25 Jul Working with aluminium
The adaptability of aluminium offers great potential for manufacturers to cut costs and reduce waste, especially through cold forming, says Mark Jennings, Technical Director at Dawson Shanahan.
Aluminium is used worldwide within a diverse range of applications, from the manufacture of soft drinks cans to supersonic aircraft. It is widely used because it is abundant, malleable, light, strong, naturally resistant to corrosion – in fact, the list of qualities offered by aluminium is too long to list here, but certainly one of the greatest is its flexibility in terms of the many ways in which it can be processed. Most commonly these have been rolling, machining and forming but it is the latter of these processes that is increasingly offering engineers some powerful and economical options.
Rolled aluminium – an ingot of aluminium passed through a hot rolling mill and cooled repeatedly until reduced to the desired thickness – satisfies the needs of the canning industry but can also be heat-treated to withstand high temperatures for use in supersonic aircraft.
Machining shapes a piece of manufactured aluminium by removing chips of the metal with a cutting tool, effectively sculpting the part to specific dimensions. This process has enabled the aeronautical and automotive industries to produce precision components but can also produce a lot of waste material.
Forming, however, is an increasingly popular method of producing parts that offers precision equal to, or greater than, alternative methods, and with considerably less waste. Forming can also offer greater strength than machining because, while bar stock grain is interrupted during machining, cold-headed components have a grain that follows the configuration of the part.
There are two forming processes: hot forming and cold forming. Hot forming allows more complex shapes to be forged under low pressures but the relatively high level of energy required to carry out the process has led many manufacturers to take advantage of cold forming, which can be plastically formed at room temperature (though pre-forming steps, annealing and high forming pressures may be required).
Cold forming can also result in a high quality, ‘burnished’ surface finish that requires little or no secondary finishing. This is because the surface finish mirrors the smooth condition and dimensions of the dies, offering powerful possibilities to end users who, for example, specify the production of containers with zero gas leakage. When manufacturing such containers it is critical that the surface remains free from scratches, which can create gas leak paths, and cold forming can yield excellent results here.
Cold forming also enables a much faster production process than die-casting or machining, and can produce some components at speeds of up to 300 per minute. Even when an element of machining is required, manufacturers of lower cost components can make significant savings. Frequently, however, the need to add machining processes to cold formed parts is often unnecessary, as many secondary processes have been eliminated by the expanded capabilities of cold-heading equipment and tooling.
The enhanced strength, surface finish and production speed enabled by cold forming aluminium is accompanied by another major benefit: reduced cost. Because cold forming is essentially the extrusion of a part from a blank, rather than the process of chipping away that characterises the machining process, there is a correspondingly small amount of waste; cold forming results in up to 80% less scrap than machine processes.
In comparison with alternatives, cold forming is a simple process that can produce complex parts at low ambient temperatures, without removing any material, and it can do so as much as 15 times faster than more conventional options. As if that weren’t enough, the significant reduction in energy consumption achieved by switching to cold forming helps to reduce not only plant costs but also carbon footprint. So, while rolling and machining remain well established processes with their own individual strengths, forming is now clearly an equally strong option that offers a range of benefits and one that engineers need to consider in order to ensure that they are producing the best quality components at the highest rate of efficiency.
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