Exploratory study of wire based ECM finishing of 316L stainless steel, implemented within a hybrid wire EDM-ECM platform

Abstract

Thermal processes such as wire electro discharge machining (wire EDM) have an intrinsic heat affected zone (HAZ) and recast layer due to their thermal removal mechanisms. This layer is adverse to the fatigue life characteristics of the manufactured parts, and has to be removed by finishing operations. Wire electrochemical machining (wire ECM) is proposed as a finishing operation, as it can dissolve conductive materials without damaging the machined surface, and is similar in mechanical operation as wire EDM. An important drawback of electrochemical machining is the low accuracy when removing large amounts of materials in one pass, which is addressed by only machining a shallow depth by ECM after roughing by EDM (i.e., finishing allowance of 15 – 70 µm, the HAZ thickness). This paper presents an experimental study of electrochemical finishing 316L stainless steel wire EDM'ed parts. To improve the machining efficiency and the accuracy of the finished parts by eliminating reclamping, the process is implemented on a wire EDM machine. The wire electrode used in EDM roughing is also used in ECM finishing and is retraced along the contour of the part with an offset to increase or decrease the interelectrode gap. The experiments presented in this paper aim to gain insight in the relationship between the process parameters of wire ECM and the resulting machined surface, with respect to the machining depth, material removal rate (MRR), and surface roughness. A number of process optimization strategies are investigated, considering parameters such as the feed rate and the number of passes. Experimental results show that wire based electrochemical machining is a viable process to finish wire EDM parts, achieving removal depths greater than 20 µm with a surface roughness below 1 µm Ra.