Metal Casting Supplier Audit Checklist for Overseas Buyers

Auditing a metal casting supplier before you sign a purchase order is not bureaucracy. It is the cheapest insurance you can buy. A foundry can look excellent on paper and still ship parts with internal porosity, the wrong material, or leaks that only show up on your test bench instead of theirs. This article is the audit checklist we use when overseas buyers visit our plant in Qingdao, and it is the same list you should bring to any supplier you are evaluating.

Start with the factory question

Overseas buyers cannot drop by casually, so most initial vetting happens on a website. That is exactly why the first audit step is to establish what the supplier actually is.

Ask directly: are you a factory, or a trading company? There are honest trading companies, but they add a layer between you and the process. When a batch goes wrong, you want to talk to the people who poured the metal, not someone who forwarded your drawing.

Waking is a real casting factory, not a trading company. That is a verifiable claim, and a plant visit is how you verify it. We have operated in Qingdao since 2002 on a 70,000 m² production base, with ISO 9001 and IATF 16949 certification, and we export to buyers in more than 40 regions. But certifications do not replace a pair of eyes on the production floor.

Before you travel, ask for the current certificates, a description of the plant layout, photos of the production floor, and a list of which processes are done in-house versus subcontracted. Also watch how fast the supplier responds to drawings and quotation requests. Quick, professional answers to a simple enquiry are an early signal of how the whole relationship will run. A supplier that hesitates on these basic questions is telling you something.

Verify the process is in-house, not subcontracted

Castings move through a chain: casting, heat treatment, machining, surface finishing, inspection, packaging. Every link is a place where quality can be lost — or quietly outsourced without your knowledge. The audit should match the supplier’s claimed processes to what your part actually needs.

For steel parts, the relevant process is silica sol investment casting, also called lost wax casting, for stainless steel, carbon steel, and alloy steel. For aluminum parts, look for low pressure aluminum casting or gravity aluminum casting. The process matters because it determines wall thickness, internal soundness, and the surface finish you can expect. Saying “we cast everything” is not an engineering answer.

Then look at what happens after the pour. Machining is where tolerances are actually delivered. If the supplier outsources machining, you are depending on a second company you never audited. Waking runs more than 400 CNC machines on its own floor, and machining is completed in the same plant as casting. The same quality team measures the casting before and after machining, and the feedback loop between the foundry and the machine shop is short. Whether your part is a pump valve body, an automotive housing, or an industrial machinery component, that handoff is where dimensions drift.

Surface finishing is the last step before packaging. Check whether the plant can handle deburring, cleaning, polishing, anodizing, plating, passivating, and coating on site, and how heat treatment is controlled. Export packaging is part of the same picture: a casting that leaves the plant without proper protection arrives with dents and scratches that become your problem.

Audit the inspection room, not the brochure

Casting defects are a fact of life. Porosity and shrinkage occur in every foundry in the world. The difference between a good supplier and a poor one is not whether defects happen — it is whether they are detected before shipment.

This is why the inspection room is the most important stop on your audit. Do not ask if the supplier has quality control. Ask what equipment is on the floor, then walk over and look at it.

At Waking, the inspection equipment includes:

• Two CMM coordinate measuring machines — a COORD3 and a ZEISS SPECTRUM — for measuring complex dimensions against the drawing.
• An XTH320 X-ray NDT system for detecting internal defects such as porosity and shrinkage that no external gauge can find.
• An inverted metallurgical microscope for analyzing material structure, including verification that heat treatment worked.
• A roundness and contour measuring instrument plus hardness testers.
• A pendulum impact tester, including low temperature impact testing, for parts that must survive cold service.
• A portable measuring arm for large or awkward parts on the shop floor.
• Leak testing and pressure testing for parts that hold pressure, such as valve bodies.

Any supplier that calls itself a casting manufacturer should be able to show you comparable equipment. A caliper and a magnifying glass are not an inspection room.

Also ask about first article inspection and sample approval. The supplier should be able to show how a new part is measured, checked, and approved before serial production starts. If that process is informal, you are the one absorbing the risk.

Materials, paperwork, and traceability

Overseas buyers often assume a material certificate is always accurate. The certificate is only as good as the system behind it. During the audit, ask to see the traceability procedure. From melt to finished part, can the supplier trace which batch a part came from? Can they pull the material certificate and the inspection report for a specific batch, together, on the spot?

Ask about material experience, not just material availability. For steel castings, Waking works with 304, 316, CF8, and CF8M stainless steel, as well as carbon steel and alloy steel. If your part is a valve body or an impeller, you want a supplier that has poured those exact materials and has the inspection routine to prove it. For aluminum parts, the relevant question is experience with aluminum alloy in low pressure or gravity casting, and how the supplier handles porosity in aluminum structures.

Paperwork is not glamorous, but it is the deliverable. Look at how batch numbers are recorded, how inspection results are filed, and how non-conforming parts are handled. If a batch fails, what happens? Is there a quarantine area and a documented disposition process? Vague answers usually mean performative traceability.

The audit checklist: ten questions to ask on the floor

Condensed into one list, here is what to ask before you leave the plant:

1. Factory or trading company? Show me where the melt actually happens.
2. Which casting process applies to my part? Is it run in your own plant?
3. Is machining in-house or subcontracted? If subcontracted, who audits the machinist?
4. Which finishing and heat treatment steps are done on site? Which are outsourced?
5. Show me your CMM. Who is trained to run it?
6. Can you X-ray a casting on demand? Which internal defects do you screen for?
7. How do you leak-test or pressure-test parts that hold pressure?
8. Show me a completed first article inspection report from a recent job.
9. Can you pull the material certificate and inspection report for one batch, right now?
10. What happens when a batch fails inspection?

None of these questions is aggressive. Good suppliers answer them quickly because they live with the answers every day. Weak suppliers hedge, change the subject, or promise to send the information next week.

Finally, treat the audit as the start of the relationship, not the end. Ask for a sample approval process before serial production, and get the exact lead time and MOQ confirmed in writing for your specific part — every casting is different. Keep the first batch inspection evidence on file so you can compare it against future shipments. Over time, that file becomes your real quality history with the supplier.

No foundry is perfect. The point of an audit is not to find one that is. The point is to find out whether the supplier’s equipment, process control, and inspection culture match the risk your parts carry. If you are buying decorative castings, the checklist gets shorter. If you are buying pressure-containing valve bodies for export, skip these checks at your own cost.