JPS6254606B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to electrical discharge machining methods, and in particular to generation of machining pulses.

When machining is performed using a pulse train of machining pulses having a pulse width τ _po and an interval τ _pff set depending on the machining conditions, the conventional means usually adopted for stable machining is to repeat the pulse train at predetermined time intervals. This was to cleanse the gap and prevent abnormal discharges such as arcs. In this case, even if an arc occurs in the middle of the pulse train, it can be extinguished at the next interruption and the machining can be stabilized. The number decreases, and when restarting the next discharge after the interruption period is completed, there are no machining debris or gas present in the gap that would trigger the discharge, and normal discharge does not return easily in a short period of time. There was a drawback that the speed decreased and the speed could not be improved to the desired level.

The present invention has been proposed to eliminate this drawback. The machining speed of electric discharge machining using a pulse train is controlled to approach the desired theoretical value.
In other words, the peak value Ip of the processing pulse during a certain period of the pulse train
increase or shorten the pulse interval τ _pff ,
Compare the response speed of control that rapidly increases the amount of energy supplied per unit time by increasing the pulse width τ _po to the response speed of servo feed control that controls the machining gap so that the average value of discharge current is maintained at a constant value. By repeating the process at a sufficiently short predetermined time interval or at a time interval depending on the discharge state of the machining gap, machining is performed with the machining gap substantially wider than machining using the pulse train of the machining pulses. It is characterized by the following.

The present invention will be explained below with reference to the drawings. Figure 1 explains the pulse train of machining pulses and the rapid control of the energy supply amount per unit time performed during a certain period of the pulse train, and shows the machining conditions, namely finishing, semi-finishing,
The pulse width τ _po and interval τ _pff of the machining pulse are set by rough machining. τ _po = 1 to 100 μs, τ _pff =
It is set to about 10 to 50 μs. Figure A shows the pulse train of this machining pulse during the predetermined time T ₂ and the interval τ _pf
Control is performed to increase the current density by shortening _f τ _pff ′,
This current density increase control is repeated at a predetermined time interval T ₁ , and the figure below shows that the current density of the machining current is increased by increasing the peak value Ip of the machining pulse during T ₂ hours, and the current density of the machining current is increased to reach the predetermined This is an example in which control is performed to repeat this at time intervals _T1 . Figure C shows the interval τ _pff
By simultaneously narrowing τ _pff ′ and increasing the peak value Ip, the T ₂ current density is increased during a set time, and this is changed at a time interval T ₁ that is controlled according to the discharge state of the gap. It was designed to be repeated.

By controlling the increase in current density, a predetermined _τpo ,
τ _pff Changes the electrical discharge state in the machining gap that is repeated with machining pulses. That is, a servo feed mechanism is usually provided on the electrode that forms the processing gap, and the servo is controlled by the gap and the signal. When the current flowing through the machining gap increases, the gap length is widened, and when the current decreases, the gap is narrowed, thereby controlling the flow of a constant current. Gap control by this servo is generally expressed by: where the gap length is l, l=k(τ _po )1/3 Ip k; constant τ _po ; machining pulse width Ip; peak value. Therefore, Ip is the peak value of one pulse, but in the case of a high frequency that cannot be followed by the servo, it can be considered as the average current value, and it can be seen that the gap length increases by increasing the average current value. As shown in FIG. 1, by controlling the current density to be increased during a certain period of the pulse train, the machining gap is widened by the servo. Since the follow-up speed of the servo mechanism is usually sufficiently slow compared to the frequency of the processing pulse train, it is possible to increase the current density by repeating it from time to time at sufficiently short time intervals compared to the response speed of the servo feed control, as shown in Figure 1. Therefore, machining can be performed with the machining gap substantially widened. It is sufficient to control the increase in current density within a range of about 1 to 30% of the total pulse train, and by repeatedly increasing the current density, processing can be performed with the gap constantly widened.

