Why/When is Taguchi Method Appropriate?

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

Taguchi Method 1st Priority : Variance Reduction2nd Priority : Factor Effects 15.“inner” L9 array with “outer” L4 and L9 NoIsE arrays Taguchi Method “inner” L18 array with “outer” L4 and L9 NoIsE arrays Taguchi Method Why/When is TaguchiMethod not Appropriate? Friday, 3rd Aug 2001 Friday, 27th July 2001 Friday, 20th July 2001 Friday, 13th July 2001 More Tips Links below Tips 12, 11, 10 

Taguchi Method “inner” L8 array with “outer” L4 and L9 NoIsE arrays Taguchi Method Useful at ALL Life-stages of a Process or Product Taguchi Method Performs Process “centering” or “fine tuning” Friday, 6th July 2001 Friday, 29th June 2001 Friday, 22nd June 2001 More Tips Links below Tips 9, 8, 7 

Taguchi Method Identifies the “right”NoIsEfactor(s) for Tolerance Design Taguchi Method Finds best settings to optimizeTWO quality characteristics Simultaneously 7. Taguchi Method When to select a ‘Larger’ OA to perform “Factorial Experiments” Friday, 15th June 2001 Friday, 8th June 2001 Friday, 1st June 2001 More Tips Links below Tips 6, 5, 4 

Taguchi MethodUsing Orthogonal Arrays for Generating Balanced Combinations of NoIsE Factors Taguchi MethodSignal-to-Noise Ratio for Quality Characteristicsapproaching IDEAL value 4. Taguchi Methodimproves " quality “ at all the life stages atthe design stage itself Friday, 25th May 2001 Friday, 18th May 2001 Friday, 11th May 2001 More Tips Links below Tips 3, 2, 1 

3. Taguchi MethodAppropriate forConcurrent Engineering 2. Taguchi Methodcan studyInteraction between Noise Factors and Control Factors 1. Taguchi’sSignal-to-Noise Ratiosare inLog form Friday, 4th May 2001 Friday, 27th April 2001 Friday, 6th April 2001 More Tips Links below

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Why/When is Taguchi Method Appropriate?