Extrusion

Abstract

Advantages and drawbacks of extrusion. Two basic methods of extrusion: direct and indirect, and their comparison. Extrusion equipments and dies. Metal flow during extrusion. Factors influencing extrusion process, such as type of extrusion, extrusion ratio, extrusion (ram) speed, approach angle of conical die and optimum semicone angle, friction and lubrication. Estimation of extrusion (ram) pressure and load for: open-die, indirect and hydrostatic extrusions, direct extrusions through conical converging die and square die under conditions of Coulomb’s sliding friction, full sticking friction and mixed sticking–sliding friction, prevailing, respectively, from the entry plane of conical die or from that of dead zone in square die to the entry to extrusion chamber. Strain rate in extrusion. Extrusion defects. Impact extrusion: direct (Hooker process) and indirect. Hydrostatic extrusion and its basic difference with conventional extrusion. Conventional hydrostatic and differential pressure hydrostatic extrusion. Advantages and disadvantages of hydrostatic extrusion. Seamless tube production by extrusion: using an external long fixed, floating or piercing type of mandrel, or without using a normal external mandrel (welding-chamber method). Extrusion of cable sheathing. Application of slip-line field to steady-state motion: 50% and 2/3 plane-strain frictionless extrusion. Upper-bound solution for plane-strain frictionless extrusion with an example. Problems and solutions.