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Lecture 12 Different types of extrusion and their characteristics Products by extrusion Types of Extrusion Direct or forward extrusion – Billet pushed through die from behind – The process is similar to forcing the paste through the opening of a toothpaste tube – Billet slides relative to the container wall – The wall friction increase the extrusion force Types of Extrusion Indirect – Die pushed into billet – Except at the die, there is no friction at the billet-container interface Types of Extrusion Types of Extrusion Impact Extrusion – Similar to indirect extrusion – Can be considered a subset of cold extrusion – Tends to look very similar to forging ,Used to make short parts with thin walls Types of Extrusion Types of Extrusion Conform Continuous extrusion forming Friction is just useful to process. Lecture 13 Process variables and metal flow in Direct Extrusion Process Variables in Direct Extrusion Process variables in direct extrusion. The die angle, reduction in cross-section, extrusion speed, billet temperature, and lubrication all affect the extrusion pressure Material Flow Easy to extrude metals and alloys – Aluminum – Copper – Magnesium – Steels – Stainless steels Difficult to extrude metals and alloys – Titanium – Refractory metals Material Flow Four patterns of material flow in extrusion The most homogeneous flow pattern – No friction at the billet-container/die interface – This type occurs when lubricant is very effective, or with indirect extrusion A second pattern is obtained when there is litter or no friction at the container wall, but some friction at the die surface, Dead-metal zone formed In the third pattern, the friction along all interface is high, the dead zone increase, billet surface material may flow into the high shear zone In the fourth pattern, due to high friction or high temperature difference between the surface and centre of the billet, the h