DE2632180A1 - DIELECTRIC FLUIDS FOR METALWORKING BY ELECTROEROSION - Google Patents

Description

PATENT LAWYERS

KLAUS D. KIRSCHNER DR. WOLFGANG DOST

.DIPl-OHEMIKER

D-8OOÖ MUNICH 2 BAVARiARiNQ as

Our reference: B 731 D / UK

Ourreference: BPH PAT 103

Date: July 16, 1976

GERMAN BP AKTIENGESELLSCHAFT
Hamburg

Dielectric fluids for metalworking by electrical discharge machining

The invention relates to dielectric liquids on the basis of hydrocarbons for use in electrical discharge machining. In these modern, versatile procedures, a Processing of electrically conductive materials using spark discharges between a tool electrode and a workpiece in a working fluid. The particular advantage of this process lies in the great accuracy with which objects of complex shape are produced even from very hard materials can.

The economy of electrical discharge machining becomes essential by the wear of the tool electrode and by the Time unit of material volume that can be removed, i.e. the removal rate on the workpiece. Both variables can be influenced by the nature of the working medium. In addition to water and silicone oils, their Use is only possible or useful in special cases,

which in practice mainly hydrocarbon oils, especially mineral oil products, used.

709884/007 &;

In the range of these hydrocarbon oils, which extends over a viscosity range from about 1.5 to 30 cSt at 20 ° C., the effectiveness in the roughing process, in which the essential metal is removed from the workpiece electrode, increases with increasing viscosity. On the other hand, however, the finishing operations required to smooth the metal surface in the spark erosion process can only be carried out with comparatively low-viscosity dielectrics (1.5 to about 6 cSt at 20 ^° C.), because in this processing stage effective flushing of even the narrowest working gaps must be guaranteed. For this reason, for many areas of application that initially require the greatest possible metal removal and then careful surface smoothing, an / optimal mode of operation is only possible by exchanging the working medium. However, this change in the dielectric affects the economic viability of the process, so that in practice both operations are carried out with one and the same working medium, lower viscosities being preferred in favor of the finishing operations, but reduced removal rates from the outset.

Another, with the use of common hydrocarbon oils The associated disadvantage is the high level of wear on the tool electrode that occurs particularly during roughing and that with increasing wear Removal rates increase and can reach up to 30 percent of the metal removal on the workpiece.

Attempts have already been made to improve the removal rate while reducing the electrode wear at the same time by carefully selecting the hydrocarbons used as the working medium or by adding additives. For example, from GB-PS 1 003 664 polycyclic aromatics with a carbon / hydrogen ratio of 0.8: 1 to 1.8: 1 are known as working fluids for spark erosion. The substances described there are compounds in whose molecules homo- and heteroaromatic rings are directly linked to one another. Apart from the fact that in many cases these compounds have an extremely unpleasant odor, their melting points are also

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view of the working temperatures in spark erosion machines mostly too high. They are therefore at most after hydrogenation or in Form of eutectic mixtures suitable as working fluids for metalworking by electrical discharge machining.

Special alloyed spark erosion oils have also been recommended to achieve higher removal rates. This is how the US PS describes 3 639 275 dielectric fluids based on mineral oils with a content of organic alkaline earth metal sulfonates and phenols certain composition. U.S. Patent 3,648,013 is U.S. Patent No. 3,648,013 Use of conductivity improvers, consisting of chromium salts special. Selected alkyl salicylic acids and alkaline earth salts Alkyl sulfosuccinic acids, see. US Pat. No. 3,708,422 mentions long-chain aliphatic amines as additives.

Apart from the difficulties that often come with meddling very small amounts of additives are associated with those described alloyed products have the disadvantage that as a result of the losses of erosion oil which occur in particular during the roughing process The additives are quickly enriched by evaporation or are subject to decomposition over time due to the electrical discharges, which can have negative effects on the erosion process. The alloyed products described are also used a reduction in electrode wear to an acceptable level is not achieved.

