Wire discharge machining device and wire discharge machining method

Abstract

The present invention provides a wire discharge machining device and method that detect concentrated discharge in real time based on the discharge position determined from the preliminary discharge current, and can calculate the accurate discharge position for use in measuring plate thickness, etc. The wire discharge machining device includes a discharge position calculation circuit that calculates the discharge position based on the preliminary discharge current detected by a current detector during a first period from the rise of the preliminary discharge current waveform supplied to the machining gap formed between the wire electrode and the workpiece until it reaches a certain current value, and a second period from the current value reaching the certain current value until the main discharge current is supplied.

Description

Technical Field

[0001] The present invention relates to a wire discharge machining device and a wire discharge machining method for machining by intermittently supplying a voltage to a machining gap formed between a wire electrode and a workpiece. Background Art

[0002] Discharge machining (EDM) is an electrical machining method in which a wire electrode and a workpiece are positioned facing each other, and voltage pulses are repeatedly supplied to the machining gap formed between the wire electrode and the workpiece, continuously generating discharges and utilizing the discharge energy for machining. A technology (CNB104640660) is disclosed. A conventional wire EDM device comprises a main power supply circuit, an auxiliary power supply circuit, and a pulse generating circuit. The pulse generating circuit controls the on / off switching elements of the main and auxiliary power supply circuits, and applies a DC voltage to the machining gap to generate discharges. When discharge occurs between the wire electrode and the workpiece, the material in the discharge-generating portion of the workpiece (discharge location) is blown away by the impact of the discharge. Subsequently, the temperature rises sharply due to heat generation, causing the workpiece material to partially melt and evaporate. The material removed from the workpiece cools and disperses as machining powder. After a predetermined period of time, the supply of voltage pulses is cut off, thereby terminating the discharge and forming a discharge mark on the surface of the workpiece, whose size is roughly proportional to the discharge current.

[0003] It is known that discharge energy is consumed not only to remove the workpiece material but also affects the electrode, damaging the electrode material. This phenomenon is called electrode wear. Electrode wear is an inevitable phenomenon in electrical discharge machining. If the discharge position is not sufficiently dispersed and concentrated discharge occurs at approximately the same location, it can cause the wire electrode to break.

[0004] Therefore, a technique is disclosed in which the discharge position during machining is measured and the application of voltage between electrodes is stopped when concentrated discharge occurs.

[0005] [Prior art literature]

[0006] [Patent Document]

[0007] [Patent Document 1] Japanese Patent No. 5037941

[0008] [Patent Document 2] Japanese Patent No. 3085040

[0009] [Patent Document 3] China Patent Publication No. CNB104640660 Summary of the Invention

[0010] [Problems to be solved by the invention]

[0011] In Patent Document 1, the discharge position in the wire electrode is determined based on the preliminary discharge current, and the application of the main discharge voltage is stopped, and machining energy calculation and output adjustment are performed. Because the preliminary discharge current is weak and susceptible to various noises (such as stray capacitance and inductance), the discharge position detection timing is delayed by 150 to 300 ns from the initial discharge.

[0012] However, when concentrated discharge is detected based on the discharge position obtained from the preliminary discharge current and application of the main discharge voltage is stopped, it is ideal to detect the discharge position at the earliest possible timing after the start of discharge.

[0013] This is because, in order to stop the main discharge in real time, after the preliminary discharge current flows between the electrodes and before the main discharge voltage pulse is applied between the electrodes, it is necessary to determine whether to stop the supply of the main discharge voltage pulse, requiring a short processing time.

[0014] Furthermore, the thickness of the workpiece is calculated using the discharge position (Patent Document 2). Unlike concentrated discharge detection, when calculating thickness based on the discharge position, it is not necessary to detect the discharge position within a short period of time. Ideally, this is done when the impact of the machining environment, such as interference, is minimal. This is because accurate discharge position measurement improves the accuracy of thickness measurement.

[0015] In view of the above problems, the main object of the present invention is to provide a wire discharge machining device and a wire discharge machining method that can detect concentrated discharge in real time based on the discharge position obtained from the preliminary discharge current, and can calculate the accurate discharge position used for measuring plate thickness, etc.

[0016] [Technical means to solve the problem]

[0017] The wire discharge machining device of the present invention includes: an auxiliary power supply circuit for applying a voltage that causes discharge to occur and supplying a preliminary discharge current to a machining gap formed between a wire electrode and a workpiece; a main power supply circuit for supplying a main discharge current to the machining gap; a current detector for detecting the discharge current flowing between a pair of current-carrying bodies disposed one above the other across the workpiece and supplying the discharge current to the wire electrode, and the machining gap; and a discharge position calculation circuit for calculating a discharge position based on each of the preliminary discharge currents detected by the current detector during a first period from a rise in the waveform of the preliminary discharge current supplied to the machining gap to a predetermined current value and a second period from the current value reaching the predetermined current value to the supply of the main discharge current.

[0018] In addition, the present invention provides a wire discharge machining method, wherein a voltage that causes discharge to occur is applied to a machining gap between a workpiece and a wire electrode, and a preliminary discharge current is supplied, and thereafter a main discharge current is supplied to the machining gap. The wire discharge machining method is characterized in that a discharge position is detected by using the current value of the preliminary discharge current in a first period from when the waveform of the preliminary discharge current supplied to the machining gap rises until it reaches a certain current value, and in a second period from when the current value reaches the certain current value until the main discharge current is supplied.

[0019] Here, the "pre-discharge current" refers to the current flowing through the machining gap due to the application of voltage from the auxiliary power circuit, and the "main discharge current" refers to the current flowing through the machining gap due to the application of voltage from the main power circuit. Furthermore, the term "discharge current" collectively refers to both the pre-discharge current and the main discharge current.

[0020] The term "discharge position" refers to the position of a discharge point on the wire electrode and is synonymous with a discharge point.

[0021] According to the present invention, the discharge position is detected based on the value of the pre-discharge current during a first period, from the rise of the pre-discharge current waveform until it reaches a certain current value, and a second period, from the time the pre-discharge current reaches the certain current value until the main discharge current is supplied. Detecting the discharge position during the first period, when the pre-discharge current is high, allows for more rapid termination of the main discharge current. Furthermore, detecting the discharge position during the second period, when the influence of the machining environment, such as interference, is less pronounced, allows for accurate calculations of plate thickness and other parameters. By detecting the discharge position during both the first and second periods, concentrated discharge can be detected and terminated in real time, allowing for the effective use of the accurate discharge position in other calculations.

