JP3006817B2 - Electric discharge machining method and apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric discharge machining method and apparatus, and more particularly to an electric discharge machining method and apparatus capable of performing stable servo feed machining even in a high frequency region such as finishing.

[0002]

2. Description of the Related Art In electric discharge machining, a voltage pulse is applied between an electrode and a workpiece (machining gap) to generate a discharge therebetween, and a predetermined energizing time (T _on ) and a pause time (T _on )
_off ) is repeated to process the workpiece. In general, the time from the application of a voltage pulse to the start of discharge is referred to as a no-load voltage application time (hereinafter simply referred to as “no-load time”),
The time from the start of discharge to the end of discharge is defined as the energization time (T _on ),
The time from the end of discharge to the application of the next voltage pulse is referred to as a pause time (T _off ).

In order to maintain a stable discharge, it is necessary to control the relative feed speed between the electrode and the workpiece (servo feed). Conventionally, this type of feed speed control appears in the machining gap. A method is known in which a gap voltage (pulse voltage) is averaged using a filter circuit, and a feed rate is controlled so that the average voltage becomes a predetermined value. Also, a method of directly counting the no-load time using a clock pulse or the like and controlling the feed rate based on the no-load time thus obtained (JP-A-50-1499, JP-A-2-109633).
No.) has also been proposed.

[0004]

In the method of detecting the average voltage of the gap voltage using a filter circuit, the average voltage of the gap voltage differs depending on the duty ratio (the ratio of the no-load time in one cycle). come. Then, in a machining region having a high discharge frequency (such as finishing machining), a machining method in which no-load time is generally shorter than a pause time or the like is performed. In such a case, the duty ratio decreases and the average voltage decreases. The value was also very small, the resolution was poor, and it was difficult to perform stable servo feed based on the average voltage.

On the other hand, according to the method of directly counting the no-load time, there is no problem in the rough machining area where the discharge frequency is relatively low, but the discharge frequency is 1M like the finish machining area.
At about Hz, the no-load time becomes extremely short,
There has been a problem that the circuit configuration for counting the number becomes very complicated and the counting accuracy is reduced. In addition, in this method, the no-load time is counted and measured at a constant sampling cycle, so that it is good if the discharge frequency is constant, but if the discharge frequency fluctuates, the no-load time cannot always be measured accurately. There was a problem.

As described above, according to the conventional method, stable servo feed processing cannot be performed in a high frequency region such as finish processing, and constant speed feed processing is often performed.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and it is an object of the present invention to accurately control an electric discharge machining gap based on a no-load time. It is an object to enable feed processing.

[0008]

In order to solve the above-mentioned problem, in the present invention, the no-load time is not directly counted by a clock pulse or the like as in the prior art, but the discharge frequency is detected first. The no-load time is obtained based on the discharge frequency and other data described later, and the relative speed between the electrode and the workpiece is controlled according to the obtained no-load time.

Further, in the present invention, the no-load time can be calculated more accurately by calculating the no-load time in consideration of a short circuit occurring during electric discharge machining.

[0010] That is, in the present invention, to detect the discharge frequency f _d and the short frequency f _s of the normal discharge respectively, of the normal discharge frequency f _d and the short circuit frequency f _s,
Normal discharge time of the energization time T _on, downtime T _off, short detection time T _s, on the basis of the energization time for short T _ons and downtime T _offs, calculates the unloading time t _w d during normal discharge. Further, a virtual no-load time t _ws at the time of short-circuit is set, and a virtual total no-load time t _wv is obtained based on the no-load time t _wd at the time of normal discharge and the virtual no-load time t _ws at the time of short. The relative position between the machining electrode and the workpiece is controlled based on the total no-load time t _wv .

[0011] Specifically, as an example, the no-load time t _wd during normal discharge, the following equation _{t wd = {1-f s} × (T s + T off + T on)} / f d - (T
_off + T _on) determined by the virtual full unloading time t _wv, and as determined by the following equation _{t wv = (t wd × f} d + t ws × f s) / (f d + f s).

