Quality Control in Metal Fabrication: Processes, Tools & Standards

At BravoFabs, quality control isn’t a checklist we run at the end — it’s embedded in every stage of CNC machining and sheet metal fabrication. Our Dongguan facility holds ISO 9001:2015 certification and serves industrial clients across Germany, the US, and Europe who demand tolerances down to ±0.005 mm.

This article walks through the actual QC processes we use daily — from incoming material verification to final dimensional reports — with the specific tools, standards, and documentation we provide to every client.

1. Incoming Material Inspection

Every batch of raw material — whether 6061-T6 aluminum, 304 stainless steel, or Grade 5 titanium — arrives with a mill test certificate (MTC) from the supplier. Our team cross-checks the certificate against the material itself: grade, heat number, thickness, and surface condition.

• Hardness testing (Rockwell / Brinell) on random samples per batch
• Chemical composition verification via handheld XRF analyzer for titanium and high-alloy steels
• Dimensional check on raw stock: thickness, flatness, and edge condition before cutting

If a batch fails any check, the entire lot is quarantined and returned. We don’t “fix it later” — bad material never reaches the machine floor.

2. First Article Inspection (FAI)

Before full production begins, the first machined part from each setup undergoes a complete dimensional inspection against the technical drawing or 3D model. We generate a First Article Inspection Report (FAIR) per AS9102 format when required by aerospace or medical clients.

Our FAI workflow follows a structured process:

• Setup verification: Confirm tooling, fixturing, and program match the production plan
• First-piece machining: Run one complete part through all operations
• CMM dimensional check: Measure every callout dimension against the drawing or 3D model
• FAIR documentation: Record all measurements in the inspection report, flag any out-of-tolerance features
• Client approval (if required): Submit FAIR for sign-off before full production begins

1. Program the Coordinate Measuring Machine (CMM) directly from the client’s STEP file
2. Measure all critical dimensions — typically 10 to 50 characteristics per part
3. Compare results to drawing tolerances; flag any dimension approaching the tolerance band
4. Adjust tool offsets or fixture position if needed; re-run until all points pass
5. Sign off the FAIR, attach measurement data, and send to the client for approval before mass production

For clients who don’t require a formal FAIR, we still run the first piece through the CMM and record the results in our internal job file. You’ll see this data in the final inspection report regardless.

3. In-Process Inspection (IPQC)

Quality doesn’t wait until the end. Our machine operators perform in-process checks at defined intervals during production:

• Critical dimensions: checked every 5–10 parts on the CMM or with calibrated micrometers/calipers, depending on batch size
• Surface finish: visual check plus profilometer measurement (Ra values) for surfaces specified on the drawing
• Thread quality: GO/NO-GO gauge check on every threaded feature; thread plug gauge to the specified class (6H, 2B, etc.)
• Process capability (Cpk): tracked for repeat orders — we aim for Cpk ≥ 1.33 on all critical characteristics

If a dimension starts drifting, the operator stops the run, adjusts, and re-verifies before continuing. We’d rather lose 30 minutes of machine time than ship 100 bad parts.

4. Welding Quality Control

For sheet metal fabrications and welded assemblies, our certified welders follow documented Welding Procedure Specifications (WPS). Inspection covers:

• Visual inspection of every weld bead: porosity, undercut, cracks, incomplete fusion
• Dye penetrant testing (PT) on cosmetic and structural welds for aluminum and stainless steel
• Weld size verification with fillet gauges against drawing callouts
• Fixture check: after welding, the assembly goes back on the fixture to verify no distortion occurred

5. Final Inspection & Documentation

Before any shipment leaves our facility, every part undergoes a final inspection. The output is a dimensional inspection report that we send to the client along with the shipment tracking number.

What’s in the report:

• Part number, PO number, batch quantity
• Drawing-specified dimensions vs. measured values (typically 5–15 key dimensions per part, or 100% for tight-tolerance parts)
• Surface finish readings (if specified)
• Thread gauge results
• Visual inspection notes (burrs, scratches, coating uniformity)
• Material certificates and process certifications (heat treatment, plating, anodizing)

We use a Mitutoyo CMM for complex geometries, Mitutoyo calipers and micrometers (calibrated quarterly to NIST-traceable standards) for manual measurements, and a TESA-Rugosurf profilometer for surface finish.

6. Non-Conformance & Corrective Action

When a part doesn’t meet spec — it happens, and what matters is how you handle it:

1. Quarantine: the non-conforming part is immediately isolated and tagged with the defect description
2. Root cause: operator error? tool wear? fixture shift? material defect? We trace back through the job record
3. Corrective action: fix the root cause, re-inspect the affected batch, and document what changed
4. Client communication: if the defect affects shipped parts or delivery timeline, we notify the client within 24 hours — no surprises

Quality Equipment We Use Daily