DE102008047237A1 - Method and device for machining a workpiece by wire spark erosion and new dielectric for it - Google Patents

Abstract

A dielectric for metal working by means of spark erosion is described, comprising as main component a hydrocarbon mixture and as minor component a conductivity-improving component. Furthermore, a method of machining a workpiece by wire spark erosion is described in which a wire is pulled as a tool through the workpiece to be machined, wherein a conductivity-improving component is applied to the wire, and a device for machining a workpiece by means of wire spark erosion, comprising a holder for the workpiece to be machined, means for guiding and drawing the wire through the workpiece and a metering device with which such a conductivity-improving component can be applied to the wire.

Description

The The present invention relates to a method for processing a Workpiece by wire spark erosion and a device for machining a workpiece by wire spark erosion. Moreover becomes a dielectric and its use in said process or described in said device.

• • Das Drahterodieren; hierbei wird als Werkzeug ein dünner Metalldraht verwendet. Mit Hilfe des Drahterodierens können auch in schwer oder nicht spanbare Werkstoffe großer Dicke sehr feine Schnitte eingebracht werden.
• • Das Senk- bzw. Bohrerodieren; hier werden Stäbe oder Negativformen als Werkzeug verwendet. Damit lassen sich sowohl Sack- als auch Durchgangslöcher erzeugen. Wenn beim Drahterodieren nicht am Rand eines Werkstücks gestartet werden kann, so kann man mit Hilfe des Startlocherodierens eine Startbohrung schaffen.

Electroerosive processes are used in particular for high-precision material processing. In this case, an electrically conductive workpiece to be machined is processed in a non-conductive liquid (dielectric). A likewise electrically conductive tool is brought into the vicinity of the material, which has a generally negative electrical voltage with respect to the workpiece. There are numerous small electrical discharges between the tool and the workpiece, ie the formation of sparks, which remove material from the workpiece. The known electroerosive methods include in particular:

• • wire eroding; Here, a thin metal wire is used as a tool. With the help of wire EDM very fine cuts can be made even in difficult or non-chipping materials of great thickness.
• • The sinker drilling; here rods or negative molds are used as a tool. This can be used to create both blind and through holes. If wire erosion can not be started on the edge of a workpiece, you can create a start hole using the start hole erosion.

at the non-conductive liquid in which the processing of the workpiece, it is classically mostly to deionized water or even to oil. Especially at The wire erosion, however, have the use of oils and hydrocarbons other than dielectric than always proved very suitable. The physical erosion process works Although, but the removal rate is low and thus the Procedure uneconomical. The cause is probably due to the low thermal conductivity of the oil or other hydrocarbons and the fact that the spark gap is very small and it subsequently leads to process degeneration due to lack of fluid exchange and lack of removal of the removal products from the working gap comes.

Also with the previously used aqueous dielectrics for The wire erosion are associated with various disadvantages, such. B. the unavoidable corrosion of machined steel materials. In the Steelwork therefore requires non-ionic corrosion inhibitors be used. These protect but only limited Corrosion. Another problem with wire erosion of hard metals with deionized water as the dielectric resulting from cobalt leaching (Cobalt leaching) during the erosion process, which is very negative the quality of the machined parts can affect, in particular, for example, dies and punches for high-performance cutting tools is. In the treatment of heavy metal, such as chromium-containing Workpieces can be more than that avoid the formation of toxic pollutants, which may problematic disposal measures of the removal products necessary.

Of the present invention was based on the object, a new alternative To provide a procedure for material processing by means of spark erosion, in which the problems mentioned not or only to a reduced extent.

These Task is solved by the dielectric and the method with the features of claims 1 and 9. Preferred embodiments of the Dielectric according to the invention can be found in the Claims 2 to 8. A preferred embodiment of the method according to the invention can be found in Claim 10. Further encompassed by the present invention is the device according to claim 11. The wording all claims are hereby incorporated by reference made to the content of this description.

One Dielectric according to the invention comprises as main component a hydrocarbon mixture and as a minor component a conductivity improving Component preferably in a proportion of between 0.00001% by weight and 10% by weight, in particular between 0.0001% by weight and 5% by weight, contained in the dielectric.

A conductivity-improving component according to the present Invention is a component that is capable of electrical Increase the conductivity of the dielectric as a whole. The conductivity-improving component can be a single chemical Compound or preferably also a mixture of several compounds include.

