射出成形における初品検査とは何ですか

What Is First Article Inspection in Injection Molding?

¹ (FAI) is a structured, documented verification process confirming that the first parts produced from a new injection mold—or a significantly modified mold—conform to every dimension, tolerance, material, and functional requirement on the engineering drawing. FAI is not a general quality check; it is a systematic, feature-by-feature measurement of 100% of all drawing characteristics on a minimum sample of 3–5 first-run parts. At ZetarMold, we treat FAI as the final gate between mold qualification and volume production.

The process originated in aerospace manufacturing under ², but today it is standard across automotive (⁴ Level 3), medical device (ISO 13485), and precision electronics industries. Any manufacturer shipping plastic components into regulated supply chains is expected to produce a documented First Article Inspection Report (FAIR). Without it, customers have no objective proof that your mold actually makes what the drawing specifies.

Why Does FAI Matter for Injection Molded Parts?

Injection molding introduces several sources of dimensional variation that only appear when steel actually runs plastic: cavity pressure distribution, cooling uniformity, gate freeze-off timing, and material shrinkage. Nominal shrinkage values published in material datasheets are averages, not guarantees. A part designed for ABS with 0.5% nominal shrinkage may actually shrink 0.45–0.65% depending on wall thickness, melt temperature, and packing pressure. FAI catches these deviations before they become a production problem.

当社の工場では、金型がT1（初回試作）の外観検査を優秀な成績で通過したものの、FAIの寸法測定により、重要なスナップフィットアームが0.15mm不足していることが判明した事例があります。これは金型の鋼材公差内ではあるものの、組み立て適合要件を外れていました。この問題をFAIで発見したことで、金型調整に2日間を要しましたが、5万個の部品生産後に発覚していたら壊滅的だったでしょう。

What Does a First Article Inspection Report Include?

A complete First Article Inspection Report (FAIR) documents every characteristic called out on the part drawing. The structure follows AS9102 Section 4, even for non-aerospace applications, because it is the most rigorous industry framework available. The report must be signed off by a qualified quality engineer and archived for the life of the part program.

Standard FAI Report Sections and Key Content

FAIR Section	What Is Documented	Typical Acceptance Criterion
部品番号と改訂	Drawing number, revision level, effective date	100% match to customer-issued drawing
Material Certification	Resin lot number, supplier CoC, material test data	Meets UL, ASTM, or customer material spec
Dimensional Ballooning	Every dimension on drawing assigned a balloon number	All features inspected; 0 open deviations
Critical Feature Measurement	CMM or caliper data for all critical dimensions	Cpk ≥ 1.33 for critical features
Visual / Cosmetic Inspection	Surface finish, color, weld lines, sink marks	Meets AQL 0.65 Level II sampling plan
Functional Test	Snap fit, thread engagement, assembly fit check	100% pass on all first-article samples
Process Parameter Record	Injection speed, melt temp, cooling time, pack pressure	Parameters archived for future reference
Customer Sign-Off	FAIR approved by customer quality representative	Written approval before production release

The dimensional ballooning section is the most labor-intensive part of a FAIR. Every tolerance callout on the drawing—linear dimensions, radii, hole diameters, ⁵ symbols—receives a unique balloon number. Each balloon is then measured on each sample part, and the actual value is recorded alongside the nominal and tolerance. Our quality team at ZetarMold typically records 60–150 balloon entries per part for a medium-complexity component.

GD&T:

FAI follows a defined sequence that ensures all verification activities are completed before any data is recorded. Shortcuts—such as measuring parts before they have fully cooled to ambient temperature, or measuring only one of the three sample parts—invalidate the inspection and typically result in customer rejection of the FAIR.

Step 1 is part conditioning. Injection-molded parts must be conditioned at 23°C ±2°C for a minimum of 4 hours (per ASTM D618) before measurement. Parts measured immediately after molding will read differently due to residual heat and stress relaxation. Step 2 is drawing review: the quality engineer balloons every dimension and assigns a unique ID. Step 3 is CMM programming or fixture setup for measurement. Step 4 is measurement of all three to five sample parts, with actual values recorded. Step 5 is material and process record archiving.

Step 6 is Cpk analysis for critical features. For any dimension with a critical-to-function tolerance, we calculate the process capability index (Cpk). The accepted minimum is Cpk ≥ 1.33, which corresponds to a process running at least 4 sigma from its nearest tolerance limit. Features below this threshold require mold rework before FAI can be approved. Step 7 is customer submission and sign-off. The complete FAIR package is transmitted to the customer; written approval is required before production begins.

Which Dimensions Are Most Critical to Measure in Injection Molded Parts?

