JPS5923938B2 - Electric discharge machining equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electric discharge machining device that performs machining by supplying machining pulses to the machining gap between a machining electrode and a workpiece by on/off control of a switch element to generate repeated electric discharges. It is.

In this electric discharge machining apparatus, two types of electric discharge machining apparatuses are known: one is to apply a pilot pulse to cause a discharge, and the other is to detect and discriminate based on resistance, impedance, etc. without causing a discharge. In the former case where a pilot pulse is applied to cause a discharge, the gap condition changes significantly between before and after the discharge, and this high-voltage pilot pulse causes tar, cutting dust, etc. It is not possible to accurately detect and judge the gap state due to changes in the distribution state of the gap.

Furthermore, since the latter method detects the gap resistance etc. in an analog way, it can only detect short circuits or open circuits, and cannot properly detect the gap state in either case. The present invention belongs to the latter category in that detection is performed without causing discharge, but a check pulse of a constant pulse width is added to the gap, thereby determining the peak value of the detection signal detected from the gap or the degree of change thereof.

The present invention will be described below with reference to an embodiment of the drawings. In FIG. 1, 1 and 2 are electrodes and a workpiece that form a machining gap, 3 is a power source for machining, 4 is a switch element thereof, and 5 is a switch element. A pulse generation circuit that adds a gate pulse to 4;
6 is a check pulse generation circuit for inspection, which does not operate while a gate pulse is applied to switch 4, but operates while the gate pulse is off, and outputs a check pulse of a constant pulse width. be.

T is a switch element inserted in the detection circuit, and by controlling this on/off, the inspection power source 8 is made conductive and a check pulse voltage is applied to the machining gap. 9 is a detection circuit that detects a current signal in the machining gap caused by a check pulse; 10 is a discrimination device that discriminates the peak value of the detection signal; the discrimination output is counted up and down by a counter 11;

That is, when the discrimination result is an optimal gap state, the count number increases, and when the gap state is abnormal, the count number decreases, and when the count number is greater than a preset constant value, the output signal is sent to the AND gate coupling circuit 12. Add to. Therefore, a signal is applied to the coupling circuit from the counter when the normal gap condition continues, and a gate pulse from the gate pulse generating circuit 5 is applied to the switch 4 to perform electrical discharge machining. In the above process, the switch 4 is turned on and off by the gate pulse from the pulse generation circuit 5, and pulse voltage is applied from the power source 3 to repeat pulse discharge to perform electric discharge machining.

When the switch 4 is on, that is, while electric discharge is occurring in the gap, the switch 7 is turned off and the state of the machining gap is not detected.
When the switch 4 is turned off to end the discharge, the check pulse generating circuit 6 is activated to output a check pulse, and the switch 7 is turned on and off to apply the check pulse voltage of the power source 8 to the gap. Note that the pulse width of this check pulse must be shorter than the ionization time of the gap, and usually about 1 to 2 .mu.Sec, and in some cases about 5 .mu.Sec. The check pulse may be applied at the same time as the discharge ends, or after a predetermined time delay. The current change in the gap when this check pulse is applied is detected by the detection circuit 9, and the detection signal is discriminated by the discrimination device 10. It varies depending on the concentration of intervening cutting powder, etc. This changing state will be explained with reference to FIG. 2. When X always applies a check pulse voltage of a constant pulse width, the current detected from the gap can be considered to be in the modes A, B, C, and D shown in the figure. A is a case where the gap is wider than the specified value and the concentration of cutting dust is low, B is a normal case, and C is an abnormal state where the gap is slightly narrower than the specified value, the concentration of cutting dust in the gap is high, or both are combined. In this case, D is short-circuited. Here Ia<Ib<I
There is a relationship c<IdlalaalOQlCQlu −>1>1>−=O, and 1 bird 1▲11” Therefore, extremely accurate detection can be achieved depending on the peak value of the detection signal pulse and furthermore on its degree of change over time. Able to make judgments.

