If you’re buying aluminum die cast parts for an assembly, “inspection” is not a single checkbox. It’s a set of methods used to prove different things: dimensions, internal integrity, sealing performance, and traceability.
A common mistake is to ask a supplier for “full inspection” without defining what you need. One buyer might mean a CMM report for a few CTQ dimensions. Another might mean X-ray for porosity risk. Another might mean a leak test with a specific pressure and hold time.
This guide helps you choose the right inspection method—without overpaying for tests that don’t actually reduce your risk.
Here is the most practical way to start: What are you trying to prove? Then choose the method that proves it.
| What you need to prove | Best inspection method | Typical output you can request | When it’s most useful |
|---|---|---|---|
| Critical dimensions and GD&T | Gauges + CMM | CMM report, gauge records | Fit/assembly surfaces, bearing bores, sealing grooves |
| Internal void risk (porosity/shrinkage) | X-ray / sectioning | X-ray images + inspection record | Pressure parts, structural areas, thick sections |
| Sealing performance | Leak test | Leak test record (pressure, hold time, pass/fail) | Housings, covers, fluid/air passages |
| Cosmetic standard | Visual inspection + photos | Appearance checklist + photo evidence | Visible parts, branding surfaces |
| First run acceptance | FAI | FAI report pack | New tooling, new revision, new supplier |
| Automotive-style approval | PPAP | PPAP deliverables | Automotive programs or customer requirement |
If you are diagnosing defect causes like porosity or cold shut, use your defect pillar page for the “why/how to fix” side:
https://casting-yz.com/die-casting-defects/
Dimensional Inspection for Die Cast Parts: Gauges and CMM
For most buyers, dimensional inspection is the foundation. A die casting can look perfect and still fail at assembly because a hole position drifted, a sealing groove is shallow, or a datum face is not flat enough.
In practice, dimensional inspection usually has two levels:
- Shop-floor checks (fast, repeatable): calipers, micrometers, pin gauges, go/no-go gauges, custom fixtures
- High-accuracy verification (more complete): CMM and sometimes optical measurement
A good supplier will not measure “everything” with CMM for every batch. That’s expensive and usually unnecessary. Instead, they’ll define CTQs (critical-to-quality features) and measure those consistently.
CMM Inspection Report: What Buyers Should Look For
If you request a CMM report, the most important part is not the number of pages. It’s whether the report is tied to the drawing and shows a clear pass/fail judgment.
What a buyer-friendly CMM report usually includes
- Part number and revision
- Drawing reference for each feature (ballooned drawing is a plus)
- Measured results vs tolerance
- Datum alignment used (how the part was set up)
- Sample quantity and date/time
- Inspector sign-off
A practical tip for RFQs
When sending an RFQ, don’t say “CMM for all dimensions” unless you really need it. Instead say something like:
- “CMM report for CTQ dimensions: A, B, C”
- “First article CMM report required”
- “Ongoing CMM checks: X pcs per lot or per shift for CTQs”
This simple wording reduces cost and speeds up quoting—while still protecting quality.
X-ray Inspection for Die Casting: When It Adds Real Value
X-ray inspection is not a universal requirement for all die cast parts. It is most valuable when internal integrity matters—especially for pressure-related parts or safety-related areas.
When X-ray is worth requesting
- The part is pressure-tight or used near fluids/air paths
- You have a known porosity risk based on geometry (thick sections, hot spots)
- Past issues show internal defects not visible from the outside
- The customer’s acceptance criteria requires it
What X-ray can and cannot prove
X-ray is great for revealing void patterns and internal discontinuities. But it does not automatically tell you the full root cause. It helps you confirm “what is happening,” then the process team uses that feedback to stabilize the process window.
If your goal is “reduce porosity,” don’t stop at “do X-ray.” Pair it with a clear control plan and in-process monitoring. That’s where quality becomes stable.
Leak Test Methods: Air, Water, Helium and Typical Use Cases
Leak testing is the inspection method buyers care about most when the part must seal. And it’s also the method most often misunderstood in RFQs.
A leak test is only meaningful when you specify:
- test medium (air/water/helium)
- pressure level
- stabilization time and hold time
- pass/fail criteria (leak rate or pressure drop)
- test coverage (which ports are sealed, which are open)
Common leak test types
- Air leak test (pressure decay): widely used for production checks
- Water immersion / bubble test: simple, visual confirmation, often for troubleshooting
- Helium leak test: very sensitive, usually for higher requirements, higher cost
A buyer-friendly way to specify leak test in an RFQ
If you don’t know the exact numbers yet, you can still be specific without guessing:
- “Leak test required. Please propose a suitable method and parameters based on part function and sealing surfaces.”
A serious supplier can propose realistic parameters and explain the cost impact.
Appearance Inspection: Standards, Photos, and Acceptance Rules
Appearance issues create the most buyer frustration because “good” can be subjective. The easiest way to prevent arguments is to define an appearance standard early.
