Wire electrical discharge machining device

Abstract

To provide a wire electrical discharge machining device enabling highly accurate machining and reducing variation in machining dimension for each device to improve reproducibility of machining dimension.SOLUTION: A wire electrical discharge machining device includes: a pulse generation circuit outputting a voltage pulse for controlling a switching element in a bipolar circuit to a gate signal generation circuit using a differential system; a gate signal generation circuit provided with a photo coupler and a switching driver, where a photo coupler receives a differential voltage pulse from the pulse generation circuit and outputs the pulse to a switching driver, and the switching driver generates a gate signal driving the switching element; and a bipolar circuit as a bridge circuit to each side of which the switching element is provided, receives the gate signal to control the switching element and supplies the voltage pulse whose polarity is periodically switched, to a machining gap between a wire and a workpiece. The photo coupler is provided with a semi-fixed resistor in a signal input route.SELECTED DRAWING: Figure 2

Description

[Technical field]

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

[0002] 2. Description of the Related Art Wire electric discharge machining apparatuses are known that apply a voltage between a wire and a workpiece to generate a discharge current between the wire and the workpiece, thereby cutting the workpiece.

[0003] Patent Document 1 discloses a wire electric discharge machining apparatus that can achieve stable quality and machining performance by adjusting the electrode voltage between the wire and the workpiece and controlling the electrode distance between the wire and the workpiece. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2018-202606 A Summary of the Invention [Problem to be solved by the invention]

[0005] In the midst of demands for more stable quality and machining performance, it has become possible to machine fine surface roughness at high speed by increasing the frequency of the electrode gap voltage pulse between the wire and the workpiece. However, in wire EDM using high-frequency pulses, a phenomenon occurs in which minute changes in pulse width caused by individual differences in the threshold voltage of the electric element T present in the transmission path of the discharge pulse accumulate and appear in the electrode gap pulse width of the final stage. This phenomenon causes machine differences, which is a major factor that inhibits the reproducibility of machining performance in the machining condition database that specifies the state of the discharge pulse.

[0006] A voltage pulse that can be treated as a square wave in the low frequency range actually has a transition region where the voltage rises and falls. Therefore, in the high frequency range, the nature of a trapezoidal wave becomes evident. The electric element T that transmits the discharge pulse has a threshold voltage V th The threshold voltage V of the electrical element T th In many cases, the specifications allow for an individual difference of about 1V. th Due to individual differences in the input pulse, there will be a difference in the timing of the rising and / or falling edge of the output pulse relative to the input pulse. As a result, the input pulse width T in and output pulse width T out However, different phenomena occur for each wire EDM machine.

[0007] For example, the input peak voltage V peak 1 / 2 of the threshold voltage V of the electrical element T th If the reference value is set to , the threshold voltage V of the electrical element T is th is the input peak voltage V peak If the output pulse width is higher than 1 / 2, out is the input pulse width T in The threshold voltage V th is the input peak voltage V peak If the output pulse width is less than half of T out is the input pulse width T in It will be longer than that (Figure 1).

[0008] In other words, the input pulse width T in Even if the reference threshold voltage V Rth (hereinafter, the reference threshold voltage) than the threshold voltage V th When is high, the reference output pulse width T Rout Output pulse width T out The reference threshold voltage V Rth than the threshold voltage V th When is low, the reference output pulse width T Rout Output pulse width T outIn a typical voltage setting, the threshold voltage V th is the reference threshold voltage V Rth Therefore, the reduction in the pulse width accumulates each time the discharge pulse passes through the electric element T, and the pulse width tends to become shorter with each stage.

[0009] Therefore, the input pulse width T in Even if the threshold voltage V of each electrical element T is the same, th Due to individual differences, the output pulse width T out This results in differences in the final discharge pulse width even for circuits with the same specifications. And because the discharge pulse width and the electric discharge machining energy are proportional, the electric discharge machining conditions differ for each device, even for devices of the same model. Due to this effect, even if the machining performance of a single wire electric discharge machining device is improved, there will be variation in the machining results even when machining is performed under the same machining conditions for each mass-produced wire electric discharge machining device, and the reproducibility of the machining dimensions for each device will be low. Therefore, there was a problem specific to wire electric discharge machining using high-frequency pulses, in that it was difficult to improve the machining dimensional accuracy of the entire machining condition database.

