JP4970476B2 - Wire cut electric discharge machine - Google Patents

Description

  The present invention relates to a wire-cut electric discharge machining apparatus that changes and sets a machining condition to a machining condition adapted to a plate thickness at a step portion when wire-cut electric discharge machining is performed on a workpiece having a step portion whose thickness changes. .

  A wire while intermittently generating a discharge by applying a voltage pulse intermittently to a machining gap formed by a wire electrode stretched between a pair of wire guides provided between the workpiece and the workpiece. 2. Description of the Related Art A wire-cut electric discharge machining apparatus is known that cuts a workpiece into an arbitrary machining shape by relatively moving an electrode and the workpiece.

  The greater the discharge energy in a single discharge, the greater the amount of material removed from the workpiece. The magnitude of the discharge energy depends on the current density of the discharge current flowing through the machining gap. Therefore, the amount of machining (amount taken) per discharge varies depending on the peak current value and pulse width of the discharge current pulse. As the machining amount per discharge increases, the machining speed increases. On the other hand, the diameter of the discharge trace increases and the outer ring mountain increases, so that the machining surface roughness becomes rough and the machining shape accuracy tends to decrease.

  When the plate thickness of the workpiece increases, the processing volume to be removed per unit moving distance in which the wire electrode moves relative to the workpiece increases, so when processing with the same machining allowance under the same processing conditions As the plate thickness increases, the distance processing speed indicated by the distance processed per unit time becomes slower.

  When the wire electrode is moved relative to the workpiece in a servo system that maintains the distance of the machining gap constant depending on the voltage between the machining gaps, the wire electrode feed rate (relative movement speed) is processed. Influenced by machining conditions in the direction. In the roughing process that roughly cuts the workpiece called the first cut, the wire electrode is sandwiched between the machining grooves formed in the workpiece, so the wire electrode is frequently short-circuited. Processing is performed by a method in which the wire electrode is processed and fed while maintaining a constant processing gap so as not to break the wire or stop processing.

  For this reason, when a workpiece having a stepped portion whose thickness changes under the same processing conditions, the distance processing speed is significantly changed at the stepped portion, and the feed rate is rapidly changed. As the wire electrode feed rate becomes slower, the discharge gap increases, so the feed rate suddenly changes at the stepped part and the discharge gap changes greatly, resulting in a change in the machining groove width, resulting in a vertical streak shape on the machining surface. Lost sites are formed. If such a shape loss portion is left on the processing surface, it cannot be removed even in the polishing step, and as a result, the required processing shape accuracy cannot be obtained.

  If the difference in plate thickness that changes at the level difference is small, the difference in machining groove width is small, so the shape of the machining groove width is corrected in the shaping process during the finishing process after the roughing process. Loss sites can be eliminated, but the number of machining operations is unnecessarily increased, resulting in additional machining time. And when the change of the plate | board thickness in a level | step difference site | part is large, the difference of a process groove width will arise so that it cannot correct in the process process of shaping. Also, if the machining volume to be removed per unit moving distance suddenly changes, the servo control cannot follow, or the machining becomes unstable due to unexpected fluctuations in the discharge gap. Disconnection occurs.

  Therefore, in order to reduce the difference in the machining groove width generated at the stepped portion or to prevent the wire electrode from being disconnected at the stepped portion, the processing conditions are changed to be adapted to the plate thickness changed at the stepped portion. ing. Since the machining groove width does not change when the feed rate is constant, the machining conditions are changed and set so that the feed rate is constant. Alternatively, if the wire electrode is fed while maintaining the machining gap constant, the feed rate and distance machining speed in a certain period can be regarded as the same, so the machining conditions are changed so that the distance machining speed is constant. Is set.

  Although it is not desirable to switch the electrical machining conditions in the middle of the machining locus, it is indispensable to eliminate the shape loss part in the step part. Therefore, the parameters of the electrical machining conditions changed and set at the level difference part can finally make the feed speed or the distance machining speed constant, so that the machining result and the machining state can be changed without being incapable of machining. Elements with the smallest possible impact are selected. Generally, the servo reference voltage or the ON time is changed and set.

  As disclosed in Patent Document 1, as a basic wire-cut electric discharge machining apparatus that changes and sets machining conditions at a stepped part, a parameter that changes when the plate thickness changes, for example, an average machining current value or a feed rate is detected. A wire-cut electric discharge machining apparatus that detects a change in sheet thickness and changes the machining conditions to suit the detected parameter value is well known. Since the machining conditions are changed and set based on a parameter that indirectly represents the change in the plate thickness, the machining gap is not always changed to a setting that is sufficiently appropriate for the actual plate thickness. Since the machining conditions are changed and set corresponding to the above, disconnection of the wire electrode can be suppressed at least.

  In order to change and set the machining conditions more accurately, for example, as shown in Patent Document 2, the detected average machining current is divided by the product of the feed speed and the machining groove width and multiplied by a predetermined coefficient to obtain a plate thickness A wire-cut electric discharge machining apparatus is conceivable that can be changed and set to machining conditions that directly adapt to the plate thickness. By changing and setting the machining conditions that are directly adapted to the plate thickness, the machining conditions can be changed and set more appropriately with respect to the actual plate thickness, and the difference in the machining groove width can be reduced.

Japanese Examined Patent Publication No. 63-25889 (2nd page, 4th column) Japanese Examined Patent Publication No. 2-29453 (page 2, column 3, column 4)

  The wire-cut electric discharge machine that changes and sets to machining conditions that directly adapt to the plate thickness is basically related to the machining volume per unit time, so the plate thickness is basically calculated based on the average machining current value. To be done. However, since the magnitude of the discharge current pulse for each discharge varies greatly depending on the machining state, there is a relatively large error between the calculated plate thickness and the actual plate thickness. Also, the average machining current value may fluctuate greatly even when the plate thickness does not change, so the machining condition is changed by misjudging that the plate thickness has changed even though it is not actually a stepped part. May be set.

