Wire electrical discharge machining apparatus and wire electrical discharge machining method

Abstract

To provide a wire electrical discharge machining apparatus that allows for easier control of the machining speed. [Solution] The inter-electrode voltage detection device detects the inter-electrode voltage between the wire electrode and the workpiece and outputs the average machining voltage at predetermined intervals. The servo curve generation unit generates a servo curve showing the relationship between the average machining voltage and the feed rate. The limit point is the intersection of the estimated average machining voltage, which is estimated to be the limit at which discharge continuously occurs between the electrodes under the machining conditions, and the feed rate suitable for the estimated average machining voltage. The feed rate output unit is configured to output the feed rate corresponding to the average machining voltage detected by the inter-electrode voltage detection device based on the servo curve generated by the servo curve generation unit. The movement control unit controls the movement device at the feed rate.

Description

[[Technical Field]]

[0001] The present invention relates to a wire electric discharge machining apparatus and a wire electric discharge machining method. [[Background Art]]

[0002] Patent Document 1 discloses a wire electric discharge machining apparatus. [[Prior Art Literature]] [[Patent Literature]]

[0003] [[Patent Document 1]] Japanese Patent No. 7104865 [[Summary of the Invention]] [[Problem to be Solved by the Invention]]

[0004] In wire electric discharge machining, a voltage pulse is applied to a predetermined gap (hereinafter referred to as the gap) formed between a wire electrode and a workpiece while relatively moving the wire electrode along a predetermined machining shape trajectory with respect to the workpiece, so that electric discharge is repeatedly generated to cut the workpiece into a desired shape. At this time, the machining accuracy for target dimensions and surface roughness generally increases as the current flowing through the gap per discharge decreases. Therefore, according to the finally required machining accuracy, the machining conditions are changed so that the magnitude of current decreases stepwise, and the wire electrode and the workpiece are relatively moved to repeatedly machine the same shape several times. Machining in which the same shape is repeated a plurality of times can be roughly divided into a rough machining step (first cut) of cutting a workpiece from a solid state, and a finishing step (second cut) of shaping the machined surface formed in the first cut (1st), corresponding to the machining method. In particular, the second cut (2nd) can be subdivided into a third cut (3rd), a fourth cut (4th) and so on in order corresponding to the number of machining passes.

[0005] Here, the gap can be broadly classified into front gap and side gap. The front gap is the distance between the wire electrode and the workpiece, generated by the discharge occurring in the direction of the wire electrode's movement. The side gap is the distance between the wire electrode and the workpiece, generated perpendicular to the direction of machining. The shape of the cut surface formed on the workpiece after machining depends on the side gap. Therefore, it can be said that the machining accuracy of the cut surface formed in each machining process can be improved by maintaining a constant side gap during machining.

[0006] To maintain a constant side gap, one method involves performing test machining beforehand and deriving a relationship between the average machining voltage and feed rate that maintains a constant side gap based on the test data obtained from that test machining, thereby controlling the feed rate during machining. Specifically, machining is performed at a constant feed rate, and data on the average machining voltage and side gap are obtained according to several offset patterns (the deviation between the movement path of the central axis of the wire electrode and the workpiece). The machining is performed multiple times under similar conditions to obtain the required number of actual data. From the obtained data, a relationship between the side gap and offset is derived for both the average machining voltage and the feed rate using an approximation method. Next, the changes in the average machining voltage and feed rate in response to changes in the side gap and offset are modeled, and the desired side gap and offset are determined based on this. Finally, the relationship between the average machining voltage and feed rate can be derived by fixing the side gap.

[0007] However, the relationship between the average machining voltage and feed rate at which the side gap remains constant differs for each set machining condition. Therefore, in such a machining speed control method, in order to accommodate the set machining conditions, it is necessary to perform multiple test machining operations in advance for each set machining condition, acquire a large amount of data, and derive the relationship between the average machining voltage and feed rate for each by performing the calculations described above, which requires more effort and cost. The machining conditions set for each machining process consist of combinations of multiple types of parameters, and there are countless combinations of multiple parameters, so it is not easy to obtain a relationship between the average machining voltage and feed rate that can immediately accommodate any machining condition.

[0008] This invention has been made in view of these circumstances, and provides a wire electrical discharge machining apparatus that can control the machining speed more easily. [Means for solving the problem]

