Metrological interpretation of a six-sigma process for improving the online optical measurement of automotive turbocharger dimensions

In this paper, a synergy between metrological concepts and six-sigma methodology was developed, in order to increase and consolidate improvements in the define, measure, analyse, improve and control intervention with reference to the online control procedure of the critical geometrical dimensions of a high-performance turbocharger for automotive applications. The metrological support is intended to be applied in terms of not only rigorously quantifying but also validating the improvement effects. The concepts and approaches typical of measurements are used with the aim of justifying and physically explaining the problems and the motivations for the obtained improvements. The consistency of the measured parameters with the production process steps is used to demonstrate the peculiarity and the newness of this approach. An analysis of the sensitivity to the interfering inputs, the uncertainty budget and the modelling of the measurement process are used by a bottom-up approach to set coherent actions which are able to improve strongly and consciously the six-sigma performance indicators.