Wire electric discharge machine

Abstract

A wire electric discharge machine (100) is provided with: a working fluid control unit (31) that controls the temperature of a working fluid (13), and acquires a temperature difference between a first temperature, which is a temperature at the time of measuring a machining result on the basis of the temperature of the working fluid (13) detected during machining, and a second temperature, which is a temperature at the time of machining; a first control unit that calculates a machining error between a size and a target size when measuring the workpiece (W) after being machined by the target size at a first temperature on the basis of the acquired temperature difference, the coefficient of thermal expansion of the workpiece (W), and the coefficients of thermal expansion of the X-axis linear scale (2b) and the Y-axis linear scale (3b); correcting the target size in real time during machining by the calculated machining error, and driving an X-axis table (2) having an X-axis drive unit (2a) and a Y-axis table (3) having a Y-axis drive unit (3a) by an axis command value based on the corrected target size; and a second control unit that determines whether or not the machining performed according to the corrected target size is qualified, and changes the shaft command value if the machining performed according to the corrected target size is not qualified.

Description

Technical Field

[0001] The present invention relates to a wire electrical discharge machining machine. Background Art

[0002] A wire electrical discharge machining machine is a device that processes a workpiece by generating an arc discharge between a wire electrode and the workpiece. In a wire electrical discharge machining machine, if a high voltage is applied between the electrodes, or the distance between the electrodes is shortened to increase the electric field strength, discharge occurs due to insulation breakdown, and the workpiece is removed by machining. Wire electrical discharge machining is usually performed in a liquid called a machining fluid. By immersing the workpiece in the machining fluid, temperature changes are suppressed, and poor machining accuracy caused by thermal expansion and thermal contraction is reduced.

[0003] Not limited to wire electrical discharge machining machines, adjustments are made in machine tools so that good machining results are usually obtained in a temperature environment of 20°C. However, due to factors such as air conditioning costs, in most cases, the machining environment is not 20°C, and only the environment for measuring the machining results is set to 20°C. If machining is performed in the above environment, the following problem may occur: due to the difference in temperature between the machining temperature and the temperature at which the machining results are measured, the workpiece expands and contracts thermally, so the machining results may not fall within the desired dimensional tolerance.

[0004] To solve this problem, Patent Document 1 proposes the following: detecting the temperature of each axis scale for detecting the movement amount of each axis of the machining machine and the temperature of the workpiece, and using the difference in the amount of expansion and contraction from the reference temperature caused by the difference in their thermal expansion coefficients as an axis movement amount correction value to correct the error.

[0005] Patent Document 1: Japanese Patent No. 4803491 Summary of the Invention

[0006] Patent Document 1 describes the following: in order to confirm the pass or fail of axis movement amount correction, it is necessary to measure the temperature and dimensions of the workpiece on the actual machine. Therefore, in the machining machine, it is necessary to replace the spindle with a temperature probe or a dimension measurement probe, and time for measurement operations outside the machining time is required. In addition, when the result of pass or fail determination of the correction is not within the allowable range, re-machining is required, and there is a problem of deteriorated productivity.

[0007] The present invention has been made in view of the above circumstances, and an object thereof is to provide a wire electrical discharge machining machine capable of performing temperature correction and determination of pass or fail of the correction in real time during machining, thereby improving productivity.

[0008] In order to solve the above problems and achieve the object, in the wire electrical discharge machining apparatus of the present invention, a voltage is applied between a workpiece immersed in a machining liquid in a machining tank and a wire electrode to generate a discharge. The position of a moving axis that relatively moves the wire electrode and the workpiece is detected by a position detector, and the detected position of the moving axis is fed back to a target value corresponding to a target dimension, and the workpiece is machined. Also, the temperature of the position detector is synchronized with the temperature of the machining liquid. The wire electrical discharge machining apparatus is characterized by including: a machining liquid control unit that controls the temperature of the machining liquid and obtains a temperature difference between a first temperature, which is the temperature at which the machining result is measured based on the temperature of the machining liquid detected during machining, and a second temperature, which is the temperature during machining; a first control unit that calculates a machining error between a dimension when the workpiece machined to the target dimension is measured at the first temperature and the target dimension based on the obtained temperature difference, the thermal expansion coefficient of the workpiece, and the thermal expansion coefficient of the position detector, corrects the target dimension in real time during machining based on the calculated machining error, and drives the moving axis based on an axis command value corresponding to the corrected target dimension; and a second control unit that determines whether the machining performed based on the corrected target dimension is acceptable, and changes the axis command value when the determination result is no.