射出成形プロセス variables directly affect four categories of dimensions that are most likely to deviate from nominal. Understanding which features are at highest risk helps quality engineers prioritize CMM time and flag potential issues during DFM review.

Wall thickness is the single most critical dimension because it controls both structural performance and cooling uniformity. Target tolerance for uniform wall sections is typically ±0.1 mm for non-critical features and ±0.05 mm for critical-to-fit interfaces. Gate location and dimensions affect fill pattern, weld line position, and surface cosmetics. Boss diameter and depth control thread engagement and press-fit retention. Snap-fit arm length and tip geometry determine assembly force and retention strength—even a 0.1 mm deviation in snap-fit tip height can increase insertion force by 30–50%.

Flatness and warpage are especially problematic for large, thin-walled parts. A 200 mm × 150 mm panel with 2 mm nominal wall thickness can warp by 0.5–2.0 mm if cooling is non-uniform or if packing pressure is not optimized. FAI flatness measurements are taken on a granite surface plate using dial indicators at a defined grid of points—typically every 25 mm. 金型流動解析 simulation can predict warpage before steel is cut, but FAI is the ground truth.

What Tools Are Used to Measure Parts During FAI?

について ³ (CMM) is the gold standard for FAI dimensional verification. A CMM probes the part surface at programmed points and reports actual coordinates versus nominal CAD data. Modern CMMs achieve measurement uncertainty of ±0.002 mm under controlled conditions. For production FAI, the CMM program is written from the 3D CAD model and then validated against the ballooned drawing to confirm every feature is captured.

Not all features require CMM. Thread gauges (go/no-go) verify thread engagement more quickly than CMM for standard thread forms. Vision systems measure 2D profile features—hole diameters, edge radii, slot widths—with sub-micron accuracy at high throughput. Digital calipers and micrometers are acceptable for non-critical features (tolerance ≥ ±0.1 mm) when calibrated to NIST-traceable standards. Optical comparators project part silhouettes for rapid profile checking on complex 2D contours.

In our factory, we operate a Zeiss Contura CMM with a 0.001 mm resolution probe for all critical-feature FAI measurements. For 少量射出成形 programs where a full CMM program may not be cost-justified, we use a combination of calibrated hand tools and a structured light 3D scanner to capture full-surface deviation maps against the CAD nominal.

How Long Does a First Article Inspection Take?

FAIの所要時間は、部品の複雑さ（図面特徴の数）、利用可能な測定機器、および顧客の報告要件によって異なります。25～40の図面バルーンを持つシンプルな2キャビティ金型では、部品のコンディショニングから完了したFAIR提出までに通常1～2日かかります。120以上のバルーン、GD&T指示、および材料トレーサビリティ要件を伴う複雑な8キャビティ医療機器部品では、5～7営業日かかる場合があります。

The biggest time drivers are CMM program development (4–16 hours for a new program) and customer-required reports with statistical analysis (Cpk calculations for 20–30 critical features). Customers who provide CAD models and a pre-ballooned drawing dramatically reduce FAI turnaround time. Those who only supply a 2D PDF drawing require our team to model the nominal geometry before CMM programming can begin.

At ZetarMold, we build FAI time into every project schedule at the mold qualification stage. Customers who treat FAI as an afterthought—requesting it only after they expected parts to ship—create delays. Our standard lead time commitment: T1 trial parts within 4 weeks of mold approval; FAI report within 5 business days of T1 parts being conditioned; production release within 3 business days of customer FAIR approval.

What Happens If a Part Fails First Article Inspection?

FAI failure means that one or more measured features fall outside their drawing tolerance on the first-article sample parts. The response depends on the nature and magnitude of the deviation. Minor deviations (within 20% of the tolerance band outside nominal) may be addressed through process adjustment—changing pack pressure, cooling time, or melt temperature—without touching the mold steel. These are documented as process NCRs and re-measured on a fresh set of conditioned parts.

Dimensional deviations that exceed process adjustment capability require mold steel modification. Steel removal (cutting more material) is straightforward; steel addition (welding or insert replacement) is more expensive and time-consuming. In either case, a partial re-FAI is performed: only the affected features and any dimensions that could have been influenced by the modification need to be re-measured. A full re-FAI is required if the modification involved significant steel removal affecting multiple cavity regions.

Some customers allow a Deviation Approval (also called a concession or waiver) for features that are marginally out of tolerance but demonstrably do not affect function or assembly. This requires engineering sign-off from the customer and a defined review timeline. Deviations are never permanent; the mold must be corrected before the next tool change or at the next scheduled maintenance window. In our factory, we track all open deviations in our ERP system and flag them for action at each mold service interval.

Frequently Asked Questions About First Article Inspection in Injection Molding

Is FAI required for every new injection mold, or only for regulated industries?

