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Wolfsburg - Karl Mayer has supplied a new Open Hybrid LabFactory in Wolfsburg, Germany, with the latest multiaxial warp knitting machine with the aim of further developing the technology to enable fibre-reinforced constructions to suit the direction of force to be mass-produced.

The KonText project is scheduled to run from 1 January 2015 to 31 December 2018 and is being carried out in cooperation with CETEX – Institut für Textil- und Verarbeitungsmaschinen gGmbH (the not-for-profit Institute of Textile and Processing Machines) and other project partners.

The idea behind the project is to separate the load-bearing carbon fibres in a multiaxial textile made from glass fibres with the multiaxial warp knitting machine, and only bring them together at exposed sections, just as happens in Nature with the knotholes in trees.

This principle of using the right material in the right place is said to reduce the weight considerably – for a car bonnet, this might be as much as 25% less than a similar, conventional component. The volume of carbon fibres, and consequently the costs, can then also be reduced.

According to Karl Mayer, producing this type of car bonnet is roughly 30% cheaper than the method using conventional CFRPs. In addition to the car bonnet, the production of floor components using the differentiated, fibre-reinforced technology also offers other advantages, since the flat components can be shaped easily by compression moulding and, as non-visible components, they do not need to have a Class A surface.

The most important modification to the installed multiaxial warp knitting machine concerned the knitting elements. In addition to the two ground guide bars, a module had to be integrated for inserting the carbon tapes, whose shog paths would enable the construction to be worked to suit the specific characteristics of the relevant force insertion patterns. It also had to be possible to work interlaced patterns, such as “knotholes”.

To achieve this objective, engineers from Karl Mayer Technische Textilien took a leaf out of the book of their colleagues working in the lace machine sector. They got to grips with the string bar technology of lace raschel machines, and adapted the electronic patterning principle so that it could be used on a multiaxial warp knitting machine.

Similar to the system of guide bars equipped with string bars, the machine was fitted with a warp yarn shogging module with two shogging units. The shogging units are arranged opposite to each other to enable them to also work crossed-over lappings, and guide the carbon-fibre material via tape guides to the knitting point.

Up to 12 of these guide elements may be arranged in a block, and they may be moved together, individually or in specific groups. The individual motor drives used offer plenty of scope for designing the zones with the load-bearing carbon tapes: as far as the density is concerned, this can be done via the distance of the individual yarn guides from each other and, as far as the elongation, or lapping construction, is concerned, this can be done by the pattern-controlled movement of the shogging unit with two independent shog rows. In general, shog paths as large as the maximum working width of the machine are possible.

 The carbon-fibre tapes are taken off from the packages in a controlled manner, and the active control system guarantees a uniform tape tension.

This multiaxial warp knitting machine with the new warp yarn shogging module went into operation in the Open Hybrid LabFactory in the third quarter of this year. The multiaxial textiles are being used for research into the next stages of the production sequences. The resin treatment processes, in particular, have to be adapted to the new geometry of the textiles, in which the yarns are concentrated in selected areas. Further developments are also planned for the multiaxial warp knitting machine. The aim is to integrate a weft yarn shogging module by the third quarter of 2017.


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