Patent Publication Number: US-2017368626-A1

Title: Electrochemical Removal Of Material From A Workpiece

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a U.S. National Stage Application of International Application No. PCT/EP2016/050148 filed Jan. 7, 2016, which designates the United States of America, and claims priority to DE Application No. 10 2015 201 080.5 filed Jan. 22, 2015, the contents of which are hereby incorporated by reference in their entirety. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to electrochemical erosion of material from a workpiece. Teachings thereof may be embodied in methods and systems for electrochemical removal of material from a workpiece. 
     BACKGROUND 
     A method and a device for electrochemical erosion are known for example from WO 2006/080948 A2 and from AU 2013242795 A1. Accordingly, devices for electrochemical erosion can be equipped with a brush or a sponge as electrolyte carriers, wherein the electrolyte in these structures can be sucked up on account of capillary forces. If these electrolyte carriers are then placed on a surface which is to be treated, then this enables a transporting of the electrolyte through the channels in the electrolyte carrier toward the surface which is to be treated. Using the devices, a method for electrochemical erosion on surfaces can be carried out. For example, in this case residues of a welding process, such as weld spatter, can be locally removed from the surface of a weld construction. 
     SUMMARY 
     The teachings of the present disclosure may be used to improve the quality of the effect of the electrochemical erosion. For example, some embodiments may include methods for electrochemical erosion of material from a workpiece ( 12 ), in which an electrolyte carrier ( 14 ) is impregnated with an electrolyte, the electrolyte carrier ( 14 ) is placed on the surface ( 27 ) of the workpiece ( 14 ), wherein the workpiece ( 14 ) comes into contact with the electrolyte and a negative potential, with regard to the workpiece ( 12 ), is created on the electrolyte carrier ( 14 ), characterized in that a mechanically guided relative movement is executed between the workpiece ( 12 ) and the electrolyte carrier ( 14 ), which movement is predetermined by means of a mechanical connection between a holder ( 11 ) for holding the workpiece and the electrolyte carrier ( 14 ). 
     In some embodiments, the electrolyte carrier ( 14 ) is adapted to the surface structure of the workpiece in such a way that this has a cross section the contour of which accurately coincides, at least in one section, with the surface of the workpiece which is to be created, wherein for the movement of the electrolyte carrier relative to the workpiece ( 12 ) provision is made for at least one degree of freedom. 
     In some embodiments, the surface which is to be created consists of a hole ( 19 ). In some embodiments, the surface which is to be created forms a part of a cylinder ( 28 ). In some embodiments, the surface which is to be created consists of a groove ( 32 ). 
     In some embodiments, the electrolyte carrier ( 14 ) is moved in a linear and/or rotational manner relative to the workpiece ( 12 ) during the erosion. In some embodiments, the workpiece ( 12 ) is moved in a linear and/or rotational manner relative to the electrolyte carrier ( 14 ) during the erosion. In some embodiments, the electrolyte carrier is guided by means of a robot. 
     In some embodiments, a component which is produced by means of an additive production process is machined by means of the electrochemical erosion. 
     Some embodiments may include devices for electrochemical erosion of material from a workpiece ( 12 ), in which a holder ( 11 ) is provided for the workpiece ( 12 ), provision is made for an electrolyte carrier ( 14 ) which consists of a material which can be impregnated with electrolyte, a negative potential, with regard to the workpiece, can be created on the electrolyte carrier ( 14 ), characterized in that provision is made between the holder ( 11 ) and the electrolyte carrier ( 14 ) for a mechanical connection which allows a relative movement with regard to at least one degree of freedom. 
     In some embodiments, the mechanical connection allows a rotation and/or translation between holder ( 11 ) and electrolyte carrier ( 14 ). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further details of the disclosure are described below with reference to the drawings. The same or corresponding drawing elements are provided in each case with the same designations and are explained several times only insofar as to how differences arise between the individual figures. In the drawing: 
         FIG. 1  shows an exemplary embodiment of the device according to the teachings of the present disclosure in schematic section and implementation of an exemplary embodiment of a method; 
         FIG. 2  shows as a side view another exemplary embodiment of the device according to the teachings of the present disclosure while implementing an exemplary embodiment of a corresponding method; and 
         FIG. 3  shows as a three-dimensional view a further exemplary embodiment of the device according to the teachings of the present disclosure while implementing a corresponding method. 
