JPH0329531B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electric discharge machine, for example, a linear or strip-shaped machining electrode, which is tensioned by a holding device and a guide device, and a controlled relative movement between the workpiece and the electrode. This invention relates to a spark discharge machine that cuts metal products and shapes them.

In spark electrical discharge machines, the tool electrode is placed close to the metal workpiece with a small gap, and an electrical discharge, or spark, is generated between the tool electrode and the workpiece, and at the same time advances the tool electrode into the workpiece. . The workpiece is eroded and the shape of the tool electrode is replicated on the workpiece. The desired machining shape is obtained by subjecting the tool electrode to a predetermined shape and/or movement. The feed of the electrode is controlled by a servo device such that a small gap (hereinafter referred to as the working gap) is always left between the metal workpiece and the electrode during machining. A liquid or gaseous cleaning medium is flowed through the working gap to cool it, remove or wash away the products of erosion, and deionize the working gap. The electrical pulses forming the spark are generated by a suitably adjustable generator to control the processing operation with respect to variable parameters such as current voltage frequency, pulse impact coefficient, interpulse spacing, etc. This operational control is further achieved by selecting the particular combination of tool electrode and workpiece materials and the liquid or gaseous cleaning medium. Those parameters are set either by the operator or by numerical control. The associated movements between the tool electrode and the workpiece are also performed manually or usually by control circuits. Preferred control circuits are described in US Pat. Nos. 3,830,996 and 3,822,374. Optimal electrical discharge machining monitoring and control methods are described in US Pat. Nos. 3,859,186 and 3,975,607. The tool electrode may be a wire or strip of suitable cross-sectional shape. The linear or strip-shaped machining electrode is unwound from the supply reel and is constantly renewed at the actual machining point. Since the cross-sectional area of the processing electrode is, for example, 0.1 mm ² to 2 mm ² , it is flexible, that is, it can bend and vibrate like the strings of a musical instrument. During machining, the tool electrode is subjected to forces that cause it to deflect and vibrate. Through recent observations of the present inventors, information regarding the conditions under which such forces are generated and acts has been obtained. It has been found that the force produced by a burst discharge or spark in the working gap is proportional to the discharge machining performed. Therefore, the deflection of the tool electrode, which affects machining accuracy, is also proportional to the degree of machining. Therefore, attempts to increase and improve the amount of electrical discharge machining inevitably result in unacceptable deflection or vibration of the machining electrode, destabilizing the machining process, reducing machining accuracy or cracking, and causing the conductive tool electrode to become unstable. This resulted in a short circuit between the wire and the workpiece, resulting in the machining being terminated midway. Since stability is the most important factor in erosive machining, electrical discharge machining has been performed with lower machining performance or lower machining accuracy as a compromise solution.

An object of the present invention is to reduce abnormal movement of a machining electrode and improve machining accuracy without reducing machining speed and performance.

According to this invention, an electrical discharge machine includes a pair of support/connection devices that support and apply tension to an elongated flexible tool electrode and electrically connect the tool electrode;
an electrical supply device connected to a connecting device, which supply device can be connected to the metal workpiece to be further processed. In operation,
A spark discharge occurs in the working gap between the tool electrode and the workpiece. Electric discharge machining of the workpiece is then performed by controlled relative motion between the tool electrode and the workpiece. According to this invention, an electrical compensation signal is applied to the tool electrode, that is, the conducting wire electrode, and an electrical signal flows between the tool electrode, that is, the conducting wire, and the workpiece. The compensation signal supply device supplies energy to create a force between the tool electrode and the workpiece of a nature that reduces spurious movements of the tool electrode caused by forces associated with electrical discharge machining.

This compensation signal is generated in the power supply generator and can control the magnitude of its output, ie voltage, current and, in the case of alternating current, frequency.

According to one embodiment, the output of the compensation signal supply device is connected to each connection device of the tool electrode via a decoupling device, for example a diode and/or a resistor.

According to another embodiment, the operating power is coupled to said two support and connection devices by being connected to the center tap of the transformer, said support and connection device pair being connected to both terminals. There is. A compensation current is supplied to the primary winding of the transformer.

In both of these embodiments, the compensation signal supply device is configured to supply a compensation current signal that flows through the tool electrode and produces a controllable electromagnetic field in the working gap, the field being e.g. Any alternating electromagnetic field of possible magnitude and frequency may be used.

