JPS63123614A - Method of electric discharge machining - Google Patents

Abstract

PURPOSE:To make a surface roughness uniform by calculating and controlling internal impedances of a power source based on impedances between electrodes so as to supply a no-load voltage higher than a spark generating voltage and to flow a specified machining voltage after a spark generation. CONSTITUTION:Detecting a voltage between electrodes 1 and 2 caused with a dc power source 7 for detection by means of a detection means 10 and calculating an impedance between the electrodes by means of an operation means 11 during a time of a pause, and using information of a previous pulse, internal impedances Rx and Ry of a machining power source 3 are set so as to supply a no-load voltage higher than a spark generating voltage during a time of no load of the present pulse and to supply a required machining current after a spark generation is detected with a detection means 9. After a specified time of a pause, a series of actions of switching a current restriction resistor array 5 through a power transistor array 4 are repeated and controlled. In this way, the optimum no-load current and the required machining current are obtained to make machinings in areas of both a large area machining and a finish machining possible.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electrical discharge machining method for an electrical discharge machine that uses a conductive machining fluid as a machining fluid.

[Conventional technology]

Figure m9 is a circuit diagram showing a machining power source according to the conventional electric discharge machining method disclosed in, for example, Japanese Patent Laid-Open No. 60-85826. In the figure, (1) is the electrode for the blade, (2) is the workpiece, (3) is the second DC power supply, (4) and (to) are the power transistors, and (5) and (to) are the above One current limiting resistor (9) is connected to the I-1 side of the power transistor (4) and (E), and a discharge occurs between the electrodes (1) and the workpiece (2). discharge detection means for detecting the discharge, @ is the switching means, (to) is the second drive circuit that drives the power transistor (4), (6) and (to) are the diodes that prevent reverse flow of current (0), ( (to) is a first drive circuit that drives the power transistor (to);
The α field is the first DC power source. In addition, the above switching means (
2) controls the first and second drive circuits U, (to).

Here, we will discuss the electrical characteristics when a conductive working fluid is used.

When using a conductive machining fluid, when it can be assumed that the machining electrode (1) and the workpiece (2) face each other as parallel plates,
The interpolar impedance Rgap can be expressed by the following equation as shown in FIG.

l ゛Rgap=ρ・D (1) However, ρ: Specific resistance of machining fluid [Ω1] l: Distance between poles [5] S: Opposing area between poles (d) Activates the second drive circuit (to) When turning on the power transistor (4), the processing electrode (
1) and the workpiece (2), a voltage vgopen(
1) occurs. According to Ohm's law, the voltage Vgopen is gap Vgopen= gap+ , E (2)
It is expressed as

However, R1: current limiting resistor E: iII current, voltage, and Hvgopen used here will be referred to as no-load voltage. The voltage between electrodes after a single discharge is defined as the arc voltage Vga
Let it be rc.

The current flowing between the electrodes is the total current supplied from the power supply, and the electrolytic current flowing according to the Ohm 0 law with respect to the impedance between the electrodes Rgap is the one when no load voltage is applied, and the one during discharge. Izar
c, the discharge that flows due to the discharge phenomenon number! Current iId:
f2 and before discharge I=Izopen (3)
During discharge, I = Id + IEarc (4) However, as can be seen from equation (1), the lower the specific resistance ρ of the machining fluid and the smaller the distance ml between the machining holes, the smaller the same area S between the machining holes. The wider the distance, the lower the inter-electrode impedance Rgap becomes. Furthermore, as is clear from equation (2), the impedance between poles Rg
When ap decreases, no-load normal pressure Vgopen decreasesZ
0 characteristic near-arc voltage Vgar (If IJ becomes low,
It is impossible to perform one-time machining without generating electrical discharge. For this reason, especially when machining large areas, it is necessary to keep the specific resistance ρ of the door solution high to some extent, and the specific resistance ρ is controlled using an ion exchange resin. If a small value of the current is desired, it is necessary to set the current limiting resistor RM to a large value, but at the same time, the no-load voltage Vgopen decreases, making it difficult to generate a discharge, which significantly reduces machining efficiency. Therefore, the following countermeasures have been taken as a method of discharge machining using conductive machining fluid.

