Extrusion Process
There are three basic types of extrusion. In the most common process (called direct or forward extrusion), a billet is placed in a chamber (container) and forced through a die opening by a hydraulically driven ram (pressing stem or punch), as shown m Fig The die opening may be round, or it may have various shapes, depending on the extruded shape desired. The function of the dummy block Is to protect the tip of the pressing stem (punch), particularly in hot extrusion. Other types of extrusion are indirect, hydrostatic, and impact extrusion.
In indirect extrusion (also called reverse, inverted, or backward extrusion), the die moves toward the unextruded billet (Figa). In hydrostatic extrusion (Figb), the billet is smaller in diameter than the chamber (which is filled with a fluid), and the pressure is transmitted to the billet by a ram. Unlike in direct extru¬sion, there is no friction to overcome along the container walls because the billet is stationary with respect to the container. A less common type of extrusion is lateral (or side) extrusion (Figc).
There are three basic types of extrusion. In the most common process (called direct or forward extrusion), a billet is placed in a chamber (container) and forced through a die opening by a hydraulically driven ram (pressing stem or punch), as shown m Fig The die opening may be round, or it may have various shapes, depending on the extruded shape desired. The function of the dummy block Is to protect the tip of the pressing stem (punch), particularly in hot extrusion. Other types of extrusion are indirect, hydrostatic, and impact extrusion.In indirect extrusion (also called reverse, inverted, or backward extrusion), the die moves toward the unextruded billet (Figa). In hydrostatic extrusion (Figb), the billet is smaller in diameter than the chamber (which is filled with a fluid), and the pressure is transmitted to the billet by a ram. Unlike in direct extru¬sion, there is no friction to overcome along the container walls because the billet is stationary with respect to the container. A less common type of extrusion is lateral (or side) extrusion (Figc).