One of the present invention was based on an object hence, easily prepared hydrocarbon oils as Working fluids for metalworking by spark erosion to make available the disadvantages outlined do not have, rather allow increased removal rates on the workpiece in the roughing process with simultaneously reduced wear of the tool electrode, but also for use in Finishing operations are suitable. This object is achieved by the invention.

The invention thus relates to dielectric fluids for metalworking by electrical discharge machining on the basis of

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Hydrocarbons, the aromatic components and optionally Contain effect-improving additives, which are characterized in that they consist of at least 30 percent by weight of compounds of the general formula I.

in which R., R-, R ", R., R_, R", R ₇ and R "each denote a saturated, straight-chain or branched alkyl radical having 1 to 6 carbon atoms or a hydrogen atom, and
η has the value 0 or 1, where

for η = 0 the sum of the _{carbon atoms present in the alkyl radicals R 1} to R _ß at most 6, and

for η = 1 the sum of the _{carbon atoms present in the alkyl radicals R 1} to R _{3 is} at most 10,

and from 0 to 70 weight percent from conventional electrical discharge machining fluids exist.

For η = 0, the compounds of the general formula I have the general formula Ia

CH.

(Ia)

'R

709884/0078

- JS "-

263218 (T.

in the R ₁ ,

<. _1Γ ^ ₀ , XX-, χ _Μ , X ^ ₁ - and R, each a saturated,

straight-chain or branched alkyl radical with 1 to 6 carbon atoms or a hydrogen atom, where the sum the carbon atoms present in the alkyl substituents is a maximum of 6.

If all of the substituents R ₁ to R 1 are hydrogen atoms, then benzylbenzene (diphenylmethane) is present.

For η = 1, the compounds of the general formula I have the general formula Ib

(Ib)

in the R ₁ ,

R,

Around

each one ge

saturated, straight-chain or branched alkyl radical with 1 to 6 carbon atoms or a hydrogen atom, where the sum of the carbon atoms present in the alkyl substituents is at most 10.

If all of the substituents R ₁ to R ₀ are hydrogen atoms, then dibenzylbenzene is present.

Examples of suitable alkyl radicals are methyl and ethyl groups, as well as straight-chain or branched propyl, butyl, pentyl and Hexyl groups.

Particularly preferred compounds of the general formula I are the monomethyl derivatives of benzylbenzene and dibenzylbenzene.

In the benzyl radicals, the alkyl radicals can be in o-, m- and / or p-position to the methylene group.

In the compounds of the general formula Ib, the two benzyl groups on the middle benzene nucleus can be in the o-, m- or p-position are to each other. The m-position is preferred here and the p-position is particularly preferred.

The electrical discharge machining fluids of the invention preferably have a viscosity that does not exceed ^{40 cSt at 20 ° C.}

Individual compounds of the general formula I have melting points which are above 20 ^° C. In general, however, in the preparation of the optionally substituted benzylbenzenes and dibenzylbenzenes, mixtures of isomers are obtained which are liquid at ordinary temperature and can therefore be used without difficulty in electrical discharge machines. Also the general formula I of different composition or structure of the electric discharge liquid are brought to the required value for the practice in a simple manner the melting point by mixing compounds.

The compounds of the general formula I are relatively easy to obtain industrially by known processes.

By mixing the compounds of general formula I with conventional ones Spark erosion fluids can change their properties can be improved, in particular with regard to the removal rate and electrode wear. This also results in a considerable one technical progress when the conventional products in the spark erosion fluids according to the invention one Make up a proportion of 70 percent by weight. However, quantities are preferred in the range from 0 to 50 percent by weight of the total mixture.

Conventional spark erosion fluids are understood to mean , for example, those based on mineral oil fractions.

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White spirit, petroleum, gas oil and light lubricating oil cuts, for example, are suitable as mineral oil fractions. These mineral oil fractions have - depending on the boiling point - a viscosity in the range from 1 to 40 cSt at 20 ^° C.

