A supplier can hold a valid ISO 9001 certificate and still deliver poor parts. A good supplier audit looks past the paperwork to whether the supplier can consistently make what you need.
Look at the process, not the manual
Spend most of your time where the product is made. Check:
- Are work instructions available at the workstation and actually followed?
- Are machines and tools maintained, with records?
- Are measuring instruments calibrated and suitable for your tolerances?
- How is nonconforming product identified and kept separate?
Follow one order end to end
Pick a recent order for your part and trace it: from order review and material receipt, through production and inspection, to dispatch. Gaps in traceability show up quickly this way.
Check capability, not just conformity
Ask for process capability data (such as Cpk) on critical characteristics. A process that only just meets tolerance will eventually produce defects.
Talk to the people doing the work
Operators and inspectors often reveal more than managers. Ask how they know a part is good, what they do when something goes wrong, and how often it happens.
Review their own supplier control
Your supplier's quality depends on their suppliers too. Check how they select, monitor and audit their own sources, especially for critical materials.
Close the loop
Agree findings at the closing meeting, set clear corrective action deadlines and verify the actions later. An audit without follow-up is just a visit.
A supplier audit done well protects your customers, reduces incoming inspection, and builds a stronger long-term relationship with the supplier.