JP2007253260A - Electrical discharge machining control method and electrical discharge machining control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent deterioration of processing efficiency, and prevent failure of a processing shape of a workpiece. <P>SOLUTION: This device comprises electrical discharge pulse number count means counting a number of electrical discharge for a predetermined sampling period in a spacing together with application of a voltage from processing voltage supply means for applying a pulse voltage to a spacing between an electrode and a workpiece, a table, in which a processing volume by electrical discharge is registered according to materials of the electrode and the workpiece, shaft transferring volume detection means detecting a processing advancing volume in a processing advancing direction in the predetermined sampling period together with processing of the spacing, side electrical discharge judgment means calculating the processing volume according to the processing advancing volume detected by the shaft transferring volume detection means based on a projection area of the workpiece opposed to the electrode and density of the workpiece, and comparing it with an actual processing volume obtained by multiplying a number of electrical discharge counted by the electrical pulse number count means with the processing volume by electrical discharge so as to detect a proportion of side electrical discharge, and side electrical discharge avoiding means changing processing conditions of the electrode and the workpiece according to the proportion of the side electrical discharge by the side electrical discharge determination means. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fine hole electric discharge machining and a sculpted electric discharge machining, and when an electric discharge machining is performed to machine into a predetermined shape, an electric discharge machining control method for detecting the occurrence of electric discharge in the side direction leading to a reduction in machining accuracy, and its The present invention relates to an electric discharge machining apparatus that performs corresponding control based on a ratio of side surface discharge.

In general, an electrode and a workpiece are arranged opposite to each other with a predetermined gap therebetween, and a discharge voltage is applied between both electrodes of the electrode and the workpiece to generate a discharge between the electrodes. There exists an electric discharge machining apparatus that processes a workpiece by relatively moving the workpiece, transfers the shape of the electrode to the workpiece, and processes the workpiece into a desired shape.
In such an electric discharge machining apparatus, when processing discharge etc. accumulated between the electrodes along with the progress of processing is distributed in the side surface direction of the electrode, when secondary discharge occurs through the processing scrap, An electric discharge phenomenon occurs in a side surface direction different from the actual machining direction, resulting in an increase in machining time and a defect in the machining shape.
Therefore, based on the gap distance between the workpiece and the electrode and the number of normal discharges, an electric discharge machining apparatus that detects normal discharge as invalid discharge on the side surface when the gap distance is more than a predetermined gap distance and adjusts the control factor is disclosed in JP This is disclosed in Japanese Patent Laid-Open No. 55-96227.

JP-A-55-96227

In the conventional electric discharge machining apparatus, the gap distance between the workpiece and the electrode is detected, and the discharge is detected in the machining progress direction or the side discharge depending on the gap distance. Since the side discharge is detected when the threshold value is larger than 50 μm, there is a problem that, regardless of how much the side discharge occurs in the previous section, it cannot be detected and a defect in the machining shape occurs.
Moreover, since the gap distance changes depending on the machining shape, condition setting, liquid processing method, etc. in electric discharge machining, there is a problem that side discharge is erroneously detected when the above threshold value is set small.

  This invention was made in order to solve the problems as described above, and by detecting the side discharge and performing appropriate response control, the side discharge is suppressed, and a discharge occurs in a direction other than the processing progress direction, It is possible to mitigate a reduction in processing efficiency and to prevent a processing shape defect of the workpiece due to side discharge.

  The present invention provides a machining voltage supply means for applying a pulse voltage to a gap between an electrode and a workpiece, and a discharge pulse for counting the number of discharges in the gap with a predetermined sampling period in accordance with the voltage application from the machining voltage supply means. Depending on the number counting means, the electrode and the material of the workpiece, a table in which the machining amount by discharge is registered in advance, and the machining progress amount in the machining progress direction in the predetermined sampling period accompanying the machining of the gap Based on the detected axial feed amount detecting means, the projected area of the workpiece facing the electrode, and the density of the workpiece, the machining amount corresponding to the machining progress detected by the axial feed amount detecting means is calculated. A side discharge determination means for detecting a ratio of side discharge by comparing the actual number of discharges counted by the number of discharges counted by the discharge pulse number counting means with the amount of machining by discharge; and Depending on the ratio of the side surface discharge by a surface discharge determination unit, those having a side discharge avoiding means for changing the machining conditions between the electrode and the workpiece, the.

  As described above, the present invention can detect the side discharge and perform the corresponding control, thereby suppressing the reduction in processing efficiency caused by the side discharge and the quality deterioration of the workpiece due to the shape defect due to the side discharge, The productivity in the electric discharge machining apparatus can be improved.