  In addition, since the average machining current value is significantly affected by parameters of other electrical machining conditions, the machining groove width and calculation coefficient change each time machining conditions are changed. The parameter needs to be reset. However, since it is difficult to set all the calculation parameters accurately for each processing condition, the processing groove width and the calculation coefficient are fixed to the material of the wire electrode and the workpiece regardless of the processing conditions. You may not be able to do reliable calculations. In addition, since the current detector cannot be provided sufficiently close to the machining gap due to physical constraints on the configuration of the electrical discharge machining circuit, it is between the detected average machining current value and the actual average machining current value in the first place. There are considerable errors that are difficult to avoid.

  For this reason, depending on the required machining shape accuracy, the error between the calculated plate thickness and the actual plate thickness may exceed the allowable range. There is a disadvantage of machining under an inappropriate machining condition that causes a difference in the machining groove width to the extent that it cannot be done.

  In particular, the discharge current pulse having the first pulse width is supplied when the machining state is relatively good corresponding to the machining state, and shorter than the first pulse width when the machining state is not relatively good. In the processing method in which the discharge current pulse having the second pulse width is supplied, the current density per discharge is large between the discharge current pulse having the first pulse width and the discharge current pulse having the second pulse width. Therefore, the method of estimating the processing volume with the average processing current value and calculating the plate thickness cannot obtain the correct processing volume, and the error between the calculated plate thickness and the actual plate thickness is too large. The processing conditions cannot be substantially determined.

  In the wire-cut electric discharge machining apparatus in which the present invention is changed to a machining condition that directly adapts to the plate thickness at a step portion where the plate thickness changes, the error between the calculated plate thickness and the actual plate thickness is reduced within an allowable range. Thus, the main object is to provide an improved wire-cut electric discharge machining apparatus capable of accurately calculating the plate thickness and appropriately changing and setting the appropriate machining conditions at the stepped portion.

In order to solve the above problems, a wire-cut electric discharge machining apparatus of the present invention includes a voltage detection device (16) that outputs an average machining voltage, a speed detection device (18) that outputs a feed speed of a wire electrode, A database of machining conditions consisting of a combination of machining conditions numbered with each machining condition number is saved, and data on the machining amount per discharge for each machining condition that determines the magnitude of discharge energy is saved corresponding to the above machining conditions And a storage device for storing data of a plurality of calculation coefficients set for each material of the wire electrode and the workpiece to be obtained when an approximate expression expressing the machining groove width by an average machining voltage is created by a predetermined approximation method ( and 13), a counter for counting the number of discharge current pulses to be supplied to a pre-set period of time (192), a feed speed and the average machining voltage in the period for each of the period Enter the number of discharge current pulses supplied during the period and process the data for the discharge per discharge corresponding to the processing conditions that determine the current discharge energy, and the wire electrode and workpiece currently used a plurality of processing amount and a product of the number of the discharge current pulse to be supplied to the period definitive in the period average machining voltage and a plurality of operation per discharge one shot to get the data of the calculation coefficient corresponding to the material of the A plate thickness calculation device (19) that calculates the plate thickness by dividing by the product of the machining groove width and the feed rate obtained by an approximate expression using a coefficient, and is adapted to the plate thickness calculated by the plate thickness calculation device (19). A command device for extracting and changing and setting machining conditions capable of making the feed speed or the distance machining speed constant from the combinations of the machining conditions in the machining condition database stored in the storage device (13). ( 5), and it has a.

Moreover, wire-cut electric discharge machining apparatus of the present invention includes a voltage detector for outputting an average machining voltage (16), the speed detecting device that outputs a feed speed of the wire electrode (18), comprising a combination of a plurality of processing conditions A database of machining conditions is stored and the amount of discharge energy for determining the magnitude of discharge energy. Data on the machining amount per discharge of a discharge current pulse having a predetermined first pulse width for each machining condition and a second shorter than the first pulse width. When data of machining amount per discharge of a discharge current pulse having a pulse width of 2 is stored in correspondence with the above machining conditions, and an approximate expression expressing the machining groove width as an average machining voltage is created by a predetermined approximation method resulting wire electrode and a storage device for storing data of a plurality of calculation coefficients that are set for each material of the workpiece (13), release of the first pulse width to be supplied to the pre-set period A counter (192) for counting the number of discharge current pulses having a second pulse width of the current pulse, respectively, the first pulse supplied to the average machining voltage and feed rate and the period in the period for each of the period The number of discharge current pulses having a width and the number of discharge current pulses having a second pulse width are input, and the discharge in the discharge current pulse having the first pulse width corresponding to a machining condition that determines the current discharge energy magnitude Data on the number of machining operations, data on the amount of machining per discharge in the discharge current pulse of the second pulse width, and data on a plurality of calculation coefficients corresponding to the currently used wire electrode and material of the workpiece, second pulse to the product of the number of the discharge current pulse obtained by the first pulse width to be supplied to the processing amount and the duration of the discharge one shot per discharge current pulse of the first pulse width The second discharge current pulse calculating a value obtained by adding the product of the average machining voltage and a plurality definitive above period and the number of the pulse width to be supplied to the processing amount and the duration of the discharge one shot per discharge current pulse width thickness computing unit for calculating a plate thickness by dividing the product of the feed and the machining groove width by using the coefficient obtained by the approximate expression rate (19), the thickness calculated by the thickness computing unit (19) A command for extracting and changing a machining condition capable of making the applied feed speed or distance machining speed constant from a combination of the machining conditions in the machining condition database stored in the storage device (13). Device (15).