In the electrical discharge machining fluids of the invention, alkyl-substituted benzenes can also be mixed with the compounds of the general formula I instead of the conventional electrical discharge machining fluids. Alkylbenzenes in which the sum of the carbon atoms of the alkyl radicals in the individual molecules is at least 3 are particularly suitable. The upper limit of the number of carbon atoms is that the viscosity of the mixture obtained should preferably not exceed ^{40 cSt at 20 ° C.} Specific examples of suitable alkylbenzenes are described in DT-PA 25 26 399.4.

In some cases, the electrical discharge machining fluids according to the invention contain preferably also additives for modifying certain properties in amounts of 0.005 to 0.5 Percentage by weight of the total mixture, e.g. oxidation inhibitors, conductivity improvers, additives with dispersing properties and / or odor improvers.

With the electrical discharge machining or spark erosion fluids according to the invention, previously unattainable removal rates are possible with, at the same time, very low wear rates on the tool electrodes. For this reason, products having a viscosity of up to about 6 cSt at 20 ⁰ C is not only excellently suitable for roughing, wherein the substantial metal removal to take place from the workpiece; rather, they can also be used to advantage in the subsequent finishing operations. This broad area of application is particularly advantageous from a technical point of view.

The higher viscosity electrical discharge machining fluids of the invention are particularly suitable for the roughing process. In this processing stage, in which high performance is

70988470078

gen, the working fluids are very strong thermal Exposed to loads. Therefore, a high flash point, low tendency to decompose and low evaporation losses are required. These properties combine the highly viscous spark erosion fluids of the invention in an ideal way. Since they are in terms of the highest possible removal rate and thereby the electrode wear that occurs practically does not differ from the low-viscosity products, there is still the advantage of that by mixing suitable components the specific properties of the electroerosion fluid required for each application can be adjusted in an optimal way.

In the examples given below, there are four spark erosion fluids according to the invention (products A, B, AC and BD), two conventional products (C and D), and one product the DT-PA 25 26 399.4 (product E) is used. All percentages relate to weight.

Product A.

It is a mixture of positionally isomeric monomethylbenzylbenzenes (Structure type Ia) with the following properties:

Viscosity: 3.99 cSt / 20 ⁰ C,

Density d _2Q : 0.987 g / ml,

Boiling point after

DIN 51 761: 280 to 285 ⁰ C,

Flash point after

DIN 51 758: 122 ⁰ C.

Product B

It is a mixture of positionally isomeric monomethyldibenzylbenzenes (Structure type Ib) with the following properties:

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Viscosity: 37.2 cSt / 20

Density d ₂₀ : 1.032 g / ml,

Boiling point after

DIN 51 761:> 350 ⁰ C,

Flash point after

DIN 51 758: 195 ⁰ CV

Product C. -..-: "." .

It is a furfural extraction and sulfuric acid treatment refined gas oil from a Middle East crude:

Viscosity: 5.78 cSt / 20 ⁰ C.

Product D -

It is a petroleum cut refined with sulfuric acid from a Middle East crude.

Viscosity: 2.02 cSt / 20 ° C> Product E -

It is a technical mixture of isomeric di-isopropyl-benzenes and (1,3-dimethyl-butyl) -benzene.

Viscosity: 1.92 cSt / 20 ⁰ C.

Product AC

It is a mixture of 50 percent product A and 50 percent product C.

Viscosity: 3.99 cSt / 2Ö ⁰ C.

708884/0076

Product BD

It is a mixture of 50 percent product B and 50 percent product D.

Viscosity: 5.22 cSt / 20 ⁰ C.

In the examples, values for the removal rate V

and the relative electrode wear, the technical progress that is achieved with the spark erosion fluids according to the invention compared to conventional products based on pure mineral oil fractions or compared to alkylbenzenes. The numerical material listed is based on tests that were carried out with an AEG Elbomat type 400 H spark erosion machine tool with Elopuls 60 pulse generator in accordance with VDI guideline 34OO using electrolytic copper as the tool electrode and SEL 2714 tool steel as the workpiece "Machine setting" specified values are settings for current level (I), pulse duration (t.) And pause duration (t) , which are clearly defined for the spark erosion system described above.

