First Article Inspection: Judging the First Shots Fairly

What the FA actually proves

A first article inspection answers one question: does this die, mounted on this machine, running this alloy at these parameters, produce a part that meets the drawing? It is not a promise about every future shot. It is a documented snapshot showing that the process was set up correctly on day one, and it becomes the baseline every later shipment is judged against.

That framing matters because a FA that only says "the parts look fine" is nearly worthless. A useful FA records how the parts were made — machine number, die temperature at start and steady state, alloy lot chemistry, hold times — so that if production drifts six months later, both sides can compare against a known starting point instead of arguing from memory.

When the FA happens — and on what

In a typical die casting project the FA is run on parts from production-intent tooling, on the production machine, with production parameters. Trial shots (T1, T2) that come out of tool tryout are usually not FA parts: the die may still be on a tryout press, and small process adjustments made at tryout legitimately change the part. The FA comes after those adjustments are frozen.

Sample quantity is a frequent point of confusion. One part is not a first article; it is a curiosity. Castings vary shot to shot with die temperature cycling, so a FA normally covers a small contiguous batch — five to ten consecutive shots is common practice. Inspecting consecutive parts also reveals drift within a run, which single-part sampling hides completely.

The dimensional layout: the core of the FA

The dimensional layout is where most of the FA effort goes, and where most disputes start. Two approaches exist and the right one depends on part criticality:

Full layout

Every dimension on the drawing is measured and reported on a ballooned print. This is the standard expectation for a new die, and for automotive work it is effectively mandatory because the layout feeds directly into the PPAP dimensional report. A full layout on a CMM with a documented datum scheme — the datums called out in the drawing's GD&T, not datums the inspector finds convenient — typically takes a few hours per part plus programming time.

Critical-dimension check

For carryover parts or minor die modifications, a reduced layout covering the dimensions affected by the change, plus the key functional features (sealing faces, bearing bores, mounting holes), may be agreed in advance. The scope must be agreed in writing before the run. A "shortened FA" that the customer discovers after the fact is worse than no FA at all.

One practical rule: measure cast features as cast, and machined features after the machining operation, on the same serialized parts. Mixing machined and as-cast samples in one layout report destroys the traceability between cause and effect — you will not be able to tell whether a bore diameter problem came from the die or from the machining fixture.

Internal quality: porosity, X-ray and leak criteria

Die castings carry some porosity by nature of the process; the FA's job is to confirm that the porosity present is the porosity the drawing allows. Three things must be written down before the first shot:

• Porosity classes by location. A pore that is harmless in a structural rib can be a leak path in a sealing face or a fatigue initiator in a machined boss. Good specifications define acceptable pore size and density by zone, often with reference to ASTM E505 severity-level reference radiographs for inspection of aluminum and magnesium castings.
• When X-ray is required. Radiography on every FA is not standard; it is required where the drawing or the customer spec calls for internal criteria — typically pressure-tight parts, parts with heavy machining into thick sections, or safety parts. The FA should then state the X-ray acceptance class and the filming locations.
• Leak test method and pressure. If the part is specified pressure-tight, the FA states the test method (commonly air-under-water immersion or pressure decay), the test pressure, and the acceptance limit. "It held" is not a result; "no bubbles at 200 kPa for 30 seconds" is.

Most FA disputes, in our experience, are not inspection failures — they are missing-criteria disputes discovered too late. Agreeing the porosity map and leak spec at the DFM stage costs an hour; discovering at the FA that the customer expected X-ray on 100% of sealing areas costs weeks. Our porosity acceptance criteria guide covers how those limits are usually written.

Alloy and material verification

The FA package should include a chemistry certificate for the actual melt used, from a spectrometer analysis of the furnace or ladle sample, referenced to the specified alloy — for example A380 or ADC12 aluminum, or Zamak 3 / Zamak 5 zinc. Chemistry drifts with recycled returns in the loop, so the certificate's alloy lot must match the FA parts' lot. For parts with mechanical property requirements, a hardness check or a tensile coupon from a separately cast sample may be added, though properties on separately cast coupons are indicative rather than identical to the part.

What the FA documentation package contains

A complete FA package for a die casting typically includes:

For automotive programs this package becomes the dimensional and material backbone of the PPAP submission. The relationship is explained in more depth in our PPAP and IATF 16949 guide for die casting buyers.

Common FA findings and what they actually indicate

FA failures usually point to a specific cause, and diagnosing them quickly keeps the project on schedule:

• Overall dimension shrinkage out of range — die temperature or alloy chemistry off; check thermal balance before touching the die.
• Porosity concentrated under machined surfaces — gate/vent design or shot parameters; see where die casting porosity comes from.
• Cold shuts or flow marks on cosmetic faces — fill pattern and die thermal balance; may need gate or runner adjustment.
• Datum mismatch in the layout — not a casting problem at all, but an inspection-plan problem; fix the datum scheme before re-measuring.
• Ejector marks exceeding the agreed depth — ejector pin sizing or timing; a die tweak, not a process redesign.

A fair rule for both sides: a finding is only a rejection if it violates a criterion that was agreed before the run. Everything else is feedback for the next revision of the process — or for the drawing.

When a new FA is required

The FA baseline survives only as long as the process does. A repeat or partial FA is standard practice after: a die is moved to a different machine; the die undergoes a repair affecting the cavity or gates; the alloy specification changes; a machining or finishing operation changes; or production resumes after a long shutdown with die reconditioning. For unchanged processes, periodic layout audits on production samples — not a full FA — are usually sufficient, and the interval belongs in the control plan.