Page 529 - Design for Six Sigma a Roadmap for Product Development

488 Chapter Thirteen

13.4.2 Main-effects chart
and interaction chart
In Taguchi experimental data analysis, plots of main-effect charts and
interaction charts are the same as those of classical experimental data
analysis.

Main-effects chart. The main-effects chart is a plot of average responses
at different levels of a factor versus the factor levels.

Example 13.13 Continuing Example 13.11, for factor A, there are two levels:
1 and 2. For level 1
26 38 16 6 3 17 18 16
Y 17.5
A 1
8
and for level 2
0 5 0 1 4 5 5 3
2.875
Y A 2
8
Plotting these two mean responses versus level, we get the main-effects
plots shown in Fig. 13.3.
Example 13.14 Continuing Example 13.13, factor A has three levels and

8 12 9 11 12 15

Y A 1 9.67; Y A 2 12.67;
3 3
21 18 20
19.67
Y A 3
3
By plotting the three mean responses versus the factor level, we get the
main-effects plot shown in Fig. 13.4.
For all factors in Example 13.12, we get the plots shown in Fig. 13.5.

Interaction chart. In a Taguchi experiment, only two-factor interac-
tions are considered, as higher-order interaction is assumed to be
insignificant. For two-factor interaction, the interaction chart is plot-
ted by displaying all factor level combinations for the relevant two fac-
tors. For example, in Example 13.13, BD is a significant interaction.
We compute

26 38 0 5 16 6 0 1
17.25; 5.75
Y B 1 D 1 Y B 1 D 2
4 4