from a Component Made of an Alloy

Description

The invention relates to a process for the local removal of a metallic layer from a component made of an alloy. The invention relates further to a device of the type disclosed in the pre- characterizing clause of Patent Claim 13 for the local removal of at least one metallic layer from a component made of an alloy.

Such a process and such a device are already known from, for example, US 6 352 636 Bl . The device, which is used for the local removal of at least one metallic layer from a component made of an alloy for an aircraft engine, comprises an electrolyte bath, which is filled with an electrolyte fluid. The component being processed is immersed in the electrolyte bath, held in said bath by means of a holding device and coupled to an electrode. Then a direct current is applied between the electrode and a counter electrode arranged at a distance from the layer to be removed and the layer is removed electrochemically. The electrolyte fluid in this case makes the charge transport possible between the electrode and the counter electrode and transports the anodically removed layer material away. The layer to be removed and the component are, as a rule, made of different materials.

What must be viewed as the disadvantage of the known process or the known devices in this case is the fact that removal of the layer is associated with a comparatively high expense. In order to ensure local removal of the layer, those regions of the component that are not supposed to be decoated must be covered in advance with a protective layer such as wax. This produces a series of error sources, particularly, a protective layer that is hard to remove and the risk of seepage in the border areas can result in unintended damage to the layers to be protected and component areas. In addition, if the process is not used continuously, the electrolyte bath must be emptied, as the case may be, and filled with a correspondingly suitable electrolyte fluid depending on the layer or component materials. This increases production costs, intensifies the environmental impact and, last but not least, must be avoided in terms of industrial safety. The object of the present invention is creating a process as well as a device of the type mentioned at the outset which makes improved local decoating of a component possible.

The object is attained according to the invention by a process according to Patent Claim 1 as well as by a device having the features of Patent Claim 13. Advantageous embodiments of the invention are disclosed in the respective subordinate claims, wherein advantageous embodiments of the process are to be viewed as advantageous embodiments of the device and vice versa.

In the case of process according to the invention for the local removal of at least one metallic layer from a component made of an alloy, in particular a component for an aircraft engine, at least the following steps are conducted: a) Coupling the component to an electrode, b) Arranging at least one counter electrode at a distance from the layer to be removed, c) Arranging an electrolyte feed channel in the region of the counter electrode and at a distance from the layer to be removed, d) Generating an electrolyte fluid current in a gap between the counter electrode and the component by introducing electrolyte fluid into the gap through the electrolyte feed channel, and e) Applying an electrical voltage between the electrode and the counter electrode, wherein a level of the voltage is adjusted such that the resulting current is sufficient for the local removal of the layer. The description of the individual steps of the process in this case only serves as a better classification and does not necessarily represent the actual sequence of steps. Thus, it may be provided that the Steps a) to d) are conducted in a deviating sequence and/or simultaneously.

The process according to the invention makes an improved local decoating of the component possible, because the component need no longer be completely immersed in an electrolyte bath. This makes it possible to reliably prevent the entire component from functioning as the electrode during polarization when applying the voltage. Instead, an electric current can flow between the counter electrode and the component connected as the electrode via the electrolyte fluid current only on the region to be decoated. As a result, the layer is removed only within the local electrochemical cell that is generated in the process. Since this is a local decoating process, a covering or protective layer for the component regions that are not supposed to be decoated is not required in contrast to the prior art, thereby making it possible to carry out the process in a considerably quicker and simpler way. Consequently, no coverings or protective layers must be removed after decoating either, thereby achieving a further acceleration and price reduction of the production process. The electrolyte fluid can be collected as needed and be used, for example, in a cyclic process and/or be recycled. The process is suitable as a rule for the local removal of a layer made of a material other than that of the alloy of the component, for example for removal of a dimensional correction layer. Alternatively or additionally, the process may also be used to remove a layer of the alloy of the component, for example in the course of a precision machining step.

An advantageous embodiment of the invention provides that the electrode be connected as an anode and/or the counter electrode be connected as a cathode. This allows an especially reliable local decoating of the component to be performed, wherein most layer/component material pairings may be processed in this manner.

Additional advantages are produced if the level of the voltage in Step e) is set between 4 V and 14 V, in particular between 6 V and 12 V and/or set in such a way that the electrochemical removal of component material is limited essentially to the region of the layer to be removed. This ensures an especially precise and reliable removal of the layer without impairing adjacent component regions and without undesired modification of the component.

