Material Extrusion (MEX) systems with dual-material capability can unlock interesting applications where flexible and rigid materials are combined. When chemically incompatible materials are concerned the adhesion between the two might be insufficient. Therefore researchers typically rely on dovetail type interlocking geometries in order to affix two bodies mechanically. However, dovetail type interlocking introduces extrusion discontinuities and relies on the material’s resistance to deformation, which is difficult to model. We propose a simple and effective 3D lattice consisting of interlaced horizontal beams in vertically alternating directions which interlock topologically: the interlaced topologically interlocking lattice (ITIL). It ensures continuous extrusion and ensures an interlock even for highly flexible materials. We develop analytical models for optimizing the ultimate tensile strength of the ITIL lattice in two different orientations relative to the interface: straight and diagonal. The analytical models are applied to polypropylene (PP) and polylactic acid (PLA) and verified by finite elements method (FEM) simulations and physical tensile experiments. In the diagonal orientation ITIL can obtain 82% of the theoretical upper bound of 8.6 MPa. ITIL seems to perform comparably to dovetail interlocking designs, while it lends itself to application to non-vertical interfaces. Optimizing the lattice for non-vertical interfaces, however, remains future work. ... Read more

The products in our day to day lives have different requirements in different regions of the product. One way of dealing with such spatially varying requirements is to divide the product into multiple parts and assign each part a different material. For example, the handle of a drill is often fitted with a rubbery material which gives it more grip when holding it. This gives the designer a choice of which regions exactly to use that material. Designers can consider the large variety of hands and ways of holding a drill. Equipped with an average distribution of gripping pressure throughout the handle, they could identify the regions with a pressure higher than some cutoff value and assign the gripping material to those regions. This means that the material properties vary abruptly over the surface; the adjacent regions on the one side of the cutoff value provide needlessly much grip, while on the other side the regions provide too little grip. The final distribution of material properties is segmented and therefore does not follow the gradual distribution of requirements optimally. In this workflow the designer is forced to reduce the continuous gripping pressure information into a binary material choice. But what if we could manufacture products with a gradient in their material properties? To answer this question we consider the material and the manufacturing technique. A Functionally GradedMaterial (FGM) is any substrate with material properties made to vary from region to region. FGMs find application for example in personalized footwear, implants, tires and airplane wings. They can improve a product’s performance by optimizing the spatial gradation of material properties throughout the product. Rather than a homogeneous block of material, FGMs consist of a fine-scale geometry of one or more base materials. The material properties of an FGM can be governed by controlling the shape of that fine-scale structure. Fused Filament Fabrication (FFF) is an additive manufacturing technique which can produce complex geometry cheaply. Thermoplastic material is heated and extruded out of a nozzle to deposit extrusion lines. These extrusion lines accumulate to formlayers, which are added on top of each other to form the final product. A 3D model is converted into toolpaths for the 3D printer, which describe the geometry of the extrusion lines the nozzle should traverse. Because of the physics involved in suchmachines, there are severalmanufacturing constraints to which the print job must adhere, such as (i) the maximum overhang angle to prevent printing in mid air, (ii) (semi-)continuous extrusion to prevent print defects at the ends of extrusion lines, (iii) integer thickness geometry (N * linewidth) to prevent overlapping extrusion lines, and (iv) chemically compatible materials to prevent a multi-material print job from disassembling during the manufacturing process... ... Read more

3D printing techniques such as Fused Deposition Modeling (FDM) have enabled the fabrication of complex geometry quickly and cheaply. Objects are produced by filling (a portion of) the 2D polygons of consecutive layers with contour-parallel extrusion toolpaths. Uniform width toolpaths consisting of inward offsets from the outline polygons produce over- and underfill regions in the center of the shape, which are especially detrimental to the mechanical performance of thin parts. In order to fill shapes with arbitrary diameter densely the toolpaths require adaptive width. Existing approaches for generating toolpaths with adaptive width result in a large variation in widths, which for some hardware systems is difficult to realize accurately. In this paper we present a framework which supports multiple schemes to generate toolpaths with adaptive width, by employing a function to decide the number of beads and their widths. Furthermore, we propose a novel scheme which reduces extreme bead widths, while limiting the number of altered toolpaths. We statistically validate the effectiveness of our framework and this novel scheme on a data set of representative 3D models, and physically validate it by developing a technique, called back pressure compensation, for off-the-shelf FDM systems to effectively realize adaptive width. ... Read more

In most layered additive manufacturing processes, a tool solidifies or deposits material while following pre-planned trajectories to form solid beads. Many interesting problems arise in this context, among which one concerns the planning of trajectories for filling a planar shape as densely as possible. This is the problem we tackle in the present paper. Recent works have shown that allowing the bead width to vary along the trajectories helps increase the filling density. We present a novel technique that, given a deposition width range, constructs a set of closed beads whose width varies within the prescribed range and fill the input shape. The technique outperforms the state of the art in important metrics: filling density (while still guaranteeing the absence of bead overlap) and trajectories smoothness. We give a detailed geometric description of our algorithm, explore its behavior on example inputs and provide a statistical comparison with the state of the art. We show that it is possible to obtain high quality fabricated layers on commodity FDM printers. ... Read more

The fabrication flexibility of 3D printing has sparked a lot of interest in designing structures with spatially graded material properties. In this paper, we propose a new type of density graded structure that is particularly designed for 3D printing systems based on filament extrusion. In order to ensure high-quality fabrication results, extrusion-based 3D printing requires not only that the structures are self-supporting, but also that extrusion toolpaths are continuous and free of self-overlap. The structure proposed in this paper, called CrossFill, complies with these requirements. In particular, CrossFill is a self-supporting foam structure, for which each layer is fabricated by a single, continuous and overlap-free path of material extrusion. Our method for generating CrossFill is based on a space-filling surface that employs spatially varying subdivision levels. Dithering of the subdivision levels is performed to accurately reproduce a prescribed density distribution. We demonstrate the effectiveness of CrossFill on a number of experimental tests and applications. ... Read more

This work presents a halftoning technique to manufacture 3D objects with the appearance of continuous grayscale imagery for Fused Deposition Modeling (FDM) printers. While droplet-based dithering is a common halftoning technique, this is not applicable to FDM printing, since FDM builds up objects by extruding material in semi-continuous paths. The line-based halftoning principle called 'hatching' is applied to the line patterns naturally occuring in FDM prints, which are built up in a layer-by-layer fashion. The proposed halftoning technique isn't limited by the challenges existing techniques face; existing FDM coloring techniques greatly influence the surface geometry and deteriorate with surface slopes deviating from vertical or greatly influence the basic parameters of the printing process and thereby the structural properties of the resulting product. Furthermore, the proposed technique has little effect on printing time. Experiments on a dual-nozzle FDM printer show promising results. Future work is required to calibrate the perceived tone. ... Read more