[0022] The current detector of the present invention includes a sensor for detecting the pre-discharge current flowing through the machining gap by application of a voltage from the auxiliary power supply circuit via an upper current-carrying body, and a sensor for detecting the pre-discharge current flowing through the machining gap by application of a voltage from the auxiliary power supply circuit via a lower current-carrying body. The discharge position calculation circuit of the present invention is characterized by acquiring the pre-discharge current from each of the sensors, calculating the integrated value of the pre-discharge current to obtain the area of ​​each, and calculating the discharge position by obtaining the ratio of the areas.

[0023] According to the present invention, the area is calculated from the integrated value of the pre-discharge current and the discharge position is calculated from the area ratio. Therefore, the influence of noise can be reduced by the integration effect due to addition.

[0024] [Effects of the Invention]

[0025] According to the present invention, the discharge position is calculated in the first period from the rise of the waveform of the preliminary discharge current supplied to the machining gap to the reaching of a certain current value and in the second period from the reaching of the certain current value to the supply of the main discharge current. Therefore, the supply of the main discharge current can be stopped quickly, and the plate thickness can be measured more accurately. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 1 is a block diagram showing a wire electrical discharge machining device 100 according to the present invention.

[0027] Figure 2 1 is a circuit configuration diagram showing an example of a circuit of the machining power supply 1 in the wire electrical discharge machining device 100 of the present invention.

[0028] Figure 3 This is a timing chart for explaining the normal operation of the wire electrical discharge machining device 100 of the present invention.

[0029] Figure 4 This is a timing chart for explaining the operation of the wire electrical discharge machining device 100 of the present invention during concentrated electrical discharge detection.

[0030] Figure 5 This is a timing chart for explaining the operation of the concentrated discharge detection circuit 431 of the wire electrical discharge machining device 100 according to the present invention.

[0031] Figure 6 This is a schematic diagram for explaining the operation of the concentrated discharge detection circuit 431 of the wire electrical discharge machining device 100 according to the present invention.

[0032] Figure 7 This is a schematic diagram for explaining the operation of the plate thickness calculation circuit 432 of the wire electrical discharge machining device 100 according to the present invention.

[0033] Figure 8 This is a schematic diagram for explaining the operation of the partial discharge detection circuit 433 of the wire electrical discharge machining device 100 according to the present invention.

[0034] Figure 9 This is a timing chart explaining the operation of the wire electrical discharge machining device 100 of the present invention during partial discharge detection.

[0035] [Explanation of Symbols]

[0036] 1: Processing power supply

[0037] 1A: Main power circuit

[0038] 1B: Auxiliary power supply circuit

[0039] 2: Voltage detector

[0040] 2A: Voltage sensor for main power supply

[0041] 2B: Voltage sensor for auxiliary power supply

[0042] 3: Current detector

[0043] 31A: Upper current sensor for main power supply

[0044] 31B: Lower current sensor for main power supply

[0045] 32A: Upper current sensor for auxiliary power supply

[0046] 32B: Lower current sensor for auxiliary power supply

[0047] 4: Decision circuit

[0048] 41: Discharge detection circuit

[0049] 42: Discharge position calculation circuit

[0050] 431: Centralized discharge detection circuit

[0051] 432: Plate thickness calculation circuit

[0052] 433: Partial Discharge Detection Circuit

[0053] 44: Pulse generating circuit

[0054] 45: Storage

[0055] 7: Control device

[0056] 71: Storage

[0057] 9: Powered body

[0058] 9A: Upper side current-carrying body

[0059] 9B: Bottom side current-carrying body

[0060] 10: Processing clearance

[0061] E: Wire electrode

[0062] W: workpiece DETAILED DESCRIPTION

[0063] <1. Configuration of Wire EDM Device 100 >

[0064] Figure 1 1 is a block diagram showing a wire electrical discharge machining device 100 according to the present invention. Figure 2 1 is a circuit configuration diagram showing an example of a circuit of the machining power supply 1 in the wire electrical discharge machining device 100 of the present invention.

[0065] The wire discharge machining device 100 moves the upper wire guide and the lower wire guide relative to the workpiece W in the XY plane, repeatedly applies a predetermined machining voltage pulse to the machining gap 10 formed between the wire electrode E and the workpiece W, and intermittently generates discharges. The discharge energy removes material from the workpiece W, and the workpiece W is cut into the desired machining shape.

[0066] The wire electrical discharge machining device 100 includes a machining power supply 1 , a voltage detector 2 , a current detector 3 , a determination circuit 4 , a control device 7 , a current-carrying body 9 , and a wire electrode E.

[0067] The machining power supply 1 is a power supply circuit for applying a voltage to the wire electrode E and the workpiece W to generate an electric discharge. The power supply 1 includes a main power supply circuit 1A and an auxiliary power supply circuit 1B. In the wire discharge machining device 100, discharge is generated by switching between the auxiliary power supply circuit 1B and the main power supply circuit 1A in response to instructions from the pulse generating circuit 44.

[0068] The main power supply circuit 1A applies a voltage for supplying a main discharge current Ia for machining to the machining gap 10. When discharge occurs in the machining gap 10 and the preliminary discharge current Ib begins to flow, the main discharge current Ia is supplied by applying the voltage of the main power supply circuit 1A.

[0069] The main power supply circuit 1A includes: a DC power supply 11 arranged in series with the machining gap 10 and outputting a DC voltage, one or more switching elements 12 arranged in series between the machining gap 10 and the DC power supply 11, a capacitor 13, and a reverse current blocking diode 14 inserted in series with the machining gap 10.

[0070] The switching element 12 is a field-effect transistor (MOSFET) with excellent rising performance and voltage resistance. The capacitor 13 is a smoothing capacitor provided in parallel with the DC power supply 11 to prevent voltage fluctuations. The reverse current blocking diode 14 prevents reverse current caused by the reverse voltage generated in the machining gap 10 from flowing back to the DC power supply 11.

[0071] The auxiliary power supply circuit 1B is a power supply circuit that applies a voltage for inducing discharge to the machining gap 10 . The application of the voltage by the auxiliary power supply circuit 1B supplies a preliminary discharge current Ib to the machining gap 10 .

