Stereolithography (STL) files, used to convert digital designs into printable layers, play a central role in the 3D printing of metallic lattice structures. Although STL files have been used for decades, it is difficult to achieve high resolution, precision, and structural integrity with STL. An international research team devised a remedy for the bulky file sizes and imprecise geometric estimates that come with STL. Researchers from the Chinese University of Hong Kong, the University of Southern California, and other institutions developed a stereolithography file format-free (STL-free) hybrid toolpath generation method for laser-based powder bed fusion (PBF-LB). The STL-free approach translates lattice geometries directly into laser toolpaths, with no intermediate step needed. The STL-free hybrid toolpath feeds a mathematical description of the geometry directly to the printer, circumventing the traditional mesh-based workflow of STL. By eliminating intermediate STL mesh, the method achieves a 90% reduction in memory usage and processing time. By directly generating laser paths from implicit geometry, the hybrid toolpath drastically improves surface finish, mechanical strength, and computational efficiency for microscale lattices. Courtesy of Chinese University of Hong Kong/Junhao Ding. The STL-free method uses contour scanning for thin, delicate walls, combined with rotational scanning at the lattice joints. This hybrid approach stabilizes heat input, minimizes structural defects, and promotes uniformity in the crystal, which is crucial for strength and toughness at the microscale. The researchers conducted experimental and numerical analyses to demonstrate the impact of STL-free toolpath engineering on mechanical behavior. They also performed cyclic loading tests and fracture morphology studies to confirm the durability of the parts fabricated using the STL-free hybrid toolpath method. A lightweight aerospace bracket printed with the new toolpath method delivered 52% higher tensile strength and absorbed five times more energy before failure, compared with conventionally-made parts. Copper cold plates built using the new method increased cooling efficiency by 60%. Metallic shell-based metamaterials, particularly at the microscale, are promising for applications in the aerospace, biomedical, and automotive industries, which require both high mechanical performance and extreme miniaturization. Beyond a 90% reduction in memory use and processing time, the STL-free hybrid toolpath strategy also enables the high-fidelity fabrication of microscale shell lattices, with a 66% increase in yield strength and a 257% improvement in elongation. It supports the fabrication of ultrathin walls, with thicknesses as low as 65?μm, while maintaining structural integrity. Through a precisely controlled laser scanning path, it ensures a steady energy input density, leading to high surface quality with a roughness as low as 3.2 μm. “By bypassing STL conversion and operating directly on implicit functions, we reduce memory usage and also unlock far better mechanical and surface properties,” professor Xu Song said. In addition to improving computational and mechanical performance and print quality, the STL-free toolpath method is versatile and can be adapted to other powder bed fusion platforms for high-precision manufacturing. “Our method bridges computational design and physical fabrication in a seamless way,” professor Wen Chen said. “It opens up new possibilities for high-performance microscale structures in fields like aerospace, biomedicine, and electronics.” In the future, the researchers will focus on expanding their method to new materials, and on integrating microstructure-aware path planning into their method. These enhancements could lead to architected metamaterials that combine strength, ductility, and long-term durability in efficient ways that cannot be achieved with existing 3D printing methods. By simplifying the link between digital design and physical build, the STL-free toolpath could broaden the potential of advanced manufacturing, where lighter, stronger, smarter parts will not only be a preference, but also a requisite. The research was published in the International Journal of Extreme Manufacturing (www.doi.org/10.1088/2631-7990/ae01ff).