JPS5973226A - Machining power supply of electric discharge machining device - Google Patents

Abstract

PURPOSE:To improve the machining speed and surface roughness by feeding a rough/medium machining power supply across electrodes through a low inductance feeder and feeding a finish machining power supply across electrodes through a low capacitance feeder. CONSTITUTION:A rough/medium mechining power supply generated by transistors 16, 18 is applied across electrodes consisting of a work 14 and an electrode 34 through a low inductance feeder. This circuit has a solenoid switch 40 near the electrodes. A finish machining power supply generated by a transistor 20 is applied across electrodes through a low capacitance feeder 42, and the feeder 38 is cut off by the solenoid switch 40 during the finish machining. Accordingly, the machining speed during the rough/medium machining and the surface roughness during the finish machining can be improved for machining.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a machining power source for an electric discharge machining device, and particularly to a machining source that supplies machining energy between a workpiece and an electrode placed opposite thereto. be.

As a machining power source for a conventional electrical discharge machining device, there is one shown in FIG. In FIG. 1, the positive side of a DC power supply 10 is connected to a workpiece 14 via a feeder 12, and the negative side is connected to the emitters of a plurality of transistors 16 to 20 as switching elements. Current limiting resistors 22 to 26 and diodes 28 are connected to the respective collectors of
- 32 are connected, one ends of the current limiting resistors 22 - 26 are connected via the common feeder 12 to an electrode 34 located opposite the workpiece 14, and one ends of the diodes 28 - 32 are connected together as described above. Connected to the positive side of the DC power supply 10,
A pulse oscillator 36 is connected to each pace of the transistors 16-20. In the illustrated example, as described above, the workpiece 14 is connected to the positive side of the DC power supply 10 and the electrode 34 is connected to the negative side, but the reverse may be the case.

A conventional processing power source has the above-mentioned circuit configuration, and its operation will be explained below. The transistors 16 to 20 are controlled on and off by a signal from a pulse generator 36,
A voltage is applied between the workpiece 14 and the electrode 34 (hereinafter referred to as the electrode gap), and this voltage application causes dielectric breakdown in the electrode gap and current flows. At this time, the current flowing between the electrodes is determined by one or a combination of transistors 16 to 20. In the transistor 20, the resistance value of the current limiting resistor 26 is set to meet the condition for obtaining the minimum surface roughness, and is usually larger than the resistance values of the other resistors 28 and 30.

FIG. 2 is a diagram of voltage and current waveforms between the machining electrodes during rough machining and semi-machining, where (a) shows the voltage waveform and (b) shows the current waveform. In FIG. 2, the rise of the current waveform is expressed by the following equation.

Here, v2 is the arc potential between the poles, R is the resistance 22~2
6, L is the inductance of the feeder 2, and inductances such as resistances are ignored.

According to the above equation, the current rise is an exponential function with a time constant of d. When the current falls, the transistor is turned off.
Starting from the time when , the stain current continues to flow due to the inductance of feeder 2, passing through diodes 28 to 32,
It becomes an exponential function with a time constant L/L. For example, 1t=10
, if L = 10 μH, the time constant is about 10 μH, and since it takes 3 to 4 times the time for the current value to decrease to a value where the influence of the current is ignored, the rest time is equal to that time. Furthermore, the time required for arc prevention is added.

Therefore, the down time is long and processing time is lost. For example, in the wire-cut electrical discharge machining method, the time required to prevent arcing is about 6 to 10 μm, so the loss in machining time is large.

Generally, in order to prevent the above-mentioned loss, efforts are made to reduce the inductance of the feeder 12 as much as possible. For example, a low inductance coaxial cable may be used for the feeder 12. - As an example, L=1μI-1, 几=1
If it is set to 0, the time constant will be 1μ, and the rest time will approach the time required for arc prevention. Figure 3 shows the voltage and current waveform diagram when using a coaxial couple with inductance, and (a) is The voltage waveform (b) is the current waveform. Comparing FIG. 2 and FIG. 3, it can be easily determined that the repetition frequency has increased.

However, low-inductance coaxial cables have large capacitance. Therefore, in low surface roughness processing, the influence of capacitance is large, and there are cases where a surface roughness of 1 to 3 μRmax cannot be obtained. That is, when a low inductance cable is used to increase the processing speed in rough machining and semi-machining, it has become impossible to perform low surface roughness machining.

This phenomenon will be explained with reference to FIG. 4. FIG. 4(a) shows the voltage waveform during finishing processing, and FIG. 4(b) shows the same current waveform.

When a voltage is applied, the stray capacitance of the low-inductance scoop is first charged, and when discharge occurs, the stray capacitance causes a capacitor discharge, and then a pulse current is supplied. In other words, no matter how small the pulse current is to obtain low surface roughness, the surface roughness is poor due to capacitor discharge due to stray capacitance, and low surface roughness processing becomes impossible.

