The present paper studies the process of electro discharge machining, estimating the relative importance of main influence factors. The first step is to evaluate the possibilities of a design of experiments based on an orthogonal array, an appropriated method to systems with multiple factors changing in numerous levels After of the realization of the experiences the theory of grey systems is used to know which combination of factors optimize all of the variables. Finally the analysis of the variance is applied to investigate which of the factors significantly affects the global answer of the system.