[0010] The present invention has been made in view of the above circumstances, and aims to reduce the threshold voltage V th This eliminates the difference in pulse width at the final stage that occurs due to the accumulation of individual differences in the number of wires, thereby providing a wire electric discharge machining device that can reduce the variation in machining dimensions between devices and improve the reproducibility of machining dimensions and machining performance. [Means for solving the problem]

[0011] According to the present invention, the following inventions are provided. [1] A wire electric discharge machining apparatus comprising a pulse generating circuit, a gate signal generating circuit, and a bipolar circuit, wherein the pulse generating circuit outputs voltage pulses for controlling a switching element of the bipolar circuit to the gate signal generating circuit in a differential manner, the gate signal generating circuit comprises a photocoupler and a switching driver, the photocoupler receives a differential voltage pulse from the pulse generating circuit and outputs it to the switching driver, the switching driver generates a gate signal for driving the switching element, the bipolar circuit is a bridge circuit having the switching element on each side, the switching element is controlled by receiving the gate signal, and a voltage pulse whose polarity periodically switches is supplied to a machining gap between a wire and a workpiece, and the photocoupler comprises a triangular resistor in a signal input path. [2] The wire electric discharge machining apparatus according to [1], further comprising a fixed resistor arranged in series with the semi-fixed resistor. Effect of the Invention

[0012] In the wire electric discharge machining apparatus according to the present invention, a triangular resistor is provided in the signal input path of the photocoupler in the gate signal generating circuit, so that the high frequency amplitude of the no-load inter-electrode pulse waveform can be adjusted for each apparatus, thereby correcting the variation in machining results due to machine differences and improving the reproducibility of the machining dimensions. [Brief description of the drawings]

[0013] [Figure 1] 1 is an explanatory diagram of a change in output pulse width Tout due to a threshold voltage Vth relative to an input peak voltage Vpeak of an electric element T. FIG. [Diagram 2] 1 is a schematic diagram of an electric discharge machining circuit 1 in a wire electric discharge machining apparatus according to an embodiment of the present invention. [Diagram 3] FIG. 4 is a diagram showing a no-load inter-electrode pulse waveform of the wire electric discharge machining device according to the embodiment of the present invention. [Figure 4]FIG. 2 is a circuit diagram of a gate signal generating circuit 30 used in the measurement. [Diagram 5] FIG. 13 is a diagram showing a no-load inter-pole pulse waveform when the resistance value of the variable resistor R64 is fixed at approximately 330 Ω and the resistance value of the variable resistor R73 is changed. [Figure 6] 13 is a graph showing the change in the potential difference between high-frequency amplitudes W1 and W2 of a no-load inter-electrode pulse waveform when the resistance value of variable resistor R64 is fixed at approximately 330 Ω and the resistance value of variable resistor R73 is changed. [Figure 7] 13 is a graph showing peak voltage values ​​A1, A2 of a no-load inter-contact pulse waveform when the resistance value of variable resistor R64 is fixed at approximately 330 Ω and the resistance value of variable resistor R73 is changed. [Figure 8] FIG. 13 is a diagram showing a no-load inter-pole pulse waveform when the resistance value of the variable resistor R73 is fixed at approximately 330 Ω and the resistance value of the variable resistor R64 is changed. [Figure 9] 13 is a graph showing the change in the potential difference between high-frequency amplitudes W1 and W2 of a no-load inter-electrode pulse waveform when the resistance value of variable resistor R73 is fixed at approximately 330 Ω and the resistance value of variable resistor R64 is changed. [Figure 10] 13 is a graph showing peak voltage values ​​A1, A2 of a no-load inter-contact pulse waveform when the resistance value of variable resistor R73 is fixed at approximately 330 Ω and the resistance value of variable resistor R64 is changed. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, embodiments of the present invention will be described. Various features shown in the following embodiments can be combined with each other. Also, each feature can be an invention independently.

[0015] 1. Wire Electric Discharge Machining Equipment In wire electric discharge machining, a predetermined voltage pulse is applied to a machining gap formed between a wire provided in a wire electric discharge machining device and a workpiece to generate intermittent electric discharges, and material is removed from the workpiece by electric discharge machining energy, cutting the workpiece into a desired machining shape. The wire electric discharge machining device is equipped with an electric discharge machining circuit 1.

