JPS5854940B2 - Hoden Kakousouchi - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electric discharge machining apparatus that processes a machining gap between a machining electrode and a workpiece by supplying machining pulses and generating repeated electric discharges by controlling on/off of a switch element. It is something.

In this electric discharge machining apparatus, a special machining pulse generator that has been previously proposed (this machine generates machining pulses by switching on and off a switch element with an independent pulse generated by a multi-pie break, etc.) There is a method in which discharge is applied to the machining gap, but in this case, the gap condition changes due to repeated discharges, which changes the discharge condition and changes the discharge pulse width and repetition frequency, making it difficult to achieve the desired results. It has the disadvantage that it cannot be processed for other purposes.

In addition, an isopulse method has been proposed in which a voltage is applied to the machining gap by on-conduction control of a switch element, and after the discharge starts, a timer or the like is used to supply current for a predetermined period of time, but in this case, the discharge repetition frequency is In addition, the servo becomes unstable, and during the waiting time for the discharge to start, cutting powder, etc., is attracted to the electrode and the workpiece due to the electric field, making it easy to generate arc discharge, etc. becomes unstable.

Moreover, this unstable and irregular discharge generates a surge voltage, which heats and destroys the transistor of the switching element.

The present invention was proposed in order to eliminate the drawbacks of the conventional method, and it is possible to perform machining only when the resistance of the machining gap when the discharge body is stopped or the physical quantity proportional to this is within a predetermined range. It is characterized in that a gap machining pulse is applied to generate electric discharge.

In other words, if the waiting time τ from applying the voltage to the machining gap to starting the discharge is long as described above, it will have various negative effects on the discharge state after the start of the discharge, and the condition of the machining gap will also be affected. If the discharge pulse width τon changes, it will have a large effect on machining effects such as low electrode consumption machining, so it is absolutely necessary to control this waiting time τW to be small and constant, and also to control the pulse width τon constant. Must be.

Therefore, the state of the machining gap is detected by its resistance value, and the switch is turned on to cause discharge only when the resistance value is within a certain range.

Detection of the state of the machining gap, that is, detection of the resistance value or a value proportional to this value, is to avoid detection during discharge where various signals are mixed, and to detect when the discharge body is stopped.

On the other hand, the waiting time τ from the time when a voltage is applied to the machining gap to start the discharge until the discharge starts is expressed as W it τ ”KX−XE−2 K .

However, K: constant (τ = sec@400), l: discharge gap length (cm), K: electrical conductivity (U/cIrL),
E: Discharge starting potential gradient (V/Crn), so this waiting time τW is controlled to be small and constant E, but experimentally or theoretically (this is often controlled to about 1 to 10% of the pulse width τon) Therefore, more stable electric discharge machining can be performed as desired.

Therefore, in order to control τ, the gap length l is determined by the servo and the discharge starting potential gradient E is determined by the machining power source, so the gap resistance value l/k must be controlled and kept small and constant. By τ.

The desired electrical discharge machining can be performed by controlling n to a set value of 1 to 10%, but if the gap length l is always controlled to be constant by a servo, then 1/k is the predetermined range. In other words, the gap length at which discharge can start (when this occurs,
When the resistance value 17k is within a predetermined range and the discharge can be started with a certain minute waiting time, the desired stable electrical discharge machining can be performed by performing pulse discharge with a machining pulse having a certain fixed on-pulse. It is.

The present invention will be described below with reference to an embodiment of the drawings. Reference numerals 1 and 2 refer to electrodes and a workpiece that form a machining gap, 3 a power source for machining, 4 a pulse switching element thereof, and 5 an oscillator for generating gate pulses. , 6 is a resistance detection circuit for detecting the resistance value of the machining gap, which is connected in series with the test power supply T and in parallel to the machining gap.

Reference numeral 8 denotes a discriminator that discriminates whether the detection signal of the detection circuit 6 is within a set range and generates a gate pulse.This output gate pulse is added to a coupling circuit 9I such as an AND gate, and the oscillator is activated only when there is a gate output. The switch 4I is configured to add a gate pulse obtained by logically multiplying the pulses from 5 to the switch 4I.

Reference numeral 10 denotes a switch element inserted in series with the detection circuit 6, which converts the gate pulse of the processing power switch 4 into the phase inversion circuit 1.
Switching is controlled by an inverted pulse signal through 1.

That is, the switch 10 operates in the opposite direction to the switch 4, and controls the detection circuit 6 to conduct through the gap only when the discharge body is stopped, thereby detecting the resistance value.

In the above processing, a gate pulse is applied from the oscillator 5 through the circuit 9 to the machining gap l (thereby turning the switch element 4 on and off), a pulse voltage is applied from the power source 3, and pulse discharge is repeated to perform electrical discharge machining.

When the switch 4 is on, that is, during discharge in the gap, the switch 10 is turned off, and when the switch 4 is turned off and the discharge is finished, that is, the discharge body is stopped (this switch 10 is turned on and the detection circuit 6 is placed in the gap). Connecting.

Therefore, the resistance of the machining gap between the discharge bodies for each repeated pulse discharge is detected by the detection circuit 6, and the detection signal is discriminated by the discrimination device 8.

If the discrimination result is within a predetermined range, the gate output continues to be output, and this is applied to the AND gate combination circuit 9, and the gate pulse combined with the pulse of the oscillator 5 is sent to the switch 4 (as the switch 4 repeats on/off switching) A machining pulse is applied to the gap and the discharge continues.

