Wire EDM

Abstract

The wire electric discharge machine (100) includes a machining fluid control unit (31) that controls the temperature of the machining fluid (13) and acquires a temperature difference between a first temperature, which is the temperature when measuring the machining result, and a second temperature, which is the temperature during machining, based on the temperature of the machining fluid (13) detected during machining; a first control unit that calculates a machining error between the dimension when the workpiece (W) machined to a target dimension is measured at the first temperature and the target dimension based on the acquired temperature difference, the thermal expansion coefficient of the workpiece (W), and the thermal expansion coefficients of the X-axis linear scale (2b) and the Y-axis linear scale (3b), corrects the target dimension in real time during machining based on the calculated machining error, and drives an X-axis stage (2) having an X-axis drive unit (2a) and a Y-axis stage (3) having a Y-axis drive unit (3a) using axis command values ​​based on the corrected target dimension; and a second control unit that determines whether machining using the corrected target dimension is successful and changes the axis command values ​​if it is unsuccessful.

Description

Technical Field

[0001] The present disclosure 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, when a high voltage is applied between the electrodes or the distance between the electrodes is shortened to increase the electric field strength, a discharge occurs due to dielectric breakdown, and the workpiece is removed by machining. Wire electrical discharge machining is generally performed in a liquid called a machining fluid. By immersing the workpiece in the machining fluid, temperature changes are suppressed, and poor machining accuracy due to thermal expansion and thermal contraction is reduced.

[0003] Not only wire electrical discharge machining machines but also machine tools are generally adjusted so that good machining results can be obtained in a temperature environment of 20°C. However, due to factors such as air conditioning costs, the machining environment is often not 20°C, and only the environment for measuring the machining results is 20°C. When machining is performed in such an environment, the workpiece expands and contracts thermally due to the difference between the temperature during machining and the temperature when measuring the machining results, so there may be a problem that the machining results do not fall within the desired dimensional tolerance.

[0004] In order to solve such a problem, in Patent Document 1, it is proposed to detect the temperature of each axis scale for detecting the amount of movement of each axis of the machining machine and the temperature of the workpiece, and correct the error by using the difference in the amount of expansion and contraction from the reference temperature due to the difference in their thermal expansion coefficients as the axis movement amount correction value.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] Patent Document 1 states that it is necessary to measure the temperature and dimensions of the workpiece on the actual machine in order to confirm whether the axis movement amount correction is correct. For this reason, the spindle of the machining center must be replaced with a temperature probe or a dimension measuring probe, which requires time for measurement work separate from the machining time. Furthermore, if the result of the correction quality judgment is not within the acceptable range, machining is required again, which leads to a decrease in productivity.

[0007] This disclosure is made in view of the above, and aims to provide a wire electrical discharge machining machine that can improve productivity by performing temperature correction and quality judgment of the correction in real time during processing. [Means for solving the problem]

[0008] To solve the above-mentioned problems and achieve the objective, the wire electrical discharge machine in this disclosure applies a voltage between the workpiece immersed in the machining fluid in the machining tank and the wire electrode to generate a discharge, detects the position of the moving axis that moves the wire electrode and the workpiece relative to each other with a position detector, feeds back the detected position of the moving axis to a target value corresponding to the target dimension to machine the workpiece, and synchronizes the temperature of the position detector with the temperature of the machining fluid. The wire electrical discharge machining machine is characterized by comprising: a machining fluid control unit that controls the temperature of the machining fluid and acquires the temperature difference between a first temperature, which is the temperature at which the machining result is measured, and a second temperature, which is the temperature at the time of machining, based on the temperature of the machining fluid detected during machining; a first control unit that calculates the machining error between the dimensions of a workpiece machined to the target dimensions measured at the first temperature and the target dimensions based on the acquired temperature difference, the thermal expansion coefficient of the workpiece, and the thermal expansion coefficient of the position detector, corrects the target dimensions 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 dimensions; and a second control unit that determines whether the machining is good or bad based on the corrected target dimensions and changes the axis command value if it is bad. [Effects of the Invention]

