Abstract:
The invention relates to a device ( 10 ) for electrochemically removing a surface of a component ( 2 ), in particular a blade of an integrally bladed rotor, comprising at least one electrode ( 12 ), which has an outer contour that corresponds to a surface of the component to be produced, and a hydraulic pressure device ( 14 ), which has a pressure piston ( 16 ) coupled to the electrode ( 12 ) and a hydraulic chamber ( 18 ) in operative connection with the pressure piston ( 16 ) for receiving the hydraulic medium, wherein the pressure piston can be loaded with an actuating force and moved relative to the hydraulic pressure device ( 14 ) by means of the hydraulic medium, wherein the hydraulic chamber ( 18 ) is fluidically encapsulated relative to the pressure piston ( 16 ). The invention further relates to a method for electrochemically removing a surface of a component ( 2 ).

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a U.S. National Phase application submitted under 35 U.S.C. §371 of Patent Cooperation Treaty application serial no. PCT/DE2010/000791, filed Jul. 8, 2010, and entitled DEVICE AND METHOD FOR ELECTROCHEMICALLY REMOVING A SURFACE OF A COMPONENT, which application claims priority to German patent application serial no. 10 2009 032 563.8, filed Jul. 10, 2009, and entitled VORRICHTUNG UND VERFAHREN ZUM ELEKTROCHEMISCHEN ABTRAGEN EINER OBERFLÄCHE EINES BAUTEILS. 
     Patent Cooperation Treaty application serial no. PCT/DE2010/000791, published as WO 2011/003400, and German patent application serial no. 10 2009 032 563.8, are incorporated herein by reference. 
     TECHNICAL FIELD 
     The invention relates to a device and a method for electrochemically removing a surface of a component. 
     BACKGROUND 
     Such a device and such a method can already be found as known from EP 1 900 466 A1. The device disclosed there comprises multiple electrodes, each having an outer contour corresponding to a surface of the component to be produced. In addition, the device comprises as the hydraulic pressure device a plurality of hydraulic pressure cylinders, each having a pressure piston coupled to an electrode and a hydraulic chamber which is operatively connected to the pressure piston. For moving the respective electrode, hydraulic medium is pumped between the two partial chambers of the hydraulic chamber so that opposing active surfaces of the pressure piston can be acted upon alternately with an actuating force by means of the hydraulic medium. In this way, the pressure piston can be moved within the hydraulic chamber in relation to the chamber, so that the electrode coupled to the pressure piston via a thrust rod is moved toward or away from the component accordingly. The component to be machined, which is designed as the blade of a rotor of a turbo machine, is essentially preformed and has an oversize dimension in the area to be machined, which is removed with the help of the electrodes via an electrochemical removal method (ECM and/or PECM), in which the component and the electrodes are arranged in an electrolyte and the surface of the component is removed in the area of the oversize dimension by applying an electric voltage and/or an electric current between the component and the at least one electrode. 
     One disadvantage of the known device is the fact that application of the desired actuating force to the pressure piston can be done only in a comparatively inaccurate and slow process, so that movement of the electrode coupled to the pressure piston is inaccurate and slow, in particular in the case of pulsed or periodic movements accordingly. Therefore, it is practically impossible to produce outer contours with small tolerances or this can be accomplished only at great effort and high production costs accordingly. 
     SUMMARY AND DESCRIPTION 
     The object of the present invention is to create a device and a method of the type defined in the introduction which will permit an improved and more precise production of an outer contour of a component. 
     This object is achieved according to the invention by a device having the features described and claimed herein and by a method having the features described and claimed herein for electrochemically removing a surface of a component. Advantageous embodiments with expedient refinements of the invention are also characterized herein, where advantageous embodiments of the device are to be regarded as advantageous embodiments of the method and vice versa. 
