The Certified Quality Process Analyst Handbook: Process Capability Measures Ch. 20 1st edition Ch. 14 2nd edition Presented by Dr. Joan Burtner Certified Quality Engineer Associate Professor of Industrial Engineering and Industrial Management

Process Control vs. Process Capability Is the process subject only to common cause variation? Control charts include upper control limit, centerline, lower control limit Monitor process using tests to identify existence of special causes Process Capability Only valid for processes that are under statistical control Measures of Capability Cp Cpk Based on specification limits set by designers and observed process mean IDM 355 Fall 2016 Dr. Joan Burtner, Associate Professor of Industrial Engineering

Analysis of Process Capability: Cp Cpk Analysis conducted on processes that have been shown to be “in-control” Only common cause variation exists in the range Only common cause variation exists in the mean Two standard measures Cp Compares variability of process to specifications Cpk Is the process sufficiently centered? IDM 355 Fall 2016 Dr. Joan Burtner, Associate Professor of Industrial Engineering

Analysis of Process Capability: Pp Ppk CR Capability Ratio (CR) Reciprocal of Cp Lower values are better Two additional measures that are used when the process is not in statistical control Pp Compares variability of process to specifications Ppk Is the process sufficiently centered? IDM 355 Fall 2016 Dr. Joan Burtner, Associate Professor of Industrial Engineering

Process Capability Calculations Use Rbar/d2 to estimate σ Evaluation Cpk > 1.33 Definitely Capable 1.00 < Cpk < 1.33 Possibly Capable Cpk  1.00 Not Capable IDM 355 Fall 2016 Dr. Joan Burtner, Associate Professor of Industrial Engineering

Process Performance Index Calculations Evaluation A Ppk value of 1 means the distance between the average and the nearest specification limit is 3 standard deviations A Ppk value of 2 means the distance between the average and the nearest specification limit is 6 standard deviations Higher Ppk values are better IDM 355 Fall 2016 Dr. Joan Burtner, Associate Professor of Industrial Engineering