[0009] The wire electrical discharge machining machine described herein offers the advantage of improving productivity by performing temperature compensation and quality assessment of the compensation in real time during machining. [Brief explanation of the drawing]

[0010] [Figure 1] Conceptual diagram showing an example configuration of a wire electrical discharge machining machine according to an embodiment. [Figure 2] A diagram illustrating machining errors in a wire electrical discharge machine according to an embodiment. [Figure 3] A diagram illustrating the method for calculating the temperature difference in a wire electrical discharge machining machine according to an embodiment. [Figure 4] Block diagram showing an example of the configuration of the control system for a wire electrical discharge machining machine according to the embodiment. [Figure 5] A diagram illustrating a method for deriving the inter-electrode distance between the workpiece and the wire in a wire electrical discharge machining machine according to an embodiment. [Figure 6] Block diagram showing the configuration for deriving the dimensions of a workpiece in a wire electrical discharge machining machine according to the embodiment. [Figure 7] Block diagram showing the configuration for determining the quality of the dimensions of a workpiece in a wire electrical discharge machining machine according to the embodiment. [Figure 8] Block diagram showing the hardware configuration of the control system for a wire electrical discharge machining machine according to the embodiment. [Modes for carrying out the invention]

[0011] The wire electrical discharge machining machine according to this embodiment will be described in detail below with reference to the drawings.

[0012] Embodiment. Figure 1 is a conceptual diagram showing an example configuration of a wire electrical discharge machining (EDM) machine 100 according to an embodiment. The wire electrical discharge machining machine 100 processes a workpiece W by generating an electrical discharge between a wire 1, which serves as a wire electrode supported between a lower arm 14 and an upper arm 15, and the workpiece W. The wire electrical discharge machining machine 100 has a support base 21, on which a column 20 is mounted. A lower arm 14 extending horizontally is provided on the lower side of the column 20, and an upper arm 15 extending horizontally is provided on the upper side of the column 20.

[0013] A lower guide 24 is provided at the tip of the lower arm 14, and an upper guide 25 is provided at the tip of the upper arm 15. The wire 1 is held vertically by the lower guide 24 and the upper guide 25. The wire 1 is fed by a wire feeding mechanism (not shown) and wound up by a wire winding mechanism (not shown).

[0014] A machining fluid 13 is stored in the machining tank 10. The workpiece W is placed on the workpiece mounting table 11, and the area around the workpiece W is filled with the machining fluid 13. The workpiece mounting table 11 is moved horizontally by the workpiece moving mechanism 4. The workpiece moving mechanism 4 has an X-axis stage 2 having an X-axis drive unit 2a that moves the workpiece W in the X direction, and a Y-axis stage 3 having a Y-axis drive unit 3a that moves the workpiece W in the Y direction. The X-axis stage 2 is provided with an X-axis linear scale 2b as an X-axis position detector that detects the position of the X-axis stage 2 in the X direction. The Y-axis stage 3 is provided with a Y-axis linear scale 3b as a Y-axis position detector that detects the position of the Y-axis stage 3 in the Y direction. Note that the positions of the X-axis stage 2 and the Y-axis stage 3 may be detected by other position detectors, such as a detector that detects the rotation speed of a ball screw.

[0015] The processing fluid control unit 31 controls the temperature of the processing fluid 13 in the processing tank 10. Voltage is applied to the wire 1 and the workpiece W by the power supply unit 32. The workpiece W is removed by generating an electrical discharge between the wire 1 and the workpiece W.

[0016] In the above configuration, the workpiece W is configured to move in the XY direction, but the wire 1 may be configured to move in the XY direction. That is, by the relative movement of the wire 1 with respect to the workpiece W in the XY direction, the workpiece W is processed into a desired shape.

[0017] The control unit 30 drives and controls the machining fluid control unit 31, the power supply unit 32, the X-axis drive unit 2a, and the Y-axis drive unit 3a.

[0018] 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 for relatively moving the wire 1 and the workpiece W are detected by the X-axis linear scale 2b and the Y-axis linear scale 3b which are position detectors, and the detected positions of the moving axes are fed back to the target dimension which is the target value commanded by the control unit 30, and machining of the workpiece W is performed. The moving axes for relatively moving the wire 1 and the workpiece W correspond to the X-axis stage 2 and the Y-axis stage 3 in this case, but in the case of a configuration in which the wire 1 moves in the XY direction, the mechanism for moving the wire 1 in the XY direction corresponds to the moving axes.