Example 1 shows that those achieved with product A according to the invention Removal rates far exceed the values obtained with the conventional product C. Nevertheless, with product A the relative electrode wear is considerably lower.

In the sizing stage of Example 1 we had to use the known product C machine settings other than those for product A according to the invention can be selected in order to achieve the best possible results in each case to achieve.

Example 2 shows that those achieved with product A according to the invention Removal rates exceed the values obtained with product E. In addition, one achieves with the product according to the invention A a considerable reduction in the relative electrode displacement

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- ■ ft- ' Z632180

schleißes.Um in the finishing stage of example 2 for the product E To achieve optimal values, as in Example 1, something else had to be done Machine settings can be selected as for the product A according to the invention.

Example 3 shows that the mixture according to the invention AC of methylbenzylbenzenes (A) and a mineral oil (C) this mineral oil (C) in terms of removal rate and electrode wear below almost is superior to all working conditions.

Example 4 shows that the mixture according to the invention BD from methyl dibenzylbenzenes (B) and a mineral oil (D) the pure Mineral oil (product D) under all working conditions, both in terms of removal rate and electrode wear, in high Dimensions is superior.

Example 5 shows that the mixture according to the invention BD with respect to one the viscosity comparable mineral oil from the prior art (product C) under almost all working conditions is superior.

Example 6 can be seen that the product according to the invention B for intensive roughing, for which it is particularly suitable because of its high flash point and its low tendency to evaporate is suitable with regard to the removal rate and electrode wear product A according to the invention is comparable.

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example 1

The performance of product A according to the invention compared with that of the conventional product C.

Machinery-
Division Removal rate (V) in
mm ³ / min 405 Product A Product C 459 Intensive-
Roughing 448 9 / 9/3 830 9/10/2 877 9/11/1 875

Relative

Electrode wear in% of V

Product A Product C

7.6
5.0
1/4

22.8

21.7

9.5

Roughing

6 / 9/3 504 269 7.6 28.0 6/10/2 501 279 3.3 15.3 6/11/1 494 282 1.1 3.5

Finishing 28, 5 19.3 1, 3 6th ,1 2 / 5/1 27 6th 19.0 1, 2 2 ,8th 2 / 6/1 20, 2 18.9 0, 8 ^v 1 , 4 2 / 7/1 2 / 8/1 2 / 9/1 2/10/1

709884/0078

- χΓ- IS ;.

Be i s ρ ie 1 2

The performance of product A according to the invention compared with that of product E.

Machine ■
setting Removal rate (V _w ) in
mm ³ / min
- - "-. - - Products Relative o /
Electrode wear (/ J)
in% of V _w A product E V Product A. product - _ - Intensive-
Roughing. 511 13.0 9 / 9/3 830 557 7.6 10.4 9/10/2 877 532 5.0 4.4 9/11/1 875 1.4 Roughing 328 14.3 6/9/3 504 331 7.6 7.2 6/10/2 501 335 3.3 1.5; - ' 6/11/1 494 1.1 Finishing 19.6 4.3 2/5/1 20.6 2.6 2 / 6/1 19.1 1.8 2 / 7/1 2/8 / T 28.5 1.3 2 / 9/1 27.6 ; 1.2 2/10/1 20.2 0.8

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Example 3

It becomes the performance of the mixture according to the invention AC compared with that of the conventional product C.

