Most quality problems in overseas manufacturing are not caused by bad factories but by unclear expectations. A supplier can only meet a standard that has been written down, agreed and checked. Effective quality control therefore starts before production — and ends before the goods leave the factory, when problems are still cheap to fix.
1. Define quality before production
- Drawings with critical-to-quality (CTQ) dimensions marked, and a general tolerance standard (e.g. ISO 2768) for everything else
- Material and finish specification, including grade, color references (Pantone/RAL) and surface texture
- Approved golden sample signed off by both sides and kept at the factory
- Defect classification: what counts as critical, major and minor
- Functional test procedure for assemblies and electronics
- Packaging and labeling requirements
2. First Article Inspection (FAI)
The first parts from production tooling or a new setup are measured against every dimension on the drawing — not just the critical ones. FAI catches setup errors, tool issues and drawing misinterpretation before a whole batch is made. For machined and molded parts, ask for a dimensional report; for assemblies, a functional and cosmetic check against the golden sample.
3. In-process inspection (DUPRO)
For longer runs, an inspection when roughly 20–60% of the order is produced (a common rule of thumb) verifies that quality has not drifted: tool wear, material lot changes, operator changes. Problems found here can still be corrected for the rest of the order.
4. Pre-shipment inspection (PSI) and AQL
When production is complete and at least most goods are packed, a random sample is inspected. Sample sizes usually follow ISO 2859-1 (ANSI/ASQ Z1.4), with an Acceptable Quality Limit (AQL) per defect class.
| Defect class | Example | Commonly used AQL |
|---|---|---|
| Critical | Safety hazard, product does not work | 0 (none accepted) |
| Major | Out-of-tolerance CTQ dimension, visible scratch on A-surface | 1.0–2.5 |
| Minor | Small cosmetic mark on a hidden surface | 2.5–4.0 |
These AQL values are common starting points, not rules — agree them per product. A typical PSI also covers quantity, packaging, labeling, carton drop test and function tests on a sample.
5. When defects are found
- Quarantine the affected lot and document defects with photos and measurements.
- Find the root cause (tool, material, process, operator, drawing).
- Agree the disposition: rework, sorting, replacement or credit — ideally pre-defined in the purchase agreement.
- Re-inspect after rework before shipping.
- Update the process or inspection plan so it does not repeat.
Who should do the inspection?
Options include the factory’s own QC, an independent third-party inspection company, or a sourcing partner with inspectors on the ground. Independent inspection adds cost but removes the conflict of interest of a factory approving its own work. For critical parts, combine a factory dimensional report with independent verification of the CTQ dimensions.
See how quality control fits into our process on the About page, or send us your drawings to discuss an inspection plan.