Ultra-fine metallic wires are becoming increasingly important in a wide range of high-tech applications. While round wires in the single-digit micrometer range are already available on an industrial scale, established flat-wire dimensions have remained largely in the double-digit micrometer range. A typical example is balance springs for mechanical watch movements, which usually feature thicknesses of approximately 25µm and widths around 100µm. Producing significantly smaller flat-wire cross-sections through cold forming has long been considered scarcely feasible.

 Against this background, the joint achievement of the two partners marks a significant technological leap. For the first time, a metallic flat wire below 2µm in thickness has been rolled reproducibly. The resulting wire measures approximately 2µm in thickness and 39µm in width, with an SEM image confirming an actual thickness of 1.84µm.

 The starting material was an ultra-fine round wire, type “BenderWire 304NX”, with a diameter of approximately 11µm, developed by Stamm Feindrahtwerk under the direction of its Managing Director, Sebastian Ablas. Producing such extremely small wire diameters depends largely on the purpose-developed “BenderWire 304NX” material, which combines exceptional purity with a precisely controlled chemical composition. The deliberate combination of material purity and alloying elements delivers outstanding technological properties, particularly in formability and process stability. At cross-sections of only a few micrometers, even minimal impurities, non-metallic inclusions, or microscopic inhomogeneities inevitably cause local stress concentrations – and ultimately wire fracture. Strict control of material purity and a precisely defined chemical composition are therefore essential for stable, reproducible forming at this scale.

 In addition to material purity, the tailored microstructure is equally critical. Stamm Feindrahtwerk specifically engineered the wire for forming, enabling both drawing and rolling at extremely small cross-sections. Without a homogeneous, fine-grained, low-stress microstructure, plastic deformation at this scale would not be feasible.

 Rolling was performed on Roder Engineering AG’s high-precision, high-rigidity “DUO40” rolling mill. The high stiffness of the mill and precise roll-gap control are critical for avoiding dimensional deviations at the sub-micrometer level. Rolls made of solid carbide ensure optimal conditions during processing in the rolling gap. This configuration ensures smooth, low-vibration operation and outstanding roll surface quality – both essential for reaching extreme deformation rates.

 The resulting flat wire reaches dimensions at the very limit of human visual perception. For comparison, a human hair measures roughly 70µm in diameter – more than 35 times thicker than this flat wire. Fig. 1 illustrates the size relationship between the starting round wire, a human hair, and the rolled flat wire.

 Reducing wire thickness from the previously established double-digit micrometer range to below 2µm opens up a step change in potential applications. New opportunities open up in particular in medical technology – for example, in highly flexible yet extremely reliable surgical instruments. Further applications are anticipated in micromechanics, sensor technology, and microelectronics, where such flat wires can unlock new design freedom.

 The successful rolling trial demonstrates that the limits of cold bulk metal forming can be pushed further into the sub-micrometer regime – provided that material quality, microstructure design, and rolling technology are optimally aligned.

Roder Engineering AG
Erlenauweg 5c
3110 Münsingen/Switzerland
Contact person is Toni Roder
Tel.: +41 33 2214731
t.roder@roder-engineering.ch
www.roder-engineering.ch

Heinrich Stamm GmbH Feindrahtwerk
Grüner Talstrasse 125
58644 Iserlohn/Germany
Tel.: +49 2371 569-0
info@stamm-wire.de
www.stamm-wire.de

Innovation Box
By rolling a flat wire down to a thickness below 2µm, Roder Engineering AG and Stamm Feindrahtwerk significantly extend the previously established limits of cold bulk metal forming. While conventional flat wires remain in the double-digit micrometer range, this work demonstrates a reproducible forming process at the sub-micrometer scale. The achievement rests on exceptional material purity, tailored microstructure design and high-precision rolling technology. It unlocks new application potential, particularly for highly flexible, reliable components in medical technology and other micro-structured applications.