Figure 9 shows Shigeoki's circuit for VV machining. In this case, two sets of current circuits are connected in parallel to the electrode (1) and workpiece (2). The actual TIF current (released TIF current) is the power transistor (4) driven by the driver circuit (13), the 20th DC 1 source (3), and the current limiting resistor (5). , diode (6
) is supplied from a circuit configured by Before the start of discharge, in addition to the above circuit, a power transistor □□□ is driven by the first drive circuit (to).
, a current limiting resistor cjB, a diode (to), and the like, and a first DC power supply α, an electrode (1)
, more current flows between the workpiece (2). That is, by allowing more current to flow during discharge, the voltage during no-load between the electrodes is increased, making it easier to induce discharge. Next, after a discharge occurs between the electrodes, the discharge detection means (9) detects the discharge, and the switching means (2) sends a signal to the first J) drive circuit oBI to turn off the power transistor (to). This means that the discharge current must be supplied only from the second direct current source (3).

At this time, the resistance value By of resistance (5) t71 is the desired surface roughness.

The value for obtaining the discharge current corresponding to the machining speed f, and the resistance value (total) of the resistance (approximately 3) correspond to the current 1 required for O) to obtain a no-load voltage sufficient to start the discharge together with the Rhl side. Set this value in advance.

In this way, the no-load voltage Vgopen can be found.

T: El: DC tfa voltage on the first drive circuit side E2: DC power supply voltage on the second drive circuit side.

[Problem that the invention seeks to solve]

The conventional electric discharge machining method uses a method of switching the internal impedance of the power supply σ) as described above.In order to calculate the internal impedance of the mlE source t71, the value of the gap impedance Rgap is determined from equation (1). In order to obtain this, there were actually the following problems.

(2) The electrode (1) and the workpiece (2) are not necessarily opposed to each other in a plane, and the distance between the electrodes cannot be directly substituted into equation (1).

■ Depending on the machining shape, as shown in Figure 11, machining
) The opposing area between the poles changes as it progresses. The change in the value of inter-electrode impedance RF&P due to this is so large that it cannot be ignored.

■ Conductive machining fluid 0) The specific resistance changes as machining progresses, and as shown in Figure 12, it has different values between the machining fluid tank, the blade tank, and the discharge gear knob. It is difficult to measure the resistivity between the tubes.

From the above points, it is difficult to calculate the machining impedance g a p 'z by measuring the machining distance 111g, the facing area S between machining poles, and the specific resistance ρ of machining fluid (). It will change as the process progresses and will go on to 7. In addition, if the internal impedance value of the 1W source is not corrected for the gap impedance that changes with the progression E, then f, C as follows.
A problem occurs.

That is, as the value of the th flow IEarc flowing during discharge changes, the #ζ machining current Id changes, as is clear from equation (4). As a result, it is no longer possible to maintain the maximum machining speed for a target machined surface roughness of 1, and the machined surface roughness is kept at 4ζ.

The present invention has been made in order to solve the above-mentioned problems, and is intended to maintain stable machining in general electrical discharge machining. : By automatically changing and setting the internal impedance of the source, the distance between the poles can be adjusted as the machining progresses. Even though the inter-electrode impedance ltgap changes due to changes in the opposing area 8 between the electrodes and the specific resistance ρ, the π surface roughness remains constant from beginning to end, and the surface roughness is always maintained at the target surface roughness. The aim is to obtain an electric discharge machining method that can achieve high speeds.

[Means for solving problems]

The electric discharge machining method according to the present invention uses the impedance between the poles to obtain the desired no-load voltage, the internal impedance of the power supply, and the desired machining current based on this data. It is configured to calculate the internal impedance of leakage.

[Effect]

The electrical discharge machining method according to the present invention is based on the internal structure of a power supply that supplies a no-load voltage higher than the discharge generation voltage during the no-load time until a polar ATC discharge occurs, while taking into consideration the detected inter-electrode impedance σ) data. Calculate the impedance value,
After the discharge occurs, the internal impedance value of the power source is controlled by a predetermined value ζ frA so that a desired machining current flows.

[Embodiments of the invention]

Hereinafter, embodiments of this invention will be described with reference to the drawings. In Figures 1 to 5, (1) is a processing electrode, (2) is a J loe object, (3) is a processing blood flow power supply, and (4) is (4-
1).