[0019] FIG. 2 is a diagram for explaining machining error in the wire electrical discharge machining machine 100 according to the embodiment. In FIG. 2, □ represents the dimension of a square. In FIG. 2, the solid-line square represents the target dimension Sa of the workpiece W, the broken-line square outside the solid line represents the dimension Sb of the workpiece W after machining performed in an environment of (20 + ΔTa)°C, and the broken-line square inside the solid line represents the dimension Sc of the workpiece W after machining measured at 20°C.

[0020] When machining is performed using the wire electrical discharge machining machine 100, if Sa is the target dimension for machining, and the temperature Ta1 when measuring the machining result matches the temperature Ta2 during machining, no correction is necessary, and the target dimension Sa can be output as is as the target value. In the wire electrical discharge machining machine 100, the temperature Ta2 during machining corresponds to the temperature of the machining fluid 13, since the workpiece W is immersed in the machining fluid 13. The temperature Ta1 when measuring the machining result corresponds to the first temperature, and the temperature Ta2 during machining corresponds to the second temperature. However, if the temperature Ta1 when measuring the machining result is a typical 20°C, and there is a temperature difference ΔTa between the temperature Ta2 during machining and temperature Ta1 (=20°C), the X-axis linear scale 2b and Y-axis linear scale 3b, which serve as the basis for axis movement in the XY direction, will expand according to their respective coefficients of thermal expansion Ea. Therefore, when a target value corresponding to the target dimension Sa is commanded, the dimension Sb of the workpiece W after machining will be as shown in equation (1) below. Sb = Sa + ΔTa × Ea ... (1)

[0021] When the workpiece W after processing is measured in an environment with a temperature Ta1 (=20°C), its dimension Sc shrinks according to the thermal expansion coefficient Eb of the workpiece W, and is given by the following equation (2). Sc = Sb - ΔTa × Eb ... (2)

[0022] Therefore, the machining error Ha between the target dimension Sa and the dimension Sc of the workpiece W after machining when measured in a 20°C environment is given by the following equation (3). Ha=Sa-Sc=ΔTa×(Eb-Ea) ···(3)

[0023] In other words, by detecting the temperature difference ΔTa, the thermal expansion coefficients Ea of the X-axis linear scale 2b and Y-axis linear scale 3b, and the thermal expansion coefficient Eb of the workpiece W in real time during machining and substituting them into equation (3), the machining error Ha can be calculated in real time. Then, as shown in equation (4) below, a correction is made by adding the machining error Ha to the target dimension Sa of the machining process to obtain the corrected target dimension Sa', and by issuing a command in real time, it becomes possible to machine without errors in real time. Sa' = Sa + Ha ···(4)

[0024] Figure 3 is a diagram illustrating the method for calculating the temperature difference ΔTa in a wire electrical discharge machining machine 100 according to an embodiment. The machining fluid control unit 31 controls the temperature of the machining fluid 13 returning from the machining tank 10 and supplies the machining fluid 13 to maintain a constant temperature. The machining fluid control unit 31 also derives the temperature difference ΔTa based on the temperature of the machining fluid 13 detected during machining. As shown in Figure 3, 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 before being returned to the machining fluid control unit 31. The temperature of the processing fluid 13 returned from the processing tank 10 to the processing fluid control unit 31 is 20°C + Td.

[0025] In the wire electrical discharge machining machine 100, the workpiece W is immersed in a machining fluid 13 whose temperature is controlled 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, 20°C+Td, when it is returned from the machining tank 10 to the machining fluid control unit 31. Therefore, the temperature difference ΔTa mentioned above is considered to be the same as the temperature Td obtained by subtracting 20°C from the temperature of the machining fluid 13, 20°C+Td, when it is returned from the machining tank 10 to the machining fluid control unit 31. Therefore, the temperature difference ΔTa can be derived by the machining fluid control unit 31 by detecting the temperature of the machining fluid 13, 20°C+Td, when it is returned from the machining tank 10 to the machining fluid control unit 31, and subtracting 20°C from the detected temperature. In this way, the processing fluid control unit 31 detects the temperature of the processing fluid 13 returning from the processing tank 10 during processing, and based on the detected temperature, acquires in real time the temperature difference ΔTa between a first temperature Ta1, which is the temperature when the processing result is measured, and a second temperature Ta2, which is the temperature during processing.

