JPH01234117A - Machining error correction control method in die milling spark erosion machining - Google Patents

Abstract

PURPOSE:To set a correct reference surface with high reliability by aligning for setting a reference surface between an electrode and a workpiece before machining utilizing a characteristic that a gap under gap detecting conditions in a certain microdischarge converges to a specified value. CONSTITUTION:Alignment for setting a reference surface between an electrode 1 and a workpiece 2 before machining is performed by causing microdischarge for a designated time under gap detecting conditions that a gap with the electrode is a specified value to avoid an error due to burr, dust or the like. Further, in order to diagnose an error due to electrode consumption and thermal deformation caused in spark erosion machining, after machining in a designated step, the electrode is moved to a reference surface setting position in the same manner before machining, and while it is switched to gap detecting conditions to cause microdischarge for a designated time, the position of the electrode after the gap with the electrode, that is, an error due to electrode consumption and thermal deformation is detected to control error correction. Thus, the reference surface can be set correctly and with high reliability, and a machining error is eliminated so as to improve machining accuracy.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention detects and diagnoses machining errors in the machining depth direction, such as errors due to machining gap changes that occur during electrical discharge machining, errors due to electrode wear and thermal deformation, and The present invention relates to a method for accurately correcting and controlling the process, and is particularly suitable for increasing the precision of die-sinking electrical discharge machining.

[Conventional technology]

Die-sinker electrical discharge machines are widely used in various industries, including the mold industry, and among them, NC-controlled electrical discharge machines that can control multi-purpose machining are becoming increasingly popular.

In general, NC-controlled electrical discharge machines, as shown in Figure 15,
It is roughly divided into a machine body that performs electric discharge machining and a control power supply body that has a built-in NG control device that performs a series of controls. An X, Y table 4 with a built-in drive mechanism for the X and Y axes is mounted on the bed 3, and a processing tank 5 is placed above it, into which the workpiece of the product to be processed is attached. ing.

Further, a quill 6 having a built-in Y-axis electrode feeding mechanism is supported by a column 7, and an electrode 1 is attached to the tip of the quill 6. 8 is a machining fluid supply device, which supplies and circulates machining fluid into the machining tank 5 and also discharges machining products (machining waste, decomposed products of machining fluid, etc.) produced by electrical discharge machining as appropriate. An appropriate amount of machining fluid can also be supplied to the vicinity of the workpiece 2 during electrical discharge machining. - On the other hand, the NC control device 9 built into the control power supply main body 9
a is for setting and registering arbitrary machining conditions and machining power supply circuit 9c
At the same time, it is possible to control the positioning of the electrode 1 and workpiece 2 via the 3-axis drive control circuit 9h, drive the Y-axis electrode feed mechanism, control the electrode position during machining, and control the X-axis, Y-axis, and Y-axis. It is now possible to perform a series of controls necessary for electric discharge machining, such as driving and swing control of the axis table mechanism.

Electrical discharge machining has traditionally been performed using a die-sinker electric discharge machine configured in this way, but with the advancement of industry in recent years, the demand for not only high-efficiency machining but especially high-precision machining has increased. There is.

Most of the machining accuracy of molded products by electric discharge machining is determined by the finishing process, but since there are many machining-related factors, it is difficult to effectively achieve high machining accuracy unless you fully understand the characteristics and interrelationships of each factor. The factors related to machining accuracy that are not possible are (1) mechanical factors, (2)
) controlling factors.

(3) Electric discharge machining phenomenon factors, (4) Temperature factors, (5)
It can be classified into other factors.

Some of these factors are physically easy to take measures against, while others are difficult to deal with, and item (3) is particularly troublesome to deal with because it involves phenomena specific to electrical discharge machining. Among these, machining errors due to changes in the machining gap that occur during electrical discharge machining and machining errors due to electrode wear have been pointed out as major factors that degrade high-precision machining. Furthermore, during electric discharge machining, the temperature of the machining fluid increases, so thermal deformation and thermal expansion errors caused by this temperature change also become a major cause of roughness.

Furthermore, setting errors that occur during positioning of the electrode and workpiece before machining are also one of the factors that cannot be overlooked.

A situation in which such an error occurs will be specifically explained using hole machining as an example.

2.3.4 outlines the machining plan and condition selection for the machining specifications of the workpiece, and the calculation method of the electrode feed amount and swing radius according to this machining process.

Table 2 Example of Hole Machining Also, Figure 17 shows an example of a flowchart of machining operations for actually performing machining using the die-sinker electrical discharge machine shown in Figure 15. Generally speaking, electrical discharge machining begins with the initial roughening. There are several steps from machining to final finishing, and each machining condition is determined by the machining speed.

Machining surface roughness, electrode wear rate, PM gap (machining gap)
Appropriate conditions are selected from the processing technology data file that describes the characteristics such as Needless to say, under the conditions of rough machining, the discharge energy is large, so high-speed machining can be performed, while under the conditions of finishing machining, the discharge energy is small and machining is performed at low speed in order to obtain the required machined surface roughness. In addition, in order to suppress or eliminate the influence of electrode wear, conditions are selected to minimize the electrode wear rate.

The electrode feed amount in the depth direction and the amount of oscillation in the radial direction.

Generally, as shown in FIG. 13 (3), it is obtained by adding and subtracting the machined surface roughness value and the machining gap value under each machining condition, and each is set based on the calculation result. In the first rough machining, it is not necessary to perform any particular oscillation (r t = O), but if the if diameter used is smaller than a predetermined value, the oscillation is added to correspond to the predetermined value. can be processed.

By programming the machining details planned in this way,
This is input into the NG control type electric discharge machine, and an electrode of a predetermined shape and a workpiece are installed at a predetermined position. After this machining preparation is completed, actual machining operation begins, and machining operations are executed as shown in the flowchart shown in FIG. The step indicates the order of the processing process, and here = 1 to 6
becomes.

