Issue Two 2012 - Issue #16
Story by Carolyn Boyd
In what could prove a lifeline for Australia’s manufacturing industry, researchers at Swinburne have found a way to slash the time it takes to make components out of aluminium and other metals.
And the solution, it seems, is all thanks to the help of a giant 3D printer for metal.
Installed in Swinburne’s Advanced Technologies Centre, at its Hawthorn campus, the machine promises to significantly reduce waste and cut cooling times in high-pressure die-casting by one-third.
Observing the way that parts are made for motor vehicles, Swinburne PhD graduate Dr Khalid Imran and his supervisor Professor Syed Masood noted that once aluminium components are cast into a steel die or mould, the molten aluminium takes a lengthy time to cool down and solidify because steel is a poor thermal conductor and tends to hold the heat in the mould. The component can’t be removed from the mould until it has cooled and hardened.
In die-casting, molten aluminium is injected into steel moulds to form complex shapes, and the moulds have a special coating to prevent the aluminium from sticking to them, meaning that once it is cool, the aluminium is then extracted from the mould.
Although die-casters pump coolants through channels in the steel moulds to hasten the process, it still takes a considerable time for the moulds to cool, explains Dr Imran. And in the competitive manufacturing industry, time equals money, particularly in Australia where wages and energy costs are high compared with countries such as China and India.
Retaining a technical edge
The Australian manufacturing industry has been under increased pressure in the wake of the global financial crisis as it struggles to compete with countries that have much cheaper labour. While it is not possible to slash labour costs in Australia, improving efficiency in an industry that has long
relied on having a technical edge could make all the difference.
“If the production rate is high then you can produce millions of parts in a very short time and that will reduce the cost of manufacturing,” explains Dr Imran, whose research promises to cut cooling times in
high-pressure die-casting by one-third.
While tooling steel tends to hold heat, another metal – copper – is quick to release it. “If the mould is copper, it will suck the heat out very quickly,” says Dr Imran. “That means the molten metal that has been injected [into the mould] will solidify very fast.”
However, the problem with copper is that being a soft metal, it has a lower melting point than tool steel and when used as a mould, it begins to interact with the molten metal injected inside it.
Nevertheless, Dr Imran hypothesised that a high-strength copper alloy could be used as a mould if it was lined with a thin layer of protective tooling steel to stop it from melting, in a process known as bimetallic tooling.
The layer effect
During his Swinburne PhD studies, Dr Imran spent six months collaborating with Jyoti Mazumder, a joint professor in mechanical engineering and materials science and engineering at the University of Michigan in the US. Professor Mazumder is an internationally recognised authority on laser-aided manufacturing including direct metal deposition, laser cladding and advanced metallurgy.
He says Dr Imran’s project was challenging as melding copper and tooling steel is like trying to bond oil and water. “Metallurgically they are not very miscible,” Professor Mazumder says.
Working closely with the POM Group, designers and builders of Direct Metal Deposition additive manufacturing systems, of which Professor Mazumder is the chief executive, and the University of Michigan, Dr Imran found a solution – sandwiching a third metal that mixes with both copper and steel in between. His research built on earlier work by the POM Group. The make-up of the bonding metal is a closely guarded secret.
Dr Imran used the additive manufacturing process of Direct Metal Deposition, or DMD, to layer the three metals and produce a predominantly copper mould.
The revolutionary concept makes components, or in this case a mould, directly from powder, ribbon or wire deposited in a layered manner, without the need for casting, forging, rolling, cutting, machining, welding or drilling. The DMD machine replicates computer-aided designs (CAD), taking them straight from design to product. At Swinburne, DMD is produced using a machine manufactured by the POM Group that is fed by up to four different metal powders and builds 3D items from scratch.
The process particularly lends itself to making moulds for die-casting, as the die cavities tend to be very complex and DMD provides a true metallurgical bond, says Syed Masood, who is Professor of Advanced Manufacturing in Swinburne’s Industrial Research Institute and a leading researcher in additive manufacturing technology.
“The bimetallic tooling is of better quality [than traditional processes],” Professor Masood says. “It has less heat-affected zones, which means less thermal cracking or thermal fatigue, and minimum distortion. We have measured the quality of the parts produced and we have proven that the quality of the parts produced by bimetallic tooling is as good as the original tooling methods.”
As well as being able to lay down multiple metals in complex patterns, the process has a major advantage over traditional tool making – little to no waste.
“You are just adding material layer by layer to get the shape, whereas the traditional manufacturing technique is to take your hunk of material and remove [parts of it] to get to the shape,” says Professor Mazumder. “In many components, 80 per cent of the material is just removed and wasted, whereas here, instead of removing 80 per cent you are just adding 20 per cent. That’s the big deal. It’s almost a paradigm shift.”
Professor Masood says the research group’s expertise and the technology are providing unique opportunities for companies to address needs in tooling development, tool and metal component repair, surface modification and coating, new alloy development and direct metal prototypes.