Moulding material

A new material that could be used in the Fused Deposition Modelling (FDM) process has been developed by researchers at Swinburne University of Technology.

It could provide a boon for plastics manufacturers, particularly those who make parts for medical applications, where only a small number are needed.

In a FDM system, plastic parts are produced when layer after layer of plastic is rapidly deposited. Each layer is 0.05-1.25mm thick and the part takes its form from a computer-generated model that is sent to a 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 form and fit.

However, Prof Syed Masood from the 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.

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.

Masood said: ’For every new plastic product, a steel mould needs to be designed, machined and cut into shape. 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, also from IRIS, developed and tested the iron-nylon composite material that can 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 in the injection-moulding process.

Masood added: ’The injection mould produced from our iron–nylon composite material is as good as any full-steel mould for short production runs.’

Masood acknowledged that limitations remain. He said: ’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.’

Nevertheless, moulds built using the technique have already been tested and plastic parts have been successfully produced. The technology is ready to be taken to market if a suitable commercial partner can be identified.