First steps
- Check the gauge (Type 1, Gage R&R).
- Plot the data in time order with subgroups.
- Investigate every signal and record the cause.
How to measure success
Signals per week and Ppk vs Cpk gap. Record the value before you start, so the effect of every action can be shown.
When these methods are the wrong choice
- SPC control charts: Characteristics without a capable gauge or with too few data.
- Multi-vari study: Problems already narrowed to two or three factors.
- MSA / Gage R&R: Nothing: do it before you trust any data.
- Standard work / work instruction: Processes that are still changing every week.
- Design of experiments (DOE): Problems whose cause is already known, or processes you cannot run for trials.
- Control plan: Nothing in series production: every IATF process needs one.
The methods in one line
| Method | What it is |
|---|---|
| SPC control charts | Separates common-cause from special-cause variation and tells the operator when to react. |
| Multi-vari study | Finds whether variation lives within the part, part to part or over time before you start experiments. |
| MSA / Gage R&R | Checks that the measurement system can see the variation you want to control. |
| Standard work / work instruction | The current best way to do a job, with key points and reasons, used for training and audits. |
| Design of experiments (DOE) | Tests several process settings at once to find the factors and interactions that drive the result. |
| Control plan | Lists every characteristic, how it is checked, how often and what the reaction plan is. |