In a further embodiment, one of the two output conductors of the compensation signal supply device is connected to the support and connection device and connected to the tool electrode, and the other output conductor is decoupled by a suitable decoupling device. Connected to the processed product. In this embodiment, a compensation signal supply device supplies a compensation voltage signal between the tool electrode and the workpiece to create a controllable electric field in the working gap, preferably an alternating electric field of controllable magnitude and frequency. , is configured to form.

In order to better understand how the invention is implemented, it will be explained below with reference to the accompanying drawings, in which: FIG.

In FIG. 1, the conductor electrode 1 is unwound from the supply reel 2 and tensioned through rollers 3 and 4 of a holding device (not shown), after which it is placed on the take-up reel 5.
wrapped around. Although the retaining device is not specifically shown, various forms of retaining device can be used, such as the linear electrodes shown and described in US Pat. No. 3,891,819. These types of holding devices can also be used in the FIG. 1 embodiment of the invention. In FIG. 1, the rollers 3 and 4 tension the conductor electrode 1 in the same way as the strings of a musical instrument; furthermore, the rollers 3 and 4 constitute current supply elements for the tool electrode, i.e. the conductor electrode 1. An operating voltage current is applied to the rollers 3 and 4 by a pulse generator 6 and flows to the tool electrode 1 and also to the workpiece 7. The workpiece 7 effectively forms an electrode, hereinafter referred to as the workpiece electrode. Pulsed current from pulse generator 6 is well known, as described, for example, in US Pat. The -output 61 of the generator 6 is decoupled (DECOUP-LING) to the two current supply conductors rollers 3 and 4.
Diodes 71, 72 and decoupling resistors 73, 74
is connected to supply current to the conducting wire electrode 1. The decoupling diodes 71, 72 supply a pulse to the working gap between the tool electrode 1 and the workpiece electrode 7 when the pulse generator 6 supplies a bipolar pulse, and in turn when a unipolar pulse is generated. It is arranged to feed only in the direction. Using a relatively large diameter tool electrode, in this case the voltage drop caused by the compensation current between the current supply conductors to the rollers 3 and 4 is sufficiently small that the decoupling diode 7
1 and 72 may be omitted. However, resistance 7
3,74 remains under all conditions. The other output 62 of the pulse generator 6 is connected directly to the workpiece electrode 7. During electrical discharge machining, the wire electrode 1 passes from the supply reel 2 in the direction of the arrow through the working gap to the take-up reel 5, so that the wire electrode 1 is constantly refreshed. The conductor electrode 1 can also be moved in the opposite direction. The desired shape 9 is produced in the workpiece electrode 7 by the associated movement between the electrodes 1 and 7 under suitable control. The various forces that act on the conductor electrode 1 within the working gap during electrical discharge machining are (a) the electric field between electrodes 1 and 7, (b) the electromagnetic field around electrode 1, (c) spark discharge, and (ni) the electric field between electrodes 1 and 7. ) It was found that the formation was caused by the generation of bubbles in the dielectric material. The resultant force of these forces (all together referred to as erosive forces) causes vibration and bending in the conductor electrode 1,
This may make the electrical discharge machining unstable and even cause a short circuit between electrodes 1 and 7.

According to the invention, a compensation circuit 8 is provided to eliminate vibrations due to this corrosive force, the output conductor 81 of which is directly connected to the roller 3 forming the current supply device. The other output conductor 82 is connected to the roller 4 which constitutes the other current supply device of the tool electrode 1. During the erosion process, the compensation circuit 8 acts in such a way that the compensation current (DC or AC) flowing through the tool electrode 1 compensates for the erosive forces acting on the electrodes 1 and 7. Here, the vibration of the electrode 1 is removed by utilizing the force generated by the electromagnetic field surrounding the conductive wire electrode 1. During the erosion process, the compensation circuit 8 connects the conductors 81, 82,
Magnitude or frequency of the compensation current flowing through the supply conductors of rollers 3 and 4 and electrode 1 (if alternating current)
Or control both. Compensation current is circuit 8
may be adjusted manually within the system, or by numerical control methods or optimization methods such as those described in the above-mentioned US patents. A control signal is applied from a conductor 83 shown in broken lines. The pulse generator 6 receives control parameters such as current, voltage, repetition frequency, pulse duty factor, pulse gap, etc. through an input conductor 63 from the above-mentioned numerical control scheme or optimization scheme, or from a known method such as that shown in the above-mentioned US patent. The pulse generator 6 itself is manually adjusted in the following manner.

