STL 2.0: A Proposal for a Universal Multi-Material Additive Manufacturing File Format

The de-facto standard STL file format has served the rapid prototyping community for over two decades, but falls short with the advent of new technological developments such as the ability to handle multiple and graded materials, specify volumetric digital inkjet patterns and surface colors. We study a variety of requirements for additive fabrication technologies and propose a new compact XML-based file format. The new Additive Manufacturing File (AMF) format allows the resolution-independent specification of geometry and material properties. Regions may be defined geometrically either using a triangle mesh, using functional representations, or through a voxel bitmap. Each region is associated with a material, which may be defined as a base (single) material or hierarchically by a combination of other materials, either functionally (enabling smooth gradients) or voxel-wise (for arbitrary microstructure). Files can be self-contained or refer to external or online material libraries. With a simple conversion, the AMF file format is both forward and backwards compatible with the current standard STL format, and the flexibility of the XML structure enables additional features to be adopted as needed by CAD programs and future additive manufacturing processes. Code and examples are publicly available.