JP2009279670A - Wire electric-discharge machining apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To keep a temperature of a processing liquid supplied to a processing aperture at a target temperature more quickly and correctly in a wire electric-discharge machining apparatus comprising a processing liquid cooler 50 for cooling the water and keeping a temperature of the water at a target temperature and a heat exchanger 52 for cooling oil with the water used as a coolant for alternatively supplying the processing liquid of the water and the oil to the processing aperture. <P>SOLUTION: A controller 20 for providing a mode signal indicating a mode is provided on the processing liquid cooler 50. The processing liquid cooler 50 sets an offset feed forward value or a cooling ability feed forward value for lowering the target temperature depending on a mode, wherein when the mode indicates a processing period with the oil used, the feed forward value is increased to be larger than a value when the mode indicates a processing period with the water used. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention relates to a wire electric discharge machining apparatus for machining a workpiece by generating an electric discharge in a machining gap formed between a wire electrode and the workpiece. In particular, the present invention selectively supplies the machining fluid mainly composed of water and the machining fluid mainly composed of oil to the machining gap, and uses only one machining fluid cooling device for the temperature of both machining fluids. The present invention relates to a wire electric discharge machining apparatus that is controlled by

In general, a wire electric discharge machining apparatus capable of removing a minute amount of material from a workpiece by electric discharge can realize a shape accuracy of several μm or less and a surface roughness of several μm Rz or less. The wire electric discharge machining apparatus includes a machining liquid supply apparatus that supplies a machining liquid to the machining gap. The machining fluid is an insulator, but changes to a conductor at a machining gap when a high voltage is applied. The main component of the working fluid is water or oil. The water is usually deionized water whose electric conductivity is controlled to several to several tens μS / cm. In most cases, the wire electric discharge machine uses water that is superior in terms of removal rate (mm ² / min).

There is known a wire electric discharge machine in which oil having stable insulating properties is used in addition to water. Water and oil are alternatively supplied to the machining gap. In many cases, water is used for roughing to cut a workpiece at high speed, and then oil is used for finishing processing to finish the cut surface of the workpiece to a required dimensional accuracy. A large current is supplied to the machining gap in the roughing process, and a small current is supplied in the finishing process. Thus, the removal rate and dimensional accuracy are harmonized by the use of water and oil.

In order to ensure high accuracy, the machining fluid supply device includes one machining fluid cooling device. Patent Document 1 discloses a working fluid cooling device that includes a temperature setting device that sets the temperature of the working fluid, a temperature sensor that detects the temperature of the working fluid, and an inverter. The amplifier outputs a command voltage according to the difference between the output of the temperature setter and the temperature sensor. The inverter controls the motor speed of the compressor that cools the machining fluid in accordance with the command voltage.

When water and oil are used, water that is often used in roughing is typically cooled by a single machining fluid cooling device. Patent Document 2 discloses a machining fluid supply apparatus further provided with a heat exchanger. Since the oil is maintained at a temperature equal to that of water by the heat exchanger, the temperature of the workpiece is prevented from changing suddenly when the machining fluid is changed.

JP-A-3-294120 Japanese Patent Publication No.62-19975

In this way, the water is cooled by only one machining fluid cooling device and maintained at the set value. However, oil is cooled using water as a refrigerant. Therefore, strictly speaking, the temperature of the oil supplied to the processing tank is always slightly higher than that of water. An object of the present invention is to provide a wire electric discharge machining apparatus in which the temperature of a machining liquid supplied to a machining gap is maintained at a target temperature more quickly and accurately.

According to one aspect of the present invention, the apparatus includes: a working fluid cooling device that cools water to maintain the temperature of the water at a target temperature; and a heat exchanger that cools oil using the water as a refrigerant. The wire electrical discharge machining apparatus that supplies oil to a workpiece and processes the workpiece further includes a control device that provides a mode signal indicating a mode to the machining fluid cooling device, and the machining fluid cooling device performs an offset feed that lowers the target temperature. A forward value is set according to the mode, and when the mode indicates a processing period in which the oil is used, the offset feedforward value is increased as compared to when the mode indicates a processing period in which the water is used. It is characterized by.

The machining liquid cooling device increases the offset feedforward value when the mode indicates a setup period for a process using the oil than when the mode indicates a setup period for a process using the water. It is good to do.

The mode indicates a first mode indicating a setup period for the processing using the water, a second mode indicating a setup period for the processing using the oil, and a finishing processing period using the water. A third mode, a fourth mode indicating a finishing process period using the oil, a fifth mode indicating a roughing period using the water, and a sixth mode indicating a roughing period using the oil The working fluid cooling device is directed from the first mode to the second mode, the third mode, the fourth mode, the fifth mode, and the sixth mode. In order, the offset feedforward value may be increased.