[0016] 2 shows a schematic diagram of an electric discharge machining circuit 1 in a wire electric discharge machining apparatus according to one embodiment of the present invention. The electric discharge machining circuit 1 is a circuit for applying a voltage for generating an electric discharge in a machining gap between a wire and a workpiece. The electric discharge machining circuit 1 may include a pulse generating circuit 10, a communication cable 20, a gate signal generating circuit 30, and a bipolar circuit 40. The electric discharge machining circuit 1 includes four systems SGU, SGL, GGU, and GGL that are respectively connected to switching elements 401a, 401b, 401c, and 401d included in the bipolar circuit 40.

[0017] 1.1 Pulse Generator 10 The pulse generating circuit 10 is a circuit that can output voltage pulses for controlling the switching elements 401a to 401d of the bipolar circuit 40 to the gate signal generating circuit 30 in a differential manner. Specifically, the pulse generating circuit 10 includes an FPGA 101 (Field Programmable Gate Array) for generating discharge pulses and a differential output driver 102. A predetermined voltage pulse generated by the FPGA 101 can be input to each terminal of the differential output driver 102 for each system connected to the switching elements 401a to 401d. In the example of FIG. 2, the system SGU is connected to the switching element 401a, the system SGL is connected to the switching element 401b, the system GGU is connected to the switching element 401c, and the system GGL is connected to the switching element 401d. For example, a voltage pulse can be input to each terminal of the differential output driver 102 so that the switching elements 401a and 401b of the bipolar circuit 40 are driven to have a reverse polarity, and the switching elements 401c and 401d are driven to have a positive polarity.

[0018] The differential output driver 102 is connected to the communication cable 20 and can output a differential voltage pulse to the gate signal generation circuit 30 via the communication cable 20. The differential output can reduce noise. The ferrite core 21 removes noise from the communication cable 20 that is passed through it.

[0019] 1.2 Gate signal generating circuit 30 The gate signal generating circuit 30 is a circuit that can receive differential voltage pulses from the pulse generating circuit 10 as inputs and generate gate signals that drive the switching elements 401a to 401d of the bipolar circuit 40. In the gate signal generating circuit 30 shown in Fig. 2, only the configuration of the SGU system is shown, but the SGU, SGL, GGU, and GGL systems have the same configuration. The symbols of the components included in the SGL, GGU, and GGL systems (not shown) are those in which the suffix "a" of the symbol of the component included in the SGU system is changed to "b" for SGL, "c" for GGU, and "d" for GGL.

[0020] The gate signal generating circuit 30 includes photocouplers 301a, 301b, 301c, and 301d connected to the switching elements 401a, 401b, 401c, and 401d, respectively, and switching drivers 302a, 302b, 302c, and 302d. The photocouplers 301a to 301d are used to transmit signals from the input side to the output side in an electrically insulated state, and receive differential voltage pulses from the pulse generating circuit 10 to output signals to the switching drivers 302a to 302d, respectively. The switching drivers 302a to 302d generate gate signals for driving the switching elements 401a to 401d.

[0021] The signal input paths of the photocouplers 301a to 301d are provided with resistors connected in series. Specifically, a fixed resistor (not shown) and semi-fixed resistors Ra, Rb, Rc, and Rd are provided. The fixed resistors are provided as protective resistors to prevent excessive current from flowing through the photocouplers 301a to 301d. The resistance value of the fixed resistors is preferably about 250 to 300 Ω. The semi-fixed resistors Ra to Rd are provided to change the value of the current flowing through the photocouplers 301a to 301d by adjusting their resistance values, thereby adjusting the inter-electrode pulse waveform applied to the wire and the workpiece. A specific adjustment method will be described later.

[0022] 1.3 Bipolar Circuit 40 The bipolar circuit 40 is a bridge circuit in which switching elements 401a to 401d are provided on each side. The switching elements 401a to 401d receive gate signals of different polarities from the gate signal generating circuit 30, and thereby each switching element 401a to 401d is controlled to supply a voltage pulse whose polarity periodically switches (hereinafter, bipolar pulse) to the machining gap between the wire and the workpiece. The switching elements 401a to 401d can be field effect transistors, for example, MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors).

[0023] In the bipolar circuit 40, the connection point of the switching elements 401a and 401c is the input section 402a, and the connection point of the switching elements 401b and 401d is the input section 402b. The connection point of the switching elements 401a and 401d is the output section 403a, and the connection point of the switching elements 401b and 401c is the output section 403b. A DC power source (not shown) is connected to the input sections 402a and 402b, and a DC voltage is applied to the input sections 402a and 402b. The output sections 403a and 403b are connected to the wire and the workpiece, respectively. The switching elements 401a to 401d are controlled to be turned on and off by the above-mentioned gate signal, so that a bipolar pulse is output from the output sections 403a and 403b, and a voltage is applied to the machining gap, enabling machining.

