MANUFACTURERS demanding greater flexibility from sheet metal forming processes could find their prayers answered by the re-emergence of a forgotten technology.
Incremental sheet metal forming has been re-discovered, with projects emerging to investigate ways to enhance it’s applicability to manufacturing.
Advanced Moulding Technologies (AMT) is one such venture that, with support from technology diffusion company QMI Solutions , is trialling the technology in the hope of fast-tracking adoption by manufacturers.
The technology differs from conventional metal forming processes in its emphasis on the use of tool movement, as opposed to dies, to achieve shapes in sheet metal.
“It’s a very simple concept,” AMT general manager Periklis Christodoulou said.
“Imagine a metal sheet held around the edges by a frame.
“If you use a rounded shaft - a forming tool - and pushed this metal sheet with it, the sheet develops significant stresses and deforms locally at the point where contact is made.
“Moving this point continuously will incrementally accumulate the deformation, and eventually make a shape.”
According to Christodoulou, incremental forming is not new.
“It was patented 40 years ago but technology was not advanced enough,” he said.
“We didn’t have automatic and numerically controlled (NC) machining - so everyone forgot about it,” he said.
The technology was recently re-introduced to the manufacturing world by Japanese innovators, where QMI Solutions discovered it and, in conjunction with the Queensland government, brought it to Australia - culminating in the establishment of AMT.
According to Christodoulou, the imperative for the technology comes from limitations in conventional pressing technologies for manufacturers dealing with more customised shapes in smaller production volumes.
He says conventional methods can be time-consuming and, in the case of processes such as casting, somewhat unreliable. However the key problem remains the cost of dies needed to shape products.
“Often a very large metal die is needed for the component being made,” he said.
“But dies are not desirable because they are very expensive, especially when you are making a few 100 components.”
Christodoulou says a large number of shapes, particularly symmetrical ones, can be made using incremental forming technology without the use of dies at all.
“It is also possible to provide support using partial dies made of timber,” he said.
“It may not be a completely die-less process, but it is still a more cost-effective way of making shapes.”
According to Christodoulou, the technology is best suited to production runs of small numbers of components made of metal sheet.
“It’s already being used to make small components made of fairly thin metal sheets, for example, fuel tanks for motorbikes, exhaust systems from engines, trunk panels, and bonnets,” he said.
However, incremental forming is not a high-speed manufacturing process, making it unsuitable for large-scale production.
“Some parts made using pressing tools in a few seconds could take several hours using incremental forming,” he said.
“So if you want to create many components, thousands per year, it’s not really cost-effective and there are more suitable techniques out there.
“But while the technique is inherently slow, what it introduces is so much flexibility that you can make shapes that normally you couldn’t.”
According to Christodoulou, this makes it ideal for sheet metal prototyping, which not only involves experimental shapes, but also small quantities.
This ability to create highly customised shapes, albeit in a time-consuming way, also makes incremental forming ideal for the creation of moulds for processes such as vacuum forming, thermoforming, low pressure injection moulding and rotational moulding..
“A perfect example of where you make things that are unique, but only a few, is large moulds,” Christodoulou said.
He says mould production could be particularly useful for fibreglass products used in boat production.
Central to the AMT venture is a trial period testing limitations of the technology.
“The first limitation is the draft angle - the angle between the wall and vertical surface - which at the moment appears to be a minimum of 30 degrees,” Christodoulou said.
“Secondly, the process is currently such that the thickness of the metal sheet changes in the process of the formation.
“Thirdly, accuracy remains a limitation. There are deviations from geometry that we are trying to understand.
“Additionally, depending on the thickness of the metal sheet you want to form, the accuracy of the shape changes, with thinner sheets reproducing more accurately.
He says the technology works with up to 4mm thick aluminium, and 3mm thick steel and stainless steel.
Despite its current limitations, Christodoulou believes the technology is promising, and that greater knowledge will help to better understand its capabilities.
“There’s a learning process about the technology’s process parameters including the speed the forming tool moves, the force it exerts on materials, areas that it touches directly, and the formation of material which occurs cumulatively,” he said.
He also highlights the importance of a trial-and-error approach to improving incremental forming technique, which he says is how some currently produced components were made, and how new shapes will continue to be discovered in the future.
While manufacturers re-discover the technology and refine the best ways to use it, the technology itself will also continue to develop.
While developments in CAD and CNC control have made the forming process possible, greater incorporation of computerisation in the future is expected to further develop the technology.
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