Where heat and lot identity is lost between the furnace and the finishing line
In the cast house a heat is a precise thing. It is a furnace charge with a composition confirmed on the spectrometer and a set of billets cast from it. Identity is clean at that moment and begins eroding almost immediately. Billets from one heat are stacked beside billets from another. Homogenising ovens take mixed loads. At the press, one billet is loaded behind the last and the metal joins, so profile emerging across a charge weld genuinely contains two heats. A system modelling that run as one lot from one heat is already reporting something untrue.
What works in practice is deciding, deliberately, where identity is broken and where a mixture is accepted, then recording which choice was made. A run can carry a list of heats rather than a single heat, provided the list is complete and the transition length is cropped and noted. Cut lengths inherit the identity of the parent, and that inheritance has to survive the saw, because the saw bench is where most plants quietly lose the thread. Ageing racks and anodising jigs mix lots by design, so the rack itself becomes a traceable unit.
Anodising and painting are where traceability stops altogether in a surprising number of plants. Material leaves inventory as at finishing and returns as finished, with nothing recorded in between. Subcontracted finishing is worse again, since the identity that left the gate frequently is not the identity that comes back. Returning material needs the same lot reference it went out with, plus the process record and the coating results, otherwise a customer complaint about a coating batch cannot be narrowed to anything smaller than a month of production.
- Heats defined at the furnace with confirmed composition, not assigned later from a delivery note
- Extrusion runs able to carry several heats, with charge weld transitions cropped and recorded
- Cut lengths inheriting parent identity through the saw bench and the packing station
- Ageing racks and anodising jigs treated as traceable units wherever lots are mixed
- Subcontracted finishing tracked out and back with identity and process results intact