WO2016147327A1

WO2016147327A1 - Electrical discharge machining apparatus

Info

Publication number: WO2016147327A1
Application number: PCT/JP2015/057963
Authority: WO
Inventors: 祐飛佐々木
Original assignee: 三菱電機株式会社
Priority date: 2015-03-17
Filing date: 2015-03-17
Publication date: 2016-09-22
Also published as: JPWO2016147327A1; JP5968565B1

Abstract

An electrical discharge machining apparatus (100) comprises: power sources (1, 2) for outputting voltage to be applied across an electrode gap (5) between an electrode (3) and a workpiece (4); switches (9, 10) for switching the voltage that said power sources (1, 2) apply across said electrode gap on and off; a detection device (6) for detecting the state of discharge in the electrode gap (5) and outputting the detection results; and a control device (8) for controlling the switches (9, 10) using the detection results from the detection device (6) to control the voltage applied across the electrode gap (5), and, on the basis of changes in the state of discharge when a first discharge is generated in the electrode gap (5), determining the conditions for generating a second discharge across the electrode gap (5). Obtained thereby is an electrical discharge machining apparatus (100) for repeatedly performing a preliminary discharge and a main discharge with which the quality of the machined surface of a multi-element conjugate material can be improved.

Description

EDM machine

The present invention relates to an electric discharge machining apparatus for machining a workpiece by electric discharge machining in which preliminary discharge and main discharge are repeated.

An electric discharge machining apparatus is an apparatus that generates a pulsed discharge between an electrode and a workpiece that are disposed opposite to each other in water, and uses the thermal energy to process the workpiece. Patent Document 1 relates to a wire-cut electric discharge machining power supply, including a high voltage main power supply, a low voltage main power supply, a sub power supply, a voltage detection circuit for detecting a gap voltage, and a power supply control circuit for controlling the application timing of each of the three power supplies. It is described that discharge is started by voltage application by a sub power source, and voltages having different pulse widths are applied by a high voltage main power source or a low voltage main power source according to information on a gap voltage after the discharge starts.

Japanese Patent Laid-Open No. 3-92220

The electrical discharge machining apparatus performs electrical discharge machining by repeating preliminary discharge and main discharge executed after the preliminary discharge. When the workpiece is a multi-element bonding material that is a difficult-to-process material, a high resistance element and a low resistance element having different resistance values are mixed, so that the state of preliminary discharge is not uniform. In order to improve the machining efficiency, it is necessary to set the intensity of the discharge pulse of the main discharge in accordance with the resistance value of the element in the workpiece that has generated the preliminary discharge.

An object of the present invention is to obtain an electric discharge machining apparatus capable of improving the quality of a processed surface of a multi-element bonded material in electric discharge machining in which preliminary discharge and main discharge are repeated.

An electric discharge machining apparatus according to the present invention includes a power source that outputs a voltage applied between electrodes between a electrode and a workpiece, a switch that turns on or off a voltage that the power supply applies to the gap, and the gap between the electrodes. A detection device that detects a discharge state and outputs a detection result; controls a switch using the detection result of the detection device to control a voltage applied between the electrodes; and a first discharge between the electrodes And a control device that determines a condition for generating a second discharge between the electrodes based on a change in a discharge state when the voltage is generated.

According to the present invention, it is possible to obtain an electric discharge machining apparatus capable of improving the quality of the machined surface of the multi-element bonding material in the electric discharge machining in which the preliminary discharge and the main discharge are repeated.

The figure which shows the electric discharge machining apparatus which concerns on Embodiment 1. The figure which shows the control apparatus with which the electric discharge machining apparatus which concerns on Embodiment 1 is provided Enlarged view of multi-element combination Enlarged view of multi-element combination Timing chart of electric discharge machining executed by electric discharge machining apparatus according to Embodiment 1 The figure which shows an example of the change by the time of the voltage between electrodes between electrodes and a workpiece or current between electrodes The figure which shows the example which determines main discharge time using change time The figure which shows an example of the table which described the relationship between the material of a workpiece, the 1st threshold value, the 2nd threshold value, a change time threshold value, and the main discharge time. The flowchart which shows an example of the process at the time of the electric discharge machining apparatus which concerns on Embodiment 1 performs an electric discharge machining The figure which shows the 2nd switch which concerns on the modification 1 of Embodiment 1. FIG. The figure which shows the electric discharge machining apparatus which concerns on Embodiment 2. Timing chart of electric discharge machining performed by electric discharge machining apparatus according to Embodiment 2

Hereinafter, an electric discharge machining apparatus according to an embodiment of the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments. Hereinafter, the term “resistance” refers to electric resistance.

Embodiment 1 FIG.
FIG. 1 is a diagram illustrating an electric discharge machining apparatus according to the first embodiment. FIG. 2 is a diagram illustrating a control device included in the electric discharge machining apparatus according to the first embodiment. The electric discharge machining apparatus 100 includes

power sources

1 and 2 that output a voltage to be applied to the gap 5 that is a gap formed between the electrode 3 and the workpiece 4, and a voltage that the

power sources

1 and 2 provide to the gap 5. Switches 9 and 10 that are turned on or off, a detection device 6 that detects the discharge state of the gap 5 and outputs a detection result, and operates the switches 9 and 10 using the detection result of the detection device 6 to open the gap 5 For generating a main discharge as a second discharge in the gap 5 based on a change in the discharge state when a preliminary discharge as the first discharge is generated in the gap 5. And a control device 8 for determining. In the first embodiment, the electric discharge machining apparatus 100 further includes a moving device 15 that moves the electrode 3 and an input device 8I that inputs control information to the control device 8.

The electric discharge machining apparatus 100 processes the workpiece 4 by applying a voltage between the electrode 3 and the workpiece 4 and generating electric discharge between the electrodes 5. Examples of the processing of the workpiece 4 include melt cutting or shape carving. The electrode 3 is a conductor. When the electric discharge machining apparatus 100 melts and cuts the workpiece 4, a wire is used for the electrode 3. When the electric discharge machining apparatus 100 engraves the workpiece 4, a mold for engraving is used for the electrode 3. In the electric discharge machining, since the electric discharge is generated between the electrode 3 and the workpiece 4, the workpiece 4 is a conductor.

