Free Quality C Charts
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This document discusses using a C chart to analyze count data for defects. It provides instructions on how to develop a C chart, including collecting count data, graphing the data, calculating the average number of defects, determining the upper and lower control limits, and analyzing the chart to identify non-random patterns indicating a potential issue with the process. An example using data from a shoe manufacturer is provided to demonstrate the steps. An exercise using data from a bolt manufacturer is also included to allow practicing the technique.
Free Quality C Charts
- 2. Develop a Count Chart Amanda Christensen, BYU MBA Class of 2009 Professor: Dr. Tom Foster
- 3. What Will Be Covered Communicate Number of Defects Collect Data Graph Data Find Nonrandom Patterns Calculate the Average Determine Limits An Example and an Exercise
- 4. The Tool Defined C Chart Graphs Number of Defects Clean Presentation Determines Whether a Process is in Control Visual Determination
- 5. Brainstorming Exercise How can this tool be used in your organization?
- 6. Communicate Number of Defects Collect Data Number of Defects per Unit Number of Defects per Inspection Lot Graph Data X-Axis Represents Number of Inspected Products Y-Axis Represents Number of Defects
- 7. Find Nonrandom Patterns Calculate the Average Find Average Number of Defects per Unit or Lot (C Bar) Add Line to Graph Representing C Bar. This is the Central Line.
- 8. Find Nonrandom Patterns Determine Limits Find Standard Deviation of Data Upper Control Limit UCL = c bar + 3*( √c bar) Lower Control Limit LCL = c bar – 3 *( √c bar) Add Limit Lines to the Graph
- 9. Next Steps Determine if Process is Random or Nonrandom Evaluate Process if Necessary
- 10. Collide Shoes A Real World Example
- 11. Collect Data Record Date and Number of Defects per Shoe 11-Oct 6 10-Oct 1 9-Oct 2 8-Oct 4 7-Oct 7 6-Oct 6 5-Oct 2 4-Oct 2 3-Oct 3 2-Oct 5 1-Oct 2 Date Defects
- 12. Graph Data
- 13. Calculate the Average Find C Bar Add C Bar, Central Line, to Graph
- 14. Determine Limits Find Standard Deviations, Then Use Formulas: UCL = c bar + 3*( √c bar) LCL = c bar – 3 *( √c bar) Standard Deviation = 1.53 UCL = 7.53 LCL = -1.64
- 16. Gentry Bolts An Exercise
- 17. Collect Data Record Number Inspected and Number Failed 10 700 5 450 10 300 9 1000 4 500 7 800 6 600 # Failed # Inspected
- 18. Graph the Data
- 19. Gentry Graph
- 20. Next Steps Calculate the Average Find Standard Deviation Calculate Upper and Lower Limits UCL = c bar + 3*( √c bar) LCL = c bar – 3 *( √c bar)
- 21. Graph the Central Line and UCL and LCL
- 23. Summary Communicate Number of Defects Collect Data Graph Data Find Nonrandom Patterns Calculate the Average Determine Limits
- 24. Readings List Calculating the (Almost) Exact Control Limits for a C-Chart. By: Kittlitz Jr., Rudolf G.. Quality Engineering, Jul-Sep2006, Vol. 18 Issue 3, p 359-366, 8 p. Statistical Methods for SPC & TQM. By: Derek Bissell. Statistical Process Control and Quality Improvement. By: Gerald M. Smith