What Is The Aluminium Extrusion Process?

Aluminium is one of the most popular metals in the world today

. As a matter of fact, aluminium is the most abundant metal found on the earth's crust. It is used for a variety of applications in the manufacturing industry. Aluminium is naturally found as bauxite and the metal can also be extracted from feldspar.

The most popular extraction methods are Bayer's method, Wohler's method and the Hall Heroult process. Once the metal is extracted as a molten liquid, it can be solidified into any desired shape. However, this process is not easy and other fabrication methods have to be used.

The non-technical term for the process that gives a proper shape to the aluminium metal is called shaping. If the extracted aluminium is in the form of a solid, mechanical working processes are made use of to give a proper shape to the metal. These processes include rolling, drawing, forging, spinning, piercing and extrusion. There are two types of mechanical working processes hot working and cold working. In hot working, the billet or the work piece is heated to a temperature above the recrystallisation temperature of aluminium (175 F). At this temperature, aluminium is deformed and new grains are formed. Using the processes mentioned before, aluminium is made into a well defined shape.

The extrusion and drawing process are quite similar. In drawing, aluminium is pulled through a die or a series of dies to reduce the diameter. Cups and conical tapered shapes can be fabricated using a special process called deep drawing. Cylinders and seamless tubes can also be fabricated using this process. In extrusion, the heated billet is forced through an orifice or a small hole that is shaped to provide the form desired. This is done under high pressure.

One can easily understand extrusion by imagining the squeezing of a tooth paste from a collapsible tube, although with a higher force. It is always easier to extrude the metal when it is soft. This is why hot extrusion is preferred to cold extrusion. Other metals like copper, nickel, magnesium and alloys like steel are also extruded using hot extrusion.

The process of hot extrusion is carried out in a special horizontal hydraulic press. The capacity may vary from 200 to 6000 tonnes. Operating temperatures may be as high as 450 C for aluminium extrusions. There are three types of hot extrusion direct, indirect and tube extrusion.

The direct or forward extrusion process employs a ram and cylinder arrangement to force the metal out of the die. In indirect extrusion, the extruded part is forced through the hollow ram. In tube extrusion, a mandrel is used to provide a shape to the inside of the tube. Impact extrusion is a type of cold extrusion that involves striking metal slugs and shaping them by impact.

Aluminium extrusions are carried out in many metal fabrication industries. Some enterprises specialise only in aluminium extrusion. Aircraft parts, rods, tubes, cartridges, cables, flooring strips and the like are manufactured using extrusion process.

by: Lawrence White

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