Power supplies

1 and 2 are DC power supplies. Hereinafter, the power source 1 is appropriately referred to as a first power source 1, and the power source 2 is appropriately referred to as a second power source 2. The voltage of the first power supply 1 is higher than the voltage of the second power supply 2. In the first embodiment, the electric discharge machining apparatus 100 includes the first power supply 1 and the second power supply 2, but the first power supply 1 is boosted or stepped down by a DC (Direct Current) / DC converter with one power supply. The second power source 2 may be used instead.

The switch 9 is provided between the second power source 2, the electrode 3 and the workpiece 4. The switch 10 is provided between the first power source 1, the electrode 3, and the workpiece 4. Hereinafter, the switch 10 is appropriately referred to as a first switch 10, and the switch 9 is appropriately referred to as a second switch 9. The first switch 10 includes

switching elements

10A and 10B. The

switching elements

10A and 10B are semiconductor elements such as bipolar transistors or FETs (Field Effect Transistors), but are not limited to these. The switching element 10 A is provided between the positive electrode of the first power supply 1 and the electrode 3. The switching element 10 B is provided between the workpiece 4 and the negative electrode of the first power supply 1.

The second switch 9 has switching

elements

9A and 9B. The

switching elements

9A and 9B are the same as the

switching elements

10A and 10B of the first switch 10. The switching element 9 A is provided between the positive electrode of the second power supply 2 and the electrode 3. The switching element 9 B is provided between the workpiece 4 and the negative electrode of the second power supply 2.

The detection device 6 includes a first detection device 6A and a second detection device 6B. The first detection device 6A detects that the absolute value of the voltage at the gap 5 in the preliminary discharge, which is the first discharge, is lower than the absolute value of the first threshold, and outputs the detection result. The second detection device 6B detects that the absolute value of the voltage at the gap 5 in the preliminary discharge is less than the absolute value of the second threshold, and outputs the detection result. In the first embodiment, both the first detection device 6A and the second detection device 6B use a comparator.

The first detection device 6A and the second detection device 6B both detect the voltage between the electrodes 5. Hereinafter, the voltage between the electrodes 5 is appropriately referred to as an electrode voltage, and the current flowing between the electrodes 5 is appropriately referred to as an electrode current. The first detection device 6A compares the detected inter-electrode voltage with the absolute value of the first threshold value, and outputs a signal when the inter-electrode voltage falls below the absolute value of the absolute value of the first threshold value. This signal is a signal indicating that the voltage between the electrodes has fallen below the absolute value of the first threshold, and will be referred to as a first signal as appropriate in the following. The first signal is input to the control device 8. The second detection device 6B compares the detected inter-electrode voltage with the absolute value of the second threshold value. The absolute value of the second threshold value is smaller than the absolute value of the first threshold value. The second detection device 6B outputs a signal when the inter-electrode voltage falls below the absolute value of the second threshold value. This signal is a signal indicating that the inter-electrode voltage has fallen below the absolute value of the second threshold, and will be referred to as a second signal as appropriate hereinafter. The second signal is input to the control device 8.

In the first embodiment, the detection device 6 includes two comparators having different thresholds, that is, the first detection device 6A and the second detection device 6B, but the detection device 6 is not limited to such a configuration. The detection device 6 may switch the threshold value of one comparator.

The control device 8 acquires the detection result of the detection device 6 and controls the switches 9 and 10 using the acquired detection result. The control device 8 applies a voltage to the gap 5 by controlling the switches 9 and 10. Thus, the control device 8 controls the switches 9 and 10 using the detection result of the detection device 6 to control the interelectrode voltage. Specifically, the control device 8 changes the time during which the second switch 9 is turned on, so that the magnitude of the peak value of the interelectrode current in the main discharge becomes constant among the plurality of main discharges. To do.

Also, the control device 8 changes the distance between the electrode 3 and the workpiece 4 by moving the electrode 3 by controlling the moving device 15. The control device 8 receives information necessary for controlling the switches 9 and 10 and the moving device 15 from the input device 8I.

The input device 8I is exemplified by a touch panel, a keyboard, a mouse, a trackball, or a combination thereof. Examples of the moving device 15 include a device provided with a linear motor and a table moved by the linear motor, or a device provided with a ball screw, an electric motor for rotating the screw, and a table moved by the ball screw.

2, the control device 8 includes a processing unit 8P, a storage unit 8M, and an input / output unit 8IO. The processing unit 8P is a processor such as a CPU (Central Processing Unit). The storage unit 8M is a RAM (Random Access Memory), a ROM (Read Only Memory), a hard disk drive, a storage device, or a storage device that combines these. The input / output unit 8IO is an interface circuit that serves as an interface between the control device 8 and an external device connected to the control device 8. The detection device 6, the switches 9, 10 and the moving device 15 shown in FIG. 1 are connected to the input / output unit 8IO.

The storage unit 8M stores a computer program for the control device 8 to execute processing for controlling the electric discharge machining apparatus 100 according to the first embodiment. The processing unit 8P reads the above-described computer program from the storage unit 8M and controls the electric discharge machining apparatus 100.

3 and 4 are enlarged views of the multi-element combination. 3 and FIG. 4 includes an element 51 and an element 52. In the multi-element combination 50, the resistance values of the

elements

51 and 52 and the particle sizes of the

elements

51 and 52 are often different. In this example, the particle size of the element 52 is larger than that of the element 51. When such a multi-element combined body 50 is subjected to electric discharge machining, the resistance values of the

elements

51 and 52 are different, and as a result, the melting amount of the

elements

51 and 52 is different. As a result, either of the

elements

51 and 52 is melted first. Large elements 52 may fall out and become vacancies. As a result, when the multi-element combined body 50 is subjected to electric discharge machining, a crater may be formed on the surface and the machining surface may become rough.

The electric discharge machining apparatus 100 determines the energy of main discharge so that both elements can be melted in a balanced manner by discriminating between a high resistance element and a low resistance element by preliminary discharge, so that the multi-element bonding material can be stabilized. While processing, improve the quality of the processed surface. Next, processing when the electric discharge machining apparatus 100 according to Embodiment 1 performs electric discharge machining will be described.

