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S tatistical P rocess C ontrol S P C

S tatistical P rocess C ontrol S P C. Definitions. Special Cause (also assignable causes) special causes refer to any factors of variation that are not always acting on the process. They affect the process in unpredictable ways. Common Cause

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S tatistical P rocess C ontrol S P C

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  1. Statistical Process Control S P C SPC Design

  2. Definitions • Special Cause (also assignable causes) • special causes refer to any factors of variation that are not always acting on the process. They affect the process in unpredictable ways. • Common Cause • common causes refer to the many sources of variation within a process that has a stable and repeatable distribution over time. The output is predictable. SPC Design

  3. Distribution Standard Normal Distribution Distribution of total points for the sum of three dices 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 SPC Design

  4. Distribution Standard Normal Distribution Bell-shaped Curve (Gauß) SPC Design

  5. Standard Normal Distribution Turning-Point  s -5 5 6 -4 -6 -2 -3 -1 0 2 3 4 1 X SPC Design

  6. Glossary and Symbols Target and Prediction ??? ? SPC Design

  7. Glossary and Symbols • x : mean valuecompute the mean value, using the following formula: the sum of values from a given sample X = number of values (sample size) SPC Design

  8. Glossary and Symbols Σ Rj • R • s2 • s = average range of subgroups m Σ s2j average variance = m Σ sj average sample standard diviation = m SPC Design

  9. Glossary and Symbols • Upper Control Limit ( UCL ) line(s) on a control chart used as a basis for judging the stability of the processFormula: UCL R= D4* R UCL x = x + A2* R UCL s = B4* s UCL x = x + A3* s SPC Design

  10. Glossary and Symbols • Lower Control Limit ( LCL ) line(s) on a control chart used as a basis for judging the stability of the processFormula: LCL R= D3* R LCL x = x - A2* R LCL s = B3* s LCL x = x - A3* s SPC Design

  11. Glossary and Symbols • Upper Specification Limit ( USL ) • Lower Specification Limit ( LSL ) • upper/ lower engineering specification limit • engineering requirement for judging acceptability of a particular characteristic SPC Design

  12. Process Potential & Capability Loss Function USL LSL Customer Requirement acceptable acceptable good good Loss Loss very good Target Value SPC Design

  13. Process Potential & Capability cp: Process Potential • an index based on long-term observation of a process in a state of statistical control pp: Preliminary Process Potential • short-term observation of process • early information of new or changed process • used for process and equipment development SPC Design

  14. Process Potential & Capability SPC Design

  15. Process Potential & Capability • PIST: • Percent of Inspection points which Satisfy the Tolerance number of characteristics satisfying tolerance PIST = x 100 total number of characteristics SPC Design

  16. Process Potential & Capability • PIPC • Percentage of Indices which are Process Capable number of characteristics with pp/ ppk 1,67 PIPC = x 100 total number of characteristics SPC Design

  17. Control Chart Header, information relating to plant, machine, shift, part number, ..... X Bar Chart showing: USL, UCL, x, ....., LSL, LCL results over time Reaktion Plan Quality References Ranges (R Chart) showing: USL, UCL, R, ....., LSL, LCL results over time relating to: R, s, s2 Instruction regarding computation, .... Individual readings, summary & dates explaning and relating to data for graph SPC Design

  18. Control Chart Header, information relating to plant, machine, shift, part number, ..... Process Log Sheet (Back of Page): Information relating any changes made to process: Example: new tooling, materials, ..... change of shift, unplanned down time, ..... maintenance, cleaning, ..... ..... all information that night be needed when investigating root causes of problems SPC Design

  19. Qualitätsregelkarte • Interpretation/ Overadjustment Upper Specification Limit Upper Control Limit Upper Warning Limit Mean Lower Warning Limit Lower Control Limit Lower Specification Limit SPC Design

  20. Bibliography • Statistical Process Control (SPC) Reference Manual, Chrysler, Ford, GM, Ausgabe 1995 • The Memory Jogger II, GOAL/ QPC, First Edition, Methuen, Mass. USA 1994 • Qualitätsmanagement von A-Z, Kaminske/ Bauer, Hanser Verlag, 2. Edition 1994 • The Six Sigma Phenomenon, Mikel Harry, Richard Schroeder SPC Design

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