JPH0551411B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a wire cut electrical discharge machining method.

[Conventional technology]

In the conventionally known wire cut electrical discharge machining equipment,
The wire electrode is usually stretched between electrode guides provided at the tips of two arms extending horizontally and parallelly from the column to the processing table above the bed, with appropriate tension applied during processing. is constantly supplied and collected from one side to the other. The distance between the electrode guides is usually within about 10 cm, and this certain range forms the processed part.

During machining, the wire electrode is not necessarily straight, but is moved in the direction opposite to the machining surface, that is, in the direction of machining feed progress, due to the discharge pressure of the discharge generated based on intermittent supply voltage pulses for machining. It is repulsed by the machined groove side on the opposite side and is curved into an arched shape. At this time, the deviation from the desired linear state is
Although it varies depending on the processing conditions, in some cases the thickness can reach several tens of micrometers in the processed part. If machining is carried out under such conditions, there may not be much of a problem when the machining contour line is a straight line, but at corners or curved sections with small curvature, the machining feed rate must be significantly reduced, which makes it difficult to achieve the desired machining. There are problems in that it becomes impossible to obtain the desired shape and the processing accuracy is forced to deteriorate.In addition, the bending of the wire electrode increases the chances of short circuits, etc., leading to electrode cutting accidents. There was also the problem that it was easy for this to occur.

As a solution to the above-mentioned problems, for example, there is an invention proposed by the present inventor, disclosed in Japanese Patent Application Laid-open No. 137840/1984. ) by applying high-frequency vibrations and using the vibrations to constantly change the tension of the electrode within a certain range, it is possible to remove deflection of the electrode due to discharge pressure and distortion due to the habit of the electrode, but this method is expensive. Further, there has been a problem in that the wire electrode still cannot have perfect linearity and the machining accuracy is insufficient.

[Problem that the invention seeks to solve]

The present invention has been made based on the above-mentioned viewpoints, and an object of the present invention is to appropriately correct the linearity of the wire electrode during processing and ensure it by a simple method, thereby improving the processing speed. It is an object of the present invention to provide a novel wire cut electrical discharge machining method that improves accuracy and minimizes the occurrence of wire electrode cutting accidents.

[Means for solving problems]

Therefore, the gist of the present invention is to provide a discharge peak current Ip, a pulse width τ _ON , a discharge peak current Ip, a pulse width τ In the wire cut electrical discharge machining method, cutting is performed by continuously supplying a series of machining current pulse trains consisting of a large number of discharge current pulses with a pulse interval τ _OFF to generate continuous pulse discharge. The object of the present invention is to perform electric discharge machining while periodically varying the pulse train characteristics determined by the Ip, τ _ON and/or τ _OFF of the series of supplied machining current pulse trains.

Note that in this specification, the term "pulse train" refers to one containing at least three pulses, and excludes one containing 0 to 2 pulses.

[Effect]

By configuring as described above, during periods when τ _OFF is long, τ _ON is short, or Ip is small, the machining average current becomes small and the influence of discharge pressure is reduced, so the linearity of the wire electrode is improved. The bulging part at the center of the thickness of the workpiece is machined at a low speed, so even corner parts and curved parts with large curvature can be machined with high accuracy according to the desired machined shape. .

〔Example〕

Hereinafter, the details of the present invention will be specifically explained with reference to the drawings.

FIG. 1 is an explanatory diagram showing the main parts of an embodiment of the apparatus for carrying out the wire cut electrical discharge machining method according to the present invention, and FIG. 2 shows details of the control circuit shown in FIG. 1. 3 and 4 are diagrams showing the waveforms of voltage pulses and discharge current pulses, and FIG. 5 is a diagram showing the waveform of the τ _OFF switching command pulse.

In Figure 1, 1 is the workpiece, 2 is the wire electrode, and 3
is the power supply pin or power supply roller, 4 is the capstan,
5 and 6 are pinch rollers, 7 and 8 are electrode guides such as boat-shaped guides, 9 is a machining fluid supply nozzle, 10 is a machining power source, 11 is a switching element for opening and closing the discharge circuit, and 12 is a control circuit.

Therefore, when using a conventional electrical discharge machining method using a conventional wire cut electrical discharge machining device,
Since the wire electrode is always subjected to a large discharge pressure, the wire electrode 2 is bent as shown in FIG. Material and thickness of the wire electrode used, electrode guides 7 and 8
It varies depending on the distance between the two, the tension applied to the wire electrode, the moving speed of the wire electrode, the discharge energy, the material of the workpiece 1, the plate thickness, the machining feed, etc., but if it is large, it can reach several tens of μm as mentioned above. . Such a deviation cannot be eliminated only by a certain tension applied to the wire electrode (usually about 1 to 1.5 kg in the case of a brass wire electrode of about 0.2 mmφ); Even if it is possible to reduce this to some extent by increasing the strength of the wire, this is not necessarily appropriate, as this would actually increase the possibility of wire breakage.

Therefore, in the present invention, as shown in FIG.
A processing power source 10 is connected between the workpiece 1 and the wire electrode 2.
and a switching element 11 controlled by a control circuit 12 to supply electrical discharge machining voltage pulses via the power supply roller 3.

FIG. 2 is a block diagram showing the configuration of the control circuit 12, in which 13 is a monostable element, 14 is a two-stage delay circuit that defines τ _OFF , 15 is a pulse oscillator, 16 and 17 are AND circuits, and 18
is an input negator, 19 is an OR circuit, and 20 is a monostable element that defines τ _ON .