FIG. 2 shows an electrical discharge machining circuit that performs such pulse generation control, in which 1 is a machining electrode, 2 is a workpiece, and a machining gap is formed by opposing each other. Reference numeral 3 denotes a power source for supplying machining power, which is connected in parallel to the machining interval via a switch 4 such as a transistor. Switch 4 on. Turn on power supply 3 by off-switching. Turn it off and apply pulses to the machining gap. 5 is an oscillator that generates a machining pulse having a set pulse width τ _po and interval τ _pff , and 6 is a resistor circuit inserted in the discharge circuit to determine and control the current peak value Ip of the machining pulse discharge. 7 is a time control device that controls the oscillator 5 at predetermined time intervals to change the oscillation output pulse interval τ _pff to τ _pff ', and also controls the circuit 6 to change the discharge current peak value Ip to Ip'. Then, constant change control of the oscillator 5 and the circuit 6 is performed using the oscillation output pulse of a multivibrator or the like as a signal. 8 is a detection circuit that detects the discharge state of the machining gap, which detects and discriminates the average voltage and current of the gap, digitally detects and discriminates the discharge voltage and current of the machining pulse, and performs integral detection. Discern. Also, high frequency components observed during normal discharge are detected and discriminated. The detection signal is discriminated by setting a discrimination level using a Schmitt method or the like to discriminate between upper and lower signals, and to perform discrimination at a plurality of levels. Reference numeral 9 denotes a control circuit operated by the discrimination signal of the detection circuit 8, which controls the time change of the time control device 7.

As described above, the machining pulses generated by the oscillator 5 have τ _po , τ _pff , etc. set in advance according to the machining conditions, thereby determining the machined surface roughness, machining speed, and machining performance. This oscillator 5 turns on the switch 4. By continuing the off control, the scheduled machining is performed. In addition, regarding gap widening/narrowing control using servo feed, in a gap state where all of the machining pulses applied to the gap are activated by electric discharge, stable machining cannot be performed because it is easy to transition to arcing, so the machining pulses applied to the gap are number 10
It is necessary to perform servo feed so that the discharge occurrence rate is approximately 80% at most. Therefore, the average current value that is the standard for servo feed control must be set based on the pulse width τon and pulse interval τoff. Ratio and peak value Ip
It is set taking into consideration not only the discharge occurrence rate but also the discharge occurrence rate. Then, the time control device 7 controls the processing pulse interval τ _pff to shorten the interval τ _pff during T ₂ hours (Figure A), increasing the current density, and after T ₂ hours have passed, the interval τ pff returns to the interval τ _pff . The machining pulses were repeated, and after T ₁ hour elapsed, the current density was increased again, and by repeating the pulse train that occasionally increased the current density, the machining gap was made wider than usual by controlling the servo feed of the electrode. Machining can be continued at intervals, increasing the effect of removing machining debris and increasing the flow of machining fluid, and reducing the arc. Stable processing can be performed in a state where short circuits and the like are unlikely to occur. time interval T ₁ ,
T ₂ etc. are set by the control device 7 so that machining can be continued in the most stable discharge state, and the time interval is set to perform rapid control of the amount of energy supplied per unit time.
T ₁ is set sufficiently short compared to the response speed of servo feed control. In addition, if the resistance circuit 6 is controlled by the time control device 7, the peak value Ip during T ₂ hours can be controlled.
The current density can be increased by controlling the increase in Ip' (Fig. 2), and by repeating this after _T1 has elapsed, it is possible to continue the same gap increase control as described above and stable machining thereby. Furthermore, if the oscillator 5 and the circuit 6 are controlled simultaneously by the time control device 7, the control can be performed as shown in Fig. C, and stable machining can be performed in both cases.