A further advantageous embodiment of the invention provides that the counter electrode in Step b) and/or the electrolyte feed channel in Step c) be arranged at a distance of between 100 μπι and 1.5 mm from the layer to be removed. As a result, different component geometries may be taken into account, on the one hand, and a reliable and process-safe contacting between the electrode and the counter electrode via the electrolyte fluid can be ensured on the other.

In another embodiment of the invention it has been shown to be advantageous if the component moves relative to the counter electrode before and/or during Step e), in particular rotates around a component axis. In this way, layers with any geometric design may be removed locally. Thereby it may basically be provided that the component be moved with respect to the stationary counter electrode, that the counter electrode be moved with respect to the stationary component and/or that both the component as well as the counter electrode be moved. In this case, the electrolyte feed channel is preferably moved along with the counter electrode. By rotating the component around a component axis, it is possible in particular for a rotationally symmetrical layer of the component to be removed especially quickly and simply.

Additional advantages are produced by a speed of the movement being selected in such a way that the electrochemical removal of component material is essentially limited to the region of the layer to be removed. This type of speed control simply and reliably prevents an undesired modification of component regions that are not supposed to be decoated.

At the same time it has been shown in another embodiment to be advantageous if a counter electrode is used which is configured to be one piece with the electrolyte feed channel in Step b). As a result, because of the low space required for the counter electrode, components with challenging geometries or inside surfaces may also be decoated reliably and simply. Moreover, this ensures an especially process-safe contacting between the component and the counter electrode via the electrolyte fluid. In addition, arranging and moving the counter electrode are simplified, because the electrolyte feed channel is automatically moved along with it and is therefore always positioned optimally.

In this case, another embodiment provides that a chemical composition of the electrolyte fluid and/or a relative position of the counter electrode with respect to the component are selected such that the electrochemical removal of the component material is limited, at least essentially, to the region of the layer to be removed. Adjusting the cited process parameters in such a way simply and reliably prevents an undesired modification of component regions that are not supposed to be decoated.

It has been shown to be advantageous in another embodiment of the invention if an integrally bladed rotor of an aircraft engine, in particular a blisk and/or a bling, and/or a component made of a high-temperature-resistant alloy, in particular a titanium-based, nickel-based and/or cobalt- based alloy, is used as a component and/or a layer made of a nickel-based alloy, in particular of a NiCrAI alloy, is locally removed. This allows an especially precise production of high-quality components for aircraft engines, wherein both the cost of the process necessary for said production and the processing time are significantly reduced.

In order to obtain an especially quick removal of the respective layer of the component, it was shown to be advantageous in another embodiment if an electrolyte fluid comprised of an inorganic acid, in particular nitric acid, and/or an electrolyte fluid comprised of a base, in particular an inorganic lye, are used in Step d). With the exception of carbonic acid and the acids derived from it, all acids that do not contain any carbon should be understood as inorganic acids in this case e.g., sulfuric acid, nitric acid, phosphoric acid, hydrochloric acid, silicic acid or boric acid. The use of nitric acid has been shown to be particularly advantageous in conjunction with the removal of a layer from a component made of a titanium alloy, because titanium alloys behave passively with respect to nitric acid. As a result, an undesired modification of the component after the local removal of the layer is advantageously precluded. Alternatively or additionally, the electrolyte fluid may be comprised of a base. In this case, all compounds which are in a position to form hydroxide ions in an aqueous solution should be understood as a base. The use of an electrolyte fluid comprising a base is, for example, advantageous in the processing of nickel-based materials. The inorganic acid and/or the base can be present in this case in a concentrated and/or diluted form. In this case, it may also be provided that the electrolyte fluid is comprised exclusively of an inorganic acid or exclusively of a base.

A further advantageous embodiment of the invention provides that at least two counter electrodes and/or at least two electrolyte feed channels are used for the local removal of a layer and/or of at least two layers. This allows a further acceleration of the process to be achieved. When using at least two counter electrodes, they may, for example, be assigned different voltage amplitudes, whereby two or more layers made of different materials may be easily taken into consideration and may be removed simultaneously. Alternatively or additionally, the two or more counter electrodes may be used for especially quick removal of large layers. Correspondingly, the two or more electrolyte feed channels make simultaneous removal of two or more layers and/or of large layers possible. In addition, different electrolyte fluids may be introduced simultaneously using the at least two electrolyte feed channels, whereby different material properties of different layers may be taken in consideration in an optimal manner. In this case, it may be provided that the at least two counter electrodes and/or the at least two electrolyte feed channels are moved relative to each other during the process.