     
    
    
     DETAILED DESCRIPTION 
     The teachings of the present disclosure may be embodied in methods and systems for electrochemical erosion. For example, in some embodiments, an electrolyte carrier is impregnated with an electrolyte. This electrolyte carrier, for example a sponge of a brush, is then placed on the surface of the workpiece, wherein the workpiece comes into contact with the electrolyte. A negative potential, with regard to the workpiece, is applied to the electrolyte carrier. This brings about an electrolytic erosion of material from the workpiece, wherein this material is electrochemically dissolved. This may be carried out in the case of metallic materials. 
     Some embodiments include a device for electrochemical erosion of material from a workpiece. This device has a holder for the workpiece. An electrolyte carrier consisting of a material which can be impregnated with electrolyte is provided, wherein this can be placed on the surface of a workpiece which is provided in the holder. Also, a negative potential, with regard to the workpiece, can be applied to the electrolyte carrier. This can be realised for example by an electrical connection point for a voltage source. This voltage source can then be connected to the electrolyte carrier by the negative pole, whereas the positive pole of the voltage source can be connected to the surface of workpiece which is located in the holder. 
     In some embodiments, a mechanically guided relative movement is executed between the workpiece and the electrolyte carrier. This is achieved by the electrolyte carrier being guided relative to the workpiece by means of a suitable mechanical device so that a defined movement of the electrolyte carrier can be executed on the surface of the workpiece. The mechanical guiding of the relative movement restricts the kinematic fixing of degrees of freedom of said relative movement, whereas the movement in other degrees of freedom is permitted. This can be achieved either by means of a suitable mechanical connection between the component and the electrolyte carrier, or use can be made of a programmable device, such as a robot arm, the movement of which can be accurately predetermined, as a result of which defined degrees of freedom are blocked and other degrees of freedom are used for the relative movement. As a result of this, it can be ensured that for example each of the regions of the workpiece which are to be machined can be fed to the treatment of the erosion in equal measure. In this way, the quality of the erosion effect can be improved. 
     In some embodiments, the electrolyte carrier is adapted to the surface structure of the workpiece in such a way that this has a cross section the contour of which accurately coincides, at least in one section, with the surface of the workpiece which is to be produced. 
     In some embodiments, a degree of freedom allows the movement of the electrolyte carrier relative to the workpiece. This degree of freedom can for example be provided by a movement direction perpendicular to the aforesaid cross section of the electrolyte carrier. In this way, structures can be produced which are defined by a cross section which extends on the workpiece in the direction of a direction which is perpendicular to the cross section. In this case, it can be for example a shoulder or a groove. This structure can be provided on or in a flat surface or else on or in the circumference of a rotationally symmetrical workpiece. 
     The surface which is to be created can also consist of a hole. This hole can be formed by means of a bore or be introduced into the component by another production method, for example an additive manufacturing process (also called an additive production process). If there are requirements on the walls of the hole for the surface condition which cannot be achieved by the selected production process for the hole, the hole can then be after machined by means of the method. The electrolyte carrier in this case has exactly the cross section of the hole. It can be introduced into the hole by means of a translational movement, wherein this movement can also be used to ensure a relative movement between the walls of the hole and the electrolyte carrier during the electrochemical erosion. If it concerns a circular cylindrical hole, the relative movement can be achieved by means of a rotation of the electrolyte carrier around its central symmetry axis. 
     The relative movement between the electrolyte carrier and the workpiece during the erosion can be rotational and/or linear. The relative movement can advantageously be created either by moving the workpiece beneath a fixed electrolyte carrier or by movement of the electrolyte carrier on the surface of the workpiece. Rotationally symmetrical components, such as shafts, can be made to rotate with respect to a fixed electrolyte carrier. If the components are very large and for example only small surface regions, such as holes, are to be machined, the electrolyte carrier may be moved relative to the stationary workpiece. 
     The electrolyte carrier can be guided by means of a robot. In this case, surfaces of the component which spatially are arranged in any manner can be machined. Machining by means of a robot may be appropriate if the geometry of the component is provided as a three-dimensional data set, in the way that this is ensured for production by means of additive manufacturing. 
     In some embodiments, the component, which is to be machined by the electrochemical erosion, is produced by means of an additive production process (also referred to an additive manufacturing). For example, laser fusion, laser sintering, and laser cladding are to be referred to as additive manufacturing processes. In this case, the components are built up in layers, and a stepped surface of the component can be formed. If the surface requirements for the components, however, require a surface quality which cannot be achieved by this “stepped” surface condition, then it is expedient to use the method according to the invention. Depending on the geometry of the component, some embodiments may include guiding the component or the use of an electrolyte carrier with a robot. 
