The raw material used is a billet. Billet is heated to its forging temperature and fed into the machine chamber. In this forward extrusion piston and out going material moves in the same direction Pressure is applied to the billet, forcing the material through the die. In forward direction since billet moves inside the drum so pressure required in overcoming the friction will be more. The length of the extruded part depends on the size of the billet and cross section area of the die
A typical sequence of operations for the forward extrusion of a solid section is as follows:
- The heated billet and the dummy block are loaded into the container.
- The billet is extruded by the force of the ram being pushed against it. This upsets the billet, then forces the metal to flow through the die. During extrusion, a thin shell of material may be left on the container walls. Extrusion is halted in order to leave a thin disk of material (butt) in the container.
- The container in separated from the die the extruded section with the butt, and the dummy block.
- The discard (butt) is sheared off.
- The shear die, the container, and the ram are returned to their initial (loading) positions.
Typical load versus ram displacement curves shows that the load in forward extrusion initially increases very rapidly as the billet upsets to fill the container. This is followed by a further increase in pressure, and extrusion begins. A somewhat cone-shaped deformation zone then develops in front of the die aperture. After the maximum load has been reached, the extrusion pressure falls as the billet length decreases until a minimum is reached, then rapidly increases again. This last pressure increase occurs because only a disk of the billet remains and the metal must flow radially toward the die aperture. Resistance to deformation increases considerably with decreasing thickness.