Additional advantages are yielded in that at least two different counter electrodes and/or at least two different electrolyte feed channels are used. The counter electrodes and/or electrolyte feed channels may each differ in this case with respect to their geometry and/or their material, whereby there is an optimum adaptability to different components, to different layers to be removed and to different electrolyte fluids. In addition, for example, different materials may be provided for the counter electrodes and/or the electrolyte feed channels, if it is not possible to produce different geometries with a single material.

A further aspect of the invention relates to a device for the local removal of at least one metallic layer from a component made of an alloy, in particular a component for an aircraft engine, wherein an improved local decoating of the component is rendered possible according to the invention in that the device comprises an electrolyte feed channel, which is arranged in the region of a counter electrode of the device and the layer to be removed, and via which an electrolyte fluid can be introduced into the gap via the electrolyte feed channel for generating an electrolyte fluid current in a gap between the counter electrode and the component. The device according to the invention renders an improved local decoating of the component possible because the component need no longer be completely immersed in an electrolyte bath. Therefore, it is possible to reliably prevent the entire component from functioning as the electrode during polarization of the component. Instead, a contact closure between the counter electrode and the component connected as the electrode occurs only on the region to be decoated via the electrolyte fluid current. As a result, the device removes the layer only within the local electrochemical cell that is generated in this process. Because the device makes local decoating possible, a covering or protective layer for the component regions that are not supposed to be decoated is also not required in contrast to the prior art. Consequently, no coverings or protective layers must be removed after decoating either, thereby making a substantial acceleration and price reduction of the production process possible. The electrolyte fluid may be collected as needed and be used, for example, in a cyclic process and/or be recycled. The process is suitable as a rule for the local removal of a layer made of a material other than that of the alloy of the component, for example for removal of a dimensional correction layer. Alternatively or additionally, the process may also be suitable for the removal of a layer of the alloy of the component, for example in the course of a precision machining step. The preferred embodiments and further developments presented in conjunction with the process according to the invention as well as their advantages are applicable correspondingly for the device according to the invention and vice versa.

An advantageous embodiment of the invention provides that the counter electrode and the electrolyte feed channel be configured as one piece. Because of this, the counter electrode and the electrolyte feed channel have an especially low requirement for space, so that even components with challenging geometries or inside surfaces may be decoated reliably and simply. In addition, this makes an especially process-safe contacting possible between the component and the counter electrode via the electrolyte fluid. In addition, arranging and moving the counter electrode are simplified, because the electrolyte feed channel is automatically moved along with it and therefore always positioned optimally.

Additional advantages are produced by the electrolyte feed channel containing a preferably removable nozzle by means of which the electrolyte fluid current can be guided. This allows a particularly precise generation and adjustment of the electrolyte fluid current so that even comparatively small, comparative large and/or geometrically challenging layers may be removed reliably. The nozzle may basically be configured for focusing, for fanning out and/or for spraying the electrolyte fluid. It may also be provided that the nozzle possesses a modifiable geometry. By configuring the nozzle to be removable, it is possible to make different nozzles available and for them to be replaced and mounted correspondingly quickly and simply. As a result, a nozzle that is optimally adapted to the respective intended use may always be used.

Another advantageous embodiment of the invention provides that the counter electrode be made of a metal alloy, in particular a titanium alloy and/or a high-grade steel. In this case, the counter electrode features a particularly high mechanical and chemical resistance with simultaneously low manufacturing costs. An analogous situation applies to the electrolyte feed channel, if the counter electrode and the electrolyte feed channel are configured to be one piece. A titanium alloy, a stainless steel or the like may be used as the metal alloy.

By designing the holding device to move the component relative to the counter electrode, in particular to rotate around a component axis, layers with any geometric design may be locally removed. In this case, it may basically be provided that the component be moved with respect to the stationary counter electrode, that the counter electrode be moved with respect to the stationary component, and/or that the component as well as the counter electrode can be moved independently of each other. In this case, it is preferred that the electrolyte feed channel is able to move along with the counter electrode. Because it is possible to rotate the component around a component axis, a rotationally symmetrical layer in particular may be removed especially quickly and simply.

In another advantageous embodiment of the invention, the electrolyte feed channel is configured to be flexible and/or rigid and/or be bordered by a wall made of a metallic and/or non-metallic material. This allows for a high level of structural flexibility of the device and a simple adaptability of the electrolyte feed channel to different use profiles.

