Laser cutting of simple and complex geometries in structural steel: toward fabrication of metastructures

Fiber laser cutting (LC) plays a crucial role in modern industrial manufacturing, offering rapid and precise machining, together with the ability to produce complex geometries that are otherwise difficult to fabricate. However, LC inherently involves complex thermo–mechanical interactions, localized heating, rapid cooling, and residual stress formation that can alter microstructures, modify material properties, and influence long-term structural performance. This study presents a comprehensive experimental investigation of fiber LC of S235 structural steel, focusing on how assist-gas type, process parameters, and geometry complexity affect cut-surface quality, thermal response, and residual stress development. Cutting trials on both straight and complex geometries were performed with oxygen, nitrogen, and compressed air as assist gases. The quality of the cuts was evaluated through visual inspection and measurements of roughness, perpendicularity, and hardness. In addition, the thermal effects and residual stresses in straight LC samples were examined using infrared camera imaging and X-ray diffraction techniques. In terms of LC of complex geometries, circular and curved features, sharp corners, closely spaced cuts, and auxetic and architected metastructural patterns were investigated. LC-assisted by air has shown superior performance compared to nitrogen- and oxygen-assisted LC in the production of small-scale features and geometries critical for metastructure fabrication. These findings underscore the significant impact of assist-gas choice on post- LC surface quality and manufacturability. Laser cutting has been illustrated as a reliable method for fabricating steel-based metastructures, wherein the geometric precision and resolution of thin features are essential for both structural integrity and functional performance.