Electrode, and a method for making such an electrode

The invention relates to an electrode for machining a workpiece having a workpiece to be machined to the facing end section with an end face as well as a method for producing such an electrode.

Turbines are often equipped with workpieces which partly have very complex shapes such as turbine blades. To produce such workpieces eroding comes increasingly used, a thermal, removing fabrication method for conductive workpieces, in which electric discharge operations between an electrode and the workpiece material is removed. With the erosion can be particularly complex recesses forming, for example, specially shaped grooves, pockets with complex cross-sectional shapes or the like. If holes are, however, introduced in ceramic coated workpieces with the aid of eroding, the holes before coating have to be introduced and the like after drilling with a polymer be closed or masked, so that they are not closed during the subsequent coating with the ceramic thermal barrier coating. After coating with the ceramic residues of masking must be removed again.

Currently no industrially available plants or proven technologies are known to drill by eroding or directly to EDM ceramic-coated workpieces without accordingly chemically modify the ceramic layer advance so that it is electrically conductive. It can therefore currently only metallic or metal-coated workpieces by means of an electrical-removal process (Electrical Discharge Machining EDM =) to be drilled, because the ceramic thermal barrier coating is not electrically conductive.

It is therefore a first object of the invention to provide an electrode which overcomes the above problem. A second object is to provide a method for producing such an electrode.

According to the invention the first object is achieved by specifying an electrode for machining a workpiece having a the workpiece to be machined facing end portion having an end face, being provided at the end portion at least partially across the face cutting, the cutting at least partially comprise a cutting material and said end portion a to a thermal ablation, in particular a spark erosion removal, includes suitable material, so that at least one abrasive, flaking action as well as a thermal, non-mechanical removal of the workpiece is simultaneously possible.

The electrode of the invention a continuous processing of a ceramic coated workpiece without previous masking of the workpiece is possible. The at least partially made of cutting material cutting end portion to allow the start of machining by a cutting removal of the rotating electrode to chipping removal of a non-conductive workpiece or its non-conductive coating. This is in this case in direction of the bore axis, which corresponds to the rotation axis of the electrode, is moved. Without loss of generality, a ceramic-coated workpiece is subsequently used for a non-conductive coated workpiece. Find the machining in a dielectric instead, the so machined worn ceramic particles from the through and around the electrode supplied dielectric washed away, and the electrode and workpiece of this are cooled. Since the end portion of the electrode, there are at least partially made of cutting material existing cutting and a material to a thermal ablation, in particular a spark erosion removal, the erosion process can start in the proper sense as thermal ablation, once the ceramic layer removed locally - that is drilled through - is. Of course, may be provided with cutting the entire electrode.

Through the electrode according to the invention also ensures the wear caused by the machining removal and the burn-up at a hole through the ceramic layer, by an associated metallic bonding layer and the metallic workpiece, that one after the completion of the bore, at the next hole again sufficient cutting with cutting material for the machining of the ceramic layer, as well as sufficient material for thermal ablation in the correct geometry bound, are available.

By inventive electrode material, time and labor is therefore saved.

The simultaneous presence of cutting as well as a suitable to a thermal ablation material an abrasive, flaking action of the ceramic layer and a thermal, non-mechanical removal of the workpiece is simultaneously possible. The electrode of the invention can be drilled in a hot gas leading workpiece with an electrically non-conductive ceramic thermal barrier coating on an EDM through the combination of a cutting and a subtractive manufacturing processes, in a two-step process, for example, cooling air holes. The processing time is shortened due to the simplified technical processes and streamlined logistics.

Preferably, the electrode for thermal, non-mechanical removal of the workpiece as the material comprises an electrically highly conductive metal having a relatively high melting point. In a preferred embodiment the material comprises a hard metal, in particular a tungsten-copper alloy. The cutting material preferably comprises a tool steel and / or cutting ceramics, and / or corundum or and / or diamond. The material and the cutting material are particularly well suited for machining ceramic layers.

Preferably, the end portion comprises a Endabschnittumfang are provided on which cutting. This allows a particularly good and fast ablation result of ceramic achieve.

In a preferred embodiment of the cutting material and the material comprise the same carbide. This simplifies the manufacture of the electrode, for example by sintering.

