A close-up of an injection moulding machine.

Imagine if you made a medical instrument which incorporates a lens in a plastic housing. It doesn’t sound too difficult until you consider that the lens measures only 2mm as it is part of a minute endoscopy camera used for internal diagnosis.

Normally the two micro-components (i.e. the lens and housing) would be made in two separate injection moulding processes and assembling them is a complicated and technically difficult procedure.

But the Engineering Faculty at the University of Malta is investigating how multi-material micro-injection moulding can be exploited to fabricate such a micro product, whereby the lens is bonded with the housing, eliminating post-assembly processes.

With such technology moulding is carried out in two phases: first a horizontal nozzle injects the plastic into the mould, which is then rotated and a second vertical nozzle injects the second plastic while the first is still hot. As they cool down, a very strong bond is formed.

There is no adhesive required and no assembly

“It means that there is no adhesive required, and no assembly. But, from a technical point of view, it also means less distortion, and much more accurate alignment. It fitslike a hand in a glove!,” said one of the research team members, Arif Rochman.

Injection moulding is used extensively by local firms like Playmobil, Baxter, Methode, Techniplast and Abertax, just to mention but a few – but clearly, the impact of this development would be at an international level.

Researcher Luke Said explained that the design of the mould commenced in October, and the mould will soon be fabricated. A paper on the research will be presented at a conference in the US in August.

The process is clearly complex. All the factors have to be right; for example, the temperature at the interface between the lens and the housing.

“And we had to get the temperature right – plastic is injected at 270°C – across the full component. The plastic has to remain viscous until it reaches all the corners of the mould, no matter how complex the shape is. For example, the endoscopy lens measures 2mm with a lens curvature of only 0.5mm but its housing measures 11mm,” Mr Said explained. This meant researching different materials for the mould until they settled on a core of beryllium copper, which has three to nine times the heat conductivity of tool steel.

The team, which includes Philip Farrugia and Pierre Vella, also had to purchase the injection moulding machine, using a grant through the Malta Council for Science and Technology through the National Research and Innovation Programme 2012. This research forms part of the X-MMIM project (R&I-2012-002) financed by the Malta Council of Science and Technology through the national Research and Innovation programme 2102. This project also roped in industrial partners, namely, Techniplast Ltd, Tek-Moulds Precision Engineering Ltd and Playmobil Malta Ltd.

“Microassembly is getting smaller and smaller so there is a very strong economic rationale for this equipment,” Dr Rochman explained.

Another advantage is that the two-material micro injection moulding machine will not cost much more than two of current single nozzle version, and companies which already have micro injection moulding machinery would still be able to adapt it to the dual nozzle.

“We are very excited about this as it shows that research can produce commercially-viable products,” Dr Ing. Farrugia said.

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