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.
Frequently Asked Questions
What should I check when profiles arrive at my warehouse?
Start with outer dimensions and length, then visual surface quality, then hardness or alloy verification against the mill certificate. For machined parts, check critical hole positions and threads with gauges. A simple 10-point incoming checklist catches most supplier issues early.
Which surface defects are common on extruded aluminium?
The usual suspects are die lines and pick-up marks, scratches from handling, colour mismatch in anodizing, and occasional bubbles or blisters on the surface. Most are cosmetic, but deep die lines or cracks affect strength and should be rejected.
How can I verify the alloy and temper actually delivered?
Ask for the mill test certificate per batch, and spot-check hardness (Webster or Brinell) and, if needed, spectrometric alloy analysis. Reputable suppliers welcome a third-party inspection at the factory before shipment.