JPS6236809B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a wire-cut electric discharge machining apparatus, and more specifically, to a concentrated discharge detection apparatus in a wire-cut electric discharge machining apparatus.

In wire cut electrical discharge machining, it is desirable for electrical discharge to occur randomly and uniformly on the machined surface of the workpiece, but sometimes electrical discharge occurs intensively and continuously at specific points on the machined surface. be. In addition, for devices with a non-storage type power source,
the desired proportion of the supplied voltage pulses, e.g. 60
Although it is desirable that discharge occurs at ~70%, this discharge occurrence ratio may exceed 80%, resulting in so-called excessive discharge.

The same thing can be said for machining power supplies that generate and supply independent machining pulse voltages by turning on and off a DC voltage source using a switch element such as a transistor; When supplying a constant or variable pulse voltage with a pulse voltage pause width, discharge begins to occur at approximately 80% or more of the pulse voltage, or the discharge starts from the time the pulse voltage is applied until the discharge starts. A state in which repeated discharges are performed such that the delay period is less than 25 to 30% of the pause width corresponds to the above-mentioned excessive discharge state.

This kind of concentrated or excessive discharge can turn into continuous arc discharge, which can lead to cutting of the electrode and damage to the workpiece, so when concentrated or excessive discharge occurs, it should be detected immediately and appropriate measures taken. It is necessary to take

Therefore, the present applicant proposed a concentrated discharge detection device in Japanese Patent Application No. 51-139502, which detects the presence or absence of concentrated discharge by detecting fluctuations in the electrical resistance of a wire electrode between a discharge point and a power supply point. However, the concentrated discharge detection device described above has the inconvenience that the detection circuit differs depending on the thickness of the workpiece.

The present invention has been made based on the above-mentioned viewpoints, and an object of the present invention is to provide a concentrated discharge detection device that can quickly detect a concentrated discharge state regardless of the thickness of a workpiece. An object of the present invention is to provide a wire-cut electrical discharge machining apparatus.

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

FIG. 1 is a circuit diagram showing an embodiment of a concentrated discharge detection device used in a wire-cut electric discharge machining apparatus according to the present invention, and FIG. 2 is a time chart showing the on-off correspondence of each switching element.
FIG. 3 is a time chart for explaining the operation of the present device in a normal discharge state, and FIGS. 4 and 5 are time charts for explaining the operation of the present device in a concentrated discharge state.

In the figure, 1 is a workpiece, 2 is a wire electrode, 3 is a power supply roller for applying a discharge voltage between the workpiece 1 and the wire electrode 2, and 4 and 5 are the processing parts of the wire electrode. A pair of current-carrying terminals for measuring resistance of wire electrodes are provided in between, 7 is a power source for machining, 8 is a switching element for opening and closing the discharge circuit, 9 is a pulse generator, 10 is between the workpiece 1 and the wire electrode 2 The generated discharge point, 11 is the power supply for the resistance measurement circuit, 12
is a switching element for opening and closing the resistance measurement circuit, 1
3 and 13 are diodes, 14 is a resistor, 15 and 1
6 have different triggering levels e ₁ and
Schmidt trigger circuit given e ₂ , 17
18 is an AND circuit, and 19 is an alarm buzzer.

Thus, the switching element 8 is a pulse generator 9
When a machining command pulse is transmitted from the wire electrode 2, conduction occurs, and at this time, a voltage is applied between the workpiece 1 and the wire electrode 2, and a discharge is generated between the two. Furthermore, the switching element 12 becomes conductive when no machining command pulse is transmitted from the pulse transmitter 9, and at this time the resistance measuring circuit is activated.

Therefore, in the case of a normal discharge state, the discharge point 1
Since the zero position moves randomly and uniformly on the machined surface, the temperature of the wire electrode 2 increases little due to discharge, and its electrical resistance hardly changes. Therefore, when the switching element 12 is conductive, the voltage e at the connection point between the resistor 14 and the Schmitt trigger circuits 15 and 16 is almost constant.

Therefore, as shown in FIG. 3, the Schmitt trigger circuits 15 and 16, which are given triggering levels e ₁ and c ₂ lower than the voltage e, are triggered at this time, but their outputs are not connected to the input negator. Since the output signals are input to the corresponding AND circuits 17 and 18 via the AND circuits 17 and 18, the outputs of the AND circuits 17 and 18 remain in the 0 state.