Additional advantages are produced, if a preferably removable splashguard device is arranged in the region of the electrolyte feed channel to limit the electrolyte fluid current. By using a splashguard device, the electrolyte fluid may be used especially efficiently, because even with higher flow rates, there are no material losses due to lateral splashing in particular. In addition, an undesired modification of regions of the component that are not to be decoated is particularly reliably prevented and industrial safety is further improved. Due to the fact that the splashguard device is configured to be removable, it can be mounted on or removed from the device quickly and simply so that a splashguard device that is optimally adapted to the geometric circumstances and/or to the electrolyte fluid being used may always be used. In this case, it may be provided that the splashguard device be arranged in an end region of the electrolyte feed channel or in the region of a nozzle on the electrolyte feed channel.

Additional features of the invention are disclosed in the claims, the exemplary embodiment as well as on the basis of the drawings. The features and combinations of features cited above in the description as well as the features and combinations of features cited subsequently in the exemplary embodiment are usable not only in the respectively indicated combination, but also in other combinations or alone without leaving the scope of the invention. The drawings show:

Fig. 1 A schematic diagram of a device for the local removal of a metallic layer from a component for an aircraft engine;

Fig. 2 An enlarged representation of Detail II shown in Fig. 1 ;

Fig. 3 A schematic diagram of an alternative embodiment of a counter electrode and of an electrolyte feed channel of the device, wherein a splashguard device is also provided;

Fig. 4 A part of a schematic diagram of an alternative embodiment of the device for removing a large layer; and

Fig. 5 A part of a schematic diagram of the device shown in Fig. 4, wherein two layers are removed simultaneously from one component.

Fig. 1 shows a schematic diagram of a device 10 for the local removal of a metallic layer 12 from a component 14, which is configured here as a blisk (bladed disk) that is known per se for an aircraft engine. Fig. 1 will be explained in the following together with Fig. 2, in which an enlarged representation of Detail II depicted in Fig. 1 is illustrated. The metallic layer 12 is a dimensional correction layer made of a NiCrAl alloy. For its part, the component 14 is made of a titanium alloy (Ti-834: Ti-5,8 Al-4 Sn-3,5 Zr-0,7 Nb-0,5 Mo-0,35 Si-0,06 C), which is nonmagnetic and has a high tensile strength and creep resistance up to approx. 600°C along with a very good fatigue strength. The layer 12 in this case runs annularly along an inside circumference of the component 14.

The device 10 features a holding device 16, which is used to hold the component 14 and according to Arrow I can be rotated around a component axis A. In addition, the device 10 includes an electrode 18 coupled to the component 14, which is connected here as an anode via a control and/or regulating unit (not shown) of the device 10. Arranged at a distance from the layer to be removed 12 is a counter electrode 20, which is connected via the control and/or regulating unit as a cathode. Finally, the device 10 includes an electrolyte feed channel 22, which is configured as one piece with the counter electrode 20 in the depicted exemplary embodiment and by means of which electrolyte fluid 24 can be introduced for generating an electrolyte fluid current in a gap S between the counter electrode 20 and the component 14. As is shown particularly clearly in Fig. 2, the electrolyte feed channel 22 or the counter electrode 20 configured as one piece with said electrode feed channel has a nozzle 26, by means of which the electrolyte fluid current can be focused. In other words, the counter electrode 20 functions simultaneously as a discharge nozzle for the electrolyte fluid 24. In the case at hand, concentrated and/or diluted nitric acid is used as the electrolyte fluid 24. This thereby ensures that the regions of the component 14 that are not supposed to be removed are not harmed, because titanium or the titanium alloy Ti-834 used behaves electrochemically passively in nitric acid. The counter electrode 20, which simultaneously forms the wall bordering the electrolyte feed channel 22, is also made of a titanium alloy and is therefore also not affected by the nitric acid.

For the local removal of the layer 12, the component 14 is first of all fastened to the holding device 16 and coupled to the electrode 18. Then the counter electrode 20 and the electrolyte feed channel 22 configured as one piece with said counter electrode are arranged at a distance of between approx. 100 μηι and approx. 1.5 mm from the layer to be removed 12, thereby forming the gap S. After positioning, the component 14 is put into a slow rotation around the component axis A via the holding device 16. Thereupon, the electrolyte fluid 24 is continuously introduced into the gap S via the electrolyte feed channel 22, whereby the electrolyte fluid current electrically connecting the counter electrode 20 to the component 14 or the electrode 18 is generated. Then, an electric voltage is generated between the electrode 18 and the counter electrode 20 by means of the control and/or regulating unit, thereby locally anodically dissolving and removing the layer 12 over the entire circumference of the component 14 due to the rotational movement. The level or the amplitude of the voltage in this case is set in such a way that the resulting current is sufficient to locally remove the layer 12. In the case of the material pairing here, a voltage between 4 V and 14 V, in particular between 6 V and 12 V, has proven to be suitable. A contact closure takes place only at those points at which the electrolyte fluid 24 encounters the component 14. As a result, the layer 12 is removed only within the "local electrochemical cell" formed hereby. It can be provided in this case that the level of voltage is varied as a function of the time and/or of the decoating progress. Alternatively or additionally, the spatial location or the distance between the counter electrode 20 and the component 14 may be varied as a function of the time and/or of the decoating progress.