     In the case of a device according to the invention, which permits an improved and more precise production of an outer contour of a component, it is provided that the hydraulic chamber is fluidically encapsulated with respect to the pressure piston. In other words, it is provided that the pressure piston is not in direct contact with the hydraulic medium but instead can be acted upon indirectly by the actuating force transmitted by the hydraulic medium. In this way, in contrast with the state of the art, the number of surfaces to be sealed within the hydraulic pressure device is greatly reduced, so that a suitably improved, more precise and more rapid application of force by the pressure piston is made possible without any risk of leakage. The hydraulic pressure device may also be designed to be leak-free without seals, so that even very high fluid pressures can be created with no problem via the hydraulic medium while the surface is being removed. In addition, the pressure piston and/or the electrode coupled to it can be moved against a high electrolyte pressure such as that which may be necessary for example for rinsing a gap between the electrode and the component. Since the pressure piston is not arranged inside the viscous hydraulic medium, rapid movements of the electrode as well as high frequency vibrational movements which may optionally be superimposed on another movement can also be represented. This yields, on the one hand, a further increase in the mapping precision, while on the other hand, damage to the component is reliably prevented because of short circuits due to the precise movability of the electrode even at high relative speeds between the electrode and the component. Due to the increased precision, thus complex and cost intensive remachining steps can be avoided and shorter processing times can be achieved. Furthermore, the device according to the invention may be designed to be especially compact, lightweight and space-saving, so that a significant increase in the mapping accuracy is achieved even with components having complex geometries and surfaces that are close together. 
     An advantageous embodiment of the invention it is provided that the hydraulic chamber is fluidically encapsulated with respect to the pressure piston by means of an elastically deformable solid state joint, in particular a membrane. This is a simple and inexpensive option with a simple design for encapsulation of the hydraulic chamber, so that the hydraulic pressure devices can be designed to be free of seals in a particularly simple manner. To move the electrode, the solid state joint may be deflected into and/or out of the hydraulic chamber in the area of elastic deformations by supplying or removing hydraulic medium, so that the pressure piston can be acted upon with the corresponding actuating force via the solid state joint. 
     To permit a uniform movement between the pressure piston and the solid state joint over the entire contact surface, it has also proven advantageous if the solid state joint is designed in the form of a ring. 
     In another advantageous embodiment of the invention it is provided that the pressure piston is coupled to a housing of the hydraulic pressure device by means of at least one spring element, in particular an elastically deformable solid state joint. This creates a simple possibility of supporting the pressure piston irretrievably and movably on the hydraulic pressure device. The solid state joint may additional fulfill the function of a rotary bearing about which the pressure piston can be pivoted, much like a windshield wiper. Furthermore, with the help of the spring element, a zero position of the pressure piston can be defined easily. 
     Additional advantages are derived in that the hydraulic pressure device comprises a restoring device by means of which the pressure piston can be acted upon with a restoring force. In this way there is a simple possibility of moving the pressure piston back out of a deflected position and back into its zero position or further into a position opposite the zero position by acting upon it with the restoring force. In this way, a further improvement in precision in removing the surfaces achieved. Furthermore, pulsed or periodic vibrational movements can be represented especially easily and with high frequencies. Furthermore, with the help of the restoring device it is possible to define a maximum deflection of the pressure piston. 
     In another embodiment, it has proven advantageous if the restoring force comprises a spring element, in particular a solid state joint and/or an additional hydraulic chamber for receiving hydraulic medium. This permits a particularly variable structural embodiment of the device. 
     In another advantageous embodiment of the invention, it is provided that the additional hydraulic chamber is fluidically encapsulated with respect to the pressure piston, preferably by means of an elastically deformable solid state joint, in particular by means of a membrane. The resulting advantages are to be seen in conjunction with the hydraulic chamber explained above. It may preferably be provided that each hydraulic chamber of the hydraulic pressure device is fluidically encapsulated with respect to the pressure piston to permit a gasket-free embodiment of the hydraulic pressure device in a simple way. 