(4-2 units... (Z power transistor group consisting of 4-nJ, (5) is (5-1 ha (5-2)...
・Consists of (5-n), each power transistor <
4-L), +4-2)... (4-n)'s Emmy/evening side 3 are connected and 1 is a current limiting resistor group, (6) and (to) prevent current from flowing backwards. 1 diode, (
7) is the detection DC power supply, (8) is the detection means for detecting the inter-electrode impedance lLgap, and αυ is the inter-electrode impedance Rg detected by the detection means aO.
A calculation means calculates the internal impedance of the source based on the impedance between the poles Rgap*T, and the internal impedance of the source based on the ap. A switching means capable of determining an OFF combination pattern, that is, a switching force, and storing a plurality of such patterns, (to) a switching means capable of determining an OFF combination pattern, that is, a switching force, and storing a plurality of such patterns, (to) an arbitrary combination of power transistor groups (4). A drive circuit that can selectively turn on the power transistor (
b) is a storage means for storing the internal impedance value of the power supply calculated by the arithmetic means circle, and αQ selects the resistor in the current limiting resistor group (5) and the power transistor connected to it, and selects the combination thereof. decoding means for determining the pattern, αη is an oscillator that sends the signal from the discharge detection means (9) to the switching stage 10, (to) is the symbol α1), Q2.
The power supply control circuit consists of α, α0゜αη, and the detection resistor switching circuit that switches the current limiting resistor (8).
(Incorporated) is a voltage divider that divides the voltage between poles.Next, we will discuss the operation of each part.

The detection means αO directly measures the interpolar impedance Rgap by a method described below as i. When these methods are used, the distance between poles in equation (1) is 1. Since the impedance Rgap between the electrodes can be directly measured without depending on the opposing area 8 between the electrodes and the specific resistance ρ of the machining fluid, the above-mentioned problems can be solved.

First, the first method is as follows. That is, during the rest time of the processing DC power supply (3), a detection voltage of the same polarity as the processing DC Wl source (3) is applied between the poles by the detection DC power supply (7), which is a separate power supply. This is a method of calculating inter-electrode impedance Rg a p from the voltage appearing between the time electrodes.

In other words, as shown in Figures 1 and 2, the detection DC power supply (
7) is provided and connected to the gap between the electrodes via a current limiting resistor (8). During detection, detection cannot be performed if discharge occurs between the electrodes, so it is necessary to set the voltage between the electrodes Vga so as not to exceed the arc voltage. O)7: Me, as shown in FIG. 1, if the electrical voltage Va of the detection DC power source (7) is set lower than the arc voltage Vgaro, control will be easier.

Even in the case of Vgarc, as shown in FIG. 2, it is detected by the detection means σQ and is 7:1! By processing the voltage gap by the calculating means (b) and switching the value of the limiting resistor (8) by the detection resistance switching circuit (llI), the electric shock voltage Va can be set to be smaller than the arc voltage VgarC. By switching the limiting resistor (8) to an optimal value, it is possible to improve the detection accuracy of the voltage VgaP detected by the detection means αO.

By the way, the power supply voltage value Va, the resistance value Ra, the measured voltage value V g a between the electrodes, and the impedance Rgal between the electrodes
l) lift has the following relationship.

Therefore, the interpolar impedance Rgap can be calculated as follows.

Further, as a second method for determining the interpolar impedance Rgap, there is the following method.

In the m3 diagram, it is for door construction lol! , voltage is applied between the electrodes by the source (3), and the impedance between the electrodes Rg is calculated from the voltage between the electrodes Vg op e n during the no-load time until the discharge occurs.
This is a method of calculating aρ. That is, if the internal impedance of the power supply when no-load voltage is applied is RIC, then the following relationship exists between the power supply voltage E1 electrode voltage Vgopep and the gap impedance Rgap.

Rgap Vgopen= gap+τ7°E
n Rgap=, -, , , , -RX (9) is calculated. Note that the above voltage between electrodes vgopen is A/
There is a method such as reading a digital value into the detection means αG via a D converter.

This method has the great advantage that the DC current @Va (7) for detecting the impedance between electrodes Rg ap and the current limiting resistor Ra (g) are not required. On the other hand, the processing power supply (3
) between the electrodes (after applying this voltage, a dielectric discharge occurs immediately), and in the case of T, the electrode-to-electrode voltage Vgopen cannot be detected during the no-load time, so there is a drawback that the electrode-to-electrode impedance RI cannot be calculated.