Machinery-
setting Removal rate (V _w ) in
mm ³ / min Relative
Electrode wear
in% of V
W. (JSf) ¹ ZVt ₀ Product AC Product C Product AC product C. Intensive-
Roughing 9 / 9/3 590 405 15.0 22.8 9/10/2 620 459 11.8 21.7 9/11/1 608 448 5.0 9.5

Roughing

6 / 9/3 370 269 15.4 28.0 6/10/2 386 279 8.1 15.3 6/11/1 381 282 2.6 3.5 Finishing 2 / 5/1 14.6 19.3 6.1 6.1 2 / 6/1 19.1 19.0 3.1 2.8 2 / 7/1 17.4 18.9 1.9 1.4

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11-

Example 4.

It is the performance of the mixture according to the invention BD compared with that of the conventional product D.

Machinery-
setting Removal rate (V) in
mm ³ / min Product D Relative ..
Electrode wear [/ Sl)
in% of V
W. 15.2 i / Vt _o Product BD Product BD Product D 18.4 Intensive-
Roughing 372 7.5 9 / 9/3 701 432 12.8 9/10/2 756 414 10.3 23.6 9/11/1 750 3.9 13.4 Roughing 2 67 2.4 6 / 9/3 418 27O 13.0 6/10/2 427 278 7.2 4.7 6/11/1 435 1.9 2.4 Finishing 18.8 1.2 2 / 5/1 18.2 18.8 5.9 2 / 6/1 22.4 17.7 3.4 2 / 7/1 23.5 1.8

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- yr-

Example 5

It is the performance of the mixture according to the invention BD compared with that of the conventional product C.

Machinery-
setting Removal rate (V) in
mm ³ / min Relative
Electrode wear (λ3)
in% of V
W. Product BD Product C Product BD Product C Intensive-
Roughing 9 / 9/3 701 405 12.8 22.8 9 / 1Ο / 2 756 459 10.3 21.7 9/11/1 750 448 3.9 9.5

Roughing

6 / 9/3 418 269 13.0 28.0 6/10/2 427 279 7.2 15.3 6/11/1 ■ 435 282 1.9 3.5 Finishing 2 / 5/1 18.2 19.3 5.9 6.1 2 / 6/1 22.4 19.0 3.4 2.8 2 / 7/1 23.5 18.9 1.8 1.4

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Example 6

It becomes the performance of the two products according to the invention A and B compared for intensive roughing.

Machine setting

Intensive roughing

9 / 9Z3

Removal rate (V _w ) in mm ³ / min

Relative electrode wear

in% of V.

Product A Product B Product A Product B

830

829

7.6

8.3

Pat en tan s slogans

-Λ

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Claims (5)

Claims 1. Dielectric fluids for metalworking by electrical discharge machining on the basis of, hydrocarbons, the aromatic components as well as, if appropriate, action-improving Contain additives, characterized that they are at least 30 percent by weight from compounds of general formula I. H ₁ in which R .., R ^, R->, R ₄ , R ₅ , Rg, - R ₇ and Rg are each a saturated, straight-chain or branched alkyl radical having 1 to 6 carbon atoms or a hydrogen atom, and η is the value O or T, where for η = O the sum of the _{carbon atoms present in the alkyl radicals R 1} to R 1, at most 6, and for η = 1 the sum of those present in the alkyl radicals R ^ to R. C atoms does not exceed 10, and from 0 to 70 weight percent from conventional electrical discharge machining fluids exist. 2. Dielectric liquids according to claim 1, characterized in that that as compounds of general formula I predominantly or exclusively monomethyl derivatives of benzylbenzene or of dibenzylbenzene (en). 709 884/0 07 » 3. Dielectric liquids according to at least one of the claims 1 and 2, characterized in that the compounds of general formula I in an amount of 50 to 100 percent by weight, based on the total amount. 4. Dielectric liquids according to at least one of claims 1 to 3, characterized in that the viscosity is the
Does not exceed 40 cSt at 20 ° C. 5. Dielectric liquids according to at least one of the claims 1 to 4, characterized in that they contain oxidation inhibitors, Conductivity improvers, additives with dispersing properties and / or odor improvers in amounts of 0.005 to 0.5 percent by weight, based on the total amount. " 70988 4/0076