According to another aspect of the present invention, the apparatus includes: a working fluid cooling device that cools water to maintain the temperature of the water at a target temperature; and a heat exchanger that cools oil using the water as a refrigerant. The wire electrical discharge machining apparatus that supplies the oil to the workpiece and processes the workpiece further includes a control device that provides a mode signal indicating a mode to the machining fluid cooling device, and the machining fluid cooling device has a cooling capacity feedforward value. It sets according to the mode, and when the mode indicates a processing period using the oil, the cooling capacity feedforward value is increased than when the mode indicates a processing period using the water. And

When the mode indicates a setup period provided for processing using the oil, the cooling fluid feed forward value is greater than when the mode indicates a setup period provided for processing using the water. It may be increased.

The mode indicates a first mode indicating a setup period for the processing using the water, a second mode indicating a setup period for the processing using the oil, and a finishing processing period using the water. A third mode, a fourth mode indicating a finishing process period using the oil, a fifth mode indicating a roughing period using the water, and a sixth mode indicating a roughing period using the oil The working fluid cooling device is directed from the first mode to the second mode, the third mode, the fourth mode, the fifth mode, and the sixth mode. In order, the cooling capacity feedforward value may be increased.

According to the present invention, in a machining period in which oil that is not directly cooled by the machining liquid cooling device is used, the machining liquid cooling device has a larger offset feedforward value or cooling capacity feed than in a machining period in which water is used. Set the forward value. Further, in the setup period for processing using oil, the machining liquid cooling device sets a larger offset feedforward value or cooling capacity feedforward value compared to the setup period for processing using water. Accordingly, the temperature of the working fluid surrounding the workpiece is maintained more quickly and accurately.

An embodiment of the wire electric discharge machine of the present invention will be described with reference to the drawings. As shown in FIG. 1, the portal column 4 is fixed to the bed 2 so as to be movable in the Y-axis direction. A table 6 is placed on the bed 2. A processing tank 10 surrounding the work 14 is fixed to the table 6. FIG. 1 shows a processing tank 10 with a side wall partially cut away. During processing, the processing tank 10 is filled with the processing liquid. A work stand 12 is provided on the bottom surface of the processing tank 10. The work 14 is fixed to the upper surface of the work stand 12.

The upper arm 3 is fixed to the front surface of the portal column 4 so as to be movable in the X-axis direction. The upper arm 3 extends downward in the processing tank 10. An upper wire guide assembly 13 is attached to the tip of the upper arm 3. The lower arm 5 is fixed to the back surface of the portal column 4 so as to be movable in the X-axis direction, and extends downward in the processing tank 10. A lower wire guide assembly 15 is attached to the tip of the lower arm 5. The wire electrode 8 is normally supported vertically between the upper and lower wire guide assemblies 13 and 15. Each of the upper and lower wire guide assemblies 13, 15 has a nozzle that injects a working fluid toward the workpiece 14.

The processing liquid supply device 30 supplies water or oil processing liquid to the processing tank 10 and regenerates the waste liquid. The machining fluid supply device 30 includes a machining fluid cooling device or a cooler 50 whose compressor is controlled by an inverter. The machining fluid cooling device 50 has a water temperature sensor and operates to maintain the water temperature at the target temperature. A temperature sensor 18 for detecting the temperature of the machine of the wire electric discharge machine is attached to the back surface of the portal column 4. Preferably, the temperature sensor 18 is disposed at the same height as the workpiece 14. The output signal of the temperature sensor 18 is supplied to the machining liquid cooling device 50 as a target temperature.

Further, the control device 20 provides a mode signal to the machining fluid cooling device 50. The mode signal represents one of the modes from No. 1 to No. 6, and defines a combination of the cooling capacity feed forward value and the offset feed forward value. FIG. 3 shows six modes in which the combinations of the cooling capacity feedforward value and the offset feedforward value are different. The cooling capacity is a value for immediately bringing the water temperature close to the target temperature immediately after the mode switching. The cooling capacity feedforward value is sufficient if it is valid for a predetermined time immediately after mode switching, for example, 1 minute, and is represented by a ratio (%) to the maximum cooling capacity. For example, when the machining liquid cooling device 50 has a maximum cooling capacity of 750 W, the cooling capacity of “15” indicates 112.5 W. However, the cooling capacity may be expressed by electric power (W) or heat quantity (Cal / h) instead of the ratio (%).

The offset is a correction value (° C.) that lowers the target temperature. For example, when the target temperature represented by the temperature sensor 18 is 23 ° C., an offset of “1.5” corrects the target temperature to 21.5 ° C. The cooling capacity feedforward value and the offset feedforward value are preset based on experiments for each mode.

