The new technique could boost the
production of medical parts and prosthetics.
Image: iStockphoto

A new technique developed by Swinburne researchers could provide a boon for plastics manufacturing, particularly in medical applications where parts – such as prosthetics – are only needed in small numbers.

By combining plastic filament, heat and a computer-aided design program with a fused deposition rapid prototyping machine, the researchers are making moulds from metal-polymer composites to create complex plastic objects.

About the size and shape of a refrigerator, the machine uses a process called Fused Deposition Modelling (FDM) through which plastic parts are produced when layer after layer of plastic is rapidly deposited. Each layer is 0.05 to 1.25 millimetres thick and the part takes its form from a computer-generated model that is sent to the rapid prototyping machine.

Although the first FDM system was launched in the early 1990s, applications have remained limited because the layer-by-layer approach it uses means that plastic is the only suitable raw material for creating parts. Most of the parts fabricated using FDM are used for design verification or checking the form and fit of a part.

However, Professor Syed Masood from Industrial Research Institute Swinburne (IRIS) saw the potential for fused deposition rapid prototyping machines to be used to create complex metal parts, assuming the machines could handle metal as the raw material.

Because the machines need the raw material to be delivered in filament form, Masood and his colleagues have spent the past few years developing metal composites that can be used in the FDM process.

“Any part of any shape can be created using fused deposition rapid prototyping machines,” Masood said. “But nobody has tried to make parts or tooling with metal-based composites. The applications increase if you can use the same FDM technology with new material and make a stronger part. One of the main applications is in the development of injection moulds.”

Injection moulding is one of the most widely used manufacturing processes for common plastic products. It involves producing a plastic part by injecting molten plastic into a closed steel mould cavity of the desired shape, allowing the plastic to cool and then ejecting the part. For each new plastic product the injection-moulding machine requires a new mould, known as a tool die. Most of these are made of hardened steel, and can be used to make up to two million parts.

“For every new plastic product, a steel mould needs to be designed, machined and cut into shape,” Masood said. “It is time-consuming and very expensive. If the part is complex, creating the mould may cost millions of dollars. So why not use a technology that can develop the mould directly on a rapid prototyping machine? It saves a lot of time and money to create a part and reduces the cost of making the mould.”

Although steel moulds are desirable for high production runs, moulding dies can be made of aluminium or softer material if they are being used to make parts with smaller production runs in the hundreds or thousands.

Dr William Song has spent three years at IRIS developing and testing an iron–nylon composite that could be extruded into filaments and fed into the fused deposition rapid prototyping machine. The material is 40 per cent metal and 60 per cent nylon plastic, so it can withstand the heat from the molten plastic that is used in injection-moulding machines.

“The injection mould produced from our iron–nylon composite material is as good as any full steel mould for short production runs,” Masood said.

The mould has already been tested in an injection-moulding machine and plastic parts have been successfully produced. The technology is ready to be taken to market if a suitable commercial partner can be identified.

Professor Masood acknowledged that limitations remain. “When you do injection moulding into this mould it will eventually give way, so it’s only good for short-run production of, say, 100, 200 or 500 parts.”