Forging presses are the second group of forging machines regularly used in impression die and large open die forging. They are commonly classified as mechanical or hydraulic, based on the means used to deliver energy. Presses deliver energy more slowly than do hammers. They are used for all alloy groups, and are used in preference to hammers for alloys that require slow deformation rates, such as harder aluminum alloys and most of the magnesium alloys. As with hammers, they usually operate vertically. The upper die is attached to the ram, and the downward stroke of the ram exerts force on the workpiece.