J.R. Kubalak, C.B. Williams
Virginia Tech DREAMS Lab,
Keywords: multi-axis robotics, design methodology, composites, load path, mechanical performance
Summary:Additive manufacturing (AM) technologies are compelling for composites manufacturing, as the geometric flexibility has the potential to reduce or eliminate the need for dedicated tooling, reduce material waste, and enable design optimization. This could revolutionize industries that must balance strength and weight metrics (e.g., aerospace, automotive, prosthetics, athletic equipment) by creating a step-change in structural efficiency while simultaneously reducing manufacturing costs. However, conventional AM processes typically produce parts with anisotropic mechanical properties that do not achieve the necessary strength characteristics for load bearing applications. In particular, the thermal characteristics of the material extrusion (ME) process result in inter- and intra-layer bonds that are weaker than the deposition direction, creating an overall anisotropic mechanical response. At the same time, the deposition process can inherently align the reinforcement in a composite material to the extrusion direction, presenting the opportunity to optimize part performance through toolpath customization. Whereas planar ME processes restrict this optimization to the XY-plane, multi-axis ME (enabled by industrial robotics arms) allow toolpath optimization in full 3D. Literature has demonstrated mechanical performance improvement using multi-axis ME, but existing multi-axis toolpath planning methods restrict freedom in both part geometry and toolpath complexity due to collision concerns between the tool head and the in-progress print. To this end, the authors have created a novel topology and toolpath optimization (TTO) workflow that optimizes material distribution and orientation for arbitrary 3D loading conditions, aligns deposition paths to those orientations, and orders them for collision-free deposition. In this presentation, the authors demonstrate mechanical performance improvement using the TTO workflow on case study load cases relative to geometrically similar structures fabricated using XY-planar deposition. In particular, specimens fabricated using a carbon fiber-loaded PLA demonstrate up to 108% improvement using the TTO workflow over conventional toolpath planning methods. The performance improvement is due to an increased alignment of the toolpath to the load paths within the part, which would not be achievable through conventional (i.e., XY-planar) or other existing multi-axis toolpath planning methods.