Patent Application
20070256938
The present invention concerns various methods for electro-chemical processing of a work piece. Further, the invention concerns methods for manufacturing a tool to be used as an electrode in an electro-chemical processing method, which tool is designed for electro-chemical processing of a work piece. Moreover, the invention concerns electrodes that are designed for usage in a method for electro-chemical processing of a work piece.
For processing work pieces and in particular for manufacturing specified work piece surfaces, material removing methods, such as milling and lathing, are generally known. A problem of these material removal methods is that small and complex work piece surfaces are not producible or only in a relatively cost-ineffective manner.
In addition, for special applications, the removal of material using electrical discharge erosion, electrolytic machining and by metal etching is known. These three methods have in common that electric current is responsible for the desired material removal from the work piece. All three above-noted methods take place in a liquid work medium.
In electrical discharge erosion, material removal or material migration takes place between two electrically-conducting contacts. In this technique, the electrodes are the shaping tool and the to-be-processed work piece. The electrical discharges in an erosion gap constitute temporal and localized discharges, whose effect on the work piece surface is characterized by cone shaped removals and removed craters. The machines driven with a pulse- or relaxation-generator can realize the methods of sinking, wire eroding, grinding and sawing. Nowadays, electrodes for the electrical discharge erosion method are produced by milling of graphite or copper, because these materials exhibit a burn-off behavior that is favorable for electrical discharge erosion. Other materials are only suitable therefor with severe restrictions.
However, in electrical discharge erosion, it is disadvantageous that the electrodes are subjected to material wear and tear and the processing of a work piece takes a long time and is thus expensive. Accordingly, this method is only utilized for very special work pieces. An economic series processing of work pieces has not been previously achievable.
In the so-called electrolytic machining, which is also known as electro-chemical milling (ECM method), it concerns an electro-chemical processing method, in which metal atoms of the anode—i.e. the work piece—go into solution under the influence of a DC voltage in an aqueous solution of salts or acids as electrolytes. It is the reverse of galvanization. In this method, the DC current flowing between the work piece and the tool shapes the work piece to the preset form by dissolving away of material particles. For determining the geometry, an electrolyte is brought up to a speed of 30 m/s by an insulated nozzle and achieves a very high material removal rate at current densities of 250 A/cm2. In particular, work piece geometries and work piece surfaces having a roughness as low as Rt=0.5 μm can be achieved without burr. Characteristic of this electrolytic machining is that very high material removal speeds and quality can be achieved. As was already indicated above, one electrode is the work piece in this method and the other electrode is the tool that has the desired profile of the work piece, so that the corresponding desired material removal takes place on the work piece. Previously, the electrolytic machining or ECM method was often utilized only for very special components, in particular for the effective deburing of metallic serial-components and/or for the surface smoothing of, e.g., turbine vanes. Recently, it has been also researched to utilize this process for manufacturing of micro-components and very precise mini-structures.
One reason for using the ECM method only for special components is that a very good flushing is necessary in order to sustain the material removal process and another reason is metal ions are removed from the work piece along the entire gap between the tool acting as the electrode and the to-be-processed work piece proportional to the current flow—as a rule, proportional to the gap distance—, whereby the required precision is not always achieved. Moreover, deep slots or similar geometries in work pieces are hardly possible with the previous electrodes for electrolyte machining, because the necessary flushing ducts can not be generated or only with substantial effort. For further information concerning electrolytic machining of work pieces, reference is made to the following documents as examples thereof: CH 538 906 A, DE 199 59 593 A1, DE 1 813 017 A, DE 1 765 890 B1, DE 17 65 890 B, U.S. Pat. No. 5,738,777, DD 287 617 A7.
GB 2 096 518 A discloses a method and a device for electrical processing of a work piece. Herein, a so-called EDM method and an ECM method are combined with each other with the usage of a strong electrolyte. The work piece, as well as a tool utilized herein for shaping the work piece, are not described in detail. Only customary copper-graphite-wires or tungsten electrodes are mentioned as electrodes.
In U.S. Pat. No. 5,833,835, a method for electro-chemical processing of a work piece in an electrolyte by applying bi-polar electrical impulses between the work piece and an electrically-conductive electrode is disclosed. Again, reference to generally customary electrodes is also made herein.
In DE 101 11 019 A1, a device and a method for structuring a surface of an electrically-conductive object, which is connected as an anode, by an ECM method are described. The disclosed ECM apparatus includes an anode and cathode; an electrolyte is disposed between the cathode and the to-be-structured surface. The structure on the surface of the object is produced using a mask integrated in the ECM apparatus. Moreover, it is also disclosed that the cathode, the mask and the to-be-structured surface can be pressed together like a sandwich.
