Executive summary
Sample approval is the formal bridge between a metal part that looks acceptable and a process that an OEM can authorize for repeat production. For a stamped bracket, machined housing, laser-cut plate, turned pin, or formed enclosure, the submitted sample is only one part of the evidence. The buyer also needs confidence that the part was made from the specified material, with the intended tooling and process, under controls that can be repeated across lots and shifts.
Two familiar frameworks are **Production Part Approval Process (PPAP)** and **First Article Inspection (FAI)**. They overlap, but they are not interchangeable. PPAP evaluates whether the supplier’s production process is sufficiently defined and controlled. FAI concentrates on verifying that the first article conforms to the engineering definition, including dimensions, notes, materials, and special characteristics. A buyer may request either framework, both, or a customized submission package. The purchase order, quality clauses, drawing, 3D model, supplier manual, and program-specific instructions take precedence over generic assumptions.
A strong approval process therefore starts before manufacturing. The supplier and buyer align the applicable revision, submission level, sample quantity, test requirements, deviation rules, and approval authority. After production, the supplier submits objective evidence, the buyer reviews both product and process information, and any open issue is resolved through a documented corrective action or concession. Approval should identify exactly what was accepted: a revision, tooling condition, material source, process route, and inspection basis.
PPAP and FAI: related purposes, different emphasis
PPAP is commonly associated with automotive supply chains, but its underlying logic is useful for many OEM programs. It organizes evidence such as design records, change documentation, process flow, risk analysis, control plans, measurement results, material or performance test results, process capability studies where required, and a formal warrant or declaration. The requested PPAP level determines how much evidence is submitted to the customer, not whether the supplier should understand the complete process internally.
FAI is widely used in aerospace, defense, industrial equipment, and other regulated or configuration-controlled environments. An FAI report typically links each drawing characteristic to an inspection result. It may include the drawing or model revision, characteristic number, nominal value, tolerance, actual result, measurement method, and the identity of the inspection equipment or record. Material and process certifications, special-process approvals, and functional test results may be attached or referenced.
| Question | PPAP emphasis | FAI emphasis | |---|---|---| | Is the product defined correctly? | Confirms design records and change status | Verifies every applicable design characteristic | | Can the process repeat production? | Reviews process planning, risks, controls, and evidence | May document the first article without fully assessing process maturity | | What is submitted? | A customer-defined submission level and warrant | A traceable inspection report with supporting records | | When is it reused? | For defined changes, new tooling, relocation, or process concerns | For a new part, design revision, or significant configuration change |
The practical decision is not to choose the fashionable acronym. It is to determine the customer’s required deliverable and then close the gaps between the requested format and the actual manufacturing risk. An OEM may ask for an FAI report plus selected PPAP elements, such as a process flow, control plan, and material certificates. Another may use its own supplier portal and forms while expecting the same underlying evidence.
Define the approval basis before making samples
The first approval meeting should establish the **approval basis**. This is the controlled set of information against which samples will be judged. It should include the latest 2D drawing, released 3D model when applicable, specifications, approved deviations, purchase-order requirements, packaging instructions, and any referenced industry or customer standard. If the drawing and model conflict, the supplier should not quietly select one. The conflict must be raised and resolved by the authorized engineering function.
Revision control is especially important for custom metal parts because a minor change can affect tooling, bend deductions, machining programs, inspection fixtures, surface treatment, or assembly fit. The submission should identify the revision used for manufacture and inspection. A sample made from an obsolete file can waste weeks even when its dimensions are otherwise good.
The parties should also agree whether the sample must come from **production-intent conditions**. For metal parts, that may mean production tooling rather than a soft prototype tool, the intended material grade and thickness, the planned heat treatment or plating route, and normal operators and inspection methods. If a temporary method is used, it should be explicitly identified. A prototype that passes geometry may still be unsuitable as evidence for a process that will later use different tooling or suppliers.
Clarify characteristics and acceptance rules
Not every drawing feature carries the same risk. The supplier should identify dimensions and notes that affect safety, regulatory compliance, assembly, sealing, fatigue, electrical grounding, or interchangeability. Customer-specific symbols may define special characteristics, but the absence of a symbol does not eliminate engineering responsibility. Hole position, thread quality, bend angle, flatness, burr limits, weld penetration, coating thickness, and edge condition can all matter depending on the application.
Acceptance rules should cover more than nominal dimensions. They should state how many samples are required, whether results must be recorded individually, what measurement uncertainty or resolution is appropriate, how visual defects are judged, and whether functional or performance tests are mandatory. A supplier should ask who can approve a deviation and whether conditional approval permits shipment, limited production, or only further sampling.
Build the evidence package around the process
A useful package tells one consistent story. The process flow shows how raw material becomes a finished part, including receiving inspection, cutting or forming, machining, joining, heat treatment, finishing, cleaning, inspection, marking, and packing. The risk analysis then identifies where a defect could arise and how serious it would be. The control plan translates the important risks into specific checks, methods, frequencies, reaction plans, and records.
For example, a stamped steel retainer may require controls for material identity, coil thickness, die condition, pierce diameter, hole-to-edge location, forming height, burr orientation, and corrosion protection. A machined aluminum manifold may require controls for billet or bar traceability, datum setup, tool wear, bore size, thread form, cleanliness, pressure testing, and surface treatment. The sample report should connect these controls to the inspection results instead of presenting unrelated spreadsheets.
Material records must be traceable to the submitted parts. The certificate should identify the material designation and applicable condition, heat or lot information where available, and the relationship between the certificate and the supplier’s receiving record. If a process such as plating, anodizing, heat treatment, welding, or nondestructive examination is outsourced, the evidence should identify the processor and applicable specification. The buyer may require approved sources or specific accreditation; those requirements must be checked rather than inferred.