At this time, the target value Z of the electrode feed amount is Z 1 ”Z e
The machining is repeated in sequence until the final finishing machining Zs (Z-) is reached. Figure 18 shows the machined hole and electrode feed amount at this time.

The figure also shows the swing radius rn during final machining.

The reference plane in the depth direction can be set arbitrarily depending on the workpiece, but for the sake of easy explanation here,
The upper surface of the workpiece is the hole to be machined.

This reference plane setting, which is performed before machining, has traditionally been performed by sensing contact between an electrode and a workpiece, and the same method is used here. Electric discharge machining is performed in the depth direction from this reference plane, and the electrode position is controlled so as to follow the progress of the machining and keep the machining gap within a certain appropriate range. As a method of controlling the machining gap, a method of detecting the average machining voltage between FAs and controlling it to a constant value is simple and has been widely used. There are several other control methods, but in any case, if the machining gap is not kept within an appropriate range, the discharge phenomenon will be disturbed and normal discharge machining cannot be maintained. It is also necessary that processed products be discharged from the processing gap so as not to adversely affect processing.

When machining is performed using such a method, the first error that occurs is an error in positioning settings before machining.

Alignment settings (reference plane settings) using touch detection.

It is susceptible to the effects of pars that tend to form at the ends of electrodes, dirt, dust, and other inclusions that adhere to the surface of the workpiece, and the amount of error (ΔOx) can range from several μm to several tens of μm. , it is extremely difficult to accurately align the reference surface. Other positioning methods other than touch sensing include 1, for example, Japanese Patent Publication No. 6
As disclosed in Japanese Patent No. 1-58255, there is a detection method that utilizes corona discharge by applying a high voltage. If this detection method is used, it is possible to avoid the above-mentioned problems, but it requires a special high-voltage power supply and control device of about 1ooov, which is much higher than the normal electric discharge machining voltage, and it is not safe. Also requires caution.

Furthermore, even if it is possible to utilize corona discharge in air, the phenomenon is different when using it in liquid or during processing, so it is difficult to handle it in the same way as in air.

On the other hand, the machining gap during electrical discharge machining is not always constant, but increases and decreases depending on various machining conditions, and fluctuates up and down in response to changes in electrical discharge machining phenomena due to the influence of machining products. For this reason, the machining gap (GaP value) value set in advance is not achieved, and the amount of difference from this set value becomes a machining error. 1st
9. Table 5 in FIG. 1 shows the electrode position and gap error after processing in the step when processing was performed using the method shown in FIG. 17. The plan before processing is Z K = HK - G, and the result after processing is Z * = Z a = Ha
G a w G a = G K f:ΔGK.

Table 5 In other words, if the actual gap value G& relative to the set value G is excessive (G K < Ga), excessive machining will occur.

On the other hand, if it is too small (G>aa), machining will be insufficient.The amount of difference from the set value is largely influenced by electric discharge and machining phenomena, and may range from several μm to several tens of μm.

Furthermore, since the temperature of the machining fluid increases during machining, this temperature change causes thermal expansion deformation. Further, even when machining is performed under low consumption conditions, the electrode is consumed during machining. Figures 20 and 21 show the situation at that time.

22, in FIG. 20, the electrode 1 is attached to the tip of the quill 6a via the electrode fixing jig 6b, and the workpiece 2
are respectively set on the table 4a via the workpiece fixing jig 4b, and are in the middle of the machining fluid (not shown). vw
is the machining volume when machining to a predetermined depth with the electrode 1 of a predetermined shape, Vc is the electrode consumption volume at that time, and Δn
c represents the length of electrode wear assuming that the wear is uniform, and ΔLe and ΔL represent the amount of thermal expansion deformation on the electrode side and workpiece side caused by the temperature rise of the machining fluid, respectively. On the other hand, the relationship between the machining time t until reaching the target machining depth HK, the temperature change ΔT at that time, and the electrode wear length ΔQc is shown in Table 6 of FIG. 23. Figure 23 9
Table 6 shows the situation of electrode wear and thermal deformation after mechanical processing.The electrode wear length is ΔQc=A-HK・δ, and the thermal expansion deformation ΔM=(Le・ρe + L−・ρW)・ΔT
The machining depth is Ha = HK±ΔH=Hg±(ΔQ
c+ΔL).

Table 6 In the case of Ml, where the discharge energy is large and the machining speed is fast, the target machining depth is reached in a shorter time than in the case of v2, where the machining speed is slow, and the temperature change ΔT1 is also larger. The electrode wear length Δnc increases in proportion to the electrode wear rate δ and the machining depth, and is expressed as ΔQc=A−H·δ. This value becomes a negative error factor for machining dimensional accuracy. On the other hand, the deformation ΔL due to thermal expansion increases in proportion to the temperature change, ΔL=(Le・/) e+ Lm 'P w)'Δ
Table 6, which is indicated by T and is a positive error factor for machining dimensional accuracy, summarizes the results shown in Figure 23. If the electrode wear is excessive (Δnc>ΔL), machining is insufficient. On the other hand, if the thermal deformation due to temperature change is excessive (ΔΩC<ΔL), excessive processing will occur. Temperature changes vary depending on the machining conditions, but during rough machining with large discharge energy, the temperature can reach over 10°C, and the thermal deformation caused by this can reach several tens of micrometers, which is rarely far greater than the value of electrode wear. In addition, H is the target machining depth, A is a constant, δ is the electrode wear rate, ρ6 is the thermal expansion coefficient of the electrode side, and ρ is the thermal expansion coefficient of the workpiece.