FIG. 5 is a timing chart of electric discharge machining executed by the electric discharge machining apparatus according to the first embodiment. When the electrical discharge machining apparatus 100 performs electrical discharge machining on the workpiece 4, preliminary electrical discharge and main electrical discharge are performed. The preliminary discharge is a discharge for breaking the insulation between the electrode 3 and the workpiece 4 before the workpiece 4 is processed by the discharge. The main discharge is a discharge after dielectric breakdown occurs between the electrode 3 and the workpiece 4 due to the preliminary discharge, and is a discharge for melting the workpiece 4. The electric discharge machining apparatus 100 processes the workpiece 4 by removing a part of the surface of the workpiece 4 by repeating the preliminary discharge and the main discharge over time.

5 shows the timing of the first control signal 13 for turning on (ON) or turning off (OFF) the first switch 10 in the preliminary discharge. MD in FIG. 5 indicates the timing of the second control signal 14 for turning on (ON) or turning off (OFF) the second switch 9 in the main discharge. V in FIG. 5 indicates an interelectrode voltage, and I indicates an interelectrode current. A change in the interelectrode voltage V is indicated by a solid line 17, and a change in the interelectrode current I is indicated by a solid line 18. In FIG. 5, Vc1 is the first threshold value Vc2 of the interelectrode voltage V, the second threshold value of the interelectrode voltage V, Ic1 is the first threshold value of the interelectrode current I, and Ic2 is the second threshold value of the interelectrode current I. is there. The absolute value of the first threshold value Vc1 is smaller than the absolute value of the second threshold value Vc2. The horizontal axis in FIG. 5 is time t.

When the electrical discharge machining device 100 starts preliminary discharge, the control device 8 turns on the

switching elements

10A and 10B of the first switch 10 by turning on the first control signal 13 at time t = t1. Then, a voltage is applied from the first power source 1 to the electrode 3 and the workpiece 4 via the first switch 10. In this state, the control device 8 controls the moving device 15 to reduce the distance between the electrode 3 and the workpiece 4. Then, dielectric breakdown occurs between the electrode 3 and the workpiece 4, and a discharge occurs between the electrodes 5. This discharge is a preliminary discharge. In the example shown in FIG. 5, dielectric breakdown occurs at the timing of time t = t2. When dielectric breakdown occurs, the interelectrode voltage V decreases.

When a preliminary discharge occurs between the electrodes 5, an arc current, that is, an electrode current I flows through the electrodes 5, and the voltage V between the electrodes drops. In the first embodiment, the electric discharge machining apparatus 100 ends the preliminary discharge at the timing of time t = t4 and starts the main discharge at the same time. At the timing of time t = t4, the control device 8 turns off the first control signal 13, thereby turning off the

switching elements

10A and 10B of the first switch 10. At the same time, the control device 8 turns on the

switching elements

9A and 9B of the second switch 9 by turning on the second control signal 14. Then, a voltage is applied between the electrode 3 and the workpiece 4 from the second power source 2 via the second switch 9. The discharge after the preliminary discharge is the main discharge.

After time t = t4, a main discharge is generated between the electrodes 5 due to the voltage of the second power supply 2 applied between the electrode 3 and the workpiece 4. As shown in FIG. 5, the inter-electrode current I of the main discharge is larger than the inter-electrode current of the preliminary discharge. Due to the main discharge, the workpiece 4 is melted, a part of the workpiece 4 is removed from the surface, and the processing proceeds. At the timing of time t = t5, the control device 8 turns off the

switching elements

9A and 9B of the second switch 9 and ends the main discharge. After the main discharge is completed, the control device 8 turns on the

switching elements

10A and 10B of the first switch 10 again at time t = t6, and repeats the preliminary discharge and the main discharge.

In the first embodiment, the control device 8 determines energy for generating the second discharge between the electrodes based on the change in the discharge state when the first discharge is generated between the electrodes. Specifically, the control device 8 sets the gap 5 between the main discharges based on the amount of time Δtc until the gap voltage V during the preliminary discharge changes from the first threshold value Vc1 to the second threshold value Vc2. A time Δtp for applying the voltage is determined. Hereinafter, the time Δtc is appropriately referred to as a change time Δtc, and the time Δtp is appropriately referred to as a main discharge time Δtp. In the main discharge, the inter-electrode voltage V is the voltage of the second power supply 2 and is constant, so the control device 8 changes the main discharge time Δtp by changing the main discharge time Δtp.

When the change time Δtc is relatively short, the resistance of the workpiece 4 is relatively low, and when the change time Δtc is relatively long, the resistance of the workpiece 4 is relatively high. That is, since the change time Δtc corresponds to the resistance of the workpiece 4, the control device 8 can determine the magnitude of the resistance of the workpiece 4 using the change time Δtc. When the workpiece 4 is a multi-element bonding material including a low resistance element and a high resistance element, when the change time Δtc is relatively short, that is, when the resistance is relatively low, the ratio of the low resistance element is large and changes When the time Δtc is relatively long, that is, when the resistance is relatively high, the ratio of the high resistance element is large. Since the control device 8 can discriminate between the low resistance element ratio and the high resistance element ratio in the workpiece 4 based on the change time Δtc in the preliminary discharge, the main discharge conditions such that both elements can be melted in a balanced manner, that is, The main discharge time Δtp can be determined.

Taking a cemented carbide which is a sintered alloy of WC—Co as an example of the material of the workpiece 4, the resistivity of WC is 19.2 × 10 ⁻⁸ Ω · m, and the resistivity of Co is 5.81 × 10. ^{Since -8} Ω · m, WC is a high resistance element and Co is a low resistance element.

In the first embodiment, the control device 8 relatively shortens the main discharge time Δtp when the change time Δtc is relatively short, and relatively sets the main discharge time Δtp when the change time Δtc is relatively long. Make it longer. By such processing, the control device 8 can keep the peak Ip of the interelectrode current I constant between when the resistance of the workpiece 4 is relatively high and when it is relatively low. Generation | occurrence | production of the void | hole of the thing 4 and the quality fall of a processed surface can be suppressed.