     To create a defined deflectability of the pressure piston and thus its respective electrode, in another embodiment of the invention it has proven advantageous if at least one stop is provided by means of which a movement of the pressure piston is to be limited. In this way an unwanted collision between the electrode and the component may be reliably prevented so that a consistently high component quality is ensured. It is possible to provide for at least two stops to be provided, by means of which opposing maximum deflections of the pressure piston are defined. 
     In another advantageous embodiment of the invention, it is provided that a regulating and/or control device is provided for generation an oscillating and/or pulsed actuating force on the pressure piston, preferably acting linearly. In this way, a variable vibrational movement of the pressure piston and/or the electrode can be generated so that forced rinsing of a gap between the electrode and the component with an electrolyte can be accomplished easily. 
     In another embodiment it has proven advantageous if the amplitude of the actuating force can be set at a value between 0.01 mm and 1.0 mm by means of the regulating and/or control device and/or a frequency of the actuating force can be set at a value between 0 Hz and 250 Hz. Optimal adaptability of the device to differently shaped surfaces and to different materials is made possible in this way. 
     In another advantageous embodiment of the invention, it is provided that the device is designed to arrange an axis of movement of the electrode at a predetermined and/or adjustable work angle, in particular at a work angle between 30° and 60° with respect to the axis of movement of the component. The axis of movement of the component is understood to be the axis along which a relative feed movement of the component toward the electrode is executed. Essentially the component and/or the device and/or the electrode may be moved. With the help of such a work angle, it is advantageously possible to rule out an excessive fluid pressure being able to build up between the electrode and the component, which could lead to bending of the component and/or the electrode. In addition, damage to the component due to short circuits is ruled out. 
     In another embodiment of the invention, it is provided that the device comprises at least one additional electrode which has an outer contour corresponding to another surface of the component to be produced, such that each electrode of the device is movable in relation to that component. In this way at least one additional surface of the component can be removed so that corresponding time and cost advantages can be achieved. It is possible to provide that at least two electrodes are to be moved via a shared pressure piston of the hydraulic pressure device. Alternatively, it is possible to provide that at least two pressure pistons are provided, each being coupled to at least one electrode and movable independently of one another. In the case of multiple pressure pistons, it has also proven advantageous for the reasons given above if the pressure piston is fluidically encapsulated with respect to its corresponding hydraulic chamber. 
     Since the device comprises at least two electrodes, which are movable in opposite directions toward one another in the direction of the component and then back again, opposing surfaces of the component can be removed simultaneously. For example, a suction side contour and a compression side contour of a blade of a rotor can thus be produced simultaneously in one pass. 
     To achieve an increased rate of mapping, it has also proven advantageous if an inlet channel for an electrolyte can be formed between at least two electrodes. In this way, the electrolyte required for the electrochemical removal can be introduced into the gap between the at least two electrodes and the surface of the component during the machining of a component. 
     Another aspect of the present invention is a method for electrochemically removing a surface of a component wherein at least the steps of providing a component, in particular a preformed component having an oversize dimension, providing at least one electrode which has an outer contour corresponding to a surface of the component to be produced and is coupled to a pressure piston of a hydraulic pressure device; the component and the at least one electrode are arranged in relation to one another in an electrolyte and the surface of the component is removed at lest in the area of the oversize dimension by applying an electrical voltage and/or an electric current between the component and the at least one electrode. An improved and more precise production of the outer contour of the component is made possible according to the invention by the fact that the pressure piston is brought into operative connection with a hydraulic chamber of the hydraulic pressure device fluidically encapsulated with respect to the pressure piston, and the pressure piston is acted upon by an actuating force at least temporarily by means of a hydraulic medium, while the surface is being removed and is moved in relation to the hydraulic pressure device. In other words, it is provided that the pressure piston is not in contact directly with the hydraulic medium but instead is acted upon indirectly by the actuating force transmitted through the hydraulic medium. In this way, in contrast with the state of the art, the number of surfaces to be sealed inside the hydraulic pressure device can be reduced substantially so that a suitably improved more precise and more rapid application of force by the pressure piston is possible without any risk of leakage. A hydraulic pressure device which is designed without seals may be used so that even very high fluid pressures can be generated via the hydraulic medium while the surface is being removed with no problem. In addition, the pressure piston and/or the electrode coupled to it may be moved against a high electrolyte pressure such as that which may be necessary for rinsing a gap between the electrode and the component, for example. Since the pressure piston is not arranged inside the viscous hydraulic medium, rapid movements of the electrode as well as high frequency vibrational movements which may optionally superimposed on an additional movement can also be achieved. In this way, there is on the one hand a further increase in the mapping accuracy, while on the other hand due to the more precise mobility of the electrode, damage to the component due to short circuits is reliably prevented even at high relative speeds between the electrode and the component due to the precise movability of the electrode. Because of the increased precision, complex and cost-intensive reworking steps can thus be avoided and shorter operating times can be achieved. Furthermore, a particularly compact, lightweight and space-saving device for removing the surface can be used so that a significant increase in the mapping accuracy can be achieved even on components having complex geometries and surfaces that are close together. Preferably the device used for removal of the surface is designed according to one of the preceding exemplary embodiments. 