[0009] As a result of diligent research, the inventors have found that, in relation to the relationship between average machining voltage and feed rate, in a finishing process with the same offset and the same machining configuration except for the plate thickness, a servo curve represented by an exponential function with two variables—the intersection of the servo reference voltage for the machining conditions set in that machining process and a predetermined standard feed rate suitable for that servo reference voltage, and the intersection of the average machining voltage at which discharge is estimated to be the limit for sustained discharge between the electrodes under the machining conditions and a feed rate suitable for that average machining voltage—can approximate characteristics derived based on precise, repeated test machining results. This led to the completion of the present invention. That is, the present invention provides the following invention. [1] A wire electrical discharge machining apparatus comprising a moving device, an inter-electrode voltage detection device, and a control device for controlling the moving device, wherein the moving device is configured to machine a workpiece by moving a wire electrode relative to the workpiece in the machining direction, the inter-electrode voltage detection device detects the inter-electrode voltage between the wire electrode and the workpiece and outputs an average machining voltage at predetermined intervals, and the control device comprises a servo curve generation unit, a feed rate output unit, and a moving control unit, wherein the servo curve generation unit generates a servo curve showing the relationship between the feed rate and the average machining voltage based on an exponential function with reference points and limit points as variables, and the reference points are relative to the machining process A wire electrical discharge machining apparatus, wherein the limit point is the intersection of a servo reference voltage set as the corresponding machining condition and a standard feed rate predetermined from the machining condition, the limit point is the intersection of an estimated average machining voltage which is estimated to be the limit at which discharge occurs continuously between the electrodes under the machining condition and a feed rate suitable for the estimated average machining voltage, the feed rate output unit is configured to output the feed rate corresponding to the average machining voltage detected by the electrode voltage detection device based on the servo curve generated by the servo curve generation unit, and the movement control unit is configured to control the movement device with the feed rate. [2] A wire electrical discharge machining apparatus as described in [1], wherein the limit point is determined by performing multiple test machining operations for the same combination of wire electrode diameter and material and workpiece material, with the same machining process differing only in the thickness of the workpiece and the machining conditions corresponding to the thickness, and the limit point is the intersection of the average machining voltage in the servo curve common to the same machining process and the feed rate suitable for the average machining voltage. Wire electrical discharge machining apparatus as described in [3][2], further comprising a servo curve data storage unit, wherein the servo curve data storage unit stores a plurality of limit points obtained in advance by performing the test machining for each of the same machining processes with the same combination of wire electrode diameter and material and workpiece material, and the servo curve generation unit generates the servo curve by obtaining the limit points corresponding to the same machining process for the combination of wire electrode diameter and material and workpiece material from the speed curve data storage unit. Wire electrical discharge machining apparatus as described in [4][3], wherein the pre-servo curve generation unit acquires the limit points from the speed curve data storage unit in correspondence with whether the machining form is a punch or a die, and generates the servo curve. Wire electrical discharge machining apparatus as described in [5][3], wherein the servo curve generation unit acquires the limit points from the speed curve data storage unit and generates the servo curve, corresponding to whether the machining form is floating with the jet nozzle in close contact or floating on one side. Wire electrical discharge machining apparatus as described in [6][3], wherein the servo curve generation unit acquires the limit points from the speed curve data storage unit in correspondence with whether the machining form is punch or die, and whether the position of the jet nozzle is floating in close contact or floating on one side, and generates the servo curve. Wire electrical discharge machining apparatus as described in [7][2], further comprising a servo curve data storage unit, wherein the servo curve data storage unit stores a plurality of servo curves obtained by performing test machining in advance for each of the same machining processes with the same combination of wire electrode diameter and material and workpiece material, and the servo curve generation unit generates the servo curve by acquiring and determining the servo curve corresponding to the same machining process for the combination of wire electrode diameter and material and workpiece material. Wire electrical discharge machining apparatus as described in [8][7], wherein the feed rate curve generation unit generates the feed rate curve by acquiring the servo curve from the speed curve data storage unit in correspondence with whether the machining form is a punch or a die, and / or whether the position of the jet nozzle is floating in close contact or floating on one side. [9] A wire electrical discharge machining method for machining a workpiece by moving a wire electrode relative to the workpiece, wherein a servo curve is generated showing the relationship between the average machining voltage between the electrodes of the wire electrode and the workpiece and the feed rate, and the feed rate is controlled based on the servo curve in accordance with the average machining voltage, the method comprising: a reference point determination step; a limit point acquisition step; a servo curve generation step; an electrode voltage detection step; a feed rate output step; and a relative movement control step, wherein the reference point derivation step is obtained by acquiring data of the servo reference voltage for machining conditions set for each machining step and data of a standard feed rate suitable for the predetermined servo reference voltage, and a reference point is determined which is the intersection of the servo reference voltage and the standard feed rate in the servo curve required for the machining step, and the limit point acquisition step is determined which is the intersection of the servo reference voltage and the standard feed rate in the required A wire electrical discharge machining method comprising: acquiring data of a limit point which is the intersection of an estimated average machining voltage, which is the average machining voltage at which discharge is estimated to be the limit at which discharge continuously occurs between the electrodes in the machining conditions of the servo curve, and a feed rate suitable for the estimated average machining voltage; generating the required servo curve using an exponential function with the reference point and the limit point as variables in the servo curve generation step; acquiring the average machining voltage at predetermined time intervals in the electrode voltage detection step; determining and outputting the feed rate corresponding to the acquired average machining voltage based on the servo curve generated in the servo curve generation step in the feed rate output step; and controlling the relative movement between the wire electrode and the workpiece with the feed rate output in the feed rate output step, and repeating the feed rate output step and the relative movement control step. A wire electrical discharge machining method as described in

[10] [9], wherein the limit point is determined by performing multiple test machining operations with the same combination of wire electrode diameter and material and workpiece material, and the same machining process, but with only the thickness of the workpiece and the machining conditions corresponding to the thickness differing, and the limit point is the intersection of the average machining voltage in the servo curve common to the same machining process and the feed rate suitable for the average machining voltage. [Effects of the Invention]

[0010] The wire electrical discharge machining apparatus according to the present invention is configured to output a feed rate corresponding to the detected average machining voltage based on a servo curve generated by an exponential function, where the horizontal axis is the average machining voltage and the vertical axis is the feed rate. The servo curve is generated by an exponential function with two variables: the intersection of the servo reference voltage for the machining conditions set in that machining process and a predetermined standard feed rate suitable for that servo reference voltage, and the intersection of the average machining voltage at which it is estimated to be the limit for continuous discharge between the electrodes under the machining conditions and a feed rate suitable for that average machining voltage. With this configuration, the relationship between the average machining voltage and the feed rate can be easily derived and the machining speed can be controlled. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic diagram of a wire electrical discharge machining apparatus 100 according to one embodiment of the present invention. [Figure 2] This is a block diagram showing the control mode of a wire electrical discharge machining apparatus 100 according to one embodiment of the present invention. [Figure 3] This is an example of a feed rate curve generated by a servo curve generation unit 92 according to one embodiment of the present invention. [Figure 4] Figures 4A, 4B, and 4C show a comparison of the feed rate curve according to the present invention with a conventional feed rate curve. [Modes for carrying out the invention]

[0012] Embodiments of the present invention will be described below. The various features shown in the embodiments below can be combined with each other. Furthermore, each feature constitutes an independent invention. In addition, any elements not specified in the claims of the embodiments below are optional and can be omitted. Furthermore, any elements not specified in the claims of the embodiments below are optional and can be omitted. Any number of zeros (for example, one or two) may be added to the end of the numerical values ​​disclosed in the following description. For example, one or two zeros may be added after "1.4" to make it "1.40" or "1.400".

