3D Knitted Fabrics: Additive Manufacturing

Thick or 3D knitted fabrics are the first objects produced by additive manufacturing. In fact, 3D knitted objects date back to the first millennium, long before digital technology and 3D printers! What's more, during the knitting process, whether industrial or manual, the material (the yarn) in the form of loops (the stitch) is brought exactly where it's needed in successive layers (the rows). For several centuries, socks, gloves and the beret, the symbol of the French, were the only garments produced by additive manufacturing - initially by hand, then, from the mid-19th century, by machine-controlled industrial processes. Since the end of the 1980s, with the development of information technology and then digital technology, industrial 3D knitting has expanded with the advent of numerically controlled machines and dedicated CAD software.

In addition to the aforementioned items, such as stockings and tights, and tubular medical or food nets, 3D knitting has been extended to other applications: integral pullovers (one-piece, seamless) for clothing, reinforcements for composite materials, thick shock-absorbing or thermoregulating materials for sports, luggage, seat coverings for the automotive industry, etc.

Production technologies vary, as do the shapes obtained. The shapes can be more or less complex, ranging from what can sometimes be defined as 2.5D, i.e. thick knitted fabrics, to real 3D occupying a volume.

Knitwear is produced in a variety of ways. They are often the result of "picked" stitches, or weft knitting, but can also be the result of warp knitting. They can use the naturally unbalanced shape of the stitch that gives rise to the rolling phenomenon, be made up of two faces separated by partitions, or be the result of a local variation in the number of stitches.

The aim of this article is to present the various techniques and the resulting products, as well as their current or potential applications.