[0009] Effects of the Invention

[0010] The wire electrical discharge machining apparatus according to the present invention has the following effects, that is, it is possible to perform temperature correction and determination of whether the correction is acceptable in real time during machining, thereby improving productivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 It is a conceptual diagram showing a structural example of the wire electrical discharge machining apparatus according to the embodiment.

[0012] Figure 2 It is a diagram for explaining a machining error in the wire electrical discharge machining apparatus according to the embodiment.

[0013] Figure 3 It is a diagram for explaining a method of calculating a temperature difference in the wire electrical discharge machining apparatus according to the embodiment.

[0014] Figure 4 It is a block diagram showing a structural example of a control system of the wire electrical discharge machining apparatus according to the embodiment.

[0015] Figure 5 It is a diagram for explaining a method of deriving an inter-electrode distance between a workpiece and a wire in the wire electrical discharge machining apparatus according to the embodiment.

[0016] Figure 6 It is a block diagram showing a structure for deriving a dimension of a workpiece in the wire electrical discharge machining apparatus according to the embodiment.

[0017] Figure 7 It is a block diagram showing a structure for determining whether the size of a workpiece is qualified in the wire electrical discharge machining machine according to the embodiment.

[0018] Figure 8 It is a block diagram showing the hardware structure of the control system of the wire electrical discharge machining machine according to the embodiment. Detailed Embodiment

[0019] Hereinafter, the wire electrical discharge machining machine according to the embodiment will be described in detail based on the drawings.

[0020] Embodiment.

[0021] Figure 1 It is a conceptual diagram showing a structural example of the wire electrical discharge machining machine 100 according to the embodiment. The wire electrical discharge machining machine 100 machines the workpiece W by causing a discharge between the wire 1 as a wire electrode supported between the lower arm 14 and the upper arm 15 and the workpiece W. The wire electrical discharge machining machine 100 has a support table 21, and a column 20 is provided on the support table 21. A lower arm 14 extending in the horizontal direction is provided on the lower side of the column 20, and an upper arm 15 extending in the horizontal direction is provided on the upper side of the column 20.

[0022] A lower guide portion 24 is provided at the front end portion of the lower arm 14, and an upper guide portion 25 is provided at the front end portion of the upper arm 15. The wire 1 is held vertically by the lower guide portion 24 and the upper guide portion 25. The wire 1 is supplied by a wire feeding mechanism (not shown) and wound by a wire winding mechanism (not shown).

[0023] The machining liquid 13 is accumulated in the machining tank 10. The workpiece W is placed on the workpiece mounting table 11, and the machining liquid 13 fills the periphery of the workpiece W. The workpiece mounting table 11 is moved in the horizontal direction by a workpiece moving mechanism 4. The workpiece moving mechanism 4 has: an X-axis table 2 having an X-axis drive portion 2a for moving the workpiece W in the X direction; and a Y-axis table 3 having a Y-axis drive portion 3a for moving the workpiece W in the Y direction. An X-axis linear scale 2b as an X-axis position detector for detecting the position of the X-axis table 2 in the X direction is provided on the X-axis table 2. A Y-axis linear scale 3b as a Y-axis position detector for detecting the position of the Y-axis table 3 in the Y direction is provided on the Y-axis table 3. In addition, the positions of the X-axis table 2 and the Y-axis table 3 can also be detected by other position detectors such as a detector for detecting the rotation speed of a ball screw.