If the discrimination result by the discrimination device 10 is normal B, an up signal is added to the counter 11, and if abnormalities A, C, and D are detected, a down signal is added to cause the counter 11 to count up and down. When the count number exceeds a set value, the counter 11 outputs a signal and applies it to the coupling circuit 12, so the gate pulse of the pulse generation circuit 5 passes through the coupling circuit 12 and is applied to the switch 4, causing a pulse discharge by controlling the on/off switch. Repeat. During the pause time of each pulse discharge, detection and determination of the gap state is performed every time, and this is detected by the counter 1.
It is counted as 1. The counter 11 outputs a signal every 10 pulses or 100 pulses, and this controls the occurrence of electrical discharge, so that the concentration of cutting powder present in the gap, wide variations in the gap length, etc. are always appropriate, and electrical discharge is likely to occur and occur. Discharge occurs only when the discharge is in the optimal discharge gap state where the discharge becomes normal discharge, and when the switch 4 is turned on and a pulse voltage is applied to the gap, the discharge starts almost synchronously, and under normal conditions, the discharge occurs for a predetermined period of time. Stable machining can be performed by repeating normal pulse discharge to complete one pulse discharge. Of course, in rough machining with a low discharge frequency, the counter 11 may be removed and a discrimination signal may be applied to the coupling circuit 12 every time one pulse is detected to control the gate pulse. Although not shown, when the discrimination result of the discrimination device 10 detects the A state, the servo device is driven to narrow the gap to an appropriate value, and when the C and D states are detected and they reach a certain count value, the servo device is driven to narrow the gap to an appropriate value. The electrode registration movement that widens and narrows the gap is performed to remove the inclusions in the gap and control the cutting dust concentration in the gap to the optimum level. However, the drive control timing of this servo device and registration movement device must be properly determined. This allows control to occur before abnormal situations such as arcs and short circuits occur, allowing stable machining to continue.

As described above, the present invention applies a check pulse with a constant pulse width shorter than the ionization time of the gap to check the state of the gap due to wide/narrow changes in the machining gap, concentration of intervening cutting powder, etc. , changes in current, resistance, etc. are detected and the peak value of the detection signal or its degree of change over time is determined, so it is possible to distinguish between the optimum state of discharge generation in the machining gap and the non-optimal state. By always performing accurate detection and applying machining pulses only when the optimum state is reached or when the rate of the optimum state is above a predetermined value, the discharge start-up occurs with a short waiting time, and after the discharge occurs, Since normal discharge is performed and the discharge can be terminated with a predetermined pulse width, each repeated pulse discharge is always constant, and the intended electric discharge machining can be performed stably.

In addition, machining gap control and cutting powder concentration control do not have to be performed all the time, but can be carried out to the minimum extent when necessary based on accurate gap condition judgment detection, so the gap length is always appropriate and cutting The powder concentration is also maintained at an appropriate level, and stable machining can be performed by reducing the occurrence of abnormal discharges such as short circuits and arc discharges. Further, the present invention detects the state of the machining gap without causing a discharge by using a check pulse with a pulse width shorter than the ionization time of the gap while the discharge body is stopped after the previous pulse discharge has ended. Therefore, there is no possibility that various signals will be mixed into the detection signal as during discharge, and from this point of view as well, there is an effect that detection and discrimination can be performed more accurately.

Furthermore, since the present invention detects the discharge without causing a discharge by using a check pulse with a pulse width shorter than the ionization time of the gap, detection is performed by applying a plurality of check pulses during the pause time between discharges. Accurate detection can be performed by outputting each pulse, which increases the signal amount and has the effect of making more accurate detection discrimination possible. Furthermore, the amount of change in the gap may be detected and determined by combining two or more voltages, currents, resistances, etc. for comprehensive detection and determination.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention, and FIG. 2 is an explanatory diagram of its operating state.

Claims (1)

[Claims] 1 Turn on/off the switch element in the machining gap between the electrode and the workpiece.
In electrical discharge machining equipment that repeatedly performs pulsed discharge using off-switching control, during the discharge pause from the end of the previous discharge until the application of pulse voltage for the generation of the next discharge, the ionization time in the machining gap increases. A pulse generator that applies one or more check pulses with a constant short pulse width, a signal detection device that electrically detects changes in the machining gap due to the check pulses, and a signal detection device that determines the peak value of the detection signal or the degree of change thereof. An electric discharge machining apparatus comprising a machining gap state detection device comprising a discrimination device and a counter that counts the discrimination output.