[0012]

According to the present invention, since the no-load time is obtained based on the discharge frequency instead of directly counting the no-load time, the no-load time can be accurately measured even in a high frequency region. Therefore, even in the high frequency region, stable servo feed processing can be performed. In addition, since the no-load time is determined in consideration of the short circuit that occurs during processing, the no-load time can be more accurately determined.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of a die sinking electric discharge machine as one embodiment of the present invention. Of course, the present invention is not limited to this embodiment, and the electric discharge machine is not limited to a die-sinking machine, but can be applied to a wire electric discharge machine.

In FIG. 1, a positive output of a power supply 1 is switched by a transistor 2 and connected to an electrode 4 through a current limiting resistor 3. The negative output of the machining power supply 1 is connected to the work 5. The normal discharge detection circuit 6 and the short detection circuit 7 detect a voltage applied between the electrode 4 and the work 5, and when a normal discharge is performed, a normal discharge pulse is output from the normal discharge detection circuit 6. When the normal discharge is not performed and a short circuit occurs, a short pulse is output from the short detection circuit 7. f _d counter 8 and f _s
The counter 9 counts the normal discharge pulse and the short pulse, respectively, to obtain a short frequency f _s and a normal discharge frequency f _d , convert them into f _s data and f _d data that can be handled by the CPU 10, and output the data to the CPU 10. I do. In the above embodiment, the short frequency f _s by the counter 8 and 9, although to obtain the normal discharge frequency f _d, is not limited to, for example, each counter performs only counts the normal discharge pulse, a short pulse, The CPU 10 may read the count value at every predetermined sampling period, and the CPU 10 may calculate the short frequency f _s and the normal discharge frequency f _d based on the count value and the sampling period.

The CPU 10 is a control circuit composed of a plurality of CPUs and a memory and the like.
Various calculations are performed based on the _s data, f _d data and other data, and a position command for controlling the gap length between the electrode 4 and the work 5 is output to a position servo control circuit 11 such as a numerical controller. The pulse train generation circuit 12 outputs a switching control signal for the transistor 2 based on a command from the CPU 10. The output of the position servo control circuit 11 is the motor 13
, And the motor 13 is mechanically connected to the electrode 4.

FIG. 2 is a block diagram showing a configuration of the normal discharge detection circuit 6 and the short detection circuit 7. As shown in the figure, the normal discharge detecting circuit 6 compares the differential amplifier 61 which receives the voltage between the electrodes by dividing the voltage between the electrodes and a predetermined reference voltage V _d (variably settable). It becomes equal to or larger than the reference voltage V _d and the comparator 62 outputs the H (logic High) signal, by differentiating the output of the comparator 62 and a differentiation circuit 63 for outputting a normal discharge pulse.

On the other hand, the short detection circuit 7 comprises a comparator 71, a flip-flop (FF) 72, and an AND gate 73, which are connected as shown in FIG. The R (reset) terminal of the FF 72 and the gate 7
3 is connected to the pulse train generating circuit 12. The pulse train generation circuit 12 outputs a reset signal to the FF 72. Further pulse train generation circuit 12, after a predetermined short detection time T _s has elapsed from the application of the machining gap voltage pulse, short check pulse to the gate 73 (H signal)
Is output. The comparator 71 includes a normal discharge detection circuit 6
Output voltage of the differential amplifier 61 and the short reference voltage V
by comparing the _s (variably configurable), when the output voltage of the differential amplifier 61 is lower than the short reference voltage V _s outputs an H signal to the gate 73. Further, when a short circuit occurs, the comparator 62 of the normal discharge detection circuit 6 outputs an L (logic Low) signal, and this L signal is inverted by the FF 72 and output to the gate 73 as an H signal. H from the pulse train generation circuit 12 to the short detection time T _s after
The signal is output to the gate 73, and the gate 73 is opened to set f _s
A short pulse is output to the counter 9. in short,
Short detection circuit 7 does not occur properly discharge after short detection time T _s, and, when the inter-electrode voltage is lower than a predetermined voltage, and outputs a short pulse.

Next, the operation of the embodiment shown in FIG. 1 will be described. When a discharge occurs between the electrode 4 and the workpiece 5, the voltage waveform between the electrodes changes as shown in FIG. That is, the transistor 2 is turned on by the pulse train generation circuit 12, and the discharge is started after the no-load time _twd in FIG. The normal discharge detection circuit 6 detects the discharge, and when the energization time T _on elapses from the start of the discharge, the transistor 2 is turned off and the discharge ends. Then the rest time T _off
After elapse, the transistor 2 is turned on again, and the same operation is repeated thereafter.

