Question

Briefly explains the importance of experimental design in engineering. Discuss some examples for its application.

Answer 1

Experimental design is a technique that enables scientists and engineers to efficiently assess the effect of multiple inputs, or factors, on measures of performance, or responses. Compared to one factor at a time, trial and error approaches, a well-designed experiment can provide clear results while dramatically reducing the required amount of testing.

Engineers are responsible for both defining products and building systems or processes that work. This requires attention to detail and ingenuity. Competitive pressure means tight development schedules and careful cost considerations.

The first step on the road from concept to products in stores involves building and testing prototypes. One way to test a prototype product, system or process is to change it in some way and measure
the effect of that change on some measure of performance. In experimental design parlance, measures of performance are called responses. Factors are aspects of the prototype that we can change or control. Usually, we are interested in understanding the effects of more than one factor, which requires multiple tests of various prototypes. Here, experimental design is about how to decide which prototypes to test and how to go about testing them.

Example of Experimental Design:

While doing interior design of a new house, the final effect of interior design will depend on various factors such as colour of walls, lights, floors, placements of various objects in the house, sizes and shapes of the objects and many more. Each of these factors will have an impact on the final outcome of interior decoration. While variation in each factor alone can impact, a variation in a combination of these factors at the same time also will impact the final outcome.

Hence it needs to be studied how each of these factors impact the final outcome, which are the critical factors impacting the most, which are the most important combination of these factors impacting the final outcome significantly.

The interior designer can plan and conduct some experiments.

Basics of Experimental Design

It allows manipulating multiple input factors and determining their effect on a desired output (response). By changing multiple inputs at the same time, Experimental Design helps to identify important interactions that may be missed when experimenting with only one factor at a time. We can investigate all possible combinations (full factorial) or only a portion of the possible combinations (fractional factorial).

A well planned and executed experiment may provide a great deal of information about the effect on a response variable due to one or more factors. Many experiments involve holding certain factors constant and altering the levels of another variable. This "one factor at a time" approach to process knowledge is, however, inefficient when compared with changing multiple factor levels simultaneously.

A well-performed experiment may provide answers to the following such as:

• What are the key factors in a process? (both controllable and uncontrollable)
• At what settings would the process deliver acceptable performance?
• What are the key, main and interaction effects in the process?
• What settings would bring about less variation in the output?

A repetitive approach to gaining knowledge should be taken up, typically involving these consecutive steps:

• A screening design that narrows the field of variables under assessment.
• A “full factorial” design that studies the response of every combination of factors and factor levels, and an attempt to zero in on a region of values where the process is close to optimization.

A basic approach to a Design of Experiment

We need to follow the below steps in sequence for conducting a Experimental Design

1. Define the problem(s)
2. Determine objective(s)
3. Brainstorm
4. Design experiments
5. Conduct experiments and collect data
6. Analyse data
7. Interpret results
8. Verify predicted results

Conclusion

Experimental Design has been in use for many years in manufacturing industry. Below are some of the benefits/improvements we can expect from conducting Experimental Designs:

• 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.