EEM332

1
EEM332

• Design of Experiments

En. Mohd Nazri Mahmud MPhil (Cambridge, UK) BEng (Essex, UK) nazriee_at_eng.usm.my Room 2.14 Ext. 6059
2
Design of Engineering ExperimentsPart 1
IntroductionChapter 1, Text

• Some basic principles and terminology
• The strategy of experimentation
• Guidelines for planning, conducting and analyzing
  experiments

3
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
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
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
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 Fishers factorial concept

7
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
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
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
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
Strategy of Experiments
Factorial ?
Factors are varied together and observe the joint
effects
Example A two-factor factorial experiment
22 factorial design
12
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
Factorial Design
14
Factorial Design
The effect of switching from oversized driver to
regular-sized driver
Driver effect (92949391)/4 -
(88918890)/4 3.25
15
Factorial Design
Ball effect (88919294)/4 - (88909391)/4
0.75
16
Factorial Design
Interaction effect (92948890)/4 -
(88919391)/4 0.25
17
Factorial Designs with Several Factors
18
Factorial Designs with Several FactorsA
Fractional Factorial
19
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
Assignment 1

• Conducting an experiment on in groups