The Certified Quality Process Analyst Handbook Process Capability

The Certified Quality Process Analyst Handbook: Process Capability Measures Ch. 20 1 st edition Ch. 14 2 nd edition Presented by Dr. Joan Burtner Associate Professor Emerita Industrial Engineering and Industrial Management Lean Six Sigma Black Belt Professional Certified Quality Engineer

Process Control vs. Process Capability Process Control ◦ 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 2020 Dr. Joan Burtner, Associate Professor Emerita, Industrial Engineering Slide 2

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 ◦ Cp standard measures Compares variability of process to specifications ◦ Cpk Compares variability of process to specifications Joan Burtner, Associate Professor Emerita, Industrial Is the. Dr. process sufficiently centered? IDM 355 Fall 2020 Engineering Slide 3

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 Compares variability of process to specifications Is the process sufficiently centered? IDM 355 Fall 2020 Dr. Joan Burtner, Associate Professor Emerita, Industrial Engineering Slide 4

Process Capability Calculations Use Rbar/d 2 to estimate σ Evaluation ◦ Cpk > 1. 33 Definitely Capable ◦ 1. 00 < Cpk < 1. 33 Possibly Capable ◦ Cpk 1. 00 Not Capable IDM 355 Fall 2020 Dr. Joan Burtner, Associate Professor Emerita, Industrial Engineering Slide 5

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 2020 Dr. Joan Burtner, Associate Professor Emerita, Industrial Engineering Slide 6