[0072] The auxiliary power supply circuit 1B includes: a DC power supply 21, which is connected in series with the machining gap 10 and in parallel with the DC power supply 11 of the main power supply circuit 1A and outputs a DC voltage; one or more switching elements 22, which are arranged in series between the machining gap 10 and the DC power supply 21; a current limiting resistor 23, which is arranged in series with the switching element 22 between the machining gap 10 and the DC power supply 21; a reverse current blocking diode 24, which is arranged in series with the DC power supply 21; a polarity switching circuit 25, which is composed of a bridge circuit of switching elements arranged between the DC power supply 21 and the switching element 22; and a capacitor 26.

[0073] The structure of the switching element 22 is essentially the same as that of the switching element 12. The current limiting resistor 23 has a resistance value sufficiently low to allow the pre-discharge current Ib flowing immediately after discharge in the machining gap 10 to remain uninterrupted. The reverse current blocking diode 24 prevents sudden current from flowing back into the auxiliary power supply circuit 1B including the DC power supply 21. The polarity switching circuit 25 selectively switches the polarity of the DC voltage output from the DC power supply 21. The capacitor 26 is a smoothing capacitor provided in parallel with the DC power supply 21 to prevent voltage fluctuations.

[0074] The voltage detector 2 is a sensor that detects the voltage between the wire electrode E and the workpiece W during no-load and discharge conditions, and includes a main power supply voltage sensor 2A and an auxiliary power supply voltage sensor 2B.

[0075] The main power supply voltage sensor 2A is provided between the main power supply circuit 1A and the upper current-carrying body 9A, and detects the voltage between the electrodes during no-load and discharge periods caused by application of the voltage of the main power supply circuit 1A.

[0076] The auxiliary power supply voltage sensor 2B is provided between the auxiliary power supply circuit 1B and the upper current-carrying body 9A, and detects the voltage between the electrodes during no-load and discharge periods caused by application of the voltage of the auxiliary power supply circuit 1B.

[0077] The inter-electrode voltage value detected by the voltage detector 2 is given to the determination circuit 4 .

[0078] The current detector 3 is a current sensor for detecting the current flowing between electrodes, and includes a main power supply upper current sensor 31A, a main power supply lower current sensor 31B, an auxiliary power supply upper current sensor 32A, and an auxiliary power supply lower current sensor 32B.

[0079] The upper main power supply current sensor 31A is a sensor that detects the current flowing between the wire electrode E and the workpiece W due to the application of voltage from the main power supply circuit 1A via the upper current-carrying member 9A. Meanwhile, the lower main power supply current sensor 31B is a sensor that detects the current flowing between the wire electrode E and the workpiece W due to the application of voltage from the main power supply circuit 1A via the lower current-carrying member 9B.

[0080] In addition, the upper current sensor 32A for the auxiliary power supply is a sensor that detects the current flowing between the wire electrode E and the workpiece W by applying the voltage of the auxiliary power circuit 1B via the upper power-carrying body 9A, and the lower current sensor 32B for the auxiliary power supply is a sensor that detects the current flowing between the wire electrode E and the workpiece W by applying the voltage of the auxiliary power circuit 1B via the lower power-carrying body 9B.

[0081] The current detector 3 is provided between the connection line of the upper current-carrying body 9A or the lower current-carrying body 9B and the machining power source 1. The current value detected by the current detector 3 is given to the determination circuit 4.

[0082] The determination circuit 4 is a circuit that controls the switching elements 12 and 22 of the machining power supply 1 on and off and calculates the discharge position based on the inter-electrode voltage value provided by the voltage detector 2, the current value provided by the current detector 3, and the machining conditions provided by the control device 7.

[0083] Specifically, the determination circuit 4 includes a discharge detection circuit 41 , a discharge position calculation circuit 42 , a concentrated discharge detection circuit 431 , a plate thickness calculation circuit 432 , a partial discharge detection circuit 433 , a pulse generation circuit 44 , and a storage unit 45 .

[0084] The discharge detection circuit 41 is a circuit that outputs a discharge occurrence signal St indicating that a discharge has occurred in the machining gap 10 when the inter-electrode voltage in the machining gap 10 falls below a reference voltage Vr. Specifically, the discharge detection circuit 41 compares the inter-electrode voltage value obtained from the voltage detector 2 with the reference voltage Vr. If the inter-electrode voltage value falls below the reference voltage Vr, the discharge detection circuit 41 outputs the discharge occurrence signal St to the pulse generation circuit 44 and the discharge position calculation circuit 42.

[0085] The reference voltage Vr is set to an appropriate value that can reliably detect, with minimal delay, the start of discharge current Ib supplied from the auxiliary power supply circuit 1B flowing through the machining gap 10 and the resulting drop in inter-electrode voltage. The data for the reference voltage Vr can be rewritten by the control device 7.

[0086] The discharge position calculation circuit 42 is a circuit that calculates the discharge position twice upon receiving the discharge occurrence signal St from the discharge detection circuit 41. When the discharge occurrence signal St is input, the discharge position calculation circuit 42 obtains current values ​​from the auxiliary power supply upper current sensor 32A and the auxiliary power supply lower current sensor 32B, and calculates the discharge position twice during the rising period Tt (first period) and the steady period Ts (second period) of the preliminary discharge current Ib. The discharge position obtained during the rising period Tt of the preliminary discharge current Ib is the first discharge position H1. n (n=1, ..., NN is the total number) and the discharge position obtained during the constant period Ts of the reserve discharge current Ib is taken as the second discharge position H2 m (m=1, ..., MM is the total number) to calculate. First discharge position H1 n and the second discharge position H2 m are stored in the storage unit 45 in chronological order, and the first discharge position H1 n is output to the concentrated discharge detection circuit 431, the second discharge position H2 m The signal is output to the partial discharge detection circuit 433 .

[0087] The concentrated discharge detection circuit 431 is based on the first discharge position H1 n The concentrated discharge detection circuit 431 is a circuit that detects whether concentrated discharge has occurred based on information from the concentrated discharge detection circuit 431. When the concentrated discharge detection circuit 431 detects the occurrence of concentrated discharge, it outputs a concentrated discharge signal Ss with a short duration to the pulse generation circuit 44.

