis drive motor 14 of an NC device 13 is corrected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a machine tool, such as a machining center, having a function of correcting thermal displacement in the axial direction of a spindle.

[0002]

2. Description of the Related Art The temperature of a spindle head, which is susceptible to the heat generated by bearings and the like due to the rotation of a spindle, and the temperature of a part, such as a bed, which are relatively unaffected, are measured. A technique for estimating the thermal displacement of the spindle in the direction of the rotation axis and correcting the relative position between the tool and the work with the axis command of the machine tool by a numerical controller is disclosed in, for example, JP-B-61-59860.
It is well known in Japanese Patent Publication No.

[0003] This technique will be described with reference to the configuration diagram of a machine tool shown in FIG. As shown in the drawing, first, a first temperature sensor 3 is attached near a bearing 2 that supports a main shaft 1, and a second temperature sensor 4 is attached to a bed 5. When the workpiece 8 is machined by rotating the tool 8 attached to the tip of the spindle 1, the temperatures of the two temperature sensors are detected by the detector 11, and the thermal displacement is calculated based on the detected temperature. The calculation is performed by the device 12. Upon receiving the calculation result, the numerical controller 13 adds and corrects the axis drive command output to the Z-axis drive motor 14. As a result, the spindle head 9 movable in the Z-axis direction is moved with the temperature corrected by the Z-axis drive motor 14 via the ball screw 15 so that the relative position between the tool and the work can be set to a desired value. It is. In FIG. 3, reference numeral 10 denotes a moving table, 16 denotes a nozzle for discharging coolant, and 17 denotes a column.

[0004]

However, in the above-mentioned conventional technique, the temperature expansion of the main shaft 1 is estimated and corrected by assuming the temperature distribution of the machine from the temperature of the specific portion. Changes in machine temperature distribution due to changes in operating conditions are not considered. That is, although the heat radiation amount of the main shaft largely changes due to the air blow, the presence or absence of cooling / lubrication of the cutting point by the coolant, the rotation speed of the main shaft, the change of the cutting load, etc., it is not considered.

[0005] Therefore, as shown in FIG. 4 as an example of dry cutting, heat generated between the spindle 1 and the tool 8 flows to the spindle head 9 via the bearing 2 and also to the tool 8. However, on the other hand, the heat generated from the cutting point during processing is transmitted from the tool 8 to the main shaft side. In the wet cutting in which a coolant is applied to the cutting point, as shown in FIG. 5, not only the heat at the cutting point is discharged to the outside by the coolant discharged from the nozzle 17, but also the tool 8 itself is cooled and the heat of the spindle 1 is reduced. Moves further to the tool side.

As a result, there is a difference in the amount of heat transmitted from the bearing 2 to the spindle head 9 in the dry cutting and the wet cutting, and it is not appropriate to correct both by the same estimation method. In addition, since the heat radiation of the main shaft at the time of low rotation is lower than that at the time of high rotation, the temperature relationship between the measurement site and the main shaft changes. As a result, a difference occurs between the estimated temperature and the actual spindle temperature.

FIG. 6 shows the relationship between the number of revolutions of the main shaft and the heat transfer coefficient of the bearing. It can be seen that the heat transfer rate increases with the increase in the number of revolutions from a low rotation to a certain level, and then stabilizes. Conversely, it can be seen that the heat transfer coefficient is low at low rotation.

Accordingly, the present invention has been made in view of the above-mentioned problems of the prior art, and an object of the present invention is to dissipate heat from a spindle in a fixed direction regardless of operating conditions of a machine tool. Is to stabilize the temperature relationship between the spindle temperature and the measurement site, and to provide a machine tool that estimates the thermal displacement of the spindle with higher accuracy.

[0009]

According to a first aspect of the present invention, there is provided a machine tool for attaching a tool to a tip of a main shaft and processing the work by relative movement between the work and the main shaft. A sensor for measuring the temperature of a specific part of the machine tool, a calculation unit for calculating the thermal expansion of the spindle from the output of the sensor, a control means for controlling a relative movement means between the workpiece and the spindle based on the calculation result, and a tip of the spindle. And cooling fluid supply means for cooling a tool attached to the tip of the spindle.

[0010] A machine tool according to a second aspect of the present invention is characterized in that the cooling fluid supply means cools the tip of the spindle and the tool shank.

[0011]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows a configuration of a machine tool, and FIG. 2 is an explanatory sectional view showing a flow of heat at a tip end of a spindle. As shown in the figure, a coolant nozzle 6 is fixed to the spindle head 9 and its outlet is directed toward the tip of the spindle 1 and the tool shank 8a of the tool holder, and is cleaner than a compressed air supply source (not shown). Compressed air is being supplied.