  The wire-cut electric discharge machining apparatus of the present invention can calculate the plate thickness without using an average machining current having unstable elements as a calculation parameter. In addition, the machining volume can be calculated by obtaining the actual machining groove width during machining. Therefore, compared with the conventional methods, the influence of the processing conditions or the processing state is less, and the plate thickness can be obtained more accurately. For this reason, the machining conditions are changed and set based on the data of the plate thickness whose error from the actual plate thickness is sufficiently small. As a result, it is possible to reduce the difference in the machining groove width generated at the stepped portion to such an extent that a desired machining shape can be finally obtained, and there is an effect that machining can be performed with the required machining shape accuracy.

It is a block diagram which shows the whole structure of embodiment. It is a flowchart which shows the process of the operation | movement in the control apparatus of embodiment. It is a graph which shows the error of the board thickness obtained by calculation, and an actual board thickness.

  FIG. 1 is a block diagram showing an overall configuration of a typical embodiment of a wire cut electric discharge machining apparatus according to the present invention. In the wire-cut electric discharge machining apparatus of the embodiment shown in FIG. 1, the components that are not directly related to the specific configuration of the machine and the invention are not shown.

  The wire cut electric discharge machining apparatus includes a main machine, a power supply device, and an accessory device. The power supply device is juxtaposed with the machine main unit. The power supply device is connected to the machine main unit with a power supply cable. The power supply device includes a control device 1 capable of performing overall control of the power supply device itself, the machine main unit, and the accessory device.

  The machine main machine has a work stand on which a workpiece is attached and installed, and a machining site is formed on the machine main machine. The machine main machine includes a pair of wire guides (not shown) provided with a workpiece interposed therebetween and a machining liquid jet nozzle. The machine main body includes at least a machine structure and a plurality of moving bodies that move in the respective control axis directions, and includes a driving device 2 that includes a plurality of servo motors that respectively drive the moving bodies.

  The power supply device includes a control device 1 and a processing power supply device 3. The power supply device supplies power for driving to the machine main unit through a power supply cable. Further, the power supply device supplies power for electric discharge machining from the machining power supply device 3. An operation panel of the control device 1 or a pendant box for remote control may be provided apart from the casing of the power supply device, but the control panel includes the operation panel and the pendant box.

  The machining fluid supply device 4 is disposed adjacent to the machine main unit. The machining fluid supply device 4 is one of the accessory devices of the machine main machine included in the machine main machine. The machining fluid supply device 4 has a machining fluid tank that stores a machining fluid for wire-cut electric discharge machining that is supplied to the machine body. The machining liquid supply device 4 supplies the machining liquid jet to the machining site through the machining liquid jet nozzle, and supplies the machining liquid to the machining tank of the machine main machine through the machining liquid supply pipe. Further, the machining liquid supply device 4 collects the machining liquid from the machining tank through the drain.

  The control device 1 includes a numerical control device 10 that outputs a command signal, a motor control device 20 that controls a plurality of servo motors of the drive device 2, a pulse control device 30 that operates the processing power supply device 3, and a machining fluid supply. A plurality of pumps of the device 4 and a machining fluid control device 40 for operating the control valve are included.

  The numerical control device 10 stores the data in the input / output device 11 for inputting / outputting data, the first storage device 12 for temporarily storing data, and the data in the first storage device 12 in a timely manner. A second storage device 13 for storing combination data and data necessary for calculating the plate thickness, a decoding device 14 for decoding the NC program, a command device 15 for outputting a command signal based on the NC data, A voltage detection device 16 that outputs an average machining voltage, a clock 17 that outputs a clock pulse having a constant frequency, a speed detection device 18 that outputs the feed rate of the wire electrode, and a plate thickness calculation device 19 that calculates the plate thickness. And having. The arithmetic device of the numerical control device 10 includes at least a decoding device 14, a command device 15, and a plate thickness calculation device 19.

  The motor control device 20 is means for controlling each servo motor of the drive device 2. The motor control device 20 calculates a motor control amount corresponding to the movement command signal output from the command device 15, supplies a drive current corresponding to the motor control amount to the servo motor, and performs positioning control of the moving body.

  The pulse control device 30 is a means for controlling the discharge circuit including the machining gap. The pulse control device 30 supplies a discharge current pulse having a desired peak current value and pulse width to the machining gap at a predetermined frequency. Hereinafter, a current that flows when a discharge occurs in the machining gap is generically referred to as a discharge current, and in particular, a discharge current that contributes to machining may be described as a machining current. In addition, a time during which a gate signal for turning on / off a switching element provided in the discharge circuit is output is referred to as an on time, and a time width of a discharge current pulse is referred to as a pulse width. However, when the on-time is described as a parameter of the electrical processing conditions, the on-time and the pulse width are substantially synonymous in the error range.

  The pulse control device 30 is supplied with a discharge current pulse having a desired peak current value and pulse width by applying a voltage to the machining gap based on the machining conditions set according to the pulse command signal output from the command device 15. As described above, the machining power supply device 3 is operated so that the circuit elements of the discharge circuit such as the DC power supply or the current limiting resistor of the machining power supply device 3 are inserted into the discharge circuit at a predetermined value. The gate signal is selectively supplied to the plurality of switching elements.

  The machining fluid control device 40 is means for controlling the pump or control valve of the machining fluid supply device 4. The machining fluid control device 40 supplies a drive voltage or a drive current to the pump or the control valve according to a machining fluid command signal from the command device 15 to control on / off of the pump and the control valve, or the rotation speed of the pump and the opening of the control valve. Adjust the degree.

  The input / output device 11 of the numerical control device 10 supplies the NC program inputted by the operator and data necessary for calculating the plate thickness to the arithmetic device and stores them in the first storage device 12 or the second storage device 13. Means. The input / output device 11 is means for outputting data to a display device including a display or an external recording device such as a printer through an arithmetic device according to an operator's request. Specifically, the input / output device 11 inputs data between an operation panel including a keyboard, a disk drive for reading and writing data to various storage media, an external storage device such as a USB memory, a display device, and an external recording device. Includes output interface.