[0088] The plate thickness calculation circuit 432 calculates the plate thickness based on the second discharge position H2 stored in the storage unit 45 in a time series manner. m The circuit calculates the plate thickness L using the information.

[0089] The partial discharge detection circuit 433 is a circuit that detects the partial discharge based on the information of the first discharge position H1n and the second discharge position H2 stored in the storage unit 45 in a time series manner. m The shape of the machined surface of the workpiece W is estimated based on the information and the local deviation of the discharge is determined.

[0090] When discharge occurs only locally in a certain area during wire EDM, the straightness of the machined surface of the workpiece W decreases, reducing machining accuracy. For example, if discharge is concentrated in the center of the machined surface, the surface may have a drum shape that is more concave than the ends. If discharge is concentrated at the ends of the machined surface, the surface may have an inverted drum shape, with the center protruding more than the ends. Therefore, the partial discharge detection circuit 433 estimates the shape of the machined surface of the workpiece W and, if it detects localized discharge, outputs a partial discharge signal Sb with a short duration to the pulse generation circuit 44.

[0091] The pulse generating circuit 44 has a gate circuit, which controls the on and off of the switching element of the processing power supply 1 according to the discharge generation signal St from the discharge detection circuit 41, the concentrated discharge signal Ss from the concentrated discharge detection circuit 431, the local discharge signal Sb from the local discharge detection circuit 433, the inter-electrode voltage value given by the voltage detector 2, the current value given by the current detector 3, and the processing conditions given by the control device 7.

[0092] Specifically, the pulse generating circuit 44 supplies a first gate signal to the switching element 12 of the main power supply circuit 1A and supplies a second gate signal to the switching element 22 of the auxiliary power supply circuit 1B via a gate circuit.

[0093] When the pulse generating circuit 44 outputs a first gate signal to the main power supply circuit 1A, the switching element 12 of the main power supply circuit 1A turns on, supplying the main discharge current Ia. Furthermore, when the pulse generating circuit 44 outputs a second gate signal to the auxiliary power supply circuit 1B, the switching element 22 of the auxiliary power supply circuit 1B turns on, supplying the backup discharge current Ib.

[0094] Specifically, the pulse generating circuit 44 refers to the machining conditions received from the control device 7 and outputs a second gate signal to turn on the switching element 22, thereby applying the voltage of the DC power supply 21 of the auxiliary power supply circuit 1B to the machining gap 10 to induce discharge. When the current value supplied by the current detector 3 detects the occurrence of discharge and the preliminary discharge current Ib rises to a set peak current value, the output of the second gate signal is stopped, the switching element 22 is turned off, and the auxiliary power supply circuit 1B is disconnected.

[0095] Furthermore, when discharge occurs in the auxiliary power supply circuit 1B and the discharge detection circuit 41 receives a discharge occurrence signal St, the pulse generating circuit 44 outputs a first gate signal to turn on the switching element 12, supplying the main discharge current Ia. Then, when the first main discharge current Ia reaches a set peak current value, the output of the first gate signal is stopped. Following the first discharge current pulse of the main discharge current Ia, the pulse generating circuit 44 receives the current detection signal from the current detector 3 and rapidly switches the switching element 12 on and off at a predetermined on-off repetition frequency of 1 MHz or more, consistent with the predetermined discharge frequency, until the main discharge current Ia decays and ceases to flow within the machining gap 10. This supplies the main discharge current Ia as a high-frequency discharge current pulse.

[0096] The storage unit 45 stores the first discharge position H1. n and the second discharge position H2 m etc.

[0097] The control device 7 is a device that controls the overall operation of the wire electrical discharge machining device 100 , and includes a storage unit 71 therein.

[0098] The control device 7 calculates the plate thickness L calculated by the plate thickness calculation circuit 432. p The data can be changed as needed to match the plate thickness L p Specifically, the processing conditions that are suitable for the plate thickness L are retrieved and extracted from the combination of multiple processing conditions stored in the storage unit 71. p Then, the control device 7 outputs a pulse command signal corresponding to the changed processing conditions to change the set processing conditions.

[0099] The storage unit 71 stores data on the processing conditions required for the action, specifically, the rest time (off time) Of, the repetition frequency of high-frequency discharge (discharge frequency) Mo above 1 MHz, the duration (pulse width) Ma of the main discharge current Ia, the applied voltage (DC power supply voltage) Vo, the processing current (peak current value) Ip, the reference voltage Vr, the current reference value Ir, the delay time Ta, etc.

[0100] The current-carrying body 9 is a member for contacting the wire electrode E and supplying current for electric discharge machining from the machining power supply 1 . An upper current-carrying body 9A and a lower current-carrying body 9B are provided above and below the workpiece W.

[0101] The wire EDM device 100 is equipped with an upper guide assembly and a lower guide assembly. In the upper guide assembly, located above the workpiece W, the upper wire guide, upper current-carrying element 9A, and machining fluid jet nozzle are integrally assembled into the housing. In the lower guide assembly, located below the workpiece W, the lower wire guide, lower current-carrying element 9B, and machining fluid jet nozzle are integrally assembled into the housing. The power supply terminals of the machining power supply 1 are connected to the upper current-carrying element 9A and the lower current-carrying element 9B, supplying current to the wire electrode E via the upper current-carrying element 9A and the lower current-carrying element 9B.

[0102] The wire electrode E is a wire-shaped tool for electrical discharge machining made of a conductive material. The wire electrode E is positioned facing the workpiece W, forming a machining gap between the wire electrode E and the workpiece W. A moving device allows for relative movement in any direction relative to the workpiece W. The wire electrode E is inserted through upper and lower wire guides and is positioned with tension applied between the upper and lower wire guides.

[0103] The wire electrode E is connected to the power terminals of the machining power supply 1 via the upper current-carrying element 9A and the lower current-carrying element 9B. The workpiece W is also connected to the power terminals of the machining power supply 1 via a current-carrying fixture. When a predetermined voltage is applied between the wire electrode E and the workpiece W by the machining power supply 1, discharge occurs between the wire electrode E and the workpiece W, thereby performing electrical discharge machining.

[0104] <2. Description of Discharge Position Calculation Circuit 42>

[0105] Figure 5 This is a timing chart for explaining the operation of the concentrated discharge detection circuit 431 of the wire electrical discharge machining device 100 according to the present invention.

