Machine crochet for textiles and components

When it comes to crocheting, many people think of a leisure hobby. However, this technique can be used to manufacture impressive products such as components made from fiber composites. In an interview with K-Mag, Jan Lukas Storck from Bielefeld University of Applied Sciences explains how a newly developed crochet machine works and how it contributes to automation.

Dr. Storck, how exactly does the CroMat technology work and what technological aspects make it possible to implement this textile technology, which was previously considered impossible to automate?

Dr. Jan Lukas Storck: Until now, crochet technology was considered impossible to automate due to the complexity of the necessary movement sequences and being able to insert the crochet hook correctly. Humans can intuitively adapt the exact movement of the crochet hook according to visual and tactile perception to be able to insert it safely - even with a deforming textile. Direct machine adaptation would require complex and expensive image processing.

To avoid this hurdle and develop a machine that is as simple as possible, we have adapted the crochet conditions so that the stitches to be pierced are in predictable positions. Simply hanging a stitch on a needle, as in machine knitting, is not sufficient here because the textile warps during production and the ideal point for inserting the crochet hook is therefore not always in the same position.

Nevertheless, due to the complexity of the motion sequences, we need ten motorized axes that are controlled by software according to the desired mesh type. However, this can be implemented using standard technology, such as that used in CNC milling machines or 3D printers.

What types of textile fibers can be processed with the CroMat?

Storck: In the current state of the CroMat prototype, there are problems with too much yarn-on-yarn friction, which somewhat limits the range of suitable yarns. Since a crocheted stitch consists of several loops (e.g. three for half double crochets), there are inevitably many points of contact between the yarn and the needles and itself. To prevent the resulting build-up of high forces that restrict crocheting, dynamic adjustment of the yarn tension during stitch formation is necessary. As this has not yet been finally implemented in the current version, we are forced to use yarns with relatively low coefficients of friction. Sewing threads are very suitable here. It doesn't matter whether they are natural or synthetic fibers.

One limitation that cannot be circumvented even with a dynamically adjustable yarn tension is the bending stiffness of the yarn. Due to the tight bending radii of the yarn when crocheting, stiff materials such as metal or glass fibers are less suitable.

In general, the yarn is subject to fewer restrictions regarding simple chain stitches, from which entire textiles can be made by machine, in contrast to manual crocheting. This is because there is less interlacing, and the bending radii are larger than with the more complex stitch types that can currently be produced (single crochet and half double crochet).

The CroMat is also to be used for three-dimensional textiles, you are talking about the production of near-net-shape fiber composites. Where and how could the CroMat be used here?

Storck: The great advantage of manual crocheting lies in the possibility of being able to stitch at any point on the already produced textile. This makes it possible to crochet complex 3D structures. The CroMat is somewhat more limited in this respect, as new stitches can generally only be formed reproducibly at stitches or points that are attached to needles. This means that the desired point must first be manually suspended on a pair of needles before the crochet hook can be inserted there. With a corresponding manual repositioning of the textile in the machine during production, 3D structures such as double T-beams - as well as more complex shapes - can be crocheted automatically.

Machine production means that crocheted textiles can be used as technical textiles for the first time. Due to the possibilities of machine crocheting of complex shapes, near-net-shape fiber composites represent a promising application. In these, the textile used as reinforcement is already manufactured in the shape of the subsequent component.

The exact potential of this young technology cannot yet be fully assessed. Much more research is needed. What we can already say is that aramid can be processed with the crochet machine and that the properties of crocheted textiles - and simple composites made from them - are generally comparable to embroidered textiles.

In this context, the CroMat can be used specifically to serve as a basis for the further development of crochet machines. On the other hand, it can be used to produce samples for further research into the properties of machine-crocheted textiles.

How does the processing of synthetic fibers in the CroMat differ from other materials such as wool or cotton?

Storck: I believe that the potential of the CroMat crochet machine lies particularly in technical applications and therefore more in the processing of synthetic fibers. Regarding home textiles or clothing, automated crocheting has the disadvantage of lower productivity compared to established textile technologies (such as knitting, warp knitting or weaving). This is because, as with manual crocheting, the machine can only form one stitch at a time. It is not possible to form a whole row of stitches in parallel, as is the case with machine knitting.

Nevertheless, the automation of the production of commercial crochet products made of natural fibers is also a conceivable field of application, because machine production will be just as fast as manual production and will also bring further advantages. However, I am particularly interested in the new possibilities for processing technical yarns into technical textiles and thus new products.

Are there ecological or economic benefits associated with this technology?

Storck: Like every innovation, the development of the CroMat also offers economic benefits. For the first time, the machine enables the technical use of crochet and the reproducible production of crocheted textiles. The corresponding technological advantage can be expanded and used economically in a variety of ways. The next step on the way to exploiting these advantages is to further develop the prototype into a machine that can be used on an industrial scale.

I see ecological advantages in the potential of the crochet machine to bypass the long supply chains in the manufacture of commercial crochet products with domestic production. This also has the advantage of no longer having to rely on manual production under poor working conditions in third world countries for such products. It is to be hoped that automation will also improve working and living conditions in such countries in the long term.