In the example shown in FIG. 5, the change time Δtc2 from the time t = t8 to t9 in the preliminary discharge starting from the time t = t7 is longer than the change time Δtc1 in the preliminary discharge starting from the time t = t2. For this reason, the state of the workpiece 4 in the preliminary discharge starting from time t = t7 has a higher resistance than the state in the preliminary discharge starting from time t = t2. The control device 8 sets the main discharge time Δtp2 in the main discharge after the preliminary discharge starting from time t = t7, and the control device 8 sets the main discharge time Δtp1 in the main discharge after the preliminary discharge starting from time t = t2. Longer than. The speed at which the interelectrode current I increases after time t = t7 is slower than after time t = t2, but the main discharge time Δtp2 is longer than the main discharge time Δtp1. For this reason, the peak Ip of the interelectrode current I in the main discharge from time t = t9 to t10 is equivalent to the value in the main discharge from time t = t4 to t5. As a result, the electric discharge machining apparatus 100 can suppress the generation of holes in the workpiece 4 and the deterioration of the quality of the machined surface.

The control device 8 starts counting time from the time when the first signal is acquired from the first detection device 6A, in the example shown in FIG. 5, from time t = t2. Next, the control device 8 finishes counting the time at the time when the second signal is acquired from the second detection device 6B, that is, at the timing of time t = 3 in the example shown in FIG. The control device 8 sets the time counted from the acquisition of the first signal to the acquisition of the second signal as the change time Δtc. The change time Δtc is t3−t2.

FIG. 6 is a diagram illustrating an example of a change in the interelectrode voltage or interelectrode current between the electrode and the workpiece with time. When a voltage is applied between the electrode 3 and the workpiece 4 to generate a discharge, a dielectric breakdown occurs between the electrodes 5 at the electrode voltage Vid. The current between the electrodes at that time is Iid. When dielectric breakdown occurs between the electrodes 5, the voltage V between the electrodes decreases with the lapse of time t, and becomes constant at the voltage Vac between the electrodes. The current between the electrodes is Iac. When the interelectrode voltage Vac is reached, arc discharge is stably generated in the interelectrode 5.

The first threshold value Vc1 of the voltage is a value lower than the interelectrode voltage Vid when the dielectric breakdown of the interelectrode 5 occurs. In the first embodiment, the first voltage threshold value Vc1 is determined in the range of 80% to 90% of the interelectrode voltage Vid, but is not limited to this range. The second threshold value Vc2 of the voltage is a value higher than the interelectrode voltage Vac when the arc discharge is stably generated in the interelectrode 5. In the first embodiment, the second voltage threshold Vc2 is determined in the range of 110% to 120% of the interelectrode voltage Vac, but is not limited to this range. The first threshold value Vc1 and the second threshold value Vc2 will be described later.

FIG. 7 is a diagram illustrating an example in which the main discharge time is determined using the change time. In the first embodiment, the main discharge time Δtp becomes longer as the change time Δtc becomes longer, and becomes shorter as the change time Δtc becomes shorter. The change time Δtc is the time during which the state of discharge between the electrodes 5 in the preliminary discharge, that is, the state of the voltage V and the current I between the electrodes in the first embodiment is changed. More specifically, the change time Δtc is a time during which the interelectrode voltage V decreases during the preliminary discharge and the interelectrode current I increases. Therefore, the shortening of the change time Δtc means that the speed at which the discharge state changes in the gap 5, more specifically, the speed at which the gap voltage V decreases and the gap current I increases decreases. . Also, the longer change time Δtc means that the rate of change of the discharge state in the gap 5, more specifically, the rate of decrease of the gap voltage V and increase of the gap current I is increased. .

In the first embodiment, the main discharge time Δtp is Δtph when the change time Δtc is longer than the change time threshold Δtcc as shown by the solid line A in FIG. 7, and the change time Δtc is less than or equal to the change time threshold Δtcc. In this case, Δtpl. The main discharge time Δtph is longer than the main discharge time Δtpl. The change time threshold value Δtcc is determined by an experiment or simulation using a computer according to the type of material of the workpiece 4. In the first embodiment, the change time threshold value Δtcc is set to 100 nsec. 2 μsec. It is set between.

When the change time Δtc is longer than the change time threshold value Δtcc, the workpiece 4 has a high ratio of high resistance elements. When the change time Δtc is less than or equal to the change time threshold value Δtcc, the workpiece 4 has a low resistance element ratio. It can be judged that it is expensive. In this way, by changing the main discharge time Δtp in two stages with the change time threshold value Δtcc as a reference, the process of determining the main discharge time Δtp by the control device 8 becomes relatively simple.

The main discharge time Δtp is not limited to the one that changes in two steps as described above, and may change in three or more steps as shown by a one-dot chain line B in FIG. Further, the main discharge time Δtp may follow a function of the change time Δtc in which the main discharge time Δtp increases as the change time Δtc increases. The function in this case may be a linear function of the change time Δt as shown by a broken line C in FIG. 7, or may be a quadratic function, a cubic function or an exponential function of the change time Δtc. By doing in this way, since the electric discharge machining apparatus 100 can set the main discharge time Δtp more finely in accordance with the resistance state of the workpiece 4, the generation of holes in the workpiece 4 and the machining surface Quality degradation can be further suppressed.

The main discharge times Δtpl and Δtph, the change in the main discharge time Δtp indicated by the alternate long and short dash line B, or the function of the change time Δtc described above can be obtained for each material of the workpiece 4 by experiments or simulations using a computer. .

FIG. 8 is a diagram showing an example of a table describing the relationship between the material of the workpiece, the first threshold value, the second threshold value, the change time threshold value, and the main discharge time. The first threshold value Vc1, the second threshold value Vc2, the change time threshold value Δtcc, and the main discharge times Δtpl and Δtph vary depending on the type of material of the workpiece 4. In the first embodiment, the first threshold value Vc1, the second threshold value Vc2, the change time threshold value Δtcc, and the main discharge times Δtpl and Δtph are obtained and described in the table TB according to the material type of the workpiece 4. To do. The table TB is stored in the storage unit 8M of the control device 8 shown in FIG.

