You can find the following definition in the GDT: "Casts metal moulds to form jewellery and silverware articles: Forms plaster model, or receives model from stock. Builds sand mould in flask, using plaster model as pattern. Places flask in furnace, or heats with blowtorch to dry and harden sand mould. Removes plaster model from flask. Melts metal in crucible or furnace and pours molten metal into channel of sand mould to cast metal mould. Opens flask and removes metal mould when metal has hardened, using pliers or tongs. "

For large stuff you would probably use "foundryman", but probably not appropriate here for dinky little objects. I'd stick with what you' suggested.

caster. Dans tous les textes que j'ai traduit de l'anglais on a toujours utilise "caster".