  The first storage device 12 is a random access memory and is a main storage device of the numerical control device 10. The first storage device 12 is means for storing data input from the input / output device 11. The first storage device 12 is means for storing a process required for the calculation by the calculation device and data required for the calculation and data obtained by the calculation.

The second storage device 13 is a hard disk drive, and is an auxiliary storage of the numerical control device 10 that can store data even when the main power supply of the power supply device is shut off and no power is supplied to the numerical control device 10. Device. The second storage device 13 is means for storing data that is required to be saved among data temporarily stored in the first storage device 12. In addition, the second storage device 13 includes a database of machining conditions composed of a combination of at least a plurality of machining conditions, calculation parameter data necessary for calculating the plate thickness, and a plurality of settings necessary for controlling the machine. A means for storing values.

  The decrypting device 14 is means for decrypting the NC program and outputting NC data. The NC program is indispensable not only for data relating to the relative movement trajectory between the wire electrode and the workpiece but also required for each processing such as the feed rate of the wire electrode, the offset value, and the hydraulic pressure of the machining fluid jet. Data on initial setting values, data on machining conditions including parameters of electrical machining conditions such as peak current value, on time, off time, servo reference voltage, power supply voltage, discharge current pulse control, servo control, corner Data relating to a specific processing control such as control is described. Therefore, the NC data output from the decoding device 14 includes at least information regarding processing conditions and specific processing control, in addition to information regarding movement.

  The command device 15 is a means for calculating a value corresponding to the NC data output from the decoding device 14 and outputting a plurality of types of command signals. When the command device 15 receives data related to relative movement, the command device 15 calculates a unit movement amount of each axis and outputs a movement command signal to the motor control device 20. The command device 15 outputs a pulse command signal to the pulse control device 30 or outputs a drive command signal to the machining fluid control device 40 when data related to the machining conditions is input. Further, when the command device 15 receives data relating to the initial set value or data relating to the specific machining control, the command device 15 outputs the setting data or the machining control command signal to the motor control device 20, the pulse control device 30, and the machining fluid control device 40. To do.

  The command device 15 inputs the data of the plate thickness calculated by the plate thickness calculation device 19, and changes and sets the machining conditions to suit the plate thickness as necessary. The command device 15 according to the embodiment retrieves and extracts a machining condition adapted to the inputted plate thickness from the plate thickness calculation device 19 from a combination of a plurality of machining conditions stored in the second storage device 13. To do. Then, the command device 15 outputs a pulse command signal corresponding to the machining condition to be changed, and changes and sets the machining condition.

  The voltage detection device 16 is means for detecting a voltage between the electrodes in the machining gap and outputting an average machining voltage to the plate thickness calculation device 19. The voltage detection device 16 can output an average machining voltage to a servo control device (not shown) of the motor control device 20. The voltage detection device 16 includes a voltage detector provided in the processing power supply device 3. The voltage detector has a detection circuit having a detection resistor connected in parallel with the machining gap, and amplifies the voltage across the detection resistor with an operational amplifier and outputs the amplified voltage. The voltage detection device 16 smoothes the inter-electrode voltage output from the voltage detector through a filter, digitally converts the smoothed voltage signal with an analog-digital converter, and calculates the average machining voltage data as a plate thickness calculation device. 19 output.

  The clock 17 is an electronic timepiece that continuously outputs clock pulses having a predetermined frequency. The unit time of the clock pulse output from the clock 17 of the embodiment is set to 1 microsecond (μsec) in consideration of the operation time of the counter. The frequency of the clock pulse of the clock 17 can be changed as necessary.

  The speed detection device 18 is means for outputting data on the feed speed of the wire electrode. The speed detection device 18 according to the embodiment always inputs a clock pulse from the clock 17 and acquires position data from the position detector every predetermined time to calculate the moving amount of the moving body in the predetermined time, or The movement command signal output from the command device 15 during the time is acquired, the movement amount at a predetermined time is calculated, and the feed rate is obtained from the movement amount at the predetermined time. The speed detection device 18 outputs feed speed data to the first storage device 12, and the first storage device 12 stores the feed speed data as a history.

  The plate thickness calculation device 19 is a means for calculating the plate thickness and outputting it to the command device 15. The plate thickness calculator 19 receives the average machining voltage data output from the voltage detector 16 and the feed speed data output from the speed detector 18 and stored in the first storage device 12. In addition, the plate thickness calculation device 19 has a plurality of calculations different for each material of the wire electrode and the workpiece, and data on the machining amount per discharge corresponding to each machining condition stored in the second storage device 13. Get coefficient data.

The plate thickness calculation device 19 calculates and outputs the plate thickness by substituting the values of the respective operation parameters acquired every predetermined time into the calculation formula shown in Equation 1. The timing for calculating the plate thickness is a preset sampling time. The plate thickness calculation device 19 acquires average machining voltage and feed rate data for each sampling time. In Equation 1, T is the plate thickness (mm), F is the wire electrode feed rate (mm / min), Vg is the average machining voltage (V), H is the machining amount per discharge (mm ³ ), n is the number of discharge current pulses supplied during the sampling period, and α, β, and γ are calculation coefficients determined by the material of the wire electrode and the workpiece.

