Abstract:
A method for electrochemically processing a workpiece surface using an electrode, which has at least one effective surface for processing the workpiece surface, and using an electrolyte, wherein the electrolyte is suctioned away from the effective surface. The invention further relates to an electrode, which has at least one electrolyte feed for supplying the electrolyte to the effective area and an electrolyte suctioning system for suctioning the electrolyte away from the effective area.

Description:
The present invention relates to a method for electrochemically machining a workpiece, and to an electrode for carrying out such a method. 
     BACKGROUND 
     Electrochemical machining (ECM) and pulsed electrochemical machining (PECM) make it possible to machine workpiece surfaces very precisely and without stress to the material. In this process, a potential differential is built up between a workpiece that serves as the anode and an electrode that serves as the cathode or tool and that is positioned across from the workpiece area that is to be machined, after which material is removed from the workpiece via an electrolyte, for example, a saline solution. Since the electrode usually replicates the desired contour of the workpiece surfaces that are to be machined, the workpiece area can be machined virtually in one step. 
     Electrochemical machining can be traced back to a Russian development and was already patented back in 1929 at the German Reich Patent Office under number DE 565765. The main difference between the ECM method and the PECM method is that with the PECM method, the electrode executes a pulsed motion in the advancing direction, so that a narrow machining gap filled with the electrolyte is opened or enlarged between the electrode and the workpiece, as a result of which the spent electrolyte can drain away more easily. 
     A problematic aspect encountered in electrochemical machining, however, is the control of the electrolyte flow. This is why German patent application DE 1515195 A1 proposes an electrode consisting of a plurality of partial electrodes that are electrically insulated from each other and that are actuated or activated as a function of a relative position between the electrode and the workpiece. 
     By the same token, German patent application DE 10 2007 023 494 A1, particularly in order to form fluid bearings, discloses the approach of providing electric insulation on the surfaces areas of an electrode from which no material is to be removed. 
     German patent application DE 10 2004 040 217 A1 of the applicant describes an ECM/PECM method for forming a cavity in a workpiece. The workpiece is placed in an electrolyte immersion bath and an energized electrode is sunk into the workpiece. However, it has been found that the resultant side surfaces of the cavity created in the workpiece, that is to say, the workpiece surfaces that are parallel to the advancing direction or the workpiece surfaces that delimit a side gap with the electrode, are formed with inferior surface quality than a bottom surface of the cavity in the workpiece, which requires subsequent machining of the side surfaces of the workpiece, as a result of which disturbances can occur in the transition area leading to the bottom surface of the workpiece. 
     Even though electrodes with retractable partial electrodes are known, their mechanical implementation is very complicated. It is also a known procedure to machine the cavity in two stages, so that the bottom surface is machined first, and then the side surfaces of the cavity. In this process, the side surfaces are sunk with a special electrode that is moved as orthogonally as possible with respect to the side surfaces. A drawback of this known variant is especially the fact that it has to be carried out with a double set of electrodes and that, when the side surfaces are sunk, a certain amount of etching can occur in the area of the bottom surface. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a method and an electrode that overcome the above-mentioned drawbacks and that allow a systematic control of the electrolyte flow and thus a localized activation of individual areas of the electrode surfaces. 
     The present invention provides a method for electrochemically machining a workpiece with an electrode that has at least one active surface for sinking a workpiece surface and with an electrolyte is characterized in that the electrolyte is suctioned off the active surface. As a result, the electrolyte flow is restricted only to the active surface or to the active area of the electrode that is actually needed, so that workpiece material is removed only there. The surface areas of the electrode adjacent to the active surface are and remain dry, so that, for example, no removal or caustic attack occur in the side gap when a workpiece surface is sunk. The electrolyte flow is systematically controlled via the active surface, and individual electrode surface areas are activated locally. Furthermore, the suctioning allows an economical use of the electrolytes since there is no a need for an immersion bath nor does the spent electrolyte drain away in an uncontrolled manner. 
