<p>Current extrusion-based 3D printing technologies adopt a layer-by-layer material deposition approach which is equivalent to stacking layers of material. This traditional 2.5D deposition plan is limited to depositing discrete, cross-sectional layers of the model. Such stacked layers are well known to induce anisotropic material behaviour subject to part orientation during fabrication. Parts are loaded in their build direction (perpendicularly to layers), have up to a 50% decrease in tensile strength, and a significant 95% decrease in toughness when compared to x-y plane loading. In this work, we adopt a z-pinning approach inspired by traditional composite manufacturing methods to create cross-layer pins for part reinforcement. Our z-pins aim to reinforce the weaker interfaces between 3D printed layers, by facilitating stronger layer adhesion and by obstructing crack propagation through the planar structure of traditional 3D prints. This adaptation of the pin reinforcement concept for 3D printing is implemented on a consumer-grade fused filament fabrication machine without the need for additional hardware. The fabrication machine is a standard linear 3-axis gantry design with off-the-shelf components. We create a custom workflow for editing the part mesh and toolpath plan that is inserted in the workflow between open-source slicing of the part file and part fabrication by the machine. This reads and edits the gcode instructions to insert the z-pin reinforcements into the existing deposition plan. A total of thirty-six tensile and flexural test specimens were fabricated using polylactic acid filament (PLA). The depth of the reinforcement pins, pin spacing, infill percentage, and the orientation of the build are perturbed to evaluate the effectiveness of the method. Tests were conducted on a calibrated Instron ElectroPuls E10000 using standard rectilinear test sample geometries. Test results show pinned tensile components exhibited up to a 25% increase in failure stress, and 300% increase in toughness when compared to the non-pinned control samples for the traditionally weak direction. Flexural strength was not significantly altered on a per-mass normalised comparison. The increase in strength is attributed to increased bonding across layers due to the added pins and abatement of delamination cracks propagating along layer boundaries. Abatement of delamination as a failure mode changes the material rupture mode to more of a desired ductile fracture of the polymer at the z-pin sites and delamination elsewhere in the plane. The results of this work provide a pathway to optimisation of material extrusion properties for anisotropic and isotropic designs by adjusting the quantity and location of z-pin reinforcements.</p>

Increased Strength of 3d Printed Parts With Z-Pin Approach

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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