GlossaryKind of term: Manufacturing termScrap
What is scrap?
Scrap is a part that fails its requirements and is taken out of use, because rework is impossible, not worth it or not allowed.
Scrap is both the decision that a nonconforming part will not be used for its intended purpose and the part itself. It is one of the possible dispositions for a nonconforming product, alongside rework, repair and use under a concession. Take a bore of ⌀12 H7: it may lie between 12.000 and 12.018 mm. If it measures 12.03 mm after reaming, there is no material left to correct it within the drawing. The part is scrapped unless the customer allows a concession or a repair, such as fitting a bush. Chips and offcuts are not scrap in this sense; they belong to normal material consumption.
What does scrap depend on?
Scrap can arise anywhere in the route: in the machine, through distortion in heat treatment, through dimensional growth in a surface treatment, through damage in transport, or only at final inspection. How likely it is depends on the ratio between tolerance and process variation, the stiffness of the part, residual stress in the material, the number of setups and the measuring method. On a one-off it often shows only at the end whether the part is good; in a batch, a first-off check and in-process checks catch much of it before an error repeats.
How does scrap work in practice?
What a scrapped part costs depends on where in the route it happens: the later, the more material, machine time and subcontract work it already carries. If the order calls for a fixed number of good parts, the replacement runs the route again, and on a small quantity that can mean setting up the operations again. A blanket scrap allowance with no basis means little for a particular part. For work with a recognisably higher risk, such as thin walls or tight form and location tolerances, you can carry a risk allowance or extra starting stock as a line of its own and check later whether it held.
What is scrap often confused with?
Scrap is not rework: a reworked part conforms afterwards, a scrapped part is replaced. Nor is every first-off you set up on scrap: it can fall within the requirements and simply have taken more time. And a nonconformity is not yet scrap: it becomes scrap only through the decision recorded in the non-conformance report.
Frequently asked questions
Does scrap belong in the estimate?
That is an estimating convention. For work with a recognisably higher risk, such as thin walls, tight geometric tolerances or a finish that changes the dimension, you can carry it as a line of its own; the actuals then show whether the allowance was enough.
Why is scrap after finishing so expensive?
Because by then the part has been through almost the whole route: material, machining in several setups, transport and the finish itself. The replacement has to go through all of it again, which costs lead time as well.
Can a nonconforming part still be delivered?
Only under a concession: the customer gives permission to use the part despite the deviation. Record that permission with the non-conformance report. Without a concession the part is reworked or scrapped.