The processed groove width is determined by αVg ² + βVg + γ. The arithmetic expression representing the machining groove width is an approximate expression obtained from data indicating the correlation between the average machining voltage value and the machining volume. The processing groove width is a distance obtained by adding the discharge gap on both sides of the wire electrode in the direction orthogonal to the processing progress direction to the wire electrode diameter. Since the wire electrode diameter does not change, the size of the processed groove width during processing depends on the size of the discharge gap. At this time, the size of the discharge gap in the servo system in which the wire electrode is fed while maintaining the machining gap constant depends on the servo reference voltage, and the servo reference voltage is generally set in consideration of the magnitude of the average machining voltage. The Therefore, theoretically, the size of the machining groove width can be expressed by the average machining voltage.

Specifically, a workpiece having a predetermined thickness is tested and processed under a plurality of processing conditions, and the average processing voltage, processing volume, and feed rate are measured every unit time, and the average processing voltage and processing groove width are calculated. Collect a lot of data that shows the relationship. Then, while approximating the collected data using a plurality of approximation methods, a suitable approximation formula was finally determined. An arithmetic expression representing the machining groove width is obtained by performing retesting and measuring the average machining voltage and the machining groove width, and comparing the machining groove width obtained by calculating with the determined approximate expression and the measured machining groove width. Thus, it has been verified that the actual groove width can be obtained accurately within the allowable error range. From this, the arithmetic expression indicating the machining groove width is not limited to αVg ² + βVg + γ expressed by Equation 1 as long as it is expressed by the average machining voltage.

  In the range of values that the average machining voltage can take under the machining conditions used in the practical machining area in wire-cut electrical discharge machining, the rate of change of the average machining voltage with respect to the change in machining volume is slight, but electrical Since the processing conditions vary depending on the material of the wire electrode and the workpiece, the calculation coefficients α, β, and γ are selected to be values appropriate for the material of the wire electrode and the workpiece. The calculation coefficients α, β, and γ are obtained when creating an approximate expression. The arithmetic coefficients α, β, and γ are stored in advance in the second storage device 13 as basic data in association with each value for each material of the wire electrode and the workpiece.

  If the change rate of the average machining voltage with respect to the machining volume is small, the test is performed for each machining condition without obtaining the machining groove width using an arithmetic expression as in the plate thickness calculation device 19 in the embodiment. An actual measurement value obtained by processing can be substituted into Equation 1 as a fixed value. However, by calculating and calculating the machining groove width each time the plate thickness is calculated, the plate thickness can always be calculated with a value close to the actual machining groove width, and the plate thickness can be calculated more accurately. Still useful in terms of what it can do.

  The machining volume in the sampling period is represented by the machining amount per discharge and the number of discharge current pulses in the sampling period. When machining is continued normally, the machining amount per discharge is exactly constant within a slight error range. Therefore, a machining volume with a very small error can be obtained from the machining amount per discharge.

  Since the amount of machining per discharge is determined by the magnitude of the discharge energy, it varies depending on the machining conditions. Therefore, the machining amount per discharge is selected and determined according to the machining conditions. Data on the machining amount per discharge is stored in the second storage device 13 in correspondence with the machining conditions. For machining amount data for each discharge per machining condition, a data field associated with each machining condition combination data in the existing machining condition database is added to the database, and the machining condition combination of each machining condition number is added. It can be recorded corresponding to each.

  The processing volume in a predetermined sampling period is the product of the processing area and the plate thickness. The processing area is the product of the processing groove width and the movement distance. Therefore, the plate thickness can be obtained by dividing the machining volume in the sampling period by the product of the machining groove width and the movement distance. The feed speed in the servo system that feeds the wire electrode while keeping the machining gap constant can be regarded as corresponding to the distance machining speed in a certain period. Since the distance machining speed is obtained by dividing the movement distance by unit time, the movement distance can be replaced with the feed speed. Accordingly, the plate thickness can be obtained by dividing the machining volume in a predetermined period by the product of the feed speed and the machining groove width.

  The calculation formula shown in Equation 1 does not include an average machining current having an unstable element with a large variation depending on the machining state, so that data of a plate thickness with a smaller error from the actual plate thickness is obtained. Therefore, there is no possibility of changing and setting the machining conditions due to erroneous determination. In addition, the data of the plate thickness is obtained in which the influence of the processing conditions and the processing state is reduced as compared with the conventional calculation methods, and the error from the plate thickness is smaller. Since the actual machining groove width is obtained from the average machining voltage every time the plate thickness is calculated, the board thickness can be calculated regardless of the fluctuation of the machining groove width.

  When the machining state is relatively good, a discharge current pulse having a relatively long first pulse width that can make the machining speed as fast as possible can be supplied from the wire electrode diameter and the wire electrode and the material of the work piece. There is a processing method for supplying a discharge current pulse of a safe and small discharge energy that has a second pulse width shorter than the first pulse width and can avoid disconnection of the wire electrode when the state is not relatively good. For example, specifically, a trapezoidal wave discharge current pulse is supplied when the machining state is good, and a triangular wave discharge current with the same peak current value as the trapezoidal wave discharge current pulse when the machining state is not good and a short on-time. A processing method for supplying a pulse is known.

As described above, when machining is performed by a machining method that selectively supplies discharge current pulses having different pulse widths, an error in the machining amount per unit time increases in the calculation formula shown in Equation 1, The thickness calculator 19 calculates and outputs the plate thickness using the calculation formula shown in Equation 2. In Equation 2, H is the machining amount per discharge (mm ³ ) when the discharge current pulse having the first pulse width is supplied, and L is the discharge current pulse having the second pulse width. Machining amount per discharge (mm ³ ), n is the number of discharge current pulses of the first pulse width supplied during the sampling period, and m is the discharge current of the second pulse width output during the sampling period This is the number of pulses, and the other calculation parameters are the same as in Equation 1.

