Evaluation of the infill algorithm for trajectory planning of pointed ends for droplet-generating 3D printers

This paper presents an evaluation of an algorithm that optimises the infills of the geometries that contain at least one pointed end. Computation of the infills, as a part of path planning, falls within the slicing procedure, which in turn is a standard process step in creating a 3D part via rapid prototyping techniques. The computation of the infill trajectories were conducted according to its final application - a droplet generating 3D printer that extrudes plastic droplets on a moving platform. The most commonly used infill techniques are several boundary contours followed by either raster lines or further contours. With these standard techniques particular geometries that contain narrow sub-geometries or pointed ends are not properly filled. The improper infilling results partly due to the limitation on the size of the extruding unit and partly due to the standard trajectories, that do not take in account particular geometry shapes. In particular, the faulty infilling results in voids (underfills) and/or bulges (over-fills). In their previous work, the authors presented a novel algorithm, that concentrates on the pointed end geometries and computes the trajectories for the droplet positioning such that the under-fills and over-fills are minimised. As an extension to the proposed algorithm, this paper presents the algorithm outcome in a form of a look-up table. To every sharp angle a number of insertions of additional droplets, as well as the number of deletions is assigned. Moreover, a 3D model of a pointed end has been sliced and filled according to the algorithmic results and compared with the 3D parts filled according to the standard infill techniques. The printed parts demonstrate the effectiveness of the improved infills. After measuring the height profile of the different parts, the parts printed as suggested by the algorithm led to the smoothest final surface.