International Journal of Scientific & Engineering Research, Volume 4, Issue 7, July-2013 2471 ISSN 2229-5518 IJSER © 2013 http://www.ijser.org Review of the Development in Process Capability Analysis Vidhika Tiwari 1 , N.K.Singh 2 Abstract— This review paper is devoted to the study for the analysis of the process capability of the manufacturing processes. The process capability indices Cp ; C pk C pm, C pmk , C py and C pc are presented, related to process parameters and the practical applications of the conventional as well as some new indices in the manufacturing industries are provided. Keywords— Quality control, Process capability index, Non-normal distribution, Gamma and Weibull Distribution,Industrial application . ——————————  —————————— 1. INTRODUCTION Process capability compares the process output with the customer’s specification. Two parts of process capability are: i) Measure the variability of the output of a process, and ii) Compare that variability with requirement specification or product tolerance. Process capability analysis is the evaluation of a production process to determine whether or not the inherent variability of its output falls within the acceptable range and process capability index or process capability ratio is a statistical measure of process capability. The concept of process capability holds meaning for processes that are in a state of statistical control. Process capability indices measure how much "natural variation" a process experiences relative to its specification limits and allows different processes to be compared with respect to how well an organization controls them. A process capability index uses both the process variability and the process specifications to determine whether the process is capable. The process capability index (PCI) is a value which reflects real-time quality status. The PCI is considered as one of the quality measurements tool. In practice, process capability indices (PCIs) are used as a means of measuring process potential and performance. Moreover, most PCIs have been developed or investigated under the assumption that components have a lifetime with a normal distribution. In many processes, the quality characteristics may follow the non-normal distribution e.g. Weibull, Exponential, and Geometric distribution etc. In some cases, the characteristics of the product may be interrelated. It is necessary to develop the process capability measure for the quality characteristics related to the above mentioned distributions and sampling distribution of their estimate. Under non normal distribution, some properties of the PCIs and their estimators differ from those of normal distribution. To utilize the PCIs more reasonably and accurately in assessing the lifetime performance of components, this study is conducted. 2. PROCESS CAPABILITY INDICES FOR QUALITY CHARACTERISTICS FOLLOWING VARIOUS DISTRIBUTIONS 2.1. PCI For Normal Distribution Process capability analysis is based on some fundamental assumptions that is, the process is stable and that the studied characteristic is normally distributed. There are several statistics that can be used to measure the capability of a process. According to the philosophy of the quality control approach, process capability indices of any process can be divided into capability indices of the first and second generation. The design of the first generation capability indexes (Cp, Cpk) is based on classical philosophy of the statistical process control. According to that philosophy all measurement results within required tolerance interval are intended to be good. Measurements outside tolerance interval are considered to be bad. Under these assumptions the two most widely used indices in industry are Cp and Cpk, where Cp was presented by Juran (1974) and Cpk by Kane (1986). 6 USL LSL Cp σ − = min , 3 3 USL LSL Cpk µ µ σ σ − −   =     ———————————————— • Mrs.Vidhika tiwari 1 is currently pursuing PhD degree program in ME & MME Departmen in ISM Dhanbad, India,vidhika.shukla@gmail.com. • Dr. N.K.Singh 2 Associate professor in ME &MME Department in ISM Dhanbad.India,nks_221@yahoo.co.in. IJSER