Process incapability index, which provides an uncontaminated separation between information concerning the process accuracy and the process precision, has been proposed to the manufacturing industry for measuring process performance. Contributions concerning the estimated incapability index have focused on single normal process in existing quality and statistical literature. | Yugoslav Journal of Operations Research Volume 19 (2009), Number 2, 215-223 DOI: A RESEARCH NOTE ON THE ESTIMATED INCAPABILITY INDEX Gu-Hong LIN Department of Industrial Engineering and Management, National Kaohsiung University of Applied Sciences, Kaohsiung, Taiwan, ROC e-mail: ghlin@ Received: March 2008 / Accepted: Februaruy 2009 Abstract: Process incapability index, which provides an uncontaminated separation between information concerning the process accuracy and the process precision, has been proposed to the manufacturing industry for measuring process performance. Contributions concerning the estimated incapability index have focused on single normal process in existing quality and statistical literature. However, the contaminated model is more appropriate for real-world cases with multiple manufacturing processes where the raw material, or the equipment may not be identical for each manufacturing process. Investigations based on contaminated normal processes are considered. Sampling distributions and r-th moments of the estimated index are derived. The proposed model will facilitate quality engineers on process monitor and performance assessment. Keywords: Contaminated normal process; incapability index 1. INTRODUCTION Process capability indices, whose purpose is to provide numerical measures on whether or not a manufacturing process is capable of reproducing items satisfying the quality requirements preset by the customers, the product designers, have received substantial research attention in the quality control and statistical literature. The three basic capability indices C p , Ca and C pk , have been defined as (. Kane, 1986; Pearn et al., 1998; Lin, 2006a): Ca = 1 − μ −m d , (1) Gu-Hong Lin / A Research Note On The Estimated 216 Cp = USL − LSL , 6σ (2) ⎧USL − μ μ − LSL ⎫ C pk = min ⎨ , ⎬ 3σ ⎭ ⎩ 3σ (3) where USL and LSL are the upper and lower specification limits preset by the customers, the product