     Preferably, the electrolyte is fed in at the center of the active surface and suctioned off at the edge area of the active surface. In this embodiment, the electrolyte suctioning means virtually surrounds the electrolyte feed means, as a result of which any accidental activation of adjacent electrolyte surfaces is effectively prevented. Depending on the size of the active surface, it can be advantageous to carry out an additional suctioning procedure in the center area. 
     In one embodiment, the electrolyte passes through the electrode all the way to the active surface and is then suctioned off the active surface through the electrode. This creates an electrolyte circuit in the electrode, thus allowing a very compact construction of the technical device. 
     In a method for forming a cavity, the electrode is positioned across from a workpiece surface that is to be machined. The active surface is then defined by switching on the electrolyte circuit comprising an electrolyte feed means and an electrolyte suctioning means. Subsequently, a cathode voltage is applied and the electrode is moved in the advancing direction until the workpiece surface has been machined to its desired contour. Then the cathode voltage is switched off, the advancing movement is halted and the electrolyte flow is interrupted. The electrolyte suctioning means is switched off as soon as the machined workpiece surface is dry. Then the above-mentioned steps are repeated until all of the workpiece surfaces to be machined such as, for instance, the side surfaces of the cavity, have been machined, whereby the advancing direction and the active surface change as a function of the workpiece surfaces that are to be machined. This multi-axial method is especially well-suited for shaping the cavity with an undercut or for shaping workpiece surfaces that are at some other angle relative to each other. In particular, with this method, the entire electrode, in other words, all of the potential active areas, can be energized at all times since the electrolyte is only fed to the active area that is needed at a given moment and it is then suctioned off the active area, at least in the edge area, so that the adjacent potential active surfaces are dry and no material is removed by them. 
     An electrode according to the invention and intended for electrochemically machining a workpiece has at least one active surface. According to the invention, at least one electrolyte feed means for feeding electrolytes to the active surface and one electrolyte suctioning means for suctioning the electrolyte off the active surface are configured in the electrode. In particular, the electrode according to the invention allows the systematic localized activation of individual active surfaces, so that it is suitable especially for electrochemical methods such as the formation of a cavity having precise bottom and side surfaces. The solution according to the invention makes it possible to dispense with known measures such as protective currents, passivation or selective caustic attack. Consequently, the resources needed in terms of equipment and control technology are very limited; in particular, the entire electrode can be energized at all times since the electrolyte is systematically fed to the active surface and then suctioned off it, so that adjacent areas of the electrode are or remain dry. 
     In one embodiment, the electrolyte feed means and the electrolyte suctioning means comprise a plurality of channels that exit from the active surface in the form of a pattern of perforations. The channels can be created, for instance, mechanically by means of a drill, although it is also conceivable to create the entire electrode by means of a generative manufacturing process. 
     In order to also increase the replication precision, however, the active surface can have a porous surface structure that is in fluid communication with the channels. 
     The electrode can be assembled like a module out of a plurality of segments that each have at least one active surface. As a result, the electrodes can be manufactured with any desired geometry and dimensions easily and inexpensively. 
     The segments can be electrically insulated from each other by means of an insulating layer, so that even in the unlikely eventuality that the electrolyte drains into non-activated surface areas of the electrode adjacent to the active surface, removal or caustic attack in this area is effectively prevented. 
     Further advantageous embodiments of the present invention are the subject matter of additional subordinated claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       An embodiment of the invention will be described in greater detail below making reference to the schematic drawings. The following is shown: 
         FIG. 1 : a cross section through an electrode according to the invention, and a first method step for creating a cavity, and 
         FIG. 2 : a second method step for creating the cavity. 
     
    
    
     DETAILED DESCRIPTION 
     In the figures, the same structural elements bear the same reference numerals whereby, for the sake of clarity, if there are several of the same structural elements in one figure, only a few of them are provided with a reference numeral. 
       FIG. 1  shows a cross section through an electrode  1  according to the invention, for purposes of creating a cavity  2  in a workpiece  4 . 
