Machine And Method For Electrochemically Polishing Indentations Within An Aluminum Wheel

Abstract

A machine for electrochemically polishing indentations within the wall of an aluminum workpiece, such as a wheel, has a cathode attached to an upper platen. The workpiece is mounted upon a lower platen which acts as an anode. Electrolyte is passed between the cathode and the anode while simultaneously a current is applied which passes through the cathode and the anode. The current is selectively pulsed to maximize polishing but at the same time to permit the flushing away of residual material and to cool the cathode and the workpiece.

1 . A machine for electrochemically polishing indentations of known geometry within the wall of an aluminum workpiece, wherein a workpiece space defines the space in which a workpiece would occupy in the machine and wherein the machine comprises:
 a) an upper platen;   b) a cathode extending from the upper platen, wherein the cathode is associated with an indentation and wherein the cathode has a shape similar to that of the indentation but smaller and is adapted to be positioned adjacent to the indentation to define a gap therebetween for the introduction of an electrolyte between the cathode and the indentation;   c) a lower platen aligned with the upper platen, wherein the lower platen is adapted to receive the workpiece and wherein the upper platen and the lower platen are movable relative to one another such that in a first position the cathodes may be distanced from the lower platen and in a second position the cathode is close to the lower platen with the cathode adjacent to the location of the indentation of a workpiece mounted to the lower platen;   d) anode shoes for contact with the workpiece, wherein the shoes are electrically conductive such that when the shoes contact the workpieces, the workpiece itself acts as an anode;   e) an entry passageway to introduce electrolyte within the gap between the cathode and the indentation of the workpiece;   f) an exit passageway to remove electrolyte from the gap between the cathode and the indentation of the workpiece;   g) a power supply to provide current between the cathode of the upper platen and the anode of the lower platen through the electrolyte therebetween; and   h) a controller for controlling the current between the cathode and the anode.   
     
     
         2 . The machine according to  claim 1 , wherein the workpiece is a wheel. 
     
     
         3 . The machine according to  claim 1 , wherein at least two cathodes extend from the upper platen, wherein each cathode is associated with an indentation, wherein each cathode has a shape similar to that of the indentation but smaller and is adapted to be positioned adjacent to the indentation to define a gap therebetween for the introduction of an electrolyte between the cathode and the indentation, and wherein the upper platen and the lower platen are movable relative to one another such that in a first position the cathodes may be distanced from the lower platen and in a second position the cathodes are close to the lower platen with the cathodes adjacent to the locations of the indentation of a workpiece mounted to the lower platen. 
     
     
         4 . The machine according to  claim 1 , wherein the controller further includes a pulsing circuit for allowing the current to be intermittently applied to the cathode thereby permitting the electrolyte to more effectively flush residue from the anode. 
     
     
         5 . The machine according to  claim 4 , wherein the controller has at least a machining mode and a polishing mode, and wherein in the machining mode, the current is high to remove a substantial amount of material from the workpiece while, in a polishing mode, the current is lower to remove a substantially less amount of material from the workpiece 
     
     
         6 . The machine according to  claim 1 , wherein the indentation is a window extending through the wall of the workpiece, the entry passageway surrounds the cathode so that the electrolyte may be introduced around the perimeter of the cathode, and the exit passageway is the window so that the electrolyte may be drained through the window. 
     
     
         7 . The machine according to  claim 6 , wherein the passageway is a series of ports about the perimeter of the cathode. 
     
     
         8 . The machine according to  claim 6 , wherein the passageway is a sleeve about the perimeter of the cathode. 
     
     
         9 . The machine according to  claim 1 , wherein the indentation is a pocket in the wall of the workpiece, the entry passageway is a slot on one side of the pocket and the exit passageway is a slot on the opposite side of the pocket such that electrolyte may be introduced within the gap from one side of the pocket and discharged from the opposing side of the pocket. 
     
     
         10 . The machine according to  claim 1 , wherein the cathode is removably attached to the upper platen so that different cathodes may be installed to accommodate indentations of different shapes. 
     
