Materials

Yield loss is the one share that never gets cheaper

Scrap is charged as a rate on units produced, not on units shipped, so every good unit carries its share of the ones lost beside it. That ratio is the same at 500 units and at 500,000. What changes is everything around it: as tooling and freight amortise away, yield loss becomes a larger and larger fraction of what is left.

The figures below hold the enclosure lid’s own order at 1,000 units constant and vary only the scrap rate, so the column is a like-for-like comparison rather than six different orders.

Thermoplastic

ABS

A rigid styrenic that moulds predictably and holds dimension. Scrap here is sprue, short shots and the first units off a cold tool.

Typical scrap

Yield multiplier

1.0204x

At 1,000 units it adds $0.09 to a $14.04 landed unit: nine cents, against $8.00 of tooling in the same unit.

Thermoset elastomer

Nitrile rubber (NBR)

Compression moulded and trimmed by hand or by die. Flash is not recoverable once cured, so every trim is yield lost for good.

Typical scrap

3.5%

Yield multiplier

1.0363x

At 1,000 units it adds $0.16 to a $14.11 landed unit. The trim loss is permanent: a thermoset cannot be reground and run again.

Metal

5052 aluminium

Sheet stock, blanked and formed. Scrap is nesting offcut plus the odd part rejected at the brake, and offcut is sold on as recoverable value.

Typical scrap

1.5%

Yield multiplier

1.0152x

At 1,000 units it adds $0.07 to a $14.02 landed unit, the lowest of the six, because offcut is recovered rather than discarded.

Metal

6061 aluminium

Billet, machined to size. Swarf is not counted as scrap because it is priced into the billet; the scrap here is the first article and the part that moves in the fixture.

Typical scrap

Yield multiplier

1.0101x

At 1,000 units it adds $0.04 to a $13.99 landed unit. A subtractive process pays for its waste up front, in the stock.

Thermoplastic elastomer

TPE overmould

A second shot bonded onto a rigid substrate. A failed bond scraps the substrate with it, so one defect destroys two parts worth of work.

Typical scrap

Yield multiplier

1.0417x

At 1,000 units it adds $0.18 to a $14.13 landed unit, the highest of the six, because the scrap takes the first shot down with it.

Composite

FR-4 laminate

Glass-reinforced epoxy, panelised and depanelised. Scrap is panel yield and the boards that fail at test after every component on them has already been paid for.

Typical scrap

2.5%

Yield multiplier

1.0256x

At 1,000 units it adds $0.11 to a $14.06 landed unit. It is the latest-occurring scrap of the six: it is lost after assembly, not before.