Document Type : Research Paper


1 Department of Applied Mechanics, Technical College-Baghdad, Middle Technical University, Iraq.

2 Control and System Engineering Department, University of Technology-Iraq.


Process capability indices are a powerful tool used by quality control engineering to measure the degree to which the process is or is not meeting the requirements. This paper studies the application of process capability indices in the evaluation of a process with asymmetric tolerances. The analyzed collected data of the cleaning liquid “Zahi”, was used to investigate the ability of the filling process to meet the requested specifications. Matlab software was used to plot ̅ ̅ control charts, normal probability, and histogram of the data gathered from the production line and further performed statistical calculations. It was observed from the control charts that the filling process is under control. In addition, it was revealed by the process capability indices that the process of filling the cleaning liquid bottle is not fitted with the target value but it is adequate.


[1] M. Ebadi and H. Shahriari, “A process capability index for simple linear profile,” The International Journal of Advanced Manufacturing Technology, Vol. 64, No. (5-8), 857-865, 2013.
[2] H.M. Judi, R. Jenal, and D. Genasan, “Quality control implementation in manufacturing companies: motivating factors and challenges,” In Applications and Experiences of Quality Control, InTech, 2011.
[3] W.M. Goble, “Control systems safety evaluation and reliability,” ISA, 2010.
[4] J.C. Chen, Y. Li, and R.A. Cox, “Taguchi-based six sigma approach to optimize plasma cutting process: an industrial case study,” The International Journal of Advanced Manufacturing Technology, Vol. 41, No. (7-8), pp. 760-769, 2009.
[5] L. Ahmad, M. Aslam, and C.H. Jun, “Designing of X-bar control charts based on process capability index using repetitive sampling,” Transactions of the Institute of Measurement and Control, Vol. 36, No. 3, pp. 367-374, 2014.
[6] C. W. Wu, W. L. Pearn, and S. Kotz, “An overview of theory and practice on process capability indices for quality assurance,” International journal of production economics, Vol. 117, No. 2, pp. 338-359, 2009.
[7] V.E. Kane, “Process capability indices,” Journal of quality technology, Vol. 18, No. 1, pp. 41-52, 1986.
[8] W. L. Pearn, and K. S. Chen, “One-sided capability indices CPU and CPL: Decision making with sample information,” International Journal of Quality and Reliability Management, Vol. 19, No. 3, pp. 221-245, 2002.
[9] L.K. Chan, S.W. Cheng, and F.A. Spiring, “A new measure of process capability: CPM,” Journal of Quality Technology, Vol. 20 No. 3, pp. 162-175, 1988.
[10] K.S. Chen, and W.L. Pearn, “Capability indices for processes with asymmetric tolerances,” Journal of the Chinese Institute of Engineers, Vol. 24, No. 5, pp. 559-568, 2001.
[11] P.K. Rajvanshi and D.R. Belokar, “Improving the process capability of a boring operation by the application of statistical techniques,” International Journal of Scientific & Engineering Research, Vol. 3, No. 5, pp. 1-6, 2012.
[12] N.L. Johnson, S. Kotz, and W.L. Pearn, “Flexible process capability indices,” Department of Statistics [University of North Carolina at Chapel Hill], 1992.
[13] J.W. Kwiecien, “Process capability calculations with nonnormal data in the medical device manufacturing industry,” Ph. D Thesis, Waldenu University, 2017.
[14] M. Kovářík, and L. Sarga, “Process capability indices for non-normal data,” WSEAS Transactions on Business and Economics, 2014.
[15] D. Grau, “Process yield, process centering and capability indices for one-sided tolerance processes,” Quality Technology and Quantitative Management, Vol. 9, No. 2, pp. 153-170, 2012.
[16] Z. Abbasi Ganji, and B. Sadeghpour Gildeh, “A class of process capability indices for asymmetric tolerances,” Quality Engineering, Vol. 28, No. 4, pp. 441-454, 2016.
[17] L. Jäntschi and S. Bolboacă, “Computation of probability associated with anderson–darling statistic,” Mathematics, Vol. 6, No. 6, pp. 88, 2018.
[18] K.S. Yogi, March, “Assessment of process capability: the case of soft drinks processing unit,” In IOP Conference Series: Materials Science and Engineering, IOP Publishing, Vol. 330, No. 1, 2018.
[19] S. Khlil, H. Alkhazraji, and Z. Alabacy, “Investigation of the process capability of water pump plastic cover manufacturing, ” International Journal of Mechanical Engineering and Technology, Vol. 9 No.11, pp. 349-359, 2018.