TWI Frequently asked questions
by Marcus Warwick
To assess the impact of critical process control factors on the quality of a finished product, a design of experiments approach is useful. This is not a trivial exercise and is best facilitated by someone experienced in thetechnique. The outcome may be achieved by systematically following a series of steps, as follows:
- Define the problem and objectives
- Define the process or system
- Identify the causal or nuisance factors
- Identify the potential control factors
- Select levels and ranges for the control factors
- Select response variable(s)
- Assess measurement gauge capability
- Choose experimental design (e.g. sample size, run order)
- Collect the experimental material
- Perform the experiment
- Analyse results to test hypothesis and to develop an empirical model
- Predict performance from optimum conditions in empirical model
- Run a confirmation trial
- Run further experiments at optimum settings
Screening experiments may be used to identify critical factors, with more refined designs then used to identify optimum process conditions.
