Last updated: 2026-09-04 · 6 min read

Mold Factory Acceptance Test (FAT) — What Must Be Proven Before a Mold Ships, and What Do You Sign To Say It Passed?

A Factory Acceptance Test is the last gate before a mold leaves the builder’s shop. A 4-phase protocol — dimensional, functional, run-at-rate, documentation — executed against criteria in the purchase contract. Every open item goes on a punch list with an owner and a due date; payment and shipment move only when the list is closed. Skip this gate and every correction costs freight, a relocation, or a press you do not have.

Key Facts

A FAT covers 4 phases: dimensional (CMM), mold hardware, short run-at-rate, and documentation package.

Pass criteria must be agreed in the purchase scope before the deposit, not invented at the trial.

The signed punch list — not a verbal OK — is the legal acceptance document that gates balance payment and shipment.

Ejector pin — A steel pin that pushes the molded part out of the cavity after cooling. Typical diameter: 2–10mm. Pin marks are visible on the part surface — position at non-cosmetic areas. Pin count and placement affect ejection force and part warpage. The related guide covers adjacent topics.

What Does a Mold FAT Actually Verify?

A FAT is not one check; it is four, each with its own evidence type. Conflating them — or running only the first — is how molds ship early and fail late.

Phase	Pass Evidence	Common Failure Caught
1. Dimensional	Full-dimension CMM report, critical features across all cavities inside tolerance	One cavity in spec, others drifting; datum face off on later shots
2. Mold hardware	Steel grade and hardness cert, slides and lifters free action, leak test, ejector mark check, nameplate and serial	Wrong or softer steel, a sticky side-action, a weeping water line
3. Run-at-rate	Short production run at agreed cycle, parts sampled at start and end of thermal steady state	A mold that makes one good shot cold then drifts warm
4. Documentation	Signed CMM reports, timestamped trial video, as-built drawings, spare-parts list, maintenance instructions	Tool ships with no record of what was corrected or which inserts are spares

Phases 1 and 2 judge the tool; phases 3 and 4 judge whether the tool can hold and prove its output in repetition. A mold that makes good parts on the builder’s best day but is built from the wrong steel or has a weeping cooling circuit is a future failure you can still avoid cheaply at this stage. Everything you cannot economically fix after shipment should be proven here.

How Do You Run a FAT That Protects You?

The FAT is only as strong as the protocol behind it. Four steps, in order:

Write the acceptance criteria before the deposit. Agree in the purchase scope what pass means per feature — the critical dimensions and their tolerance class, the cosmetic standard (signed limit sample, ΔE and gloss numbers, viewing geometry), the run-at-rate length, and the document list. Doing this while you still hold the balance payment as leverage is the whole point; adding criteria after the parts are on the table lets the builder treat them as moving goalposts.
Judge on measured evidence across all cavities. Require the CMM report to cover critical features on parts from every cavity, so an 8-up tool is accepted because all eight hold, not the best one. Read the numbers, not a summary. Where a fixture or gauge exists for a fit-critical feature, use it at the FAT.
Inspect the mold hardware, not only the molded output. Walk the tool: confirm steel grade and heat treatment against spec, that slides and lifters act smoothly and return fully, that parting and shut-offs are sound with no smear that will flash later, that cooling circuits hold pressure, and that ejector action releases without witness-mark damage on a visible face. Verify the nameplate and serial match your asset records.
Close the punch list before balance and shipment. Capture every finding as an item with an owner and a due date. Make release of the final payment and the crate conditional on critical items being resolved and re-verified. A mold that ships conditionally accepted without your hold on the balance becomes a mold you chase across a border for corrections you already saw.

Process parameter — A controllable variable in the injection molding process: melt temperature, injection speed, holding pressure, cooling time, mold temperature. Each parameter affects part quality — deviations cause defects. Parameters are set during T1 and locked for production. The related guide covers adjacent topics.

“The parts look good” is exactly the claim that survives a rushed sign-off and collapses in production. A FAT replaces opinion with a document: measured numbers, a real run, and a punch list that gates payment.

Key parameter identified — critical variable confirmed against spec.

Tolerance within achievable range — commercial ±0.15mm or tighter as needed.

Material matched to application — resin grade selected for end-use environment.

Process window validated at T1 — parameters locked after first trial.

Inspection method defined — CMM, visual, or functional test specified.

Frequently Asked Questions

Is a FAT the same as approving T1 parts?

No. T1 is the first-shot review — the tool has been built, samples exist, and you and the builder read the dimension report together to decide what to correct. Most first trials have findings; that is expected.

The FAT is the later, formal gate where the corrections are done and the tool must demonstrate it meets the acceptance criteria on a run, across cavities, with hardware and documentation verified. You approve T1 to define the work; you pass a FAT to release shipment.

Do I have to attend the FAT in person?

It is ideal for a high-value or risky tool, but a well-run FAT can be witnessed remotely if the evidence is objective and independent. What matters is that the proofs do not depend on trust: full-dimension report with real numbers per cavity, a continuous run-at-rate video with timestamp and mold serial, photographs of hardware checks, and signed documents delivered before the balance.

Where a live or recorded trial video is not offered and you are asked to accept a summary, that is a gap to close, not to waive. Either send a third-party inspector or make acceptance explicitly conditional on receiving the full evidence package with a hold-back until a confirmatory run at your own press passes.

What is the difference between a FAT and a run-at-rate or SAT?

A Factory Acceptance Test happens at the builder’s shop before the tool ships. A Site Acceptance Test and formal run-at-rate happen after installation on your machine, where the tool will actually run.

The FAT proves the tool can produce to spec under the builder’s conditions and gets you past the pay-and-ship milestone; the SAT proves it does the same in your facility, on your press, with your automation and operators. Agreeing both in the contract prevents a situation where the mold passed an ocean away and then cannot hold your cycle at home.

Key Takeaways

A FAT is 4 phases — dimensional, hardware, run-at-rate, documentation — each with its own evidence type; running only one phase is not acceptance.
Pass criteria must be written into the purchase scope before the deposit, not invented at the trial when leverage has shifted.
The signed punch list gates balance payment and shipment; a verbally accepted mold with no document is an unenforceable handshake.

A FAT is not a formality.
It is the last point in the build where a correction costs a bench job instead of a teardown across a border. Run all four phases, insist on measured evidence, and let no money or crate move until the punch list says it can.