In this way, (1) alignment error that occurs before processing (2)
Errors due to electrode wear that occur during machining (3) Errors due to thermal expansion deformation due to temperature changes, (4) Errors due to changes in machining gap, etc. are interrelated and affect the machining dimensional accuracy as shown in Table 1.

Therefore, in order to improve the accuracy of machining, it is particularly necessary to solve each of these error factors, and effective error detection methods and error correction control methods for this purpose have been strongly desired. Several detections have been made so far.

Although detection methods and correction control methods have been proposed, at present no method has been proposed that can accurately detect and eliminate the above-mentioned errors.

As a device for controlling the temperature of machining fluid, for example, JP-A-61
As disclosed in Publication No.-86130.

There is a device that preheats the heating liquid using a preheating device and at the same time circulates it through the processing machine body to keep the temperature constant during processing. If such a device is used, it is possible to avoid the problem of errors caused by temperature changes, but other error factors cannot be completely eliminated.

For this reason, other methods must be used, and the above-mentioned device is a large-scale device, so it is not functional.

There is an economic problem.

On the other hand, as a method for detecting electrode wear, for example, as disclosed in Japanese Unexamined Patent Publication No. 150937/1982, the electrode is faced to an electrode tip detection plate before and after electrical discharge machining, and a weak discharge is caused to detect the tip position. There is a method to detect electrode wear based on changes. Although it is considered to be a promising means of detecting electrode wear, the electrode tip detection plate is fixed at a considerable distance from the workpiece to be processed, so there is a risk that alignment with the workpiece may be hindered. . In addition, although it is said that a weak discharge is performed for a short time, the gap condition at that time is not disclosed at all.The surface condition of the electrode tip before and after machining is different, so the gap condition during a weak discharge changes. Therefore, if this effect is not taken into consideration, accurate electrode position detection may not be possible, and there is a risk that the error will increase on the contrary. There is no disclosure whatsoever regarding thermal deformation due to temperature changes.

In addition, as a method for measuring and correcting machining errors, for example, as disclosed in JP-A-58-160018, machining is interrupted midway and the machining depth is actually measured using a measuring probe. There is a method of correcting the error with the desired depth. However, since there is a processing product at the bottom of the processed hole immediately after processing, it is likely to be affected by this, making accurate measurement difficult. For this reason, removal of the processed product or a special removal device is required, and the above method requires a large-scale measuring device, so it is not functional.

There is an economic problem.

[Problem to be solved by the invention]

The present invention has been made in view of the above-mentioned technical issues and problems of the prior art, and utilizes the characteristic that the gap converges to a specific value under certain micro-discharge gap detection conditions. It accurately aligns the workpiece with the workpiece, and also detects and diagnoses a series of machining errors in the machining depth direction, such as errors due to machining gap changes that occur during electrical discharge machining, errors due to electrode wear and thermal deformation, etc. The purpose of this invention is to provide an effective control method for accurate correction control and higher accuracy in electrical discharge machining.

[Means for Solving the Problems] The control method of the present invention specifies the gap between the electrode and the workpiece at a specific position on the top surface of the workpiece on a predetermined reference plane setting table installed in a predetermined manner or which can be substituted for the reference surface setting table before starting machining. A micro discharge is generated for a predetermined time under the gap detection conditions that result in a value, and after setting a reference surface in the machining depth direction by detecting the position, the predetermined machining is started,
More after that.

After machining the specified step, move the electrode to the reference plane setting position and switch to the gap detection condition to generate a micro discharge for a predetermined period of time to close the gap.

The position of the electrodes after they are bundled is detected, and errors due to electrode wear and thermal deformation that occur during machining are detected by comparing the detected value with the value set before the start of machining. After making corrections according to the settings, and further moving the electrode after this reset to the hole after machining, the gap between the electrode and the machined surface of the workpiece is converged while generating a micro discharge for a predetermined period of time under the gap detection conditions. Detects the electrode position, uses the detection results to calculate the error due to gap changes that occur during machining, and after calculating the machining depth, calculates the amount of machining error in the machining depth direction with respect to the predetermined value at the time of machining planning. Then, when it is determined from this calculation result that correction machining is necessary, the electrode feeding is controlled to correct the machining error amount to perform the correction machining. Also.

Another control method involves detecting machining errors due to electrode wear and thermal deformation after machining a specified step using the same method as above, and then correcting the amount of error by resetting the reference plane. The subsequent electrode was moved to the position of the hole to be machined, and the next step of machining was performed while controlling the electrode feed to correct the amount of error. Furthermore, another control method of the present invention not only performs correction control for machining errors caused by electrode wear and thermal deformation as described above, but also performs correction control for machining errors caused by changes in machining gap. After detecting the electrode position at the point where the electrode feed reaches a specified depth midway, the machining conditions are switched to the gap detection conditions described above, and the gap between the machining surface and the machining surface is converged while generating a micro discharge for a predetermined period of time. Detects the electrode position, and from both detection results, detects the error amount due to machining gap change or machining depth error amount that occurred during machining, and then controls the electrode feed to correct this error amount. The feature is that the processing is restarted.

The method of the present invention uses a die-sinker electric discharge machine to send an electrode to five workpieces from a predetermined position in a predetermined depth direction,
In addition, in a method for correcting and controlling machining errors that occur during machining of a workpiece while controlling electrode feed in the order of a series of machining steps from rough machining to finishing machining, a reference set at a predetermined position before the start of machining is used. At a specific position on the top surface of the workpiece that can be used as a surface setting table or as a substitute, a micro discharge is generated for a specified period of time under the gap detection conditions that the gap between the electrode and the electrode becomes a specific value, and the reference plane in the machining depth direction is determined by detecting that position. After making the settings, start a predetermined machining, and then further move the electrode to the reference plane setting position and switch to the gap detection condition after the machining of the step specified in the machining process,
The electrode position is detected after the gap is converged by generating a micro discharge for a predetermined period of time, and the detected value is compared with the value set before the start of machining. Errors due to electric pf4 consumption and thermal deformation that occur during machining are calculated. The error is corrected by resetting the reference plane, and the electrode after this resetting is moved again to the hole after machining, and the electrode and machining are performed while generating a micro discharge for a predetermined time under the gap detection conditions. Detect the electrode position after converging the gap with the workpiece surface, and from the detection result,
After calculating the error due to the gap change that occurred during machining and calculating the machining depth, calculate the amount of machining error in the machining depth direction with respect to the predetermined value at the time of machining plan. Based on this calculation result, it is determined that correction machining is necessary. The present invention is characterized in that when the amount of machining error is corrected, electrode feed is controlled to perform correction machining to correct the amount of machining error.

