Block 25 Control Charts 13

658 views

Published on

Published in: Technology, Business
  • Be the first to comment

Block 25 Control Charts 13

  1. 1. Senior/Graduate HMA Course Quality control/quality assurance Control ChartsConstruction QC/QA Control Charts 1
  2. 2. Control ChartsConstruction QC/QA Control Charts 2
  3. 3. Variation - Chance Causes - Assignable CausesConstruction QC/QA Control Charts 3
  4. 4. Chance Causes1. Everything varies2. Individuals are unpredictable3. Groups from a constant system tend to be predictable Construction QC/QA Control Charts 4 8-31
  5. 5. Example: Chance Causes1. People live to different ages2. No one knows how long he or she will live3. Insurance companies can predict the percentage of people who will live to certain ages Construction QC/QA Control Charts 5
  6. 6. Assignable CausesIf identified - It can be eliminatedConstruction QC/QA Control Charts 6
  7. 7. Benefits of Control Charts- Early Detection of Trouble- Decrease Variability- Establish Process Capability- Reduce Price AdjustmentCosts- Decrease InspectionFrequencyConstruction QC/QA Control Charts 7
  8. 8. Benefits of Control Charts• Basis for Altering Specification Limits• Permanent Record of Quality• Provide a Basis for Acceptance• Instill Quality AwarenessConstruction QC/QA Control Charts 8
  9. 9. Control Chart Analysis AASHTO “To Develop a Quality Control/Quality Assurance Plan for Hot Mix Asphalt”Construction QC/QA Control Charts 9
  10. 10. Upper control limit Lower control limit 1 2 3 4 5 6 7 Lot NumberConstruction QC/QA Control Charts 10
  11. 11. Statistical Control Chart Upper Control Limit Data Points Target Value Lower Control LimitConstruction QC/QA Control Charts 11
  12. 12. Five lines on a statistical process control chart • Target value • Warning upper control limit • Warning lower control limit • Action upper control limit • Action lower control limitConstruction QC/QA Control Charts 12
  13. 13. Upper Control Limit Mean Lower Control Limit 1 2 3 4 5 6 7 Lot NumberConstruction QC/QA Control Charts 13
  14. 14. Statistical Control Charts Upper and Lower Warning Control Limits UWCL = X + { 2 (s) / (n)1/2 } LWCL = X + { 2 (s) / (n)1/2 }Construction QC/QA Control Charts 14
  15. 15. Statistical Control Charts Upper and Lower Action Control Limits UWCL = X + { 3 (s) / (n)1/2 } LWCL = X + { 3 (s) / (n)1/2 }Construction QC/QA Control Charts 15
  16. 16. Example Problem• Given: – Target asphalt binder content: 5.7 % – Standard deviation – 0.25 % – The rolling average is based on five data pointsConstruction QC/QA Control Charts 16
  17. 17. Example Problem warning limits UWCL = X + { 2 (s) / (n)1/2 } UWCL = 5.7 + { 2 (.25) / (5)1/2 } UWCL = 5.9Construction QC/QA Control Charts 17
  18. 18. Example Problem warning limits LWCL = X - { 2 (s) / (n)1/2 } LWCL = 5.7 - { 2 (.25) / (5)1/2 } LWCL = 5.5Construction QC/QA Control Charts 18
  19. 19. Example Problem warning limits UACL = X + { 3(s) / (n)1/2 } UACL = 5.7 + { 3 (.25) / (5)1/2 } UACL = 6.0Construction QC/QA Control Charts 19
  20. 20. Example Problem warning limits LACL = X - { 3 (s) / (n)1/2 } LACL = 5.7 - { 3 (.25) / (5)1/2 } UWAL = 5.4Construction QC/QA Control Charts 20
  21. 21. Look for Assignable Cause If:• One point is outside of control limits• Eight consecutive points are on one side ofthe target value Construction QC/QA Control Charts 21
  22. 22. Interpreting X & R Charts
  23. 23.  Chart 6 Action Limit (UCL) 5 Warning Limit% Air Voids 4 3 Action Limit (LCL) 2 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 Sample Number
  24. 24. Range (R) Chart 8 (UCL) 7 6% Air Voids 5 4 3 2 1 (LCL) 0 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 Sample Number
  25. 25. Control Charts Rules of Thumb Lack of Control Occurs When: Change in X, R Constant Change in R, X Constant Change in Both X & R
  26. 26. Sustained Shift in  6 Action Limit Mean Incr eases 5 War ning Li mi t% Air Voids 4 3 2 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 Sample Number
  27. 27. Trend in  6 Action Limit 5 Warning Limit% Air Voids 4 3 Production "Upward Drift" 2 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 Sample Number
  28. 28. Irregular Shift in  6 Action Limit (UCL) 5 Warning Limit% Air Voids 4 3 Action Limit (LCL) 2 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 Sample Number
  29. 29. Sudden Change in R 9 8 (UCL) 7% Air Voids 6 5 4 3 2 1 (LCL) 0 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 Sample Number
  30. 30. Gradual Change in R 9 8 (UCL) 7 6% Air Voids 5 4 3 2 1 (LCL) 0 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 Sample Number
  31. 31. Irregular Shift in  & R 6 Action Limit (UCL) 5 Warning Limit% Air Voids 4 3 Action Limit (LCL) 2 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 Sample Number
  32. 32. Lack of Control? 6 Single Point Above Action Limit Action Limit 5 Warning Limit% Air Voids 4 3 Eight Points Below Target 2 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 Sample Number
  33. 33. Questions?Construction QC/QA Control Charts 33

×