  Therefore, the wire-cut electric discharge machining apparatus according to the present invention can obtain data on a plate thickness with a smaller error from the actual plate thickness even in the case of machining in which discharge current pulses with large and small discharge energy are mixed. It can be changed and set to an appropriate machining condition that directly adapts to the actual plate thickness. Note that the machining volume per unit time in Equation 2 is obtained by calculating and adding the machining amount per unit time for each discharge current pulse having a different pulse width, so that three or more types of discharge currents having different pulse widths are obtained. When the pulse is supplied, the arithmetic expression can be modified so that the machining amount is obtained and sequentially added for each discharge current pulse having a different pulse width according to the number of types.

  The plate thickness calculation device 19 includes, as attached devices, a time counter 191 that measures a sampling time as a timing for calculating the plate thickness and a pulse counter 192 that counts the number of discharge current pulses. However, since such a one-up counter can substitute the first storage device 12 by preallocating a part of the storage area in the first storage device 12 as a counter, a new counter is not necessarily added. It is not required to be provided.

  The time counter 191 is a means for measuring the sampling time. The time counter 191 inputs a clock pulse of the clock 17 and outputs a time-up signal to the plate thickness calculator 19 when the number of input clock pulses reaches a preset sampling time. To reset.

  The pulse counter 192 is a means for counting the number of discharge current pulses. The pulse counter 192 in the embodiment counts the number of gate signals that turn on and off the switching elements that are output from the pulse control device 30 and supply the discharge current pulses. When the time-up signal is input from the time counter 191, the sheet thickness calculator 19 requests the pulse counter 192 for data on the number of discharge current pulses. The pulse counter 192 outputs data on the number of discharge current pulses in the sampling period to the plate thickness calculator 19 in response to a request from the plate thickness calculator 19 to reset the count value.

  The pulse counter 192 of the embodiment does not input a gate signal and does not count the number of discharge current pulses when the machining gap is short-circuited and the interelectrode voltage does not rise to the no-load voltage. When the machining gap is short-circuited, the pulse control device 30 immediately stops the output of the gate signal and turns off the switching element because no voltage is not output from the voltage detector. Therefore, since the gate signal is very short and almost no discharge current flows, the pulse counter 192 does not identify the short gate signal. Further, the pulse counter 192 can be configured not to count the number of discharge current pulses when a signal indicating a short circuit is input from the voltage detector and the machining gap is short-circuited.

  When a relatively long discharge current pulse having a first pulse width and a discharge current pulse having a second pulse width are supplied, the pulse counter 192 generates a gate signal for generating a discharge current pulse having a first pulse width, Since the gate signal that supplies the discharge current pulse having the pulse width of 2 is different, the discharge current pulse having the first pulse width and the discharge current pulse having the second pulse width are respectively corresponding to the type of the gate signal. Separate and count.

  The pulse counter 192 can be modified so that the voltage detector outputs a voltage signal of the interelectrode voltage, and counts the number of discharge current pulses by counting each discharge in the machining gap. The configuration that directly counts the discharge in the machining gap can count only the machining current pulse by discriminating the invalid discharge with the voltage signal of the interelectrode voltage when not counting the invalid discharge that does not contribute to machining. It is valid.

  FIG. 2 is a flowchart showing an operation process in the controller of the wire cut electric discharge machining apparatus of the present invention. The process shown in FIG. 2 is specifically explained by the control device shown in FIG. However, the process shown in FIG. 2 is obtained by extracting only the process according to the present invention from the operation of the control device.

  The numerical controller 10 detects a setting flag when processing a workpiece having a stepped portion, and executes the process shown in FIG. When the control device 1 can obtain three-dimensional shape data of a workpiece or a desired machining shape, it is determined from the three-dimensional shape data whether the workpiece has a stepped portion, and a setting flag is set to “step machining”. Can be set automatically. The process shown in FIG. 2 is performed during machining, and is terminated regardless of the position of the step in the process when the machining is finished.

  In the initial state, the count values of the time counter 191 that measures a preset sampling time and the pulse counter 192 that measures the number of discharge current pulses are reset to 0 (S1). The plate thickness calculator 19 activates the time counter 191 simultaneously with the start of machining and starts measuring the sampling time.

  The pulse counter 192 counts up the number n of discharge current pulses during the sampling period. At this time, it is possible to count only the number of machining current pulses by separating the effective discharge contributing to machining and the ineffective discharge not contributing to machining. When counting only the number of machining current pulses, a step of separating effective discharge and ineffective discharge is performed before the step of counting up the number n of discharge current pulses. However, the difference between effective discharge and ineffective discharge for each discharge in wire-cut electric discharge machining has an effect on the machining volume during a certain period, except for short-circuiting, where no discharge occurs substantially, compared to die-cut electric discharge machining. Therefore, the benefit of counting only the number of machining current pulses is not great.

  When the electric discharge machining is performed by the machining control method in which the pulse counter 192 switches and supplies the discharge current pulses having different pulse widths corresponding to the machining state (S3), the pulse width of the supplied discharge current pulse is the first. If the pulse width is 1 (S4), the number n of discharge current pulses having the first pulse width is counted up (S5). When the pulse width of the supplied discharge current pulse is the second pulse width (S4), the number m of discharge current pulses having the second pulse width is counted up (S6).

  During the sampling period, the speed detection device 18 detects the speed every predetermined time and outputs feed speed data. The first storage device 12 records feed rate data (S7). The first storage device 12 in the numerical control device 10 according to the embodiment can store a history of the feed rate in association with the relative position and time.

  When the time counter 191 detects the sampling time (S8), a time-up signal is output from the time counter 191 to the plate thickness calculator 19. When the time-up signal is input from the time counter 191, the plate thickness calculation device 19 acquires data of each calculation parameter required for the calculation formula represented by Equation 2 (S 9).

