Electrolytic polishing method and device and method for producing a cathode

Abstract

In a method and a device for electrolytically polishing inner surfaces of a recess in a workpiece made of metal, in particular a workpiece printed in three dimensions, provision is made that a cathode is introduced into the recess and polishes the inner surface of the recess using an electrolyte having a slow diffusion rate.

1 . A method of electrolytically polishing an inner surface of a recess in a workpiece made of metal, characterized by the steps of:
 (A) immersing the workpiece in an electrolyte containing a salt, water and alcohol having a minimum weight proportion of from 20-70% per liter of electrolyte;   (B) connecting the workpiece to a positive pole so that the workpiece forms an anode;   (C) providing at least one cathode in the electrolyte and the recess;   (D) providing a relative movement between the electrolyte and the workpiece; and   (E) applying an electric voltage between the anode and the at least one cathode.   
     
     
         2 . The method according to  claim 1 , characterized in that the workpiece consists of a nickel alloy, chromium alloy, or light metal. 
     
     
         3 . The method according to  claim 1 , characterized in that a cathode is connected to a negative pole of a power source by an electric line and is inserted into the recess in the workpiece for treating the inner surface of the recess. 
     
     
         4 . The method according to  claim 3 , characterized in that the cathode is formed to be flexible. 
     
     
         5 . The method according to  claim 3 , characterized in that at least one electrically insulating spacer projects laterally from the cathode. 
     
     
         6 . The method according to  claim 5 , characterized in that a plurality of spacers that are axially spaced from each other are provided on the cathode. 
     
     
         7 . The method according to  claim 5 , characterized in that the cathode together with the spacer(s) is formed as a circular brush and the insulating spacers are projecting filaments or in that the cathode is an elongated body having a groove that is helical on its outer surface and transports electrolyte. 
     
     
         8 . The method according to  claim 5 , characterized in that, after a first polishing step, the cathode is moved relative to the workpiece to expose a support portion at which the spacer was previously located opposite the workpiece, and carrying out a second polishing step for polishing the support portion. 
     
     
         9 . The method according to  claim 1 , characterized in that the outer surface of the workpiece is polished simultaneously with the inner surface by applying the electrical voltage. 
     
     
         10 . The method according to  claim 1 , characterized in that, in order to achieve the relative movement between the electrolyte and the workpiece, the electrolyte is pumped and flows past the workpiece and/or the workpiece is moved in the container receiving the electrolyte. 
     
     
         11 . The method according to  claim 1 , characterized in that at least one cathode has a surface which is located opposite the workpiece and which is profiled. 
     
     
         12 . The method according to  claim 1 , characterized in that the workpiece, and additionally the at least one cathode and/or a support structure forming an anode, is produced by a generative manufacturing method. 
     
     
         13 . The method according to  claim 12 , characterized in that a workpiece is used on which the cathode and/or a support structure forming an anode is co-printed by the generative manufacturing method. 
     
     
         14 . The method according to  claim 13 , characterized in that metal grains having diameters of from 20 to 60 μm are used for printing. 
     
     
         15 . The method according to  claim 12 , characterized in that, the support structure is configured as a support plate and during the electrolytic treatment, the workpiece is seated on the support plate which forms the anode. 
     
     
         16 . The method according to  claim 15 , characterized in that a cathode for external treatment of the workpiece is fastened to the support plate by means of an electrically insulating mounting. 
     
     
         17 . The method according to  claim 1 , characterized in that, during the treatment, the electrolyte has a maximum temperature of 20°, and/or a pH of up to 6.8 or between 9 and 12. 
     
     
         18 . The method according to  claim 1 , characterized in that the cathode is inserted into the recess and electrolyte is pumped into the gap between the cathode and the inner surface, of the workpiece opposite to it. 
     
     
         19 . The method according to  claim 1 , characterized in that the cathode is introduced into the recess more deeply and less deeply in relation to the recess by means of a motor drive or manually. 
     
     
         20 . The method according to  claim 1 , characterized in that the cathode has a side which faces the workpiece and which, prior to the treatment of the workpiece, has a constant gap with respect to the side of the workpiece which faces it, and manufactured after the treatment of the workpiece. 
     
     
         21 . A method of manufacturing a cathode for the electrolytic treatment of a workpiece, the cathode having a side facing the workpiece to be treated characterized by the steps of:
 (a) determining an outer geometry of the cathode at least in the region of the side facing the workpiece, wherein electric and/or magnetic fields that are present between the cathode and the workpiece during the electrolytic treatment are determined and the outer geometry of the cathode is determined taking into account a constant current density on that side of the workpiece which faces the cathode, and   (b) generating the cathode by a generative manufacturing method on the basis of the outer geometry determined.   
     
     
         22 . A device for electrolytic anodic polishing of an inner surface of a recess in a workpiece made of metal, comprising a container filled with an electrolyte, the electrolyte containing a salt, an alcohol having a minimum weight proportion of from 20 to 70%, and water, a holding device for the workpiece, a cathode which is movable relative to the recess and has an electrical insulation in sections on its outside and is connected to a power source by a cable, a drive being provided for generating a relative movement between the electrolyte present in the recess and/or the cathode, on one hand, and the workpiece, on the other hand. 
     
     
         23 . The device according to  claim 22 , characterized in that a laterally flexible cathode is provided, portions of which are provided with an electrical insulation projecting on the outside and forming a spacer. 
     
     
         24 . The device according to  claim 22 , characterized in that, in addition to the cathode introduced into the recess, at least one external cathode is provided for polishing the outer surface of the workpiece. 
     
     
         25 . The device according to  claim 22 , characterized in that a change holder is provided for fixing the cathode, the change holder being equipped with a power and/or electrolyte connection and/or a drive for moving the cathode. 
     
     
         26 . The method according to  claim 1 , characterized in that the workpiece is a metallic workpiece produced by a generative manufacturing method. 
     
     
         27 . The method according to  claim 12 , characterized in that the workpiece and additionally the at least one cathode and/or a support structure forming an anode, is produced using laser sintering. 
     
     
         28 . The method according to  claim 18 , characterized in that the electrolyte is pumped into the gap through a separate electrolyte conduit connected to the recess. 
     
     
         29 . The device according to  claim 22  for the electrolytic anodic polishing of an inner surface of a recess in a workpiece made of metal and printed in three dimensions.