The thesis is based on an internship experience at Alstom Ferroviaria SpA in Savigliano, where I worked in quality department. The following article provides a general overview related to the railway industry, focusing mainly on the reality of the company Alstom Ferroviaria S.p.A. and, more specifically, on the Lean Six Sigma projects from which the company gains great profits. The main objective of this thesis is to describe the Lean Six Sigma project for the elimination of the manual 45° grinding phase at wheel/disc preparation that I had the opportunity to actually follow. In the paper, all phases of the DMAIC (Define, Measure, Analyze, Improve, Control) tool are explored in depth, both from a theoretical and practical point of view: are described the tools and how they were applied to the case study is explained.