JPH01295716A - Power supply device for electric discharge machining - Google Patents

Abstract

PURPOSE:To prevent a metal in an electrode side from being dissolved adhering to a workpiece side by providing a main power source, subpower source and a subpower source polarity switching circuit alternately switching applied polarity of this subpower source. CONSTITUTION:In the case of an electric discharge machining power supply device having a main power source 1 and a subpower source 2, first the subpower source 2 is applied generating an electric discharge. The subpower source 2 alternately switches its applying polarity by a subpower source polarity switching circuit 26. In this way, a mean value of voltage, applied between gaps, is decreased. Electrolytic action is controlled by the mean value of the applied voltage, but because the mean value of the voltage is decreased (to zero if possible) as described in the above, the electrolytic action decreases, preventing even elution of a metal in a side of a workpiece 9 and of a metal in a side of a wire electrode 10.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a power supply device for an electric discharge machine that applies a voltage between a workpiece and an electrode to machine the workpiece by electric discharge.

[Conventional technology]

Some conventional electrical discharge machining power supply devices have two power supplies, a main power source and a sub power source, in order to increase the machining speed. In such a power supply device for electric discharge machining, the role of the auxiliary power supply is to start electric discharge. Therefore, the current capacity is assumed to be small. First, the sub power source is applied, and when the discharge starts, the main power source is applied. A high-voltage, large-current power source is used as the main power source. The applied polarity is positive on the workpiece side and negative on the electrode side. According to such a II power supply device for electric discharge machining, it is possible to flow a pulse current with a narrow width and a high peak value,
Machining speed becomes faster. However, electrical discharge machining is performed while supplying machining fluid to the discharge portion, and water is usually used as the machining fluid. Therefore, while immersed in water, a positive voltage is applied to the workpiece side and a negative voltage is applied to the ft pole side, so that an electrolytic action is performed. As a result, metals with a high ionization tendency contained in the workpiece are eluted, making the workpiece susceptible to rust. Furthermore, if the workpiece is a cemented carbide containing cobalt as a binder, the cobalt will be eluted and the material will deteriorate. Therefore, the polarity applied by the main power source and the sub power source is reversed to reduce the electrolytic effect. That is, the main power is applied so that the workpiece side is positive and the electrode side is negative, but the auxiliary power is applied with the opposite polarity. Applying the main power with the above polarity is a requirement for electrical discharge machining. This is because if the main power source is applied with the opposite polarity, the discharge becomes unstable, resulting in disadvantages such as a reduction in machining speed and increased wear on the electrodes. An example of a document related to such a technique is Japanese Patent Laid-Open No. 56-56341.

[Problem to be solved by the invention]

(Problems) However, the above-described power supply device for electric discharge machining has the following problems. The first problem is that the metal on the electrode side is eluted and adheres to the workpiece side. The second problem is that the machined surface of the workpiece is roughened and the electrodes are damaged. (Description of Problem) First, the first problem will be explained. The electrolytic action depends on the average value of the applied voltage, but the time from when the auxiliary power source is applied until the discharge starts (the so-called discharge delay time) is It varies, but in total, it is longer than the time the main power is applied. Therefore, when the auxiliary power source is applied in a manner opposite to the main power source, the average voltage applied to the gap between the workpiece and the electrode becomes positive on the electrode side and negative on the workpiece side. As a result, the metal on the workpiece side is prevented from eluting, but the metal on the electrode side elutes and adheres to the workpiece side (scalping).
. Next, the second problem will be explained. The current path of discharge is called a discharge column, and when a discharge occurs between the workpiece and the electrode, a discharge column is formed between the two. Figure 4 shows the case of wire electrical discharge machining as an example.
This figure shows the changes in the discharge column formed between the electrode (electrode) and the workpiece. FIG. 4(a) shows the state at the beginning of the discharge, and FIG. 4(b) shows the state after the discharge has continued for a while. At the beginning of discharge, the current flows by slightly breaking the insulation of the gap, so the discharge column is thin as shown in FIG. 4(a), the current is concentrated in this thin discharge column, and the current density is high. However, as time passes, the space around the original discharge pillar also becomes low in resistance, and the discharge pillar becomes as shown in Figure 4 (b).
It becomes thick like. The thicker the wire, the lower the current density. Therefore, the current density characteristics of the discharge are as shown in FIG. At the beginning of the discharge, the current density is high, but it becomes smaller as time passes. In the conventional electric discharge machining power supply device with two power supplies, the main power is immediately applied as soon as the sub power is applied and the start of discharge is detected, so the main power is applied when the discharge column is thin. Become. Then, at a time when the discharge column is thin and the current density is already high, a large current is poured from the main power source, which is a more powerful power source, which may roughen the machined surface of the workpiece or damage the electrode. It turns out. If the electrode is a wire, the damaged part may get caught on a wire guide or the like, leading to wire breakage. An object of the present invention is to solve the above-mentioned problems.

