3D printing continuous stainless steel fiber reinforced polymers

Bundles of stainless steel fiber are used to reinforce layers of 3D printed plastic parts to create a robust, electrically conductive composite material.

Metal 3D printed composite parts are produced containing a polymer matrix and continuous 316L stainless steel fiber bundles (SSF). A 3D printable polymer-SSF filament is first made with a specialized filament maker. The filament is then 3D printed to create a robust composite with the potential to transmit signals as an electrically conductive material.

Continuous stainless steel polymer filaments have been produced using specialized components, by layering 316L SSF with polymers in 3D printed parts to create a robust composite with the potential to transmit signals as an electrically conductive material.

The SSF bundle in this printing study consisted of 90 fibers, each with a 14 µm diameter. The bundle was then coated with polylactic acid (PLA) to produce PLA-SSF continuous filaments with tailored diameters between 0.9 to 0.5 mm. These were then used to print composite parts using the Fused Filament Fabrication (FFF) 3D printing technique.

Inspections of the PLA-SSF composite samples were conducted to evaluate mechanical performance (interlaminar shear strength and tensile property testing), volume fraction and porosity (CT scans and cross-section studies), as well as morphology (microscopy and SEM examination).

The steel fiber volume fraction (VF) in the printed composite structures was controlled in the range of 6 to 12 VF%. The samples exhibited a homogeneous distribution of steel fibers in the PLA matrix. Increasing the volume fraction and lowering the porosity of the PLA-SSF structure, is achieved by alterations to the 3D printing parameters and printer modifications. Parameters include layer height, path width, temperature and cooling.

Based on mechanical testing studies, it was demonstrated that SSF reinforcement of the PLA resulted in a significant improvement in mechanical performance, a 5-fold increase in interlaminar shear strength (ILSS). Tensile strength testing revealed that the PLA-SSF composite outperformed other PLA- carbon fiber composites. Furthermore, the PLA-SSF composite is made from polymers that are supplied responsibly, the composite has excellent recycling potential and can contribute to a circular economic material.

There is considerable potential for printed steel composites for individualized conductive composite applications. Compared with previous reports from the literature on 3D printed metal fiber-reinforced polymer composites, the stainless steel composites significantly enhanced mechanical performance. In terms of sustainability, 3D printing has the advantage of minimizing material wastage during part fabrication, both the steel and the biopolymer PLA thermoplastic used in the fabrication of the composites are readily recyclable.

"It is very exciting that you have been using continuous stainless steel fibers for 3D printing with a continuous path and such a high volume fraction with low porosity," says Mazher Iqbal Mohammed, Leader of Product Design Engineering at Loughborough University.

PLA-SSF continuous filaments can be fabricated on a normal polymer printer with minimum modifications, which opens up the potential for a broad range of users to utilize this technology. It provides an alternative to other reinforcing fibers currently used in aerospace, biomedical, marine and energy sectors. Potentially for high-pressure containers, faraday cages, signal or information transmission vessels with competitive strength values compared to continuous carbon fiber structures.

Provided by University of Sheffield