Experimental study of surface roughness in Electric Discharge Machining (EDM) based on Grey Relational AnalysisAshanira Mat Deris, Azlan Mohd Zain, Roselina Sallehuddin and Safian SharifMATEC Web Conf., 78 (2016) 01015DOI: https://doi.org/10.1051/matecconf/20167801015