Process Capability Plots for One-Sided Specification Limits

Abstract We extend the idea of process capability plots from the case of two-sided specification intervals to derive a graphical method useful when doing capability analysis having one-sided specification limits. The derived process capability plots are based on existing capability indices for one-sided specification limits. Both the cases with and without a target value are investigated. Under the assumption of normality we suggest estimated process capability plots to be used to assess process capability at a given significance level. Theoretical results are given for determining the significance level as well as power for the method. The presented graphical approach is helpful to determine if it is the variability, the deviation from target, or both that need to be reduced to improve the capability. Examples are presented.

[1]  D. Owen,et al.  On the distributions of the estimated process capability indices , 1989 .

[2]  Kerstin Vännman,et al.  Process capability indices for one-sided specification intervals and skewed distributions , 2007, Qual. Reliab. Eng. Int..

[3]  Samuel Kotz,et al.  Process Capability Indices—A Review, 1992–2000 , 2002 .

[4]  Kerstin Vännman,et al.  Distributional properties of estimated capability indices based on subsamples , 2003 .

[5]  Kerstin Vännman.  Safety Regions in Process Capability Plots , 2006 .

[6]  Kerstin Vännman,et al.  The Effect of Pooled and Un-Pooled Variance Estimators on Cpm When Using Subsamples , 2004 .

[7]  W. L. Pearn,et al.  Testing process capability for one-sided specification limit with application to the voltage level translator , 2002, Microelectron. Reliab..

[8]  Samuel Kotz,et al.  Process Capability Indices , 1993 .

[9]  Wen Lea Pearn,et al.  An algorithm for calculating the lower confidence bounds of CPU and CPL with application to low-drop-out linear regulators , 2003, Microelectron. Reliab..

[10]  Kerstin Vännman,et al.  Families of Capability Indices for One-Sided Specification Limits , 1998 .

[11]  Kerstin Vännman,et al.  Process capability plots—a quality improvement tool , 1999 .

[12]  Kerstin Vännman,et al.  A Graphical Method to Control Process Capability , 2001 .

[13]  Kuen-Suan Chen,et al.  One‐sided capability indices CPU and CPL: decision making with sample information , 2002 .

[14]  Fred A. Spiring,et al.  A New Measure of Process Capability: Cpm , 1988 .