[0024] The machining fluid control unit 31 controls the temperature of the machining fluid 13 in the machining tank 10. A voltage is applied to the wire 1 and the workpiece W by the power supply unit 32. By generating a discharge between the wire 1 and the workpiece W, the workpiece W is subjected to removal machining.

[0025] In addition, in the above structure, the workpiece W is configured to move in the XY directions, but it may also be configured to move the wire 1 in the XY directions. That is, the wire 1 moves relative to the workpiece W in the XY directions, whereby the workpiece W is machined into a desired shape.

[0026] The control unit 30 performs drive control on the machining fluid control unit 31, the power supply unit 32, the X-axis drive unit 2a, and the Y-axis drive unit 3a.

[0027] The detected values of the X-axis linear scale 2b and the Y-axis linear scale 3b are fed back to the control unit 30. In the wire electrical discharge machining machine 100, the positions of the moving axes that relatively move the wire 1 and the workpiece W are detected by the X-axis linear scale 2b and the Y-axis linear scale 3b as position detectors, and the detected positions of the moving axes are fed back to the target dimensions as target values indicated by the control unit 30, and machining is performed on the workpiece W. The moving axes that relatively move the wire 1 and the workpiece W correspond to the X-axis table 2 and the Y-axis table 3 in this case, but in the case of the structure in which the wire 1 moves in the XY directions, the mechanism that moves the wire 1 in the XY directions corresponds to the moving axes.

[0028] Figure 2 is a diagram for explaining machining errors in the wire electrical discharge machining machine 100 according to the embodiment. In Figure 2 , □ represents the dimension of a square. In Figure 2 , the solid-line square represents the target dimension Sa of the workpiece W, the dashed-line square outside the solid line represents the dimension Sb of the machined workpiece W machined in an environment of (20 + ΔTa)°C, and the dashed-line square inside the solid line represents the dimension Sc of the machined workpiece W measured at 20°C.

[0029] When machining is performed by the wire electrical discharge machining machine 100, if Sa is set as the target size of machining, correction is not required when the temperature Ta1 at the time of measuring the machining result is the same as the temperature Ta2 during machining, and the target size Sa can be directly output as the target value. In the wire electrical discharge machining machine 100, since the workpiece W enters the machining fluid 13, the temperature Ta2 during machining corresponds to the temperature of the machining fluid 13. The temperature Ta1 at the time of measuring the machining result corresponds to the first temperature, and the temperature Ta2 during machining corresponds to the second temperature. However, the temperature Ta1 at the time of measuring the machining result is usually 20°C. When there is a temperature difference ΔTa between the temperature Ta2 during machining and the temperature Ta1 (=20°C), the X-axis linear scale 2b and the Y-axis linear scale 3b that are the reference for the axis movement in the XY direction expand due to their respective thermal expansion coefficients Ea. Therefore, the size Sb of the machined workpiece W when specifying the target value corresponding to the target size Sa becomes the following formula (1).

[0030] Sb = Sa + ΔTa × Ea · · · (1)

[0031] When measuring the machined workpiece W in an environment with the temperature Ta1 (=20°C), the size Sc will contract according to the thermal expansion coefficient Eb of the workpiece W, so it becomes the following formula (2).

[0032] Sc = Sb - ΔTa × Eb · · · (2)

[0033] Therefore, the machining error Ha between the target size Sa and the size Sc when measuring the machined workpiece W in an environment with 20°C becomes the following formula (3).

[0034] Ha = Sa - Sc = ΔTa × (Eb - Ea) · · · (3)

[0035] That is, during machining, the temperature difference ΔTa, the thermal expansion coefficient Ea of the X-axis linear scale 2b and the Y-axis linear scale 3b, and the thermal expansion coefficient Eb of the workpiece W are detected in real time and substituted into formula (3), so that the machining error Ha can be calculated in real time. Moreover, as shown in the following formula (4), correction is performed by adding the target size Sa of machining and the machining error Ha, and the corrected target size Sa' is obtained, and an instruction is issued in real time, so that machining can be performed without error in real time.

