batirse el cobre

A fixed idiom meaning to work hard, strive, or fight tenaciously for something — often for a modest or thankless goal: se batió el cobre para sacar adelante el negocio. It comes from coppersmiths' workshops, where hammering (batir) a copper sheet into shape took loud, tireless, repeated blows — a folk image for stubborn effort documented as far back as Covarrubias's 1611 Tesoro de la lengua castellana.

• Se batió el cobre durante años para sacar el proyecto adelante. — He worked tirelessly for years to get the project off the ground.
• Hay que batirse el cobre si quieres que te asciendan. — You have to really put in the work if you want to get promoted.
• Los sindicatos se batieron el cobre por el nuevo convenio. — The unions fought hard for the new labor agreement.

Despite containing cobre (copper), this has nothing to do with metal in modern use — it's a fixed idiom for hard effort/struggle, not a literal or industrial verb.