Machine Crochet for Textiles and Components
When they hear the word ‘crochet’, many people think of a leisure hobby that has been attracting varying numbers of enthusiasts for decades. Yet this technique can certainly be used to produce impressive products, such as components made from fibre composites. In an interview with K-Mag, Jan Lukas Storck from Bielefeld University of Applied Sciences ( ) explains how the crochet machine they have developed works and how it contributes to automation.
CroMat: How two needles per stitch enable automated crocheting
Dr Storck, how exactly does the CroMat technology work, and which technological aspects make it possible to implement this textile technique, 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 required movements and the difficulty of inserting the crochet hook correctly. Humans can intuitively adjust the precise movement of the crochet hook based on visual and tactile perception to ensure they can insert the hook securely – even when the fabric is deforming. A direct mechanical adaptation would require complex and expensive image processing.
To overcome this hurdle and develop the simplest possible machine, we have adapted the conditions for crocheting so that the stitches into which the hook is to be inserted are located at predictable positions. Simply hanging a stitch on a needle, as in machine knitting, is not sufficient here, because the fabric warps during production and so the ideal point for inserting the crochet hook is not always in the same position.
The trick with the CroMat is to loop a stitch onto two needles. This ensures that the correct position for reproducible insertion of the crochet hook is always exactly between the needles of a pair. This eliminates the need for cumbersome image processing and allows for a relatively simple and cost-effective design of the crochet machine.
Nevertheless, due to the complexity of the motion sequences, we require ten motorised axes, which are controlled by software according to the desired stitch type. However, this can be implemented using standard technology, such as that used in CNC milling machines or 3D printers.
CroMat: Yarn requirements and potential for 3D textiles
What types of textile fibres can be processed using the CroMat?
Storck: In the current version of the CroMat prototype, problems arise when yarn-to-yarn friction is too high, which somewhat limits the range of suitable yarns. As a crocheted stitch consists of several loops (for example, three in the case of half double crochet), there are inevitably many points of contact between the yarn and the hooks, as well as between the yarn strands themselves. To prevent the build-up of high forces that restrict crocheting, dynamic adjustment of the thread tension during stitch formation is necessary. As this has not yet been fully implemented in the current version, we are currently obliged to use yarns with relatively low coefficients of friction. Sewing threads are very well suited for this purpose. It makes no difference whether they are natural fibres ( ) or synthetic fibres ().
One limitation that cannot be overcome even with dynamically adjustable thread tension is the yarn’s bending stiffness. Due to the tight bending radii of the yarn during crocheting, stiff materials such as metal or glass fibres are less suitable.
Generally speaking, the yarn is subject to fewer restrictions when it comes to simple slip stitches, which – unlike manual crocheting – can be used to produce entire textiles by machine. This is because there are fewer interlacing loops and the bending radii are larger than in the more complex types of stitches currently producible (single crochet and half double crochet).
The CroMat is also intended for use with three-dimensional textiles; you mention the production of fibre composites with contours close to the end shape. Where and how could the CroMat be used in this context?
Storck: The great advantage of manual crocheting lies in the ability to insert the hook at any point on the textile that has already been produced. This makes it possible to crochet complex 3D structures. The CroMat is somewhat more limited in this respect, as, generally speaking, new stitches can only be formed reproducibly on existing stitches or at points suspended on needles. Consequently, the desired point must first be manually suspended on a pair of needles before the crochet hook can be inserted there. By manually repositioning the fabric within the machine during production, 3D structures such as double-T beams – as well as more complex shapes – can be crocheted automatically.
Thanks to ‘ ’ machine production, crocheted textiles can now be used as technical textiles for the first time. Given the capabilities of machine crocheting with regard to complex shapes, fibre-reinforced composites with close-to-contour geometries represent a promising application. In these, the textile used as reinforcement is manufactured in the (complex) shape of the future component.
The exact potential of this emerging technology cannot yet be definitively assessed. Significantly more research is required for this. What we can already say is that aramid can be processed using a crochet machine and that, in general, the properties of crocheted textiles – and simple composites made from them – are comparable to those of embroidered textiles.
In this context, the CroMat can be put to practical use, on the one hand to serve as a basis for further developments in crochet machines. On the other hand, it can be used to produce samples to further investigate the properties of machine-crocheted textiles.
CroMat: Potential for technical textiles and local production
To what extent does the processing of synthetic fibres in the CroMat differ from that of other materials such as wool or cotton?
Storck: I believe that the potential of the CroMat crochet machine lies particularly in technical applications and, consequently, more in the processing of synthetic fibres. When it comes to 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 stitches across an entire row simultaneously, as is the case with machine knitting.
Nevertheless, automation of the production of commercial crochet products made from natural fibres is also a conceivable area of application, because machine production will be similarly fast to manual production and will, moreover, bring further advantages. However, I find the novel processing possibilities for transforming technical yarns into technical textiles – and thus into new products – particularly interesting.
Are there any environmental or economic benefits associated with this technology?
Storck: Like any innovation, the development of the CroMat also offers economic advantages. For the first time, the machine enables the technical application of crocheting and the reproducible production of crocheted textiles. The corresponding technological advantage can be expanded and exploited economically in a wide variety of ways. The next step towards fully realising these benefits is the further development of the prototype into a machine suitable for industrial use.
I see environmental benefits in the crochet machine’s potential to bypass the long supply chains involved in the manufacture of commercial crochet products by enabling local production. This also has the advantage of meaning that such products are no longer reliant on manual production under poor working conditions in developing countries. It is to be hoped that, in the long term, automation will also improve working and living conditions in such countries.