Further, as a method for determining the impedance between poles Rgap, there is a method as shown in No. 8. In the fourth factor, some of the power transistor groups (4) are turned on even during the rest time, and the value of the current limiting resistor (5) is set sufficiently large so that the voltage between the electrodes is 01 below the arc voltage. 2
u current, at that time +r appears between poles and calculated from 2 voltage Vgz -r
Find a way to do it. Here, if the internal impedance of the nine thoughts during the rest time is reduced by Rz, the sudden voltage E and the voltage between electrodes Vgz
There is the following relationship between the pole-to-pole impedance 1Lfrap and the pole-to-pole impedance 1Lfrap.

Rgap vg"-Rz+,gap" Therefore, the impedance between poles Rgap can be calculated as gz Rgap=D]77・R2aQ. Current limiting resistance (g) IL a
It has the great advantage that it is not necessary. Well, during the rest time, detect the voltage Vgz between the electrodes and check the impedance l between the electrodes.
In order to calculate Lg n p, as mentioned above, r: a.
can be calculated.

Furthermore, as a method for determining the 112 impedance Rgap, there is a fourth method as follows. In Fig. 5 1ζ, during the down time of the machining power supply (3), a detection DC type # (7) which is a separate power supply has a voltage value lower than the arc voltage VgarO.
According to fζ, a detection voltage having the same polarity as that of the machining crown (3) is applied between the poles, and the impedance between the poles Rg a p is calculated from the voltage appearing between the poles at this time. In this method, the current limiting resistor of the detection DC power supply (7) is replaced by the electric current limiting resistor group (5)
There is a characteristic that the DC current W for detection is
ls! (7) Q)@It has the great advantage that the flow limiting resistor (8) is not required.

The calculating means αD calculates the internal impedance value of the r:lit source according to each of the situations listed below based on the interpolar impedance RF a p measured by the detecting means αG.

In contrast to the no-load state G after application of the 1-1 voltage and before discharge, the no-load voltage Vgo is sufficiently high for discharge to occur.
The electric internal impedance Rx1 is enough to obtain the pen.
Calculate. As soon as it is detected that a discharge has occurred L7, the internal impedance of the power source is switched from RX to the internal impedance of the power source) L7 to obtain the desired discharge current Id during the discharge, but the power transistor etc. Since the element (4) has a sweep and a switching delay time, the time between the poles during that time is expressed as 7-W14.
The current Ibpeak flows as shown in FIG. 6(b). Since a current greater than the desired discharge chamber current Id flows by an instantaneous current Ibpaalζ, there is a drawback that the machined surface is roughened.

Inpeak=-Izarc-"-vg"C
E-Vgarc b, x value.

At this time, the no-load voltage Vgopen, the gap impedance B・gap, and the %ffi part impedance Rx
The relationship between is, However, what about E? The voltage of the current power source (3), i.e., the no-load voltage Vg o p a
n and the impedance between γ and l! From Jrap, the power supply internal impedance RX is calculated using the αη formula.

Second, during discharge, the impedance between electrodes Rgap
Accordingly, the electrolytic chamber flow IfarO that does not contribute to processing changes
changes f, 2f, and the discharge current Ide-T required for machining
In order to control F-1, the discharge current Id and the electrolytic current Ir
The total impedance Rgap of the entire Hayabusa flow including arc
It is controlled accordingly. Now during discharge σ) Electrolyte chamber flow I, ra
rc and discharge current Id are expressed by the following equation.

Here, R7 is the internal impedance of the power supply, and is the combined resistance value formed by the combination 1 of the current side>v resistance group (5). Well, the arc voltage Vgarc is the 7th
As shown in Figure C, it has been experimentally confirmed that the discharge current depends on Id+. To measure the impedance R between poles
The internal impedance R7 of the power source can be calculated from g a p , the desired discharge current value Id, and the arc voltage Vgarov value. The internal impedance values Rx and Ry of the power source calculated by the calculation means 0 are stored in the storage means α sent to.

As a method of calculating the inter-electrode impedance Rgap, a method of applying a voltage between the electrodes during the rest period (as described above).