When the electric discharge machining apparatus 100 performs electric discharge machining on the workpiece 4, the operator of the electric discharge machining apparatus 100 inputs the material type of the workpiece 4 from the input device 8I shown in FIG. The processing unit 8P that has acquired the type of the input material reads the table TB from the storage unit 8M. Then, the processing unit 8P uses the material type as a search key, refers to the read table TB, and inputs the first threshold value Vc1, the second threshold value Vc2, the change time threshold value Δtcc, and the main value. The discharge times Δtpl and Δtph are retrieved and obtained from the table TB. The control device 8 controls the first switch 10 and the second switch 9 by using the acquired first threshold value Vc1, second threshold value Vc2, change time threshold value Δtcc, and main discharge times Δtpl and Δtph, to process the workpiece. The object 4 is subjected to electric discharge machining. By doing so, the electric discharge machining apparatus 100 can perform electric discharge machining on the workpiece 4 under appropriate conditions when electric discharge machining is performed on the workpiece 4 of a plurality of different types of materials. It is possible to suppress degradation of the quality of the processed surface. In addition, since the operator sets the conditions for electric discharge machining only by inputting the type of the workpiece 4, there is an advantage that the operation becomes easy.

FIG. 9 is a flowchart showing an example of processing when the electric discharge machining apparatus according to Embodiment 1 executes electric discharge machining. In step S 101, the control device 8 shown in FIG. 1 turns on the first switch 10 to apply the first voltage, which is the voltage of the first power supply 1, between the electrode 3 and the workpiece 4. Next, in step S102, the processing unit 8P compares the interelectrode voltage V with the first threshold value Vc1.

When the inter-electrode voltage V is equal to or higher than the first threshold value Vc1 (step S102, No), the control device 8 waits until the inter-electrode voltage V falls below the absolute value of the first threshold value Vc1. When the inter-electrode voltage V is lower than the absolute value of the first threshold value Vc1, that is, when the inter-electrode voltage V becomes less than the first threshold value Vc1 (step S102, Yes), the control device 8 performs the process in step S103. Proceed to In step S103, the control device 8 starts counting time from the timing when the inter-electrode voltage V falls below the absolute value of the first threshold value Vc1.

Next, in step S104, the processing unit 8P compares the interelectrode voltage V with the second threshold value Vc2. When the inter-electrode voltage V is greater than or equal to the second threshold value Vc2 (step S104, No), the control device 8 waits until the inter-electrode voltage V falls below the absolute value of the second threshold value Vc2. When the inter-electrode voltage V falls below the absolute value of the second threshold value Vc2, that is, when the inter-electrode voltage V becomes less than the second threshold value Vc2 (step S104, Yes), the control device 8 performs the process at step S105. Proceed to

In step S105, the control device 8 finishes counting the time, and obtains the change time Δtc using the counted time. Furthermore, the control device 8 applies a second voltage, which is the voltage of the second power supply 2, between the electrode 3 and the workpiece 4 by turning on the second switch 9. By this operation, a main discharge is generated between the electrode 3 and the workpiece 4. The control device 8 starts counting time from the timing when the second switch 9 is turned on, that is, the timing when the main discharge is started. Next, it progresses to step S106 and the control apparatus 8 calculates | requires main discharge time (DELTA) tp from change time (DELTA) tp.

In step S107, the control device 8 compares the elapsed time ts from the timing of starting the main discharge with the main discharge time Δtp. When the elapsed time ts has not reached the main discharge time Δtp (step S107, No), the control device 8 waits until the elapsed time ts reaches the main discharge time Δtp. When the elapsed time ts has reached the main discharge time Δtp (step S107, Yes), in step S108, the control device 8 ends the main discharge by turning off the second switch 9. When Step S101 to Step S108 are completed, the control device 8 returns to Step S101 and repeats Step S101 to Step S108 until the electrical discharge machining of the workpiece 4 is completed.

Modification 1
FIG. 10 is a diagram illustrating a second switch according to the first modification of the first embodiment. In the embodiment described above, the peak Ip of the interelectrode current I is made constant between different main discharges by changing the main discharge time Δtp. In the first modification, the peak Ip of the interelectrode current I is made constant between different main discharges by changing the interelectrode voltage V.

The second switch 9a includes a voltage adjusting device 9Aa provided between the positive electrode of the second power source 2 and the electrode 3, and a switching element 9B provided between the negative electrode of the second power source 2 and the workpiece 4. . In the voltage regulator 9Aa, a plurality of switching elements 16TA, 16TB, 16TC, and 16TD connected in series and a plurality of resistors 16RA, 16RB, 16RC, and 16RD connected in series are connected in parallel. The plurality of switching elements 16TA, 16TB, 16TC, and 16TD are turned on and off by the control device 8, respectively. The switching elements 16TA, 16TB, 16TC, and 16TD are semiconductor elements such as bipolar transistors or FETs (Field Effect Transistors), but are not limited to these.

The voltage adjusting device 9Aa has the highest resistance when all of the plurality of switching elements 16TA, 16TB, 16TC, and 16TD are turned off. When the switching elements 16TA, 16TB, 16TC, and 16TD are turned on in this order, the resistance gradually increases. Lower. The voltage regulator 9Aa has the lowest resistance when all of the plurality of switching elements 16TA, 16TB, 16TC, and 16TD are turned on. The voltage regulator 9Aa can change the voltage drop between the second power supply 2 and the electrode 3 by switching on and off the plurality of switching elements 16TA, 16TB, 16TC, and 16TD. For this reason, the 2nd switch 9a provided with voltage regulator 9Aa can change the voltage V between electrodes.

When the interelectrode voltage V is applied between the electrode 3 and the workpiece 4 by the second switch 9a, the control device 8 turns on at least the switching element 9B. When only the switching element 9B is turned on, since all the resistors 16RA, 16RB, 16RC, and 16RD of the voltage regulator 9Aa are interposed between the second power source 2 and the electrode 3, the interpolar voltage V is the smallest. Become. When the switching element 9B and at least one of the plurality of switching elements 16TA, 16TB, 16TC, and 16TD are turned on, the inter-electrode voltage V becomes larger than when only the switching element 9B is turned on.

