Otimização da retificação das pontas dos anéis de pistão de aço inoxidável martensítico com cobertura de nitreto de cromo

Abstract

In the scope within in the automotive industry the machining processes are widely applied. Among them, the grinding process is widely used for finishing parts that require low roughness and dimensional tolerance, with the premise of achieve product features and reducing losses as much as possible that is, assurance the product quality and reduce manufacturing costs. In this context, this work presents a strategical approach to reduce variability in the grinding process of the tips of nitrided martensitic stainless steel (MS066-N1) piston rings, with chromium nitride (CrN) coated applied by the physical vapor deposition process (PVD). In this work, an experimental design (DOE) was created, in the Response Surface methodology configuration with 3 levels and 3 factors. The input variables were the abrasive grain size of CBN grinding wheel, the grinding wheel rotation parameter (RPM) and the feed parameter (GPM). The methodology applied was experimental planning, which support in defining the optimal machine parameterization, aiming to reduce the process variability and reach dimensional features stability in the specification average of the characteristic gap between piston rings tips. The closest optimization parameters and available on the machine was with abrasive grain size of CBN grinding wheel (B46), the grinding wheel rotation speed parameter (5200 RPM) and the feed parameter (9,0 GPM). To validate the optimization parameters, a study of capability analysis was created which demonstrated through the levels of Cp, Cpk and Pp, Ppk, that the process reached the expected stability, where the percentage of parts outside the specified or defective was reduced from 5,79% to 0,00%.