The present invention has been made in view of the above-mentioned conventional problems, and its purpose is to improve the machining speed of rough machining and semi-machining, and to provide a power source for machining that is capable of machining with low surface roughness. be.

In order to achieve the above object, the present invention provides a machining power supply for an electric discharge machining device having a rough/medium machining circuit and a finishing machining circuit, in which the output of the rough/medium machining circuit is transmitted through a low-inductance feeder. The output of the finishing circuit is configured to be applied between the poles via a low capacitance feeder, and when finishing is done, an electromagnetic switch that cuts off the low inductance feeder is connected to the pole. A machining power source for an electric discharge machining device characterized by being installed nearby.

Hereinafter, preferred embodiments of the present invention will be described based on the drawings. FIG. 5 shows a circuit diagram of the power supply for machining according to the present invention, in which the same parts as in FIG. 1 are denoted by the same reference numerals.
24 is connected to the electrode 34 via a low inductance cable 38 and an electromagnetic switch 4° provided near the poles, and the resistor 26 is connected to the electrode 34 via a low capacitance cable 42.
The configuration is such that the two are connected to each other.

The embodiment of the present invention consists of the above configuration, and its operation will be explained below. During rough machining and semi-machining, the output of the pulse oscillator 36 turns on the transistors 16 and 18, closes the electromagnetic switch 40, and applies a voltage between the poles. At this time, since the machining current flows through the low inductance cable 38, the voltage and current waveforms between the electrodes are
), the machining speed can be increased as described above.

Next, during the first finishing process, machining to reduce the surface roughness of the bevel, the electromagnetic switch 40 is opened to disconnect the low inductance scoop 38. That is, voltage is applied between the poles only through the low capacitance cable 42 to generate discharge. The voltage waveform and current waveform between the electrodes during this finishing process are different from the waveforms shown in Figures 6(a) and (b), and the current waveform in Figure 6(b) is different from the conventional one and is pulse-shaped. Furthermore, the discharge energy is controlled to a desired value, making it possible to perform machining with low surface roughness. At this time, the influence of the inductance L of the low capacitance scoop 42 is ignored because the resistance value L of the resistor 26 is sufficiently large. - For example, the inductance L of a low capacitance cable = 101IH.

If the resistance value is 0=250Ω, the time constant is 0.04sec.
Tonashi is completely ignored. Note that the reason why the low inductance cable 42 is cut off near the gap during the finishing process is that if the low inductance scoop 42 is connected between the lines, this stray capacitance will cause a low surface roughness process. This is because it becomes impossible.

As detailed above, the present invention applies voltage between poles through a low inductance scoop during rough machining and semi-machining,
During finishing and low surface roughness machining, voltage is applied between the poles via a low capacitance scoop, and the low inductance scoop is separated near the pole using an electromagnetic switch, etc. Therefore, it is possible to improve the machining speed during rough machining and semi-machining, and to improve the surface roughness during finishing machining.

[Brief explanation of drawings]

Figure 1 is a circuit configuration diagram of a machining power supply of a conventional electric discharge machining device, Figure 2 is a voltage/current waveform diagram during rough machining and semi-machining in the machining power supply, and Figure 3 is a diagram of the machining power supply with low power consumption. Figure 4 is a voltage and current waveform diagram during rough machining and semi-machining when using an inductance cable. Figure 4 is a voltage and current waveform diagram during finishing machining when using the above low inductance cable. Figure 5 is a diagram of the voltage and current waveforms during finishing machining using the low inductance cable. FIG. 6 is a circuit configuration diagram showing an embodiment of the power supply for processing, and FIG. 6 is a diagram of voltage and current waveforms during finishing processing in the power supply for processing of the present invention. Identical members in each figure are given the same reference numerals, 10 is DC, 12
is a feeder, 14 is a workpiece, 16 to 20 are transistors, 22 to 26 are resistors, 28 to 32 are diodes, 34
is an electrode, 36 is a pulse, 38.42 is a feeder (couple), and 40 is an electromagnetic switch. Agent Patent attorney Shin Kuzuno - (1 person) 165- Figure 2 Figure 3 Figure 4 Figure 6 (b)

Claims (1)

[Claims] (1) In a machining power source for an electrical discharge machining device that has a rough/medium machining circuit and a finishing machining circuit, the output of the rough/medium machining circuit is supplied between the machining holes via a low inductance feeder, and The output of the finishing circuit is configured to be applied between the poles via a low capacitance feeder,
A machining power source for an electric discharge machining device, characterized in that an electromagnetic switch is provided near the machining gap to shut off the low inductance feeder during finishing machining.