A first temperature sensor 3 is mounted in the vicinity of a bearing 2 supporting the main shaft 1, a second temperature sensor 4 is mounted on a bed 5, and the temperatures of the two temperature sensors are detected by a temperature detector 11. The amount of thermal displacement is calculated by the calculation device 12 based on the detected value, and the calculation result is received.
The Z-axis drive motor 14 is controlled by the numerical controller 13 for correcting the axis drive command output to the
The point that the spindle head 9 that can move in the axial direction is moved is the same as the conventional technique.

When the relative speed of the gas and the solid is larger than a certain value, the change in the heat transfer rate due to the change in the relative speed becomes small. In addition, the pressure is supplied at a pressure to obtain a sufficient relative speed in a state where the surface of the tool shank 8a and the main shaft are not rotating.

By doing so, the heat flow of the spindle becomes almost as shown by the arrow in FIG. 2 under any cutting conditions because the cooling power of the cooling fluid is large. The amount of heat transmitted to the cutting surface is less affected by cutting conditions. Therefore, heat radiation from the spindle end or the tool holder can be kept constant irrespective of the rotation speed of the spindle, and the relationship between the temperature measured by the temperature sensor and the temperature of the spindle can be kept constant regardless of the rotation speed of the spindle. This makes it possible to enhance the accuracy of the thermal displacement correction mechanism. The reason why the tool shank 8a is specified as the direction of the nozzle outlet is that the shape and the position with respect to the main shaft are defined, and the cooling conditions are stable even in different tool holders.

In this case, by controlling the amount, pressure or speed of the cooling fluid in accordance with the number of revolutions of the main shaft, it is possible to more accurately control the heat radiation, and to further improve the accuracy of the thermal displacement compensating mechanism. In addition, by controlling and supplying the temperature of the cooling fluid, the thermal displacement can be corrected more accurately. Further, the cooling fluid does not have to be compressed air.Depending on the cutting conditions, another cooling fluid such as water or a cutting fluid having a higher cooling effect can be used. It is also effective to properly use the cooling fluid according to the above.

In the above-described embodiment, the mechanism for cooling only the spindle end of the spindle that protrudes from the spindle head has been described. However, the cooling fluid adversely affects the mechanism of the spindle rotation support portion of the spindle head. This is because there is a possibility that grease may be scattered by the pressure of the cooling fluid in the case of support by a grease-lubricated bearing, or that lubrication failure may occur due to negative pressure in the case of an oil-air lubricated bearing. .
However, it is effective to cool the spindle in the spindle head with due consideration given to these concerns. In addition, the shape and configuration of each part may be appropriately changed and embodied without departing from the spirit of the present invention.

[0017]

As described above in detail, according to the first aspect of the present invention, the accuracy of the well-known thermal displacement correction function is greatly improved by a simple and inexpensive configuration in which the cooling fluid is supplied to the tip of the spindle. It has a remarkable effect that it can be performed.

According to the second aspect of the present invention, in addition to the effect of the first aspect, the cooling condition is stabilized even with different tool holders.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a machine tool showing an example of an embodiment of the present invention.

FIG. 2 is an explanatory longitudinal sectional view showing heat conduction at a tip end of a spindle shown in FIG. 1;

FIG. 3 is a configuration diagram of a conventional machine tool.

FIG. 4 is an explanatory longitudinal sectional view of a tip end of a spindle showing heat conduction in conventional dry cutting.

FIG. 5 is an explanatory longitudinal sectional view of a tip end portion of a spindle showing heat conduction in conventional wet cutting.

FIG. 6 is a diagram showing a relationship between a rotation speed of a main shaft and a heat transfer rate of a bearing.

[Explanation of symbols]

1. Spindle, 2. Bearing, 3. First temperature sensor, 4.
・ Second temperature sensor, 5 ・ Bed, 6 ・ Nozzle (coolant nozzle), 7 ・ Work, 8 ・ Tool, 8a ・ ・
Tool shank, 9 ... spindle head, 11 ... temperature detector, 12 ... arithmetic unit, 13 ... numerical controller, 14 ...
・ Z axis drive motor, 15 ・ ball screw.

Claims (2)

[Claims] 1. A sensor for measuring a temperature of a specific portion of a machine tool in a machine tool for attaching a tool to a tip of a spindle and processing the workpiece by relative movement between the workpiece and the spindle.
A calculation unit for calculating the thermal expansion of the spindle from the output of the sensor; control means for controlling relative movement means between the workpiece and the spindle based on the calculation result; and a cooling fluid for cooling the spindle tip and a tool attached to the spindle tip. A machine tool comprising a supply unit. 2. The cooling fluid supply means cools a tip end of a spindle and a tool shank portion.
A machine tool according to claim 1.