Examples of embodiments of the present invention are as follows.

(1) Detection of a series of machining errors occurring in electric discharge machining and correction control thereof are performed after machining the final step, and can also be performed after machining a specified step as necessary prior to that.

(2) Using a die-sinker electrical discharge machine, feed the electrode from a predetermined position to a predetermined depth on the workpiece.

In addition, in a method for correcting and controlling machining errors that occur during machining of a workpiece while controlling electrode feed in the order of a series of machining steps from rough machining to finishing machining, a reference set at a predetermined position before the start of machining is used. At a specific position on the top surface of the workpiece that can be used as a surface setting table or as a substitute, a micro discharge is generated for a predetermined time under the gap detection conditions where the gap with the electrode becomes a specific value, and the reference in the machining depth direction is determined by detecting that position. After setting the surface, predetermined machining is started, and then, after machining the step specified in the machining process, the electrode is moved to the position of the reference surface setting and the gap detection condition is switched to generate a micro discharge. The electrode position is detected after the gap has converged after a predetermined period of time, and errors due to electrode wear and thermal deformation that occur during machining are detected by comparing the detected value with the value set before the start of machining. The error is corrected by resetting the reference plane, and the electrode after this resetting is moved to the machining hole position again to perform the next step of machining while controlling the electrode feed to correct the error amount. What I did.

(3) In (2) above, the detection of errors due to electrode wear and thermal deformation that occurs during electrical discharge machining is performed at least after machining before the final step, and also after the first rough machining or after machining the specified step. I tried to do it more than once.

(4) Using a die-sinker electric discharge machine, feed the electrode from a predetermined position to a predetermined depth direction of the workpiece, and control the electrode feed in the order of a series of machining steps from rough machining to finishing machining. In a method for correcting and controlling machining errors that occur during machining of a workpiece, before the start of machining, on a reference plane setting table installed at a predetermined position or at a specific position on the top surface of the workpiece that can be substituted for - A micro discharge is generated for a predetermined time under the gap detection condition that the gap with the electrode becomes a specific value, and after setting a reference plane in the machining depth direction by detecting the position, a predetermined machining is started, and then the above-mentioned After machining the step specified in the machining process, move the electrode to the reference plane setting position and switch to the gap detection condition, generate a micro discharge for a predetermined period of time, and detect the electrode position after converging the gap; Errors due to electrode wear and thermal deformation that occurred during processing are detected from the results of comparison between the detected value and the value set before starting machining, and the error is corrected by resetting the reference plane. is moved to the machined hole position again, and the next step is machined while controlling the electrode feed to correct the error amount. Also, during this process or during machining of another specified step, the electrode feed The electrode position is detected at the point where the metal reaches a specified depth, the machining conditions are switched to the gap detection conditions, and the electrode position is determined after converging the gap with the machining surface while generating a micro discharge for a predetermined period of time. Based on the results of both of these detections, an error due to a change in the machining gap or an error in the machining depth that occurs during machining is detected, and the electrode feed is controlled to correct this error amount and subsequent machining is restarted. What I did.

(5) In (4) above, detection of errors due to machining gap changes or machining depth errors that occur during electric discharge machining and correction control machining of the amount of error are performed during the final step of machining, and prior to that, as necessary. The configuration is such that it can be performed even during the processing of a specified step.

[Effect]

As described above, in the present invention, the alignment of the reference plane between the electrode and the workpiece before machining is performed by generating a micro discharge for a predetermined period of time under the gap detection condition that the gap between the electrode and the workpiece becomes a specific value. Therefore, errors due to the effects of pars, which tend to form at the ends of the electrode surface, dirt, dust, and other inclusions adhering to the processed surface, are avoided, and accurate and reliable reference plane setting can be achieved. In addition, in order to diagnose errors due to electrode wear and thermal deformation that occur during electrical discharge machining, after machining the specified step, move the electrode to the set position on the reference surface and switch to the gap detection conditions as before machining starts. The electrode position is detected after the gap between the electrode and the electrode is converged while generating a micro discharge for a predetermined period of time.

The value of the electrode position at that time changes from the value set before starting machining by the difference between the electrode wear error and thermal deformation error, so the amount of error due to the electrode wear and thermal deformation mentioned above can be determined from the amount of change. . Furthermore, by resetting the reference plane, this error amount can be corrected and controlled to the electrode feed amount in the processing direction, and correction processing can also be performed. By performing this error correction control process in the next step, it is possible to correct the error amount due to electrode wear and thermal deformation without any problem, whether it is a positive value or a negative value.

After that, in order to diagnose errors due to changes in machining gap caused by electric discharge machining and errors in machining depth, the gap detection conditions are set such that the gap converges to a specific value after diagnosing the error or during machining of a specified step. Then, the gap between the machined surface and the machined surface is converged while a continuous micro-discharge is generated by the vertical movement of the electrode for a predetermined period of time. By calculating the amount of change between the electrode position at that time and the electrode position during machining,
The amount of error relative to the machining gap setting value can be calculated.