[0026] The temperature command value 20°C+Tb output from the control unit 30 to the processing fluid control unit 31 is, for example, the same as the ambient temperature Te. Alternatively, the temperature command value 20°C+Tb may be set to a temperature that is a constant temperature difference from the ambient temperature Te.

[0027] In the wire electrical discharge machining machine 100, the temperatures of the X-axis linear scale 2b and Y-axis linear scale 3b are synchronized with the temperature of the machining fluid 13. That is, in the wire electrical discharge machining 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 Y-axis linear scale 3b are synchronized. For example, by passing the machining fluid 13 through the block to which the X-axis linear scale 2b and Y-axis linear scale 3b are attached, the temperatures of the X-axis linear scale 2b and Y-axis linear scale 3b are synchronized with the temperature command value of the machining fluid 13, 20°C+Tb. However, if the temperature command value 20°C+Tb output from the control unit 30 to the machining fluid control unit 31 is the same as the ambient temperature Te, the temperatures of the X-axis linear scale 2b and Y-axis linear scale 3b may be assumed to be the same as the ambient temperature Te, and the temperatures of the X-axis linear scale 2b and Y-axis linear scale 3b may be synchronized with the temperature of the machining fluid 13.

[0028] Furthermore, in the wire electrical discharge machining machine 100, when performing 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, which allows a discharge to be generated between the workpiece W and the wire 1, depending on the material of the workpiece W. Therefore, material-specific control parameters, including the voltage Va and the discharge distance Sh, are determined according to the material of the workpiece W. Accordingly, by adding the value of the thermal expansion coefficient Eb of the workpiece W for each material to the material-specific control parameters, the thermal expansion coefficient Eb of the workpiece W can be obtained when machining.

[0029] Furthermore, since the thermal expansion coefficients Ea of the X-axis linear scale 2b and Y-axis linear scale 3b are constant regardless of the material of the workpiece W, if they are set as control parameters independent of the material, the thermal expansion coefficient Eb can be obtained during machining.

[0030] Figure 4 is a block diagram showing an example of the configuration of the control system of a wire electrical discharge machining machine 100 according to an embodiment. The control system of the wire electrical discharge machining machine 100 comprises a control unit 30, a machining fluid control unit 31, a control parameter storage unit 33, a material-specific 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-specific 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, the X-axis drive unit 2a and the Y-axis drive unit 3a are shown as drive units 2a and 3a, with some parts omitted.

[0031] The control unit 30 controls the components of the wire electrical discharge machining machine 100 based on the NC program. The NC program includes the target dimensions Sa of the workpiece W and the material of the workpiece W.

[0032] The control parameter storage unit 33 stores control parameters that are independent of the material. The control parameters stored in the control parameter storage unit 33 include the thermal expansion coefficients Ea of the X-axis linear scale 2b and the Y-axis linear scale 3b.

[0033] The material-specific control parameter determination unit 34 stores material-specific control parameters for each material of the workpiece W, including the voltage Va supplied to the workpiece W, the discharge distance Sh, and the thermal expansion coefficient Eb of the workpiece W.

[0034] When machining begins, the control unit 30 outputs a control parameter output command to the control parameter storage unit 33, outputs material information of the workpiece W to the material-specific control parameter determination unit 34, and outputs a target temperature command Tb to the machining fluid control unit 31. The control unit 30 also outputs the target dimension Sa of the workpiece W to the target dimension output unit 36.