     
         11 . The machine according to  claim 1 , wherein the upper platen is slidably mounted for moving between the first position and the second position. 
     
     
         12 . The machine according to  claim 1 , wherein the upper platen and the lower platen are electrically insulated from the anodes and the cathodes attached thereto. 
     
     
         13 . The machine according to  claim 1 , further including flexible non-porous material surrounding each cathode and entry passageway, wherein the material is adapted to mate against the workpiece to provide a water-tight seal between the upper platen and the workpiece. 
     
     
         14 . The machine according to  claim 1 , wherein the anode shoes are movable from a first position away from the workpiece space to a second position within the workpiece space such that the shoes would contact a workpiece mounted within the workpiece space. 
     
     
         15 . The machine according to  claim 1 , wherein the lower platen is indexable such that a workpiece having multiple indentations may be rotated to align different indentations with the cathode. 
     
     
         16 . The machine according to  claim 1 , further including a collector tank for collecting electrolyte after it has passed through the gap between the cathode and the anode. 
     
     
         17 . A method for electrochemically polishing indentations of known geometry within the wall of an aluminum workpiece, wherein a workpiece space defines the space in which a workpiece would occupy in the machine and wherein the method comprises the steps of:
 a) mounting an aluminum workpiece upon a platen;   b) attaching at least one anode to the workpiece;   c) positioning at least one cathode within an indentation of the workpiece, thereby defining a gap between the cathode and the anode;   d) introducing a flow of electrolyte within the gap;   e) introducing a current between the cathode and the anode; and   f) pulsing the current to permit the flowing electrolyte to flush the indentation surface.   
     
     
         18 . The method according to  claim 17 , wherein the workpiece is a wheel. 
     
     
         19 . The method according to  claim 17 , wherein the step of pulsing the current is a two step process in which in a machining step the current is greater to remove a substantial amount of material while in a subsequent polishing step the current is less to remove a substantially less amount of material. 
     
     
         20 . The method according to  claim 19 , wherein the current for the machining step is approximately 50 milliseconds on and 25 milliseconds off. 
     
     
         21 . The method according to  claim 19 , wherein the current for the polishing step is approximately 40 milliseconds on and 20 milliseconds off. 
     
     
         22 . The method according to  claim 17 , wherein the current is between approximately 12,000 and 15,000 amperes and the voltage is between approximately 0 and 25 volts direct current. 
     
     
         23 . The method according to  claim 17 , wherein the current is pulsed at a rate of between approximately 20-25 milliseconds on and between approximately 8-30 milliseconds off. 
     
     
         24 . The method according to  claim 17 , wherein the flow of electrolyte is in the range of 25-55 gallons per minute. 
     
     
         25 . The method according to  claim 18 , wherein for a wheel having a diameter of 20 inches, the flow rate is between 45-50 gallons per minute. 
     
     
         26 . The method according to  claim 18 , wherein for a wheel having a diameter of 18 inches, the flow rate is between 30-35 gallons per minute. 
     
     
         27 . The method according to  claim 17 , wherein the electrolyte is recirculated to provide electrolyte within the gap. 
     
     
         28 . The method according to  claim 17 , wherein the electrolyte is filtered to remove residue before recirculation. 
     
     
         30 . A method for electrochemically polishing indentations of known geometry within the wall of an aluminum workpiece, wherein a workpiece space defines the space in which a workpiece would occupy in the machine and wherein the method comprises the steps of:
 a) mounting an aluminum workpiece upon a platen;   b) attaching at least one anode to the workpiece;   c) positioning at least one cathode within the indentation within the workpiece, thereby defining a gap between the cathode and the anode;   d) introducing a flow of electrolyte within the gap; and   e) introducing a pulsing current between the cathode and the anode, wherein the current is on for a predetermined period to polish the workpiece indentation and then off for a predetermined shorter period to permit the flowing electrolyte to flush the indentation surface.