In the first modification, when the change time Δtc is relatively long, since the discharge is performed with the high resistance element, the control device 8 controls the voltage adjustment device 9Aa of the second switch to increase the inter-electrode voltage V. When the change time Δtc is relatively short, the discharge is performed with the low resistance element. Therefore, the control device 8 controls the voltage adjustment device 9Aa of the second switch to decrease the interelectrode voltage V. By doing in this way, even if the main discharge time Δtp is the same, the control device 8 can change the rate of change in which the interelectrode current I increases, so that the polarities can be changed between the high resistance element and the low resistance element. The peak Ip of the intercurrent I can be made the same. As a result, the electric discharge machining apparatus 100 can suppress the generation of holes in the workpiece 4 and the deterioration of the quality of the machined surface.

In the first modification, the voltage adjustment device 9Aa includes a plurality of switching elements 16TA, 16TB, 16TC, and 16TD and a plurality of resistors 16RA, 16RB, 16RC, and 16RD, but is not limited thereto. The voltage adjusting device 9Aa may be a DC / DC converter, or a device having a plurality of DC power sources having different voltages and a switch for selecting a power source for supplying a voltage to the gap 5 from the plurality of DC power sources. There may be.

Modification 2
In the first embodiment described above, the detection device 6 shown in FIG. 1 detects the interelectrode voltage V, but may detect the interelectrode current I. In this case, the first detection device 6A compares the detected interelectrode current I with the first threshold value Ic1 of the current shown in FIG. 5, and the interelectrode current I exceeds the absolute value of the first threshold value Ic1. In the case, the first signal is output. The second detection device 6B compares the detected interelectrode current I with the second threshold value Ic2 of the current. The absolute value of the second threshold value Ic2 is larger than the absolute value of the first threshold value Ic1. The second detection device 6B outputs a second signal when the interelectrode current I exceeds the absolute value of the second threshold value Ic2. The first threshold value Ic1 and the second threshold value Ic2 of the current can be the current I between the electrodes when the voltage V between the electrodes is the first threshold value Vc1 and the second threshold value Vc2.

In the first embodiment, as shown in FIG. 5, the control device 8 continues to turn on the first switch 10 until dielectric breakdown occurs. However, depending on the processing conditions, the first switch 10 continues until dielectric breakdown occurs. The voltage may be applied to the gap 5 by repeatedly turning on and off. When the latter is used, it is difficult for the detection device 6 to detect that the absolute value of the interelectrode voltage V is lower than the absolute value of the first threshold value Vc1 and the absolute value of the second threshold value Vc2. . Therefore, when the first switch 10 is repeatedly turned on and off until dielectric breakdown occurs, the detection device 6 determines the absolute value of the interelectrode current I, the absolute value of the first threshold value Ic1 of the current, and the second value. The change time Δtc is obtained using the absolute value of the threshold value Ic2. In this way, the detection device 6 can obtain the change time Δtc regardless of the processing conditions.

In the second modification, when the control device 8 keeps turning on the first switch 10 until the dielectric breakdown occurs, the change time Δtc using the inter-electrode voltage V and the first threshold value Vc1 and the second threshold value Vc2. If the first switch 10 is repeatedly turned on and off until dielectric breakdown occurs, the change time Δtc may be obtained using the interelectrode current I and the first threshold value Ic1 and the second threshold value Ic2. . And the control apparatus 8 may determine the voltage given to the space | interval 5 by main discharge using the calculated | required change time (DELTA) tc, more specifically, the time which gives a voltage, or the magnitude | size of a voltage. When the interelectrode current I is used, the change time Δtc is the time from the timing when the interelectrode current I exceeds the absolute value of the first threshold value Ic1 to the timing when the interelectrode current I exceeds the absolute value of the second threshold value Ic2.

As described above, the control device 8 determines the voltage applied to the gap 5 in the main discharge based on the change time Δtc in which the gap voltage V in the preliminary discharge changes, and the gap in the preliminary discharge. Based on the change time Δtc during which the current I changes, the voltage applied to the gap 5 in the main discharge may be switched depending on the form of the preliminary discharge. By doing in this way, since the electric discharge machining apparatus 100 can obtain the change time Δtp even under various machining conditions, an appropriate main discharge time Δtp can be set for the workpiece 4. As a result, the electric discharge machining apparatus 100 can suppress the generation of holes in the workpiece 4 and the quality degradation of the machined surface under various machining conditions.

Embodiment 2. FIG.
FIG. 11 is a diagram illustrating an electric discharge machining apparatus according to the second embodiment. In the second embodiment, the electrical discharge machining apparatus 100b includes a switch, more specifically, the first switch 10b includes a bridge circuit and a detection device 6b, and applies positive and negative voltages from the first power supply 1 to the gap 5 to each other. Other structures of the electric discharge machining apparatus 100b according to the second embodiment are the same as those of the electric discharge machining apparatus 100 according to the first embodiment.

The first switch 10b is provided between the first power source 1, the electrode 3, and the workpiece 4. The first switch 10b forms a bridge circuit by a plurality of switching

elements

10A, 10B, 10C, and 10D. The

switching elements

10A, 10B, 10C, and 10D are semiconductor elements such as bipolar transistors or FETs (Field Effect Transistors), but are not limited thereto.

Switching elements

10A and 10C form the upper arm of the bridge circuit, and switching

elements

10B and 10D form the lower arm of the bridge circuit. A connection part between the switching element 10A and the switching element 10D is connected to the electrode 3, and a connection part between the switching element 10C and the switching element 10B is connected to the workpiece 4. The control device 8 controls the plurality of switching

elements

10A, 10B, 10C, and 10D.

When the switching element 10A and the switching element 10B are turned on, the positive electrode of the first power supply 1 and the electrode 3 are connected, and the negative electrode of the first power supply 1 and the workpiece 4 are connected. For this reason, the interelectrode current I flows from the electrode 3 toward the workpiece 4. When the switching element 10C and the switching element 10D are turned on, the positive electrode of the first power source 1 and the workpiece 4 are connected, and the negative electrode of the first power source 1 and the electrode 3 are connected. For this reason, the interelectrode current I flows from the workpiece 4 toward the electrode 3. As described above, when the switching element 10A and the switching element 10B and the switching element 10C and the switching element 10D are alternately turned on and off, the polarities of the electrode 3 and the workpiece 4 are reversed to give the interelectrode voltage V. Can do.