[Means to solve the problem]

In order to solve the first problem, the electric discharge machining power supply device of the present invention is provided with a main power supply, a sub-power supply, and a sub-power supply polarity switching circuit that alternately switches the applied polarity of the sub-power supply. . In addition, the above-mentioned No. 1. In order to solve the second problem together, it is necessary to provide a main power supply, a sub-power supply, a sub-power supply polarity switching circuit that alternately switches the application polarity of the sub-power supply, and a discharge caused by application of the sub-IT source for a predetermined period of time. The present invention is provided with means for detecting the continuation of the application, and means for starting application of main power in response to a signal from the means.

[For production]

In a power supply device for electric discharge machining having a main power source and a sub power source, the sub power source is first applied to generate electric discharge. The polarity of the applied auxiliary power source is alternately switched by the auxiliary a6IAs switching circuit. This reduces the average value of the voltage applied across the gap (preferably to O). This reduces the electrolytic action and prevents the elution of metal from the workpiece side and from the electrode side. Furthermore, it detects the start of discharge by the auxiliary power source, and also detects whether the discharge continues for a predetermined period of time. If the discharge continues for a certain period of time, the discharge column will develop and become thicker during that time. When the current density becomes small, apply the main power. Although the current from the main power source is larger than the current from the auxiliary power source, the current density is reduced so that it does not damage the electrode or workpiece.