[0013] 1. Wire electrical discharge machining apparatus 100 1.1 Processing machine body 1 The processing machine body 1 comprises a wire electrode 2, a wire guide mechanism 3, a power supply unit 4, a moving device 5, and an inter-electrode voltage detection device 6.

[0014] The wire guide mechanism 3 comprises an upper guide assembly 31 and a lower guide assembly 32, respectively, which are provided above and below the workpiece W placed on the work stand 11. The upper guide assembly 31 and the lower guide assembly 32 each comprise a housing 33, a wire guide 34, and a current-carrying body 35, with various components housed within the housing 33. The wire electrode 2 is stretched between the wire guides 34 of the upper guide assembly 31 and the lower guide assembly 32 and is positioned and guided by the upper and lower wire guides 34. The current-carrying body 35 is connected to the power supply unit 4. The current-carrying body 35 is also movable in a direction substantially perpendicular to the direction in which the wire electrode 2, guided by the wire guide 34, is stretched, and power is supplied when the current-carrying body 35 contacts the wire electrode 2.

[0015] The moving device 5 is configured to drive a plurality of moving bodies (not shown) to move the wire electrode 2 relative to the workpiece W in the direction of machining, while maintaining the gap formed between the wire electrode 2 and the workpiece W according to the feed rate output from the control device 9, thereby machining the workpiece W.

[0016] The moving device 5 includes moving bodies in a plurality of control axis directions for relatively moving the wire electrode 2 with respect to the workpiece W, and respective servo motors (not shown) for driving and moving each moving body. The moving device 5 synchronously drives the servo motors of each moving body under the control of the control device 9, whereby the wire electrode 2 relatively moves with respect to the workpiece W along a predetermined machining path and a standard feed speed. Various configurations can be applied to the moving bodies depending on the specifications of the wire electric discharge machining apparatus 100. For example, in the wire electric discharge machining apparatus 100 shown in Fig. 1, the table 10 on which the work stand 11 is erected is used as a moving body that reciprocates in one horizontal linear axis direction (X axis), and the saddle 20 carrying the table 10 is configured as a moving body that reciprocates in another horizontal linear axis direction (Y axis) orthogonal to the X axis direction.

[0017] The inter-electrode voltage detection device 6 detects the inter-electrode voltage between the wire electrode 2 and the workpiece W, and can output an average machining voltage that is the average of the detected inter-electrode voltages at predetermined time intervals. The inter-electrode voltage constantly fluctuates because it repeatedly drops due to the occurrence of electric discharge after a no-load voltage is applied, no voltage is applied during a predetermined off time, and then rises again. Therefore, the average machining voltage, which is the average value of the inter-electrode voltages, is calculated and can be used for feed speed control and the like.

[0018] The average machining voltage is the average value of the inter-electrode voltage within the measurement target time. The detection time for detecting the average machining voltage ranges from 0.01 μsec to 1 μsec, and the measurement target time (sampling period) of the average machining voltage in servo control depends on the required response performance of the moving device 5 including the moving body, but 0.05 msec to 2 msec is appropriate. In other words, the predetermined time is 0.05 msec to 2 msec. Specifically, the predetermined time is, for example, 0.05, 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45, 0.50, 0.55, 0.60, 0.65, 0.70, 0.75, 0.80, 0.85, 0.90, 0.95, 1.00, 1.05, 1.10, 1.15, 1.20, 1.25, 1.30, 1.35, 1.40, 1.45, 1.50, 1.55, 1.60, 1.65, 1.70, 1.75, 1.80, 1.85, 1.90, 1.95, 2.00 msec, and may be within a range between any two of the numerical values exemplified herein.

[0019] The inter-electrode voltage detection device 6 can be provided in any configuration and at any position as long as it can detect the inter-electrode voltage and output the average machining voltage. For example, the inter-electrode voltage detection device 6 can remove vibration components of a voltage waveform with a filter and average the voltage waveform. Alternatively, the inter-electrode voltage detection device 6 may perform sampling-holding or peak-holding on the voltage waveform. Further, for example, the inter-electrode voltage detection device 6 may output the average machining voltage as analog data or digital data.

[0020] 1.2 Control device 9 The control device 9 controls the operation of the wire electric discharge machining apparatus 100. The control operation of the control device 9 will be described below. In addition, the servo control described in the present specification is assumed to be mainly applied to cuts after the second cut. Therefore, any known speed control configuration may be used for the servo control in the first cut. In the following description, for convenience of explanation, a case where the control configuration according to an embodiment of the present invention is applied to the second cut will be described.

[0021] Each component of the control device 9 may be implemented by software or by hardware. If implemented by software, various functions can be realized by the CPU executing a computer program. The program may be stored in the built-in memory unit or in a computer-readable, non-temporary recording medium. Alternatively, the program may be read from an external memory unit and implemented through so-called cloud computing.