[0035] The control parameter storage unit 33 outputs the thermal expansion coefficients Ea of the X-axis linear scale 2b and the Y-axis linear scale 3b to the machining error detection unit 35. The material-specific control parameter determination unit 34 outputs the thermal expansion coefficient Eb of the workpiece W corresponding to the material included in the input material information to the machining error detection unit 35. The material-specific control parameter determination unit 34 also outputs the discharge distance Sh corresponding to the material included in the input material information to the axis command value control unit 37. The material-specific control parameter determination unit 34 also 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 controls the temperature of the machining fluid 13 supplied to the machining tank 10 to 20°C+Tb according to the input target temperature command Tb. Furthermore, as explained in Figure 3, the processing fluid control unit 31 detects the temperature of the processing fluid 13 returned from the processing tank 10 to the processing fluid control unit 31, which is 20°C+Td. It then calculates the temperature Td by subtracting 20°C from the detected temperature 20°C+Td, and outputs this temperature Td as the aforementioned temperature difference ΔTa to the processing error detection unit 35.

[0036] The machining error detection unit 35 calculates the machining error Ha using the input thermal expansion coefficients Ea and Eb, the temperature difference ΔTa, and the aforementioned equation (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 and machining error Ha, and the aforementioned equation (4).

[0037] The target dimension output unit 36 ​​outputs the calculated corrected target dimension 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 dimension Sa' based on the target dimension Sa' and the discharge distance Sh. The target dimension output unit 36 ​​outputs the axis command value Sg to the X-axis drive unit 2a and the Y-axis drive unit 3a, and drives and controls the X-axis stage 2 and the Y-axis stage 3.

[0038] Thus, in the wire electrical discharge machining machine 100, the machining error Ha is calculated based on the thermal expansion coefficients Ea and Eb and the temperature difference ΔTa, a target dimension Sa' corrected to cancel out the machining error Ha is determined, and the X-axis stage 2 and Y-axis stage 3 are driven by the axis command value Sg determined from the target dimension Sa' and the discharge distance Sh, thereby obtaining error-free machining results at the temperature Ta1 at which the machining results are measured.

[0039] Next, a configuration for determining the quality of the machining result by correcting the target dimensions will be described. Figure 5 is a diagram illustrating a method for deriving the inter-electrode distance Hc, which is the discharge distance between the workpiece W and the wire 1, in the wire electrical discharge machine 100 according to the embodiment. Figure 6 is a block diagram illustrating a configuration for deriving the dimension Se of the workpiece W in the wire electrical discharge machine 100 according to the embodiment. Figure 7 is a block diagram illustrating a configuration for determining the quality of the dimensions of the workpiece W in the wire electrical discharge machine 100 according to the embodiment. In Figures 6 and 7, the X-axis stage 2 and Y-axis stage 3 are shown as stages 2 and 3, partially omitted, and the X-axis linear scale 2b and Y-axis linear scale 3b are shown as scales 2b and 3b, partially omitted. Also, in Figure 7, the X-axis stage 2 and Y-axis stage 3 are shown as stages 2 and 3, partially omitted, and the X-axis drive unit 2a and Y-axis drive unit 3a are shown as drive units 2a and 3a, partially omitted. The workpiece dimension calculation unit 41, target dimension temperature conversion unit 42, dimension comparison unit 43, and axis command value control unit 37 shown in Figure 7 correspond to the second control unit.

[0040] As shown in Figure 5, in order to determine the dimension Se of the workpiece W, the inter-electrode distance Hc between the workpiece W and the wire 1 is detected from the waveform of the discharge voltage generated between the workpiece W and the wire 1. That is, the distance calculation unit 40 uses the voltage drop V due to the discharge current when a discharge occurs and the discharge current value A to calculate the electrical resistance R between the workpiece W and the wire 1 as shown in equation (5) below. R = V / A ... (5) Furthermore, since the space between the workpiece W and the wire 1 is filled with a processing fluid 13 whose electrical resistivity ρ is known, the inter-electrode distance Hc can be determined by the following equation (6). Hc = R / ρ ... (6) Figure 5 shows that the inter-pole distance Hc can be determined when the voltage drop is V, and a closer inter-pole distance Hc' can be determined when the voltage drop is lower V'.

