Graph Theory Driven Toolpath Design for Mex AM

Abstract

Polymer material extrusion (MEX) additive manufacturing (AM) toolpath design has been driven by toolpath algorithms that are robust and computationally inexpensive. These contemporary algorithms fail to minimize travel moves – toolpaths where no material is deposited. It has been shown that continuous toolpaths, toolpaths that have no travel moves, increase the bond strength between adjacent roads deposited. This increase in bond strength leads to increased part strength when continuous toolpaths are used throughout the part. A reduction in travel moves is especially impactful in pellet-fed MEX AM systems, where precise control of the flow rate is not possible, leading to larger and more frequent defects at start-stop locations. This thesis presents a graph theory based toolpath generation algorithm, entitled GRATER – the GRAph Theory based slicER – that when compared to contemporary toolpath generation softwares, or “slicers”, reduces travel moves by up to 95%, reduces travel distance by a factor of 3, and reduces build time by approximately 25%. Further advantages of continuous toolpaths are shown for parts which have regions within a layer built using different processing parameters, such as infill density. Contemporary slicers consider these regions independently, using discontinuous toolpaths to deposit material within the layer. By generating a continuous toolpath for the layer containing varying process parameters, the effective ultimate stress of parts is shown to increase 33% under various strategies.