FAIは、航空宇宙（AS9102）、自動車（PPAP）、医療機器（ISO 13485 / FDA 21 CFR Part 820）のサプライチェーンにおいて必須です。しかし、精密組み立て向けの射出成形金型を運用するメーカーは、業界を問わずFAIを実施すべきです。なぜなら、生産規模で寸法不適合を発見するコストは、構造化された初品検査のコストをはるかに上回るからです。ZetarMoldでは、公差が±0.15mm未満の生産プログラムや、機能上重要な適合インターフェースを有する組み立てにおいて、顧客の業界セクターに関係なくFAIを推奨しています。

How many parts are typically inspected during FAI?

The standard minimum is 3–5 parts from the actual production mold, running under production-intent process parameters. For multi-cavity molds, parts should be taken from every cavity—not just one representative part. If you have a 4-cavity mold, a proper FAI measures parts from all four cavities and records cavity-specific data. Cavity-to-cavity variation is a common failure mode in injection molding; FAI is the only way to confirm that all cavities are within tolerance simultaneously. Some customers specify larger sample sizes (10–30 parts) for statistical process capability calculations.

What is the difference between FAI and PPAP?

FAI (First Article Inspection) is a measurement and verification activity—it confirms that a specific part from a specific mold meets its drawing. PPAP (Production Part Approval Process) is a broader submission package required by automotive customers that includes FAI data as one of its 18 required elements, alongside design records, process flow diagrams, control plans, MSA studies, and capacity analysis. PPAP Level 3 (the most common) requires all 18 elements to be submitted to and approved by the customer. FAI is necessary but not sufficient for PPAP; PPAP wraps FAI inside a larger quality management framework.

Can FAI be performed by the molder, or must it be done by an independent lab?

ほとんどの商業および産業用途では、成形業者自身の品質チームが、校正済みでNISTトレーサブルな測定機器を使用してFAIを実施します。顧客はFAIRをレビューし承認します。航空宇宙および防衛用途では、顧客自身の品質代表者または第三者検査機関によるFAIの立会いを要求する場合があります。FDA監視下の医療機器用途では、FAIデータが有効と見なされる前に、測定システム分析（MSA / Gage R&R調査）を実施し、成形業者の測定プロセス自体が有能であることを実証する必要がある場合があります。

一部の特徴が「実寸法未報告」と記載されたFAIRを受け取った場合、どうすればよいですか？

図面に記載され、バルーン付き検査計画に含まれるすべての特徴は、測定および報告されなければなりません。「未報告」の項目は不完全なFAIを示し、正式な承認には適しません。測定が欠落する一般的な理由には、標準工具ではアクセスが困難な特徴（治具や特殊プローブが必要）、図面バルーン作成中にうっかり省略された特徴、または破壊試験が必要な特徴（内部肉厚のための断面カット）があります。各ケースについて、成形業者は測定データを提供するか、顧客の逸脱を要求するか、代替測定方法を使用する必要があります。正式に承認されていない限り、空白または「N/A」の項目があるFAIRは受け入れないでください。

How does material shrinkage affect FAI results in injection molding?

Material shrinkage is the primary reason why injection-molded part dimensions differ from the mold cavity dimensions, and it is a major source of FAI failures. Most engineering thermoplastics shrink 0.3–2.0% as they cool from melt temperature to ambient. The mold cavity is intentionally cut oversize by the expected shrinkage factor, but actual shrinkage varies with wall thickness, melt temperature, packing pressure, cooling rate, and material lot. FAI catches cases where actual shrinkage deviates from the design assumption. When FAI shows a systematic dimensional offset across all measured features, the root cause is almost always a shrinkage factor error, which is corrected by steel adjustment.

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1. First Article Inspection: First Article Inspection (FAI) is a formal validation process that verifies the first production part or assembly from a new or modified manufacturing process meets all engineering design requirements before mass production begins. ↩

2. AS9102: AS9102 refers to the aerospace industry standard that defines requirements for First Article Inspection reports, specifying documentation, dimensional verification, and material certification procedures. ↩

3. Coordinate Measuring Machine: A Coordinate Measuring Machine (CMM) is a precision metrology device that measures the physical geometrical characteristics of a part by probing its surface with a contact or non-contact sensor, typically achieving accuracy within ±0.001 mm. ↩

4. PPAP: PPAP (Production Part Approval Process) is an automotive industry standard that requires suppliers to demonstrate, through documented evidence including FAI data, that their manufacturing process can consistently produce parts meeting all customer specifications. ↩

5. GD&T： GD&T（幾何公差）は、部品特徴の形状、サイズ、方向、位置の許容変動を定義するために技術図面で使用されるエンジニアリング表記システムであり、精密製造における普遍的な言語を提供します。 ↩