In this way, the pulse interval τoff and the peak value Ip
Machining is carried out with the machining gap _{substantially widened} due to the control of Even if debris is generated and the gap is widened, there is just the right amount of machining debris in the gap that will trigger the discharge, so the discharge rate will not decrease and the efficiency will be maintained at the desired discharge rate. It is possible to perform good processing. Further, if the energy sudden increase control per unit time is performed in accordance with the discharge state of the gap, the machining can be further stabilized and the machining can be performed with high efficiency. In other words, the response speed of servo feed control is slower than the frequency of the machining pulse train, so servo feed control cannot quickly respond when the discharge condition becomes unstable. For example, even if a machining pulse is applied, the discharge Even if the number of no-load discharges that do not start increases and the rate of discharge occurrence decreases, it takes time to narrow the gap and restore the desired rate of discharge occurrence, resulting in a decrease in machining speed. In addition, when performing rapid energy supply control at predetermined time intervals,
For example, when an arc occurs, the amount of energy supplied may be increased by chance, which may further worsen the discharge condition. Therefore, when the detection circuit 8 detects the discharge state and an increase in no-load discharge is detected from the average voltage or current of the gap, the control circuit 9 controls the time control device 7 to rapidly increase the amount of energy supplied. ,
By increasing the amount of machining debris that triggers discharge, it is possible to quickly return to the desired rate of discharge occurrence, and also to detect arcing or short circuit conditions based on the detection results of discharge voltage, current, or high frequency components observed during normal discharge. When detected, the time control device 7 is controlled by the control circuit 9 to prevent a sudden increase in the amount of energy supplied, thereby allowing efficient machining to be performed in a stable machining state. Note that when the detection circuit 8 detects the occurrence of an arc or a short circuit, it is desirable that the output signal of the control circuit 9 is used to stop the output of the oscillator 5 and temporarily stop the supply of machining pulses to the gap. .

Note that the amount of energy supplied per unit time may be controlled by controlling the machining pulse width _τpo .
Even if τ _po is increased, the machined surface roughness will only become rougher to the 1/3 power, making it easy to put into practical use. Furthermore, when Ip is increased, for example, even if Ip doubles, the machined surface roughness only increases by about 1.2 times, which is 10μRmax.
When controlling Ip to double in the processing of , the machined surface roughness only increases to about 11 to 12 μRmax, which is sufficient for practical use.

As described above, the present invention performs control to widen the gap by increasing the amount of energy supplied per unit time at sufficiently short time intervals compared to the response speed of servo feed control, and this control is repeated. In practice, machining is performed with a gap that is wider on average compared to conventional machining that repeats constant pulses, which improves the removal effect of machining debris and the flow effect of machining fluid. arc. Short circuits can be prevented and extremely stable machining can be continued.
The machining pulse train is repeated at a value set according to the machining conditions, etc., and the desired machining can be easily performed. By stabilizing machining, it is possible to reduce the number of times pulse train interruption control and electrode rapid jump control, which are performed to remove machining debris and gas generated in the machining gap, can be reduced compared to conventional methods, making it possible to stop machining. Time can be reduced and processing speed can be increased. In addition, even if the machining gap is widened, there will be a certain amount (constant concentration) of machining debris in the machining gap that will trigger the discharge, so it is necessary to generate the discharge at the desired rate of discharge. Efficient machining can be performed at the desired machining speed. The machining efficiency was particularly excellent in finishing machining, which was conventionally inefficient, and could be improved by about 2 to 3 times.

[Brief explanation of the drawing]

Figure 1 is a pulse waveform diagram explaining the present invention, Figure 2 is a pulse waveform diagram explaining the present invention.
The figure is a circuit diagram of one embodiment of the present invention. 1 is an electrode, 2 is a workpiece, 3 is a power source, 4 is a switch, 5 is a processing pulse oscillator, 6 is a current control resistance circuit, 7 is a time control device, 8 is a discharge state detection circuit, and 9 is a control circuit. .

Claims (1)

[Claims] 1. A pulse train of machining pulses having a pulse width τon and an interval τoff set according to machining conditions is supplied to the machining gap to generate electric discharge, and the discharge current is detected to maintain a constant average current value. In electrical discharge machining in which servo feed control is performed between the electrodes and the workpiece forming the machining gap so that the machining gap is sag, the machining pulse height value Ip is controlled to increase, the pulse interval τoff is shortened, or the pulse By repeating control to rapidly increase the amount of energy supplied per unit time for a certain period of the pulse train by controlling one or more of the increasing controls of the width τ at sufficiently short time intervals compared to the response speed of the servo feed control, An electrical discharge machining method characterized in that machining is performed with a machining gap substantially wider than machining using the pulse train of machining pulses. 2. The electrical discharge machining method according to claim 1, wherein the time interval is a predetermined time interval that is sufficiently short compared to the response speed of the servo feed control. 3. The electric discharge machining method according to claim 1, wherein the time interval that is sufficiently short compared to the response speed of the servo feed control is a time interval that is changed and controlled according to the electric discharge state of the machining gap.