[0036] Sa' = Sa + Ha · · · (4)

[0037] Figure 3This is a diagram for explaining a method of calculating the temperature difference ΔTa in the wire electrical discharge machining machine 100 according to the embodiment. The machining fluid control unit 31 controls the temperature of the machining fluid 13 returned from the machining tank 10 and supplies the machining fluid 13, thereby controlling the machining fluid 13 to a constant temperature. In addition, the machining fluid control unit 31 derives the temperature difference ΔTa based on the temperature of the machining fluid 13 detected during machining. As Figure 3 shown, the control unit 30 outputs a temperature command value of 20°C + Tb to the machining fluid control unit 31. The machining fluid control unit 31 controls the temperature of the machining fluid 13 supplied to the machining tank 10 based on the temperature command value of 20°C + Tb. As a result, the machining fluid 13 supplied from the machining fluid control unit 31 to the machining tank 10 is controlled to 20°C + Tc. The machining fluid 13 in the machining tank 10 is cooled and heated by the supplied machining fluid 13 and then returns to the machining fluid control unit 31. The temperature of the machining fluid 13 returned from the machining tank 10 to the machining fluid control unit 31 becomes 20°C + Td.

[0038] In the wire electrical discharge machining machine 100, the workpiece W is immersed in the machining fluid 13 whose temperature is managed by the machining fluid control unit 31, and the temperature of the workpiece W is synchronized with the temperature of the machining fluid 13. The temperature of the machining fluid 13 during machining is synchronized with the temperature of the machining fluid 13 returned from the machining tank 10 to the machining fluid control unit 31, which is 20°C + Td. Therefore, the above temperature difference ΔTa is considered to be the same as the temperature Td obtained by subtracting 20°C from the temperature of the machining fluid 13 returned from the machining tank 10 to the machining fluid control unit 31, which is 20°C + Td. Therefore, regarding the temperature difference ΔTa, the temperature of the machining fluid 13 returned from the machining tank 10 to the machining fluid control unit 31, which is 20°C + Td, is detected, and 20°C is subtracted from the detected temperature, whereby the machining fluid control unit 31 can derive it. As described above, the machining fluid control unit 31 detects the temperature of the machining fluid 13 returned from the machining tank 10 during machining, and based on the detected temperature, the temperature difference ΔTa between the first temperature Ta1, which is the temperature when measuring the machining result, and the second temperature Ta2, which is the temperature during machining, is obtained in real time.

[0039] The temperature command value of 20°C + Tb output from the control unit 30 to the machining fluid control unit 31 is set to be the same as the external gas temperature Te, for example. As the temperature command value of 20°C + Tb, a temperature obtained by changing the external gas temperature Te by a certain temperature can be adopted.

[0040] In the on-line electric discharge machine 100, the temperatures of the X-axis linear scale 2b and the Y-axis linear scale 3b are synchronized with the temperature of the machining fluid 13. That is, in the on-line electric discharge machine 100, the temperature of the machining fluid 13, the temperature of the workpiece W, and the temperatures of the X-axis linear scale 2b and the Y-axis linear scale 3b are synchronized. For example, the machining fluid 13 is passed through the module where the X-axis linear scale 2b and the Y-axis linear scale 3b are installed, so that the temperatures of the X-axis linear scale 2b and the Y-axis linear scale 3b are synchronized with the temperature command value of 20°C + Tb of the machining fluid 13. In addition, when the temperature command value of 20°C + Tb output from the control unit 30 to the machining fluid control unit 31 is set to be the same as the external gas temperature Te, it can be assumed that the temperatures of the X-axis linear scale 2b and the Y-axis linear scale 3b are the same as the external gas temperature Te, and the temperatures of the X-axis linear scale 2b and the Y-axis linear scale 3b are synchronized with the temperature of the machining fluid 13.