Preferably, the blades are geometrically defined cutting. This occurs, for example, if the number of edges and / or the position of the workpiece are known. Alternatively or additionally, the cutting edges are geometrically undefined cutting. This occurs, for example, when the number of cutting edges, and the location to the workpiece can only be described using statistical characteristic quantities.

According to the invention the second object is achieved by the provision of a method for producing an above mentioned electrode for machining a workpiece with the following steps:<ul><li>Providing a base electrode, with a side facing the workpiece end, having to take a thermal ablation, in particular a spark erosion removal, suitable material and cutting material</li><li>Attaching defined cutting edges and / or geometrically undefined cutting edges at least in an end face of the end portion, so that at least one abrasive, flaking action as well as a thermal, non-mechanical removal of the workpiece is enabling simultaneously.</li></ul>

The inventive method of cooling air holes can be drilled in a hot gas leading workpiece with an electrically non-conductive ceramic thermal barrier coating is now on an EDM machine with the electrode itself in a two-step process. This improves the efficiency of processing, since the workpiece compared to the prior art is no longer masked, and then has to be ceramic coated, but may be drilled after the complete coating in a single pass. The quality of the machining result is also improved because the hole in the ceramic and the workpiece can be flawlessly performed in selected geometry, while the masking there always strong discontinuities occur which may have negative influence on the cooling effect and the integrity of the layer connection. The processing time is due to the simplified technical processes and streamlined logistics also shortened.

Preferably, the attachment of the geometrically defined cutting and / or geometrically undefined cutting edges is performed by a dresser. Since the cutting of the electrode become dull during the ceramic drilling and the electrode during eroding further wear (erosion) learns that automatically tracked electrode or a new substitute electrode by means of a dressing is provided again with a cutting geometry before drilling the next hole. This is a very simple method of manufacturing such an electrode.

In a preferred embodiment the dressing is performed by the dressing according to the principle of Senkerodierens or / and wire erosion or / and with dressers. For this purpose, an electric discharge machine can be used as it is also used for machining the workpiece.

Further features, properties and advantages of the present invention will become apparent from the following description with reference to the accompanying figures. Therein is shown schematically:<dl id="dl0001" compact="compact"><dt>FIG 1:</dt><dd>a cross section of a first electrode 1 according to the invention,</dd><dt>FIG 2:</dt><dd>a cross section of a second electrode of the invention 100th</dd></dl>

<figref idrefs="f0001">1 shows</figref> shows a cross section of a first electrode according to the invention 1. This is in particular a rod or tubular electrode. This first electrode 1 of the invention comprises a removal to suitable material 22 as well as a cutting material 21. In this case, as the cutting material 21, for example, diamond, boron nitride, tool steels, sintered materials, cutting ceramics, corundum or diamond are used. Here, the suitable for the removal material 22 such as copper and / or copper alloy, or another material with a high melting point and high electrical conductivity. The electrode 1 corresponds to a so-called hybrid electrode. Also other materials may be provided in the electrode first In addition, the electrode 1 an end portion 4 and a top portion 3. This can be specified in advance. The end portion 4 has an end face 5 and a Endabschnittsumfang eighth These are provided with defined cutting edges 10th Of course, also geometrically undefined cutting edges (not shown) may be provided. The entire electrode 1 with geometrically undefined cutting edges 10 may be provided both at the beginning of section 3 and the end portion 4 and / or with defined cutting edges (not shown) at the end. 4 Also 5 may be provided with cutting edges 10 of course only the end face.

The geometrically defined cutting 10 have a geometrically defined form. The end portion 4 thus has an exactly defined blade geometry. This means that, for example, the number of blades, and the location of the cut 10 to the workpiece 50 are known and describable. Also, of course, the end portion 4 more cutting material 21 having a top portion 3 (not shown). This is possible, for example, when the base electrode; that is, the electrode 1 is made prior to the introduction of the cutting edges 10 by sintering. This is advantageous when a particularly hard coating material, for example, a hard ceramic layer 51 on the workpiece 50, must be machined or drilled before the erosion process.

