Most sheet metal parts, including the body, are formed by a machine that presses a piece of sheet metal between two halves of a mold (die). Because metal in parts shaped by only one die tends to wrinkle, crack, or tear, multiple dies are generally used to form each component. The tub sub-assembly is manufactured automatically. After being rolled into a drum shape, the side is welded. The weld is then smoothed out and the drum is placed on an expander, which stretches the tub into its final shape. A bottom is then welded onto the drum, and this weld is also smoothed.