  Specifically, the plate thickness calculation device 19 requests and inputs data of the number n of discharge current pulses having the first pulse width and the number m of discharge current pulses having the second pulse width in the sampling period to the pulse counter 191. To do. Further, the plate thickness calculation device 19 calculates the machining amount H per discharge of the discharge current pulse having the first pulse width adapted to the current machining conditions from the machining condition database stored in the second storage device 13. And data of the machining amount L per discharge of the discharge current pulse having the second pulse width.

  At the same time, the plate thickness calculation device 19 inputs the data of the average machining voltage Vg from the voltage detection device 16 and also inputs the data of the feed speed F from the speed detection device 18 through the first storage device 12. In addition, the plate thickness calculation device 19 selectively extracts and acquires the calculation coefficients α, β, γ determined by the wire electrode and the material of the workpiece stored in the second storage device 13.

  After obtaining the data of each calculation parameter, the plate thickness calculation device 19 calculates the plate thickness T by substituting the value of the calculation parameter into the calculation formula shown in Equation 2 (S10). When discharge current pulses having different pulse widths are not supplied, the number m of discharge current pulses having the second pulse width is 0. The plate thickness T obtained is the same. The plate thickness calculation device 19 immediately outputs the calculated plate thickness T to the command device 15 having the main calculation function of the numerical control device 10.

  The command device 15 determines whether or not the plate thickness T is greater than or less than a required threshold value when a preset change in the machining conditions is input when new plate thickness T data is input from the plate thickness calculation device 19. To do. If the input new sheet thickness T data is a value that requires changing setting of the machining conditions (S11), the commanding device 15 stores the machining conditions adapted to the input sheet thickness in the second storage device 13. Search and extract from the database of processing conditions.

  When the change in the plate thickness is small, the difference in the processing groove width is small. Therefore, it is not necessary to change and set the processing conditions every time the plate thickness is changed slightly, which may result in an undesirable processing result. Therefore, in the wire cut electric discharge machining apparatus of the embodiment, the machining conditions are changed and set every 10 mm of plate thickness. Therefore, the threshold value required to change the machining conditions is a multiple of 10 mm.

  The command device 15 stores the new machining condition extracted from the machining condition database in the first storage device 12 to change and set the machining condition, and the pulse controller 30 changes the pulse corresponding to the newly changed machining condition. A command signal is output (S12). The pulse control device 30 sets the changed machining conditions. Further, the command device 15 outputs a machining fluid command signal corresponding to the machining conditions changed and set as necessary to the machining fluid control device 40.

  The numerical controller 10 calculates the plate thickness in the sampling period for each predetermined sampling time while detecting the average machining voltage and the feed rate. The machining conditions are changed when it is determined that the machining conditions need to be changed with respect to the current machining conditions based on the calculated thickness every time the thickness is calculated until machining is completed. Repeat setting.

  FIG. 3 shows the difference between the plate thickness calculated by the calculation method of the present invention and the actual plate thickness change in the wire-cut electric discharge machining apparatus of the embodiment and the plate calculated by the conventional calculation method based on the average machining current. Shown in comparison with thickness. The black rhombus plot shows the thickness data calculated by the conventional calculation method, and the white circle plot shows the data calculated by the calculation method of the present invention. However, in order to make it easy to understand the error of the plate thickness calculated with respect to the fluctuation of the average machining current value, the discharge current pulse having the first pulse width and the first pulse width are shorter than the first pulse width corresponding to the no-load time. A processing method of switching and supplying the discharge current pulse of the second pulse width is performed, and the calculation method employs a method of calculating the plate thickness by the calculation formula shown in Equation 2.

  The upper graph in FIG. 3 shows the plate thickness value calculated when the servo reference voltage is decreased stepwise for each moving distance of 10 mm. The servo reference voltage is a parameter of an electrical machining condition that may be changed to make the feed speed constant in order to finally change the plate thickness and reduce the difference in the machining groove width. As shown in FIG. 3, in the conventional calculation method, when the servo reference voltage is changed, the error between the calculated plate thickness and the actual plate thickness becomes too large, and the setting is changed to an appropriate machining condition. However, in the calculation method of the present invention, even if the servo reference voltage is changed, the error between the calculated plate thickness and the actual plate thickness is within the allowable range, and can be changed and set to appropriate machining conditions. I understand.

  The middle graph of FIG. 3 shows the value of the plate thickness calculated when the pulse width of the discharge current pulse having the second pulse width is decreased stepwise for every moving distance of 10 mm. However, the pulse width of the discharge current pulse having the first pulse width is not changed. The pulse width of the discharge current pulse is a parameter of an electrical machining condition that may be changed to make the distance machining speed constant in order to reduce the difference in the machining groove width by changing the plate thickness. Further, the pulse width of the discharge current pulse having the second pulse width always changes depending on the machining state. As shown in FIG. 3, in the conventional calculation method, when the pulse width of the discharge current pulse is changed, the error between the calculated plate thickness and the actual plate thickness becomes too large, and the processing conditions are changed to appropriate ones. Although there is a high possibility that it cannot be set, in the calculation method of the present invention, the error between the calculated plate thickness and the actual plate thickness is within the allowable range even if the pulse width of the discharge current pulse is changed, It can be seen that the machining conditions can be changed.

  The lower graph of FIG. 3 shows the value of the plate thickness calculated when the plate thickness is reduced stepwise for each moving distance of 10 mm and the processing conditions are adapted to each plate thickness. As shown in FIG. 3, in the conventional calculation method, the error between the plate thickness calculated and the actual plate thickness is relatively large due to the influence of the machining conditions that are changed and set when the plate thickness is changed. In addition, since the calculated value of the plate thickness varies, there is a possibility that the setting is not changed to an appropriate processing condition at an appropriate timing. On the other hand, in the calculation method of the present invention, a slight miscalculation occurs immediately after the change of the plate thickness, but the error between the plate thickness calculated by converging the variation immediately and the actual plate thickness is within the allowable range, and is accurate. It can be seen that the machining conditions can be changed and set appropriately.