Furthermore, the machining depth and the machining error relative to its target value can be calculated in the same manner. By correcting the calculated error amount to the electrode feed amount and restarting machining, a series of machining errors in the machining depth direction are eliminated.

In this way, a series of machining errors, such as errors due to electrode wear and thermal deformation that occur during electrical discharge machining, and errors due to changes in machining gap, are accurately and quickly detected and diagnosed, and correction control is performed to improve machining accuracy. can be significantly improved.

[Example] Hereinafter, the content of the present invention will be specifically described with reference to Examples. 1st
The figure shows a flowchart of 78 examples of machining operations illustrating the content of the present invention, including setting of a reference plane before machining based on gap detection conditions, detection and correction of errors due to electrode wear and thermal deformation that occur during machining, and further machining. A method is disclosed for detecting a series of machining errors in the machining depth direction, including errors due to gap changes, and controlling correction thereof. In addition, FIGS. 2 to 6 each explain the contents shown in FIG.
As shown in the figure, first, a micro discharge is generated for a predetermined period of time under a gap detection condition in which the gap between the electrode and the electrode becomes a specific value using the reference leveling table 27 set at a predetermined position. Reference plane table 2
As for the setting location 7, an appropriate location is selected depending on the shape of the workpiece, preferably a location close to the machined hole. Further, if the reference surface setting table 27 can be used instead, the base surface can be set on the upper surface of the workpiece. In this figure, the height Hc of the reference leveling table 27 may be O and il+. The gap detection conditions mentioned here are conditions where the discharge energy is extremely small, such as when performing best surface machining, and the applied voltage may be at the same level as normal machining conditions, for a predetermined period of time (for example, 20 to 6
0 seconds) By causing a micro-discharge, the gap with the electrode 1 becomes constant (gc). It stops at the point where the gap becomes constant,
The point obtained by subtracting gc from the electrode position Zao at that time is the upper surface of the reference surface exposing table 27, and the reference surface (Zoo=Z-o+t
<c=0). The amount machined by the above-mentioned micro-discharge is horizontally small and can be ignored. Further, the gap value gc is stable and has a small variation range of ±2 μm or less.

After setting the reference plane accurately in this way, tttp
A is moved to the processing position (relative movement with the workpiece by XY child table movement, but hereinafter referred to as electrode movement for convenience) and predetermined processing is started. The predetermined machining is the same as before (see Fig. 17), but in the present invention, as shown in Fig. 1, machining errors in the depth direction are detected and diagnosed after machining the specified steps, and the errors are corrected. Control. The method is carried out according to the steps shown in FIGS. 4, 5, 6, and 8.

When the electrode feed amount in the specified machining step reaches the target value (Za = Z), the electrode 1 is moved from the state shown in Fig. 4 where the machining is completed to the reference surface leveling table 27, and then the gap detection condition is entered. The gap is converged while causing intermittent micro discharges for a predetermined period of time by vertical movement of the electrode. Electrode position after convergence'
As shown in FIG. 5, ItZao' changes by the difference between the electrode wear error ΔQC caused during machining and the thermal deformation error ΔL due to temperature change, and Z. '=(ΔQc−ΔL)−g
c.

Therefore, the change in electrode position before and after machining (ΔZa).

= Z ao' Z *o), it is possible to detect the amount of error due to electrode wear and thermal deformation (ΔZao = ΔQc
-ΔL).

Furthermore, the above error amount can be corrected by resetting the reference plane here. That is, Zao' =Z
By resetting ao=gc, the error is corrected as shown in Figure 6 and Table 8 (ΔQe-ΔL=ΔZba)-
After setting the reference plane, the electrode 1 is again moved to the machined hole position and sent in the depth direction, and the gap detection condition is again changed to generate intermittent micro discharge for a predetermined period of time due to the vertical movement of the electrode. The electrode stopping position Zah' at the point where the six gaps converging and becoming constant (gc) with respect to the processing surface becomes Zda+ΔZL. ΔZ+, m corresponds to the amount of error due to electrode wear and thermal deformation corrected in the previous step. From the correlation between the electrode position immediately after machining (Za = Z) and the electrode position after a microdischarge based on the gap detection condition where the gap converges to a specific value (gc) as described above,
The machining gap Ga during machining and the gap error amount ΔG for its set value GK are calculated as shown in Table 8 (ΔG=Gk-Gh=Gw
-(Zah Za+gc)), and similarly, the machining depth H& during machining is Zaa+Δ ZL 處+
gc-He: Calculated as Za + Ga + Δ Zt, a-Hc, and furthermore, the machining depth error (ΔHK = H to -H&) with respect to the target machining depth H can be calculated,
ΔH=ΔG+ΔZLa=ΔG+ΔQc−ΔL.

8 If the value of HK is positive (H>Ha), the machining depth is insufficient, indicating that the machining gap Ga during machining is too small or the electrode wear error ΔQc is excessive.0On the contrary, ΔHx If the value of is negative (H<Ha), excessive machining has occurred, and the machining gap Ga is too large or the thermal deformation error ΔL is greater than the electrode wear error Δmc. Therefore, it is determined whether correction machining is necessary based on this result, and if HK>H&, in which the value of ΔH is positive, the machining error amount is corrected to ΔHa=ΔZK and machining is restarted. The electrode feed amount Z after correction becomes 2+ΔZ. Note that when Hx<Ha, there is no need to perform correction machining.The detection timing and number of times of the series of machining errors in the depth direction described above can be specified arbitrarily, so for example, after the final step of finishing machining, In addition, prior to this, it is preferable to specify a step after the first rough machining or after machining in the vicinity, and it is also possible to increase the number of times if necessary. Thermal deformation errors due to temperature changes are most likely to occur during rough machining, where the electrical discharge energy is large and the machining volume is large, as shown in Figure 18, and electrode wear that occurs during electrical discharge machining is also proportional to the machining depth. It has the property of increasing. Furthermore, the machining gap, which is proportional to the magnitude of the discharge energy, tends to have a large rate of change under conditions of rough machining or machining in the vicinity thereof. Therefore, by specifying the timing of error detection as described above, it is not only possible to detect and diagnose a series of machining errors caused by these factors at an early stage and eliminate them. Processing errors can also be eliminated at the end. As described above, by using the present invention, machining errors in the machining depth direction can be detected, diagnosed, and corrected quickly and accurately, so that machining results with higher precision can be obtained than with conventional methods.