FIG. 2 shows another embodiment of a compensation circuit 8 for compensating for the erosive forces occurring during the erosive process. The remaining members are the same as those in FIG. 1 and are designated by the same numerals. Therefore, only the differences in circuit connections will be explained below. The erosive pulse generator 6 has its output conductor 6
1 is connected to the two current supply conductors of rollers 3 and 4 via a secondary winding 110 of a transformer 10. Output conductor 61 is connected to the center tap of secondary winding 110 to prevent feedback of compensation current to compensation circuit 8. The compensation circuit 8 is connected by two output conductors 81 and 82 to the primary winding 12 of the transformer 10 and transmits an alternating current to the tool electrode 1 via the current supply conductor rollers 3 and 4. In this way the erosive forces are compensated in the same way as shown in FIG. The magnitude and frequency of the compensation current is adjusted manually in the compensation circuit 8 or via the conductor 83 by means of numerical control or optimization. In the embodiment shown in FIGS. 1 and 2, the compensation circuit 8 generates an alternating current that compensates for the erosive forces, the frequency of which is sufficiently different from the resonant frequency of the tool electrode 1.

FIG. 3 shows other connections of the circuit 8, in which similar parts to those shown in FIGS. 1 and 2 are designated with the same reference numerals. The circuit 8 of FIG. 3 is connected to the current supply conductor rollers 3 and 4 through a conductor 81. It is sufficient that the compensation circuit 8 is connected by an output conductor 81 to only one of the rollers 3 and 4, the other output conductor 82 of the circuit 8 being connected to the output conductor 62 of the erosion pulse generator 6. ing. conductors 81 and 61
Decoupling diodes 71 and 72 are inserted, and the compensation circuit 8 supplies a compensation voltage (DC or AC voltage) between the electrode 1 and the workpiece 7. The magnitude and/or frequency (in the case of alternating current) of the compensation voltage is adjusted manually in the compensation circuit 8 or in a numerically controlled or optimized manner via the control conductor 83. Pulse generator 6 and compensation circuit 8
The synchronizing conductor 11 between the working gap 9 and the working gap 9 synchronizes the compensation voltage with respect to the operating voltage in the working gap 9 in order to compensate for erosive forces in the working gap 9. The pulse generator 6 supplies pulses via conductors 61 and 62 to the working gap 9 between the electrode 1 and the workpiece 7 in a known manner. The compensation circuit 8 supplies a compensation voltage to the working gap 9 via conductors 81 and 82, for example in the erosion pulse gap. A compensation voltage may be applied to a particular group of pulses from the pulse generator 6. In this case, the magnitude of the compensation voltage may be different. in this case,
Synchronization between the compensation circuit 8 and the pulse generator 6 must take place via the conductor 11. A compensation voltage is applied to the gap 9 between the electrode 1 and the workpiece 7, so that the tool electrode 1 is not subjected to resonance effects.

The compensation power provided by the compensation circuit 8 can be controlled in various ways. In FIG. 4, for example, power at a commercial power supply voltage and frequency is transformed by a transformer T, rectified by a diode rectifier circuit REC,
It is waved by capacitor FC. A voltage of the appropriate value then appears at terminals T1 and T2. The terminal T2 is connected to the second switch S1 via the first switch S2, and the second switch S1 is connected to the conductor 82 and the resistor R.
1, R2, R3... can be selectively connected to Rn. Conductor 81 also shown in FIGS. 1 to 3
is directly connected to terminal T1. Switch S2
Assume that it is closed. By selectively engaging resistors R1, R2...Rn, the power applied to conductors 81 and 82 can be controlled. Switches S1 and S shown in FIG. 4 as mechanical switches
2 can be replaced by an electronic switch. In particular, switch S2 can be a fast-acting electronic switch that interrupts the application of the selected current at frequency f, as indicated by the arrow. Switch S2
are controlled to open and close from the broken line 11, thereby opening and closing the conductors 81 and 82 as explained in connection with FIG.
It can also be used to synchronize the supply of power to. If switch S2 is open, compensation power is disconnected from the entire system.