In DE 102 37 324 A1, a method for producing an electrode for the electro-chemical processing of a work piece and an electrode produced according to the method are disclosed. Herein, an electrode body made of an electrically-conducting support material is coated on the surface with an insulating material. Then, a removal of the insulating material takes place in portions of the surface of the electrode body, which portions correspond to the structure that should be formed in the surface of the work piece by electro-chemical processing.
EP 0 223 401 A1 shows a partially-conducting cathode for an electro-chemical processing. The cathode comprises a processing surface, of which at least a part is comprised of non-conducting and conducting materials that are layered on top of each other, wherein the spacing and the thickness of the non-conducting and conducting materials are selected so that a too-deep removal of material on a convex radius of the work piece surface is decreased.
In addition, a PEM method, which is an adaptation of the classic electro-chemical method, is noted. This method was developed by the firm PEM Technologiegesellschaft für electro-chemische Bearbeitung mbH/Deutschland. The PEM technology concerns a modified variation of the above-explained ECM method and thus is to be subsumed under the generic ECM method and/or electrolyte milling or general electro-chemical processing. The PEM technology relies upon the direct and largely proportional dependence of the gap distance between the electrode and the work piece and the consequent achievable geometry- or surface precisions. The necessary flushing of the gap with fresh electrolyte can no longer be realized at gaps of about 10 μm. Accordingly, this gap distance represents the limit for the classic EMC [sic, ECM] method. Since a simultaneous removal of material and flushing is not possible in the classic ECM method, the two procedures are alternately performed in the PEM method. A removal of material takes place in a narrowest-possible gap; the flushing of the gap takes place in a largest-possible gap (several tenths of a millimeter). This leads to an oscillating electrode movement. In the PEM method, approximately 50 Hz is realized. That is, higher surface precisions can be achieved by changing the gap width. Thus, it concerns, in principle, a cavity sinking method with a vibrating electrode. A DC voltage is applied between the electrode and the work piece, as was described above with respect to the ECM method, whereby the work piece dissolves away in accordance with the geometry of the descending electrode. Components thereby result having arbitrarily complex geometric shapes in nearly all electrically-conducting metals, such as e.g., highly-aged steel, rolled steel, powder-metallurgic steel as well as super alloys (e.g., nickel-based alloy).
Access to applications is thus opened up with the PEM method that could not formerly be produced, or only uneconomically produced, with the known methods of electrical discharge erosion or with the classic electro-chemical removal of material.
The electrodes necessary for the performance of the ECM method and the PEM method were formerly produced with the classic methods, such as milling, erosion or etching.
According to a first aspect of the present invention, a method for electro-chemical processing of a work piece is proposed, in which a work piece is constructed in layers from a conductive material, in particular, using rapid prototyping technology. The work piece constructed in layers is contacted in an anodic manner and a tool serving as an electrode is disposed opposite to a to-be-processed site of the work piece such that a gap remains therebetween. The tool is contacted in a cathodic manner and a conductive medium is brought into the gap between the work piece and the tool so that current flows by applying an electronic voltage and metal ions are dissolved from the work piece by electrolysis, whereby a defined removal of material from the work piece takes place according to the contour of the tool.
A further aspect of the present invention comprises a [sic, method] for processing a work piece, in which, in alternative to the above-mentioned inventive processing method, the tool serving as an electrode is produced in a layered-construction manner using rapid prototyping technology instead of the work piece. According to the invention, a metallic work piece is contacted in an anodic manner and a tool constructed in layers using a rapid prototyping method is disposed opposite to a to-be-processed site of the work piece such that a gap remains therebetween. The tool is contacted in a cathodic manner and a conductive medium is brought into the gap so that current flows by applying an electronic voltage and metal ions are dissolved from the work piece by electrolysis, whereby a defined removal of material from the work piece takes place. It is noted that a metal layer is applied to at least a part of the outer side of the produced electrode, in case the individual layers, from which it was constructed, are comprised of an electrically non-conductive material.
An alternative of the above-mentioned method comprises the production in a layered-construction manner of the work piece as well as the tool serving as the electrode.
According to a further aspect of the present invention, a method for producing a tool to be utilized as an electrode in an ECM method is proposed, which tool is designed for electro-chemical processing of a work piece. In this aspect, the electrode is produced in a layered-construction manner using a rapid prototyping method, wherein an outer contour desired for the removal of material from the work piece in the ECM method is fabricated on the electrode. In case the layers of the produced electrode are comprised of an electrically non-conducting material, a metal layer is applied in a known manner to at least a part of the outer side of the produced electrode that should effect a removal of material from the work piece. In the latter case, the application of the metal layer can take place, e.g., by galvanization, in a CVD method, PVD method, varnishing, spraying or the like.
In an exemplary embodiment of the above-mentioned inventive method, during production of the electrode or the tool in a layered-construction manner, at least one duct is fabricated, which duct leads to the outer side of the electrode or the tool, respectively, in order to supply a conductive medium into a working gap between the electrode and the work piece during use of the electrode or the tool, respectively, in the ECM method or to be able to suction the conductive medium through the duct.
