JP2582357B2 - Electric machining method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Application of the Invention) The present invention relates to an electric discharge machining method in which an intermittent electric discharge is performed between an electrode and a work to be interposed between the electrode and the work. The present invention relates to an electric machining method for causing the electric machining.

(Prior art) The electric discharge machining method performs engraving or drilling on an object by intermittently sparking in an insulating medium between a working electrode and a conductive workpiece. Or a technique for cutting an object. This technology is widely used in various metal processing today because of its features that it is not affected by the hardness of the object and that it can be expected to have a processing accuracy close to a mirror finish with a surface roughness of ± 0.2 μm or less. ing.

By the way, in this electric discharge machining method, a mineral oil (kerosene) is mainly used as an insulating medium higher than before. However, since mineral oil is flammable, there is a danger of a fire occurring if continuous processing is performed unattended. Therefore, the use of pure water has recently been attempted. In the present processing method, it is effective to add an additive to the insulating medium in order to improve the processing efficiency, and there have been many proposals for additives for this purpose, such as ethylene glycol and propylene glycol. And polar polymers such as polyacrylic acid and polyacrylamide, and nonionic compounds such as polyethylene glycol (for example, Japanese Patent Publication No. 59-4,
253, JP-A-60-71,120 or JP-A-61-4,623).

However, despite the fact that these additives significantly increase the processing speed, there is almost no prospect of practical use up to the present. The main reason for this is that it is difficult to reduce the consumption rate of the electrode to 1% or less, which is a practical level, in the case of the aqueous working fluid, unlike the case of the mineral oil-based working fluid. The electrode consumption rate is reduced in proportion to the increase in the processing speed).

In addition to the above, one of the main causes that none of the past promising proposals have reached the practical stage is abnormal wear of the electrodes. That is, the working fluid in which a polar organic compound is added to kerosene or water causes abnormalities such as partial wear of the electrodes and a change in shape due to reattachment of the working iron powder, apart from apparent electrode consumption (by weight measurement). As a result, the current amount has to be reduced as a result, and as a result, low-efficiency machining is inevitable.

(Object of the Invention) The present invention has an electrode wear rate that is close to an epoch-making, and even when used continuously for a long time, can keep the rate at most 1% or less, and furthermore, there is no abnormal wear. It is another object of the present invention to provide a practical electric machining method that does not cause machining defects.

(Means for Achieving the Object) As a result of intense research on a number of new and known organic substances, the present inventor has performed processing by discharging a pulse current to a work material immersed in a working fluid. In doing so
The working fluid contains a polyoxyalkylene chain compatible with the working fluid in which at least most of the ionic substance has been removed in advance by another process so that the resistance value of the aqueous solution is 20,000 Ωcm or more. By adding a nonionic compound, good working with a working fluid having a stable specific resistance value is performed, the electrode wear rate is remarkably low, and even if the electrode is used continuously for a long time, the rate can be reduced to 1 at most. % Or less, and it has been found that a practical electric machining method can be provided that does not cause abnormal consumption of the electrode.

Examples of nonionic compounds having a polyoxylene chain that is compatible with the working fluid, useful in the practice of the present invention, include:
Polyethylene glycol, nonionic surfactant or there are such following compounds containing 3 or more oxyalkylene group having a carbon as a residue other than this, RO a _(wherein R is an alkyl group having 3 to 8 carbon atoms, a is an integer of 3 to 6),
-Φ-O -, - C≡C-, CH 2 = CH-CH 2 - or -S- no problem also contain groups such as. However, it is necessary that the non-ionic compound be previously removed from contaminating ionic substances by a separate process so that the aqueous solution has a resistance value of 20,000 Ωcm or more.

That is, since a general polyoxyalkylene compound is produced using a basic or acidic catalyst as a catalyst at the time of its production, it is common knowledge that it contains a neutralized salt of the catalyst except in special cases. The neutralized salt of these catalysts is usually 200 _PPm
To reach to 500 _PPm, if these neutralized salt is mixed into the working fluid as a result, the allowed to decrease significantly the resistivity value of the machining fluid, it becomes impossible good processability. For this reason,
The processing accelerator added to the processing liquid is preferably as small as possible in the amount of ionic substance. Specifically, the aqueous solution usually needs to have an aqueous solution resistance of 20,000 Ωcm or more.

Incidentally, as a method for removing contaminating ionic substances from a nonionic compound in the present invention, generally, there have already been some proposals, for example, Japanese Patent Publication No. 37-5597.
No. 41-21,237, No. 45-33,194, No. 52-1
No. 0,018 and U.S. Pat. No. 4,316,948. In the present invention, any of these methods may be employed, however, these ionic substances have a resistance value of an aqueous solution of a non-ionic compound of at least 20,000 Ωcm in a separate step, at least before being blended into the working fluid. Must be removed. The reason is that the small deionizer attached to the processing machine has only the necessary and sufficient capacity to keep the specific resistance value of the processing fluid itself constant, It is very difficult to remove large amounts of contaminating ions from the wastewater, and if a large amount of ionic substances is mixed into the working fluid, not only will the deionizer be overloaded, but also the deionization function will decrease rapidly. This is because the specific resistance of the working fluid becomes unstable and good working becomes impossible.

(Examples) Hereinafter, embodiments of the invention will be described with reference to examples. However, it is needless to say that exemplification does not directly limit inclusion and extension of the invention idea.

Reference Example 1 The polyoxyalkylene compounds shown in Table 1 were polymerized by a known method.

Example 2 A 2% amount of synthetic aluminum silicate was added to the compound of Example 1, and the mixture was stirred in an autoclave at 120 ° C for 6 hours, and the solid content was filtered to obtain a purified product shown in Table-2.

Example-3 After dissolving the compound A-1 in Table 1 and the compound B-1 in Table 2 in ion-exchanged pure water, the specific resistance was measured, and the result was as shown in FIG. However, in the figure, the curve indicated by -O- indicates the data of the compound B-1, and the curve indicated by-●-indicates the data of the compound A-1.

Example-4 Table using the compounds of A-1 and B-1 of Example-3
A processing experiment was performed under the conditions of No. 3.

The results are shown in FIGS. 2 and 3.

When the compound B-1 represented by the curve-○-was used, no abnormal discharge occurred even when the concentration of the additive was increased to 50%.
Although the processing speed could be improved, when the control compound A-1 represented by -x- was used, abnormal discharge occurred even at a low concentration of about 2%, and the processing became impossible.

(Effects) As described above, the present invention provides
A non-ionic compound from which at least most of the ionic substance has been removed is added to the working fluid so that the resistance value of the aqueous solution is 20,000 Ωcm or more, and the working fluid is processed. Processing is performed, and the electrode wear rate is remarkably low.
% Or less, and can contribute to the development of precision machining technology through the result that a practical electric machining method without abnormal wear can be provided.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the concentration of the test compound in pure water and the specific resistance value, FIG. 2 is a graph showing the relationship between the concentration of the test compound and the processing speed, and FIG. 4 is a graph showing the relationship between the concentration of a test compound and the electrode consumption rate (the description of the symbols is also shown in the figure).

Claims (1)

(57) [Claims] When a pulse current is discharged to a workpiece immersed in a working fluid and the working fluid is processed, the working fluid is preliminarily subjected to another process so that the aqueous solution has a resistance value of 20,000 Ωcm or more. An electric processing method comprising adding a nonionic compound containing a polyoxyalkylene chain compatible with the working fluid, from which at least most of the ionic substance has been removed.