Getting silicone into perfect shape with the aid of intricate mould inserts

Getting silicone into perfect shape

AMA, Ateliers de Moules Andrésiens, in Grossoeuvre, France specialises in silicone mouldings. On the basis of its expertise acquired over many years, the family business designs and produces complex injection moulds. In the production of small mould inserts, the specialists trust in the MV1200R wire-cut EDM system with its dependable repeat accuracy.

A multitude of components made of silicone are needed in the electronics, vehicle engineering, medical technology, measuring instrumentation, chemical & pharmaceutical, and aerospace industries and even sports equipment manufacture. For this material has special properties that clearly set it apart from other plastics. Its hardness and elasticity can be varied over a large range. In addition, silicone withstands temperatures up to 360 °C while being resistant to ageing. Even on exposure to extreme stressing, e.g. solar radiation, liquids and chemicals, this plastic retains its beneficial properties in the long term.

Elastic and resistant to ageing

Numerous branches of industry therefore use silicone for components that have to stay gas- and liquid-tight under testing environmental conditions. Owing to its elastic behaviour, this is even possible on seal surfaces with imprecisely defined geometries. Parts of protective and diving goggles and of breathing masks for use in aircraft, in the chemical industry, mining and power stations are therefore made of silicone. Electrical and electronic plug connectors that have to work reliably in the long term in tough conditions, e.g. outdoors or in road, rail and construction vehicles, are also fitted with sealing elements made of silicone. The same applies to components in medical technology, among other things in devices for cardiovascular surgery and in ear, nose and throat (ENT) medicine. In addition, silicone feels pleasant to the touch. Sports equipment manufacturers in particular therefore produce grips made of this material. Because of its elastic and good damping properties, silicone components are also a material of choice in occupational safety, among other things in hard hats.

MV1200R operating with high repeat accuracy.

Specially designed injection moulds

Silicone components can also be produced with integrated metal elements, Alexandre Vigneux, owner and managing director of the mouldmaking company in Grossoeuvre, tells us. In this connection he shows us an oil dipstick for an internal combustion engine. Also possible is multi-component injection moulding that combines an elastic silicone with a rigid, dimensionally stable plastic.

For this, AMA designs the best-possible component geometry as well as the injection moulds required for their production. The company produces and assembles them and tests them on injection moulding machines specially equipped for them. Injection moulding is only possible, Vigneux adds, with specially balanced parameters. The silicone injected in two separate components into the mould cavity expands, while conventional thermoplastics, on the other hand, shrink in volume as they cool in the cavity.

Thanks to the highly reliable wire threader, I can let the MV1200R run unmanned for up to 50 hours.

Bérengère Vigneux. Daughter of Managing Director Alexandre Vigneux.

These factors have to be taken into account when designing and ­building the injection moulds. Like with conventional thermoplastics, it is still possible to create highly intricate features and the tiniest geometries on the moulded components – as required, for example, in medical technology and specifically for heart surgery. For pumps, cannulae and valves, highly filigree, flexible and elastic sealing elements can be produced using silicone that function extremely dependably for a long time. “Being able to produce such components has given us a unique reputation beyond the immediate region – something made possible by our knowledge accumulated over many years and our wide-ranging experience of the processing of silicone,” Vigneux explains.

Intricate mould inserts with repeat accuracy to the nearest 0.01 mm

To produce tiny structures in injection-moulded silicone, AMA naturally needs suitable mould inserts and slides for the injection moulds. And this is true, for instance, of an injection mould for producing helmet shells and the matching helmet inserts (webbing with a width adjustable strap), which are provided with narrow, dovetail grooves. With the aid of these grooves, the two components can be easily and firmly joined together. AMA produces the mould inserts required for this mainly on the MV1200R wire EDM system from Mitsubishi Electric – a machine programmed and operated largely by the owner’s daughter Bérengère Vigneux, who is very interested, she says, in innovative technology. This is why she decided early on to continue her father’s business.

Before investing in the ­current MV1200R, the company in ­Grossoeuvre had already had experience of an FX10 and of wire-cutting machines of rival manufacturers. Bérengère Vigneux sees the special advantage of wire-cutting technology in its unmanned operation: “The wire EDM is capable of cutting several mould inserts from a single plate over the weekend. High-speed cutting would only be possible in the presence of a highly skilled operator.” She also mentions another feature with which the MV1200R excels: “This wire EDM system is very easy to program, set up and operate.” After only a few days of training, she learned the main functions and programming and operating procedures – child’s play, as she puts it. She now communicates her knowledge to other employees on the job. Since programming is easy, it is also quick – another benefit in her view. And this frees up staff for other tasks. At AMA, the MV1200R is usually set up and used during two day shifts with an operator for relatively short cutting jobs. In the afternoons and before weekends, Bérengère also sets up the wire-cutting machine for longer-running machining operations. “Thanks to the highly reliable wire threader, I can let the MV1200R run unmanned for up to 50 hours. As it can be relied on to cut the programmed components, it proves – despite the longer machining time – to be much more economic than high-speed cutting on a much more cost-intensive milling machine which also always requires a skilled worker to monitor the process,” the owner’s daughter continues.

Highly reliable wire threading.

Less maintenance and expert, available after-sales service
In making their investment, Alexandre Vigneux and his daughter Bérengère mainly concentrated on purchasing a technically mature, reliable machine. They wanted one that would meet current needs in terms of simple programming and operation. In addition, it should ensure repeat accuracy of less than 0.01 mm. “We often produce mould inserts with recurrent geometries and contours for multi-cavity moulds. It is therefore essential for us that the wire EDM cuts all contours absolutely identically. The components fitted later in the multi-cavity moulds naturally have to be totally indistinguishable,” says Alexandre. Over and above these technical requirements, AMA also attached importance to an after-sales service that is constantly available and at short notice. A high-tech machine, Bérengère adds, can only sustain high productivity and profitability if it is constantly available. However, this is only possible with a rapidly available service.

On the strength of their excellent experience of the FX10 wire EDM system from the Japanese manufacturer, supplied by its French licensed distributor Delta Machines, they again chose a wire-cutting machine from Mitsubishi Electric as their replacement investment in 2016. “The MV1200R has a larger workspace than the FX10. With the same consumption of wire, filters and dielectric, we have now improved productivity and economy, boosting our capacity without increasing costs,” she says describing the advantages of the MV1200R. The MV1200R operates much more dependably, she continues, and requires less maintenance than the machines from the competition.

 

Interview