A rolling mill is a machine used in the metalworking industry to shape and reduce the thickness of metal sheets and bars. It operates by passing metal through a series of rollers, which apply pressure to stretch and compress the material. This process can improve the metal's strength and surface finish. There are different types of rolling mills, including hot rolling and cold rolling mills. In hot rolling, metal is heated above its recrystallization temperature, making it easier to shape. In cold rolling, metal is processed at room temperature, resulting in a smoother finish and tighter tolerances.