Report

Statistical Process Control (SPC) Tools ISE 412 Spring 2014 ISE 412 Spring 2014 1 Why do we need SPC tools? • We need Quality! • With SPC, the process is monitored through sampling. • Considering the results of the sample, we can prevent or improve the our week point in production lines. ISE 412 Spring 2014 2 ISE 412 Spring 2014 3 What do SPC tools monitor? Process variability Random o common causes o inherent in a process o can be eliminated only through improvements in the system No-Random o special causes o due to identifiable factors o can be modified through operator or management action ISE 412 Spring 2014 4 What are SPC tools? 1. 2. 3. 4. 5. 6. 7. 8. Histogram Check Sheet Pareto Chart Cause and Effect Diagram Defect Concentration Diagram Scatter Diagram Control Chart … ISE 412 Spring 2014 5 What are SPC tools? • Histogram Example 1 ISE 412 Spring 2014 6 What are SPC tools? • Check Sheet ISE 412 Spring 2014 7 What are SPC tools? • Pareto Chart Example 2 ISE 412 Spring 2014 8 What are SPC tools? • Cause and Effect Diagram (example3) ISE 412 Spring 2014 9 What are SPC tools? • Defect Concentration Diagram ISE 412 Spring 2014 10 What are SPC tools? • Scatter Diagram (example4) ISE 412 Spring 2014 11 What are SPC tools? • Control Charts! Control Chart 35 Number of Errors 30 UCL=28.0 25 20 Avg=16.0 15 10 5 0 LCL=4.0 5 10 15 20 Week ISE 412 Spring 2014 12 Why Control Charts? ISE 412 Spring 2014 13 What kinds of Control Charts do we have? • Attribute – a product characteristic that can be evaluated with a discrete response – good – bad; yes – no 1. Fraction nonconforming (P-chart) 2. # nonconforming per inspection (C-chart) • Variable – a product characteristic that is continuous and can be measured 1. Range (R-chart) – weight - length 2. Mean (x bar-chart) 3. Variability (S-chart) ISE 412 Spring 2014 14 Application of Control Charts • • • • Outlier Run Trend Cyclicity ISE 412 Spring 2014 15 Process Capability Analysis • Process capability is the ability of the process to meet the design specifications for a service or product. • Nominal value is a target for design specifications. • Tolerance is an allowance above or below the nominal value. ISE 412 Spring 2014 16 Process Capability Analysis ISE 412 Spring 2014 17 Process Capability Analysis • Specification Limits • Control Limits • Natural Tolerance Limits = + 3 = − 3 = = /c4 or /d2 Example 5 Nominal value Lower Limit 20 ISE 412 Spring 2014 Upper Limit 25 30 18 Process Capability Ratios • Process Capability Ratio, Cp: the tolerance width divided by 6 standard deviations (process variability). Cp = Upper specification - Lower specification 6 Example 5 ISE 412 Spring 2014 19 Process Capability Ratios • One-side Process Capability Ratio: − = 3 − = 3 Example 5 ISE 412 Spring 2014 20 Process Capability Ratios Nominal value Lower Limit 20 Upper Limit 25 ISE 412 Spring 2014 30 21 Process Capability Ratios Cp value could not indicate the proper process capability if the process is not centered since Cp does not account for where the process mean is with respect to the specifications. To alleviate this issue, another process capability index, Cpk is used: Cpk=min(Cpu,Cpl) ISE 412 Spring 2014 22 Cp Vs Cpk ISE 412 Spring 2014 23 Summary SPC tools: Capability Ratios: Histogram, Check Sheet, Pareto Chart, Cause and Effect Diagram, Defect Concentration Diagram, Scatter Diagram, Control Chart, And so more − = 6 − = 3 − = 3 = , } ISE 412 Spring 2014 24