1. DOX 6E Montgomery1 EEM332 Design of Experiments En. Mohd Nazri Mahmud MPhil (Cambridge, UK) BEng (Essex, UK) nazriee@eng.usm.my Room 2.14 Ext. 6059

2. DOX 6E Montgomery2 Design of Engineering Experiments Part 1 – Introduction Chapter 1, Text Some basic principles and terminology The strategy of experimentation Guidelines for planning, conducting and analyzing experiments

3. DOX 6E Montgomery3 Introduction to DOX An experiment is a test or a series of tests Experiments are used widely in the engineering world –Process characterization & optimization –Evaluation of material properties –Product design & development –Component & system tolerance determination “All experiments are designed experiments, some are poorly designed, some are well-designed”

4. DOX 6E Montgomery4 Engineering Experiments Reduce time to design/develop new products & processes Improve performance of existing processes Improve reliability and performance of products Achieve product & process robustness Evaluation of materials, design alternatives, setting component & system tolerances, etc.

5. DOX 6E Montgomery5 The Basic Principles of DOX Randomization –Running the trials in an experiment in random order –Notion of balancing out effects of “lurking” variables Replication –Sample size (improving precision of effect estimation, estimation of error or background noise) Blocking –Dealing with nuisance factors

6. DOX 6E Montgomery6 Strategy of Experimentation “Best-guess” experiments –Used a lot –More successful than you might suspect, but there are disadvantages… One-factor-at-a-time (OFAT) experiments –Sometimes associated with the “scientific” or “engineering” method –Devastated by interaction, also very inefficient Statistically designed experiments –Based on Fisher’s factorial concept

7. DOX 6E Montgomery7 Strategy of Experiments Example: The golf experiment: –Type of driver (regular or oversized) –Type of ball (balata or three-piece) –Walking vs. riding –Type of beverage (water or beer) –Time of round (morning or afternoon) –Weather (cool or hot, windy or calm) –Type of golf spike (metal or soft) –Etc, etc, etc…

8. DOX 6E Montgomery8 Strategy of Experiments Best Guess ? Select and arbitrary combination of factors, test them and observe. Change the level of factors based on observations Example: Select oversized driver, balata ball, golf cart and water as beverage and the resulting score is 87. It was observed that there were several wayward shots with the big driver. Therefore, change to regular-size driver and play again.. What is your assessment on this approach? Can we guarantee that we can arrive at the BEST combination?

9. DOX 6E Montgomery9 Strategy of Experiments One factor at a time ? Riding, regular size driver and drinking water improve the score Type of ball has no effect What is your assessment on this approach?

10. DOX 6E Montgomery10 Strategy of Experiments If use regular-sized driver, type of beverage has no effect If use oversized driver, type of beverage has an effect Interaction between factors

11. DOX 6E Montgomery11 Strategy of Experiments Factorial ? Factors are varied together and observe the joint effects Example: A two-factor factorial experiment 2 2 factorial design

12. DOX 6E Montgomery12 Factorial Designs In a factorial experiment, all possible combinations of factor levels are tested The golf experiment: –Type of driver –Type of ball –Walking vs. riding –Type of beverage –Time of round –Weather –Type of golf spike –Etc, etc, etc…

13. DOX 6E Montgomery13 Factorial Design

14. DOX 6E Montgomery14 Factorial Design The effect of switching from oversized driver to regular-sized driver Driver effect = (92+94+93+91)/4 - (88+91+88+90)/4 = 3.25

15. DOX 6E Montgomery15 Factorial Design Ball effect = (88+91+92+94)/4 - (88+90+93+91)/4 = 0.75

16. DOX 6E Montgomery16 Factorial Design Interaction effect = (92+94+88+90)/4 - (88+91+93+91)/4 = 0.25

17. DOX 6E Montgomery17 Factorial Designs with Several Factors

18. DOX 6E Montgomery18 Factorial Designs with Several Factors A Fractional Factorial

19. DOX 6E Montgomery19 Planning, Conducting & Analyzing an Experiment 1.Recognition of & statement of problem 2.Choice of factors, levels, and ranges 3.Selection of the response variable(s) 4.Choice of design 5.Conducting the experiment 6.Statistical analysis 7.Drawing conclusions, recommendations

20. DOX 6E Montgomery20 Assignment 1 Conducting an experiment on in groups