FIGS. 7 and 8 show another embodiment of the present invention, which shows a method for detecting and correcting errors caused by electrode wear and thermal deformation. Although the reference leveling table 27 is used in FIGS. 3 and 3, an example is disclosed in which micro discharge is directly generated on the upper surface of the workpiece in the vicinity of the machining position without using it. The procedure for detecting errors due to predetermined machining operations and electrode wear and thermal deformation occurring during machining is the same as described above, but the subsequent error correction machining is configured to be performed in the next step of machining. There is. As shown in Figure 7, after the electrode feed in the specified machining step reaches the target value (Za = Zx) and the machining is completed, the electrode is moved to the same reference leveling position as before machining started. At the same time, the gap detection conditions are changed so that the gap becomes a specific value. As shown in Figures 8 and 9, by generating intermittent micro-discharges for a predetermined period of time due to the vertical movement of the electrode, it is possible to avoid the effects of unevenness and deposits on the electrode surface that occur during machining, and The gap between the electrode 1 and the surface of the workpiece 2 converges to a specific value (gc). As mentioned above, the stopping position Zao' of the electrode after convergence is the same as before machining (
How much difference between electrode wear error ΔQc and thermal deformation error ΔL changes than Zao = gc)?
L)-gc. From this result, the amount of error (Z-o=
ΔQc−ΔL) can be detected.

Furthermore, the electrode position with respect to the reference plane is reset (Z ao'
=Zao=gc), ΔQc−ΔL=
Error correction can be made with ΔZL. What is the process for correcting that error?

Executed in the next step of machining.

The timing and number of times of error detection described above can be arbitrarily specified depending on the shape and size of the workpiece, the machining conditions, and the machining process. As shown in the machining plan shown in Figure 16, the number of processes from the initial rough machining to the final finishing machining is 6 (
Processing steps = 1 to 6. n=6) To show a machining example, if the timing of error detection in Fig. 7 is specified as =1 and =n-1, the error detection will be 2 after the first rough machining and after the machining before the final machining. They will be rushed together. Further, error correction after error detection is performed in the first step of processing of n = 2 and = n = 6, respectively. In the final finishing process, since the workpiece shape is small, errors due to electrode wear and thermal deformation are extremely small and have almost no influence. In this way, it is possible to quickly eliminate thermal deformation errors and electrode wear errors caused by temperature changes, which are most likely to occur in the course of rough machining where discharge energy is large and machining volume is large. In addition, errors caused in subsequent machining can be eliminated, and the possibility of excessive machining depth after machining can be avoided, making it possible to obtain highly accurate machining results. Although an example in which error detection and correction processing are carried out twice is shown here, the number of times of error detection and correction processing can be increased.

It goes without saying that the first detection time can be changed to another step. The machining error correction control method of the embodiment described above is particularly effective when electrical discharge machining is performed on a shape where machining errors are likely to occur due to electrode wear or thermal deformation.

FIG. 10, FIG. 11, and FIG. 12 are other embodiments of the present invention, and show a method for detecting and correcting machining errors due to changes in machining gap that occur during a predetermined machining process. During machining of a specified step, first, the start time is determined as shown in FIG. 11, and, for example, the electrode position Z& value at the point where the electrode feed amount Z& during machining reaches ZK-β is calculated. One β in Z indicates that the predetermined target value is short by β.
The value of β can be arbitrarily determined, for example, it may be determined as the machined surface roughness value Rmaxk under the machining process.
After calculating the electrode position za during machining, the gap detection conditions are changed so that the gap with the machining surface becomes a specific value (gc), and the gap is converged while causing intermittent micro-discharge due to the vertical movement of the electrode for a predetermined period of time. , calculate the electrode position after convergence in the same way as above. Since the electrode position changes from moment to moment according to changes in the discharge phenomenon, it is recommended to determine a stable measurement position (for example, the point at timing t1), measure the value at that position several times, and average it. The reason why it takes a certain amount of time for the 0 gap to converge to a specific value is because the processing products from the previous stage remain, and it is necessary to remove them sufficiently, and the vertical movement of the electrode is Its role is to promote its emission. The required convergence time tc is about 30 to 60 seconds. The amount processed during this time is extremely small and can be ignored. Incidentally, if it is desired to simplify the above calculation process, it is preferable to obtain the electrode stop position after completing the required machining and micro-discharge, as described in FIG. 1.

The machining gap value G& during machining is calculated from the measured change in the positions of both electrodes Δgd=Zd-Z&(G&=Δga+gc
) L, r, and the depth Ha during machining is also calculated (Ha=Z
a+gc), then 〇K is calculated as the gap error amount for the machining gap value GK during machining planning (ΔGK=G
x Ga), and the error amount ΔHO of the machining depth can also be calculated at the same time (ΔHG=H=β−Ha ”ΔGK). From this result, the error amount can be corrected to the electrode feed amount (ΔGK).
Za = ΔG K = ΔHQ) and machining is restarted. The corrected electrode feed amount ZK' becomes 2+ΔZo, and the remaining machining amount becomes β−ΔZo.

