First Article Inspection (FAI) Process for Custom Silicone Components

Pull the packet apart before you look at the part.

First article on a custom silicone component exists to prove that *this* tool, *this* grade, *this* cure, and *this* trim made a part that matches the drawing. It is not a capability study (that is later). It is not a PPAP unless you asked for one. It is not an AS9102 form unless you are in that system and you specified it. Most industrial, consumer, and medical-adjacent silicone jobs need the substance of FAI, not an aerospace form number.

What the packet has to contain

Build it in this order. If a shop skips a layer, the rest is decoration.

1. The drawing you will hold them to, ballooned.

Every dimension and note you care about gets a bubble number. If you send a pretty CAD PDF with no balloons, you will get a “FAI” that measured five easy outsides. Balloon flash max, gate remnant, hardness, color if it is a spec, post-cure, and the fit diameters that actually mate.

If you use a formal first-article form (AS9102-style or a shop equivalent), the form is only a table that points at those balloons. The drawing is the contract.

2. Material identity.

Grade name and manufacturer, lot/batch, hardness target, color paste if any, mix or part-A/B lot for LSR. A cert that says “silicone, RoHS” is not a material cert. For FDA 21 CFR 177.2600, LFGB, ISO 10993, or USP Class VI claims, the cert must match the *compound*, not the factory’s wish.

3. Process state of the measured parts.

As-molded or post-cured, and for how long at what temperature. Silicone dimensions and hardness move with post-cure. Measuring the wrong state is a fake pass.

4. Dimensional report against the balloons.

Method named: CMM, optical, caliper, pin, vision. LSR parts deform under a probe. Soft Shore A wants contact strategy, not a macho CMM program copied from a steel housing. Record actuals, not pass/fail ticks only.

5. Visual standard.

Flash, voids, flow lines, contamination, transparency, knit. Photos with the same lighting you will use in incoming. A “visual OK” line with no photos is how arguments start at incoming inspection.

6. Tool identity.

Tool number, cavity number if multi-cavity, revision of the insert. An 8-cavity FAI that reports one cavity is a 1-cavity FAI with seven strangers.

That is the packet. Everything else (IMDS, full capability, GR&R, biocompatibility reports) is extra and must be named at RFQ.

How to run it on the shop floor

Sequence, not a meeting.

1. Freeze drawing rev and balloons before steel (or aluminum) is cut. FAI against a moving rev is theatre.
2. Complete tryout until the process window is boring: temperatures, shot, vacuum, cure, post-cure.
3. Pull first-article parts from a *continuous* short run, not from the three prettiest shots in a bowl.
4. For multi-cavity, pull from every cavity. Report every cavity. If a cavity is blocked, the FAI says so.
5. Measure after the agreed post-cure and after the agreed trim. If you will ship untrimmed, measure untrimmed.
6. Hardness on a thick enough section, or on a companion slug, because a 1 mm lip will lie on a durometer.
7. Pack the packet with the parts, cavity-tagged.

If dimensional fails, stop. Do not “FAI the next lot.” Either the tool, the shrink factor, or the process is wrong. Recut or reprocess, then new first article. Partial waivers belong on a signed deviation, not in email.

Silicone-specific traps

Softness. A Shore 10A gasket will move in a vise. Fixturing and low-force probes are part of the method. Write them down so incoming can repeat.

Flash as a dimension. If flash max is 0.15 mm, it is a balloon, not a vibe.

Shrink vs RTV samples. Platinum RTV vacuum-cast parts are a different shrink story than heat-cured LSR. Do not FAI LSR against a model that was tuned on RTV.

Post-cure yellowing and size. Transparent and medical parts need the visual after post-cure, not before.

Inhibition leftovers. Sticky first articles on platinum are a chemistry fail. They do not belong in the dimensional table.

Family tools. Each unique cavity is its own first article, even if the PO thought it was one part.

What FAI does not prove

A passing FAI does not prove 10,000 parts. It proves the recipe *can* hit the drawing. Capability, control plans, and incoming sampling are separate. Do not skip FAI because you plan a Cpk later. Do not skip control because FAI was green.

It also does not prove the tool class. A Class 105 can pass first article on shot 12 and fail on shot 200. If life matters, put a short run and a shutoff photo in the packet, not just one piece.

Buyer actions that make FAI useful

• Send balloons with the RFQ, not after tryout.
• State the form: shop table vs your template vs a named aerospace standard *if you actually need it*.
• State sample size: often 1-5 per cavity for custom silicone, not a mystery.
• Book incoming inspection to the same balloons. If your IQC uses a different drawing, you bought two truths.

End the PO note with: “First article = ballooned drawing + material cert (grade/lot) + dimensional actuals per balloon + visual photos + cavity ID, measured in the ship state (post-cure/trim yes or no). No photo-only FAI.”

FAQ

Is a photo of a nice part an FAI?

No. FAI is a packet: ballooned drawing, material identity with grade and lot, process state, dimensional actuals against those balloons, visual photos, and tool/cavity ID. It is not a capability study, not PPAP unless you asked, and not AS9102 unless you specified that system.

Why must the measured parts name as-molded versus post-cured?

Silicone dimensions and hardness move in the oven. Measuring the wrong state is a fake pass. Measure after the agreed post-cure and after the agreed trim; if you will ship untrimmed, measure untrimmed.

Does a green FAI prove the next 10,000 parts?

It proves this tool, grade, cure, and trim can hit the drawing. Capability and control plans are separate. A Class 105 can pass on an early shot and fail later; if life matters, put a short run and a shutoff photo in the packet, not one pretty piece.

Why is an 8-cavity report on a single cavity incomplete?

Each pocket is its own first article. Pull from a continuous short run, not the three prettiest shots in a bowl, and report every cavity. A blocked cavity must be stated. Family tools are unique cavities even if the PO thought they were one part.

What PO note kills photo-only FAI?

First article equals ballooned drawing plus material cert (grade/lot) plus dimensional actuals per balloon plus visual photos plus cavity ID, measured in the ship state. Send balloons with the RFQ, not after tryout, and book incoming to the same balloons.