A further aspect of the present invention concerns a method for producing a tool to be used as an electrode in an ECM method for the electro-chemical processing of a work piece. This further inventive method comprises the steps: producing a body from a plurality of layers using a rapid prototyping method, the respective contours of the body, when taken together, forming the outer contour of the electrode body desired for the removal of material from a work piece in the ECM method. Thereafter, a molding of the body comprised of a plurality of layers takes place for producing a casting mold, the casting mold inner contours having, as a result of the molding, the outer contour of the electrode body desired for the removal of material from a work piece in the ECM method. Then, an electrode body is cast in the produced casting mold, whereby the outer contour of the electrode body desired for the removal of material from a work piece in the ECM method is achieved. Finally, an electrically conductive layer is applied to at least a part of the surface of the cast electrode body, in case the electrode body itself is comprised of a non-conductive material. The methods for applying the electrically conductive layer, such as a metal coating, are generally known. In particular, reference is made to the above-explained, exemplary selection of suitable metal coating methods.
A further aspect of the present invention concerns an electrode for usage in an ECM method for electro-chemical processing of a work piece. This inventive electrode comprises an electrode body comprised of a plurality of layers produced using rapid prototyping technology, the respective contours of the layers together forming the outer contour of the electrode body desired for the removal of material from a work piece in the ECM method. An electrically conductive layer is applied to at least a part of the surface of this electrode body, in case the layers are not comprised of a conductive material.
Finally, a further aspect of the present invention concerns an electrode for usage in an ECM method for electro-chemical processing of a work piece. In this aspect, the inventive electrode comprises an electrode body having an outer contour desired for the removal of material from a work piece in the ECM method. In this aspect, the electrode body is produced by casting in a casting mold, the casting mold inner contour is set by molding of a body that is composed of a plurality of layers produced using rapid prototyping technology, and the respective contours of the layers, when taken together, form the outer contour of the electrode body desired for the removal of material from a work piece in the ECM method.
The concept underlying the invention is to meld rapid prototyping technology, which is known in completely other fields, for the layered-construction of a body having complex surface structures with the ECM method. For the first time, precise metallic work pieces and tools can be produced in a simple, cost-effective manner and in a very short time. In particular, electrodes for usage in ECM methods are producible for the first time with previously unachievable surface structures and precisions. Thus, the previous ECM methods are now employable for completely new work piece processings. Due to the precise and cost-effective production of electrodes in a layered-construction manner corresponding to the rapid prototyping technologies, which are known for layered-construction in other fields, complex work pieces can thus also be economically fabricated in the known ECM methods. In particular, because the electrodes are not subjected to wear and tear in the ECM methods, the particular advantages of layered-construction of the electrodes now can be utilized in large series-manufacturing of work pieces with complex surfaces and surfaces having high precision.
In particular, it is also possible for the first time to provide flushing- and/or suction ducts in the electrodes for the ECM method or also in the work pieces, which are constructed in layers, and are to be processed using an ECM method. Especially complex flushing- and/or suction duct systems, in particular, can also be produced in the electrodes (i.e. in the work piece and/or in the tool for the ECM method). In this connection, a flushing- or suction duct system comprises a plurality of ducts that lead to different sites on the surface of the electrodes and enable a specific supply or discharge of electrolyte.
In summary, it is to be understood that the proposed combination of ECM methods and a layered-construction of electrodes using rapid prototyping methods enables the realization of fast and automatable systems for producing complex work pieces. High precision and complex structures on the work pieces can be achieved. In particular, very smooth components, i.e. having low roughness, are also economically producible. In particular, any metallic material is also usable as the material. There are, in principle, no significant limitations and many copies of work pieces are producible in an arbitrary manner. For the first time, an optimization of the flushing of the electrolyte in the ECM method can be realized. As was explained above, the above-mentioned PEM technology is, in particular, combinable with the proposed inventive methods.
In a further exemplary embodiment of the present invention, a flushing and/or suction of the electrolyte can, e.g., alternatively take place. In a further exemplary embodiment, ducts or bores specific only for supplying and ducts or bores specific only for suctioning can alternatively be provided.
A further exemplary embodiment of the present inventive method provides that the application of ultrasound is superimposed during the metal ion removal in order to, e.g., increase the flushing effect.
A further exemplary embodiment of the present invention provides that processing takes place with vibrations in various effective directions again in order to increase the flushing effect or to increase the precision of the material removal from the work piece. In this way, complex, specific shapes, such as screw threads, under-cuts, inner threads or gear geometries could be produced.
In particular, it is possible using the inventive method to simultaneously process a plurality of work pieces made of the same or different metals in the ECM method.
