First steps
- Feasibility review with production and suppliers.
- Capability data from similar parts.
- Agree tolerances before design freeze.
How to measure success
Number of late design changes. Record the value before you start, so the effect of every action can be shown.
When these methods are the wrong choice
- PFMEA / DFMEA: Fixing a problem that has already happened; update it after the 8D instead.
- Process capability (Cpk): Unstable processes; make them stable first.
- Design of experiments (DOE): Problems whose cause is already known, or processes you cannot run for trials.
- APQP: Problems in a running series process.
- Hypothesis tests: Exploring causes; use it to confirm them.
The methods in one line
| Method | What it is |
|---|---|
| PFMEA / DFMEA | Analyses how a process or design can fail, rates the risk (AP) and defines prevention and detection. |
| Process capability (Cpk) | Compares the process spread and centring with the tolerance and predicts PPM. |
| Design of experiments (DOE) | Tests several process settings at once to find the factors and interactions that drive the result. |
| APQP | Five-phase launch plan with gates, so problems are prevented before SOP. |
| Hypothesis tests | Proves whether a difference (before / after, machine A / B) is real or chance. |