By performing machining error correction control in this manner, machining errors or machining depth errors due to changes in the machining gap that occur during machining can be easily diagnosed and accurately eliminated. The above error detection start time and number of times can be specified arbitrarily.For example, it can be specified to be performed not only in the final step machining process but also in the preceding intermediate step machining process. Start time,
As shown in Figures 11 and 12, Za = z is set at a point in the middle of machining, but it is also possible to set zJI = zK after machining, which simplifies the calculation process for the electrode position. . In addition, when changing the setting to z&=zK, as described in FIG. 1, it is sufficient to determine whether or not correction processing is necessary and then perform correction control for processing errors. What is the machining error correction control method?

The various conditions of this example are shown in zero-order Table 9, which is particularly effective when performing electrical discharge machining of a shape that is likely to cause machining errors due to machining gap changes.

Table 9 The embodiment shown in FIG. 13 detects and diagnoses both machining errors due to electrode wear and thermal deformation and machining errors due to changes in machining gap, and performs correction control.

Setting a reference plane using gap detection conditions before starting machining, and detecting machining errors due to electrode wear and thermal deformation that occur during machining.
The method of correction is as described in FIGS. 7 and 8. Furthermore, the method for detecting and correcting machining errors due to machining gap changes is as described in FIGS. 10, 11, and 12, but here, a procedure for mutually performing both types of correction control will be described. First, after machining the specified step, move the electrode to the reference leveling position in the same way as at the start of machining, switch to the gap detection condition, and calculate the amount of error due to electrode wear and thermal deformation (ΔZ- o=ΔQ
c-ΔL) is detected. Further, after error correction (ΔQc−ΔL=ΔZi, a) by the method of resetting the base surface, the electrode is moved to the position of the machining hole again and the next step of machining is performed.

After correction, the electrode feed amount Z becomes +ΔZL.

The above-mentioned error amount is corrected by the processing in this step. Then, during the machining of this step, a machining error due to a change in machining gap is detected. The electrode position 1f at the point where the corrected electrode feed amount Za' (Za+ΔZhm) during machining reaches, for example, Z'-β! The fZa' value is calculated, and then the gap detection conditions are changed so that the gap with the machined surface becomes a specific value (gc), and the gap is converged while a small 11i discharge is generated for a predetermined period of time. Position Zd' (
Za+ΔZL) is calculated.

Calculated amount of change in both electrode positions Δga Za'-Z
Machining gap during machining from a'(Ga=Za'Za'+
gc) and machining depth (Ha=Za'+KC). Then, as described in Fig. 11, the gap error amount (ΔG K = GK - aa) and the machining depth error amount (ΔHa = Hx - β - Ha = ΔGx) can be calculated, and from this result, the Correct the error amount to the electrode feed amount (ΔZa
K=ΔGK) and restart machining. The electrode feed amount ZK' after re-correction becomes Z+ΔZLa+ΔZa=Z+ΔZ. As mentioned above, ΔZL corresponds to the amount of error due to wear and thermal deformation (ΔQc−ΔL=ΔZLa), and has already been corrected.

The remaining machining amount by restarting machining is β−ΔZ
It becomes G.

By performing machining error correction control in this manner, it is possible to eliminate alignment errors before starting machining.

A series of machining errors in the machining depth direction, such as errors due to electrode wear and thermal deformation that occur during machining, and errors due to changes in machining gap, can be diagnosed and accurately resolved. The start time and number of times of error detection can be specified arbitrarily as described above. For example, error detection due to power consumption and thermal deformation is specified as =1 and =n-1, and error due to machining gap change is specified. When the detection is specified as 2=2 and 2=n, each error correction process after the error detection is executed twice in steps of 2=2 and 2=n.

In this way, a series of machining errors that occur under machining conditions with large discharge energy can be quickly eliminated.

Furthermore, any machining errors that occur during subsequent machining can be eliminated in the final step of machining. It goes without saying that the number of times the error detection and error correction processes are performed can be further increased, and the initial detection timing can be changed to another step.

The machining error correction control method of the embodiment described above is particularly effective for electric discharge machining where electrode wear errors, thermal deformation errors, machining gap errors, etc. are likely to occur, and the machining accuracy is significantly higher than that of conventional methods. It is possible to improve the

Finally, the overall configuration of a die-sinker electric discharge machine for implementing the present invention is shown in FIG. 14, in which an electrode 1 and a workpiece 2 are
A machining power source 9 connected to outputs pulse voltage and current corresponding to predetermined machining conditions and gap detection conditions instructed by the NC control device 11. The inter-electrode voltage detection circuit 24 detects the inter-electrode voltage of the discharge generated between the electrode 1 and the workpiece 2, transmits the detection signal to the NC control device 11 and the electrode feed servo control circuit 16, and detects the electric discharge. Let them determine whether the condition is good or bad. The electrode 1 is installed at the tip of an electrode feed mechanism 12 connected to a Z-axis pulse servo motor 13, and is driven and controlled by an electrode feed servo control circuit 16 via an amplifier 15. The electrode feed servo control circuit 16 operates based on a command signal from the NC control device 11, and
The electrode position is appropriately controlled according to the discrimination result of the discharge state under each machining condition. In addition, it has a function to periodically move @t4i1 up and down based on specified machining conditions and gap detection. A pulse encoder 14 connected to the pulse servo motor 13 detects the movement position of the electrode 1 in response to a position command, and the detection signal is fed back to the electrode feed servo control circuit 16 and the NC control device 11.

The workpiece 2 placed on the xY table 4 is mounted on the XY table mechanism 17 and is controlled by the XY child table movement control circuit 23. A series of control commands for aligning the electrode 1 and the workpiece 2 and for moving and swinging the workpiece 2 are N.
It is transmitted from the C control device 11.