[0022] When implemented in hardware, it can be implemented using various circuits such as ASICs (Application Specific Integrated Circuits), FPGAs (Field Programmable Gate Arrays), or DRPs (Dynamically Reconfigurable Processors). In this embodiment, various types of information and the concepts encompassing them are handled, which are represented by high and low signal values ​​as a set of binary bits consisting of 0s and 1s, and communication and calculations can be performed by the aforementioned software or hardware configurations.

[0023] As shown in Figure 2, the control device 9 according to this embodiment includes a machining condition holding unit 91, a servo curve generation unit 92, a feed rate output unit 94, a movement control unit 95, and a power supply control unit 96. The control device 9 may further include a servo curve determination unit 93.

[0024] 1.2.1 Machining condition holding section 91 The machining condition holding unit 91 holds a dataset. The dataset includes a machining condition table containing machining requirements and machining conditions for each machining method, as well as feed rate data corresponding to the machining conditions (standard feed rate and suitable feed rate, described later). In the following description, machining conditions refer to parameters that must be set before machining in order to operate the wire electrical discharge machining apparatus 100 according to the desired machining for each machining process. Machining conditions include, for example, current, voltage, on time, off time, servo reference voltage, pressure of the machining fluid jet, and tension of the wire electrode 2. In particular, machining conditions that include electrical elements are called electromachining conditions. Machining conditions are provided to the control device 9. The values ​​of the machining conditions may be changed during machining.

[0025] The processing conditions vary greatly depending on the combination of the diameter and material of the wire electrode 2 and the material and thickness of the workpiece W. In the following explanation, the preconditions required to determine the initial settings of these processing conditions are referred to as processing requirements. Furthermore, the processing conditions may also change depending on whether it is punching or die processing, and whether the upper and lower jet nozzles are floating at both ends, floating at one end, or in contact with each other in the processing fluid jet supply method. In the following explanation, the differences in processing types or processing methods for which it is desirable to categorize the conditions in order to determine the initial settings of these processing conditions are collectively referred to as processing forms.

[0026] 1.2.2 Servo curve generation unit 92 The servo curve generation unit 92 can generate and store a servo curve that shows the relationship between the feed rate and the average machining voltage. Specifically, the servo curve generation unit 92 generates a servo curve that shows the relationship between the feed rate and the average machining voltage using an exponential function with two variables: a reference point and a limit point. The reference point is the intersection of the servo reference voltage, which is set as a machining condition corresponding to the desired machining process, and a predetermined standard feed rate that is determined in advance from the set machining conditions, in the servo curve required for the desired machining process. The limit point is the intersection of the average machining voltage (referred to as the estimated average machining voltage) at which it is estimated that discharge will continuously occur between the electrodes under the set machining conditions, and a feed rate suitable for the estimated average machining voltage.

[0027] Furthermore, the servo curve generation unit 92 may include a servo curve data storage unit 92a. The servo curve data storage unit 92a can store multiple limit points. Each of the multiple limit points is determined by performing test machining in advance for each machining process with the same combination of wire electrode diameter and material and workpiece material W.

[0028] The servo curve generation unit 92 can extract and acquire limit points corresponding to the combination of diameter and material of the wire electrode 2 and the material of the workpiece W, as well as the offset, from among the multiple limit point data stored in the servo curve data storage unit 92a.

[0029] Furthermore, the servo curve generation unit 92 may be configured to generate a plurality of servo curves in advance according to machining conditions and store them in the servo curve data storage unit 92a.

[0030] Here, we will explain the reference point and the limit point. First, the reference point is determined based on the reference side gap in the desired machining process. The side gap is the value obtained by subtracting the diameter of the wire electrode 2 and the remaining material from the offset. In other words, the reference point is determined based on the offset in the desired machining process. The offset value in the desired machining process is set in the NC program and held by the machining condition holding unit 91.

[0031] The reference point can be determined by the servo reference voltage of the machining conditions set in accordance with the offset in the desired machining process and the standard feed rate in that desired machining process. The servo reference voltage (machining conditions) and standard feed rate data are both stored in the machining condition holding unit 91. In particular, the standard feed rate data has already been collected when repeated test machining is performed with the same machining conditions as those set in advance for the desired machining process, and is stored in advance together with the machining condition table, and can be acquired simultaneously when setting the machining conditions. Here, the average machining voltage and the corresponding feed rate that can achieve the desired side gap are tentatively referred to as the ideal average machining voltage and ideal feed rate in order to distinguish them from the average machining voltage and feed rate acquired and used during machining in the present invention.

[0032] This section explains the ideal average machining voltage and the corresponding ideal feed rate. In actual machining, the machined surface in the second cut has surface irregularities caused by the first cut. However, a machined surface without such irregularities is defined as the ideal machined surface. When performing a second cut on an ideal machined surface, machining at a constant machining speed results in a constant material removal rate per unit time, allowing for the detection of a constant average machining voltage and the maintenance of a constant side gap. The constant average machining voltage and constant machining speed when machining this ideal machined surface represent the ideal average machining voltage and the corresponding ideal feed rate. In other words, the ideal average machining voltage and ideal feed rate that can achieve the desired side gap are uniquely determined.

[0033] As already explained, in the wire electrical discharge machining apparatus 100, the machining condition holding unit 91 holds a dataset in which, for each machining requirement (diameter and material of the wire electrode 2 and material and plate thickness of the workpiece W) and machining type (punch and die, close contact, double floating, and single floating), the servo reference voltage (ideal average machining voltage), the standard feed rate suitable for that servo reference voltage (ideal feed rate), and the offset value at that time are recorded.

[0034] Since this dataset is created based on data obtained from test machining performed in advance, the entire machined surface after the first cut in the test machining is not the ideal machined surface. However, by focusing on any single point (a small section) on the machined surface, it is possible to obtain the average machining voltage and feed rate when machining that point, as well as the offset at that time. Therefore, the dataset records the ideal average machining voltage and ideal feed rate corresponding to each offset.

