JPH10296540A - Electrical discharge machining device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To carry out electrode consumption correction with higher precision in the machining condition in which generation probability of a pose split is greatly changed by a slight change in a machining area by arranging an electrode consumption quantity correcting means correcting an electrode feeding quantity in the machining direction and in the oscillating direction on the basis of a determined electrode consumption quantity. SOLUTION: Continuing times are sorted into four types, and a pulse generation quantity integrating means 5 according to a continuing time classifies pulses detected by means of an electrical discharge pulse detecting means 6 so as to integrate them. A consumption correction quantity calculating means 3, which calculates an actual consumption correction quantity on the basis of consumption correction data 1 according to a continuing time and the integration data from the pulse generation quantity integration means 5 according to a continuing time, calculates a whole consumption quantity Wtotal by the present time according to an expression: Wtotal = ΣPi*Wi (i=1-n), when a generation rate according to a continuing time is represented by Pi while consumption correction data according to a continuing time is represented by Wi. An NC controller 4 adds the consumption quantity Wtotal to a feeding quantity in a machining condition so as to find an actual feeding quantity.

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 apparatus for correcting an electrode feed amount in a machining direction and a swing direction by more accurately calculating an electrode consumption amount in the electric discharge machining apparatus.

[0002]

2. Description of the Related Art An electric discharge machining apparatus performs machining of a work by intermittently generating an electric discharge between an electrode and a work. In the machining, a gap called a gap is formed between the electrode and the work. The surface of the workpiece exists and has a surface roughness determined by electrical conditions such as a peak current value of a discharge pulse generated in the gap, and the electrodes also have a characteristic of being consumed by electrical conditions.

Generally, under electrical conditions in which the processing speed is high, both the gap and the surface roughness are large, and the consumption of the electrodes is small. On the other hand, under electrical conditions where the surface roughness is fine, there is a tendency that the gap is narrow, the processing speed is slow, and the electrode consumption is large.

For this reason, when performing machining with a high machining speed and fine surface roughness by electric discharge machining, the machining speed is increased as an average of the entire machining while switching from an electrical condition having a large surface roughness to an electrical condition having a small surface roughness. Processing is performed so that a work having a fine surface roughness can be obtained.
As a method of switching the electric conditions, a value called a feed amount is experimentally obtained and set in advance as a value corresponding to the electric condition, and the current electric condition is to set the electrode by the corresponding feed amount in the machining feed direction and the swing direction. A method is used in which it is determined that the process has been completed when it can be moved to the next condition, and the condition is switched to the next electrical condition with a finer surface roughness.

The relative position between the electrode and the workpiece is controlled by a gap control, which is a control in which the electrode escapes in a direction in which no discharge is generated when the discharge is concentrated, and is advanced in a traveling direction when the discharge is small. Is being done,
When the electrode reaches the target position, that is, when the electrode can be moved in the machining feed direction and the swing direction by the feed amount, it can be considered that the machining under the current electric condition has been completed.

The above-mentioned feed amount can be experimentally determined from the current electric conditions and the previous electric conditions, and the gap and the surface roughness under the current electric conditions and the surface roughness under the previous electric conditions are considered. Further, in order to prevent the work from being finished smaller than the target size due to further consumption of the electrodes, the consumption amount of the electrodes is added to the electrode feed amount in the machining direction and the swing direction. Generally, the term “machining condition” in electric discharge machining refers to a condition including an electrical condition and a feed amount, and hence the term “machining condition” will be used in the following description.

Since electric discharge machining has the above characteristics, a plurality of machining conditions are set in advance in accordance with the machining speed and the surface roughness. Is selected as a start condition, and processing is performed while sequentially switching the processing conditions, a predetermined surface roughness can be obtained at the maximum processing speed.

The conventional method will be described with reference to FIGS. FIG. 5 is a control block diagram of the electric discharge machining apparatus for machining according to the machining feed amount in the machining conditions. Reference numeral 8 denotes a discharge power supply, which processes a work by applying a voltage to a gap between the electrode 9 and the work 10 to generate a discharge. Reference numeral 2 denotes a processing condition, which comprises an electrode feed amount in consideration of electric conditions and electrode consumption. Reference numeral 4 denotes an NC control device for processing the workpiece 10 with a specified surface roughness and a specified accuracy by issuing a command to move the electrode 9 to the shaft driving means 7 in accordance with the processing condition 2.

FIG. 6 shows an example of a processing condition table. In FIG. 6, the portion of the electric condition is common and is omitted.
According to this processing condition table, according to the processing condition of R9, the processing was performed 17 microns in the processing direction and 14 microns in the swing direction.
8 is changed to the processing condition. If the specified dimensions are similarly processed under the processing conditions of R8 and R7, the processing is completed. In the processing conditions of FIG. 6, the electrode consumption amount obtained from the electrode consumption rate has already been added to the feed amount.