     The cavity  2  that is to be created is indicated by the dotted line and, in its cross section, it should have a bottom surface  6  which, in this embodiment, runs parallel to the surface  8  of the workpiece  4 , a side surface  10  which extends at a right angle between the bottom surface  6  and the top surface  8 , as well as a side surface  12  situated on the opposite side, which is arranged with respect to the bottom surface  6  and the top surface  8  in such a way that an undercut  14  is formed. 
     The electrode  1  has an electrode element that, like a module, consists of a base segment  18  and a side segment  20 , which are electrically insulated from each other by means of an insulating layer  22 . 
     The base segment  18  has a front surface  24  that can be activated as the active surface and that serves to form the bottom surface  6  which has a plurality of first outlet openings  26  and first inlet openings  28  for an electrolyte. In the embodiment shown, the first outlet and inlet openings  26 ,  28  form a pattern of perforations and they are arranged alternately next to each other, whereby the first inlet openings  28  can be arranged in the center and edge areas of the front surface  24 , while the first outlet openings  26  can be arranged only in the center area, so that, in a view onto the front surface  24 , the first inlet openings  28  in the edge area surround at least the first outlet openings  26  in the center area. In order to form the side surfaces  10  that run at a right angle, the base segment  18  has a lateral surface  30  that extends at a right angle to the front surface  24  and that is formed by a closed wall  32 . 
     An electrolyte feed means  34  and an electrolyte suctioning means  36  are integrated into the base segment  18  for purposes of forming an electrolyte circuit. Relative to the figure sheet viewed crosswise, the electrolyte feed means  34  has a horizontal feed channel  38  that serves to distribute the electrolyte in the crosswise or widthwise direction of the base segment  18  (direction of flow indicated by the arrows  40 ) that is in fluid communication with a plurality of first vertical feed channels  42  (the appertaining direction of flow indicated by the arrow  44 ). The first vertical feed channels  42  open into the first outlet openings  26  of the front surface  24 . The electrolyte suctioning means  36  has a plurality of first vertical suctioning channels  46  (the appertaining direction of flow indicated by the arrow  48 ) that are open towards the front surface  24  via the first inlet openings  28  and that are in fluid communication with a horizontal suctioning channel  50  (direction of flow indicated by the arrows  52 ). 
     For purposes of forming the upright side surface  12  or for purposes of forming the undercut  14 , the side segment  20  has an active surface or a slanted surface  54  which can be activated and in which a pattern of perforations consisting of a plurality of second outlet openings  26 ′ is formed. Second inlet openings  28 ′ are formed in the edge area of the slanted surface  54  and thus in the area where the slanted surface  54  makes a transition to the front surface  24 . The side segment  20  has an integral electrolyte feed means  56  and an integral electrolyte suctioning means  58  that can be actuated independently of the electrolyte feed means  34  and of the electrolyte suctioning means  36  of the base segment  18 . The electrolyte feed means  56  as well as the electrolyte suctioning means  58  each have at least one second feed channel  42 ′ that runs approximately vertically as well as a second suctioning channel  46 ′ that, on the one hand, are in fluid communication with the second inlet openings  26 ′ or the outlet openings  28 ′ for purposes of feeding the electrolyte to the slanted surface  54  or of suctioning it off the slanted surface  54  and, on the other hand, they are in fluid communication with each other via a plurality of perforations  60 . 
     The insulating layer  22  extends essentially in the vertical direction  62  of the electrode  1  and has a curved section  64  that opens into the transition area at the edge. The curved section  64  and a correspondingly curved layout of the first feed channels  42  and of the suctioning channels  46  in the vicinity of the transition area allow the formation of the bottom surface  6  exclusively by means of the front surface  24  of the base segment  18 . Since the suctioning according to the invention takes place at least in the edge area of the slanted surface  54  and of the front surface  24 , preferably only first and second inlet openings  28 ,  28 ′ or suctioning channels  46  are arranged in the transition area and they are insulated from each other by the insulating layer  22 . 