[0106] When the discharge generation signal St is input, the discharge position calculation circuit 42 calculates the discharge position twice during the rising period Tt and the steady period Ts of the reserve discharge current Ib.

[0107] In the wire electrical discharge machining device 100, a discharge current Is is supplied to the workpiece W from two locations, one above and one below the upper current-carrying element 9A and the other below the lower current-carrying element 9B, via the discharge point on the wire electrode E. This creates a parallel circuit: a circuit where the discharge current Is flows from the upper current-carrying element 9A to the workpiece W via the discharge point, and a circuit where the discharge current Is flows from the lower current-carrying element 9B to the workpiece W via the discharge point. Because the wire electrode E is a resistor, the discharge point can be detected by using the current detector 3 to detect the current difference in the circuit caused by the difference in resistance ratio.

[0108] In the present invention, time series data of the upper pilot discharge current Isu and the lower pilot discharge current Isd are obtained from the upper auxiliary power supply current sensor 32A and the lower auxiliary power supply current sensor 32B. This time series data is integrated over time to determine the area, and the discharge position is calculated based on the area ratio of the upper pilot discharge current Isu to the lower pilot discharge current Isd.

[0109] The first discharge position H1 calculated during the specific rising period Tt n The calculation method is as follows.

[0110] From time t2 to time t21, time series data of the upper pilot discharge current Isu is sequentially acquired from the upper current sensor 32A for the auxiliary power supply, and time series data of the lower pilot discharge current Isd is sequentially acquired from the lower current sensor 32B for the auxiliary power supply. To improve detection accuracy, these data are passed through a bandpass filter to extract only a specific frequency band.

[0111] Then, based on the extracted time series data, the integrated value Qsu of the upper pilot discharge current Isu with the rising period Tt as the time width is calculated. Similarly, the integrated value Qsd of the lower pilot discharge current Isd with the rising period Tt as the time width is calculated. The first discharge position H1 is calculated by calculating the area ratio of the integrated value Qsu of the upper pilot discharge current Isu to the integrated value Qsd of the lower pilot discharge current Isd. n .

[0112] Time t2, which serves as the start time of the rising period Tt, is the time when the discharge position calculation circuit 42 receives the discharge occurrence signal St. Time t21, which serves as the end time of the rising period Tt, is the time when the preliminary discharge current Ib begins to flow into the machining gap 10 and gradually increases, then becomes limited to a certain value. Time t21 can be set by detecting the differential change of the preliminary discharge current Ib, which is the sum of the upper pilot discharge current Isu and the lower pilot discharge current Isd, and by ensuring that the differential change falls within a predetermined range. Alternatively, time t21 can be set by adding a predetermined time width to time t2.

[0113] The calculated first discharge position H1 n The signal is stored in the storage unit 45 and output to the concentrated discharge detection circuit 431 .

[0114] The second discharge position H2 calculated during the constant period Ts mThe calculation method is similar. From time t22 to time t3, time-series data of the upper pilot discharge current Isu is sequentially acquired from the upper auxiliary power supply current sensor 32A, and time-series data of the lower pilot discharge current Isd is sequentially acquired from the lower auxiliary power supply current sensor 32B. Next, to improve detection accuracy, the time-series data is passed through a low-pass filter to remove noise and extract only a specific frequency band. Based on the extracted time-series data, the integrated value Qsu of the upper pilot discharge current Isu over a constant period Ts is calculated. Similarly, the integrated value Qsd of the lower pilot discharge current Isd over a constant period Ts is calculated. The second discharge position H2 is calculated by calculating the area ratio between the integrated value Qsu of the upper pilot discharge current Isu and the integrated value Qsd of the lower pilot discharge current Isd. m .

[0115] Time t22, which is the start time of the constant period Ts, is the time when the rising period Tt ends and the reserve discharge current Ib stabilizes at a constant value. Time t22 may be obtained by adding a predetermined time width Tb to time t2. Alternatively, time t22 may be obtained by detecting a differential change in the reserve discharge current Ib and detecting that the value of the differential change stabilizes within a predetermined range.

[0116] Furthermore, time t3 , which is the end time of the constant period Ts, is the time obtained by adding the delay time Ta to time t2 .

[0117] The calculated second discharge position H2 m The signal is stored in the storage unit 45 and output to the partial discharge detection circuit 433 .

[0118] <4. Description of Concentrated Discharge Detection Circuit 431>

[0119] Figure 6 This is a schematic diagram for explaining the operation of the concentrated discharge detection circuit 431 of the wire electrical discharge machining device 100 according to the present invention.

[0120] The concentrated discharge detection circuit 431 is based on the first discharge position H1 n Specifically, it is assumed that the circuit detects whether concentrated discharge has occurred based on the information of the storage unit 45 and the time s1. n-1 The first discharge position H1 calculated after the start of machining is stored in chronological order. n-1 When at time s n Calculate the first discharge position H1 n When the concentrated discharge detection circuit 431 is at the first discharge position H1 nThe concentrated discharge detection range W1 is set to a certain width as the center. Here, the concentrated discharge detection range W1 is the range on the F axis of the wire electrode E when the wire electrode feed direction F is set as the F axis. The concentrated discharge detection circuit 431 is based on the time s n Retrospective time series, for time s n Previous first discharge position H1 n-1 It is determined whether the data are continuous for a predetermined number P1 and are included in the concentrated discharge detection range W1.

[0121] For example, when the prescribed number P1=3, from the time s n Retrospective time series, for time s n-1 The first discharge position H1 n-1 , time s n-2 The first discharge position H1 n-2 and time s n-3 The first discharge position H1 n-3 If the concentrated discharge detection circuit 431 determines that all the components are within the concentrated discharge detection range W1, it determines that concentrated discharge has occurred and outputs a concentrated discharge signal Ss with a short duration to the pulse generation circuit 44.

[0122] Here, the concentrated discharge detection range W1 is set wider than the small range width W2 used in the partial discharge detection circuit 433 described later. This is because the first discharge position H1 n Since the data is acquired during the rising period Tt, it is easily affected by noise, and the determination of the occurrence of concentrated discharge is configured to have a certain width.

[0123] <5. Description of Plate Thickness Calculation Circuit 432>

[0124] Figure 7 This is a schematic diagram for explaining the operation of the plate thickness calculation circuit 432 of the wire electrical discharge machining device 100 according to the present invention.