[0010]

In the conventional processing conditions, the electrode consumption is added to the feed amount, but in some cases, the electrode consumption cannot be sufficiently corrected. In other words, even if the electrode does not reach the target position, the machining under the current machining conditions is terminated due to the exhaustion of the electrode, and as a result, a predetermined machining surface roughness cannot be obtained, and insufficient machining due to the electrode exhaustion. There has been a problem that predetermined shape accuracy cannot be obtained.

The cause of this is that the characteristics of electrode wear are not determined solely by the electrical conditions, but are greatly affected by the facing area between the electrode and the workpiece. In particular, pulse cracking occurs when the facing area is large and the finishing conditions are satisfied. This is because electrode consumption is greatly increased. This pulse cracking
As in the waveform examples of the discharge voltage V and the discharge current I shown in FIG. 4A, the phenomenon is that the discharge cannot be maintained within the discharge duration and is divided into a plurality of pulses. The discharge duration and electrode consumption tend to be such that the longer the discharge duration, the less the electrode consumption, and the shorter the discharge duration, the more the electrode consumption,
As shown in FIG. 4A, in a state where the pulse crack occurs, the electrode consumption increases. In addition, the machining condition table measures gap / surface roughness and electrode consumption by experiments, and the feed amount is set in consideration of electrode consumption.
There was also a problem that the electrode area used for this experiment was different from the electrode area used for actual processing.

In order to solve this problem, conventionally, processing conditions were created by performing an experiment for measuring the gap / surface roughness and electrode wear for each electrode area. However, the pulse cracking phenomenon also depends on the processing conditions. With slight changes,
The occurrence situation has changed greatly, and in most cases, even if the electrode consumption is corrected for each area, it is insufficient. For example, under the processing conditions where a surface roughness of “6S” is obtained, the electrode consumption rate is 7% when the diameter of the electrode processing surface is 30 mm, but the electrode consumption rate when the processing surface diameter is 60 mm. Is 20
It becomes 0%.

Further, the actual electrode has a complicated shape and an accurate area cannot be obtained, so that accurate wear correction is almost impossible. Therefore, under the processing conditions where pulse cracking occurs,
There has been a problem that the correction of the processing feed amount is not sufficiently performed, and the surface roughness according to the processing conditions cannot be obtained, or the specified processing accuracy cannot be obtained.

Conventionally, it has been considered that electrode wear is affected by conditions such as a small change in area, machining current, machining voltage, and the like. In practice, however, electrode wear is determined by the on-time of the discharge pulse and the peak current. When a pulse crack occurs, one discharge pulse is further divided into a plurality of pulses, and the on-time of the divided pulse is not constant, and the number of pulses is not constant because the pulse is divided. However, electrode wear was the main factor that changed depending on the area. SUMMARY OF THE INVENTION It is an object of the present invention to provide an electric discharge machining apparatus that performs electrode wear correction with higher accuracy under machining conditions in which the probability of occurrence of pulse cracks greatly changes due to a slight change in the machining area.

[0015]

SUMMARY OF THE INVENTION The present invention relates to an electric discharge machining apparatus, and an object of the present invention is to provide a discharge pulse detecting means for detecting the generation of a discharge pulse, and a discharge continuation of the detected discharge pulse. A pulse generation amount integrating means for measuring a time and integrating a pulse generation ratio with respect to the entire pulse of the discharge duration for each discharge duration; and a storage unit for storing an electrode consumption corresponding to the discharge duration as electrode consumption correction data. And an electrode consumption amount determining means for determining an electrode consumption amount up to the present time from the pulse generation ratio integrated by the duration and the electrode consumption correction data, and determining the electrode consumption amount in the machining direction and the swing direction from the determined electrode consumption amount. This is achieved by providing an electrode consumption amount correction unit that corrects the electrode feed amount.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an electric discharge machine according to the present invention will be described below with reference to FIGS. FIG.
FIG. 3 is a control block diagram of the electric discharge machine. 1 is consumption correction data by duration, 2 is processing condition, 3 is consumption correction amount calculating means, 5 is pulse generation amount integrating means by duration, 6
Is a discharge pulse detecting means for detecting a pulse crack.

The discharge pulse detecting means 6 detects a pulse breaking waveform as shown in FIG. 4A based on the discharge voltage V or the discharge current I, and measures the actual discharge duration of each divided pulse. . In this example, the duration T1,
The pulse having the duration T2 and the duration T3 can be detected as "1". Note that the pulse shown in FIG. 4A is a pulse having a duration T0 shown in FIG. 4B when no pulse crack occurs.