     It has been found to be advantageous when two electrodes are provided and are moved in opposite directions toward one another in the direction of the component and then back again in removal of the surface. In this way, opposing surfaces of a component can be machined and removed simultaneously, which results in corresponding time and cost advantages. For example a suction side contour and a compression side contour of a blade for a turbo engine can be produced at the same time. 
     By superimposing a feed movement of the component along one axis of movement is superimposed on the movement of each electrode at least in removal of the surface, creating especially precise kinematics optimally adapted to the respective component geometry, which makes it possible to achieve high mapping precision in short process times. 
     Special cost advantages are obtained when a blade of a rotor, in particular an integrally bladed rotor is machined as the component because special time and cost reductions can be achieved here due to the high precision and speed of the method according to the invention. Furthermore, complex post-processing steps may be omitted. 
     Another aspect of the present invention relates to a hydraulic pressure device which has a pressure piston that is connectable to an electrode and a hydraulic chamber operatively connected to the pressure piston to receive the hydraulic medium, such that the pressure piston can be acted upon by an actuating force by means of the hydraulic medium and is movable in relation to the hydraulic pressure device. An improved and more precise production of the outer contour of the component according to the invention is made possible by the fact that the hydraulic chamber is fluidically encapsulated with respect to the pressure piston. The resulting advantages can be derived from the preceding descriptions. The hydraulic pressure device according to the invention is characterized in particular for use in an apparatus and/or a method according to any one of the preceding exemplary embodiments. 
     Additional features of the invention are derived from the claims, the exemplary embodiments and on the basis of the drawings. The features and combinations of features mentioned in the description above as well as the features and combinations of features mentioned in the exemplary embodiments below can be applied not only in the respective combinations indicated but also in other combinations or alone without going beyond the scope of the present invention 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In these drawings: 
         FIG. 1  shows a schematic sectional view of an apparatus known from the state of the art (i.e., prior art) for electrochemically removing a surface of a component; 
         FIG. 2  shows a schematic sectional view of an apparatus according to the invention for electrochemically removing a surface of a component; 
         FIG. 3  shows a schematic sectional view of a first exemplary embodiment of a hydraulic pressure device; 
         FIG. 4  shows a schematic sectional view of a second exemplary embodiment of a hydraulic pressure device; 
         FIG. 5  shows a schematic sectional view of a two electrodes of the apparatus shown in  FIG. 2  at the start of an electrochemical removal step; and 
         FIG. 6  shows a schematic sectional view of two electrodes of the apparatus shown in  FIG. 2  after conclusion of the electrochemical abrasion step. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a schematic sectional view of an apparatus  1  known from the state of the art for electrochemically removing a surface of a component  2  with the help of a pulsed electrochemical method (PECM). The component  2  which has an oversize dimension at least in the area to be removed is moved, forming a gap  3  in relation to the electrodes  4  of the apparatus  1 , wherein for reasons of simplicity, the hydraulic mechanisms of apparatus  1  which move the electrodes  4  have not been shown. The electrodes  4  are moved toward one another according to the double arrows  1   a  perpendicularly or in a circle with mechanical pulses superimposed, while component  2  executes a feed movement according to arrow  1   b  along an axis A of movement. Removal of the surface of the component  2  is performed with the help of an essentially known electrochemical method (ECM or PECM) at least in the area to be removed. Component  2  is an integrally bladed compressor impeller of a turbo machine. 