     A biaxial method for actuating the electrode  1  for purpose of forming the cavity  2  will be explained below. First of all, the electrode  1  is positioned across from the workpiece  4  in the area of the surface  8  that is to be machined. Then the electrolyte circuit of the base segment  18  is switched on. The electrolyte is fed via the electrolyte feed means  34  through the base segment  18  and then exits from the first outlet openings  42  in the area of the front surface  24 . The electrolyte is subsequently suctioned off the front surface  24  or the active surface via the first inlet openings  46 , and returned through the base segment in this process. Then a cathode voltage is applied and the electrode  1  is moved in the vertical direction  62 , so that the surface  8  is sunk until sufficient material  66  has been removed and the bottom surface  6  has been formed. Due to the suctioning of the electrolyte in the edge area of the front surface  54 , the lateral surface  30  remains dry, so that, in spite of the fact that the lateral surface  30  is energized, it does not function as an active surface. The side surface  10  is formed directly by or during the sinking of the surface  8 , whereby, despite the fact that the lateral surface  30  slides along the side surface  10 , disturbances of the side surface  10  are prevented by the suctioning of the electrolytes in the edge area of the front surface  24 , or else in the edge area where the front surface  24  makes a transition to the lateral surface  30 . In contrast to this, due to the positioning of the slanted surface  54 , a wedge-shaped side gap  70  is formed between the slanted surface  54  and an opposite side workpiece surface  68 , so that the entire surface of the slanted surface  54  is at a distance from the workpiece surface  68  when the surface  8  is sunk. In spite of this, due to the edge suctioning, the slanted surface  54  remains dry in the area of the front surface  24 . As soon as the bottom surface  6  has been formed, the cathode voltage is switched off, the advancing movement in the vertical direction  62  is halted, and subsequently the electrolyte flow  34  is blocked. The electrolyte suctioning means  36  is only switched off once the bottom surface  6  has dried sufficiently so that further material removal or a caustic attack is prevented. 
     Once the bottom surface  6  has been formed, the upright side surface  12  or the undercut  14  of the cavity  2  is formed as shown in  FIG. 2 . Towards this end, the electrolyte feed means  56  and the electrolyte suctioning means  58  are activated in order to feed the electrolyte to the slanted surface  54  or to subsequently suction it off again, so that now the slanted surface  54  functions as an active surface. The front surface  24  of the base segment  18  remains dry, so that no further material is removed in the area of the bottom surface  6 . Then the side segment  18  is energized and the electrode  1  is moved in the crosswise direction  72  as shown in  FIG. 2  until sufficient material  74  has been removed and the side surface  12  or the undercut  14  has been formed in accordance with the desired contour. Then the cathode voltage is switched off, the advancing movement in the crosswise direction  72  is halted and the electrolyte flow  56  is interrupted. The electrolyte suctioning means  58  is then only switched off when the upright side surface  14  has dried sufficiently. The electrode is removed from the cavity  2  once the side surface  12  has been formed. The cavity  2  with the bottom surface  6  as well as the side surfaces  10 ,  12  have now been machined to their desired contour, whereby the suctioning according to the invention prevents an active attack in adjacent areas of the individual active surfaces  24 ,  54 , so that there is no need for subsequent machining, especially in the transition area between the bottom surface  6  and the slanted surfaces  10 ,  12 . 
     A method is disclosed here for electrochemically machining a workpiece surface  8 ,  68  with an electrode  1  that has at least one active surface  24 ,  54  for machining the workpiece surface  8 ,  68  and with an electrolyte, said method involving the electrolyte being suctioned off the active surface  24 ,  54 , and furthermore, an electrode  1  is disclosed that has at least one electrolyte feed means  34 ,  56  for feeding the electrolyte to the active surface  24 ,  54  and an electrolyte suctioning means  36 ,  58  for suctioning the electrolyte off of the active surface  24 ,  54 .