With the electrode 1 according to the invention, can be both cut or removed as eroded simultaneously. There are, therefore, non-metallic and metallic workpieces 50 processed with such an electrode. 1

<figref idrefs="f0001">FIG 2</figref> however, shows an electrode 100, which includes a suitable material 22 and as a cutting material 21, a hard metal 10; ie the electrode 100 is like having carbide 10. Again, the electrode 100 an end portion 4 and a top portion 3. The end portion 4 also has an end face 5 and a Endabschnittsumfang eighth These are provided with defined cutting edges 10th Of course, geometrically indefinite cutting may be 10 provided and / or in the end face 5. Subsequently geometrically fixed or indefinite cutting or a combination of both the simple halt sake are referred to as cutting 10 here. In this case, the hard metal 10 is particularly suitable for cutting a coated with a ceramic layer 51 the workpiece 50, because it has the necessary degree of hardness. However, the hard metal 10 in the electrode 100 can also be used to erode. This means that with such an electrode 100, which is composed of only a metal, in essence, can be eroded and cut simultaneously. It can be used instead of tungsten carbide 10 any material or any combination of materials, which is characterized by high hardness, metallic properties and good electrical and thermal conductivity.

If coatings processed from non-conductive materials, it is advantageous that the cutting material 21 or the cemented carbide 10 is always harder than this non-conductive material. This also applies to a machining of a workpiece 50 without coating of the electrode 1 according to the invention, 100. The cut 10 may of course be attached in the novel electrode 1,100 at the beginning of section 3 and the end portion. 4

The electrode 1.100 inventive example cooling air holes in a hot gas leading workpiece 50 can now be drilled with an electrically non-conductive, ceramic thermal barrier coating 51 in a two step process. This improves the efficiency of the processing. The quality of the processing result is also improved, since the geometry of the bore in the area of ​​the ceramic layer 51 can be perfectly executed virtually, while a masking process, as has been mentioned in the prior art, there always arise strong discontinuities in the geometry of the negative may affect the cooling effect and the integrity of the ceramic layer connection to the workpiece 50th

The electrode 1.100 invention a continuous processing of a ceramic coated workpiece 50 without masking and / or the exchange of a machine tool is possible. Since the cut 10 of the electrode 1,100 are truncated during the ceramic drilling and electrode undergoes 1,100 eroding further wear (erosion) that automatically tracked electrode 1,100 or a new substitute electrode by means of a dressing is before drilling the next hole again with a cutting edge geometry provided.

This saves material, time and labor. So also does the wear of the electrode 1,100 by chipping removal and burn in a hole through the ceramic layer 51, ensure by an associated metallic bonding layer and the metallic workpiece 50 that enough after completion of the bore at the next hole again Cut 10 tied with a cutting material 21 for processing the ceramic layer 51, as well as enough material 22 for thermal ablation in the correct geometry, are available.

By the simultaneous presence of the cutting edges 10 as well as a suitable material to a thermal ablation 22 an abrasive, a metal-cutting removal of the ceramic layer 51 and a thermally non-mechanical removal of the workpiece 50 is also possible.

To prepare these electrode 1,100 can directly in front of the drilling operation, for example by means of a fast-Hole- or hole electric discharge machine (not shown) integrated dressing unit (not shown) on the principle of lowering or wire erosion, but also by means of a dressing (not shown) with rotating dressing rolls (not shown), a cutting edge geometry in the end face 5 and for example, the peripheral surface 8 of the electrode are 1,100 introduced. This can have a geometrically defined shape, or also, for example, by dressing in a very rough board (not shown) are provided by EDM with geometrically undefined cutting edges. This may combine the geometrically undefined cutting a stochastic dental field, in a sense similar to a very coarse sandpaper.

With the geometric un- / specific cutting 10 the ceramic thermal barrier coating is now by the rotation of the electrode 1,100 and with a feed to start drilling first 51 processed divisive. If the processing in a dielectric (not shown) is performed, then a rinse, in particular a pressure flushing, the electrode 1,100 with this dielectric (not shown) for cooling the electrode 1,100 and the workpiece 50 already during the processing of the ceramic layer 51 itself, and to Fort rinsing the Abtragsprodukte be used. Once the ceramic layer 51 is pierced and exposed, the electrically conductive metal of the workpiece 50, the erosion process starts as usual with metallic materials. Since the cut 10 of the electrode 1,100 are truncated during the ceramic drilling and electrode 1,100 experiencing eroding further wear, for example by combustion, which automatically tracked electrode or a new substitute electrode before drilling the next hole is not by means of the dressing described above ( shown) again with a cutting geometry.