Lecture 12 Different types of extrusion and their characteristics Course Hour: 2 Basic requirements: Acquainting with the principles of direct extrusion, indirect extrusion, hydrostatic extrusion and Impact Extrusion Emphasis: Direct extrusion Difficulties: Principles of extrusion

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

Extrusions Extrusions, and examples of products made by sectioning off extrusions.

Types of Extrusion Indirect – Die pushed into billet – Except at the die, there is no friction at the billet-container interface

Types of Extrusion Even more recent development (1950's) Advantages Hydrostatic Even more recent development (1950's) Advantages – No friction at walls – Can successful extrude brittle materials – Yield stress reduced by hydrostatic pressure – Room temperature operation Disadvantages – Limited industrial applications – Complex tooling – High pressure experience required

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 Lateral – Like direct, but material comes out of the die at right angles to the direction in which the billet is pushed

Types of Extrusion Conform Continuous extrusion forming Friction is just useful to process.

Lecture 13 Process variables and metal flow in Direct Extrusion Course Hour: 2 Basic requirements: Acquainting with the dependent and independent variables in extrusion; grasping the four types of metal flow in extrusion Emphasis: Variables and metal flow types in extrusion Difficulties: The effect factors of the metal flow in 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

Extrusion Independent Variables Die angle Extrusion ratio (ratio of input to output cross sectional areas Circumscribing circle diameter Shape factor – Ratio of perimeter of shape to cross-sectional area – a circular shape has the minimum – A measure of the complexity of the extrusion Temperature of billet Ram speed Lubricant Product design

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 high shear zone extends further back. Pipe or extrusion defect may occur

Lecture 14 Extrusion force and hot extrusion practice Course Hour: 2 Basic requirements: Grasping the calculations of extrusion force; acquainting with hot extrusion practice, advantages, disadvantages, temperature and lubrication Emphasis: Hot extrusion practice Difficulties: Extrusion force calculation

Extrusion Force In ideal deformation, For perfectly plastic material, with a yield stress Y, the energy dissipated in deformation per unit volume is, Work done is, The extrusion pressure at the ram p is,

Extrusion Practice — Hot Extrusion Advantages – Lower stresses – Sometimes the only way to extrude certain metals • e.g. Titanium, refractory alloys, high strength alloys Disadvantages – Higher die wear – Oxide film buildup results in non-uniform flow, inclusions and poor surface finish – Cooling of billet in container results in nonuniform flow – Distorted parts

Extrusion Practice — Hot Extrusion

Hot Extrusion — Lubrication Molten glass supplied as a coating of glass frit Lower melting alloys as a can Also – reduces sticking to container walls – prevents contamination