Why/When is Taguchi Method Appropriate?

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
Taguchi Method Appropriate Signal-to-Noise Ratio
for Quality Characteristics approaching IDEAL
value (next 7 slides)
Tip 5
Friday, 18th May 2001
3
Taguchis SN Ratio Quality Characteristics
approaching IDEAL value

• Taguchis 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
• Taguchis SN-Ratio for LARGER-THE-BETTER
• quality characteristics is usually a desired
  output, for example
• Bond strength
• Critical Current
• Taguchis 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
Taguchis 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
Taguchis SN Ratio Quality Characteristics
approaching IDEAL value

• Taguchis SN-Ratio for smaller-the-better
• ( quality characteristics is usually an
  undesired output, say Defects )
• S/N Ratio ? 10 Log10 ( 1/n ? Yi2 )
• Taguchis SN-Ratio for LARGER-THE-BETTER
• ( quality characteristics is usually a desired
  output, say Current )
• S/N Ratio ? 10 Log10 ( 1/n ? 1/Yi2 )
• Taguchis SN-Ratio for NOMINAL-the-best
• ( quality characteristics is usually a nominal
  output, say Diameter )
• S/N Ratio ? 10 Log10 ( ?2 / ?2 )

6
Taguchis 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
Taguchis 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
• Taguchis 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
Taguchis 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
Taguchis 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
• Taguchi Method
• 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
• Taguchi Method
• Useful at ALL Life-stages of a Process or
  Product
• Taguchi Method
• 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. Taguchis Signal-to-Noise Ratios are in Log
  form

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