Appearance inspection is usually more reliable when:
- you define which surfaces are cosmetic vs non-cosmetic
- you define acceptable levels of flash, scratches, pits, discoloration
- you use photos or a reference sample as a standard
For visible parts, a simple photo-based checklist can be more useful than long written descriptions.
FAI Report for Die Casting: When You Need It and What It Includes
FAI (First Article Inspection) is the buyer’s way to say: “Before we approve production, prove the part matches the drawing.”
FAI is most commonly needed when:
- new tooling is launched
- a new supplier starts production
- drawing revision changes
- the process changes in a way that could affect CTQs
Typical FAI contents for die casting
- CMM or measurement report for key dimensions (often ballooned drawing)
- material certificate if required
- visual/appearance confirmation
- functional checks if applicable
FAI is a practical middle ground: it gives you confidence without requiring heavy “PPAP-style” documentation.
PPAP for Die Casting: Typical Deliverables and Buyer Checklist
PPAP (Production Part Approval Process) is commonly required for automotive programs and some high-control industrial programs. It’s more structured than FAI.
You don’t need to memorize every PPAP element to buy die cast parts. What matters is knowing what you should receive and what it proves.
Typical PPAP deliverables (buyer-friendly checklist)
- design records and revision control
- process flow and control plan
- PFMEA (when required)
- measurement results and capability evidence for CTQs (when required)
- material and performance test results (when required)
- part submission warrant (PSW)
A realistic approach is to align PPAP depth with the part’s risk. If you’re not an automotive buyer, you can still borrow PPAP thinking: define CTQs, define reaction plans, and keep traceability.
How Inspection Links to IQC, IPQC, and OQC Records
Inspection methods answer “how do we test?”
IQC/IPQC/OQC answer “when do we test, and how do we release parts?”
If you want the meanings and differences of those checkpoints in die casting, see:
https://casting-yz.com/iqc-vs-ipqc-vs-fqc-vs-oqc-in-aluminum-die-casting/
A practical supplier uses both:
- the right method (CMM/X-ray/leak test)
- at the right checkpoint (incoming / in-process / outgoing)
- with clear records and traceability
That combination is what reduces surprises for buyers.
Are You Looking for a Reliable Aluminum Die Casting Supplier
If you share your drawing, CTQs, appearance standard, and whether you need FAI or PPAP, we can recommend the inspection plan that matches your risk—without adding unnecessary cost.
For RFQs, the fastest way is to tell us:
- which dimensions are CTQs
- whether sealing or internal integrity matters
- what documents you want with shipment (CMM report, leak test record, photos, etc.)
FAQ
What should I include in an RFQ if I want a CMM report, but I don’t want to pay for “everything”?
Ask for a CMM report on CTQ dimensions only. The clean wording is: “CMM report required for CTQs (list them or mark them on the drawing).” You can also specify timing: “Full CMM for first article, then ongoing sampling for CTQs per lot or per shift.”
When is X-ray inspection actually necessary for die cast parts?
X-ray is most justified when internal integrity affects function—especially pressure-tight parts, fluid/air passages, or geometry with hot spots that is known to increase porosity risk. If the part is cosmetic-only and non-sealing, X-ray often adds cost without reducing meaningful risk.
For leak testing, what test details must be defined to make results comparable between suppliers?
At minimum: test medium, pressure, stabilization time, hold time, and pass/fail criteria (leak rate or pressure drop). Also clarify which ports are sealed and what surfaces form the seal. Without these, two suppliers can both say “passed” while testing very different conditions.
Is FAI enough, or do I need PPAP?
FAI is usually enough for many industrial programs: it proves the first production parts match the drawing. PPAP is typically required for automotive or high-control programs and includes a fuller “process proof” package (control plan, flow, sometimes PFMEA, and structured submission). If your customer doesn’t require PPAP, FAI + CTQ control + traceability is often the practical path.
What does a buyer-auditable inspection record look like for die casting shipments?
Look for basic traceability and sign-off: part number/revision, lot/batch linkage, sample size, results vs acceptance, date/time, and inspector release. If it’s a special test (X-ray/leak test), the record should also show the test method/parameters, not just “pass.”
If defects happen, how should inspection methods connect to corrective action?
Inspection confirms “what” happened; corrective action addresses “why.” A practical loop is: confirm with the right method (e.g., X-ray for porosity pattern), quarantine affected lots, adjust process, then verify improvement with repeated checks before returning to normal sampling.
I’m not technical—what’s the simplest way to choose between CMM, X-ray, and leak test?
Think in three questions:
- “Do I need dimensional proof?” → CMM
- “Do I need internal integrity proof?” → X-ray
- “Do I need sealing performance proof?” → leak test
Many parts only need one of these, plus a clear first-article check.
