SPC Basics

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SPC Basics

• Rajesh Tahiliani

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Inspection

• Inspection puts emphasis on the final product
• It is after the fact (quality cannot be inspected
  into a product).

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Statistical Process Control
SPC puts emphasis on prevention of defects
using statistical methods, such that the entire
process is monitored, and adjusted
appropriately to ensure correct
performance. Source Summers, Donna C. S.
Quality, 5th ed. Prentice Hall. Page 12.
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Tools of SPC

• Paretto Chart
• Cause and Effect diagram
• Scatter plot

• Variable control charts
• Attribute control charts

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Some Probability Rules

• Rule of Addition
• General Rule of Multiplication
• Special Rule of Multiplication

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Probability Distributions

• Normal Distribution (X-bar or Mean chart)
• Binomial Distribution (p-chart)
• Poisson Distribution (c-chart)

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Quality Costs

• Prevention Cost
• Appraisal Cost
• Internal failure Cost
• External failure Cost

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Prevention and Appraisal (good)

• Prevention
• Education
• Training
• Planning

• Appraisal
• Audits
• Measurements
• Laboratory related

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Failure Costs (bad)

• Internal (before the customer finds out)
• External (the customer finds out)

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Green Red Space

• Green Space (work done for the first time)
• Good
• Red Space (rework)
• Not good

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