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Six Sigma explained through SPC and Control Limits

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Explaining Six Sigma to a layman in simple terms is always challenging. This presentation was prepared for non-process professionals to understand Six Sigma concept.

Published in: Design, Business, Technology
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Six Sigma explained through SPC and Control Limits

  1. 1. R. Attri Engineering Management Series, Paper No. 3, April 2010Six Sigma ProcessSimplifiedexplained through SPC and ControllimitsRaman K. AttriApril 2010R. Attri Engineering Management Series, Paper No. 3, April 2010
  2. 2. R. Attri Engineering Management Series, Paper No. 3, April 2010Six Sigma DefinedProcess characterization to optimize all manufacturingprocesses to achieve Cp and Cpk value equal to 2.0.Measure to define the capability of a processGoal for improvement that reaches near-perfectionSystem of Management approach to achieve highest qualityand performance
  3. 3. R. Attri Engineering Management Series, Paper No. 3, April 2010Process Variations vs QualityExample of a metal block of required length =10cmTolerance= +1%UCL= 10.1cmLCL= 9.9cm
  4. 4. R. Attri Engineering Management Series, Paper No. 3, April 2010Process Variations vs QualityPlot of Sample Data Over Time0204060801 5 9 13 17 21TimeSampleValueSampleValueUCLAverageLCLLengthincm9.910.1samplesAny block of length less than 9.9cm andmore than 10.1cm is said to have a“defect”.Two “opportunities” for defects – one inlength and one in breadth
  5. 5. R. Attri Engineering Management Series, Paper No. 3, April 2010Process Variations vs QualityPlot of Sample Data Over Time0204060801 5 9 13 17 21TimeSampleValueSampleValueUCLAverageLCLLengthincm9.910.1samplesAny block of length less than 9.9cm andmore than 10.1cm is said to have a“defect”.Two “opportunities” for defects – one inlength and one in breadth
  6. 6. R. Attri Engineering Management Series, Paper No. 3, April 2010Process Variations vs QualityPlot of Sample Data Over Time0204060801 5 9 13 17 21TimeSampleValueSampleValueUCLAverageLCLLengthincm9.910.1samplesAny block of length less than 9.9cm andmore than 10.1cm is said to have a“defect”.Two “opportunities” for defects – one inlength and one in breadth
  7. 7. R. Attri Engineering Management Series, Paper No. 3, April 2010Process Variations vs QualityPlot of Sample Data Over Time0204060801 5 9 13 17 21TimeSampleValueSampleValueUCLAverageLCLLengthincm9.910.1samplesAny block of length less than 9.9cm andmore than 10.1cm is said to have a“defect”.Two “opportunities” for defects – one inlength and one in breadth
  8. 8. R. Attri Engineering Management Series, Paper No. 3, April 20103-Sigma vs 6-Sigma Process68.2%95.4%99.6%99.9%1 σ2 σ3 σ6 σ6-σ process target 99.9% of thesamples within UCL and LCL. A 0.1 %error margin (below specified quality)LSL USL
  9. 9. R. Attri Engineering Management Series, Paper No. 3, April 2010σ-level in terms of defectsConcept of DPM coined by Bill Smith of MotorolaProcess capability is calculated using statistical toolsProcess capability in terms of σ is a symbol of quality forcustomer.
  10. 10. R. Attri Engineering Management Series, Paper No. 3, April 2010Process variations hit bottom-line ofoperationsQuality issues in product variations may result in unhappycustomers and eventually lose of salesHigherCostsReducedSalesProductVariationPoorQualityUnhappyCustomers
  11. 11. R. Attri Engineering Management Series, Paper No. 3, April 2010Process ControlFrequency(length)SizeLower control limit Upper control limit(a) In statisticalcontrol and capableof producing withincontrol limits, 6 Sigma
  12. 12. R. Attri Engineering Management Series, Paper No. 3, April 2010Process ControlFrequency(length)SizeLower control limit Upper control limit(a) In statisticalcontrol and capableof producing withincontrol limits, 6 Sigma(b) In statistical controlbut not capable ofproducing withincontrol limits3-Sigma
  13. 13. R. Attri Engineering Management Series, Paper No. 3, April 2010Process ControlFrequency(length)SizeLower control limit Upper control limit(a) In statisticalcontrol and capableof producing withincontrol limits, 6 Sigma(b) In statistical controlbut not capable ofproducing withincontrol limits3-Sigma(c) Out of control
  14. 14. R. Attri Engineering Management Series, Paper No. 3, April 2010Measuring Process Capabilityσ6LSLUSLC p−=σμ3LSL−σμ3−USL=pkC Lesser of orProcess capability is a measure of therelationship between the natural variation ofthe process and the design specificationsA capable process must have a Cp or Cpkof at least 1.0A capable process is not necessarily in thecenter of the specification, but it falls withinthe specification limit at both extremesSix Sigma quality requires a Cp = 2.0
  15. 15. R. Attri Engineering Management Series, Paper No. 3, April 2010Meanings of Cpk MeasuresCpk = negative numberCpk = zeroCpk = between 0 and 1Cpk = 1Cpk > 1
  16. 16. R. Attri Engineering Management Series, Paper No. 3, April 2010Process Design Options3-Sigma process if off centre causes capability issue6-Sigma process allows for 1.5 Sigma Process ShiftAccounts for long term variability and complexity of process(Ranges from 1.4 to 1.6 sigma)3.4 DPMO = area under curve at 4.5 sigma level
  17. 17. R. Attri Engineering Management Series, Paper No. 3, April 2010End-to-End Effectiveness is Key
  18. 18. R. Attri Engineering Management Series, Paper No. 3, April 2010Goal of Six SigmaSigma DPMO Yield Cpk1.5 500,000 50% 0.503.00 66,800 93.320% 1.003.50 22,700 97.730% 1.174.00 6,210 99.3790% 1.334.50 1,350 99.8650% 1.505.00 230 99.9770% 1.676.00 3.4 99.99966% 2.00Goal of Six Sigma is to drive up Cp and Cpk to at least 2!
  19. 19. R. Attri Engineering Management Series, Paper No. 3, April 2010Author’s contactFor any questions or training queries, contact the author:Raman K. Attrirkattri@rediffmail.comAuthor has over 15 years of project management, product development and quality management experience in leadingMNC product development corporations. He has earned numerous international certification awards - CertifiedManagement Consultant (MSI USA/ MRA USA), Certified Six Sigma Green Belt Professional (Six Sigma India),Certified Quality Director (ACI USA), Certified Engineering Manager (SME USA), Certified Project Director (IAPPMUSA), to name a few. His research and training interests are in learning, development, performance management,research management and product development. He holds MBA, Executive MBA, Masters in Technology and Bachelorin Technology. In addition to this, he has 60+ educational qualifications, credentials and certifications in his name..

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