Chopping and changing offers design flexibility

The ability to automatically place exactly the right volume and length of fibre at specific positions within composite components offers massive potential to designers. They will be able to tailor the physical properties of a component throughout its body, strengthening it in exactly the right places. The first installation in the UK is currently under way in a major automotive tier one supplier. As well as adding fibres in the right place, the process can also remove or minimise them where they are not needed, saving on the overall weight of the component – a feature which is of particular importance to the automotive and aerospace industries which use this moulding process very heavily. The process, known as LFI-PUR (long-fibre injection of polyurethane), is the brainchild of Krauss Maffei, a leading light in the world of plastic processing hardware. The company sees its process eliminating many of the quality and cost drawbacks associated with the use of more expensive glass fibre mats and preforms used in the S-RIM (structural reaction injection moulding) process. The unit uses a microprocessor to deliver a controlled mix of chopped glass fibre and polyurethane into an open mould. The quantity (up to 50% content) and the length (12.5 to 100mm) of the glass fibres, and the volume of the polyurethane in which they are mixed, are varied as they are poured by a robot into the mould. By varying the two components relative to each other, the component’s physical attributes can be determined. This will allow the designer to tailor specific areas instead of relying on the physical and structural properties of a fixed fibre/polymer mixture throughout the design. Applications have already seen the light of day in the automotive industry with internal body panels and structures reaping the benefits on offer. And with the first major UK installation just taking place, the capabilities on offer should certainly not be ignored by the engineering community outside that of automotive. There are countless industries where designers have had to rely on bulk physical properties of composite structures under the basic guise that they will be strong and light. Now that they can dictate where they are strong and light, the options on offer have grown considerably. Krauss Maffei says that its new process will offer other benefits as well as those imparted into the final product. These include many to do with the actual manufacturing process, such as: fewer manufacturing steps as there is no need to handle, position and load glass preforms; no loss of glass mat as trimming becomes a superfluous activity; higher levels of repeatability; and the process is more user friendly as it has none of the health and safety issues associated with handling glass mats. Regarding the installation itself, the company offers a number of options, notably that installations are flexible and can be based on either linear or rotary geometry. There are also a number of mould carrier solutions including the company’s own Star Trac overhead conveyor system. A typical installation comprises a number of key components. These include the main robot-mounted processing unit which injects the glass fibre and PUR reaction blend into the open mould. An optional oscillating unit uses air to spread the pouring jet, providing fast filling and better overlapping of individual pouring tracks for larger moulds. The cutting unit, as the name suggests, is responsible for cutting the roving’s glass fibres into precise lengths and quantities. These are then transported via the roving guideway to mix with the PUR supplied by a metering machine, the metering itself being controlled by a process control unit which uses open- and closed-loop monitoring to control all quality-determining parameters. Finally, a mixing head cleaner ensures that all wetted parts are cleaned after each cycle. There is also a comprehensive range of mould carriers to provide optimum mould clamping and positioning depending on the demands and envelope of the product. Present applications include dashboard carriers on BMW 5 and 7 series and the Renault Espace as well as side door panels for the Mercedes CLK which integrates the LFI-PUR with a fabric trim. With regard to future applications, the company is driven by many of the whims of the automotive industry which is continuing to segment the market and create more niche vehicles and associated production runs. Looking further ahead Krauss Maffei is looking to ‘future proof’ the process by developing a natural fibre (NFI) process using materials such as sisal. Although this material is currently an expensive alternative to glass, it does have the benefit in that it can be burnt off which will aid the growing recycling demands being placed by governments on the automotive and associated industries. Carbon also gets the chop It appears that across the pond similar steps are being taken. In this case US researchers are developing a process which aims to reduce the unit costs of carbon-carbon composites. At around $50 (£33) per pound these composites are too costly to have many commercial uses. The majority of their appearances are in disc brakes for motorsport and aviation. So, the aim of the research is to get the price down to $10 (£6.70) per pound making them a far more attractive proposition to the mainstream car companies. The process uses robotics to rapidly change the size and orientation of carbon fibres from one section of a brake disc to another. Using it, the engineers have manufactured a brake material that contains short fibres on the surface and longer fibres below. “The short fibres possess great potential for good friction performance, and the longer fibres have better strength characteristics,” says Thomas Siegmund, an associate professor of mechanical engineering at Purdue University. The research, which is not yet complete, also involves Honeywell Aircraft Landing Systems and the National Composite Centre and was the recipient of a $2million fund created to nurture research leading to highly skilled jobs.