TPI May 2013

Aluminium for every application By Mark Jennings, Dawson Shanahan Ltd

Surface finish can also be precisely controlled with cold forming, achieving results that other processes could only achieve at far greater cost. Pre-forming steps may be required because, owing to the lack of heat, formability is low, and annealing and high forming pressures may also be necessary during the process. However, cold forming can still offer a significantly faster process option than die-casting or machining from solid aluminium. Where lower cost components are concerned, the statistics for cold forming are particularly impressive: parts can be produced at rates of up to 300 per minute, compared to more expensive and time-consuming machining processes. Manufacturers can also consider employing a combination of cold forming and machining, again making significant savings. Though it is clear that time and money can be saved by cold forming, this method is far more than simply an economy option. Cold forming is also capable of producing parts that are stronger than machined components.

T he malleability, lightness and abundance of aluminium have ensured its popularity within engineering, while its resistance to corrosion and conductivity have only contributed to that success. The additional fact that aluminium can be economically recycled to retain 100 per cent of its natural qualities makes it a suitable metal to employ as we all strive for sustainability, so it is important to consider the range of processes that can be applied to aluminium in order to bring specific benefits to many different applications. The three most common methods of processing aluminium are machining, forming and, the most widespread of all, rolling. Aluminium is rolled by passing an ingot of the metal through a hot rolling mill. It is then cooled before being subjected to the same process several times until reduced to a thickness of between 4 and 6mm. The aluminium can then be cold rolled to a thickness of as little as 0.05mm. 50 per cent of the world’s aluminium is rolled, largely for the packaging of everyday disposable items such as canned beverages, but rolled aluminium can also be subjected to secondary processes for use in more demanding applications, such as supersonic aircraft, where heat-treated aluminium can withstand extremely high temperatures. Strain-hardening alloys can be used in pressure vessels, cryogenic tanks, rail carriages and so on, while heat-treatable alloys provide material for the construction of missiles and armour plating. Machining, in which a cutting tool removes chips of metal to achieve precise dimensions, is another familiar process used in the industry for shaping manufactured aluminium. The aeronautical and automotive industries have made good use of this fine precision technique; the machining of parts for the aeronautical industry can result in the removal of 95 per cent of the volume present, leaving behind a light but resilient part tooled from the remaining 5 per cent. The third method of machining aluminium is forming, an entirely different way of processing manufactured aluminium not always thoroughly considered by engineers and which, therefore, needs to be explored in a little more depth than rolling or machining. There are two distinct forming processes: hot forming and cold forming. A more complex shape can be forged from parts of greater weight and volume using hot forming, but the high temperatures required make a correspondingly high demand on energy. Cold forming offers a strong, economical alternative if, for instance, the complexity offered by hot forming is unnecessary.

The malleability, lightness and abundance of aluminium have ensured its popularity within engineering

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