Embodiment 1 FIG.
In the present embodiment, by utilizing the fact that the amount of machining (removal) per discharge is determined to some extent, by multiplying the number of occurrences of electrical discharge, the total amount of machining associated with electric discharge machining is calculated, Compare the machining progress amount in the machining progress direction by electric discharge machining and the machining amount in the machining progress direction obtained from the relationship between the machining progress direction in the machining progress direction and the projected area in the machining progress direction (machining progress amount × projected area × workpiece density). Thus, the machining ratio based on the side surface discharge other than the machining progress direction is obtained and reflected in the electric discharge machining control.

FIG. 1 is a block configuration diagram showing an electric discharge machining apparatus according to the present embodiment.
The electrode 1 is positioned in the machining progress direction in the Z-axis direction based on a servo amplifier provided on the main shaft, and based on the pulse voltage applied by the machining power supply 4, the distance between the electrode 1 and the workpiece 2 is The electric discharge is generated and the workpiece 2 is processed into a predetermined shape.
During machining, the average voltage detection unit 5 detects the average voltage between the electrodes, and compares it with a predetermined servo reference voltage to move the electrode 1 in the machining progress direction when the average voltage is high. When the average voltage is pulled, the distance between the electrodes is controlled to increase.

The discharge pulse number counting unit 6 is a counting part that reads an inter-electrode voltage, detects an effective discharge, and counts the number of discharge pulses, for example, as disclosed in JP-A-5-293714. Is output to the side surface discharge determination unit 8.
The shaft feed amount detection unit 7 is for detecting the discharge position, detects how much machining has progressed on the workpiece 2 based on the encoder value and the linear scale value, and discharges the side surface. Output to the determination unit 8.
The machining data input unit 9 inputs electrode material, workpiece material, and surface area data (projected area) corresponding to the machining area of the workpiece 2 as seen from the machining progress direction, and discharge set on the machine This is the part that determines the machining current, discharge pulse width, pause time, interelectrode voltage, average voltage, jump speed, jump-up amount, and jump-down time. In particular, the surface area data has a function of automatically calculating by reading drawing data such as CAD.

The side surface discharge determination unit 8 is a calculation formula that can calculate the machining weight per discharge from the machining current and the discharge pulse width according to the combination of the electrode material and workpiece material input in advance by the machining data input unit 9. Alternatively, a table is provided for each machining current and discharge pulse width, and the machining weight during a sampling period is calculated from the number of discharge pulses and the machining weight per discharge.
The processing weight m per discharge is obtained from the current value Ip and the pulse width τp using Equation 1.
m = A · Ip ^B · τp Equation 1
Here, in the case of the combination of the copper electrode and the steel material, A = 1.5 × 10 ² and B = 1.5, and in the case of the combination of the graphite electrode and the steel material, A = 1.17 × 10 ² and B = 1.5.

Even if it is not Formula 1, the processing weight per sampling section can be obtained by having the processing weight per discharge for the current value and pulse width measured experimentally in advance for each electrode material and workpiece.
On the other hand, the processing volume is calculated from the projected area obtained from the CAD data and the processing progress amount in the processing progress direction within the predetermined sampling period output from the axial feed amount detection unit 7, and further the workpiece volume is calculated. It is also possible to obtain the processing weight from the density.

As a result of comparison between the actual total processing weight Mr based on the actual number of discharges by the side discharge determination unit 8 and the processing weight Mc calculated from the axial feed in the processing progress direction, if Mc / Mr <0.7, side discharge occurs. Therefore, it can be determined that machining that does not contribute to the designated machining progress direction has been performed.
That is, this processing amount ratio can be calculated as the side discharge rate.

From the side discharge occurrence rate information, the side discharge avoiding unit 10 performs the corresponding control by changing the jump-up amount and the target average voltage so as to suppress the side discharge.
For example, when 0.3 ≦ Mc / Mr <0.7, the jump-up amount is increased, and when Mc / Mr <0.3, corresponding control is performed so that the average voltage is set to −10V. If the state of Mc / Mr <0.7 continues, corresponding control for increasing the jump-up amount and decreasing the average voltage is performed.
Also, the side discharge rate before and after executing the corresponding control is confirmed, and if Mc / Mr (after the corresponding control) ≧ 1.2 × Mc / Mr (before the corresponding control), it is judged to be effective for suppressing the side discharge. Then, the corresponding control is executed as it is. In general, since the processing depth often causes side discharge, the corresponding control is continuously performed.
On the other hand, if Mc / Mr (after corresponding control) <1.2 × Mc / Mr (before corresponding control), it is determined that the corresponding control is not effective, and the state before the corresponding control is restored, and another corresponding control is executed.