The conductivity-improving component preferably contains at least one compound having at least one functional group selected from -OH, -COOH, -NH ₂ , -NHR, -SH and -SO ₃ H or one or more derivatives thereof, where R is alkyl, aryl, Alkylaryl or arylalkyl radical and wherein one or more carbon atoms may also be substituted by heteroatoms. A derivative should be understood to mean in particular a salt of one of the compounds in question.

In addition to the mentioned functional group pen, the at least one compound may optionally also have other functional groups that do not carry hydrogen, such as. B. -OR, -COOR, -SO ₃ R, -SiO ₂ R, -NRR ', -CHO and -CO-R, wherein R and R' are independently alkyl, aryl, alkylaryl or arylalkyl radicals and wherein a or more carbon atoms may also be substituted by heteroatoms.

The conductivity-improving component is particularly preferably suitable for polyhydric alcohols and their ethers such as sorbitol, polyalcohols, polyalcohol ethers, polyvinyl alcohols, polyethylene glycols and their ethers, carboxylic acids, fatty acid soaps of alkali or alkaline earth metals, salts of alkyl sulfates of higher primary or secondary alcohols of the general formula ROSO ₃ M (cf. M = alkali, alkaline earth metal, R = alkyl, aryl, arylalkyl or alkylaryl) or (RR ') CHOSO ₃ M, C ₁₂ to C ₂₂ sulfonic acids, alkylarylsulfonic acids or their salts, such as. B. Dodecylbenzenesulfonic acid.

Further particularly suitable compounds are non-volatile nitrogenous Compounds such as amines or amides or their salts, in particular oligomeric or polymeric amines and amides.

Examples which may be mentioned are polyethoxyalkylamines or -amides of the general formula R ¹ N [(R ² O) _m R] [(R ³ O) _n H] or R'CON [(R ² O) _m R] [(R ³ O ) _n H] mentioned, wherein R ¹ to R ³ alkyl groups, wherein R 'is preferably those having at least 8 carbon atoms, preferably at least 12 C-atoms, and n, m is equal to 1 or greater, as shown in DE 31 088 43 described. In addition, in particular polyamines or polyamine copolymers or mixtures of such compounds with other, in particular polymeric compounds in question. In addition to simple polyamines such. As polyvinylamine suitable non-volatile polyamines are advantageously obtained from the reaction of aliphatic primary monoamines such as n-octylamine or n-dodecylamine or N-alkyl-substituted aliphatic diamines such as. Nn-hexadecyl-1,3-propanediamine and epichlorohydrin. These polyaminopolyols have not only amino groups but also hydroxyl groups. An overview of such polyamine copolymers is in the US 3,917,466 contain.

Particularly suitable polymers for use together with polyamines or polyamine copolymers are polysulfone copolymers. The polysulfone copolymers are preferably substantially unbranched and have a molar ratio of 1: 1 of olefins and SO ₂ units. An overview of suitable polysulfone copolymers is also in US 3,917,466 contain. For example, 1-decene polysulfone may be mentioned. Mixtures containing polysulfone copolymers, a polyamine and a long-chain sulfonic acid are disclosed in U.S. Pat US 5,026,795 and US 4,182,810 described.

More preferably, the conductivity-improving component comprises a polysulfone copolymer and / or a polymeric polyamine and / or an oil-soluble sulfonic acid and / or a derivative thereof, in particular a mixture with a polysulfone copolymer and a polymeric polyamine and an oil-soluble sulfonic acid. Mixtures of this type are for example in the WO 00/68274 or WO 02/040554 described.

preferred Sulfonic acids are mono- or disubstituted phenyl or Naphthyl sulfonic acids. With such a combination were achieved particularly good results in wire eroding, what in the Example will be discussed in more detail.

The at least one compound can the main component, the hydrocarbon mixture, in principle diluted or undiluted added, wherein However, the use in a solution is preferred. Especially preferred is the use in an inert hydrocarbon.

In In some embodiments, the conductivity improving Component have organometallic compounds. Preferably however, the conductivity-improving component is substantially free from organometallic compounds, in particular heavy metal organic compounds.

The Hydrocarbon mixture (the main component) of an inventive Dielectric is preferably composed of saturated, aliphatic, acyclic hydrocarbons. In preferred embodiments it is essentially free of aromatic hydrocarbons. This should be understood in particular that the proportion of aromatic hydrocarbons is less than 1 wt .-%. In some preferred embodiments may be the hydrocarbon mixture but also be added specifically aromatic hydrocarbons.

Preferably the hydrocarbon mixture has a boiling point> 160 ° C, in particular> 200 ° C, on. In a further development, it may be preferable for the boiling point of the Hydrocarbon mixture is below 300 ° C.

