Cost-effective low-pressure moulding using Macromelt

Although headquartered in Perth, Australia, Mobilarm's European operation is located in Beverley, UK, where the main focus of manufacturing is the company's Sea Marshall range of man overboard systems, or to give them their industry name: Maritime Survivor Locating Devices (MSLD). These innovative units transmit a continuous homing signal on a frequency of 121.5MHz, which is detected and tracked on a Mobilarm base unit aboard the parent vessel. The signal can also be tracked by international search and rescue operations. First launched in 1979, Sea Marshall is now the leading MSLD system in the North Sea, where over 5000 units are in daily use.

Until recently the company was subcontracting its requirement to encapsulate part of the aerial unit on the Sea Marshall system. Here, a small cable connects to a PCB that features side-firing LEDs. Part of the configuration is a delicate antenna spring that requires encapsulation.

Ian Pinder, Production Manager at Mobilarm Europe, explains: "When we first started product encapsulation, our supplier was producing overmoulds using conventional injection moulding techniques. However, there was insufficient grip at the cable end so we extended downwards, effectively doubling the size of the overmould. This solved the gripping problem, but because the larger overmould required greater pressure and temperature to achieve the required flow, components were literally being blown off the PCB. We were getting 40 per cent fall-out rates, which was completely unacceptable."

In the hunt for an alternative process, a series of web searches and telephone calls led to the door of Engineering Solution, which through its partnership with Henkel, provides manufacturers across a host of industry sectors with a low-pressure moulding service complete with machine, aluminium mould tools and Henkel's Macromelt. Macromelt moulding is in a category between casting and injection moulding. It is non-aggressive, highly cost effective and fast. Because low pressures are involved, typically 2-20bar, lower cost mould tools can be employed. And of course the technology is suitable for encapsulating and enclosing delicate components and assemblies, providing protection from vibration fatigue and atmosphere/liquids that could promote corrosion or conductive paths.

Greatly reduced failure rate

Installed 18 months ago at Mobilarm's Beverley facility, the system is delivering a host of benefits, as Mr Pinder confirms: "Our failure rate has dropped to 1 per cent," he says, "and to be honest, this typically results from a PCB failure or bad joint in manufacturing - we can safely say that Macromelt is 100 per cent successful."

Approximately 10g of Macromelt is used for each Mobilarm overmould, which encapsulates the electroplated steel antenna spring and PVC cable. The overmoulds, which are produced using an HB-500 ESL hand-held machine and single-stage aluminium mould set, measure around 50mm in length and 20mm in diameter. The operating pressure is 5bar, while temperature is 220-230degC. The cycle time is around 30s in jet with a further 30s required for cooling - vastly superior to traditional potting methods. The Beverley site currently produces around 1000 overmoulds every month.

Mr Pinder states: "The system has more than paid for itself already. Not only have we saved the cost of subcontracting, but the 40 per cent fall-out rate has been eliminated. Furthermore, while we could recycle the cable and antenna spring from rejected systems, we had to write-off the cost of the PCB and the overmould."

Looking forward, Mobilarm is currently developing a new beacon variant that features a modification to the antenna - there is now a GPS module on the side. Engineering Solution has provided an aluminium mould set and prototype units are already being produced.

Mr Pinder says: "The Macromelt system is so quick and cost effective that it not only aids a far easier prototype phase - project costs are reduced dramatically - it also supports tremendous flexibility in manufacture. We no longer require a batch of 500 to justify the cost of injection moulding. If we only need 10, for example, we can make them quickly and inexpensively."

To find out more about low-pressure moulding with Macromelt, go to www.henkel.co.uk.