[0041] In addition, in the on-line electric discharge machine 100, during machining, it is necessary to change the voltage Va supplied from the power supply unit 32 to the workpiece W and the wire 1 and the discharge distance Sh at which discharge can occur between the workpiece W and the wire 1 according to the material of the workpiece W. Therefore, the material-classified control parameters including the voltage Va and the discharge distance Sh are determined according to the material of the workpiece W. Therefore, in the material-classified control parameters, by adding the value of the coefficient of thermal expansion Eb of the workpiece W classified by material, the coefficient of thermal expansion Eb of the workpiece W can be obtained during machining.

[0042] In addition, the coefficients of thermal expansion Ea of the X-axis linear scale 2b and the Y-axis linear scale 3b are constant regardless of the material of the workpiece W. Therefore, if they are set as control parameters independent of the material, the coefficient of thermal expansion Eb can be obtained during machining.

[0043] Figure 4 It is a block diagram showing a structural example of the control system of the wire electric discharge machine 100 according to the embodiment. The control system of the wire electric discharge machine 100 has a control unit 30, a machining fluid control unit 31, a control parameter storage unit 33, a material-classified control parameter determination unit 34, a machining error detection unit 35, a target dimension output unit 36, and an axis command value control unit 37. The control unit 30, the control parameter storage unit 33, the material-classified control parameter determination unit 34, the machining error detection unit 35, the target dimension output unit 36, and the axis command value control unit 37 correspond to the first control unit. In Figure 4 part of the X-axis drive unit 2a and the Y-axis drive unit 3a are omitted and shown as drive units 2a, 3a.

[0044] The control unit 30 controls the components of the wire electric discharge machine 100 based on the NC program. The NC program includes the target dimension Sa of the machining of the workpiece W and the material of the workpiece W.

[0045] Control parameters independent of the material are stored in the control parameter storage unit 33. Among the control parameters stored in the control parameter storage unit 33, the coefficient of thermal expansion Ea of the X-axis linear scale 2b and the Y-axis linear scale 3b is included.

[0046] In the material-classified control parameter determination unit 34, material-classified control parameters including the voltage Va supplied to the workpiece W, the discharge distance Sh, and the coefficient of thermal expansion Eb of the workpiece W are stored for each material of the workpiece W.

[0047] If machining starts, the control unit 30 outputs a control parameter output instruction to the control parameter storage unit 33, outputs the material information of the workpiece W to the material-classified control parameter determination unit 34, and outputs a target temperature instruction Tb to the machining fluid control unit 31. In addition, the control unit 30 outputs the target dimension Sa of the workpiece W to the target dimension output unit 36.

[0048] The control parameter storage unit 33 outputs the coefficient of thermal expansion Ea of the X-axis linear scale 2b and the Y-axis linear scale 3b to the machining error detection unit 35. The material-classified control parameter determination unit 34 outputs the coefficient of thermal expansion Eb of the workpiece W corresponding to the material included in the input material information to the machining error detection unit 35. In addition, the material-classified control parameter determination unit 34 outputs the discharge distance Sh corresponding to the material included in the input material information to the axis command value control unit 37. In addition, the material-classified control parameter determination unit 34 outputs the voltage Va corresponding to the material included in the input material information to the power supply unit 32. The machining fluid control unit 31 performs control in accordance with the input target temperature instruction Tb so that the temperature of the machining fluid 13 supplied to the machining tank 10 becomes 20 °C + Tb. In addition, as Figure 3 described in the above, the temperature 20 °C + Td of the machining fluid 13 returned from the machining tank 10 to the machining fluid control unit 31 is detected, the temperature Td obtained by subtracting 20 °C from the detected temperature 20 °C + Td is calculated, and the temperature Td is output to the machining error detection unit 35 as the aforementioned temperature difference ΔTa.