【Example】

Embodiments of the present invention will be described in detail below with reference to the drawings. (Configuration of Apparatus) FIG. 1 shows a power supply device for electrical discharge machining according to an embodiment of the present invention. In Figure 1, 1 is the main power supply, 2 is the sub-power supply,
3 is a lead inductance, 4 is a resistor, 5 and 6 are switching transistors, 7.8 is a diode, 9 is a workpiece, 9-1 is a machining trajectory, IO is a wire electrode, 11 is a conductor, 12 is a discharge duration detection circuit , 13 is a comparator, 14 is a monostable multi-bi break, 15 is a logic circuit, 16 is a flip-flop circuit, 17 is a synchronization clock input terminal, 18
1 is a sub-gate pulse generation circuit, 19 is a main gate pulse generation circuit, 20.21 is a pulse width setting signal, 22 to 25 are switching transistors, 26 is a sub-power supply polarity switching circuit, 27 is a switching signal generation circuit, N is a same polarity application circuit, R is a reverse polarity application circuit, N+, Nz, Rt, R
t is a control terminal of the switching transistor, and 5 is a reference voltage. The main power supply 1 is a high-voltage, large-current power supply, and when the switching transistor 5 is turned on, the power supply 6fA1→lead inductance 3−switching transistor 5−
Diode 7 → Workpiece 9 → Wire electrode 1〇-Electronic 11
-1 electric current is applied through a path called B1. The switching transistor 5 is turned on when the main gate pulse generation circuit 19 supplies the main gate pulse. The main gate pulse from the main gate pulse generation circuit 19 is generated in response to the output from the flip-flop circuit 16. The pulse width T, 48 of the main gate pulse is set in advance by the pulse width setting signal 20. The sub power supply 2 has a lower voltage than the main power supply 1, and the current flows through the resistor 4.
It is small and limited by. The applied polarity of the sub-power source 2 is determined by the sub-'r4 source polarity switching circuit 26. The sub power supply polarity switching circuit 26 includes a homogeneous application circuit N consisting of switching transistors 22 and 23 that are turned on at the same time.
(Normal) and a reverse polarity applying circuit R (Reverse) consisting of switching transistors 24 and 25 which are also turned on at the same time. 5. These switching transistors turn on. A signal from the switching signal generation circuit 27 is sent to each control terminal N+, N
This is when t, Rt, and Rz are manually applied. Switching transistor 22.2 of same polarity application circuit N
3 is turned on and switching transistor 6 is turned on, sub taIX2 - resistor 4 - switching transistor 6 → diode 8 → switching transistor 2
The voltage is applied through the path 2-workpiece 9-wire electrode 10-conductor 11->switching transistor 23-auxiliary power supply 2. In addition, the switching transistor 2 of the reverse polarity application circuit R
4 and 25 are turned on and the switching transistor 6 is turned on, the subtype a2-resistor 4->switching transistor 6->diode 8->switching transistor 24->conductor 11->wire electrode 10-workpiece 9-switching transistor 25- It is applied through the path of the sub power supply 2. The switching transistor 6 is turned on when the sub-gate pulse is supplied from the sub-gate pulse generating circuit 18. The sub-gate pulse from the sub-gate pulse generation circuit 18 starts when a predetermined pause period (pause width T4.) has elapsed, and ends when a predetermined period (discharge pulse width TsH) has elapsed after receiving the output from the comparator 13. It is a pulse that This discharge pulse width 'rsi+ is not the voltage application time of the sub power supply 2, but the time from the start of discharge (that is, after the discharge current begins to flow) until the application of the sub power supply 2 is discontinued (Fig. 2 (a), Figure 3 (a)
), discharge pulse width T3H and pause width T5. is preset by the pulse width setting signal 21, and the diode 7 is a reverse current blocking diode, which prevents the voltage from being applied to the switching transistor 5 when the auxiliary power supply 2 is applied. do. Diode 8 is also a similar diode. The discharge duration detection circuit 12 is a circuit that detects whether the discharge generated by applying the sub power source 2 has exceeded mvt for a predetermined time, and comparators 13. Monostable multivibrator14. It consists of a logic circuit 15. The flip-flop circuit 16 shapes the output signal of the discharge duration detection circuit 12 and outputs it to the main gate pulse generation circuit 19.
It is intended to provide the desired form to the customers. Note that the clock input to the synchronization clock input terminal 17 is for synchronizing the operation of the apparatus as a whole. Therefore, although it is added to each part constituting the device, only the main parts are shown in FIG. (Operation of Apparatus) Next, the operation will be explained with reference to FIGS. 2 and 3. FIG. 2 is a waveform diagram when the sub-t:a is applied with the same polarity as the main power supply, and FIG. 3 is a waveform diagram when the sub-power supply is applied with the opposite polarity to the main power supply. (A) When the sub power supply is applied with the same polarity as the main power supply, the same polarity application circuit N is turned on, and when the switching transistor 6 is turned on by the sub gate pulse, the sub power supply 2 is applied. Figure 2 (b) shows the gap voltage caused by the sub power supply 2 (
Strictly speaking, this is the gap voltage assuming that only the sub power supply 2 continues to be applied). It usually takes some time before discharge starts. This time may be long or short depending on the gap situation and the like. In Figure 2 (b), time 1. The stone is represented as a discharge begins. The discharge column at this time is thin as shown in FIG. 4(a). Comparator 13 detects the occurrence of discharge. The reference voltage vll of the comparator 13 is chosen to be greater than the voltage across the gap when a discharge occurs. Therefore, when a discharge occurs,
The comparator 13 outputs a signal to that effect, and this signal is input to the sub-gate pulse generation circuit 18 as well as to the monostable multi-bi break 14. As described above, when the sub-gate pulse generation circuit 18 receives the discharge generation signal, the sub-gate pulse generation circuit 18 generates the discharge pulse width T' according to the time.
The sub-gate pulse is maintained until ss has elapsed. In addition, the monostable multi-bi break 14 is shown in Fig. 2 (c).
It outputs an output pulse with a predetermined width TI4 as shown in FIG. The predetermined width T,4 is determined by the circuit constant of the monostable multi-bi break 14. The logic circuit 15 performs an AND operation between the monostable multi-bibreak 14 and the comparator 13. Therefore, when the logic circuit 15 outputs an output, it means that the discharge is still continuing even after the predetermined width 714 has elapsed since the start of the discharge. The above-mentioned predetermined width TI4 is set to be the time from when the discharge starts until the discharge column becomes thick as shown in the meridian diagram (b).
Set as appropriate (for example, 0.5 μs to 2 μs) e. If the synchronization clock that first arrives at the clock terminal CK after input from the logic circuit 15 to the D terminal of the flip-flop circuit 16 is GK+b (second Figure (d)), C
Time when K, 6 arrived 1. , flip-flop circuit 1
6 outputs an output signal from the Q terminal. When this output signal is input to the main gate pulse generation circuit 19, the pulse width T, .
The main gate pulse is output. As a result, the switching transistor 5 is turned on and the voltage 'a1' is applied. FIG. 2(f) shows the gap voltage when the earth voltage a1 is applied. (2) is the discharge sustaining voltage. The rear end of the waveform has a gently descending shape due to the influence of inductance and the like. Note that the end time of the sub-gate pulse and the end time of the main gate pulse do not necessarily coincide. This is because the starting point of each pulse is undefined, and the width of each pulse is set in advance. FIG. 2(G) shows the waveform of the gear voltage, which is a combination of FIGS. 2(B) and 2(F). FIG. 2(H) shows the gap current. The part I is
This is the discharge current when sub-type 'a2 is applied, and the part ■7 is:
This is the discharge current when the earth'a1 is applied. (B) When the sub power supply is applied with the opposite polarity to the main power supply When the reverse polarity application circuit R is turned on and the switching transistor 6 is turned on by the sub gate pulse, the sub power supply 2 is applied. FIG. 3 shows the waveforms at this time, and FIGS. 3(A) to 3(H) correspond to FIGS. 2(A) to (H), respectively. The only difference is that the waveform of the auxiliary power source 2 is upside down from that in FIG. 2. In this case as well, the main power source 1 is applied after the discharge continuation detection circuit 12 confirms that the discharge has continued for a certain period of time (after the discharge column becomes thicker). As understood from the operations (A) and (B) above,
In the present invention, whether the sub power source 2 is applied with the same polarity as the main power source 1 or the opposite polarity, after the discharge is started due to the application of the sub power source 2, the discharge column becomes thicker than expected. After waiting for a certain period of time, the main power supply 1 is applied. In this way, a large current will not be applied to the thin discharge column, so that the machined surface of the workpiece and the electrode will not be roughened. (C) ffi property switching and electrolytic action As described above, electrolytic action becomes more active when the average voltage applied across the gap is large. If the average voltage is positive on the workpiece side and negative on the electrode side (that is, the same as the applied polarity of the main power source 1), the metal on the workpiece side will be eluted. If the polarity of the average voltage is opposite to the above, the metal on the electrode side will be eluted. As is clear from Figure 2 (G), the sub power supply 2 is connected to the main power supply 1.
The average voltage when applied with the same polarity as the main power supply 1 is the same polarity (positive on the workpiece side, negative on the electrode side). If electrical discharge machining is continued in this state, the metal on the workpiece side will be eluted. In Figure 3 (G), the average voltage when the sub-type /s2 is applied with the opposite polarity to that of Doryu a1 is as follows: (upper part), but its polarity is the same as that of the sub power supply 2. If the discharge delay time (time from application to start of discharge) when applying sub-tai2 is short, the waveform portion below the zero line will be small, so the opposite may occur. be. However, −
In general, it is more likely to have the same polarity as subtype a2. Therefore, while applying the sub-type 'a2 with the same polarity and applying it with the opposite polarity, we set the duration of each application so that the average voltage across the gap is small (preferably zero). Adjust the intensity (for example, lengthen the time when applying the opposite polarity). The application time is adjusted by the switching signal generation circuit 27. Since the average voltage is thus reduced, the electrolytic effect is reduced.