The pulse generation amount integrating means 5 for each duration is shown in FIG.
As shown in the figure, the pulse is integrated and counted for each pulse duration time Ti.
The pulses are classified into four types of μsec, 1 to 5 μsec, 5 to 10 μsec, and 10 μsec or more, and the pulses detected by the discharge pulse detection means 6 are classified and integrated. As a result, the integrated value of the pulse number can be output as it is. However, the integrated value of the duration time Ti and the total number of pulses are used so that the consumption correction amount calculating means 3 can easily use the integrated value. The ratio is determined, and as shown in FIG. 3, the occurrence ratio Pi is determined.

FIG. 2 shows an example of the consumption correction data 1 for each duration. Although the electrode wear value Wi experimentally obtained in advance for each pulse duration Ti is stored in this data, the experimental value does not need to be measured for each processing area, and may be a numerical value measured for a small area. The following calculation is easier if the method of setting the range of the pulse duration time Ti is the same for both the data integrated by the pulse number integrating means and the consumption correction data.

The consumption correction amount calculating means 3 is a part for calculating the actual consumption correction amount from the consumption correction data 1 for each continuous time and the integrated data of the pulse number integrating means 5 for each continuous time. , Wiring consumption data by duration
Then, the total consumption Wtotal up to the present time can be calculated by the following equation (1).

[Equation 1] Wtotal = ΣPi * Wi (i = 1 to n)

The NC controller 4 can obtain the actual feed amount by adding the consumption amount Wtotal obtained by the above equation 1 to the feed amount in the processing conditions. In this case, the feed amount in the processing conditions is an actual feed amount, and it is not necessary to consider electrode consumption in advance. In addition, when setting the correction data of the electrode wear amount, conventionally, it was necessary to experimentally measure the electrode wear amount for each electrical condition in the processing conditions, and further, it was necessary to measure for each electrode area, In the present invention, it is only necessary to measure for each discharge duration time Ti. There is no need to measure experimentally for each area. If the actual feed amount can be obtained, thereafter, processing can be performed in the same manner as in the related art to correct the electrode consumption.

Since the consumption correction data 1 for each duration is affected by the peak value of the discharge current, it must be provided for each peak value. However, pulse cracking is a problem in actual machining only in finish machining. A sufficient effect can be obtained by having the consumption correction data classified by duration only for the discharge current peak value used in the finishing process.

In this embodiment, the duration is classified into four. However, this classification does not need to be fixed, and the number of classifications and the range of the duration can be set in any manner. The effect is obtained. In addition, the discharge pulse detection unit can detect all the pulses and sequentially calculate the consumption correction amount in real time.However, the discharge pulse data is sampled and stored at an appropriate timing, and the state is changed to an offline state. It is only necessary to perform the integration of the number of pulses for each duration and the calculation of the consumption correction amount to correct the feed amount before switching the current processing conditions.

In this embodiment, the case where each component is realized as a device different from the NC control device has been described. However, the same effect can be obtained even if this component is realized in the NC control device.

[0025]

As described above, according to the present invention, the electrode wear correction can be performed with higher accuracy under the processing condition in which the occurrence probability of the pulse crack changes greatly due to a slight change in the processing area. An electric discharge machining apparatus that is close to the specified surface roughness and can obtain the specified machining accuracy can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic block diagram showing one embodiment of an electric discharge machine according to the present invention.

FIG. 2 is a diagram showing an example of consumption correction data for each duration of the electric discharge machine of the present invention.

FIG. 3 is a diagram showing an example of a pulse number integration result for each duration of the electric discharge machining apparatus of the present invention.

FIG. 4 is a diagram showing an example of a discharge voltage / current waveform when a pulse crack has occurred and when it has not occurred.

FIG. 5 is a schematic block diagram showing an example of a conventional electric discharge machine.

FIG. 6 is a view showing one embodiment of conventional processing conditions.

[Explanation of symbols]

 1 Consumption correction data by duration 3 Consumption correction amount calculation means 5 Pulse generation amount integration means by duration 6 Discharge pulse detection means 9 Electrode 10 Work V Voltage I Current T0, T1, T2, T3 Discharge duration

Claims (1)

[Claims] A discharge pulse detecting means for detecting generation of a discharge pulse, a discharge duration of the detected discharge pulse is measured, and a pulse generation ratio of the discharge duration to the entire pulse is integrated for each discharge duration. A pulse generation amount integrating means, a storage unit for storing an electrode consumption amount corresponding to the discharge duration as electrode consumption correction data, and a pulse generation ratio integrated for each duration and the electrode consumption from the electrode consumption correction data to the current time. An electric discharge machining apparatus comprising: an electrode wear amount determining means for determining an amount; and an electrode wear amount correcting means for correcting an electrode feed amount in a machining direction and a swing direction from the determined electrode wear amount. .