Surface and Sub Surface evaluation in Coated-Wire Electrical Discharge Machining (WEDM) of INCONEL® alloy 718

Wire Electrical Discharge Machining (WEDM) is one of the most versatile and useful technological processes for cutting complex shapes made of conductive materials such as those typical of aerospace applications. With the aim to optimize process parameters, this paper studies the surface and subsurface modifications of INCONEL® alloy 718 (UNS N07718) machined by WEDM using a Zinc coated brass wire. Machining was performed under roughing and finishing conditions by setting different values of discharge energy and wire feed rate. Surface roughness of the cut surfaces was measured as well as the micro-hardness profile on polished sections. WED-machined surfaces and their cross sections were also observed by Scanning Electron Microscope (SEM) and analyzed by Energy Dispersive X-ray Spectroscopy (EDS) to evaluate possible variations of the surface chemical composition. In this investigation, results are discussed as a function of the feed rate and of the single pulse discharge energy, which is determined by duration, peak current and discharge voltage of the discharge pulse. The research demonstrates that the required surface roughness can be achieved by properly setting the feed rate and the single pulse discharge energy on the WEDM machine. Experimental results also show that under the re-melted layer thickness no significant white layer formation or thermal modification occur, indicating that the chosen set of operating parameters minimizes secondary and unwanted chemical reactions.