[0049] The machining error detection unit 35 calculates the machining error Ha using the input coefficients of thermal expansion Ea, Eb, and the temperature difference ΔTa and the aforementioned formula (3). The machining error detection unit 35 outputs the calculated machining error Ha to the target dimension output unit 36. The target dimension output unit 36 calculates the corrected target dimension Sa' using the input target dimension Sa, the machining error Ha, and the aforementioned formula (4).

[0050] The target size output unit 36 outputs the calculated and corrected target size Sa′ to the axis command value control unit 37. The axis command value control unit 37 determines the axis command value Sg required to machine the target size Sa′ based on the target size Sa′ and the discharge distance Sh. The target size output unit 36 outputs the axis command value Sg to the X-axis drive unit 2a and the Y-axis drive unit 3a to drive and control the X-axis table 2 and the Y-axis table 3.

[0051] As described above, in the wire electrical discharge machining machine 100, the machining error Ha is calculated based on the thermal expansion coefficients Ea, Eb, and the temperature difference ΔTa, and the corrected target size Sa′ is determined in a manner that cancels out the machining error Ha. The X-axis table 2 and the Y-axis table 3 are driven by the axis command value Sg determined according to the target size Sa′ and the discharge distance Sh, so as to obtain a machining result without error at the measured temperature Ta1 of the machining result.

[0052] Next, a structure for determining whether the machining result obtained by correcting the target size is acceptable will be described. Figure 5 FIG. is a diagram for explaining a method of deriving the discharge distance, i.e., the interelectrode distance Hc, between the workpiece W and the wire 1 in the wire electrical discharge machining machine 100 according to the embodiment. Figure 6 FIG. is a block diagram showing a structure for deriving the size Se of the workpiece W in the wire electrical discharge machining machine 100 according to the embodiment. Figure 7 FIG. is a block diagram showing a structure for determining whether the size of the workpiece W is acceptable in the wire electrical discharge machining machine 100 according to the embodiment. In Figure 6 、 Figure 7 part of the X-axis table 2 and the Y-axis table 3 are omitted and shown as tables 2 and 3, and part of the X-axis linear scale 2b and the Y-axis linear scale 3b are omitted and shown as scales 2b and 3b. Additionally, in Figure 7 part of the X-axis table 2 and the Y-axis table 3 are omitted and shown as tables 2 and 3, and part of the X-axis drive unit 2a and the Y-axis drive unit 3a are omitted and shown as drive units 2a and 3a. Figure 7 The workpiece size calculation unit 41, the target size temperature conversion unit 42, the size comparison unit 43, and the axis command value control unit 37 shown in

[0053] As Figure 5As shown, in order to obtain the size Se of the workpiece W, the inter-polar distance Hc between the workpiece W and the wire 1 is detected according to the waveform of the discharge voltage occurring between the workpiece W and the wire 1. That is, the distance calculation unit 40 calculates the resistance R between the workpiece W and the wire 1 using the voltage drop V caused by the discharge current during discharge and the discharge current value A, as shown in the following formula (5).

[0054] R = V / A · · · (5)

[0055] In addition, since the machining fluid 13 with a known resistivity ρ fills the space between the workpiece W and the wire 1, the inter-polar distance Hc can be obtained by the following formula (6).

[0056] Hc = R / ρ · · · (6)

[0057] In Figure 5 it is shown that when obtaining the inter-polar distance Hc at the voltage drop V, at a lower voltage drop V′, a closer inter-polar distance Hc′ is obtained.

[0058] As Figure 6 shown, the workpiece size calculation unit 41 calculates the size Se of the workpiece W by subtracting the inter-polar distance Hc obtained by the distance calculation unit 40 from the current axis position Sd measured by the X-axis linear scale 2b and the Y-axis linear scale 3b, as shown in the following formula (7).

[0059] Se = Sd - Hc · · · (7)

[0060] In addition, as Figure 7 shown, the target size temperature conversion unit 42 obtains the converted target size Sb′ obtained by converting the corrected target size Sa′ calculated by the target size output unit 36 to the temperature Ta2 during machining, based on the thermal expansion coefficient Ea of the X-axis linear scale 2b and the Y-axis linear scale 3b stored in the control parameter storage unit 33 and the temperature difference ΔTa obtained by the machining fluid control unit 31, as shown in the following formula (8).