[0125] The plate thickness calculation circuit 432 calculates the plate thickness based on the second discharge position H2 stored in the storage unit 45 in a time series manner. m The thickness L of the workpiece W is calculated using the information p (p=1, ..., PP is the total number of plate thicknesses).

[0126] Specifically, the plate thickness calculation circuit 432 calculates the plate thickness based on the second discharge position H2 stored in a time series format. m The second discharge position H2 is calculated from the data m The distribution in the F-axis direction, according to the second discharge position H2 m The upper and lower limit positions in the F-axis direction are used to calculate the plate thickness L. pThe plate thickness calculation circuit 432 calculates the second discharge position H2 by the discharge position calculation circuit 42. m Calculate plate thickness L p , and the plate thickness L p Output to the control device 7.

[0127] <6. Description of Partial Discharge Detection Circuit 433>

[0128] Figure 8 This is a schematic diagram for explaining the operation of the partial discharge detection circuit 433 of the wire electrical discharge machining device 100 according to the present invention.

[0129] The partial discharge detection circuit 433 detects the second discharge position H2 stored in the storage unit 45 in chronological order. m Specifically, the second discharge position H2 calculated after the start of machining is stored in the storage unit 45 in chronological order. m The partial discharge detection circuit 433 divides the wire electrode E on the F axis from the position where it contacts the upper conductive body 9A to the position where it contacts the lower conductive body 9B into a small range of width W2. Here, the small ranges divided into the small ranges of width W2 are sequentially designated as W21, W22, ..., W2 from the position where it contacts the upper conductive body 9A. q ,…,W2 Q (q=1, 2, ..., QQ is the number of divisions) The partial discharge detection circuit 433 calculates the second discharge position H2 every time after the start of machining. m When included in the small range W2 q The second discharge position H2 m The number of data (count number) is counted, and then the calculation is included in the small range W2 q The second discharge position H2 m The count number of the small range W2 is greater than the predetermined threshold value TH. Then, the small range W2 is stored in the storage unit 45. q , the count number and the information that the count number is greater than the threshold value TH are grouped.

[0130] When at time s2 m+1 Calculate the second discharge position H2 m+1 When the partial discharge detection circuit 433 outputs the second discharge position H2 from the discharge position calculation circuit 42, m+1 Small range W2 q Detection is performed and the number of data (count number) is counted. Then, in the area containing the second discharge position H2 m+1 Small range W2 qWhen the count number is equal to or greater than the threshold value TH, it is determined that the discharge is localized, and a partial discharge signal Sb with a short duration is output to the pulse generating circuit 44 .

[0131] Here, the first discharge position H1 may be output from the discharge position calculation circuit 42 to the partial discharge detection circuit 433. n+1 , according to the first discharge position H1 n+1 Specifically, the partial discharge detection circuit 433 may also output a partial discharge signal Sb when receiving the first discharge position H1. n+1 When the first discharge position H1 is included n+1 Small range W2 q Detection is performed, including the first discharge position H1 n+1 Small range W2 q When the count number is greater than or equal to the threshold value TH, it is determined that the discharge is localized, and a partial discharge signal Sb with a short duration is output to the pulse generating circuit 44. This allows the supply of the discharge current Is to be stopped more quickly.

[0132] Here, the small range width W2 used in the partial discharge detection circuit 433 is set to be narrower than the concentrated discharge detection range W1 used in the concentrated discharge detection circuit 431. This is because the second discharge position H2 m The constant period Ts is obtained, so the influence of the disturbance is suppressed, and the first discharge position H1 is calculated. n More accurate discharge location.

[0133] <7. Description of Normal Operation and Concentrated Discharge Detection Operation of Wire EDM Device 100>

[0134] Figure 3 This is a timing chart for explaining the normal operation of the wire electrical discharge machining device 100 of the present invention. Figure 4 This timing diagram illustrates the operation of concentrated discharge detection in the wire EDM device 100 of the present invention. In the diagram, Agate represents the waveform of the second gate signal, Vg represents the waveform of the inter-electrode voltage in the machining gap 10, St represents the waveform of the discharge generation signal, Mgate represents the waveform of the first gate signal, and Is represents the waveform of the discharge current in the machining gap 10.

[0135] The operator inputs and sets the data of arbitrary machining conditions in advance into the control device 7. The machining condition data is stored in the storage unit 71 of the control device 7. The machining condition data stored in the storage unit 71 or the switching signal based on the machining condition is output to the pulse generating circuit 44 during machining.

[0136] The data of the machining conditions required for the operation of the machining power supply device of the embodiment include, for example, the rest time (off time) Of, the repetition frequency (discharge frequency) Mo of high-frequency discharge above 1 MHz, the duration (pulse width) Ma of the main discharge current Ia, the applied voltage (DC power supply voltage) Vo, the machining current (peak current value) Ip, the reference voltage Vr, the current reference value Ir for judging whether the discharge current is flowing, and the delay time Ta.

[0137] The control device 7 outputs data on the machining conditions, including the off time Of, the discharge frequency Mo, and the pulse width Ma, to the pulse generating circuit 44. The pulse generating circuit 44 then sets the machining condition data in the setting circuit. Furthermore, the control device 7 outputs a switching signal based on the applied voltage Vo to the variable DC power supply 11, thereby setting the DC power supply voltage to the applied voltage Vo. Furthermore, the control device 7 outputs data on the reference voltage Vr used to detect the occurrence of discharge to the voltage detector 2.

[0138] In addition, the control device 7 receives the new plate thickness L from the plate thickness calculation circuit 432. p In the case of data with plate thickness L, the input p The processing condition is adapted to the changed setting and the data of the newly changed processing condition is output to the pulse generating circuit 44.

[0139] During machining, the pulse generating circuit 44 measures the off-time Of of the machining conditions set by the setting circuit. At time t1 after the set off-time Of has elapsed, the pulse generating circuit 44 outputs a second gate signal Agate. The second gate signal Agate output by the pulse generating circuit 44 is supplied to the gate of the switching element 22 of the auxiliary power supply circuit 1B. As a result, the switching element 22 turns on, and a DC voltage for causing discharge from the DC power supply 21 of the auxiliary power supply circuit 1B is applied to the machining gap 10.

