A method and device for pre-heating a first molding surface of a mold with an open position and a closed position defining a closed cavity between the first pre-heated molding surface and a second molding surface. A core is inductively heated outside the mold by placing the core inside a coil having an AC current passing there through. The core is inserted between the molding surfaces of the mold in the open position. The first molding surface is preheated by transferring the heat between the core and the first molding surface. The core is then removed and the mold is closed.