Foundry

The Foundry is a building that smelts two ore resources into ingots that can then be further processed into new parts. It is unlocked by the player in Tier 4 with the Steel Processing milestone.

Smelting
Since the Foundry is for combining multiple ore resources into a single resource, it cannot be used for smelting single ore resources into single ore resources nor does it behave like a tier 2 smelter.