During the spark erosion treatment process, the workpiece and conductive wire (thin wire)
A force is generated between the workpiece and the tool electrode due to an explosive discharge that tends to bend the tool electrode. Since these forces are not uniform, the bending of the tool electrode varies.

The voltage between the tool electrode 1 and the workpiece electrode 7 due to the pulse generator 6 forms an electrostatic field. This electrostatic field is proportional to the square of the voltage and tends to attract the tool electrode 1 and the workpiece electrode 7. A current is flowing through the tool electrode 1. Therefore, when cutting a ferromagnetic material, an electromagnetic field proportional to the square of the current is also generated,
Similarly, the tool electrode and the workpiece are attracted. The effects of electrostatic and electromagnetic fields are well known and fundamental to electrical technology. These forces act in turn as erosive forces and tend to reduce the bending of the conductor from the workpiece.

The various erosive forces and electric/electromagnetic fields due to the voltage across the gap between the workpiece and the tool electrode and the current flowing through the tool electrode are not self-compensating, nor are they constant or uniform. The compensation power applied to the tool electrode by conductors 81 and 82 transforms the electric and electromagnetic fields due to voltages and currents resulting from the machining process itself, effectively compensating the entire force acting on the tool electrode.

The voltage and current supplied for compensation are determined by first measuring changes in the electric and electromagnetic fields, and then calculating the required compensation current or voltage.
These values are stored, for example, in a numerical control device or in a suitable device. These machine tool numerical control devices, commonly used as discharge erosion devices, store information relating to discharge frequency, gap voltage, discharge current, etc. There is no fixed theory as to the required compensation voltage or current, respectively; the actual compensation current and voltage magnitude and frequency (in the case of alternating ones) depend on many variables, primarily the The relationship depends on the material of the workpiece, its size, thickness, etc., and the best one is determined experimentally and stored in the numerical control device. The results of these investigations can be tabulated and the same numerical control device can be used to control the operation of the electrical discharge machining process and to control the compensation current and voltage in magnitude and frequency (including zero frequency) to obtain effective compensation. can be memorized.

Practical Example Using the apparatus shown in FIG. 1, a workpiece 7 made of steel with a thickness of 30 mm was cut using a wire electrode 1 with a diameter of 0.25 mm. In this case, a pulse having a no-load open circuit voltage of 300 V, a pulse peak current value of 200 A, a pulse width of 1.2 microseconds, and an average machining current of 3 A was applied between the workpiece 7 and the wire electrode 1 from the pulse generator 6. The feeding speed of wire electrode 1 is 0.5 mm/min. The gap width between the wire electrode 1 and the workpiece 7 was 0.295 mm. In this case, if only the pulse generator 6 was used without the compensation circuit 8, the wire electrode 1 would be deflected by about 0.1 mm to 0.2 mm. However, using the compensation circuit 8 shown in Fig. 4, the voltage across the capacitor FC is 300V, R1 = 30
Ω, R2=15KΩ, R3=1KΩ, R4=500Ω,
When Rn=330Ω, capacitor FC=47μF, switch S1 is set to R4, and switch S2 is closed, the above-mentioned deflection of wire electrode 1 disappears. Even when switch S2 was turned on and off in the range of 1 to 50,000 Hz, the above-mentioned deflection could be eliminated.

In the case of Fig. 2, a compensation current of 20A and 1500Hz is applied, and in the case of Fig. 3, in the same state, but with the workpiece 7 being a non-ferromagnetic material, 300V and 30KHz are applied.
By applying a voltage of , it was possible to compensate for the deflection, that is, the strain force.

FIG. 5 shows a detailed diagram of the basic circuit of the portion A surrounded by the two-dot chain line in FIG. 4. Switch S1 has been replaced by transistor TR1, and further transistor connections for other resistors are not shown, but they will be self-explanatory. The transistors themselves are controlled by optocouplers OC1 and OC2 to provide complete voltage isolation. The optical couplers OC1 and OC2 are digital storage devices, for example, product name SN7475N (manufactured by Intel Corporation).
Connected to TTL (Transistor・Transistor・Logic) logic circuit. Digital storage device DS is
Coupling resistors CR1, CR2...CRn are coupled to the optical coupler, respectively. The digital storage device DS is connected to a data bus 83 (FIGS. 1-3) and inputs signals from the numerical processing control device. The operation of this circuit is basically almost the same as that shown in FIG.