In the case of the "eighth method", the power source circle impedance value Rz, which is set so that the inter-electrode voltage becomes lower than the arc voltage during the rest period, is also sent to the storage means (b). The switching means (a) performs switching to select normal work during no-load time, R7 during discharging, and Rz during rest time from among RX, Ry, and Rz. The configuration of the current limiting resistor group (5) is determined at the design stage of the power supply, but the decoding means αQ is composed of Rx, approximately, Rz
In order to achieve the internal impedance of the value, the current limiting resistor! (5) Decide which resistors to use in combinationL, Select the power transistors connected to the determined resistors to be used, and create a combination pattern of the power transistors.-For example, Sat=01 +a2 +・・・・・・+Qn… (To) 1
1LX ”X-π] However, αI, Q2...Q, is 0 or 1 MaT
:If Rx is replaced by Ry, then the equation (to) still holds true.R+, R2,...Rn are current limiting resistors (5-1).

(5-2)... Resistance value of (5-n).

tk=1.2...nノ Determine the sequence of numbers such that ÷.

By the way, the target no-load voltage Vg op e n
requires a minimum arc voltage vFare, but in principle any voltage is acceptable as long as it is higher than that.

Now, when the target value of the no-load voltage vgopen is determined, there are two types of control: control that matches the target value, and control that does not lower the target value E, especially when the target value is easily obtained. Be able to think. In other words, when the electrode area S is small and the inter-electrode impedance l (gap is sufficiently large),
A case like the latter may occur.

However, the detection of group 9 by the discharge detection stage (9) is
The height of the no-load voltage Q+ depends on the time delay of discharge detection since S is compared with the voltage between electrodes with respect to a discharge reference voltage. It is better to keep the no-load voltage as constant as possible, and it is preferable that the no-load voltage be controlled by the calculation means (6) to keep it constant. , the interpolar impedance approximately gaP can be calculated by the detection means αG, and the calculated data can be outputted once for each KL pulse.

The calculating means αη is output once for each voltage pulse G by the detecting means αO, and y: inter-electrode impedance Rgap.
Based on! Calculate the internal impedance of the song.

By the way, when determining the internal impedance of the power supply based on the inter-electrode impedance output from the detection means αG, the following method is available as a method for processing data of the calculated inter-electrode impedance Rg a p.

The first method is to calculate the internal impedance for the next pulse from the interpolar impedance Rg a p that is output once for each pulse.

In other words, this method attempts to use the information on the inter-electrode impedance during the previous pulse to determine the internal impedance when applying the current pulse, and is able to immediately respond to changes in the inter-electrode situation. It is.

But let it go! During machining, disturbances such as accumulation of machining powder may cause temporary short-circuits or short-circuits between the machining electrodes. Under such conditions, the voltage between the machining electrodes may be zero or less than fζ.
Indicates a close value. That is, in equations (8), (9), and 00, zero is substituted for Rga, Rgopen, and Rgz, and a value close to that is substituted for π. As a result, Rgap approaches zero, and (b) Rx is calculated using equation (2).

Ry also approaches zero. This means that the violet current power supply for processing (3)
This means supplying a large current between the poles through a very small resistance. A discharge with a large amount of energy is generated at the T point, and a machined surface with a roughness greater than the intended surface roughness is formed.

In order to compensate for the drawbacks mentioned above, a second method is to use the latest n data (n
There is a method of calculating the average value Rga p-m of ≧2) and using the result to calculate the internal impedance. For example, as shown in the conceptual diagram of FIG. 8, consider a single memory with addresses 1 to n. For this memory, Rgap
In this method, new data input from outside is always input at address 1, and previously existing data is moved to address +1 and stored. do. If you do this, the memory will store data of the latest telephone number + 71n R gaps.

Using the contents of this memory +7), the calculation means (6) executes the calculation to obtain the average value Rga p-m, and this value is also used to calculate the internal impedance of the power supply.

Alternatively, the following eighth method can be considered using the memory described in the second method. It is the latest σ)n gap impedance Rgap that is stored in the memory.
This method uses Rgap with the maximum value as the representative value. By appropriately selecting the size of n, it is possible to avoid adopting an Rgap value of zero or close to zero, which occurs when a short circuit occurs or is close to a short circuit.