[0035] The limit point indicates the average machining voltage at which a discharge occurs when voltage is applied to the gap, and the corresponding feed rate. The limit point can be determined, for example, by performing multiple test machining operations with the same combination of wire electrode diameter and material and workpiece material W, and the same offset, but with only the thickness of the workpiece W and the corresponding machining conditions differing. The limit point is the intersection of the average machining voltage in the servo curve common to the same machining operation and the feed rate suitable for that average machining voltage. In other words, if the machining requirements other than the plate thickness are the same, the same limit point can be used regardless of the plate thickness.

[0036] Furthermore, suitable feed rates have already been collected by repeatedly performing test machining under the same machining conditions as those set in the desired machining process, and are stored in advance along with the machining condition table, and can be acquired simultaneously when setting the machining conditions. Therefore, in the wire electrical discharge machining apparatus 100 of this embodiment, the limit point is pre-input into the machining condition holding unit 91 before the start of machining.

[0037] The process for generating a servo curve according to one embodiment of the present invention will now be described. First, in order to determine the reference point, the servo curve generation unit 92 obtains data on the servo reference voltage and data on the standard feed rate suitable for the servo reference voltage, which are predetermined in accordance with the machining conditions at that time, from the machining condition holding unit 91, based on the machining conditions already set for the desired machining process. Then, the servo curve generation unit 92 determines the reference point, which is the intersection point of the servo reference voltage and the standard feed rate in the servo curve required for the desired machining process.

[0038] Furthermore, the servo curve generation unit 92 can acquire data from the machining condition holding unit 91 for the limit point on the requested servo curve, which is the intersection of the estimated average machining voltage, which is estimated to be the limit at which discharge continuously occurs between the electrodes under the machining conditions already set for the desired machining process, and the feed rate suitable for the estimated average machining voltage. Next, the servo curve generation unit 92 generates the requested servo curve using an exponential function with the reference point and the limit point as variables. The generated servo curve is a curve defined as an exponential function passing through the two points, the reference point and the limit point.

[0039] Theoretically, if an ideal surface is machined in actual processing, and the values ​​in the dataset are obtained from the results of machining an ideal surface, then the dataset values ​​should be used as they are for processing. However, as mentioned above, undulation occurs in the machined surface, so if the dataset values ​​are applied directly to perform the second cut, the speed control will be at a constant feed rate corresponding to the desired side gap, and the undulation from the first cut will be directly reflected.

[0040] In one embodiment of the present invention, the servo curve generated is configured to use a curve defined as an exponential function passing through a reference point and a limit point obtained from a dataset. By using such a servo curve for servo control, even on a machined surface where waviness exists from the first cut, the waviness can be reduced so that it is not directly reflected, making it possible to machine with relatively high precision (specific experimental results will be described later).

[0041] Furthermore, according to the configuration of one embodiment of the present invention, by simply obtaining one limit point in advance through test machining for each machining process with the same offset, using the same diameter and material of the wire electrode 2 and the material of the workpiece W, it is possible to generate a servo curve regardless of the difference in plate thickness in machining processes with the same offset, using the same diameter and material of the wire electrode 2 and the material of the workpiece W. Therefore, compared to the conventional configuration, which involves performing multiple overall experimental machining operations, acquiring a large amount of machining data, and deriving a servo curve based on the obtained data, in order to obtain a servo curve that can suppress waviness in finishing operations where the material removal amount varies and the side gap changes uncertainly on the machined surface, it is possible to generate a servo curve more simply.

[0042] Next, we will explain the generation of the servo curve in detail using Figure 3. As mentioned above, the dataset held by the processing condition holding unit 91 records processing requirements, processing condition tables for each processing type, and feed rate data corresponding to the processing conditions. However, for the sake of explanation, we will focus only on the plate thickness among the processing requirements.

[0043] This section describes a scenario in a dataset where, for nine different plate thicknesses (20, 30, 40, 50, 60, 70, 80, 90, and 100 mm), the standard feed rate is pre-determined and recorded for each thickness relative to the servo reference voltage, which is the ideal average machining voltage for the machining conditions. In the example shown in Figure 3, all machining requirements except plate thickness—namely, the diameter and material of the wire electrode 2 and the material of the workpiece W—are the same, and the limit points are common. Figure 3 displays all the servo curves corresponding to each plate thickness. The servo curves are exponential curves generated using the reference points A to I for each plate thickness shown in Table 1, and the common limit point. [Table 1]

[0044] First, several different plate thicknesses are selected for test processing to determine the common limit point across different plate thicknesses. Preferably, at least three different plate thicknesses are selected. More preferably, plate thicknesses are selected in 10 mm increments from 20 mm to 100 mm, as shown in Table 1.

[0045] Then, test machining is performed at the selected plate thickness to obtain the servo characteristics for each plate thickness (the shape of the test servo curve, which is the relationship with the feed rate obtained from the test machining results using a standard feed rate). For example, servo characteristics for plate thicknesses of 20mm, 30mm, and 60mm are obtained.

[0046] Next, a provisional limit point is determined at the point where the average machining voltage is estimated to be the limit at which discharge occurs continuously between the electrodes for each selected plate thickness that has been test-machined. As a result of the test machining, there may be cases where there is no overlapping point in the servo characteristics of all plate thicknesses. In that case, the intersection of the average machining voltage in the servo characteristics of each plate thickness, which can be considered to be the limit at which discharge occurs between the electrodes in common with respect to the feed rate suitable for that average machining voltage, and the corresponding feed rate can be set as the provisional limit point. The average machining voltage that can be considered common can be the average machining voltage when the feed rate increases sharply in the servo characteristics. The point at which the feed rate increases sharply often shows roughly the same average machining voltage regardless of the plate thickness, and this can be set as the common provisional limit point.

