Electrochemical machining, electrochemical polishing, electrochemical through-mask etching, and electrochemical deburring are examples of electrochemical material removal processes whereby metal is removed from a work piece by an anodic electrochemical reaction.
In electrochemical machining, the counter electrode or cathode consists of a geometric shape which can be a mirror image of the approximate desired final geometric shape of the machined work piece, and material is removed by an anodic electrochemical reaction. Electrochemical machining processes are often used in the manufacturing of gun barrels where the internal surface is rifled as described in, for example, U.S. Pat. No. 5,819,400, the entirety of which is hereby incorporated by reference herein. In electrochemical polishing, asperities are selectively removed by an anodic electrochemical reaction that can result in a smooth work piece surface, for example as described in published U.S. Patent Application No. 2011/0303553 by Inman, the entirety of which is hereby incorporated by reference herein.
In electrochemical through-mask etching, material is removed by an anodic electrochemical reaction through a mask on a workpiece surface as described in, for example, published U.S. Patent Application No. 2011/0176608 by Taylor, the entirety of which is hereby incorporated by reference herein.
In electrochemical deburring, rough edges and burrs are removed by an anodic electrochemical reaction as described in, for example, a Pulse/Pulse Reverse Electrolytic Approach to Electropolishing and Through-Mask Electroetching, in Products Finishing Magazine Online by Taylor, posted Sep. 26, 2011, the entirety of which is hereby incorporated by reference herein. The removal of material by an anodic electrochemical reaction as described herein is understood to include electrochemical machining, electrochemical polishing, electrochemical through-mask etching, electrochemical deburring, and the like, and these terms are used interchangeably to describe the electrochemical removal of material. Compared to mechanical machining processes such as mechanical cutting, thermal machining, electric discharge machining, or laser cutting, electrochemical material removal is a non-contact machining process that typically does not result in a mechanically or thermally damaged surface layer on the machined work piece. Electrochemical material removal can have strong utility as a manufacturing technology for fabrication of a wide variety of metallic parts and components.
As reported by Rajurkar (K. P. Rajukar, D. Zhu, J. A. McGeough, J. Kozak, A. De Silva, “New Developments in Electro-Chemical Machining” Annals of the CIRP Vol 82(2) 1999), the entirety of which is hereby incorporated by reference herein, electrochemical machining can have numerous advantages relative to traditional machining. These advantages include applicability to hard and difficult to cut materials, low tool wear, high material removal rate, smooth bright surface finish, and/or capability to produce parts with complex geometries. For example, electrochemical machining can be used for the production of helicopter engines (e.g., U.S. Pat. No. 6,554,571, the entirety of which is hereby incorporated by reference herein), artillery projectiles, large caliber cannon, turbine cooling technology (e.g., U.S. Pat. No. 6,644,921, the entirety of which is hereby incorporated by reference herein), and/or gun barrels.
While electrochemical material removal can have many advantages from the perspective of component manufacturing, one impediment to wider adoption is that the material removed from the workpiece can form an insoluble metal hydroxide and/or hydrated metal oxide sludge. The metal containing sludge is typically filtered, dried, and shipped to third party vendors for disposal in a landfill and/or recycling at considerable cost.
For example, as reported in Electrochemical Machining of Gun Barrel Bores and Rifling by Wessel (“Electrochemical Machining of Gun Barrel Bores and Rifling,” Naval Ordnance Station, Louisville Ky., September 1978. http://handle.dtic.mil/100.2/ADA072437″), the entirety of which is hereby incorporated by reference herein, during the boring and rifling process in a neutral or slightly alkaline sodium nitrate electrolyte for a 5 inch gun barrel, in which approximately 250 in3 of metal is removed, approximately 350 gallons of centrifuged metal containing electrolyte sludge can be produced. This volume of sludge is approximately 80,000 in3—more than 300 times the volume of the solid metal removed.
Accordingly, those skilled in the art seek an alternative to conventional electrochemical material removal whereby the generation of large volumes of insoluble metal containing sludge is substantially avoided and/or the valuable removed materials can be recycled.
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