Indirect Extrusion
Indirect extrusion is mostly used at the production of cables, bars and copper cross-section. This method is also used for the extrusion of high alloy aluminium. The die is placed into the stem with a space at the tip and pushed into the container. Whilst the container may move towards the die, in the same manner, the die may move inside the container. The billet remains fixed during the whole extrusion after being placed inside the container and this prevents the friction between the container liner and the billet. The metal flow is more homogenous at the indirect extrusion compared with the direct extrusion. There is no friction between the billet and the liner at the indirect extrusion. Thus, an extended billet pressing is ensured. Compared with other methods, a higher extrusion speed and a longer profile can be obtained. Also a lesser burr generation and high product quality belong among its advantages.
Disadvantages;
Direct Extrusion
At the direct extrusion, the heated billet in placed inside the container and extruded through the die. The movement direction of the stem is the same of the flow direction of the billet. There is a friction between the billet and the inner surface of the container during the process and this results in the application of a higher pressure against the friction force of the stem. Not the whole of the billet can be extruded and the part called “Butt” is discarded in every pressing cycle and directed to recycling. Direct extrusion provides the opportunity to obtain profiles in a larger variety and width.
Disadvantages;