[0061] Sb′ = Sa′ + ΔTa × Ea · · · (8)

[0062] In addition, in Figure 7 the workpiece size calculation unit 41, as Figure 6 described in

[0063] The dimension comparison unit 43 compares the dimension Se of the workpiece W calculated by the workpiece dimension calculation unit 41 with the target dimension Sb' after temperature correction calculated by the target dimension temperature conversion unit 42, and determines whether the machining result obtained by correcting with the target dimension is acceptable or not. The dimension comparison unit 43 determines whether the difference between the dimension Se of the workpiece W and the target dimension Sb' after temperature correction falls within the allowable range, and outputs the determination result to the axis command value control unit 37.

[0064] When the determination result falls within the allowable range, the axis command value control unit 37 determines that the machining error Ha obtained by formula (3) is good, and the correction ends here. However, when the determination result does not fall within the allowable range, the axis command value control unit 37 changes the current axis command value Sg, thereby changing the axis position Sd, and controls so that the difference between the dimension Se of the workpiece W and the target dimension Sb' after temperature correction falls within the allowable range. That is, when the dimension Se of the workpiece is larger than the target dimension Sb', by changing the axis command value to Sg', the axis position is set to the axis position Sd' closer to the workpiece W, and controls so that the dimension of the workpiece W becomes a smaller dimension Se'. When the dimension Se of the workpiece W is smaller than the target dimension Sb', by changing the axis command value to Sg'', the axis position is set to the axis position Sd'' farther from the workpiece W, and controls so that the dimension of the workpiece W becomes a larger dimension Se''. The above control is repeated until the determination result converges within the allowable range, and thus machining without machining error can be performed.

[0065] As described above, according to the embodiment, the machining fluid control unit 31 derives the temperature difference ΔTa based on the temperature of the machining fluid 13 during machining, calculates the machining error Ha based on the thermal expansion coefficients Ea and Eb and the temperature difference ΔTa, determines the target dimension Sa′ after correction in such a way as to cancel the machining error Ha, and drives the X-axis table 2 and the Y-axis table 3 based on the axis command value Sg of the determined target dimension Sa′. Therefore, a machining result without error can be obtained in real time at the temperature Ta1 at which the machining result is measured. Therefore, performing temperature correction in real time during machining can improve the productivity of machining. In addition, the dimension Se of the workpiece W calculated by the workpiece dimension calculation unit 41 is compared with the target dimension Sb′ after temperature correction calculated by the target dimension temperature conversion unit 42, and the pass / fail determination of the machining result obtained by the correction of the target dimension is performed. Therefore, it is possible to grasp in real time whether the temperature correction of the axis movement is correctly performed. Therefore, temperature correction and pass / fail determination of the correction can be performed in real time during machining, and the productivity can be improved. In addition, when the pass / fail determination is No, the current axis position Sd is changed. Therefore, it is possible to efficiently produce a machined workpiece without machining error.

[0066] Here, the hardware structure of the control system including Figure 4 the control unit 30, the control parameter storage unit 33, the control parameter determination unit 34 classified by material, the machining error detection unit 35, the target dimension output unit 36, and the axis command value control unit 37 shown in Figure 7 and the distance calculation unit 40, the workpiece dimension calculation unit 41, the target dimension temperature conversion unit 42, and the dimension comparison unit 43 shown in Figure 8 is described.

[0067] The control system of the wire electrical discharge machining machine 100 can be implemented by a hardware structure 406 including Figure 8 the arithmetic device 404 and the storage device 405 shown in. The arithmetic device 404 is, for example, a CPU (Central Processing Unit) microprocessor, a microcomputer, or a DSP (Digital Signal Processor). The storage device 405 is, for example, a RAM (Random Access Memory) or a ROM (Read Only Memory).