[0041] As shown in Figure 6, the workpiece dimension calculation unit 41 calculates the dimension Se of the workpiece W by subtracting the inter-pole distance Hc from the current axis position Sd, as shown in equation (7) below, based on the inter-pole distance Hc obtained by the distance calculation unit 40 and the current axis position Sd measured by the X-axis linear scale 2b and the Y-axis linear scale 3b. Se = Sd - Hc ... (7)

[0042] Furthermore, as shown in Figure 7, the target dimension-temperature conversion unit 42 obtains a converted target dimension Sb' by converting the corrected target dimension Sa' to the processing temperature Ta2, as shown in equation (8) below, based on the corrected target dimension Sa' calculated by the target dimension output unit 36, the thermal expansion coefficients Ea of the X-axis linear scale 2b and Y-axis linear scale 3b stored in the control parameter storage unit 33, and the temperature difference ΔTa obtained by the processing fluid control unit 31. Sb' = Sa' + ΔTa × Ea ···(8)

[0043] Furthermore, in the workpiece dimension calculation unit 41 shown in Figure 7, the dimension Se of the workpiece W is calculated based on the inter-pole distance Hc obtained by the distance calculation unit 40 and the current axis position Sd measured by the X-axis linear scale 2b and the Y-axis linear scale 3b, as explained in Figure 6.

[0044] The dimension comparison unit 43 compares the dimension Se of the workpiece W calculated by the workpiece dimension calculation unit 41 with the temperature-corrected target dimension Sb' calculated by the target dimension temperature conversion unit 42, and determines whether the machining result is good or bad due to the correction of the target dimension. The dimension comparison unit 43 determines whether the difference between the dimension Se of the workpiece W and the temperature-corrected target dimension Sb' is within the allowable range, and outputs the determination result to the axis command value control unit 37.

[0045] The axis command value control unit 37 determines that the machining error Ha calculated by equation (3) is good if the judgment result falls within the acceptable range, and terminates the correction. However, if the judgment result does not fall within the acceptable range, the axis command value control unit 37 changes the axis position Sd by changing the current axis command value Sg, and controls the system so that the difference between the dimension Se of the workpiece W and the target dimension Sb' after temperature correction falls within the acceptable range. That is, if the dimension Se of the workpiece is larger than the target dimension Sb', the axis command value is changed to Sg' to set the axis position closer to the workpiece W, to axis position Sd', and the dimension of the workpiece W becomes a smaller dimension Se'. If the dimension Se of the workpiece W is smaller than the target dimension Sb', the axis command value is changed to Sg'' to set the axis position further away from the workpiece W, to axis position Sd'', and the dimension of the workpiece W becomes a larger dimension Se''. By repeating this control until the judgment result falls within the acceptable range, machining without machining errors can be performed.

[0046] As described above, according to the embodiment, the processing fluid control unit 31 derives a temperature difference ΔTa based on the temperature of the processing fluid 13 during processing, calculates a processing error Ha based on the thermal expansion coefficients Ea and Eb and the temperature difference ΔTa, determines a corrected target dimension Sa' to cancel out the processing error Ha, and drives the X-axis stage 2 and Y-axis stage 3 with the axis command value Sg based on the determined target dimension Sa'. Therefore, a processing result without error at the temperature Ta1 where the processing result is measured can be obtained in real time. Consequently, temperature correction is performed in real time during processing, and the productivity of processing can be improved. Furthermore, the dimension Se of the workpiece W calculated by the workpiece dimension calculation unit 41 is compared with the temperature-corrected target dimension Sb' calculated by the target dimension temperature conversion unit 42 to determine whether the processing result is good or bad due to the correction of the target dimension. Therefore, it is possible to grasp in real time whether the temperature correction of axis movement is being performed correctly. For this reason, temperature correction and the good or bad judgment of the correction can be performed in real time during processing, and productivity can be improved. Furthermore, if the quality judgment is negative, the current axis position Sd is changed, allowing for the efficient production of workpieces without machining errors.