6 and 5 are similar except that a transistor chopper circuit is provided so that alternating current is applied to lines 81 and 82. For example, the chopper frequency Fz corresponding to the number of closings f of switch S1 in FIG.
can be guided directly into the system, i.e. can be controlled from the outside. This frequency depends on the variables listed above, and also on the cleaning fluid, the tension of the electrode, its material, and other variables. The vibration frequency of the electrode without compensation current can be easily determined under the given operating conditions,
A compensation frequency can then be applied. Transistor chip is a switching transistor
It includes ST1 and ST2, an output transformer TO and a second transformer guiding the switching frequency Tf.

FIG. 7 shows a voltage control circuit, which is used, for example, in the embodiment of FIG. resistor R1,
R2...Rn are combined with resistor RD to form a voltage divider. The voltage developed at the junction of this voltage divider is directed to an emitter follower output transistor TRO and an output coupling resistor RO. Figure 7 shows another transistor TS controlled by the optocoupler OCS and providing synchronization;
is controlled by a synchronizing signal from a pulse generator 6 or a frequency controller, for example a line 11 connected to a suitable variable frequency source. Since the signal coming from the pulse generator 6 through the line 11 is of such a nature that it disables the optocoupler OCS, the output coupling transistor TRO is discharged, i.e. during the presence of pulses from the pulse generator 6. , it's a turn off. The operating voltage of the pulse generator 6 is therefore not interfered with by another compensation voltage occurring during the application of pulses from the pulse generator 6 itself.

Control of the compensation power is performed digitally by a digital storage device DS, as shown. The amplifier may be any power amplifier similar to that used in the final stages of high fidelity power systems known, for example, in radios, records and other audio reproduction equipment. The data bus 83 from the numerical control device is a digital
It must be connected via an analog converter to supply an analog signal to a power amplifier as described above.

Various modifications and variations are possible and the features described in connection with the embodiments may be used together with others within the spirit of the invention.

For a detailed explanation of the various forces that act on the conductor wire or thin wire electrode during electrical discharge machining operations, please refer to the German Technical Society Journal (VDI-
“Effect of Forces Occurring in Spark−
Erosive Cutting” (1976, vol.
118, No. 1, January, pp. 13-17).

[Brief explanation of the drawing]

FIG. 1 shows a simplified arrangement of the tool electrode and its support device, the workpiece and the circuit supplying the machining power; FIG. 2 shows the different circuit connections;
3 shows further connections, FIG. 4 shows a schematic diagram of the compensation signal supply device, and FIGS. 5 to 7 each show the circuit diagram of FIG. 4 in detail for each embodiment. It is something that 1... Wire electrode, 2... Supply reel, 3, 4...
... Roller, 5 ... Take-up reel, 6 ... Pulse generator, 7 ... Workpiece, 8 ... Adjustment circuit, 9 ... Processing shape, 10 ... Transformer, 11 ... Synchronous conductor, 1
2...Primary winding, 61, 62...Output conductor, 7
1, 72...Diode, 73, 74...Resistor,
81, 82...output conductor, 110...secondary winding.

Claims (1)

[Scope of Claims] 1. An electrical discharge machining method that eliminates reductions in electrical discharge machining accuracy and electrical discharge machining speed caused by deflection or lateral vibration of a wire electrode under mechanical tension during an electrical discharge machining process, comprising: In addition to the machining process, the wire electrode 1 is electrically influenced, and the electromagnetic field generated by this electrical influence causes the deflection or lateral vibration of the wire electrode 1 during the electrical discharge machining process. An electric discharge machining method characterized in that the generated force is compensated. 2. Normal electric power for performing electrical discharge machining in electrical discharge machining equipment that eliminates deterioration in electrical discharge machining accuracy and electrical discharge machining speed caused by deflection or lateral vibration of the linear electrode under mechanical tension during the electrical discharge machining process. Supply means 6
In addition to this, it is further characterized in that a compensation generating means 8 is connected to the line electrode 1 or the line electrode 1 and the workpiece 7 to compensate for the force that causes the deflection of the line electrode. Electrical discharge machining equipment.