Prefers the dielectric has an electrical conductivity in the dielectric Range between 5 pS / m and 500,000 pS / m, preferably between 5 pS / m and 50,000 pS / m, more preferably between 50 pS / m and 5,000 pS / m, more preferably from about 2000 pS / m.

Next the hydrocarbon mixture and the conductivity-improving Component may be a dielectric according to the invention optionally contain one or more conventional additives, which are added to specific properties such. As the viscosity of the dielectric or its chemical resistance to improve. In question are in particular additives for oil-based Dielectrics. Such additives are known to the person skilled in the art and must in the context of the present application is not described in detail become.

The Dielectric according to the invention can be mixed in "ready" State can be used as a mixture in which the conductivity-improving component in the above-mentioned proportion between 0.00001 wt .-% and 10 wt .-% already included. Surprisingly However, it turned out to be particularly advantageous, the conductivity-improving component to add only during Erodiervorgang. This is the subject of the method according to the invention for machining a workpiece by wire spark erosion.

at a method according to the invention for processing of a workpiece by wire spark erosion, as it is is common in such methods, a wire as a tool pulled through the workpiece to be machined. The eroding process begins either at a starting point on the workpiece edge or in a start hole drilling. This is preceded by drilling or sinking EDM introduced into the workpiece. Through this the wire must if necessary be threaded.

In particular, the method according to the invention is characterized in that a conductivity-improving component is applied to the wire, as described above. The conductivity-improving component thus preferably comprises at least one compound having at least one functional group selected from -OH, -COOH, -NH ₂ , -NHR, -SH and -SO ₃ H or a derivative thereof (see above). Optionally, the at least one compound is contained in a carrier liquid, which may be based for example on organic solvents such as toluene. The carrier may also contain alcoholic components (eg isopropanol) as well as petroleum derivatives.

The Applying to the wire is preferably done immediately before Entering the wire in the workpiece. The wire can sprayed with the conductivity-improving component, for example or immersed in the conductivity-improving component The method of application is basically free selectable. However, care should be taken that all sides of the wire as evenly as possible wetted with the conductivity-improving component become. It has proved to be useful, the Wire through with the conductivity-enhancing component filled reservoir into which the wire preferably fully immersed. The wire can be through, for example an opening whose diameter is substantially the outer diameter corresponds to the wire, be led out of the reservoir again.

Of the wetted with the conductivity-improving component Wire can then subsequently the material to be machined to cut. The cutting process is preferably carried out in a dielectric, as the main component, the above-described hydrocarbon mixture and optionally further conventional additives. The conductivity improving Component is only during the actual erosion process mixed with the other components, the inventive Dielectric is formed so to speak "in situ".

A Inventive device for processing a Workpiece by wire EDM with which a includes such a method includes a Holder for the workpiece to be machined, means for guiding and pulling the wire through the workpiece and a metering device with which the described conductivity-improving Component can be applied to the wire.

at the means for guiding and pulling the wire are involved in particular, suitable coils, drive and deflection rollers, as known from the prior art. Preferably, wire guides above and below the holder for the workpiece arranged, which support the wire, suppress vibrations and guarantee a straight cut. The wire is preferably in the upper part of the invention Device wound on a spool and can from there over several pulleys led to the upper wire guide become. From there he can with a defined tension through the Workpiece and the lower wire guide pulled become. The pulling direction is preferably vertical, so may accumulating Erosion waste rinsed particularly well out of the kerf become.

As described above, the application of the conductivity-improving component preferably takes place immediately before the wire enters the workpiece. The metering device is correspondingly arranged in preferred embodiments directly above the holder for the workpiece. When dosing, it may be z. B. act to the reservoir described above with the opening, but there are also many other technical solutions conceivable, such as spraying or means for brushing the leitverversververbes sernde component on the wire.

• – Vergleichsweise geringere Korrosion an Werkstück und Maschine
• – Durch den im Vergleich zu Wasser geringeren Funkenspalt wird eine höhere Abbildungsgenauigkeit erreicht
• – Konstante Abtragsverhältnisse ermöglichen Mikroschnitte
• – Nahezu keine Kobaltauswaschungen bei Hartmetallen und PKD
• – Durch die geringere Wärmeleitung (gegenüber wässrigen Dielektrika) entstehen keine Mikrorisse durch Thermoschocks
• – Bessere Oberflächenqualität
• – Kein Befall durch Bakterien, Pilze oder Hefen
• – Hohe Alterungsbeständigkeit

