1. 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

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

3. 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..

4. 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

5. 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 )

6. 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

7. 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 ]

8. 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 ]

9. 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

10. 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 

11. 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 

12. 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 

13. 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 

14. 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

15. end