[0019] However, as shown in FIG. 3 (B), when the inter-electrode voltage be passed short detection time T _s from the discharge pulse is applied to the processing between the gap does not reach a predetermined reference value, a short Thereafter, a short-circuit voltage is applied, and the transistor 2 is controlled by the short-circuit energizing time T _ons and the quiescent time T _offs , and a short-circuit current flows. The values of T _ons and T _offs are arbitrarily set according to the processing conditions and stored in the CPU 10.

The normal discharge frequency f _d is output from the f _d counter 8, and the short frequency f _s is output from the f _s counter 9.
Is output to the CPU 10 as data. Further, in the gap length control, the energizing time T _on , the pause time T _off, and the short detection time T _s for performing the electric discharge machining are set in advance, and are stored as data in the CPU 10 in this embodiment. . Relationship between these values is represented as _{f d × (t wd + T} off + T on) + f s × (T s + T offs + T ons) = 1 (1). From equation (1), the no-load time t _wd during normal discharge is _calculated.
After calculating _{the, t wd = {1-f} s × (T s + T offs + T ons)} / f d - a _{(T off + T on) (} 2).

On the other hand, when a short circuit occurs, a short current flows as described above, and the concept of a no-load time as in a normal discharge does not originally exist. However, now, to introduce the concept of a virtual no-load time t _ws at the time of short-circuit from the point of view of correcting the no-load time t _wd at the time of normal discharge, a virtual no-load time of the no-load time t _wd and short at the time of normal discharge The average with t _ws is _defined as a virtual total no-load time t _wv .
The virtual total no-load time t _wv is a no-load time in consideration of the occurrence of a short circuit, that is, a no-load time t _wd during normal discharge.
Is corrected in consideration of the short circuit. Therefore, it is possible to more appropriately control the discharge gap length based on the virtual total no-load time t _wv . Since the virtual no-load time t _ws at the time of short circuit is virtual, FIG.
(B) is indicated by a chain line.

[0022] The normal discharge frequency f and the sum of the _d and the short frequency f _s and all the discharge frequency f _m, the virtual total no-load time t
_wv is represented by _{t wv = (t wd × f} d + t ws × f s) / f m (3). Here, the virtual no-load time t _ws during a short circuit
= 0 is set. This is because it is generally considered that the virtual no-load time t _ws at the time of a short circuit need not be included in the no-load time. Therefore, the desired virtual no-load time t
_wv is _{(2) (3) t wv} = t d / f m × than formula _{[{1-f s × (} T s + T offs + T ons)} / f d - (T off + T on)] and (4) Become.

Next, the calculation operation of _twv will be described with reference to the flowchart of FIG. 4. First, the CPU 10 outputs the normal discharge frequency f _d , f _d from the f _d counter 8 and f _s counter 9 respectively.
The short frequency f _s is read (step S1), and T _on , T _off , T _s , T _offs , and T _ons are read from the memory (step S2), and the no-load time during normal discharge is obtained based on the above equation (2). _twd is calculated (step S3). Next, the virtual no-load time t _ws (t _ws = 0 in the case of the embodiment) at the time of short circuit is read from the memory (step S4),
The virtual total no-load time t _wv is obtained from the equation (3) (step S5).

The CPU 10 outputs a position command for controlling the gap length between the electrode 4 and the work 5 to the position servo control circuit 11 based on the calculated virtual total no-load time t _wv . The position servo control circuit 11 drives the motor 13 according to a given position command, and controls the gap length between the electrode 4 and the work 5.

In the above embodiment, the virtual no-load time t _ws = 0 at the time of short-circuit is set. However, the virtual no-load time t _ws at the time of short-circuit may be set arbitrarily according to the processing conditions. For example, in the actual electric discharge machining, not only the voltage value as shown in FIG. 3 (B) but also the intermediate voltage waveform in the middle of FIG. 3 (A) and FIG. Some high voltage values appear (for example, when the plate thickness of the work is large). In such a case, the virtual no-load time t _ws may be set to a value according to the processing conditions such as the thickness of the work, instead of zero.