The dielectric according to the invention proved to be particularly suitable for wire EDM. Compared to the classic dielectrics mentioned above, the following advantages have been observed:

• - Comparatively lower corrosion on workpiece and machine
• - Due to the lower spark gap compared to water, a higher imaging accuracy is achieved
• - Constant removal ratios allow micro cuts
• - Almost no cobalt washes on hard metals and PCD
• - Due to the lower heat conduction (compared to aqueous dielectrics) no microcracks caused by thermal shocks
• - Better surface quality
• - No infestation by bacteria, fungi or yeasts
• - High aging resistance

Further Features of the invention will become apparent from the following example in conjunction with the subclaims. The individual features can each individually or in combination realized with each other in an embodiment of the invention be. The example is only for explanation and for a better understanding of the present invention and is in no way limiting.

example

One 0.25 mm thick brass wire was starting from a coil in the upper Part of an eroding machine over several pulleys an upper and a lower wire guide out, between which a workpiece to be machined from steel was arranged. By driving rollers, the wire was defined with a Drawn tension through the workpiece and then disposed of. The workpiece was in a liquid dielectric cut. This consisted essentially of synthetic aliphatic Hydrocarbons. Disposed by permanent flushing the dielectric the resulting Erodierabfall from the kerf.

immediate before the wire entered the workpiece to be machined, It was replaced by a conductivity-improving component led, in which he immersed fully. At the conductivity improving Component was the commercially available Antistatic Costelan AS 100 (H. Costenoble GmbH & Co. KG, Eschborn, Germany), a composition containing polymeric nitrogen and sulfur compounds in kerosene.

Of the Wire wetted with the antistatic then entered the workpiece and cut this with high imaging accuracy. It was neither the above-mentioned cobalt leaching nor a Corrosion of the workpiece observed.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - DE 3108843 [0013]
• US 3917466 [0013, 0014]
• - US 5026795 [0014]
• - US 4182810 [0014]
• WO 00/68274 [0015]
• WO 02/040554 [0015]

Claims (11)

Dielectric for metalworking by spark erosion, comprising as the main component a hydrocarbon mixture and as a minor component a conductivity improving Component, the latter being present in a proportion between 0.00001% by weight and 10 wt .-% is included. Dielectric according to claim 1, characterized in that the conductivity-improving component contains at least one compound having at least one functional group selected from -OH, -COOH, -NH ₂ , -NHR, -SH and -SO ₃ H or a derivative thereof, wherein R Alkyl, aryl, alkylaryl or arylalkyl radical and wherein one or more carbon atoms may also be substituted by heteroatoms. Dielectric according to Claim 1 or Claim 2, characterized characterized in that the conductivity-improving component a polysulfone copolymer and / or a polymeric polyamine and / or an oil-soluble sulfonic acid and / or contains a derivative thereof. Dielectric according to one of the preceding claims, characterized in that the hydrocarbon mixture of saturated, aliphatic, acyclic hydrocarbons. Dielectric according to one of the preceding claims, characterized in that the hydrocarbon mixture substantially is free of aromatic hydrocarbons. Dielectric according to one of the preceding claims, characterized in that the hydrocarbon mixture a Boiling point> 160 ° C, in particular> 200 ° C, has. Dielectric according to one of the preceding claims, characterized in that the conductivity improving Component substantially free of organometallic compounds is. Dielectric according to one of the preceding claims, characterized in that it has an electrical conductivity in the range between 5 pS / m and 500,000 pS / m, in particular between 5 pS / m and 50,000 pS / m. Method for processing a workpiece by means of Wire spark erosion, in which a wire as a tool through the zu working workpiece is pulled, taking on the wire before entering the workpiece a conductivity improving Component is applied. A method according to claim 9, characterized in that the conductivity-improving component contains at least one compound having at least one functional group selected from -OH, -COOH, -NH ₂ , -NHR, -SH and -SO ₃ H or a derivative thereof, wherein R Alkyl, aryl, alkylaryl or arylalkyl radical and wherein one or more carbon atoms may also be substituted by heteroatoms. Device for machining a workpiece by means of wire spark erosion, comprising a holder for the workpiece to be machined, means for guiding and pulling the wire through the workpiece, and a metering device with which a conductivity-improving component, preferably at least one compound with at least one functional group selected from OH, -COOH, -NH ₂ , -NHR, -SH and -SO ₃ H or a derivative thereof, wherein R is alkyl, aryl, alkylaryl or arylalkyl radical and wherein one or more carbon atoms may also be substituted by heteroatoms, can be applied to the wire.