     The disadvantage of this machining is that the gap  3  between the electrodes  4  and the component  2  cannot be rinsed adequately in particular in the area of an annular space  3   a  and therefore a gradual advance with a larger gap  3  must be selected. The mapping precision in the annular space  3   a  is therefore low. When the rate of advance is increased however the risk of damage to the component  2  due to short circuits increases drastically. Furthermore, a synchronized superimposed vibrational movement of the component  2  is problematical because of its comparatively great mass. The known apparatus  1  has a comparatively high weight and a high need for design space in order to achieve the required rigidity for precise movement of the electrodes  4 . Since the tolerances of large machines are naturally greater because of the heat influence and the effect of long lever arms, so substantial effort is involved in producing components  2  with small tolerances. 
       FIG. 2  shows a schematic sectional view of an apparatus  10  according to the invention for electrochemical removal of a surface of a component  2 , which is present in the form of a blade of an integrally bladed rotor. The apparatus  10  comprises two electrodes  12  arranged opposite one another, each having an outer contour corresponding to a surface of the component  2  to be produced. A hydraulic pressure device  14  is allocated to each electrode  12 , each hydraulic pressure device  14  having a pressure piston  16  coupled to the respective electrode  12  and having a hydraulic chamber  18  for holding hydraulic medium, operatively connected to the pressure piston  16 . The hydraulic medium may be introduced into the hydraulic chambers  18  through corresponding supply channels  20  according to the arrows IIa so that the pressure pistons  16  are acted upon with an actuating force by means of the hydraulic medium and are moved in relation to the respective hydraulic pressure device  14 . Accordingly by removing the hydraulic medium out of the hydraulic chambers  18  against the direction of the arrows IIa, a termination of application of the actuating force can be achieved so that the electrodes  12  coupled to the pressure pistons  16  can be moved toward the component  2  or away from it according to the double arrows IIa. The movement of the electrodes  12  is controlled by a regulating and/or control unit of apparatus  1  (not shown) so that for example a linearly oscillating or pulsed actuating force can be produced on the pressure piston  16  and a corresponding vibrational or pulsed movement of the electrodes  12  can be produced. For example, the amplitude of the actuating force may be set at a value between 0.01 mm and 1.0 mm and/or a frequency of the actuating force may be set at a value between 0 Hz and 250 Hz. 
     The apparatus  10  is designed for minimal dimensions so that the length of its elements shown here, i.e., the length of the hydraulic pressure devices  14  and the electrodes  12  amounts to no more than five times the surface length of the component  2  to be machined. Essentially, the hydraulic pressure devices  14  can be manufactured by so-called rapid manufacturing methods because of their compact and simple structure, so this yields corresponding cost advantages. 
     The apparatus  10  is designed so that the axes of movement of the electrodes  12  symbolized by the double arrows IIb are arranged at a work angle of approx. 45° to the axis A of the movement of component  2 . In this way, a forced rinsing of a narrow gap  22  between the component  2  and the electrodes  12  with electrolyte can be achieved in the blade area as well as in the annular space of the component  2  with an appropriately accurate design of the outer contour of the electrodes  12 . In addition, there is the possibility of moving the electrodes  12  perpendicularly toward the component  2  or away from it according to the arrows IIc and/or moving the component  2  toward the electrodes  12  and/or away from them along the axis of movement A according to the arrows IId. For example, speeds on the order of 0.01 m/min to 2.50 mm/min may be provided here. The advancing movements of the electrode feed and the component feed may be embodied as conventional NC axes. 