  The wire-cut electric discharge machining apparatus according to the embodiment described above specifically shows a preferable configuration, and therefore, as some examples have already been shown, the scope does not depart from the technical idea of the present invention. Can be modified, replaced, combined, and applied.

  The present invention is used in a wire cut electric discharge machining apparatus. The wire-cut electric discharge machining apparatus according to the present invention does not cause an unexpected disconnection of the wire electrode when machining a workpiece having a stepped portion, so that an unacceptable machining shape error does not occur. Excellent and contributes to the development of wire cut electric discharge machining.

DESCRIPTION OF SYMBOLS 1 Control apparatus 2 Drive apparatus 3 Processing power supply apparatus 4 Processing liquid supply apparatus 10 Numerical control apparatus 11 Input / output apparatus 12 1st memory | storage device 13 2nd memory | storage device 14 Decoding apparatus 15 Command apparatus 16 Voltage detection apparatus 17 Clock 18 Speed Detector 19 Plate thickness calculator 20 Motor controller 30 Pulse controller 40 Working fluid controller 191 Time counter 192 Pulse counter

Claims (4)

A voltage detection device that outputs the average machining voltage, a speed detection device that outputs the feed rate of the wire electrode, and a database of machining conditions that are a combination of a plurality of machining conditions are stored for each machining condition that determines the magnitude of the discharge energy . Data on the machining amount per discharge is stored in correspondence with the machining conditions, and the approximation of the wire electrode and work piece obtained when creating an approximate expression expressing the machining groove width by the average machining voltage by a predetermined approximation method A storage device for storing data of a plurality of calculation coefficients set for each material, a counter for counting the number of discharge current pulses supplied in a preset period, and the average machining voltage in the period for each period Before the processing conditions for determining the current magnitude of the discharge energy and inputting the feed rate and the number of discharge current pulses supplied during the period The processing amount and the period per said discharge one shot to get the data of the plurality of arithmetic coefficients corresponding to the material of the processing amount data and currently have the wire electrode and the workpiece using per discharge one shot is divided by the product of the supplied the discharge current pulses the average machining voltage and the machining groove width obtained by the approximate equation using the plurality of calculation coefficients a product of the number of definitive to the period and the feed rate A plate thickness calculation device for calculating a plate thickness, and a machining condition that can make a feed speed or a distance machining speed adapted to the plate thickness calculated by the plate thickness calculation device constant is stored in the storage device. A wire-cut electric discharge machining apparatus, comprising: a commanding device that extracts, changes, and sets a combination of machining conditions in a machining condition database . In the plate thickness calculation device, the plate thickness T, the machining amount H per discharge, the number n of discharge current pulses supplied during the preset period, the feed rate F during the period, and the average machining during the period ^2. The wire according to claim 1, wherein when the machining groove width in the period is obtained by the approximate expression αVg ² + βVg + γ as the voltage Vg and the plurality of calculation coefficients α, β, γ, the wire thickness is calculated by the following equation. Cut electrical discharge machining equipment.

A voltage detection device that outputs the average machining voltage, a speed detection device that outputs the feed rate of the wire electrode, and a database of machining conditions that are a combination of a plurality of machining conditions are stored for each machining condition that determines the magnitude of the discharge energy . processing amount of data of the discharge one shot per discharge current pulse having a predetermined first discharge current pulse machining amount of data and the shorter than the first pulse width second pulse width of the discharge one shot per pulse width Is stored in correspondence with the machining conditions, and a plurality of values set for each material of the wire electrode and workpiece to be obtained when an approximate expression expressing the machining groove width by an average machining voltage is created by a predetermined approximation method. a storage device for storing data of the arithmetic coefficient, the number of discharge current pulses having a second pulse width of the discharge current pulse of said first pulse width to be supplied to the pre-set period A counter for counting Re respectively, of the number and the second pulse width of the discharge current pulse of said first pulse width to be supplied to the average machining voltage and the feed rate and the period in the period in each said period of time Data on the machining amount per discharge and the second pulse in the discharge current pulse having the first pulse width corresponding to the machining conditions for determining the current magnitude of the discharge energy while inputting the number of discharge current pulses The first pulse width is obtained by obtaining data of the machining amount per discharge in a discharge current pulse having a width and data of the plurality of calculation coefficients corresponding to the wire electrode currently used and the material of the workpiece. The discharge current pulse having the second pulse width is the product of the machining amount per discharge of the discharge current pulse and the number of discharge current pulses having the first pulse width supplied during the period. Using the average machining voltage and the plurality of calculation coefficients a value obtained by adding the product of the number of the discharge current pulse of said second pulse width machining amount to be supplied to the period definitive in the period per discharge one shot A plate thickness calculation device that calculates the plate thickness by dividing by the product of the machining groove width obtained by the approximate expression and the feed rate, and a feed rate or distance machining adapted to the plate thickness calculated by the plate thickness calculation device A wire-cut electric discharge machining comprising: a command device that extracts and changes a machining condition capable of making the speed constant from a combination of the machining conditions stored in the machining condition database stored in the storage device apparatus. Oite the thickness computing device, the thickness T, the processing of the processing amount of the discharge one shot per discharge current pulse of the first pulse width H, discharge one shot per discharge current pulse of said second pulse width the amount L, the number n of the discharge current pulse of said first pulse width to be supplied to the pre-set period, the number m of the discharge current pulse of said second pulse width supplied to the period, in the period feed rate F, the average machining voltage Vg in the period, the plurality of calculation coefficients alpha, beta, and a gamma, when the processed groove width in the period is determined by the approximate expression αVg 2 ⁺ βVg ⁺ γ, the plate thickness by the following formula The wire-cut electric discharge machining apparatus according to claim 3, wherein is calculated.

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