[0068] The structure shown in the above embodiment represents a part of the content of the present invention, and can also be combined with other known technologies, and can be appropriately combined within the scope of not departing from the gist of the present invention, or a part of the structure can be omitted or changed.

[0069] Description of reference numerals

[0070] 1 wire, 2 X-axis table, 2a X-axis drive unit, 2b X-axis linear scale, 3 Y-axis table, 3a Y-axis drive unit, 3b Y-axis linear scale, 4 workpiece moving mechanism, 10 machining groove, 11 workpiece mounting table, 13 machining fluid, 14 lower arm, 15 upper arm, 20 column, 21 support table, 24 lower guide portion, 25 upper guide portion, 30 control unit, 31 machining fluid control unit, 32 power supply unit, 33 control parameter storage unit, 34 control parameter determination unit classified by material, 35 machining error detection unit, 36 target dimension output unit, 37 axis command value control unit, 40 distance calculation unit, 41 workpiece dimension calculation unit, 42 target dimension temperature conversion unit, 43 dimension comparison unit, 100 wire electrical discharge machining machine, 404 arithmetic unit, 405 storage device, 406 hardware structure.

Claims

1. A wire electrical discharge machining apparatus that applies a voltage between a workpiece immersed in a machining liquid in a machining tank and a wire electrode to generate a discharge, detects the position of a moving axis that relatively moves the wire electrode and the workpiece by a position detector, feeds back the detected position of the moving axis to a target value corresponding to a target dimension, machines the workpiece, and synchronizes the temperature of the position detector with the temperature of the machining liquid. The wire electrical discharge machining apparatus is characterized by comprising: a machining liquid control unit that controls the temperature of the machining liquid, and obtains a temperature difference between a first temperature, which is the temperature at which the machining result is measured based on the temperature of the machining liquid detected during machining, and a second temperature, which is the temperature during machining; a first control unit that calculates a machining error between a dimension when the workpiece machined to the target dimension is measured at the first temperature and the target dimension based on the obtained temperature difference, the thermal expansion coefficient of the workpiece, and the thermal expansion coefficient of the position detector, corrects the target dimension in real time during machining by the calculated machining error, and drives the moving axis by an axis command value based on the corrected target dimension; and a second control unit that determines whether the machining performed with the corrected target dimension is acceptable, and changes the axis command value if it is not acceptable.

2. The wire electrical discharge machining apparatus according to claim 1, wherein the axis command value is determined based on the corrected target dimension and a discharge distance set corresponding to the workpiece.

3. The wire electrical discharge machining apparatus according to claim 1 or 2, wherein the machining liquid control unit supplies the temperature-controlled machining liquid to the machining tank, detects the temperature of the machining liquid returned from the machining tank during machining, and obtains the temperature difference based on the detected temperature.

4. The wire electrical discharge machining apparatus according to any one of claims 1 to 3, wherein the machining liquid is passed through a module on which the position detector is installed.

5. The wire electrical discharge machining apparatus according to any one of claims 1 to 4, wherein the second control unit comprises: a distance calculation unit that obtains a distance between the workpiece and the wire electrode, i.e., an interelectrode distance; a workpiece dimension calculation unit that calculates the dimension of the workpiece after machining at the second temperature based on the current position of the moving axis detected by the position detector and the interelectrode distance; a target dimension temperature conversion unit that calculates a converted target dimension obtained by converting the corrected target dimension to the second temperature using the temperature difference and the thermal expansion coefficient of the position detector; and and A dimension comparison unit that calculates a dimension difference between the dimension of the workpiece calculated by the workpiece dimension calculation unit and the converted target dimension, and changes the axis command value until the dimension difference falls within an allowable range when the dimension difference does not fall within the allowable range.

6. The wire electrical discharge machining machine according to claim 5, characterized in that the inter-electrode distance is obtained based on the voltage drop during discharge of the voltage applied to the workpiece and the wire electrode.

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