Quick Answer
Custom metal parts quality inspection checklist — buyers should verify five categories: dimensional accuracy, material properties, surface condition, functional requirements, and documentation. Without a systematic inspection process, defective parts reach production and cause costly field failures. Here is what to check and why it matters.
Why Inspection Matters
Skipping or skimping on inspection means defective parts reach production. The cost of thorough inspection is always less than the cost of defects reaching customers:
| Failure Stage | Cost Impact | Example |
|---|---|---|
| Inspection cost | Low (hours per shipment) | FAI: 4–8 hours; Production: 1–2 hours/lot |
| Rework at incoming | Moderate | Return parts, supplier fixes |
| Production line stop | High | Parts don’t fit, line down hours/days |
| Field failure | Very high | Warranty, recall, customer loss |
| Safety incident | Extreme | Liability, reputation damage, legal |
The earlier you catch defects, the lower the cost.
Five Inspection Categories
Category 1: Dimensional Inspection
Verify the part matches the drawing dimensions within specified tolerances:
- First article inspection (FAI): Full dimensional report on first parts from new tooling or new supplier; every dimension measured and recorded
- Production dimensional check: Key dimensions measured against drawing tolerances; sampling per agreed plan
- GD&T verification: Position, flatness, perpendicularity, concentricity per drawing GD&T callouts
- Critical dimension report: All dimensions marked pass/fail on a dimensional report; stored for traceability
Category 2: Material Verification
Verify the part is made from the correct material with correct properties:
- Material certificate: Foundry provides chemistry report (cast analysis) and mechanical test results; each heat/lot has unique ID
- Heat lot traceability: Each heat/lot of material has unique identification; parts marked with heat lot
- Hardness test: For heat-treated parts, verify hardness meets specification (Brinell, Rockwell, or Vickers per drawing)
- Mechanical testing: Tensile, yield, elongation, impact — for critical applications per drawing requirements
Category 3: Surface Condition
Inspect surface quality visually and with measurement as required:
- Visual inspection: No visible cracks, tears, hot tears, cold shuts, misruns, inclusions, or surface defects
- Surface finish measurement: Ra value measured if specified on drawing; typical: Ra 3.2–12.5 µm for castings
- Dye penetrant (PT): For surface crack detection on critical areas; red dye penetrant and developer
- Magnetic particle (MT): For ferrous parts; detects surface and near-surface cracks
- Flash removal: All flash at parting line and gates removed flush; no sharp edges remaining
Category 4: Functional Requirements
Test the part under actual or simulated service conditions:
- Pressure test: For fluid or pneumatic parts — air underwater, pressure decay, or helium leak test per specification
- Fit-check: Part mates with assembly components correctly; try actual assembly if possible
- Weight check: Weight within expected range (indicates correct material density and wall thickness)
- X-ray or CT scan: For critical parts, verify internal soundness; detects porosity, inclusions, shrinkage
Category 5: Documentation and Traceability
Verify all required documentation accompanies the parts:
- Certificate of Conformance (C of C): Supplier certifies parts meet all specification requirements
- Material certificates: Chemistry and mechanical properties per heat/lot; matches parts in shipment
- Dimensional report: FAI or dimensional summary as required; signed by quality inspector
- Heat treatment records: If heat treated, furnace records (time, temperature) and hardness test results
- First Article Inspection Report (FAIR): AS9102 format or equivalent for aerospace/defense
Inspection Level by Application
| Application | Required Inspection | Sampling | Examples |
|---|---|---|---|
| Non-critical structural | Basic dimensional + visual | AQL-based sampling | Brackets, general hardware |
| Precision fit | Full dimensional + material cert | 100% critical dims | Gears, bearing seats, pump parts |
| Pressure-containing | Full dimensional + pressure test + material cert | 100% pressure test | Valve bodies, pump housings |
| Safety-critical | FAI + material + NDT + full documentation | 100% critical features | Aerospace, automotive, medical |
Acceptance vs. Rejection Criteria
Clear criteria prevent disputes:
- Dimensional: Any dimension outside drawing tolerance = reject
- Visual defects: Hot tears, cracks, or misruns = reject (no repair without buyer approval)
- Pressure test: Any leak = reject or return for repair (buyer engineering approval required)
- Material cert: Any out-of-spec property = reject
- Documentation: Missing cert or documentation = reject (return for complete documentation)
Defect Disposition Process
Not all defects mean scrap. Define the disposition process:
- Buyer engineering review: Define which defects require engineering disposition vs. which are automatic reject
- Repair assessment: Can the defect be repaired without compromising function? (weld repair, machining, etc.)
- Repair approval: Buyer must approve repair procedure before repair happens
- Repair documentation: Repair procedure, inspection results, and final approval documented for traceability
- Use-as-is: Some minor defects may be accepted use-as-is with engineering approval
Before finalizing the sourcing decision, many OEM buyers also compare First Article Inspection, Quality Assurance, Casting Defects Prevention, and Source Inspection to clarify process fit, cost trade-offs, tolerance expectations, and supplier risk.
If you need application-specific guidance, drawing review, or a quotation, you can Contact YCUMETAL.
Buyer Checklist
- Is there a First Article Inspection (FAI) report from new tooling?
- Are all critical dimensions measured and documented?
- Is material certification provided with each shipment?
- Is hardness testing required and documented?
- Has visual inspection been completed and signed off?
- Are pressure tests specified and completed (if applicable)?
- Is the Certificate of Conformance provided?
- Are defects dispositioned by qualified engineering before parts are accepted?
- Is traceability maintained (heat lot, part marking, documentation)?
FAQ
What is First Article Inspection?
FAI is a complete dimensional and material verification of the first parts from new tooling, a new supplier, or after a significant process change. It confirms the tooling produces parts that meet all drawing requirements before production continues.
How many parts should be inspected in production?
Depends on risk. High-risk parts (safety-critical, pressure-containing) warrant 100% inspection. Lower-risk parts use statistical sampling (C=0, AQL-based). Sampling plan should be agreed with supplier before production.
Who pays for inspection?
Typically the buyer pays for incoming inspection. However, supplier should provide FAI and material certs at no extra charge. Negotiate inspection costs as part of supplier agreement.