A Comparative Study of Process Capability Indices of Normal and Non-normal for Capacitor Output Process

Abstract

This research study with volume capacitance data about 30 lots of Capacitor Output Process from a manufacturer during January – August 2016 by sampling one lot per week to complete the entire products. The random data was used to investigate in Process Capability Indices. It was found that the volume capacitance data in these manufactured Capacitors was shown in negatively skewed curve with no features of a normal distribution. Analysis on Process Capability Indices applied by the normal distribution formula (C_p (u,v)) against the non-normal distribution formula (C_Np (u,v)) resulted in higher values of C_Np than C_p (u,v) when compared to all values of u and v. The non-normal distribution formula reflects on both the indices and the manufacturing process capability lower than the reality. Seeing that, the similar values of such indices were resulted from a use of normal and non-normal distribution formula when the collective data are relatively symmetric. In consequence, it is advisable that the non-normal distribution formula is required when the production process data shows no features of normal distribution. This finding is greatly useful for the production analyst in factories who would be fully convinced how to select the appropriate process capability index formulas in order that its benefit gained would dramatically improve Thailand- based industry as a whole.