[0026]

As described above, according to the present invention, the discharge frequency during machining is detected, and the no-load time is calculated based on the detected value and the preset energizing time and pause time. Therefore, the no-load time can be accurately calculated even in the high frequency region. for that reason,
In a high frequency region such as finishing, an effect that stable servo feed processing can be performed is obtained.

[0027] In particular, according to the present invention, by assuming the virtual unloading time t _ws at short, it will be able to control in consideration of the time short, various processed virtual unloading time t _ws at short If set appropriately according to the conditions (for example, t _ws = 0), almost ideal discharge servo machining can be performed.

[Brief description of the drawings]

FIG. 1 is a block diagram of one embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a normal discharge detection circuit and a short detection circuit of FIG. 1;

FIG. 3 is a waveform diagram showing a voltage between contacts at the time of normal discharge and at the time of short-circuit.

FIG. 4 is a flowchart illustrating a CPU operation for calculating a virtual total no-load time t _wv .

[Explanation of symbols]

1 power supply 2 transistor 3 current limiting resistor 4 electrode 5 workpiece 6 normal discharge detection circuit 7 short detection circuit 8 f _d counter 9 f _s counter 10 CPU 11 position servo control circuit 12 a pulse train generation circuit 13 motor

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Kiyoshi Kaneda 359 3-3, Masu, Aikawa-cho, Aiko-gun, Kanagawa Prefecture Inside the Makino Milling Machine Co., Ltd. JP-A-61-121820 (JP, A) JP-A-3-55122 (JP, A) JP-A-62-88514 (JP, A) JP-A-2-298426 (JP, A) JP-A-50-1499 (JP, A) , A)

Claims (3)

(57) [Claims] Discharge is generated by applying intermittently the voltage pulse in accordance with a preset energization time T _on and downtime T _off for normal electrical discharge in the discharge machining gap between the 1. A machining electrode and the workpiece together, the machining gap by applying a search voltage for searching for short to determine normal discharge or short on the basis of the inter-electrode voltage of a predetermined short detection time T _s after, at the time of short preset short A voltage is applied according to a current supply time T _ons and a pause time T _offs for applying a voltage, and the workpiece is machined by moving the machining electrode and the workpiece relative to each other. the _d and short frequency f _s respectively detected, the discharge frequency f _d and the short frequency f _s, the energization time T _on during normal discharge, rest time T _off, the short detection time T _s Electricity supply time at the time of the short T _ons and pause time T
The non-load time t _wd during normal discharge is calculated based on the _offs , the virtual no-load time t _ws during short-circuit is set, and the no-load time t _wd during normal discharge and the virtual no-load time t during short-circuit are set. obtains a virtual full unloading time t _wv based on _ws, electric discharge machining method based on said virtual full unloading time t _wv controlling the relative position between the machining electrode and the workpiece, characterized in that. 2. A no-load time t _wd during the normal discharge, the following equation _{t wd = {1-f s} × (T s + T off + T on)} / f d - (T
_off + T _on) determined by the method of claim 1 for determining the virtual full unloading time t _wv, by the following equation _{t wv = (t wd × f} d + t ws × f s) / (f d + f s) . Discharge is generated by applying intermittently the voltage pulse in accordance with a preset energization time T _on and downtime T _off for normal electrical discharge in the discharge machining gap between 3. A machining electrode and the workpiece together, by applying a search voltage for searching for short in the machining gap to determine normal discharge or short on the basis of the inter-electrode voltage after a predetermined short detection time T _s passes, for short, which is set in advance at the time of short and the applied voltage in accordance with energization time T _ons and downtime T _offs, the machining electrode and the workpiece an electric discharge machining apparatus for machining a workpiece by relatively moving the discharge frequency f _d of the normal discharge means for detecting, means for detecting a short-circuit frequency f _s, the discharge frequency f _d and the short frequency f _s, the energization time T _on during normal discharge, rest time T _off, the short detection Thailand Time T _s , short-circuit energization time T _ons and pause time T
means for calculating a no-load time t _wd during normal discharge based on _offs; a means for setting a virtual no-load time t _ws during short-circuit; and a virtual no-load time t _wd during normal discharge and a virtual no-load time during short. means for calculating a virtual full unloading time t _wv by the load time t _ws, equipped with a means for controlling the relative position between the machining electrode and the workpiece based on the virtual full unloading time t _wv An electric discharge machine characterized by the above.