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Why/When is Taguchi Method Appropriate?. Tip #5 Taguchi Method Appropriate Signal-to-Noise Ratio for Quality Characteristics approaching IDEAL value. Friday, 18 th May 2001. Tip #5.
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Why/When is Taguchi Method Appropriate? Tip #5 Taguchi Method AppropriateSignal-to-Noise Ratio for Quality Characteristics approaching IDEAL value Friday, 18th May 2001
Tip #5 Taguchi Method AppropriateSignal-to-Noise Ratio for Quality Characteristics approaching IDEAL value(next 7 slides) Friday, 18th May 2001
Taguchi’s SN RatioQuality Characteristics approaching IDEAL value • Taguchi’s SN-Ratio for smaller-the-better • quality characteristics is usually an undesired output, for example • Defects like pin holes, particulates in deposition processes • Unwanted by-product or side effect • Taguchi’s SN-Ratio forLARGER-THE-BETTER • quality characteristics is usually a desired output, for example • Bond strength • Critical Current • Taguchi’s SN-RatioforNOMINAL-the-best • quality characteristics is usually a nominal output, for example • most parts in mechanical fittings have nominal dimensions • Ratios of chemicals or mixtures are nominally the best type. • Thickness should be uniform in deposition /growth /plating /etching..
Taguchi’s SN RatioQuality Characteristics approaching IDEAL value • But what about quality characteristics that approach an ideal value? • Examples are • Efficiency : all efficiencies approach the ideal value of 100% • Weld strength : approaches the ideal strength of the material • Critical temperature or Critical current density for High Temperature superconductors (YBCO) : These approach ideal values, say 92K and 108 A/cm2 • Which SN-Ratio is most suitable among the following ? • smaller-the-better • LARGER-THE-BETTER • NOMINAL-the-BEST
Taguchi’s SN RatioQuality Characteristics approaching IDEAL value • Taguchi’s SN-Ratio for smaller-the-better ( quality characteristics is usually an undesired output, say Defects ) • S/N Ratio = – 10 Log10 ( 1/n Yi2 ) • Taguchi’s SN-Ratio forLARGER-THE-BETTER ( quality characteristics is usually a desired output, say Current ) • S/N Ratio = – 10 Log10 ( 1/n 1/Yi2 ) • Taguchi’s SN-Ratio for NOMINAL-the-best ( quality characteristics is usually a nominal output, say Diameter ) • S/N Ratio = 10 Log10 ( 2/ 2 )
Taguchi’s SN RatioQuality Characteristics approaching IDEAL value • Generally, we would state that this value should be “LARGER-THE-BETTER” • However, there exists an IDEAL value!!! • QUESTION still IS “Which SN-Ratio is most suitable among the following ?” • LARGER-THE-BETTER • smaller-the-better • Nominal-the-best
Taguchi’s SN RatioQuality Characteristics approaching IDEAL value • Reword the SN-Ratio for smaller-the-better to indicate ‘the approach to IDEAL value’ by saying “Smaller-the-difference-from-IDEAL-the-better” • Taguchi’s SN-Ratio for smaller-the-better is now modified ( for quality characteristics approaching IDEAL output ) • S/N Ratio = – 10 Log10[1/n (YIDEAL-Yi ) 2 ]
Taguchi’s SN RatioQuality Characteristics approaching IDEAL value • If our nominal values arefar awayfromIDEAL value • SN-Ratio for LARGER-THE-BETTER will give good additivity (prediction and results will match well) • If our nominal values arealready closetoIDEAL value • SN-Ratio forsmaller-the-better (the modified form)will give good additivity (prediction and results will match well) = – 10 Log10[1/n (YIDEAL-Yi ) 2 ]
Taguchi’s SN RatioQuality Characteristics approaching IDEAL value • SN-Ratio for LARGER-THE-BETTER tends to predict optimistic (LARGER) values • Sometimes the value exceeds maximum possible value !? • SN-Ratio forsmaller-the-better (the modified form)always predicts values pessimistically (LESS than ideal value) • TRY BOTH, Select one with less ANOVA error Friday, 18th May 2001
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