Process capability improvement of an engine connecting rod machining process

Abstract

Statistical process control is an excellent quality assurance tool to improve thequality of manufacture and ultimately scores on end-customer satisfaction. SPCuses process monitoring charts to record the key quality characteristics (KQCs)of the component in manufacture. This paper elaborates on one such KQC of themanufacturing of a connecting rod of an internal combustion engine. Here thejourney to attain the process potential capability index (Cp) and the process performance capability index (Cpk) values greater than 1.33 is elaborated by identifying the rootcause through quality control tools like the cause-and-effect diagram andexamining each cause one after another. In this paper, thedefine-measure-analyze-improve-control (DMAIC) approach is employed. Thedefinition phase starts with process mapping and identifying the KQC. The nextphase is the measurement phase comprising the cause-and-effect diagram and datacollection of KQC measurements. Then follows the analysis phase where theprocess potential and performance capability indices are calculated, followed bythe analysis of variance (ANOVA) of the mean values. Finally, the processmonitoring charts are used to control the process and prevent any deviations. Byusing this DMAIC approach, standard deviation is reduced from 0.48 to 0.048, theCp values from 0.12 to 1.72, and the Cpk values from 0.12 to 1.37, respectively.