Electrochemical Turning

Electrochemical Turning The electrochemical machining process can be used to perform tasks that would traditionally be accomplished by a single-point cutting tool on a lath.electrochemical turning (ECT) is used to remove material from the internal surface (ID), external surface (OD), or face of rotating electrically conductive work-pieces. Figure 1 depicts the ECT process performing an OD turning operation. If the particular ECT machine has sufficient power, tools are constructed to be as wide as the final shape being generated. Using the technique, contoured shapes can be plunged into the work-piece in a single pass. During operation, the ECT tool never contacts the work-piece; a gap is constantly maintained between the two. The gap is continuously flooded with electrolyte, which is delivered through holes in the tip of the tool. The equipment used for ECT resembles a conventional lathe except for the additional enclosures to contain the corrosive electrolyte and the addition of the power supply. Because ECT is rather limited in its use, equipment is made by special order. Depending upon the application, machines can be configured as either a vertical or horizontal lathe. Power supplies have attached to ECT machines with ratings as high as 20,000 amp. Very thin work-piece sections can be turned of faced with ECT because ther is no physical contact between the ECT tool and work-piece. Disks as thin as 0.12 mm (0.005 in.) can be turned without distortion because there are no tool forces. In addition, material hardness has no influence on removal rates and ther is no tool wear to decrease quality or productivity.

ECT is a special application of ECM. The principles of ECM are applied in the process to electrolytically machine rotating work-piece. Peripheral cuts and face cuts are accomplished as illustrated in figure 2. ECT is distinguished from a related process, electromechanical machining (EMM), in the ECT employs a noncontacing tool and all metal removal is accomplished via elecrolytic action. In contrast, EMM is a traditional machining process in every way except that electrolyte is flooded over the work-piece surface to soften it prior to mechanical metal removal by traditional tools. Application Large disk forgings are machined using ECT. In some cases, fullface electrodes are plunged into a rotating disk. Bearing races have been finished, with close tolerances and with surface roughness held to less than 5 μ in.(0.13 μ m)Ra . Another application, AISI 316 stainless steel work-piece (2.5" ,6.35 mm diam) are electrochemical turned, using an electrolyte of NaCl and NaNo3 (2:3), to a surface finish of less than 10 μ in.(0.25 μ m)Ra with outof-roundness of less than 0.0002" (0.005 mm) TIR. Operating parameters Material removal rates and tolerances are similar to those achieved in ECM. Tolerance holding capability usually is between ±0.00150.003" (0.038-0.08 mm). Under unusual conditions, tolerances can be held to ±0.001" (0.03mm); and in rate cases, tolerances can be held to ±0.0005" (0.013 mm).

Surface finish under normal conditions can be held to about 16-63 μ in. (0.4-1.6 μ m) Ra . with particular care, surface roughness can be held to as low as 8μ in.(0.2μ m)Ra : under special conditions, surface roughness can be controlled to 4μ in.(0.1μ m)Ra. Equipment Peripheral and face ECT machines are available on special order. Capacities are provided up to about 20,000 A. one horizontal electrochemical lathe is equipped with 5000 A power supply. The lathe is used to hold 0.0003" (0.008mm) tolerances.