The factors which determine the success of the extrusion operation may be high-temperature-stress related, surface related, or structure related. These features are reviewed and it is shown that the extrusion pressure cannot be expressed as a simple function of the extrusion ratio but must include a term which expresses pressure dependency as a function of the temperature-compensated strain rate. It is also shown that surface quality and surface recrystallization may also be expressed as a function of the temperature-compensated strain rate. A limit diagram is presented showing the effect of ram speed upon the contracting loci and incorporating recrystallization and surface-quality bounds.
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