Extrusion

Extrusion

Extrusion is a process used to create objects of a required cross-sectional profile. A material (may be metal or nonmetal) is pushed through a die of the desired cross-section.
Extrusion may be continuous (theoretically producing indefinitely long material) or semi-continuous (producing many pieces). The extrusion process can be done with the material hot or cold.
Ex.- formation of pipe, rubber belt base extrusion, metal and plastic rod formation.

Type of extrusion process

On the basis of temperature

Hot extrusion- 

In this process, the metal is heated so that it can easily take the shape of the die. 

Properties

• Grains are refined
• The surface may be oxidized due to the high-temperature surface directly contact with the atmosphere
• Special care of product produced
• Highly accident pron process
• Difficult to achieve precise tolerance

Metal billet- The form of metal in which metal is likely to flow when a small force is applied

Cold extrusion- 

In this process, metal is compressed with high compression pressure (with the help of hydraulic and another heavy compressor) so that the metal takes the shape of the die.

Properties

• Grains are not refined
• Chances of residual stress
• Surface quality is better than hot extrusion
• Precise Tolerance can be achieved

On the basis of the direction-

Forward extrusion- 

In this process metal billet are pressed with the help of piston I.e. the only piston is movable and the rest of the system is in the rest
Properties

• A large amount of material losses
• Eddies form at the corner of the cylinder
• 3-5% material removed as waste.

Backward extrusion-

•  In this process piston is in the rest and cylinder is in the motion.
• the billet in the container remains stationary and hence produce no friction.
• extrusion pressure is not affected by length.
• In this process, minimum waste are formed because chances of Eddie formation is minimized
• Due to no friction, it is better than forward extrusion