     In some embodiments, there is a mechanical connection between the holder and the electrolyte carrier which allows a relative movement with regard to at least one degree of freedom. The positive pole of a voltage source can be connected to the workpiece and the negative pole of a voltage source can be connected to the electrolyte carrier. As a result of this, the the electrolyte carrier is impregnated with an electrolyte in the process. The mechanical connection of electrolyte carrier and workpiece may be accurately defined by its clamping in the holder, which is why the erosion effect as a result of the effected electrochemical erosion (e.g. electro polishing) can be accurately predetermined. In this case, the mechanical connection may allow a rotation and/or translation between holder and electrolyte carrier. 
     Some embodiments may include a device for electrochemical erosion such as that shown in  FIG. 1 . The device may include a holder  11  into which a workpiece  12  can be inserted. The workpiece  12  is provided with a hole  13  in the form of a bore, to be machined by means of the electrochemical erosion. For this purpose, a cylindrical electrolyte carrier  14  in the form of a sponge is introduced into the bore from the top. To this end, the electrolyte carrier  14  is fastened to a device  15  which for vertical displacement has a linear guide  16 . The translational movement in the direction of the indicated double arrow  17  can also be used in order to create a relative movement between the electrolyte carrier  14  and the workpiece  12 . 
     The electrolyte carrier  14  may be mounted on a supply pipe  18  which has holes  19  through which the electrolyte can make its way into the electrolyte carrier  14 . Through pores  20  of the sponge-like structure of the electrolyte carrier  14 , the electrolyte then reaches the walls of the hole  13 . It then trickles into a collecting pan  21  from where it can be fed again to the device  15  via a suction pipe which is equipped with a pump  22 . There, it makes its way into the supply pipe  18  again. 
     The device is also equipped with a motor  24  which can rotate the supply pipe  18  corresponding to the indicated double arrow  25 . With this, the electrolyte carrier  14 , which encompasses the supply pipe  18  in a ring-like manner, also rotates around the symmetry axis  30  of the supply pipe  18 . This may create a relative movement between the electrolyte carrier  14  and the workpiece  12 . 
     Also shown is a voltage source  26 , the plus pole of which is in contact with the workpiece  12  and the minus pole of which is in contact via the device  15  with the electrically conducting supply pipe  18 . By applying the potential, the wall of the hole  13  is electrochemically eroded. During this process, constituents of the workpiece material dissolve, and as a result of this the surface may be smoothed. It is also possible to dissolve impurities from the material of the workpiece and to improve for example the corrosion properties of the surface. 
     According to  FIG. 2 , a shaft is to be machined as the workpiece  12 . The surface  27  of this shaft has at its ends two regions which are to be used as running surfaces and therefore are to have a surface condition which is to be improved by the electrochemical erosion (electro polishing). These regions, considered geometrically, constitute parts of cylinders  28 . The shaft also has an annularly extending groove  29  which is also to be after machined by electrochemical erosion. 
     For the purpose of machining, the workpiece  12 , via the rod-like holder  11 , is rotatably supported around its symmetry axis  30  in bearings  31 . The rotation is indicated by the double arrow  25  and is executed by means of the motor  26 . During the rotation of the workpiece, the device  15 , via the linear guide  16 , is deposited from above onto the circumference of the component  12 , wherein three electrolyte carriers  14  in the form of sponges come into contact with the component  12 . Two of these electrolyte carriers erode material from the surface of the component  12  in the region of the cylinder  28 . The third electrolyte carrier  14  is adapted in its cross section in such a way that it accurately fits into the groove  29 . In this way, both the groove flanks  32  and the groove bottom  33  can be machined in the groove  29  at the same time. 
     A suction pipe  23  with a pump  22  and a structure comparable to the supply pipe  18  for supply of the electrolyte carrier  14  are not shown in  FIG. 2 , but are realized in a similar way to the embodiment according to  FIG. 1 . In this way, the electrolyte can be fed from the collecting pan  21  to the electrolyte carriers  14  and via the pores  20  be transported to the surface  27 . 
     According to  FIG. 3 , the surface  27  which is to be treated consists of an annular region on a flat component  12 . Used as an electrolyte carrier  14  in the case of  FIG. 3  is a brush which is fastened on a robot arm  34 . By means of this, the electrolyte carrier  14  can be repeatedly guided over the annular region of the surface  27  which is to be treated, wherein a material erosion is carried out in the process.