Univariate and Multivariate Process Capability Indices—Measures of Process Performance—A Case Study

Abstract

Process capability indices like Cp, Cpk, Cpm and Cpmk are commonly used in industry to assess the competence of a process to conform the control limits on quality parameters of process study. As product designs are complicated to meet international standards and consumers’ requirements are changeable rapidly, quality characteristics must be analyzed simultaneously to improve product’s quality and also to consider the aspect of multicollinearity among different quality characteristics. The objective of this paper is to measure univariate and multivariate capability indices to assess performance of multistage processes of paper manufacturing at Paswara Papers Ltd., Meerut. The paper manufacturing has various stages, namely pulping, screening, cleaning, deinking, refining, pressing, steam drying, bleaching, steam drying and size press. Different capability indices are measured for various processes of paper manufacturing. The results reveal that multivariate process capability indices, introduced by Shahriari and Lawrence (fourth industrial engineering research conference, pp 304–309, 1995, [6]) [Cpm = 0.6197], gives higher capability as compared to Taam and Liddy (J Appl Stat 20:12, 1993, [5]) [MCpm = 0.1408], and Pan and Lee (Qual Reliab Eng Int 26:3–15, 2010, [7]) [NMCpm = 0.0130].