For example, in the mode (mode “6”) indicating the rough machining period using oil, the cooling capacity feedforward value is obtained as follows. First, roughing using oil is performed for approximately two hours. The working fluid cooling device 50 begins to cool the water, and when the temperature of the oil slowly reaches the target temperature, the cooling capacity is usually stabilized at a certain value. The value of the cooling capacity is set as the cooling capacity feed forward value in the mode “6”.

As shown in FIG. 2, the dirty processing liquid in the processing tank 10 is discharged to the processing liquid supply device 30 through the discharge pipe 16 by opening the discharge valve 17 at an appropriate time. Waste water is recovered in the water recovery tank 32 and waste oil is recovered in the oil recovery tank 42. Waste water is sent to the filter 34 by the pump 33 and then stored in the water supply tank 36. Water in the water supply tank 36 is supplied to the processing tank 10 through a valve 38 by a pump 37. Waste oil is sent to the filter 44 by the pump 43 and then stored in the oil supply tank 46. Oil in the oil supply tank 46 is supplied to the processing tank 10 through a valve 48 by a pump 47.

The water in the water supply tank 36 is passed through the machining liquid cooling device 50 and the heat exchanger 52 by the pump 37 and returned to the water supply tank 36. The oil in the oil supply tank 46 is passed through the heat exchanger 52 by the pump 47 and returned to the oil supply tank 46. Thus, the machining fluid cooling device 50 directly cools the water, and the heat exchanger 52 cools the oil with the water refrigerant.

A process in which the control device 20 controls the machining fluid cooling device 50 will be described with reference to FIG. The process starts when the wire electrical discharge machine is activated. The control device 20 supplies a mode signal representing one of the six modes “1” to “6” to the machining fluid cooling device 50. When the mode value increases, the machining fluid cooling device 50 increases the cooling capacity feedforward value and the offset feedforward value.

First, in step S1, the control device 20 sets the mode to “1” for setup. The mode “1” indicates a setup period for preparing processing using water. The setup period is a period in which the machining of the workpiece 14 is not started although the wire electric discharge machining apparatus is activated. In step S2, if water is designated as a working fluid supplied to the processing tank 10 by an operator input or a program, the process proceeds to step S3. In step S2, if oil is designated as the processing liquid supplied to the processing tank 10, the process proceeds to step S7. In step S7, the control device 20 switches the mode to “2”. Mode “2” indicates a set-up period in preparation for processing using oil. The mode is switched from “1” to “2” so that the temperature of the processing liquid in the water supply tank 36 or the processing liquid in the oil supply tank 46 is the same, and the processing liquid cooling device 50 is supplied with a cooling capacity feed-for. Each of the word value and the offset feed forward value is set to a large value.

During the setup period, the work 14 is fixed to the work stand 12 with a suitable fastening tool. On the other hand, the wire electrode 8 is stretched vertically between the upper and lower wire guide assemblies 13 and 15. Furthermore, the processing fluid designated from the water supply tank 36 or the oil supply tank 46 is supplied to the processing tank 10 until the work 14 is immersed.

When machining is started in step S3, the process proceeds to step S4. When determining that the roughing has been started in step S4, the control device 20 switches the mode to “5” in step S5. Mode “5” indicates a roughing period in which water is used. If the control device 20 determines that finishing is started in step S4, the control device 20 switches the mode to “3” in step S5. Mode “3” indicates a finishing period in which water is used. Roughing is a process of cutting the workpiece 14 at a high speed, and the finishing process is a process of finishing the cut surface of the roughly processed workpiece 14 to a required dimensional accuracy.

Subsequent to step S7, when machining is started in step S8, the process proceeds to step S9. When determining that the roughing has been started in step S9, the control device 20 switches the mode to “6” in step S10. Mode “6” indicates a roughing period in which oil is used. When the mode is “6”, the machining fluid cooling device 50 sets the cooling capacity feedforward value and the offset feedforward value to the largest values. When the control device 20 determines that finishing is started in step S9, the mode is switched to “4” in step S11. Mode “4” indicates a finishing period in which oil is used.

During processing, the processing liquid is supplied from the water supply tank 36 or the oil supply tank 46 to the upper and lower wire guide assemblies 13 and 15 by a jet pump (not shown), and is injected from the upper and lower nozzles onto the workpiece 14. . In rough machining in which a large current is supplied to the workpiece 14, the pressure of the machining fluid sprayed onto the workpiece 14 is greater than in finishing machining. Therefore, in the roughing process in which the jet pump rotates at a higher frequency, the mode value is set larger than in the finishing process. The overflow liquid in the processing tank 10 is discharged to the water recovery tank 32 or the oil recovery tank 42. The waste liquid is filtered by the filter 34 or 44 and sent to the water supply tank 36 or the oil supply tank 46. The water in the water supply tank 36 is always circulated through the machining liquid cooling device 50 and the heat exchanger 52. The oil in the oil supply tank 46 is always circulated through the heat exchanger 52.

