Material certification
Documented proof that material meets its specification, traceable to a mill test report, and a requirement that changes how you buy, store and cut it.
A material certificate ties the metal in a part back to a mill test report showing its chemistry and mechanical properties. On commercial work it is often optional. On aerospace, defence and regulated work it is mandatory and it reaches into operations rather than staying in the paperwork.
The consequences are practical. Material has to be segregated so lots do not mix, identity has to survive every operation including outside processing, and the certificate has to be retrievable years after the last delivery.
It also removes flexibility that commercial work takes for granted. The offcut from another job cannot be used, because its lot identity belongs to a different order, which is a real yield cost that never appears as a line.
Buying changes too. Certified material costs more, the list of approved mills is shorter, and minimum quantities may exceed what the programme needs, which turns a material decision into an inventory commitment. What AS9100 adds to the number works through where those costs land.