[0140] At time t1, the preliminary discharge current Ib(Is) does not flow in the machining gap 10. Then, at time t2, after an unspecified discharge standby time Tw from time t1, when discharge occurs in the machining gap 10, the preliminary discharge current Ib(Is) begins to flow in the machining gap 10, causing the inter-electrode voltage Vg to drop sharply. At this time, the preliminary discharge current Ib(Is) gradually increases.

[0141] When the inter-electrode voltage Vg decreases, the inter-electrode voltage Vg becomes lower than the reference voltage Vr. As a result, the voltage detector 2 outputs a discharge generation signal St having a short duration to the pulse generation circuit 44 and the discharge position calculation circuit 42 .

[0142] When the discharge occurrence signal St is input, the discharge position calculation circuit 42 obtains current values ​​from the auxiliary power supply upper current sensor 32A and the auxiliary power supply lower current sensor 32B, and calculates the discharge position twice during the rising period Tt and the constant period Ts of the preliminary discharge current Ib.

[0143] The first discharge position H1 as the discharge position in the rising period Tt calculated by the discharge position calculation circuit 42 n and the second discharge position H2 during the constant period Ts m is stored in the storage unit 45, and the first discharge position H1 n is output to the concentrated discharge detection circuit 431, the second discharge position H2 m The signal is output to the partial discharge detection circuit 433 .

[0144] The plate thickness calculation circuit 432 calculates the plate thickness based on the second discharge position H2 stored in the storage unit 45 in a time series manner. m The thickness L of the workpiece W is calculated using the information p , and the plate thickness L p The data is output to the control device 7.

[0145] The partial discharge detection circuit 433 detects the second discharge position H2 m The information is used to determine whether the discharge is locally biased. If the discharge is locally biased, a partial discharge signal Sb with a short duration is output to the pulse generating circuit 44. The operation during partial discharge detection will be described later.

[0146] The concentrated discharge detection circuit 431 detects the first discharge position H1 n The concentrated discharge is determined based on the information of the pulse generator circuit 44. When the concentrated discharge is detected, a concentrated discharge signal Ss with a short duration is output to the pulse generator circuit 44.

[0147] When the discharge generation signal St is input from the voltage detector 2, the pulse generation circuit 44 outputs the first gate signal Mgate at time t3, which is delayed by a time Ta from time t2. The switching element 12 of the main power supply circuit 1A then turns on, supplying a large main discharge current Ia from the main power supply circuit 1A to the machining gap 10. At this time, the second gate signal Agate is maintained, so the voltage of the DC power supply 11 of the main power supply circuit 1A is superimposed, causing the discharge current Is (the sum of the preliminary discharge current Ib and the main discharge current Ia) to rise rapidly to the set peak current value Ip.

[0148] On the other hand, when the pulse generating circuit 44 receives the concentrated discharge signal Ss from the concentrated discharge detecting circuit 431 between time t2 and time t3, it does not output the first gate signal Mgate and stops outputting the second gate signal Agate. Figure 4 ). As a result, the switching element 12 of the main power supply circuit 1A and the switching element 22 of the auxiliary power supply circuit 1B both become non-conductive, the inter-electrode voltage Vg drops rapidly, and the discharge current Is (preparatory discharge current Ib) drops sharply, thereby extinguishing the arc. In this case, at time t9 when the discharge current Is no longer flows, the pulse generating circuit 44 starts measuring the off time Of of the set processing condition. Then, at time t10 after the off time Of has passed, the second gate signal Agate is output again to turn on the switching element 22 of the auxiliary power supply circuit 1B, thereby starting the next discharge ( Figure 4 ).

[0149] When the pulse generating circuit 44 does not receive the concentrated discharge signal Ss from the concentrated discharge detecting circuit 431 between time t2 and time t3 ( Figure 3 ), after outputting the first gate signal Mgate, the output of the first and second gate signals Mgate and Agate ceases at time t4, a predetermined time period corresponding to the preset pulse width Ma. Consequently, at time t4, both the switching element 12 of the main power supply circuit 1A and the switching element 22 of the auxiliary power supply circuit 1B become non-conductive. As a result, the inter-electrode voltage Vg drops sharply, and the discharge current Is drops sharply from the set peak current value Ip, extinguishing the arc at time t5.

[0150] After the pulse generating circuit 44 supplies the first discharge current Is after the discharge occurs, it outputs the first gate signal Mgate ( Figure 3 Therefore, after stopping the output of the first gate signal Mgate, the pulse generating circuit 44 outputs the first gate signal Mgate again at time t6 after the pause width τoff determined by the discharge frequency Mo and the pulse width Ma.

[0151] While the discharge current Is (main discharge current Ia) continues to flow in the main power supply circuit 1A, the first gate signal Mgate is output at a high frequency according to the set discharge frequency Mo, and the switching element 12 of the main power supply circuit 1A is repeatedly turned on and off at a high speed to supply the discharge current Is.

[0152] At time t7, when the discharge current Is decays over time and falls below the current reference value Ir, and no longer flows, the pulse generating circuit 44 stops outputting the first gate signal Mgate, turning off the switching element 12 and beginning to measure the off-time Of for the set machining conditions. Then, at time t8, after the off-time Of has elapsed, the second gate signal Agate is again output, turning on the switching element 22 of the auxiliary power supply circuit 1B, thereby initiating the next discharge cycle.

[0153] <8. Description of Operation of Wire EDM Device 100 During Partial Discharge Detection>

[0154] Figure 9 This is a timing chart explaining the operation of the wire electrical discharge machining device 100 of the present invention during partial discharge detection.

[0155] When the pulse generating circuit 44 outputs the second gate signal Agate at time t1, a DC voltage for causing discharge is applied from the DC power supply 21 of the auxiliary power supply circuit 1B to the machining gap 10. Discharge occurs in the machining gap 10 at time t2. Subsequently, the preliminary discharge current Ib gradually increases in the machining gap 10, causing the inter-electrode voltage Vg to drop sharply. Due to this drop in the inter-electrode voltage Vg, the voltage detector 2 outputs a discharge occurrence signal St to the pulse generating circuit 44 and the discharge position calculation circuit 42.

[0156] When the discharge generation signal St is input from the voltage detector 2, the pulse generation circuit 44 outputs the first gate signal Mgate at time t3, supplying the main discharge current Ia from the main power supply circuit 1A to the machining gap 10. The discharge current Is, which is the sum of the preliminary discharge current Ib and the main discharge current Ia, rises sharply to the set peak current value Ip.