[0047] Then, the exponential function for each plate thickness is derived from the already known reference points and the provisional limit points. For example, when the plate thicknesses are 20mm, 30mm, and 60mm, three exponential functions are derived from the reference points A, B, and E and the provisional limit points.

[0048] Next, the curve based on the exponential function is corrected so that the deviation between the exponential function derived using the provisional limit point for each plate thickness and the servo characteristics obtained in the test machining is minimized. Specifically, in actual machining (especially for linear machining paths), the difference between the exponential function derived using the provisional limit point and the servo characteristics obtained in the test machining is compared within the range of average machining voltage (range of average machining voltage fluctuation) that may occur, and common points between the two are found and allocated evenly so that the maximum difference is minimized. Then, a curve passing through the allocated common points is obtained and this is the servo curve for the machining requirements and machining conditions at that time. Finally, the limit point of the servo curve for each plate thickness is set as a common limit point for each plate thickness in the same machining process under the same machining requirements and conditions.

[0049] The more plate thicknesses that can be selected, the smaller the error between the actual limit and the provisional limit point for each selected plate thickness can be. For example, when different plate thicknesses are selected in 10mm increments from 20mm to 100mm. Therefore, it may be possible to set the provisional limit point as the limit point. When setting the provisional limit point as the limit point, the curve based on the previously derived exponential function is used as the servo curve.

[0050] If no test machining has been performed, and all machining requirements except plate thickness are the same, and the machining conditions are the same, the servo curve for the same machining process can be determined and set based on an exponential function using the limit points and reference points obtained as described above. For example, when the plate thickness is 58 mm, the reference point for a 58 mm plate thickness can be obtained from the servo curve for a 60 mm plate thickness that is already known, and the servo curve can be determined by deriving an exponential function from that reference point and limit point. Furthermore, if necessary, the curve based on the exponential function can be corrected using the servo curve data for a 60 mm plate thickness that is already stored.

[0051] 1.2.3 Servo curve determination unit 93 The servo curve determination unit 93 sets the servo curve to be executed, which has already been generated by the servo curve generation unit 92. If the servo curve generation unit 92 holds multiple servo curves, the servo curve determination unit 93 is configured to determine the servo curve corresponding to the current machining conditions from among the multiple servo curves held by the servo curve generation unit 92.

[0052] The servo curve determination unit 93 determines a suitable servo curve based on various machining conditions input to the wire electrical discharge machining apparatus 100. The servo curve determination unit 93 is configured to switch the curve applied at the transition between cuts (for example, when transitioning from a second cut to a third cut) or when the machined shape changes (for example, when transitioning from a straight shape to a corner shape).

[0053] The servo curve determination unit 93 can determine the timing for switching the servo curve by judging the change in plate thickness using known methods or means provided for other systems that automatically switch processing conditions in response to changes in plate thickness, which are referred to as "step processing." For example, it is conceivable that the step position could be determined from pre-stored three-dimensional shape data, the change in plate thickness based on data of numerous discharge points obtained by means for detecting discharge points, extreme changes in feed rate based on cumulatively recorded feed rate data, extreme changes in average processing voltage based on cumulatively recorded average processing voltage data, or the step position based on data of the position of the processing fluid jet nozzle.

[0054] To explain using the example in Figure 3, for example, when machining a workpiece W in a machining path where the plate thickness changes to 20 mm, 30 mm, and 20 mm, the servo curve determination unit 93 first determines curve A as the servo curve. Next, if a change in plate thickness is detected while machining using curve A, the servo curve determination unit 93 determines that the plate thickness has moved to a location with a thickness of 30 mm and determines curve B as the servo curve. If a change in plate thickness is detected while machining using curve B, the servo curve determination unit 93 determines that the plate thickness has moved to a location with a thickness of 20 mm and can again determine curve A as the servo curve.

[0055] 1.2.4 Feed rate output unit 94 The feed rate output unit 94 can output a feed rate corresponding to the average machining voltage based on the servo curve. Specifically, the feed rate output unit 94 can acquire the servo curve determined by the servo curve determination unit 93 and output a feed rate corresponding to the average machining voltage acquired from the inter-pole voltage detection device 6 to the movement control unit 95 based on that servo curve. If the servo curve generation unit 92 has generated only one curve, the feed rate output unit 94 can directly acquire the servo curve from the servo curve generation unit 92.

[0056] 1.2.5 Movement Control Unit 95 The movement control unit 95 is configured to control the movement device 5 according to the feed rate output from the feed rate output unit 94. This allows the wire electrode 2 to be moved relative to the workpiece W at a feed rate suitable for the current machining conditions in response to changes in the side gap.

[0057] 1.2.5 Power supply control unit 96 The power control unit 96 controls the power supply device 4 according to the electrical processing conditions obtained from the processing condition holding unit 91. This ensures that a predetermined voltage is applied to the gap in a timely manner.

[0058] 2. Wire electrical discharge machining method This section describes a wire electrical discharge machining method for a workpiece W using the wire electrical discharge machining apparatus 100 according to this embodiment.

[0059] The wire electrical discharge machining method of this embodiment comprises a servo control preparation step and a machining step. The servo control preparation step is performed before the machining step and includes a reference point determination step, a limit point acquisition step and a servo curve generation step. The machining step may include, as steps related to the feed rate control of the wire electrode 2, at least an inter-electrode voltage detection step, a feed rate output step and a relative movement control step.

[0060] In this embodiment of the wire electrical discharge machining method, once the operator operating the wire electrical discharge machining apparatus 100 has provided the apparatus 100 with the essential machining requirements, machining conditions, and machining mode required for the desired machining, a servo control preparation step is performed prior to machining.