【Effect of the invention】

As described above, the electric discharge machining power supply device of the present invention provides the following effects. ■ The average voltage applied across the gap between the workpiece and the electrode is reduced by adjusting the period during which the sub power source is applied with the same polarity as the main power source and the period during which it is applied with the opposite polarity. Therefore, the electrolytic action is reduced and the elution of not only the metal on the workpiece side but also the metal on the electrode side is prevented. ■ After the discharge starts due to the application of the auxiliary power supply (after the discharge column is formed), the main power is applied at the moment when the discharge continues for a while and the discharge column becomes thicker, so the machined surface of the workpiece is No roughening or damage to the electrodes. Therefore, in the case of wire electric discharge machining, no damaged portion is created in the wire that is the electrode, and therefore, there is no possibility that the damaged portion will be caught on a wire guide or the like and disconnected.

[Brief explanation of the drawing]

Fig. 1: Electrical discharge machining power supply according to an embodiment of the present invention Fig. 2: Waveform diagram when the sub power source is applied with the same polarity as the main power source Fig. 3: Sub power source is connected to the main power source Figure 4: Waveform diagram when applying with opposite polarity Figure 5: Diagram showing changes in discharge column Figure 5: Current density characteristic diagram of discharge In the diagram, ■ is the main? 11 and 2 are sub-power supplies, 3 are lead inductances, 4 are resistors, 5 and 6 are switching transistors, 7 and 8 are diodes, 9 is a workpiece, 10 is a wire electrode, 11 is a conductor, 12 is a discharge duration detection circuit , 13
is a comparator, 14 is a monostable multi-bi break, 15 is a logic circuit, 16 is a flip-flop circuit, 17 is a synchronization clock input terminal, 18 is a sub-gate pulse generation circuit, 1
9 is a main gate pulse generation circuit, 20.21 is a pulse width setting signal, 22 to 25 are switching transistors, 26 is a sub power supply polarity switching circuit, 27 is a switching signal generation circuit, N is a same polarity application circuit, and R is a reverse polarity application circuit. This is a voltage application circuit. Patent applicant: Discharge Precision Machining Research Institute Co., Ltd. Representative Patent Attorney Mori 1) Hiroshi (3 others)? ＋20 η3 (2) 11″￥彎;subject (I) (0) 爾I+Fig.

Claims (2)

[Claims] (1) A power supply device for electrical discharge machining, comprising a main power supply, a subpower supply, and a subpower supply polarity switching circuit that alternately switches the applied polarity of the subpower supply. (2) A main power source, a sub power source, a sub power source polarity switching circuit that alternately switches the applied polarity of the sub power source, means for detecting that the discharge caused by application of the sub power source has continued for a predetermined period of time, and the means 1. A power supply device for electric discharge machining, comprising means for starting application of main power in response to a signal from the main power source.