[0157] When the discharge occurrence signal St is input, the discharge position calculation circuit 42 obtains current values ​​from the auxiliary power supply upper current sensor 32A and the auxiliary power supply lower current sensor 32B, and calculates the discharge position twice during the rising period Tt and the constant period Ts of the preliminary discharge current Ib.

[0158] The second discharge position H2 which is the discharge position for the constant period Ts calculated by the discharge position calculation circuit 42 m The signal is stored in the storage unit 45 and output to the partial discharge detection circuit 433 .

[0159] The partial discharge detection circuit 433 detects the second discharge position H2 stored in the storage unit 45. m-1 Information, according to each small range W2 q From the start of processing, the small area W2 q The second discharge position H2 mFurthermore, the number of data including the second discharge position H2 output from the discharge position calculation circuit 42 is counted. m Small range W2 q Perform calculations in the small range W2 q When the count number is greater than the threshold value TH, the partial discharge signal Sb is output to the pulse generating circuit 44 ( Figure 9 ).

[0160] In normal operation, the pulse generating circuit 44 supplies the first discharge current Is after the discharge occurs, and then outputs the first gate signal Mgate in a manner that repeatedly turns on and off the switching element 12 at a high frequency of 1 MHz or higher according to the set discharge frequency Mo and pulse width Ma. However, when the partial discharge signal Sb is received from the partial discharge detecting circuit 433 at time t12, the output of the first gate signal Mgate is stopped after the time of receipt. Figure 9 As a result, both switching element 12 of main power supply circuit 1A and switching element 22 of auxiliary power supply circuit 1B become non-conductive, causing inter-electrode voltage Vg to drop sharply, and discharge current Is (preparatory discharge current Ib) to drop sharply, extinguishing the arc. In this case, at time t13, when discharge current Is stops flowing, pulse generating circuit 44 begins measuring the off-time Of for the set machining conditions. Then, at time t14, after the off-time Of has elapsed, the second gate signal Agate is output again, turning on switching element 22 of auxiliary power supply circuit 1B and initiating the next discharge cycle.

[0161] The machining power supply device according to the embodiment described above has shown several specific examples, but is not limited to the same configuration as the embodiment and can be modified in various ways without departing from the technical concept of the present invention.

[0162] [Industrial Applicability]

[0163] The present invention can be used in metal processing. In particular, the processing power supply device of the present invention is beneficial to wire cutting.

Claims

1. A wire electrical discharge machining device comprising: An auxiliary power supply circuit applies a voltage that causes discharge to occur to a machining gap formed by the wire electrode and the workpiece and supplies a pre-discharge current; A main power supply circuit supplies a main discharge current to the machining gap; a current detector detects the discharge current flowing between a pair of current-carrying bodies arranged above and below the workpiece and supplying the discharge current to the wire electrode and the machining gap, the discharge current including the pre-discharge current and the main discharge current, the pair of current-carrying bodies including an upper current-carrying body and a lower current-carrying body; and a discharge position calculation circuit, based on a first period from the rise of the waveform of the pre-discharge current supplied to the machining gap to the reaching of a certain current value and a second period from the reaching of the certain current value to the supply of the main discharge current. The discharge position is calculated based on each of the pre-discharge currents detected by the current detector. The current detector includes a sensor for detecting the pre-discharge current flowing through the machining gap due to application of a voltage from the auxiliary power supply circuit via the upper current-carrying body, and a sensor for detecting the pre-discharge current flowing through the machining gap due to application of a voltage from the auxiliary power supply circuit via the lower current-carrying body. The discharge position calculation circuit obtains the pre-discharge current from each of the sensors, calculates the area of ​​each pre-discharge current by calculating the integrated value of the pre-discharge current, and calculates the discharge position.

2. The wire discharge machining device according to claim 1, wherein The wire electrical discharge machining device further includes a concentrated discharge detection circuit configured to detect concentrated discharge based on a discharge position calculated during the first period.

3. The wire discharge machining device according to claim 2, wherein: When the concentrated discharge detection circuit determines that concentrated discharge has occurred, the wire electrical discharge machining device stops supplying the main discharge current from the main power supply circuit to the wire electrode.

4. The wire discharge machining device according to claim 1, wherein The wire electrical discharge machining device calculates the plate thickness based on the discharge position calculated during the second period.

5. The wire discharge machining device according to claim 1, wherein The wire electrical discharge machining device further includes a partial discharge detection circuit configured to estimate a shape of a machined surface of the workpiece based on a discharge position calculated during the second period and determine that the discharge is locally biased.

6. A wire discharge machining method, characterized in that: A voltage that causes discharge to occur is applied to a machining gap between a workpiece and a wire electrode, and a preliminary discharge current is supplied; thereafter, a main discharge current is supplied to the machining gap; the discharge current flowing between a pair of current-carrying bodies disposed one above the other across the workpiece and supplying the discharge current to the wire electrode and the machining gap is detected, the discharge current including the preliminary discharge current and the main discharge current, the pair of current-carrying bodies including an upper current-carrying body and a lower current-carrying body; a discharge position is detected based on current values ​​of the preliminary discharge current during a first period from when a waveform of the preliminary discharge current supplied to the machining gap rises until it reaches a certain current value, and during a second period from when the waveform reaches the certain current value until the main discharge current is supplied; the discharge position detection step comprises obtaining the preliminary discharge current from a sensor that detects the preliminary discharge current flowing through the upper current-carrying body and a sensor that detects the preliminary discharge current flowing through the machining gap through the lower current-carrying body, calculating the discharge position by calculating integrated values ​​of the preliminary discharge current to obtain areas. 7 . The wire discharge machining method according to claim 6 , further comprising determining concentrated discharge based on the discharge position calculated during the first period.

8. The wire discharge machining method according to claim 7, wherein: When concentrated discharge is detected, supply of the main discharge current to the wire electrode is stopped.

9. The wire discharge machining method according to claim 6, wherein: The plate thickness is calculated based on the discharge position calculated during the second period.

10. The wire discharge machining method according to claim 6, wherein: Furthermore, the shape of the machined surface of the workpiece is estimated based on the discharge position calculated during the second period, and it is determined that the discharge is locally biased.

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