[0061] In the servo control preparation process, the first step is to determine the reference point. In the reference point determination process, data for the servo reference voltage of the machining conditions set for the desired machining process and data for the standard feed rate suitable for the servo reference voltage are acquired. At this time, the standard feed rate data is determined in advance by test machining or other means in accordance with the machining requirements, machining conditions, and machining method, and is automatically determined when the machining requirements, machining conditions, and machining method are given by the operator. Then, the reference point, which is the intersection point of the servo reference voltage and the standard feed rate on the servo curve required for the desired machining process, is determined.

[0062] Next, a limit point acquisition process is performed. In the limit point acquisition process, data for the limit point, which is the intersection of the estimated average machining voltage (the point at which discharge is estimated to occur continuously between the electrodes under the machining conditions of the required servo curve) and the feed rate suitable for that estimated average machining voltage, is acquired from one or more servo curves stored in the servo curve data storage unit 92a. For example, referring to Figure 3, it can be assumed that data for common limit points in nine curve data sets is stored.

[0063] After the limit point acquisition process, the servo curve generation process is performed. In the servo curve generation process, the required servo curve can be generated using an exponential function with the reference point and limit point as variables.

[0064] Once the servo control preparation process is complete, the machining process is performed. In the desired machining process, the inter-electrode voltage detection process, the feed rate output process, and the relative movement control process are repeated. In the inter-electrode voltage detection process, the average machining voltage is acquired at predetermined time intervals. In the feed rate output process, the feed rate corresponding to the average machining voltage acquired in the inter-electrode voltage detection process is calculated and output based on the servo curve generated in the servo curve generation process. In the relative movement control process, the relative movement between the wire electrode 2 and the workpiece W is controlled by the feed rate output in the feed rate output process. As a result, the movement control unit 95 can machine the workpiece W by removing material from the workpiece W with a predetermined amount while moving the wire electrode 2 relative to the workpiece W at the target feed rate output from the control device 9.

[0065] In this process, the servo curve determination unit 93 can determine the current machining status from among multiple servo curves and determine a servo curve that is suitable for the current machining status.

[0066] 3. Effects In the wire electrical discharge machining apparatus 100 and wire machining method according to one embodiment of the present invention, the only data that is required to be acquired in advance by experimental or test machining, depending on the machining requirements (diameter and material of the wire electrode 2 and the material of the workpiece W) and machining conditions, excluding the plate thickness, is the data of a single limit point. As already described, the servo curve can be generated using the limit point data and the reference point data acquired using a dataset provided in advance to the wire electrical discharge machining apparatus 100. With this configuration, the machining speed can be easily controlled, and the servo curve can be generated before the start of the machining process, thereby reducing the computational processing burden on the wire electrical discharge machining apparatus 100 during machining.

[0067] Furthermore, the servo curve used in the wire electrical discharge machining apparatus 100 and the wire machining method of the embodiment according to one embodiment of the present invention is a curve represented by an exponential function that passes through a reference point and a limit point. The servo curve in the embodiment can be approximated by a servo curve derived by performing test machining multiple times and acquiring a large amount of data (see the comparative experiment described later for details). Therefore, by performing speed control using the servo curve according to one embodiment of the present invention, machining can be performed while keeping the side gap relatively constant, thus maintaining a certain level of machining accuracy.

[0068] 4. Other Embodiments Furthermore, the present invention can also be implemented in the following embodiments.

[0069] In the embodiment described above, the inter-pole voltage detection device 6 was configured to calculate the average processing voltage, but it may also be configured to calculate it using any component provided by the control device 9.

[0070] In the embodiments described above, the servo curve was generated before the start of the desired machining process. However, since the servo curve generation load is smaller in the servo curve generation according to the present invention, it may be configured to generate the servo curve required for the next machining process while the desired machining process is being carried out. For example, the servo curve used for the third cut can be generated during the machining process of the second cut.

[0071] 5. Comparative experiment This section describes experimental results comparing the servo curve according to the present invention with a conventional servo curve. The servo curve according to the present invention is a servo curve set by defining a reference point and a limit point and generating an exponential function that passes through them. The conventional servo curve is a servo curve derived by performing multiple test machining operations and using an approximation method to find the relationship between the average machining voltage and feed rate such that the side gap remains constant, based on a large amount of test data obtained from the test machining operations.

[0072] In this experiment, the servo curve according to the present invention was used as an example, and the conventional servo curve was used as a comparative example. Each servo curve was generated under the conditions shown in the table below. [Table 2]

[0073] Figure 4A shows the servo curves for Example 1 and Comparative Example 1, Figure 4B shows the servo curves for Example 2 and Comparative Example 2, and Figure 4C shows the servo curves for Example 3 and Comparative Example 3. In Figures 4A to 4C, the dashed lines represent the examples, and the solid lines represent the comparative examples. From Figures 4A to 4C, it can be seen that the servo curves of the examples generally match the trends of the corresponding comparative examples, indicating that the servo curves according to the present invention can approximate conventional servo curves. [Explanation of Symbols]

[0074] 1: Processing machine body 2: Wire electrode 3: Wire guide mechanism 4:Power supply 5: Mobile device 6: Inter-pole voltage detection device 9: Control device 10: Table 11: Work stand 20: Saddle 31: Upper guide assembly 32: Lower guide assembly 33: Housing 34: Wire guide 35: Conductor 91: Machining condition holding section 92: Servo curve generation unit 92a: Servo curve data storage unit 93: Servo curve determination unit 94: Feed rate output section 95: Movement Control Unit 96: Power supply control unit 100: Wire EDM machine W: Workpiece

