Why/When is Taguchi Method Appropriate? Tip #5 Taguchi Method Appropriate Signal-to-Noise Ratio for Quality Characteristics approaching IDEAL value Friday, 18th May 2001

Tip #5 Taguchi Method Appropriate Signal-to-Noise Ratio for Quality Characteristics approaching IDEAL value (next 7 slides) Friday, 18th May 2001

Taguchi’s SN Ratio Quality 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 for LARGER-THE-BETTER quality characteristics is usually a desired output, for example Bond strength Critical Current Taguchi’s SN-Ratio for NOMINAL-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 Ratio Quality 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 Ratio Quality 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 for LARGER-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 Ratio Quality 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 Ratio Quality 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 Ratio Quality Characteristics approaching IDEAL value If our nominal values are far away from IDEAL value SN-Ratio for LARGER-THE-BETTER will give good additivity (prediction and results will match well) If our nominal values are already close to IDEAL value SN-Ratio for smaller-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 Ratio Quality 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 for smaller-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

Earlier Tips Links below Friday, 27th July 2001 Friday, 20th July 2001 Friday, 13th July 2001 Taguchi Method “inner” L9 array with “outer” L4 and L9 NoIsE arrays “inner” L18 array with “outer” L4 and L9 NoIsE arrays Taguchi Method Why/When is Taguchi Method not Appropriate? Tips 12, 11, 10 

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

Earlier Tips Links below Taguchi Method Identifies the “right” NoIsE factor(s) for Tolerance Design Taguchi Method Finds best settings to optimize TWO 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 Tips 6, 5, 4 

Earlier Tips Links below Friday, 25th May 2001 Friday, 18th May 2001 Friday, 11th May 2001 Taguchi Method Using Orthogonal Arrays for Generating Balanced Combinations of NoIsE Factors Taguchi Method Signal-to-Noise Ratio for Quality Characteristics approaching IDEAL value 4. Taguchi Method improves " quality “ at all the life stages at the design stage itself Tips 3, 2, 1 

Earlier Tips Links below Friday, 4th May 2001 Friday, 27th April 2001 Friday, 6th April 2001 3. Taguchi Method Appropriate for Concurrent Engineering 2. Taguchi Method can study Interaction between Noise Factors and Control Factors 1. Taguchi’s Signal-to-Noise Ratios are in Log form

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