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The Views of Long Term and Short Term Process Capability Indices- A Comparison

Yerriswamy Wooluru, D. R. Swamy, P. Nagesh


For the last two decades, process assessment has employed the use of process capability measures (Cp,Cpk and Cpm ) and process performance measures (Pp, Ppk and Ppm).In the production process validation process, know the difference between long term and short term process capability is an important issue. The objective of this paper is to compare the short term process capability and long term process capability for boring operation using classical method and analysis of variance method. The long term and short term process capability indices have been interpreted based on classical method and one-way analysis of variance (ANOVA).Methodology adopted is illustrated with a case study data pertaining to the boring operation. The study reveals that long term process capability statistics are lower than those of short term one in both the methods and it is concluded that the difference in their magnitude is due to the cumulative effect of chance causes of variation over the period of time. The results have been compared and presented.


short term, long term capability, inherent process variation, total process variation, process capability

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