G-code generation in a NURBS workflow for precise additive manufacturing

Abstract

Purpose Non-uniform rational B-splines (NURBSs) are the de facto standard for representing objects in computer-aided design (CAD). The purpose of this paper is to discuss how to stick to this standard in all phases of the additive manufacturing (AM) workflow, from the CAD object to the final G-code, bypassing unnecessary polygonal approximations. Design/methodology/approach The authors use a commercial CAD system (Rhino3D along with its programming environment Grasshopper) for direct slicing of the model, offset generation and trimming. Circular arcs are represented as quadratic NURBSs and free-form geometry as quadratic or cubic polynomial B-splines. Therefore, circular arcs are directly expressible as G2/G3 G-code commands, whereas free-form paths are rewritten as a succession of cubic Bézier curves, thereby admitting exact translation into G5 commands, available in firmware for AM controllers, such as Marlin. Findings Experimental results of this paper confirm a considerable improvement in quality over the standard AM workflow, consisting of an initial polygonization of the object (e.g. via standard tessellation language), slicing this polygonal approximation, offsetting the polygonal sections and, finally, generating G-code made up of polyline trajectories (G1 commands). Originality/value A streamlined AM workflow is obtained, with a seamless transfer from the initial CAD description to the final G-code. By adhering to the NURBS standard at all steps, the authors avoid multiple representations and associated errors resulting from approximations.

Influence of Slicing Strategy on FFF Parts Dimensional Deviations

“…Therefore, slicing is critical in the final part appearance and dimensional deviations. Some approaches to the slicing issue focus on adaptive slicing [6] and direct slicing [7]. However, despite the clear advantages of these approaches to improve the printing results, they are challenging to integrate into the product development AM pipeline where STL representation (discrete tessellation of the 3D CAD model) and hence the indirect slicing is "the fact" the standard used in AM [8], and their implementation, as well as adaptive or local adaptive layer height algorithms, although possible, is a complex task and not included in most slicing applications.…”