"做锻工" can be translated as "to work as a forger" or "to be engaged in forging work" in English.
Here, "forger" refers to someone who works in forging, typically shaping metal by heating it and then hammering or pressing it into the desired form. Alternatively, "to be engaged in forging work" more directly describes the activity of performing forging tasks.
In a more colloquial or job-title context, you might also hear "forging technician" or simply "forger" (though "forger" can sometimes have a negative connotation in other contexts, referring to someone who falsifies documents, so context is important). For a more general or descriptive term, "forging worker" or "worker in forging" would also be understandable.