The drive circuit (to) of the next+t power transistor group (4) decodes the data of the selected combination pattern of power transistors sent from the switching means (1B power), A signal that turns on the power transistor is output to the connected signal line.

As mentioned above, change the internal impedance of the source in response to the change in the interpole impedance ap, and in response to each of the following situations during each voltage pulse.

■ When applying voltage between the poles after the previous pause, w
1. RX to calculate the internal impedance of the source using equation (6)
shall be.

■ When the discharge detection means (9) detects that a discharge occurs between the electrodes, the detection signal is switched to the switching means (2).
and switches the internal impedance from RX to approximately y calculated using the @ formula.

(2) When the desired voltage pulse time has passed γ At this point, all power transistors are turned off for a rest period.

Processing progresses by repeating the above operations in row 1 (row 1).

In addition, in this example, a general-purpose electrical discharge machine has been described.
The same effect can be achieved with wire carts and electric dischargers.

〔Effect of the invention〕

According to the present invention, the inter-electrode impedance is detected in response to the change in the inter-electrode impedance caused by the change in the release state between the electrodes, and the power source is adjusted based on the data. Configure with Z number to calculate internal impedance 1
As a result, the optimum no-load current and desired machining current can be obtained. Therefore, while maintaining a stable flow state, it is possible to obtain an electric discharge machined surface with a uniform surface roughness that is uniquely determined by the setting of machining conditions. It is possible to obtain an inexpensive and practical electric discharge machining method in the area of machining and finishing, and it is responsible for extremely effective effects.

[Brief explanation of the drawing]

at< is the circuit diagram of the machining power source in the electrical discharge machining method according to one embodiment of the present invention σ), Figures 2N to m5 are circuit diagrams of the machining power source in another method of the present invention, and Figure 6 is the machining power supply circuit diagram of the machining power source in the electric discharge machining method according to one embodiment. Voltage and inter-electrode current O) Waveform factor, Figure 7 shows the correlation between arc voltage and discharge current, Figure 8 is a conceptual diagram of the first memory that stores the latest inter-electrode impedance data, @9 The figure is for machining in the conventional electrical discharge machining method! : Muku 0! The circuit diagram, Fig. 10, is a configuration diagram of the interpole Q/configuration in the case of r and −, and Fig. 11 is for complex shapes! FIG. 12 is a diagram showing the increase in the opposing area as the pole progresses, and FIG. In the figure, is (1) for processing? pole, (2) is the far Loe field, (3) is the processing electric M, (4) is the power transistor i
, (5) is a current limiting resistor group, (7) is a detection DC voltage υ,
(9) is discharge detection means, αG is detection means, (B) is calculation means, (6) is switching means, (to) is drive circuit, α storage means, αG is decoding means, (to) is control It is a circuit. In addition, in the figures, the same reference numerals indicate the same or equivalent parts.

Claims (3)

[Claims] (1) Using a conductive machining fluid as the machining fluid, a pulsed voltage is repeatedly applied between the poles formed by the electrode and the workpiece to generate an electrical discharge, and the discharge energy is used to machine the workpiece. In the electric discharge machining method to be carried out, an impedance between the electrodes and the workpiece is detected, which is formed from the distance between the electrode and the workpiece, the opposing area, and the specific resistance of the conductive machining liquid, and a voltage is applied between the electrodes to generate electric discharge. During the no-load time until the discharge occurs, the internal impedance value of the power supply that supplies a no-load voltage higher than the discharge generation voltage is calculated by the calculating means from the above inter-electrode impedance value, and the value is changed to that value, and the discharge occurs. After detecting this, in order to obtain the desired discharge current, the internal impedance value of the power source that causes a predetermined machining current to flow is calculated from the inter-electrode impedance value, and is controlled to be changed to that value, and the current is passed for a predetermined time. The electrical discharge machining method is characterized in that the series of operations is repeatedly controlled after a predetermined pause time. (2) There are n resistor groups connected in parallel, and the reciprocal of each resistance value Rk (k=1, 2...n) has a binary configuration, and the n resistors have a binary configuration. 2. The electric discharge machining method according to claim 1, wherein a desired internal impedance of the power source is set by the selected combination. (3) The electric discharge machining method according to claim 1, further comprising a machining voltage detecting means that uses an analog/digital converter to input a machining voltage value into a calculation means.