This document intends to provide a quick guide to determine the factors/ interaction of factors that would have statistically significant effect on the output of interest. A simple way to do so is by constructing a normal probability plot of effects. Figure 1 is an example of such plot.
Data points that fall along the straight line (black dots) correspond to factorial effects with negligible influence on the output; while outliers that deviate greatly from the line (red dots) are factors/ interaction of factors that have a significant effect on the output. Figure 1 illustrates that factors A,C,D, and the interaction between factors A and D, are primary factorial effects that influence the output.
Figure 1: An example of normal probability plot
2.0 Experiment Design
The experiment of interest aims to evaluate the joint effects of four factors on injection molding products’ critical dimension. The four factors are listed in Table 1, with an alphabet assigned to each factor for easy referral in this report.
A Mold Temperature
B Holding Pressure
C Injection Rate
D Cooling Time
Table1: Four factors under investigation
Single replicate Factorial design is chosen for the investigation as it provides the smallest number of runs for which k factors can be studied in a complete factorial design. With four factors of interest, each at two levels, an experimental measurement from each of treatment combinations are required for the analysis. Table 2 shows the setting of the four factors for all treatment combinations.
Treatment Combination Factorial Effect
A B C D
1 (1) - - - -
2 a + - - -
3 b - + - -
4 ab + + - -
5 c - - + -
6 ac + - + -
7 bc - + + -
8 abc + + + -
9 d - - - +
10 ad + - - +
11 bd - + - +
12 abd + + - +
13 cd - - + +
14 acd + - + +
15 bcd - + + +
16 abcd + + + +
Table 2:Test matrix showing possible treatment combinations for a... [continues]
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