Due to the locally confined effect of the decoating process described in the foregoing, other layers 28 of the component 14 do not need to be covered or otherwise protected if they are made of the same material as the layer 12. However, because a contact between the electrolyte fluid 24 and surrounding component material frequently cannot be completely avoided, it can be provided that different process parameters such as voltage, selection of the electrolyte fluid 24, rate of flow of the electrolyte fluid 24, rotation speed and position of the component 14 may be selected such that an undesired modification of the regions of the component 14 that are not supposed to be decoated is reliably prevented and the removal is confined to the layer 12.

Fig. 3 shows a schematic diagram of an alternative embodiment of a counter electrode 20 and an electrolyte feed channel 22 of the device 10 that is again configured to be one piece with said counter electrode. In contrast to the foregoing exemplary embodiment, a splashguard device 30 for limiting the electrolyte fluid current is arranged in the region of the electrolyte feed channel 22 or the nozzle 26. Electrolyte fluid 24 splashing off the component 14 is collected in this case with the aid of the splashguard device 30 so that no undesired fluid losses occur, an undesired modification of regions of the component 14 that are not supposed to be decoated is avoided in a particularly reliable manner and in addition, industrial safety is improved. The splashguard device 30 in this case can be removed from the electrolyte feed channel 22 or the counter electrode 20 and thus may be replaced quickly and simply for an alternative splashguard device 30 in order to make an optimum adaptation to different component types and component geometries possible. P T/IB2010/002210

12

Fig. 4 shows part of a schematic diagram of an alternative embodiment of the device 10 for the removal of a large layer 12 from a component 14. In contrast to the previous exemplary embodiments, the device 10 shown here includes two counter electrodes 20a, 20b and two electrolyte feed channels 22a, 22b. The counter electrode 20a and the electrolyte feed channel 22a as well as the counter electrode 20b and the electrolyte feed channel 22b are respectively configured as one piece and arranged side by side. Nozzles 26a, 26b are attached to the end regions of the electrolyte feed channels 22a, 22b respectively, by means of which the currents of the electrolyte fluids 24a, 24b may be guided. As a result, the comparably large layer 12 may be locally removed in the above-described manner in one process step, thereby yielding advantages in terms of time and cost.

Fig. 5 shows part of a schematic diagram of the device 10 depicted in Fig. 4, wherein two geometrically different layers 12a, 12b that are spatially separated from one another are simultaneously removed from a component 14. For this purpose, in contrast to the foregoing exemplary embodiment, two geometrically different counter electrodes 20a, 20b and two geometrically different electrolyte feed channels 22a, 22b are used. The counter electrode 20a and the electrolyte feed channel 22a as well as the counter electrode 20b and the electrolyte feed channel 22b are again respectively configured as one piece and arranged at a distance from one another. In this case, it can basically be provided that the counter electrodes 20a, 20b and the electrolyte feed channels 22a, 22b can be moved relative to each other so that different relative distances or spatial alignments may be adjusted before or during the process. Alternatively or additionally, gaps S of different sizes may be adjusted between the electrolyte feed channels 22a, 22b and the layers 12a, 12b. Geometrically different nozzles 26a, 26b are attached to the end regions of the electrolyte feed channels 22a, 22b, by means of which the electrolyte fluid currents 24a, 24b may be guided to the respective layer 12a, 12b in a targeted manner. Alternatively or additionally, it may be provided that at least one of the nozzles 26a, 26b features a modifiable geometry in order to make a particularly precise adjustment of the electrolyte fluid current to the respective layer 12a or 12b possible.

The parameter values disclosed in the documents for defining process and measuring conditions for characterizing specific properties of the subject of the invention are to be viewed as included in the scope of the invention even in terms of deviations, e.g., due to measuring errors, system errors, weighing errors, DIN tolerances and the like.