The operation of the control circuit 12 is as follows.

The two-stage delay circuit 14 defines a short pause time τ _OFF1 and a long pause time τ _OFF2 .

Now, suppose that the monostable element 13 is triggered and a short output pulse is oscillated, and the output pulse is sent to the two-stage delay circuit 14. The two-stage delay circuit 14 has the rest times τ _OFF1 and τ _OFF2.
After the passage of time, the output terminals 14-1 and 14-
The pulse from the former is sent to the AND circuit 16, and the pulse from the latter is sent to the AND circuit 17.

On the other hand, the pulse oscillator 15 oscillates a pause time switching command pulse at a predetermined repetition frequency, and during the period when its output is in state 1, the AND circuit 1
6 passes the pulse corresponding to the short pause time τ _OFF1 , while the AND circuit 17 passes the input negator 18
is provided, the pulse that should define the long pause time τ _OFF2 cannot pass through this AND circuit 17 and is cut off.

The pulse that defines its short pause time τ _OFF1 is
After passing through the AND circuit 16, the OR circuit 19
and triggers the monostable element 20. The output of the monostable element 20 is in state 1 for a time equal to the supply time τ _ON of the voltage pulse, during which the switching element 11 is turned ON.

On the other hand, the monostable element 20
The output pulse triggers the monostable element 13 at its trailing edge to oscillate a short pulse, so that the same cycle is repeated.

Conversely, when the pulse from the pulse oscillator 15 changes to state 0, the AND circuit 16 is closed, the pulse corresponding to the short rest time τ _OFF1 is cut off, and the AND circuit 17 is opened instead and the pulse corresponding to the long rest time τ _OFF2 is cut off. pass. The pulse is OR circuit 19
, triggers the monostable element 20, and turns on the switching element 11 for the time τ _ON . In this case as well, the monostable element 20
The output pulse triggers the monostable element 13 at its trailing edge, so that the same cycle as above is repeated.

Therefore, as shown in FIGS. 3 to 5, a period in which the pause time is τ _OFF1 and a period in which the pause time is τ _OFF2 are periodically repeated in response to ON and OFF of the pulse from the pulse oscillator 15.

In other words, the control circuit 12 generates a voltage pulse with an appropriate pulse width and controls the pause time τ _OFF to be switched in two stages, long and short, as shown in FIGS. 2 to 5.

Thus, in the method of the present invention, the control circuit 12:
First, electric discharge machining is performed by applying a voltage pulse with a period determined by the supply time τ _ON and the rest time τ _OFF1 using a conventional method, and then the wire electrode 2 shown in FIG. 1 is bent and the workpiece 1 is machined. When the part curves accordingly, the straightness of the wire electrode near the center of the machining part of the workpiece 1 is improved by extending the pause time τ _OFF1 to a longer time τ _OFF2 and cutting down the average machining current. If the wire electrode 2 is advanced to the position shown by the two-dot chain line in the same state, the curvature of the processed portion will be corrected, and then the processing method will be returned to the conventional processing method and processed at high speed. . By repeating this method one after another, all problems caused by the bending of the wire electrode 2 can be prevented without substantially impairing the average processing speed.

Note that the configuration of the present invention is not limited to the above-mentioned embodiments. For example, in order to achieve the object of the present invention, it is sufficient to periodically lower the average machining current, so the above-mentioned τ _OFF Along with or in place of the switching, the voltage pulse supply time τ _ON or the machining peak current Ip may be switched in two or more stages of large and small steps, and also used in combination with the vibrating device by the present inventor described in the prior art section. Furthermore, the shape, dimensions, etc. of each component can be freely changed within the scope of the purpose of the present invention, and the present invention encompasses all of them.

〔Effect of the invention〕

Since the present invention is configured as described above, when the present invention is used, it is possible to obtain a desired machining shape even in corner portions and curved portions with large curvature, and high-precision electrical discharge machining can be performed. Furthermore, it is possible to provide a novel wire-cut electric discharge machining method that causes fewer wire electrode cutting accidents and that is extremely inexpensive and simple without requiring any complicated equipment.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the main parts of an embodiment of the apparatus for carrying out the wire cut electrical discharge machining method according to the present invention, and FIG. 2 shows details of the control circuit shown in FIG. 1. 3 and 4 are diagrams showing the waveforms of voltage pulses and discharge current pulses, and FIG. 5 is a diagram showing the waveform of the τ _OFF switching command pulse. DESCRIPTION OF SYMBOLS 1... Workpiece, 2... Wire electrode, 3... Power supply roller, 4... Capstan, 5, 6... Pinch roller, 7, 8... Electrode guide, 9... Machining liquid supply nozzle.

Claims (1)

[Claims] 1. Between a wire electrode and a workpiece that are opposed to each other with a predetermined machining interval in an appropriate machining fluid, a discharge peak current Ip, a pulse width τ _ON , and a pulse interval τ _OFF are applied. A wire cutter that performs cutting by continuously supplying a series of machining current pulse trains (including at least three pulses; the same shall apply hereinafter) consisting of discharge current pulses to generate continuous pulse discharge. In the electric discharge machining method, electric discharge machining is performed while periodically varying the pulse train characteristics determined by the above Ip, τ _ON and/or τ _OFF of the above series of machining current pulse trains that are continuously supplied. The above wire cut electrical discharge machining method characterized by: