A first article inspection (FAI) is the point where a drawing stops being a promise and becomes data. For a machined medical part, the FAI report is often the first document a supplier quality engineer opens, and it decides whether the part moves on to the OEM’s own verification and validation or goes back to the shop.
This article explains what a medical device machining first article inspection should contain, how it relates to the buyer’s validation work, how many parts to inspect, and what happens when a characteristic fails. It is written for engineers and supplier quality staff at OEMs buying machined parts from the shops we work with in southern Vietnam, but the structure applies to any supplier.
What FAI is for, and what it is not
An FAI is a full, documented verification of every requirement on the drawing and purchase order, performed on parts made with the production process: the intended machine, program, fixtures, tools, material source and finishing vendors. Every dimension, every GD&T callout, every note and every specification referenced in the title block is checked and recorded.
What FAI is not:
- It is not a sampling inspection. Every characteristic is measured on every FAI part.
- It is not process validation. It shows that these parts conform, not that the process will keep producing conforming parts.
- It is not a regulatory approval of anything. The device maker owns design controls, process validation, biocompatibility, cleaning and sterilization validation, and regulatory submissions. The shop supplies parts to the drawing and to the quality requirements on the purchase order. Medical Device Machining only reviews drawings and matches them to shops.
When an FAI is required
Typical triggers, usually written into the quality agreement or purchase order:
- A new part number, or the first order from a new shop.
- A new drawing revision that affects form, fit, function or a specified process.
- A change in manufacturing process: new machine, new program strategy, new fixture, relocation, or a change of finishing vendor.
- A change in material source.
- A gap in production longer than the period defined by the buyer.
For a change, a partial (delta) FAI covering only the affected characteristics is common, provided the buyer agrees.
What the FAI package contains
| Section | What it shows | Common gaps |
|---|---|---|
| Ballooned drawing | Every requirement numbered, including notes and title block references | Notes and general tolerances not ballooned |
| Characteristic results table | Balloon number, requirement, tolerance, method, actual value, pass or fail | Ranges written instead of actual values |
| CMM report | Raw measurement data with datum setup and alignment | Report does not reference balloon numbers |
| Material certificates | Mill or manufacturer certificate, heat or lot number, specification | Heat number not traceable to the parts shipped |
| Process certificates | Passivation, electropolish, anodize, heat treatment, with the standard and lot | Certificate names the process but not the standard |
| Visual and functional checks | Burrs, edge breaks, thread gauging, fit checks | “Visual OK” without criteria |
| Part identification | Part number, revision, serial or lot, marking verification | Laser marking content not checked against drawing |
| Sign-off | Inspector, date, equipment IDs and calibration status | Gauge IDs missing |
The ballooned drawing
Each requirement on the drawing gets a unique number. This includes basic dimensions that control a GD&T feature, general tolerance blocks, surface finish symbols, notes such as “break all sharp edges 0.1 to 0.2 mm”, and specifications cited in notes, such as a passivation standard. If a requirement is not ballooned, it has not been checked.
The characteristic results table
For each balloon: the requirement as written, the tolerance, the inspection method and gauge ID, the actual measured value for each FAI part, and the result. Actual values matter. “Within tolerance” tells the buyer nothing about how close to the limit a feature sits, and a feature at 90 percent of its tolerance band on the first article is worth a conversation before production.
The CMM report
The coordinate measuring machine output supports the results table for features that need it: profile, position, runout, flatness, perpendicularity and concentricity. The report should state the datum reference frame and alignment method, match the datum scheme on the drawing, and use balloon numbers so the reviewer can cross-check. The partner shops verify GD&T on CMM, supported by optical comparators and height gauges.
Material certificates
For Ti-6Al-4V, the certificate should name the specification on the drawing, for example ASTM F136 when specified, show chemistry and mechanical properties, and carry the heat number. The shop’s traveler should link that heat number to the parts in the FAI. For 316L, 17-4 PH and medical grade PEEK the principle is the same: certificate, specification, lot traceability to the shipped parts.
Process and finish certificates
Secondary processes are part of the first article. Passivation of stainless steel is typically called out per ASTM A967, and the certificate should state the method (for example, a citric or nitric acid treatment), the lot, and any verification test specified on the drawing. Background on the chemistry is in the passivation overview. Electropolishing of 316L, Type II or III anodizing, and heat treatment of 17-4 PH need their own certificates with the standard and condition stated.
More detail on the standard documentation set is on the quality and documentation page.
AS9102-style format as a template
AS9102 is an aerospace standard, but its structure is widely used as an FAI template for machined medical parts because it is complete and easy to audit:
- Form 1, part number accountability: part number, revision, drawing number, the organization performing the FAI, and whether it is a full or partial FAI.
- Form 2, product accountability: raw material, specifications, special processes and the suppliers who performed them, and functional tests.
- Form 3, characteristic accountability: one line per balloon with the requirement, result and method.
If your company uses its own FAI form, attach it to the RFQ. The format is less important than completeness and traceability.
Measurement methods by feature type
The rule of thumb is that the measurement system should resolve roughly one tenth of the tolerance band, and never worse than about one quarter. For a ±0.005 mm feature, that points toward a CMM or precision bore gauge, not a caliper.
| Feature type | Typical method | Notes |
|---|---|---|
| Outside diameters, lengths | Micrometer, height gauge, CMM | Caliper only for loose tolerances |
| Bores, H6 or H7 fits | Pin gauges, bore gauge, CMM | Go/no-go plus actual value where tolerance is tight |
| Threads | Thread plug and ring gauges | Record gauge IDs; pitch diameter by wires if specified |
| Profile, position | CMM | Datum setup must match the drawing |
| Flatness, perpendicularity | CMM, surface plate with indicator | State the sampling points or scan density |
| Runout, concentricity | CMM, V-block or between centers with indicator | Method should match the datum definition |
| Small radii, edge breaks, jaw teeth | Optical comparator, vision system | Overlay chart or measured values |
| Surface roughness | Contact profilometer | Record Ra and cutoff length |
| Laser marking | Visual against drawing, verification of content | Check UDI content if marked |
Within the capability window of the partner shops, linear tolerances are typically ±0.01 mm and best ±0.005 mm on 5-axis, with bores to H6 and shafts to h5 on suitable features. Surface roughness as machined is Ra 1.6 µm typical and Ra 0.8 µm best case. These values are confirmed per drawing, not guaranteed in advance. See the capabilities page for detail.
Sample sizes
There is no single correct number; the buyer sets it. Common patterns:
- One part from the production process, which is typical AS9102 practice.
- Three or five parts, common among medical OEMs to see part-to-part variation early.
- One part per stream: one per fixture, spindle, pallet or cavity when the process runs in parallel.
- Larger samples for capability studies, for example when the buyer’s validation plan calls for Cpk data on critical characteristics. This is a separate study defined by the buyer, not a standard FAI.
State the FAI quantity in the RFQ. Measuring every characteristic on five parts instead of one changes inspection time and therefore price.
How FAI relates to the buyer’s validation
The OEM’s quality system decides whether a machining process needs validation or whether the output can be fully verified by inspection. Where validation is required, the IQ/OQ/PQ protocols are owned by the buyer or specified by the buyer, and executed with the shop’s support. The FAI then serves as evidence that the first parts from the qualified setup conform. It feeds validation; it does not replace it.
A practical sequence many OEMs use: prototype FAI, drawing and process freeze, production FAI on the frozen process, then any buyer-defined OQ or PQ runs and capability studies, then production release. Each step and its acceptance criteria belong in the buyer’s supplier quality plan.
When a characteristic fails
A failed characteristic on a first article is information, not a disaster, as long as it is handled openly:
- Record the actual value. The report shows the measured result and marks it as a failure. It is never adjusted or re-measured until it passes without explanation.
- Contain. Parts are segregated and tagged as nonconforming.
- Root cause. Program, fixture, tool wear, thermal growth, datum interpretation, or a drawing ambiguity.
- Buyer disposition in writing. Rework, remake, or use-as-is under a deviation. Only the buyer can accept a nonconforming part, and only through its own process.
- Correct and re-verify. After the correction, a partial FAI covers the failed characteristic and any feature the change could affect.
If the root cause is a tolerance that is difficult to hold for reasons unrelated to function, the DFM feedback at the quote stage is the best time to raise it. The drawing remains the buyer’s decision.
Requesting FAI in your RFQ
To get an FAI package that matches your supplier quality plan, include in the RFQ:
- The drawing with revision, and whether you supply a ballooned copy or expect the shop to balloon it.
- Your FAI form, or confirmation that an AS9102-style format is acceptable.
- FAI quantity and any per-stream requirement.
- Material specification and required certificates.
- Process specifications for passivation, electropolish, anodize or heat treatment.
- Any capability study or validation support you will need later, so it is quoted up front.
When your package is ready, send it through the RFQ form. The first response, with DFM feedback, comes within 24 business hours.