Injection mold tooling (soft vs hard)

A "soft" tool, often aluminum or pre-hardened steel, costs less and can be made faster, which suits bridge production, pilot runs and modest volumes. A hardened-steel tool costs more and takes longer, but holds tolerances over many more shots and can have multiple cavities to cut per-part cost. The plastics industry's SPI mold classes are a common shorthand for expected life, from Class 105 (prototype, roughly 500 cycles or fewer) to Class 101 (over a million cycles); published ranges for the middle classes differ between sources.

Mold-flow simulation before cutting steel predicts filling, weld lines, sink and warp, and guides gate placement.

Where it bites: tool ownership, storage and transfer rights belong in the contract, because a tool you paid for but can't move is leverage against you. Tool changes after cutting add weeks.