The company says it is closing the plant because of the global financial crisis.
Calcast, which is based at Campsie outside Derry city, makes cylinder heads for the Ford Explorer.
At one point it had 250 employees.
Calcast is a subsidiary of French-owned car components firm Montupet, a major supplier to the Ford motor company.
It has a second plant in Northern Ireland at Dunmurry near Belfast.
Employees at the Campsie site were told they could go home immediately, but a staff spokesman said most of the workers were staying put to make sure management treated them properly over redundancy pay.