Measurement records should identify the instrument or method used. A coordinate measuring machine, optical system, height gauge, thread gauge, pin gauge, micrometer, hardness tester, or coating-thickness instrument may each be appropriate for different characteristics. The method should suit the geometry and tolerance. A measurement number without a clear characteristic reference, unit, method, or part identification is difficult to audit and easy to misinterpret.
A practical approval sequence
1. Review the design and commercial documents
Before cutting material, compare the drawing, model, specifications, purchase order, and quality clauses. Confirm units, revision, material, finish, packaging, marking, and required records. Identify missing information and raise questions through the agreed change or clarification channel.
2. Confirm process and tooling readiness
Document the planned route and identify production-intent equipment. Review die, fixture, gauge, CNC program, welding procedure, or inspection fixture readiness. Verify that tool features will support the required geometry and that maintenance or tool-life controls are defined. If the sample uses an interim tool, label the limitation and obtain written agreement on what the sample can prove.
3. Manufacture and identify the samples
Produce the agreed quantity under controlled conditions. Record material and process lots, equipment or tool identification, date, operator or work center where required, and any rework. Segregate samples from unrelated parts. Marking must not damage functional surfaces or obscure inspection features.
4. Inspect and test against the approved definition
Inspect all required characteristics, not just those that are easy to measure. Use calibrated equipment under a suitable measurement environment. Record actual values and units, including individual results when requested. Complete functional, performance, cleanliness, coating, hardness, or destructive testing when the drawing, specification, risk, or customer requirement calls for it.
5. Assemble and submit the package
Check that the report, sample labels, material certificates, process records, photographs, test results, and deviation forms agree. Internal review should catch mismatched revisions, missing characteristic numbers, inconsistent units, illegible scans, and results reported against the wrong lot. Submit through the buyer’s required channel and retain the complete controlled record.
6. Resolve findings and obtain a defined disposition
The buyer’s response may be approved, approved with conditions, rejected, or returned for clarification. Each nonconformance should have an owner, containment decision, root-cause analysis when appropriate, corrective action, and verification plan. Do not treat silence or receipt of samples as approval. Production release should be tied to a documented disposition from the authorized customer representative.
Common failure modes and trade-offs
The most common failure is **sample approval without process understanding**. A hand-finished or selectively adjusted sample can meet the drawing while concealing a weak forming, machining, or finishing process. The remedy is to disclose nonstandard operations and define whether the sample is representative of production.
A second failure is a report that lists dimensions but omits requirements in notes, specifications, or the model. Threads, radii, edge breaks, weld symbols, surface texture, cleanliness, and marking are frequently overlooked because they do not fit a simple dimensional table. A characteristic-by-characteristic review of the complete definition reduces this risk.
Another problem is excessive reliance on capability indices. Process capability studies can be useful when the process is stable and the sampling method is appropriate, but a calculated index does not repair biased measurement, mixed lots, tool adjustment between readings, or an unstable process. Capability evidence should be interpreted with control charts, sampling logic, and knowledge of the process. Where a process is short-run or inherently difficult to study, the buyer and supplier should agree on a practical alternative.
Measurement disagreement is also common. Different datums, fixture methods, temperature conditions, probing strategies, or gauge designs can produce different conclusions. A buyer may measure the part in an assembly fixture while the supplier uses a free-state setup. The solution is not to average contradictory numbers; it is to align the measurement definition and, where necessary, conduct a joint correlation study.
Finally, approval can become too broad. Acceptance of one lot does not automatically approve a material substitution, tool relocation, new finishing source, altered inspection method, or drawing revision. Change control should define when resubmission, partial submission, or customer notification is required.
RFQ and pre-production checklist
An international OEM buyer can reduce ambiguity by placing the following questions in the RFQ or kickoff package:
- Which framework is required: PPAP, FAI, customer-specific submission, or a combined package?
- Which submission level, form, language, file format, and sample quantity apply?
- What drawing, model, specification, and purchase-order revision is the approval basis?
- Which characteristics are special, critical, safety-related, functional, or regulatory?
- Must samples use production-intent tooling, material, finishing source, and inspection equipment?
- Which material, heat-treatment, coating, cleanliness, welding, or test certificates are required?
- Are approved processors, laboratories, gauges, or measurement methods specified?
- What are the rules for deviations, conditional approval, rework, and shipment before approval?
- What events trigger resubmission, including design changes, tooling changes, relocation, or supplier changes?
- Who is authorized to approve, reject, or grant a temporary concession?
Before submission, the supplier should additionally verify that every sample is linked to a lot, every report uses the correct revision, all actual results are legible and complete, certificates match the material and process records, and open issues have a documented disposition. The buyer should confirm that the evidence demonstrates both conformance and representativeness rather than merely presenting a polished first-off sample.
Conclusion
A disciplined sample approval process turns a custom metal part into a controlled manufacturing commitment. **FAI** is valuable for proving that the first article matches the engineering definition; **PPAP** adds a broader examination of how the supplier will control repeat production. Buyer-specific requirements determine the final format and may be stricter or more focused than either framework.
The most reliable approvals are built on early revision alignment, production-intent sampling, traceable materials and processes, suitable measurement methods, and clear dispositions for every exception. When the package connects drawing characteristics to process controls and objective records, the OEM gains more than a passing sample: it gains a defensible basis for production release, change management, and ongoing supplier quality.
References
[1]: https://www.aiag.org/quality/automotive-core-tools "AIAG Automotive Core Tools" [2]: https://iaqg.org/standards/9102 "IAQG 9102 Aerospace First Article Inspection Requirements" [3]: https://www.iso.org/standard/62085.html "ISO 9001:2015 Quality Management Systems"