A method to produce a product includes the steps of: providing a mold including an upper mold (40) and a lower mold (30), the upper mold defining a plurality of through holes (43); providing a metal piece (10), a hot melt adhesive, and a nonmetal cover layer (50) between the upper and lower molds, the hot melt adhesive arranged between the hot melt adhesive and the cover layer; closing the mold; heating the mold to melt the hot melt adhesive; conducting high-pressure gas into the mold via the through holes to press the cover layer toward the metal piece; opening the mold to pick up an intermediary product having the metal piece and the cover layer attached thereto by means of the adhesive; and applying a sealing layer (60) which joins corresponding free edges of the metal piece and the cover layer to the intermediary product through injection molding technology.