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roll forming[′rōl ‚fȯrm·iŋ]
the process in which a pressing tool is used to form hollow, symmetrical parts from sheet or preformed billets. The pressing tool advances from the center of the billet outward, the latter being mounted in a rotating mandrel. The area of local plastic deformation occurs as a helical line on the surface of the billet. The configuration of the mandrel corresponds to the shape of the finished part.
The pressure tools used in roll forming include forming bars and forming rollers and rolls of various shapes, which are set into rotation by the rotating billet. Small parts are roll formed in universal horizontal or vertical lathes. Roll forming is widely used to make bottoms for containers that are over 3 m in diameter, for example, large cisterns, tanks, and kettles. The method is suitable because roll-forming tools require much less force than those used in other processes, such as stamping.
For cold-working steel and nonferrous bottoms up to 4 m in diameter and 25 mm thick, specialized roll-forming lathes are used; for steel bottoms up to 7 m in diameter and 165 mm thick hot working with these specialized lathes is used, which involves several operations with intermediate reheating of the billet.