【正文】 because a large amount of strain hardening renders the material brittle. The frictional characteristics of the two forming processes are also entirely different. For example, the coefficient of friction in cold forming is generally of the order of , whereas that in hot forming can be as high as . Further, hot forming lowers down the material strength so that a machine with a reasonable capacity can be used even for a product having large dimensions. The typical forming processes are rolling, forging, drawing, deep drawing, bending, and extrusion. For a better understanding of the mechanics of various forming operations, we shall briefly discuss each of these processes.Rolling In this process, the job is drawn by means of friction through a regulated opening between two powerdriven roll. The shape and size of the product are decided by the gap between the rolls and their contours. This is a very useful process for the production of sheet metal and various mon sections, ., rail, channel, angle, and round.Forging In forging, the material is squeezed between two or more dies to alter its shape and size. Depending on the situation, the dies may be open or closed.Drawing In this process, the crosssection of a wire or that of a bar or tube is reduced by pulling the workpiece through the conical orifice of a die. When high reduction is required, it may be necessary to perform the operation in s