Toolpath Generation for Fused Filament Fabrication of Functionally Graded Materials

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...