The detection device 6b includes a first detection device 6A, a second detection device 6B, a third detection device 6C, and a fourth detection device 6D. The first detection device 6A and the second detection device 6B are the same as those described in the first embodiment. Each of the third detection device 6C and the fourth detection device 6D detects the interelectrode voltage. The third detection device 6C compares the detected inter-electrode voltage with the absolute value of the third threshold value, and outputs a signal when the inter-electrode voltage falls below the absolute value of the absolute value of the first threshold value. This signal is a signal indicating that the inter-electrode voltage has fallen below the absolute value of the third threshold value, and is hereinafter referred to as a third signal as appropriate. The third signal is input to the control device 8. The fourth detection device 6D compares the detected inter-electrode voltage with a fourth threshold value. The absolute value of the fourth threshold value is smaller than the absolute value of the third threshold value. The fourth detection device 6D outputs a signal when the inter-electrode voltage falls below the absolute value of the fourth threshold value. This signal is a signal indicating that the inter-electrode voltage has fallen below the absolute value of the fourth threshold value, and is hereinafter referred to as a fourth signal as appropriate. The fourth signal is input to the control device 8.

In the second embodiment, the detection device 6b includes four comparators having different thresholds, that is, the first detection device 6A, the second detection device 6B, the third detection device 6C, and the fourth detection device 6D. 6b is not limited to such a thing. The detection device 6b may switch the threshold value of one comparator.

FIG. 12 is a timing chart of electric discharge machining executed by the electric discharge machining apparatus according to the second embodiment. PD1 in FIG. 12 indicates the timing of the first control signal 27 for turning on or off the switching element 10A and the switching element 10B of the first switch 10b in the preliminary discharge. PD2 in FIG. 12 indicates the timing of the first control signal 28 for turning on or off the switching element 10C and the switching element 10D of the first switch 10b in the preliminary discharge. 12 indicates the timing of the second control signal 29 for turning on or off the second switch 9 in the main discharge. In FIG. 12, V indicates the interelectrode voltage, and I indicates the interelectrode current. A change in the interelectrode voltage V is indicated by a solid line 36, and a change in the interelectrode current I is indicated by a solid line 39. In FIG. 12, Vc1 is the first threshold value of the interelectrode voltage V, Vc2 is the second threshold value of the interelectrode voltage V, Vc3 is the third threshold value of the interelectrode voltage V, and Vc4 is the fourth threshold value of the interelectrode voltage V. It is. The third threshold value Vc3 is a negative voltage having the same absolute value as the first threshold value Vc1. The fourth threshold value Vc4 is a negative voltage having the same absolute value as the second threshold value Vc2. In FIG. 12, Ic1 is a first threshold value of the interelectrode current I, Ic2 is a second threshold value of the interelectrode current I, Ic3 is a third threshold value of the interelectrode current I, and Ic4 is a fourth threshold value of the interelectrode current I. It is. The absolute value of the first threshold value Ic1 is smaller than the absolute value of the second threshold value Ic2. The absolute value of the first threshold value Ic1 is equal to the absolute value of the third threshold value Ic3, and the absolute value of the second threshold value Ic2 is equal to the absolute value of the fourth threshold value Ic4. The horizontal axis of FIG. 12 is time t.

The control device 8 turns on the switching element 10A and the switching element 10B according to the control signal 27, applies the electrode 3 as positive and applies the interelectrode voltage V to the electrode 3 and the workpiece 4, and generates a preliminary discharge in the interelectrode 5 Let The control device 8 determines the main discharge time Δtp1 using the change time Δtc1 obtained by the preliminary discharge, and turns on the second switch 9 to generate the main discharge in the gap 5.

When the main discharge based on the preliminary discharge with the electrode 3 as positive is completed, the control device 8 turns on the switching element 10C and the switching element 10D by the control signal 28, and applies the voltage V between the electrodes with the workpiece 4 as positive. It gives to the workpiece 4 and the electrode 3 and a preliminary discharge is generated between the electrodes 5. The control device 8 determines the main discharge time Δtp2 using the change time Δtc2 obtained by this preliminary discharge, and turns on the second switch 9 to generate the main discharge in the gap 5. The change time Δtc2 is the fourth threshold value Vc4 at which the absolute value of the interelectrode voltage V is the absolute value of the interelectrode voltage V from the timing when the absolute value of the interelectrode voltage V falls below the absolute value of the third threshold value Vc3 of the interelectrode voltage V This is the time until the timing when the absolute value is below.

When the main discharge based on the preliminary discharge with the workpiece 4 as positive is completed, the control device 8 turns on the switching element 10A and the switching element 10B according to the control signal 27, makes the electrode 3 positive, and sets the electrode voltage V to the electrode. 3 and the workpiece 4 and a preliminary discharge is generated between the electrodes 5. The control device 8 determines the main discharge time Δtp3 using the change time Δtc3 obtained by this preliminary discharge, and turns on the second switch 9 to generate the main discharge in the gap 5.

When the electric discharge machining apparatus 100b performs the electric discharge machining on the workpiece 4, the control device 8 causes the preliminary discharge with the electrode 3 as positive and the main discharge based on the preliminary discharge, the preliminary discharge with the workpiece 4 as positive, and this The main discharge based on the preliminary discharge is executed alternately with the elapse of time t. Since the electric discharge machining apparatus 100b alternately applies a positive voltage and a negative voltage to the electrode 3, the average voltage between the electrodes 5 can be 0 volts. As a result, in addition to the operation and effect of the electric discharge machining apparatus 100 according to the first embodiment, the electric discharge machining apparatus 100b suppresses the electric corrosion of the workpiece 4 even when the machining liquid is water, thereby reducing the quality of the machined surface. The effect | action and effect that can be suppressed are produced.

