Incoming inspection: what to check, in what order, and what to write down
A goods-in check that takes twenty minutes per lot catches the failures that cost a shift. The order of the checks matters as much as the checks themselves.
At a glance
Specification at a glance
| Check | Method | Acceptance to write into the procedure |
|---|---|---|
| Documents | Match label reference to mill certificate and inspection record | Every lot traceable, no missing reference |
| Thickness | Micrometer at three points across the part | Within the stated tolerance, recorded per lot |
| Diameter or size | Caliper or template on a sample of pieces | Within the drawing tolerance on the fed part |
| Flatness | Surface plate, 24 hours after receipt | Millimetres over the part, stated per part size |
| Surface | Visual under good light, both faces | No scratches deeper than the agreed limit, no roll marks on the cooking face |
| Edge | Visual and touch on a sample | No burr that catches a glove, no separation visible at the edge |
| Bond | Bend test on one piece, or ultrasonic if the file requires | No opening at the interface |
| Packing | Count per stack, interleaving, protection | Matches the packing specification |
| Draw trial | Three to five parts in production tooling | No failure mode that the sample did not show |
Documents first, because they gate the rest
If the label reference does not match the mill certificate, stop. Nothing else you measure can be attributed to a batch, and a quality file without traceability is a file that fails an audit later. This check takes two minutes and prevents the expensive version of the same problem.
Measure the part you feed the press
Thickness on the sheet and thickness on the disc are not the same measurement once the material has been cut and the stress released. Measure what goes into the press, at three points, and record it. This is also the measurement that settles arguments later, because the supplier's inspection record measured the same thing at their end.
Flatness needs a day
A stack that is flat on arrival can show dishing the next morning as the stress redistributes. Check on the surface plate after 24 hours, on pieces taken from the middle of the stack rather than the top, and record the figure. If it moves, you have a stress problem to raise with the supplier before the lot is consumed.
The five-part draw
Before releasing a lot to production, draw three to five parts in the real tooling. It costs minutes and tests the only thing the paperwork cannot: how this lot behaves under load. Record the failure mode if there is one, because the mode points at the cause: edge, anneal, gauge or tooling.
What to do when a lot fails
Quarantine, photograph, and report with the batch reference plus the measurement that failed. A supplier can act on "thickness 2.35 mm at three points, tolerance 2.4 to 2.5" and cannot act on "material seems thin". The record you took at goods-in is the whole argument.
Questions
Common questions
Do I need to inspect every lot?
Documents, dimensions and a visual check on every lot; flatness and a draw trial at least on the first lot and then on a sampling basis agreed with your quality team.
What if flatness fails after 24 hours?
Quarantine the lot, record the figure, and report it with the batch reference. Dishing is a stress and anneal issue, and the supplier can only act on the number.
Can I rely on the supplier's inspection record?
It is the starting point, not the acceptance. Your goods-in check is what protects your production line.
Which failure mode is most common?
Edge separation during drawing, usually traceable to edge quality or an under-annealed batch. Wrinkling at the flange points at the draw ratio or the tooling.
Should I keep a retained sample?
Yes, one piece per lot with its label. When a later batch behaves differently, the retained sample settles the comparison.