     The electrolyte may in turn be supplied according to the arrows IIe, so that the two electrodes  12  form a feed channel  24  for the electrolyte. Then an electric voltage, preferably a pulsating DC voltage and/or an electric current preferably a pulsating DC current is applied between the component  2  and the electrodes  12  for removal of the surface of the component  2  at least in the area of the oversize dimension. 
     The movement of the electrodes  12  at the angle of feed with a high mapping precision and short processing times at the same time is achieved through the specially designed apparatus  10 . As shown in  FIG. 2  the hydraulic pressure devices  14  are each embodied as compact movement units, such that the two hydraulic chambers  18  are both fluidically encapsulated with respect to their respective pressure pistons  16  by the corresponding solid state joints  26 . The hydraulic pressure devices  14  are thus free of seals and act on the pressure pistons  16  exclusively with elastic deformation of the solid state joint  26 . With the help of the apparatus and/or the hydraulic pressure devices  14 , essentially a significant increase in the mapping precision of the component  2 , a significant reduction in size and cost reduction of the apparatus  10  and an increased quality of the components  2  produced in this way are made possible. 
       FIG. 3  shows a schematic sectional view of a first exemplary embodiment of the hydraulic pressure device  14  which is suitable for use in the apparatus  10  shown in  FIG. 2 . For reasons of simplicity, the pressure piston  16  is not shown. The hydraulic pressure device  14  comprises a housing  28  which forms the base body. The solid state joint  26 , which is embodied as a membrane in an annular shape is integrated into the housing  28 . By supplying the hydraulic medium according to arrow IIa to the hydraulic chamber  18 , which also has an annular shape, an actuating force is generated on the pressure piston  16  applied to the solid state joint  26 . To move the pressure piston  16  back into its zero position, the housing  28  comprises a resetting device  30 , which is designed in the present case as a solid state joint integrally embodied in the housing  28  and by means of which the pressure piston  16  can be acted upon by a restoring force acting opposite the actuating force. 
       FIG. 4  shows a schematic sectional view of a second exemplary embodiment of the hydraulic pressure device  14 . In contrast with the exemplary embodiment shown previously, the housing  28  consists of a housing top part  28   a  and a housing bottom part  28   b . The pressure piston  16  is connected to the housing  28  of the hydraulic pressure device  14  by means of two spring elements  32  so that its zero position is defined. The spring elements  32  are also designed as elastically deformable solid state joints. The housing top part  28   a  and the housing bottom part  28   b  each comprise a hydraulic chamber  18   a  and  18   b , which is in turn encapsulated in fluid-tight manner with respect to the pressure piston  16  by means of solid state joints  26 . By pumping the hydraulic fluid through the supply channels  20   a ,  20   b  according to the double arrow IIa, the pressure piston  16  may be acted upon with an actuating force or a restoring force. The movement of the pressure piston  16  is limited by two stops  34   a ,  34   b.    
       FIG. 5  shows a schematic sectional view of the two electrodes  12  of the apparatus  10  shown in  FIG. 2  at the start of an electrochemical removal step in which the electrodes  12  are moved with an oscillating vibrational movement according to the double arrow V. The amplitudes thereby implemented are between 0 and 1 mm at a frequency of 0 to 250 Hz. 
       FIG. 6  shows a schematic sectional view of the electrodes  12  of the apparatus  10  shown in  FIG. 2  after conclusion of the electrochemical removal step. The exact image of the outer contour of the electrodes  12  on the surface of the component  2  is discernible here in particular. 
     The parameter values given in the documents for defining process and measurement conditions for characterization of specific properties of the subject matter of the invention are also to be regarded as covered within the context of the invention—also within the realm of deviations for example due to measurement errors, system errors, weighing errors, DIN tolerances and the like.