Modified example.
In the second embodiment described above, the detection device 6b shown in FIG. 11 detects the interelectrode voltage V, but may detect the interelectrode current I. In this case, the third detection device 6C compares the detected interelectrode current I with the third threshold value Ic3 shown in FIG. 12, and the absolute value of the interelectrode current I exceeds the absolute value of the third threshold value Ic3. In the case, the third signal is output. The fourth detection device 6D compares the detected interelectrode current I with a fourth threshold value Ic4. The absolute value of the fourth threshold value Ic4 is larger than the absolute value of the third threshold value Ic3. The fourth detection device 6D outputs a fourth signal when the absolute value of the interelectrode current I exceeds the absolute value of the fourth threshold value Ic4. Since the first detection device 6A and the second detection device 6B are the same as those in the first embodiment, the description thereof is omitted.

In the second embodiment, the control device 8 continues to turn on the first switch 10b until dielectric breakdown occurs, as shown in FIG. 12, but depending on the processing conditions, the first switch 10b until the dielectric breakdown occurs. The voltage may be applied to the gap 5 by repeatedly turning on and off. When the latter is used, the detection device 6b determines that the absolute value of the interelectrode voltage V is the absolute value of the first threshold value Vc1, the absolute value of the second threshold value Vc2, the absolute value of the third threshold value Vc3, and the fourth value. It is difficult to detect that the absolute value of the threshold value Vc4 is below the absolute value. Therefore, when the first switch 10b is repeatedly turned on and off until dielectric breakdown occurs, the detection device 6b detects the absolute value of the interelectrode current I, the absolute value of the first threshold Ic1 of the current, the second The change time Δtc is obtained using the absolute value of the threshold value Ic2, the absolute value of the third threshold value Ic3, and the absolute value of the fourth threshold value Ic4. In this way, the detection device 6b can obtain the change time Δtc regardless of the processing conditions. When the interelectrode current I takes a negative value, the change time Δtc is the time from the timing when the interelectrode current I exceeds the absolute value of the third threshold value Ic3 to the timing when the interelectrode current I exceeds the absolute value of the fourth threshold value Ic4. It is.

In the modification, when the control device 8 continues to turn on the first switch 10 until dielectric breakdown occurs, the inter-electrode voltage V, the first threshold value Vc1, the second threshold value Vc2, the third threshold value Vc3, and the first threshold value Vc3. When the change time Δtc is obtained using the threshold value Vc4 of 4 and the first switch 10 is repeatedly turned on and off until dielectric breakdown occurs, the interelectrode current I, the first threshold value Ic1, the second threshold value Ic2, The change time Δtc may be obtained using the third threshold value Ic3 and the fourth threshold value Ic4. By doing so, the electric discharge machining apparatus 100b can obtain the change time Δtp even under various machining conditions, so that the main discharge time Δtp appropriate for the workpiece 4 can be set. As a result, the electric discharge machining apparatus 100b can suppress the generation of holes in the workpiece 4 and the deterioration of the quality of the machined surface under various machining conditions.

The configuration described in the above embodiment shows an example of the contents of the present invention, and can be combined with another known technique, and can be combined with other configurations without departing from the gist of the present invention. It is also possible to omit or change the part.

1 power supply (first power supply), 2 power supply (second power supply), 3 electrodes, 4 workpieces, 5 poles, 6, 6b detection device, 6A 1st detection device, 6B 2nd detection device, 6C 3rd detection Device, 6D fourth detection device, 8 control device, 8IO input / output unit, 8M storage unit, 8P processing unit, 8I input device, 9, 9a switch (second switch), 9A, 9B, 10A, 10B, 10C, 10D , 16TA, 16TB, 16TC, 16TD switching element, 9Aa voltage regulator, 10, 10b switch (first switch), 16RA, 16RB, 16RC, 16RD resistance, 100, 100b electric discharge machine, I interelectrode current, Ic1, Vc1 1st threshold, Ic2, Vc2, 2nd threshold, Ic3, Vc3, 3rd threshold, Ic4, Vc4, 4th threshold, TB Buru, V, Vac, Vic inter-electrode voltage, .DELTA.tc change time, Derutatcc change time threshold, [Delta] tp main discharge time.

Claims

A power supply that outputs a voltage applied between the electrode and the workpiece,
A switch that turns on or off a voltage that the power source applies to the electrodes;
A detection device for detecting a discharge state between the electrodes and outputting a detection result;
Based on the change in the discharge state when the first discharge is generated between the electrodes by controlling the switch using the detection result of the detection device to control the voltage applied between the electrodes. A control device for determining a condition for generating a second discharge in between;
An electrical discharge machining apparatus comprising:
The controller is
As the rate of change of the discharge state in the first discharge becomes slower, the time of the second discharge is lengthened or the voltage applied between the electrodes in the second discharge is increased. The electric discharge machining apparatus according to claim 1.
The controller is
Determining a voltage applied between the electrodes in the second discharge based on a time during which a voltage between the electrodes in the first discharge changes;
Determining a voltage applied between the electrodes in the second discharge based on a time during which a current between the electrodes in the first discharge changes;
The electric discharge machining apparatus according to claim 1, wherein the EDM is switched.
The detection device includes:
A first detection device for detecting that an absolute value of a voltage between the electrodes in the first discharge is lower than an absolute value of a first threshold;
A second detection device that detects that the absolute value of the voltage between the electrodes in the first discharge is less than the absolute value of a second threshold value that is smaller than the absolute value of the first threshold value. And including
The controller is
Determining a voltage applied between the electrodes in the second discharge based on a time from a timing when the absolute value of the first threshold value is reduced to a timing when the absolute value of the second threshold value is reduced. The electrical discharge machining apparatus according to claim 1, wherein the electrical discharge machining apparatus is characterized.
The detection device includes:
A first detection device that detects that an absolute value of a current between the electrodes in the first discharge exceeds an absolute value of a first threshold;
A second detection device that detects that the absolute value of the current between the electrodes in the first discharge exceeds the absolute value of a second threshold value that is larger than the absolute value of the first threshold value. And including
The controller is
Determining a voltage applied between the electrodes in the second discharge based on a time from a timing at which the absolute value of the first threshold is exceeded to a timing at which the absolute value of the second threshold is exceeded. The electrical discharge machining apparatus according to claim 1, wherein the electrical discharge machining apparatus is characterized.
The discharge according to any one of claims 1 to 5, wherein the switch includes a bridge circuit and applies a positive / negative voltage between the electrodes when the first discharge is generated. Processing equipment.