On the other hand, when a concentrated discharge occurs between the workpiece 1 and the wire electrode 2, the temperature of the wire electrode 2 rises, albeit locally, and its electrical resistance increases. In this case, the rate of change in electrical resistance due to temperature rise is:
It differs based on various factors such as the electrode material and the diameter of the electrode, but if these factors are identified, the rate of change in the electrical resistance mentioned above can also be determined.
When using a 0.3mm copper wire electrode, if a temperature rise of approximately 300℃ or more occurs in one or more localized areas of the wire electrode's machining discharge area,
It should be assumed that a concentrated discharge that leads to a wire electrode breakage accident has occurred, and the increase in the electrical resistance value of the wire electrode in the machining discharge area at that time is equal to the total resistance value.
0.1% or more. Therefore, the current flowing through the resistor 14 when the switching element 12 becomes conductive decreases, so that the resistor 14 and the Schmitt trigger circuit 15
The voltage e at the connection point with and 16 changes in a sufficiently detectable manner in relation to the change in the electrical resistance of the wire electrode and the resistance of the resistor 14.

Therefore, as shown in FIG. 4, when the voltage e has a value between the triggering levels _e1 and _e2 of the Schmitt trigger circuits 15 and 16, the output of the Schmitt trigger circuit 15 becomes 0, and the output of the Schmitt trigger circuit 15 becomes 0. The output of the AND circuit 17 becomes state 1 and the alarm buzzer 19 is activated.

The concentrated discharge further progresses, as shown in Figure 5.
When the voltage e becomes lower than the triggering level _e2 of the Schmitt trigger circuit 16, the output of the Schmitt trigger circuit 16 also becomes 0, and the corresponding AND circuit 18
When the output becomes state 1, a control device (not shown) is activated to stop the electrical discharge machining apparatus and eliminate the concentrated electrical discharge.

When the above-mentioned concentrated discharge state occurs, the above-described excessive discharge state usually occurs at the same time, which increases the temperature rise of the wire electrode 2.

Further, the above-mentioned excessive discharge state can occur even if the above-mentioned concentrated discharge state does not occur, for example, when the gap between the wire electrode 2 and the workpiece 1 becomes smaller overall than the desired value, or when the machining fluid It can be generated independently when the distribution update rate decreases, and the present invention can also deal with such cases.

Since the present invention is configured as described above, according to the present invention, concentrated discharge can be detected by the same detection circuit regardless of the thickness of the workpiece, and thus it can be detected reliably and quickly. Accordingly, it is possible to provide a wire cut electrical discharge machining apparatus equipped with a concentrated discharge detection device.

Note that the configuration of the present invention is not limited to the above-mentioned implementation sequence, and the configuration of the power supply circuit, resistance measurement circuit, etc. can be freely changed within the scope of the purpose of the present invention, and the present invention It encompasses all of the above.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of a concentrated discharge detection device used in a wire-cut electric discharge machining apparatus according to the present invention, and FIG. 2 is a time chart showing the on-off correspondence of each switching element.
FIG. 3 is a time chart for explaining the operation of the present device in a normal discharge state, and FIGS. 4 and 5 are time charts for explaining the operation of the present device in a concentrated discharge state. DESCRIPTION OF SYMBOLS 1... Workpiece, 2... Wire electrode, 3... Power supply roller, 4, 5... Current-carrying terminal for wire electrode resistance measurement, 9
...Pulse transmitter, 10...Discharge point, 19...Alarm buzzer.

Claims (1)

[Claims] 1 A pair of current-carrying terminals for wire electrode resistance measurement provided sandwiching the processed portion of the wire electrode, and a current for wire electrode resistance measurement when no processing pulse is transmitted to the processed portion of the wire electrode via the pair of current-carrying terminals. and a resistance measuring circuit that detects fluctuations in the electrical resistance of the wire electrode by detecting fluctuations in the pulse current or pulse voltage based on fluctuations in the electrical resistance of the wire electrode between the pair of current-carrying terminals through the pulse of the current-carrying terminal. A wire cut electrical discharge machining device characterized by comprising a detection device.