[0024] 2. Pulse adjustment method FIG. 3 is an example of a diagram showing a high-frequency no-load inter-electrode pulse waveform. W1 is the high-frequency amplitude on the positive polarity side, and W2 is the high-frequency amplitude on the reverse polarity side. A1 is the peak voltage on the positive polarity side, and A2 is the peak voltage on the reverse polarity side. In the pulse adjustment method according to the present invention, the high-frequency amplitudes W1 and W2 of the inter-electrode pulse waveform of each electric discharge machining device are adjusted to be set to a specified value. For example, the specified value can be 80 to 90 V, and it is preferable to adjust it to be within ±3 V of the specified value.

[0025] The high frequency amplitudes W1 and W2 can be adjusted by changing the resistance values ​​of the semi-fixed resistors Ra to Rd provided in the signal input paths of the photocouplers 301a to 301d. For example, in the example shown in FIG. 3, the high frequency amplitude W1 can be adjusted by changing the resistance value of the semi-fixed resistor Rb provided in the gate signal generating circuit 30 connected to the switching element 401b. The high frequency amplitude W2 can be adjusted by changing the resistance value of the semi-fixed resistor Rd provided in the gate signal generating circuit 30 connected to the switching element 401d. If the resistance values ​​of the semi-fixed resistors Ra to Rd are made too small, there is a risk that the ferrite core 21 provided in the communication cable 20 will generate heat. Therefore, it is preferable that the resistance values ​​of the semi-fixed resistors Ra to Rd are adjusted in a range of 300Ω or more.

[0026] In a wire electric discharge machining apparatus using high frequency pulses, the threshold voltage V of an electric element T provided in an electric discharge machining circuit 1 is th The pulse width of the final inter-pole pulse may vary from the pulse width of the input pulse. th Due to individual differences, the pulse width of the inter-electrode pulse differs for each device, causing machine-to-machine differences in the machining results. By changing the resistance values ​​of the semi-fixed resistors Ra to Rd, the input current to the photocouplers 301a to 301d changes, and the rise of the voltage pulse also changes. This changes the minute time it takes for the photocouplers 301a to 301d to reach their threshold voltages, and the pulse width also changes. When the pulse width changes, the high-frequency amplitudes W1 and W2 of the no-load inter-electrode pulse in the final stage also change.

[0027] Therefore, in a wire electric discharge machining device using a high frequency pulse, the size of the pulse width can be evaluated by the magnitude of the high frequency amplitudes W1, W2 of the no-load inter-electrode pulse waveform. Specifically, the larger the high frequency amplitudes W1, W2, the longer the pulse width tends to be, and the longer the pulse width, the greater the electric discharge machining energy. In this pulse adjustment method, the high frequency amplitudes W1, W2 of the no-load inter-electrode pulse in the final stage are adjusted to a preset value, thereby adjusting the threshold voltage V of the electric element T. thThis pulse adjustment method enables high-precision machining using high-frequency pulses, while at the same time making the electric discharge machining energy by each electric discharge machining device uniform and improving the reproducibility of the machining dimensions. Note that in this specification, high precision refers to high precision in the machining dimensions and fine surface roughness of the machined surface.

[0028] By configuring the input current of the photocouplers 301a to 301d to be adjusted by changing the resistance value instead of adjusting the magnitude of the voltage pulse output by the pulse generating circuit 10, which is the original voltage, it is possible to correct the machine difference without changing the generated pulse. Also, since the correction can be performed in units of 1 ns, which is shorter than the minimum clock time (for example, 12.5 nsec) used in the pulse generating circuit, the pulse correction can be performed with high accuracy.

[0029] 3. Working Example Specific experimental results of the pulse adjustment method will be described below.

[0030] 3.1 Overview By changing the resistance values ​​of variable resistors R64, R73 provided in the signal input paths of photocouplers 301b, 301d provided in the gate signal generating circuit 30 of the electric discharge machining circuit 1, the effect on the no-load inter-electrode pulse waveform was evaluated.

