First steps
- Collect 4 weeks of scrap data by defect type, station and shift.
- Pareto by cost, not only by count.
- Pick the top defect, check the gauge, then analyse causes with data.
How to measure success
Scrap rate (%) and scrap cost per month. Record the value before you start, so the effect of every action can be shown.
When these methods are the wrong choice
- Pareto chart: A single defect type with one known cause.
- Ishikawa (fishbone): Proving a cause; it only lists candidates to verify.
- SPC control charts: Characteristics without a capable gauge or with too few data.
- Cost of poor quality (COPQ): Root cause analysis.
- FPY / RTY: Field failures.
- MSA / Gage R&R: Nothing: do it before you trust any data.
- A3 report: Formal customer complaints that require an 8D form.
The methods in one line
| Method | What it is |
|---|---|
| Pareto chart | Ranks defect types or causes so the team works on the vital few first. |
| Ishikawa (fishbone) | Structured brainstorm of possible causes by 6M: man, machine, method, material, measurement, environment. |
| SPC control charts | Separates common-cause from special-cause variation and tells the operator when to react. |
| Cost of poor quality (COPQ) | Puts a money value on scrap, rework, sorting, warranty and complaints to set priorities. |
| FPY / RTY | First pass yield per step and rolled throughput yield of the whole line. |
| MSA / Gage R&R | Checks that the measurement system can see the variation you want to control. |
| A3 report | One-page PDCA story: background, current state, root cause, countermeasures, follow-up. |