Non-Linear through-Hole Fabrication By Electrochemical Machining
Authors: Moran Andrew , Skinn Brian , Snyder Stephen , van Newkirk Shane , Horonzy Mike , Hall Timothy , Taylor E. Jennings 
Published: July 2021

Electrochemical machining (ECM) is a manufacturing technology that precisely removes material from metallic workpieces by electrochemical oxidation and dissolution into a working electrolyte. ECM is especially well suited for workpieces to be fabricated from "difficult to cut" materials, and is able to produce parts with complicated/intricate geometries. In ECM, an electrochemical cell is established with the workpiece as the anode and a shaped tool as the cathode; after engaging a suitable electrical potential, the shaped tool is advanced into the workpiece and a mirror image of the tool is formed. Compared to mechanical or thermal machining processes, where material is subtracted by cutting or by electric/laser discharges, respectively, ECM does not suffer from tool wear or introduce a heat-affected surface layer to the workpiece. As a result, ECM has strong utility as a manufacturing technology for a wide variety of workpiece materials and ultimate part geometries, and encompasses machining, deburring, boring, radiusing and polishing processes, among others. As noted, ECM provides particular value when applied to high-strength/tough, brittle, and/or work-hardening materials such as high strength steel, chrome-copper alloy (C18200), nickel alloy (IN718), cobalt-chrome alloy (Stellite 25), tantalum-tungsten alloy (Ta10W), molybdenum and tungsten, since the material removal process involves no mechanical interaction between the tool and the part.
This talk will summarize recent work performed to demonstrate the feasibility of non-linear through-hole machining in tubular metallic substrates by ECM, through application of a multi-step forming process. One category of feature that is often challenging to fabricate in hard-to-machine materials is a non-linear passage or through-hole. This is in contrast to a straight passage, which is generally uncomplicated to achieve with many methods, whereas in general non-linear through-holes in tube walls must be machined from both the inner and outer diameter of the wall. For easily-machined materials, machining steps taking place on the inner diameter of the workpiece can be accomplished with a sufficiently advanced multi-axis CNC mill, but for hard-to-machine materials it is difficult or impossible to achieve the necessary bearing force and/or angle of approach of the tool. Thermal machining methods (electric discharge machining, etc.) are viable in some cases, but as noted above will result in a heat-affected layer on the machined surface that is problematic in many applications. Experimental ECM results will be presented for fabrication of "chevron" through-hole features (~90° path axis deflection) in both planar and annular workpieces, embodying a proof-of-concept demonstration and an early step in development of an ECM methodology for fabricating integrated muzzle brake vane apertures directly into the barrel wall of large-bore cannon.

Figure Caption

(Top left) Patent drawing of modular muzzle brake concept for cannon, showing overall design and cross-section of a single vane, with vane passage geometry highlighted in orange. (Bottom left) Schematic 3D model of a cannon barrel with integrated muzzle brake vanes. (Top right) Schematic of two-sided ECM fabrication of nonlinear “chevron” passage in a composite stack of flat coupons. (Bottom right) Photographs of cross-sectioned flat steel coupons with fabricated “chevon” passages.

Reference

(from figure) Cler, D.L. and D. Forliti. U.S. Patent No. 7,600,461, issued 13 Oct 2009.

Figure 1