Process Capability Assessment

1. Process Capability Assessment Devor, Chang, and Sutherland Chapter 10 Dr. Joan Burtner, Assoc. Prof. of Industrial Engineering

2. Process Control vs. Process Capability • Process is “in-control” • Only common cause variation in range • Only common cause variation in mean • No violations of “tests for control chart interpretation” listed in front cover of text • Process capability • Is process capable of meeting tolerances? • Does the process conform to specifications? • Potential problems • The process is off-center from the nominal. • The process variability is too large relative to the tolerances. • The process is off-center and has large variation. Dr. Joan Burtner, Assoc. Prof. of Industrial Engineering

3. Process Capability • Process Capability Analysis is appropriately conducted only on processes that have been shown to be “in-control” • Two standard measures • Cp • Compares variability of process to specifications • Cpk • Compares variability of process to specifications • Considers the question: “Is the process sufficiently centered?” Dr. Joan Burtner, Assoc. Prof. of Industrial Engineering

4. Process Capability Calculations • Calculations • Estimated values Dr. Joan Burtner, Assoc. Prof. of Industrial Engineering

5. Process Capability Evaluation • Guidelines for Evaluation of Cp • Cp < 1.00 Not Capable • Guidelines for Evaluation of Cp • Cpk > 1.33 Definitely Capable • 1.00 < Cpk < 1.33 Possibly Capable • Cpk < 1.00 Not Capable Dr. Joan Burtner, Assoc. Prof. of Industrial Engineering

6. Loss Function Evaluation • Loss function and its relation to quality is shown in Figure 10.10 • The Quadratic Loss Function is exhibited in Figure 10.11 • Calculations involve: • a loss coefficient (k) • the target (m) • the distance from the target (x) Dr. Joan Burtner, Assoc. Prof. of Industrial Engineering