FIG. 2 is a diagram illustrating an example of response control execution.
In the section A, the side surface discharge rate is not large and an effective discharge is performed.
In the section B, the effect of discharging machining scraps is reduced due to factors such as a deeper processing depth, and the side surface discharge rate gradually increases.
In section C, the side discharge rate exceeds the threshold value of 30% and the response control 1 jump-up amount is increased.
In section D, response control 1 detects the side discharge rate after execution and compares it with the value before execution of response control 1. In this case, since the effect of the response control 1 was not obtained, the other response control 2 average voltage is lowered in the section E.
After executing the corresponding control 2, the side surface discharge rates were similarly compared to confirm that the side surface discharge rate was lowered. Thereafter, the processing is performed in the state after the control.

According to this embodiment, the rate of side discharge is automatically recognized in this way, and when the value exceeds a certain value, the rate of side discharge is reduced by taking measures to suppress side discharge, and the processing proceeds Efficient electric discharge machining is performed in the direction, and defects in the machining shape can be prevented.
Compared to the conventional technology, the ratio of side discharge can be detected even if the bottom gap distance is not large, so that it is possible to control the response at high speed, so that it is possible to prevent defects in the machining shape and machining efficiency. Also go up.
Since this detection method is based on the machining amount per discharge, it can be determined more accurately than the method of determining from the gap distance that changes depending on the discharge state.
Moreover, there exists an effect which can suppress a side surface discharge more effectively by having several correspondence control.
Since these processes are automatically performed, there is an effect that the operator can perform efficient processing only by inputting a simple material and processing area.

It is a block diagram which shows the structure of an electric discharge machining apparatus. It is a time chart for demonstrating operation | movement of an electric discharge machining apparatus.

Explanation of symbols

  1 electrode, 2 workpiece, 3 servo amplifier, 4 machining current supply means, 5 pole average voltage detection means, 6 discharge pulse number counting means, 7 axis feed amount detection means, 8 side discharge judgment means, 9 machining data input Means, 10 Side discharge avoidance means.

Claims (5)

Machining voltage supply means for applying a pulse voltage to the gap between the electrode and the workpiece;
With the voltage application from the machining voltage supply means, a discharge pulse number counting means for counting the number of discharges in the gap for a predetermined sampling period;
According to the material of the electrode and workpiece, a table in which the machining amount by discharge is registered in advance,
Along with the machining of the gap, an axial feed amount detecting means for detecting a machining progress amount in the machining progress direction in the predetermined sampling period;
Based on the projected area of the workpiece facing the electrode and the density of the workpiece, the machining amount corresponding to the machining progress detected by the axial feed amount detection means is calculated, and counted by the discharge pulse number counting means. Side discharge determination means for detecting the ratio of the side discharge by comparing with the actual machining amount obtained by multiplying the number of discharges performed by the machining amount by discharge;
Side discharge avoiding means for changing the processing conditions of the electrode and the workpiece according to the ratio of the side discharge by the side discharge determination means,
An electrical discharge machining apparatus comprising:   The electrical discharge machining apparatus according to claim 1, wherein the machining amount is registered in advance in the table in which the machining amount by electric discharge is registered in advance according to an electrical condition between the electrodes and the workpiece.   The electric discharge machining apparatus according to claim 1, wherein the side surface discharge avoiding unit changes the machining conditions with a side surface discharge ratio of 30% as a threshold value.   4. The electric discharge machining apparatus according to claim 3, wherein the amount of jumping of the electrode is controlled as the machining condition change by the side surface discharge avoiding means. A discharge pulse number counting step of counting the number of discharges in the gap for a predetermined sampling period with application of a pulse voltage to the gap between the electrode and the workpiece,
According to the material of the electrode and workpiece, a table in which the machining amount by discharge is registered in advance,
Along with the machining of the gap, an axial feed amount detection step for detecting a machining progress amount in the machining progress direction in the predetermined sampling period;
Based on the projected area of the workpiece facing the electrode and the density of the workpiece, a machining amount corresponding to the machining progress detected in the axial feed amount detection step is calculated and counted in the discharge pulse number counting step. A side discharge determination step of detecting a rate of side discharge by comparing the actual number of discharges multiplied by the amount of machining by discharge previously registered according to the material of the electrode and workpiece,
In accordance with the ratio of the side surface discharge in the side surface discharge determination step, the side surface discharge avoiding step for changing the processing conditions of the electrode and the workpiece,
An electrical discharge machining method comprising:

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