[0047] Here, we will describe the hardware configuration of the control system, which includes the control unit 30, control parameter storage unit 33, material-specific control parameter determination unit 34, machining error detection unit 35, target dimension output unit 36, and axis command value control unit 37 shown in Figure 4, and the distance calculation unit 40, workpiece dimension calculation unit 41, target dimension temperature conversion unit 42, and dimension comparison unit 43 shown in Figure 7. Figure 8 is a block diagram showing the hardware configuration of the control system of a wire electrical discharge machining machine 100 according to an embodiment.

[0048] The control system of the wire electrical discharge machining machine 100 can be implemented by a hardware configuration 406 including the arithmetic unit 404 and memory device 405 shown in Figure 8. The arithmetic unit 404 is, for example, a CPU (Central Processing Unit), microprocessor, microcomputer, or DSP (Digital Signal Processor). The memory device 405 is, for example, RAM (Random Access Memory) or ROM (Read Only Memory).

[0049] The configurations shown in the embodiments described above are merely examples of the content of this disclosure and can be combined with other known technologies, and parts of the configuration can be omitted or modified without departing from the gist of this disclosure. [Explanation of Symbols]

[0050] 1 Wire, 2 X-axis stage, 2a X-axis drive unit, 2b X-axis linear scale, 3 Y-axis stage, 3a Y-axis drive unit, 3b Y-axis linear scale, 4 Workpiece moving mechanism, 10 Machining tank, 11 Workpiece mounting table, 13 Machining fluid, 14 Lower arm, 15 Upper arm, 20 Column, 21 Support base, 24 Lower guide, 25 Upper guide, 30 Control unit, 31 Machining fluid control unit, 32 Power supply unit, 33 Control parameter storage unit, 34 Material-specific control parameter determination unit, 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 EDM machine, 404 Calculation unit, 405 Storage device, 406 Hardware configuration.

Claims

1. A wire electric discharge machine which applies a voltage between a workpiece immersed in a machining fluid in a machining tank and a wire electrode to generate an electric discharge, detects a position of a movement axis which moves the wire electrode and the workpiece relatively with a position detector, feeds back the detected position of the movement axis to a target value corresponding to a target dimension, thereby machining the workpiece, and synchronizes a temperature of the position detector with a temperature of the machining fluid, a machining fluid control unit that controls the temperature of the machining fluid and obtains a temperature difference between a first temperature, which is a temperature at which a machining result is measured, and a second temperature, which is a temperature during machining, based on the temperature of the machining fluid detected during machining; a first control unit that calculates a processing error between a dimension of the workpiece processed to the target dimension when measured at the first temperature based on the acquired 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 processing based on the calculated processing error, and drives the moving axis based on an axis command value based on the corrected target dimension; a second control unit that determines whether machining based on the corrected target dimension is acceptable, and changes the axis command value if the machining is unacceptable; A wire electric discharge machine comprising:

2. The axis command value is determined based on the corrected target dimension and a discharge distance set corresponding to the workpiece.

2. The wire electric discharge machine according to claim 1 .

3. The machining fluid control unit supplies the machining fluid whose temperature has been controlled to a machining tank, detects the temperature of the machining fluid returning from the machining tank during machining, and obtains the temperature difference based on the detected temperature.

2. The wire electric discharge machine according to claim 1 .

4. The machining fluid is passed through a block to which the position detector is attached.

2. The wire electric discharge machine according to claim 1 .

5. The second control unit is a distance calculation unit for calculating an inter-electrode distance between the workpiece and the wire electrode; a workpiece dimension calculation unit that calculates a dimension of the workpiece after machining at the second temperature based on the current position of the movement axis detected by the position detector and the inter-electrode distance; a target dimension temperature conversion unit that calculates the target dimension after converting the corrected target dimension into the second temperature using the temperature difference and a thermal expansion coefficient of the position detector; a dimension comparison unit which calculates a dimension difference between the dimension of the workpiece calculated by the workpiece dimension calculation unit and the converted target dimension, and if the dimension difference is not within an allowable range, changes the axis command value until the dimension difference is within an allowable range; 5. The wire electric discharge machine according to claim 1, further comprising:

6. The electrode distance is determined based on a voltage drop during discharge of a voltage applied to the workpiece and the wire electrode.

6. The wire electric discharge machine according to claim 5.

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