The resistance value of the machining gap is the pulse width τ of the pulse discharge.

□, varies depending on machining conditions such as peak value rp, and is greatly affected by dirt on the electrode and changes in the quality of interstitial inclusions (generated gas, machining debris, etc.) that occur not only during but also after discharge. For example, the finish In machining, the potential gradient E is 10 to 29 KV/c.
1111 Pulse width τon is 0.1 to 5 μs and resistance value is 5
Ω for 0 to 5, E for medium machining to 5 to 10 ■/cr111
τ.

. 1~10μS1, resistance value is 50~IKΩ, rough machining is E
■/cIrL1τ for 1 to 5.

. 5 to 100μS1 resistance value changes from 10 to 500Ω, and by experimentally detecting the conditions in which the best electrical discharge machining can be performed, the standard value and standard range of the gap resistance while the discharge body is stopped is determined, and this is determined by a discrimination device. (Thus, if the detection signal of the detection circuit 6 falls within this standard range, it is possible to easily determine whether the discharge just before detection was good or bad, or whether it was normal or not. A gate pulse is output and applied to the coupling circuit 9, and when an abnormality such as arc discharge is detected, the gate pulse applied to the coupling circuit 9 is turned off, so the gate pulse coupled with the pulse of the oscillator 5 is sent to the switch 4.
Do not participate in the discharge, leave it off and stop discharging.

In addition, when the normal state of the machining gap is determined by resistance detection, and while the normal state continues, a gate pulse is applied to the coupling circuit 9, so the gate pulse combined with the pulse of the oscillator 5 is applied to the switch 4 and the switch is switched. 4 on
Off control (Thus, a predetermined machining pulse is applied from the power source 3 to cause pulse discharge.

This pulse discharge occurs when the switch 4 is turned on and the voltage from the power source 3 is applied to the machining gap, when the gap condition is normal and within a predetermined range f.
This means that the resistance value 1/k is 1 and l/k is within a certain range, which means that the waiting time τ□
is the pulse width τ determined by the machining conditions.

. Since the waiting time τ is set to be within the range of 1 to 10% of When the gate pulse is turned off and one pulse of discharge is completed, and the constant off pulse of the gate pulse is completed, the switch 4 is turned on and the power supply voltage 3 is applied to the gap, and the next pulse discharge is repeated, but at this time, τ is small and constant. The gap state is within the range (because the switch 4 is turned on and off only when this occurs, τ is always constant, and even if the switch 4 is turned on and off with the gate pulse from the fixed oscillator 5 and a constant machining pulse is applied) The discharge pulse width τ from the time the discharge starts until the switch off and the discharge ends.

. is always constant and has a constant pulse width τ.

Machining can be performed by repeating n discharges, and therefore high-precision machining can be performed under the desired conditions such as no electrode consumption.Also, since the 1-pulse discharge energy is always constant, the machining speed is faster than conventional methods with the same machined surface roughness. is enhanced.

In addition, since the power switch 4 is turned on and off to generate discharge only when the machining gap is normal and within a predetermined range, arc discharge is less likely to occur, and the waiting time τ can be controlled to a minimum, unlike the conventional method. The state in which high voltage is applied until a discharge occurs continues for a long time (this eliminates the phenomenon of machining debris adhering to the electrode, and prevents abnormal discharges such as arcs and short circuits from occurring in the future. can be prevented to a minimum.

Also on hiatus τ. ff is the minimum constant value of the oscillator 5I, which is equal to the off pulse of the gate pulse.
It is also controlled at a constant frequency by the gate pulse from the oscillator 5'', and high-speed machining can be performed at the highest frequency under stable machining conditions.

Furthermore, since the number of discharge repetitions is constant in this way, and the follow-up control of the machining gap can be controlled so as to perform discharge at this constant number of discharge repetitions, follow-up control is easy and stable control can be performed.

In addition, since machining gap follow-up control and discharge can be performed stably in this way, surge voltages are not generated, accidents such as damage to the power switch are eliminated, and long-life use is possible, which is extremely effective.

In addition, to detect the state of the machining gap, it is possible to use not only the resistance value, but also various physical quantities such as impedance, voltage, current, high frequency, and other electromagnetic waves proportional to this value. Methods such as checking a certain part, for example, only for a short period of time immediately after the end of discharge, or checking several times in the middle and late stages, can be used as appropriate.

In either case, the detection is performed while the discharge is stopped, so there is no disturbance in the detection signal unlike the detection during the discharge, and the machining gap can always be detected and discriminated accurately.

[Brief explanation of the drawing]

The figure is a block circuit diagram of an embodiment of the present invention.

Claims (1)

[Claims] 1. Force between electrode and workpiece U machining gap l In an electric discharge machining apparatus that applies machining pulses by on/off switching control of a switch element, a pulse oscillator that applies a gate pulse to the switch element is provided to control the state of the machining gap. A detection device is provided for detection by detecting the resistance value of the machining gap during the stoppage of the discharge body or a physical quantity proportional to this from the end of the previous discharge until the next pulse voltage is applied, and the detection signal of the detection device is provided. A discrimination control device is provided which allows applying a gate pulse from the pulse oscillator to the switch element O only when it is within a set range by determining a discrimination criterion having upper and lower limits of normal values. Characteristic electrical discharge machining equipment.