Claims

1. A wire electrical discharge machining apparatus comprising a moving device, an inter-pole voltage detection device, and a control device for controlling the moving device, The moving device is configured to process the workpiece by moving the wire electrode relative to the workpiece in the direction of processing, The inter-electrode voltage detection device detects the inter-electrode voltage between the wire electrode and the workpiece and outputs the average machining voltage at predetermined intervals. The control device comprises a servo curve generation unit, a feed rate output unit, and a movement control unit. The servo curve generation unit generates a servo curve showing the relationship between the feed rate and the average machining voltage based on an exponential function with respect to a reference point and a limit point as variables. The aforementioned reference point is the intersection of the servo reference voltage, which is set as a machining condition corresponding to the machining process, and the standard feed rate predetermined from the machining conditions. The limit point is the intersection of the estimated average machining voltage, which is estimated to be the limit at which discharge occurs continuously between electrodes under the machining conditions, and the feed rate suitable for the estimated average machining voltage. The feed rate output unit is configured to output the feed rate corresponding to the average machining voltage detected by the inter-pole voltage detection device based on the servo curve generated by the servo curve generation unit. The wire electrical discharge machining apparatus is configured such that the movement control unit controls the movement device at the feed rate.

2. A wire electrical discharge machining apparatus according to claim 1, The limit point is determined by performing multiple test machining operations with the same combination of wire electrode diameter and material and workpiece material, and the same machining process, but with only the thickness of the workpiece and the machining conditions corresponding to the thickness differing. The limit point is the intersection of the average machining voltage and the feed rate suitable for the average machining voltage in the servo curve common to the same machining process, in a wire electrical discharge machining apparatus.

3. A wire electrical discharge machining apparatus according to claim 2, It is further equipped with a servo curve data storage unit, The servo curve data storage unit stores a plurality of limit points that have been determined in advance by performing the test machining for each of the same machining processes with the same combination of wire electrode diameter and material and material of the workpiece. The servo curve generation unit generates the servo curve by obtaining the limit points corresponding to the same machining process for combinations of wire electrode diameter and material and workpiece material from the servo curve data storage unit.

4. A wire electrical discharge machining apparatus according to claim 3, The servo curve generation unit acquires the limit points from the servo curve data storage unit in accordance with whether the processing method is a punch or a die, and generates the servo curve. Wire electrical discharge machining equipment.

5. A wire electrical discharge machining apparatus according to claim 3, The servo curve generation unit acquires the limit points from the servo curve data storage unit and generates the servo curve, corresponding to whether the processing method is floating with the jet nozzle in close contact or floating on one side. Wire electrical discharge machining equipment.

6. A wire electrical discharge machining apparatus according to claim 3, The servo curve generation unit acquires the limit points from the servo curve data storage unit in accordance with whether the processing form is a punch or a die, and whether the position of the jet nozzle is in close contact or partially floating, and generates the servo curve. Wire electrical discharge machining equipment.

7. A wire electrical discharge machining apparatus according to claim 2, It is further equipped with a servo curve data storage unit, The servo curve data storage unit stores a plurality of servo curves obtained by performing the test machining in advance for each of the same machining processes with the same combination of wire electrode diameter and material and workpiece material. The servo curve generation unit generates the servo curve by acquiring and determining the servo curve corresponding to the same machining process for combinations of wire electrode diameter and material and workpiece material. Wire electrical discharge machining equipment.

8. A wire electrical discharge machining apparatus according to claim 7, The servo curve generation unit acquires the servo curve from the servo curve data storage unit and generates the servo curve, corresponding to whether the processing form is a punch or a die, and / or whether the position of the jet nozzle is floating in close contact or floating on one side. Wire electrical discharge machining equipment.

9. A wire electrical discharge machining method in which a wire electrode is moved relative to the workpiece to process the workpiece, In a wire electrical discharge machining method that generates a servo curve showing the relationship between the average machining voltage between the electrodes of the wire electrode and the workpiece and the feed rate, and controls the feed rate in accordance with the average machining voltage based on the servo curve, This includes a reference point determination step, a limit point acquisition step, a servo curve generation step, an inter-pole voltage detection step, a feed speed output step, and a relative movement control step. In the aforementioned reference point determination step, data of the servo reference voltage for the machining conditions set for each machining process and data of a predetermined standard feed rate suitable for the servo reference voltage are acquired to determine the reference point, which is the intersection point of the servo reference voltage and the standard feed rate in the servo curve required for the machining process. In the limit point acquisition step, data is acquired for the limit point, which is the intersection of the estimated average machining voltage, which is the average machining voltage at which discharge is estimated to be the limit at which discharge continuously occurs between the electrodes under the machining conditions in the required servo curve, and the feed rate suitable for the estimated average machining voltage. In the servo curve generation step, the required servo curve is generated by an exponential function with the reference point and the limit point as variables. In the inter-electrode voltage detection step, the average processing voltage is acquired at predetermined time intervals. In the feed rate output step, the feed rate corresponding to the acquired average machining voltage is determined and output based on the servo curve generated in the servo curve generation step. In the relative movement control step, the relative movement between the wire electrode and the workpiece is controlled by the feed rate output in the feed rate output step. A wire electrical discharge machining method comprising repeating the feed rate output step and the relative movement control step.

10. A wire electrical discharge machining method according to claim 9, The limit point is determined by performing multiple test machining operations using the same combination of wire electrode diameter and material and workpiece material, with the same machining process, but varying only the thickness of the workpiece and the machining conditions corresponding to the thickness. The aforementioned limit point is the intersection of the average machining voltage and the feed rate suitable for the average machining voltage in the servo curve common to the same machining process. Wire electrical discharge machining method.

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