[0031] 3.2 Measurement method FIG. 4 shows a circuit diagram of the system in which the pulse adjustment method of this experiment was performed among the gate signal generating circuits 30. In this experiment, the resistance values ​​of the variable resistors R64 and R73 of the gate signal generating circuits 30 of the system GGL and the system SGL were changed to confirm the change in the no-load inter-electrode pulse waveform. Specifically, (1) the no-load inter-electrode pulse waveform when the resistance value of the variable resistor R64 was fixed at about 330Ω and the resistance value of the variable resistor R73 was changed between 0 and 450Ω, and (2) the no-load inter-electrode pulse waveform when the resistance value of the variable resistor R73 was fixed at about 330Ω and the resistance value of the variable resistor R64 was changed between 0 and 450Ω were measured. The no-load inter-electrode pulse waveform was confirmed using an oscilloscope.

[0032] 3.3 Measurement results (1) Change in no-load inter-contact pulse waveform due to the resistance value of variable resistor R73 Figure 5 shows the no-load inter-electrode pulse waveform when the resistance value of variable resistor R64 is fixed at approximately 330 Ω and the resistance value of variable resistor R73 is changed. Figure 6 shows the change in the potential difference of the high-frequency amplitudes W1 and W2 of the no-load inter-electrode pulse waveform. Figure 7 shows the peak voltage values ​​A1 and A2 of the no-load inter-electrode pulse waveform. When the resistance value of variable resistor R73 changes, the high-frequency amplitude W1 on the positive polarity side changes, but the high-frequency amplitude W2 on the reverse polarity side changes very little (Figure 6). The amount of change in the high-frequency amplitude W1 with respect to the change in resistance value (0 to 450 Ω) was 58 V. The peak voltage values ​​A1 and A2 changed very little (Figure 7).

[0033] (2) Change in no-load inter-contact pulse waveform due to the resistance value of variable resistor R64 Figure 8 shows the no-load inter-electrode pulse waveform when the resistance value of variable resistor R73 is fixed at approximately 330 Ω and the resistance value of variable resistor R64 is changed. Figure 9 shows the change in the potential difference of the high-frequency amplitudes W1 and W2 of the no-load inter-electrode pulse waveform. Figure 10 shows the peak voltage values ​​A1 and A2 of the no-load inter-electrode pulse waveform. When the resistance value of variable resistor R64 changes, the high-frequency amplitude W2 on the reverse polarity side changes, but the high-frequency amplitude W1 on the positive polarity side changes very little (Figure 9). The amount of change in the high-frequency amplitude W2 with respect to the change in resistance value (0 to 450 Ω) was 46 V. The peak voltage values ​​A1 and A2 changed very little (Figure 10).

[0034] From the above results, it was found that it is possible to adjust the no-load inter-contact pulse waveform by changing the resistance values ​​of the variable resistors R64 and R73 provided in the signal input paths of the photocouplers 301b and 301d. Since the peak voltage values ​​A1 and A2 hardly changed, it was found that the machine difference of the high frequency pulse waveform can be corrected by adjusting only the resistance values ​​of the variable resistors R64 and R73. [Explanation of symbols]

[0035] 1: Electrical discharge machining circuit 10: Pulse generation circuit 101: FPGA 102: Differential output driver 20: Communication cable 21: Ferrite core 30: Gate signal generation circuit 301a~301d: Photocouplers 302a to 302d: switching drivers 40: Bipolar circuit 401a to 401d: switching elements 402a, 402b: Input section 403a, 403b: Output section A1, A2: Peak voltage value Ra~Rd: Semi-fixed resistor T: Electrical element T in : Input pulse width T out : Output pulse width T Rout : Reference output pulse width V peak : Input peak voltage V th : Threshold voltage V Rth : Reference threshold voltage W1: High frequency amplitude W2: High frequency amplitude

Claims

1. A wire electric discharge machining apparatus including a pulse generating circuit, a gate signal generating circuit, and a bipolar circuit, the pulse generating circuit differentially outputs a voltage pulse for controlling a switching element of the bipolar circuit to the gate signal generating circuit; the gate signal generation circuit includes a photocoupler and a switching driver, the photocoupler receives a differential voltage pulse from the pulse generation circuit and outputs the differential voltage pulse to the switching driver, and the switching driver generates a gate signal for driving the switching element; The bipolar circuit is a bridge circuit in which the switching element is provided on each side, and the switching element is controlled by receiving the gate signal to supply a voltage pulse whose polarity periodically switches to the machining gap between the wire and the workpiece; The photocoupler includes a semi-fixed resistor in a signal input path of the wire electric discharge machining apparatus.

2. 2. The wire electric discharge machining apparatus according to claim 1, The wire electric discharge machining apparatus further comprises a fixed resistor arranged in series with the semi-fixed resistor.

Images