Cold Upsetting

a cold impression die forging operation for manufacturing parts and semifinished products with localized thicker portions; it is accomplished by reducing the length of a section of the workpiece (local upsetting) without heating the metal. It is the principal operation used in producing bolts, screws, and rivets. Such items are made on automatic upsetters, which additionally perform other operations (cutting off, piercing, knurling) so that the parts produced require no machining; production rates may be as high as several hundred items per min.

Cold upsetting ensures a desirable fiber in the macrostructure of the metal so that the strength and abrasion resistance of the parts are improved. The increase in the diameter of the work-piece during upsetting is restricted by the longitudinal rigidity or by the chance of material failure with the formation of longitudinal cracks. There is no loss of rigidity (no distortion of the axis) if the length of the section being upset is less than 2.5 times the diameter of the workpiece. When necessary, a longer section can be upset in several stages by successively increasing the diameter with a corresponding reduction in the length of the section. In order to reduce the risk of material failure in the workpiece, multistage upsetting is accompanied by intermediate recrystallization annealing. (See alsoCLOSED IMPRESSION DIE FORGING and COLD FORGING AND SHEETMETAL FORMING.)