In a further exemplary embodiment of the present invention, the processing in an ECM method of a plurality of work pieces can take place separately in a first phase, such as e.g., a contour-approximating electrolytic machining, and in a second phase, a common processing of the plurality of work pieces, e.g., an electrolytic machining for achieving a specified counter on both components, takes place.
The layered-construction methods in rapid prototyping technologies and/or the rapid prototyping methods, which come into use for the present invention, could be methods that fabricate metallic work pieces as well as synthetic material components. Methods for fabrication of metallic components could, e.g., be the following methods: DMLS of the firms EOS and MCP, IMLS of the firm 3D Systems, Lasercusing of the firm Konzeptlaser, Laserschmelzen of the firm Trumpf, Electron Beam Melting of the firm Arcam, and Electron Beam Sintering. An example of a layered-construction method, which generates synthetic material components and can come into use in the present invention, is stereo-lithography.
Inventive electrodes can be hollow according to an exemplary embodiment of the present invention and/or can possess a special filling. The filling can, in particular, be a conductive web or powder in order to facilitate the transmission of high amounts of currents.
In a further exemplary embodiment of the present invention, inventive electrodes can also have an inner crystal lattice structure or a sintered structure or also can be constructed in shells. In particular, multi-part constructed electrodes for multi-phase processing are also possible. The inventive construction of electrodes for usage in ECM methods also makes possible different structural areas on electrodes.
Inventive electrodes for an ECM method can also be produced that are produced by a casting method in connection with the rapid prototyping layered-construction. As casting methods, vacuum casting, front casting [Frontguss], investment casting, waste-wax casting, Gilvac method, precision casting, etc. are suitable, so that the inventive electrodes result from a positive mold. However, electrodes in layered-construction are also producible for usage in ECM methods that result by a casting method from a negative mold, such as vacuum casting, front casting [Frontguss], investment casting, precision investment casting, Gilvac method, precision casting, etc.
Additionally, it is noted that not only the methods expressly mentioned herein are to be subsumed under the term “rapid prototyping method” and “rapid prototyping technology” with reference to the present invention, but also all further methods and technologies that a skilled person associates with the field of rapid prototyping methods. In general, all methods that construct a body in layers fall within this term. Moreover, all possible combinations of individual layer-construction methods are to be subsumed under the above-mentioned terms.
For a better explanation and understanding, several exemplary embodiments of the present invention are described in greater detail in the following with the assistance of the appended drawings.
a)-h) show various surface structures of inventive electrodes;
A first exemplary embodiment of the present invention is explained in more detail in the following with reference to
As is shown in partial step I of
As soon as the desired layer 3 is completed, the just exposed and cured synthetic material part is downwardly lowered to the new desired layer thickness. The new liquid synthetic material layer 13 above the top layer 3 is again exposed and thereby hardened. Layers 3 provided in an arbitrarily contourable manner and possibly with openings, etc., result thereby, which layers together form an electrode body 1. As shown in
This electrode body 1 constructed in layers in the stereo-lithography method is comprised of synthetic material in the described example. The electrode body 1 can be made conductive by mixing appropriate materials into the synthetic material that is curable by the laser 15. In case this conductivity does not suffice in order to utilize such an electrode body 1 in the ECM method, such an electrode 1 can also be provided with a metallic coating 2, as will be explained below.
It will be assumed for steps II-IV that the electrode body 1 is electrically conductive. In step II, the electrode 1 is provided with an electronic terminal connection 17 that is connected with the DC power source via a cable 19. A work piece 21 is likewise provided with a terminal connection 23 and is connected with the DC power source via a cable 25. In this embodiment, the work piece 21 forms the anode; the tool, i.e. the electrode 1, forms the cathode. This assembly is disposed in a known ECM-machine or a PEM-machine.
In step III, an electrolyte 32 is introduced by a nozzle 33 and via an intermediate space 32 into a working gap 50 between the electrode body 1 and the work piece 21. The desired material removal from the work piece 21 takes place thereby. For further details in this connection, reference is made to the known operating methods of ECM-machines or PEM-machines.
As shown in step IV, a desired cavity 35 is now produced in the work piece 21 by gradually adjusting the height of the electrode 1 and/or the work piece 21. This cavity 35 can then achieve a desired defined contour corresponding to the outer contour of the electrode body 1 that was fabricated by the layered-construction method.
In
The illustration in
As already explained in the background section,
In
a)-10h) show various surface structures that are producible on an electrode 1 for an ECM method according to the present invention. Thus, grooves, conductive channels, elevations, special-structured surfaces and surface gaps or the like can be made that improve the supply and discharge of electrolyte in the ECM method, or with which it can be better controlled where material removal from the work piece takes place.
In
The same also applies for the electrode body illustrated in
In
Finally,
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2004 057 527.4 | Nov 2004 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP05/10384 | 9/26/2005 | WO | 5/23/2007 |
