Quality Control in Sheet Metal Fabrication: Our Inspection Process

Follow a single sheet of steel through the workshop, and you’ll see it being measured, compared, and recorded again and again. Every inspection step has a purpose – to make sure that when the part leaves the factory, its dimensions, strength, and surface finish are exactly as required.

Steel sheets and tubes are placed on the inspection table as soon as they arrive. The inspector uses a vernier caliper to check thickness – common gauges like 1.0mm, 1.5mm, 2.0mm must stay within ±0.05mm tolerance. A roughness comparator is used to look for mill scale, scratches, or oil stains. Non‑conforming materials are rejected immediately and never enter the cutting area.

The first part cut by the laser machine is taken to the inspection station. Digital calipers and a height gauge measure critical hole positions, edge distances, and contour dimensions. For complex shapes, a profile projector or CMM (coordinate measuring machine) compares the actual data with the CAD drawing. Only after the first article passes a full dimension check can the machine continue cutting.

Each time the press brake is repositioned, the operator measures the bending angle with a protractor or universal angle gauge – typical accuracy target is ±0.5°. A depth gauge verifies the flange length. Every 20–30 parts, the QC inspector randomly picks one and places it on a dedicated checking fixture to simulate assembly, checking for twist or interference after bending.

On welded assemblies, a weld gauge checks leg height, undercut, and cracks. For load‑bearing or sealed components, dye penetrant testing or an air leak test is performed. A feeler gauge measures weld gaps, and a visual inspection confirms there are no missed welds or burn‑through.

After powder coating or plating, a coating thickness gauge measures the film (e.g., 60–120μm for powder coating). A cross‑cut adhesion test uses a special blade and tape to check if the coating peels off. A color difference meter compares the part with a master standard to ensure batch‑to‑batch color consistency.

Before shipment, a random sample is drawn according to AQL standards. Go/no‑go thread gauges check every tapped hole, and fixture gauges verify the center‑to‑center distance between adjacent mounting holes. An inspection report with actual measured values of key dimensions is placed inside the packaging. Only after passing final inspection does the part receive a “PASS” label and get loaded for delivery.

Throughout this process, every measurement is recorded on the in‑process check sheet. The equipment matters – but what makes every piece of sheet metal stand up to scrutiny is this complete, step‑by‑step inspection system.