Frankfurt am Main, 28 October 2011 – Mid-tier machinery manufacturers, too, are attracted by the exceptional lightness of carbon-fibre-reinforced plastics. But the change-over is far from easy: one manufacturer of textile machinery reports on his change-over to carbon-fibre-reinforced plastic components, and his initial experience with a specialised machine tool.
In the field of composites, Liba Maschinenfabrik GmbH from Naila in Franconia has plenty of experience to draw on. The company manufactures systems for making semi-finished textile products (glass- and carbon-fibre-reinforced fabrics, e.g. for the rotor blades of wind power installations, and concrete reinforcements). “The most important topic at present is the automobile”, explains Managing Director and proprietor Karlheinz Liebrandt. “2012 will see the world’s first use of carbon-fibre-reinforced plastics in large-scale automotive production applications, featuring the new L-Car from BMW.
It’s a premiere that’s a trailblazer: since it is expected to persuade other sectors to try out a material that’s ideally suited for transforming today’s lightweight-construction dream into tomorrow’s engineered reality. For quite a long time now, Liba has already been using carbon-fibre-reinforced plastics for components in its machines that are subjected to high thermal and mechanical stresses. “One of our most important components made of carbon-fibre-reinforced plastics (CFRPs) are what are called the knitting element holders”, says Liebrandt.
Using carbon-fibre-reinforced plastics: problems sorted
These bars possess a length of up to 6.6 metres, with a complex cross-sectional shape, on which as many as 8,000 knitting needles are fitted. To make sure that textile knitting proceeds with the requisite precision, the length of the bars should always remain constant even at fluctuating temperatures – with minimal tolerances. Hitherto, pultruded aluminium-magnesium profiles had been used, whose length fluctuated in response to temperature changes. “Since we’ve been using carbon-fibre-reinforced plastic, which hardly expands at all, we are encountering almost no problems whatever when starting a machine up”, reports a gratified Karlheinz Liebrandt.
But, he warns, the change-over demands a rethink: the design engineer, for instance, had to adopt a quite different approach when developing a component made of carbon-fibre-reinforced plastic. “This material behaves differently from aluminium, which exhibits the same mechanical strength in all directions”, comments Liebrandt. With carbon-fibre-reinforced plastic, by contrast, which is what is called an anisotropic material, I can influence the mechanical strength using the position of the fibres in each direction. For example, we lay fibres at an angle of 45 degrees to the longitudinal direction, so as to achieve a high level of torsional stiffness.”
Although Liebrandt, as a vendor of machines for producing carbon-fibre-reinforced fabrics, is more familiar than others with the intricacies involved in machining carbon-fibre-reinforced plastics, the ten years spent in getting to grips with these materials cost him “blood, sweat, tears and a whole lot of money”. “It was a lengthy, expensive and painful process with plenty of setbacks, because when I started out on the market ten years ago there was no relevant expertise available, and because I couldn’t rely totally on my experience in building planes, for example”, he reminisces.
Lengthwise milling machine also “gets to grips with” 8-metre components
Machining had hitherto been carried out on a conventional machine tool, which otherwise mills aluminium and steel. At the end of August 2011, the company took delivery of its first machine tool for milling carbon-fibre-reinforced plastics, from EiMa Maschinenbau GmbH in Frickenhausen. According to Karlheinz Liebrandt, this lengthwise milling machine was the sole feasible choice, because his researches had revealed that it was the only one able to handle very long and narrow tool-holders made of carbon-fibre-reinforced plastic. The new one is able to mill components with a maximum length of eight metres.
The machining centre of the Alpha C type has been fitted with new tool-holders made by WNT Deutschland GmbH in Kempten and special milling cutters from Karnasch Professional Tools GmbH in Heddesheim. In comparison to a conventional milling machine, the new one operates at a spindle speed more than twice as high (1,800 revolutions per minute) and mills at a feed rate of up to 20 metres a minute. “The output has already risen by 40 per cent”, reports the company’s proprietor. “I’m confident we can get even more out of it once we’ve revamped the entire infrastructure.” In the long term, the new machine is expected to achieve at least double the output, primarily in order to downsize the production costs of the carbon-fibre-reinforced parts. To quote Liebrandt: “I could also imagine us accepting orders for carbon-fibre-reinforced products from outside firms – if we should ever prove unable to utilise the machine’s full capacity with our own components.”
Getting started with young engineers
What’s the pioneer’s advice for first-time users who want to mill carbon-fibre-reinforced plastics instead of steel and aluminium? Liebrandt recommends hiring young mechanical engineers who’ve already learned how to develop and machine carbon-fibre-reinforced components at university. They will then know, as well, that you cannot drill a hole with a thread in a component made of carbon-fibre-reinforced plastic, but that a metal insert has to be used instead. “This engineer should then also assume stringent responsibility for the production operations and for training the staff involved”, is the expert’s advice.
To cite an example from actual operation: the CFRP dust possesses very high electrical conductivity. If this dust settles on electrical contacts, short-circuits may occur. So the company has to seal off the entire area, and especially the electronics, against the ultra-fine carbon dust, particularly as Liba machines the material in dry mode. “You need very good extractor units with correspondingly fine filters”, says Liebrandt. “We used to have to work with cooling lubricants, which caused a lot of problems for us with cleanliness.”
But even for experts in carbon-fibre-reinforced plastics, like Liebrandt and his team, there is still plenty to learn. This is why the company is also taking part in the VDMA-Forum “Composite Technology”. “In this technology, you see, everything moves at very high speeds”, comments Liebrandt. He sees the forum, however, as also an opportunity to establish contacts with potential partner firms for possible alliances, since, he says, no one can “master by himself” this very widely ramified technology. Liebrandt also sees another upcoming information platform in the shape of the METAV 2012, where the VDW (German Machine Tool Builders’ Association) will be joining forces with various partners to host a special show entitled “Composites World Arena”, with an accompanying lecture forum,. “Our production people will most definitely be travelling to Düsseldorf, to bring themselves up to speed on the latest state of the art *when it comes to tool design and machine tool technology.”
Author: Nikolaus Fecht, specialist journalist from Gelsenkirchen
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