Inspection Starts at the Drawing
Before a single profile is measured, the acceptance criteria must exist on paper. Your drawing should state which dimensions are critical, which tolerances apply, and which standard governs – EN 755-9, ASTM B221 or GB/T 5237. Buyers often skip this step, then discover at incoming inspection that "too long" or "too bent" was never defined. A drawing with clear critical dimensions, a stated standard and an agreed sampling plan turns inspection from an argument into a procedure. If the supplier’s drawing differs from yours, reconcile it before production, not after delivery.
The Five Checks That Matter
Five checks catch the overwhelming majority of quality issues. First, dimensions: measure critical cross-section sizes with callipers or a micrometer against the drawing – wall thickness, slot width, overall width. Second, straightness and twist: lay the profile on a flat table and check the gap with a feeler gauge; a 3-metre profile should be visibly true. Third, surface quality: look for die lines, scratches, bubbles, pitting, and – after anodising – colour and gloss variation across the batch. Fourth, hardness: a Webster hardness tester should read 8-12 HW for 6063-T5, and 12-14 HW for T6; soft profiles bend and strip threads. Fifth, cut quality: ends should be square, burr-free and consistent in length within the agreed tolerance.
Sampling, Reports and Documentation
Agree the sampling plan before production: first-article full inspection, then AQL-based random sampling for the rest of the batch. For a serious order, ask for three documents: the material certificate (MTC) confirming alloy and temper, the hardness report, and the dimensional inspection report. These are not formalities – they are the evidence chain if something goes wrong later. Many buyers also specify third-party inspection (SGS, TUV, Bureau Veritas) for large or critical orders; a well-run extrusion plant will arrange it without friction, and will hold samples from each batch for reference.
How to Handle Disputes
When a problem does surface, follow the evidence trail: keep samples, take photos with a scale reference, and check the failing dimension against the agreed drawing and standard – not against a general sense of "quality". If the batch genuinely fails the agreed criteria, the remedy is usually rework or replacement of the affected portion, not a full-order argument. Clear communication beats escalation: share the measured data, not just a complaint. At Siken Aluminum every shipment ships with dimension, hardness and material reports, our QC team keeps batch samples on file, and we welcome third-party inspection at our plant – because a profile that fails inspection costs both sides money.