The pulse motors 18 and 19 for driving and the pulse encoders 20 and 21 for detecting the moving position have the same function as the Z axis described above. Machining fluid is supplied and circulated (not shown) to the machining tank 5 from a machining fluid supply bag [8], and at the same time, an appropriate amount of machining fluid is supplied to the vicinity of the electrical discharge machining area, and machining products are appropriately discharged from the machining gap. It is now possible to do so.

On the other hand, the error detection circuit 25 detects changes in the electrode position before and after transition to the gap detection condition in which one gap converges to a specific value, and from the detection results, detects errors due to electrode wear and thermal deformation that occurred during machining, and It detects and diagnoses a series of machining errors such as errors due to gap changes and machining depth errors.
The detection and diagnosis results are transmitted to the NC control device 11 and the error correction circuit 26. Further, the error correction circuit 26 sets error correction corresponding to the error detection and diagnosis results, and at the same time sends a control signal instructing electrode feed correction and correction processing to the NC control device! Send to 11.

By using the die-sinker electric discharge machine configured as described above, the above-described machining error detection 9 diagnosis and correction control in electric discharge machining of the present invention can be executed, and the object thereof can be achieved.

The present invention is not limited to machining a round hole shape as shown in the embodiment, but can be similarly implemented to machining a wide variety of shapes. Furthermore, for the horizontal feed control machining method, which performs machining while controlling the X-axis or Y-axis feed instead of the Z-axis feed,
The present invention can be applied by converting the control in the axial direction.

〔Effect of the invention〕

As described above, the present invention uses the characteristic that the gap converges to a specific value under certain micro discharge gap detection conditions to align the reference plane setting between the electrode and the workpiece before machining. ,
In addition, we can accurately eliminate a series of machining errors, such as errors caused by machining gap changes that occur during electrical discharge machining, errors caused by electrode wear, and thermal deformation.
In addition, the system quickly detects and diagnoses the results and performs correction control.

Errors caused by traditional contact sensing methods are avoided, allowing for accurate and reliable reference surface setting, while eliminating a series of processing errors that were difficult with conventional error detection and correction methods. This can significantly improve machining accuracy. Furthermore, the processing error correction control method of the present invention can be performed quickly and accurately using a simple control circuit.
It eliminates the need to interrupt machining to measure machining errors, which is the conventional method, and does not require the use of special measuring equipment, making it highly functional.

It has an economic effect.

[Brief explanation of the drawing]

FIG. 1 is a flowchart of the machining operation showing one embodiment of the present invention, and FIGS. 2, 4, 5, 6, and 8 respectively show the m-pole and Figure 3 is a diagram showing the relationship between the electrode operation and time to explain the movement in Figure 2, and Figure 7 is a diagram showing another embodiment of the present invention. FIG. 9 is a flowchart of the processing operation shown, and FIG. 9 is a characteristic diagram showing changes over time in the electrode operation of the example shown in FIG. 8, and FIGS. 10 and 11. FIG. 13 is a flowchart of machining operations showing still another embodiment of the present invention, FIG. 12 is a characteristic diagram showing changes over time in machining results according to the flow of 11th UiA, and FIG. 14 is a die-sinking machine implementing the present invention. FIG. 15 is a perspective view of a conventional die-sinker electrical discharge machine; FIG. 16 is a dimension definition explanatory diagram that defines machining conditions in an example of hole machining;
Figure 7 is a flowchart of the machining operation according to the conventional example, and Figure 18 is an enlarged view of the vicinity of the machined hole showing the relationship between the machined hole and the electrode feed amount.
Figure 19 is an explanatory diagram of the electrode position and gap error occurrence situation when machining with the conventional method shown in Figure 17, Figure 20 is a cross-sectional view showing the positional relationship of the machining equipment according to the same method, and Figure 21 is Fig. 20 is a characteristic diagram showing the error occurrence situation due to electrode wear according to the conventional example, Fig. 22 is a characteristic diagram showing the error occurrence situation also caused by thermal deformation, and Fig. 23 is processing using the conventional method shown in Fig. 20. FIG. 3 is an explanatory diagram of the occurrence of electrode wear and thermal deformation when 1I71 2nd part! 3rd Mouth 4 Mouth Offering δ Day 9th Day // Drawing 12 Mouth Passage ft T 74th Mouth 15th Mouth 2...1 Crop 5...Bed 4...X, Y Chi 7" Le 5...Processing tank service /6 [1 17th day 18th day 19th feather stingray F7

Claims (1)

[Claims] 1. Using a die-sinker electric discharge machine, feed the electrode from a predetermined position to a predetermined depth direction of the workpiece, and machine the workpiece while controlling the electrode feed in the order of a series of machining steps from rough machining to finishing machining. In a method for correcting and controlling machining errors that occur during machining of an object, before the start of machining, an electrode is A micro discharge is generated for a predetermined time under the gap detection conditions where the gap becomes a specific value, and after setting a reference in the machining depth direction by detecting its position, a predetermined machining is started, and then further specified in the machining process. After processing the step, move the electrode to the reference plane setting position, switch to the gap detection condition, generate a micro discharge for a predetermined period of time, and detect the electrode position after converging the gap,
Errors due to electrode wear and thermal deformation that occurred during machining are detected from the comparison results between the detected value and the value set before the start of machining, and the errors are corrected by resetting the reference plane. At the same time as moving the latter electrode again to the hole after machining, detecting the electrode position after converging the gap between the electrode and the machined surface of the workpiece while generating a micro discharge for a predetermined period of time under the gap detection conditions, and detecting the position of the electrode. From the results, calculate the error due to the gap change that occurred during machining, and after calculating the machining depth, calculate the machining error amount in the machining depth direction with respect to the predetermined value at the time of machining plan, and perform correction machining from this calculation result. 1. A machining error correction control method in die-sinking electrical discharge machining, characterized in that when it is determined that the machining error amount is necessary, correction machining is performed by controlling electrode feed to correct the machining error amount.