Design of Forming Processes: Bulk Forming
1 Design of Forming Processes: Bulk Forming Chester J. Van Tyne Colorado School of Mines, Golden, Colorado, U.S.A. I. BULK DEFORMATION atures relative to the melting point of the metal. Hot working occurs at temperatures above tJllerecrystalliza- Bulk defonnation is a metal-fonning process where the tion temperature of the metal. There is a third temper- defonnation is three-dimensional in nature. The pri- ature range, warm working, which is being critically mary use of the tenn bulk deformation is to distinguish it examined due to energy savings and is, in some cases, from sheet-fonning processes. In sheet-forming opera- used by industries. tions, the defonnation stressesare usually in the plane of the sheet metal, whereas in bulk defonnation, the 1. Cold Working Temperatures defonnation stresses possess components in all three Cold working usually refers to metal deformation that is coordinate directions. Bulk defonnation includes metal carried out at room temperature. Th,~ phenomenon working processes such as forging, extrusion, rolling, associated with cold work occurs wht:n the metal is and drawing. deformed at temperatures that are about 30% or less of its melting temperature on an absolute temperature scale. During cold work, the metal ,~xperiences an II. CLASSIFICATION OF DEFORMATION increased number of dislocations and elltanglement of PROCESSES these dislocations, causing strain hardening. With strain hardening, the strength of the metal increases with The classification of deformation processescan be done deformation. To recrystallize the metal, ;i thermal treat- in one of several ways. The more common classification ment, called an anneal, is often needed. During anneal- schemes are based on temperature, flow behavior, and ing, the strength of the metal can be drastically reduced stressstate.
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