PPAP for Die Castings: What Automotive Buyers Should Ask For

What PPAP actually is

PPAP (Production Part Approval Process) is defined by the AIAG PPAP manual, currently in its 4th edition, and is mandatory practice across the automotive supply chain under IATF 16949:2016. It is not a certificate — it is a dossier of objective evidence that the production process, run at rate, produces parts to print.

The package contains 18 elements. For a die casting buyer, the load-bearing ones are: design records and the dimensional report against them; material and performance test results; process capability studies; measurement system analysis (MSA); control plan; and the Part Submission Warrant (PSW) that summarizes everything else. The remaining elements — DFMEA, PFMEA, flow diagrams, appearance approval and so on — give context for how those results were achieved.

Where IATF 16949 ends and PPAP begins

A common buyer mistake is treating an IATF 16949 certificate as if it were part approval. It is not. IATF 16949:2016 is a quality management system standard: it says the supplier's processes, traceability and corrective-action loops are audited to an automotive-grade framework. PPAP says this specific part, from this specific die, on this specific machine and alloy lot, meets the drawing.

You need both, and they answer different sourcing questions. The certificate screens the supplier; the PPAP package approves the part. A supplier can hold a valid IATF certificate and still fail a PPAP if the die is unstable or the measurement data is thin.

The five submission levels — and which to pick

PPAP defines five submission levels. The customer tells the supplier which level to submit, and the level determines what is retained by whom:

• Level 1 — PSW only (with appearance approval report where applicable). Fits low-risk renewals.
• Level 2 — PSW with product samples and limited supporting data.
• Level 3 — PSW with samples and complete supporting data. The default for new safety-critical or function-critical castings.
• Level 4 — PSW plus other requirements defined in the control plan.
• Level 5 — PSW with all data available for on-site review at the supplier.

For a new EV inverter or motor-controller housing, Level 3 is the right ask: it puts the complete dimensional table, material certs and capability studies in the customer's hands. For a cosmetic renew of an unchanged bracket, Level 1 with a fresh PSW is usually sufficient. Over-requesting levels on commodity parts burns supplier goodwill; under-requesting on critical parts moves the risk into your launch.

The elements that carry the most weight for castings

Dimensional results measured to casting datums

The dimensional report must be measured against the datum scheme on the drawing — typically the machined datum faces, not the as-cast surface. As-cast features should be evaluated against the casting tolerance band (die casting typically holds ±0.1 mm on small to mid-size features; machined features on our lines are held to ±0.05 mm on 5-axis CNC). A report that mixes datum schemes looks complete and answers nothing.

Material certification by heat lot

Aluminum die castings are commonly produced from ADC10 or ADC12, magnesium from AZ91D, and the cert must trace to the actual heat or alloy lot used in the significant production run, not to a generic spec sheet. For housings with flame-retardance or thermal requirements, performance test results belong in the package too.

Porosity and leak criteria

For gas-tight or pressure-tested housings, the PPAP should state the X-ray acceptance criteria by pore size and location, and the leak test method with test pressure. The porosity mechanism and its control is a process discussion — see our guide on vacuum die casting and porosity control for the physics behind the criteria.

Capability: Cpk 1.33 on significant characteristics

Per the AIAG PPAP manual, capability studies from a significant production run should show Cpk ≥ 1.33 on significant characteristics. On castings, distinguish as-cast features (capability is bounded by the die and process) from machined features (capability is bounded by the CNC operation). Forcing Cpk 1.33 on an as-cast feature specified at the edge of casting capability is a design conversation, not a documentation one.

Common failure modes that delay PPAP approval

From the buyer's chair, four patterns cause most die casting PPAP rejections:

• Datum mismatch — the report is measured to a convenient surface instead of the drawing datum scheme, so every number needs re-verification.
• Material certs without lot traceability — a compositional spec sheet proves nothing about the melt that filled the die.
• Thin capability data — fewer than the agreed run size, or Cpk computed on machined-only features while the risk sits in as-cast walls.
• Criteria agreed after the fact — porosity limits or leak test pressures that were never written into the control plan, so the supplier's evidence and the customer's expectation diverge.

All four are preventable at the DFM stage. Agreeing the datum scheme, criteria and run size before steel is cut is exactly what our prototyping and DFM process is for.

What to expect from a supplier like OKDieCast

OKDieCast is the die casting brand of Shenzhen Leijing Technology Co., Ltd., operating a 22,000 m² integrated plant with high-pressure and vacuum die casting, 5-axis CNC machining to ±0.05 mm, surface treatment and CMM-based inspection under one roof, and full batch traceability reports with every shipment. The site is ISO 9001 and IATF 16949 certified — the system side of the equation.

On the evidence side, the first article inspection is the backbone of any submission: our guide to first article inspection for die castings explains what gets checked and why. PPAP builds directly on that foundation — the FA becomes the dimensional element, batch reports become the material and traceability element, and the significant run data feeds the capability study.

If you are sourcing an EV motor-controller housing or battery structure, the practical starting points are our product lines and the automotive application notes under solutions; drawings can go to our engineering team for DFM review and a quote within 24 hours.