The control device 20 performs the determination in step S4 or S9, for example, depending on the pressure setting of the machining fluid injected to the workpiece 14. However, the control device 20 may determine which of roughing and finishing is started based on the setting of other processing conditions.

Regardless of which mode is selected during processing, when the processing ends in step S12, the process proceeds to step S13. If the next machining is scheduled in step S13, the process returns to step S1. Otherwise, the power to the wire electric discharge machine is cut off and the process ends.

In the present invention, in the processing period in which oil that is not directly cooled by the processing liquid cooling device 50 is used, the control device 20 increases the mode value compared to the processing period in which water is used. Moreover, in the setup period prepared for the process using oil, the control device 20 increases the mode value compared to the setup period prepared for the process using water. Therefore, the temperature of the working fluid surrounding the workpiece 14 is maintained more quickly and accurately.

It is a front view which shows the wire electric discharge machining apparatus of this invention. FIG. 2 is a piping diagram showing the machining fluid supply device of FIG. 1. It is a flowchart which shows operation | movement of the control apparatus of FIG.

Explanation of symbols

2 ... Bed 3 ... Upper arm 4 ... Portal column 5 ... Lower arm 6 ... Table 8 ... Wire electrode 10 ... Processing tank 12 ... Work stand 13 .... Upper wire guide assembly 14 ... Work 15 ... Lower wire guide assembly 16 ... Discharge pipe 17 ... Discharge valve 18 ... Temperature sensor 20 ... Control device 30 ... Processing fluid supply device 32 ... water recovery tank 33 ... pump 34 ... filter 36 ... water supply tank 37 ... pump 38 ... valve 42 ... oil recovery tank 43 ... pump 44 ... Filter 46 ... Oil supply tank 47 ... Pump 48 ... Valve 50 ... Working fluid supply device 52 ... Heat exchanger

Claims (6)

A machining fluid cooling device that cools water and maintains the temperature of the water at a target temperature; and a heat exchanger that cools oil using the water as a refrigerant, and supplies the water and the oil to a workpiece. In the wire electric discharge machining apparatus to be machined, a control device for providing a mode signal indicating a mode to the machining fluid cooling device is provided, and the machining fluid cooling device sets an offset feedforward value for lowering the target temperature according to the mode. The wire electric discharge machining apparatus increases the offset feedforward value when the mode indicates a machining period in which the oil is used, compared to when the mode indicates a machining period in which the water is used. The machining liquid cooling device increases the offset feedforward value when the mode indicates a setup period for a process using the oil than when the mode indicates a setup period for a process using the water. The wire electric discharge machining apparatus according to claim 1. The mode indicates a first mode indicating a setup period for the processing using the water, a second mode indicating a setup period for the processing using the oil, and a finishing processing period using the water. A third mode, a fourth mode indicating a finishing process period using the oil, a fifth mode indicating a roughing period using the water, and a sixth mode indicating a roughing period using the oil The working fluid cooling device is directed from the first mode to the second mode, the third mode, the fourth mode, the fifth mode, and the sixth mode. The wire electric discharge machining apparatus according to claim 1, wherein the offset feedforward value is increased in order. A machining fluid cooling device that cools water and maintains the temperature of the water at a target temperature; and a heat exchanger that cools oil using the water as a refrigerant, and supplies the water and the oil to a workpiece. In the wire electric discharge machining apparatus to be machined, a control device for providing a mode signal indicating a mode to the machining fluid cooling device is provided, the machining fluid cooling device sets a cooling capacity feedforward value according to the mode, and the mode is The wire electric discharge machining apparatus characterized in that when the machining period using the oil is indicated, the cooling capacity feedforward value is increased as compared with when the mode indicates the machining period using the water. When the mode indicates a setup period provided for processing using the oil, the cooling fluid feed forward value is greater than when the mode indicates a setup period provided for processing using the water. The wire electric discharge machining apparatus according to claim 1, which increases. The mode indicates a first mode indicating a setup period for the processing using the water, a second mode indicating a setup period for the processing using the oil, and a finishing processing period using the water. A third mode, a fourth mode indicating a finishing process period using the oil, a fifth mode indicating a roughing period using the water, and a sixth mode indicating a roughing period using the oil The working fluid cooling device is directed from the first mode to the second mode, the third mode, the fourth mode, the fifth mode, and the sixth mode. The wire electric discharge machining apparatus according to claim 1, wherein the cooling capacity feedforward value is increased in order.

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