FDM parts are 50-80% weaker along the Z-axis than in XY, and no slicer automatically optimizes part orientation to prevent real-world mechanical failures

Every FDM-printed part has a hidden structural weakness that most users do not understand until something breaks: interlayer bonds are dramatically weaker than the continuous filament paths within each layer. Tensile tests consistently show FDM parts achieving only 20-50% of their XY-plane strength when loaded along the Z-axis (perpendicular to layers). A functional bracket printed in PLA might withstand 40 MPa of tensile stress in XY but only 10-15 MPa in Z -- effectively making it a component with an invisible weak plane that will fail unpredictably under real-world loads. This matters because 3D printing is increasingly used for functional parts, not just prototypes. Drone arms, tool holders, jigs, fixtures, end-use brackets -- these parts experience complex, multi-directional loads. When a hobbyist prints a camera mount and it snaps in half during a flight, or a factory fixture fails and drops a workpiece, the root cause is almost always delamination along layer boundaries that were oriented perpendicular to the primary load path. The user did not choose this orientation deliberately -- they hit 'slice' with the default flat-on-bed orientation and trusted the slicer to produce a sound part. The slicer did not warn them that their part has a 4-5x strength differential depending on load direction. This persists because slicer software treats orientation as a geometric problem (minimize supports, minimize print time) rather than a structural engineering problem. No mainstream slicer -- not Cura, PrusaSlicer, or Bambu Studio -- accepts load case inputs and optimizes orientation for mechanical performance. Doing this properly would require integrating basic FEA (finite element analysis) into the slicing workflow, mapping stress fields onto possible orientations, and recommending the one that keeps critical stresses parallel to layer planes. The tooling exists separately (Fusion 360, SolidWorks Simulation), but the workflow gap between CAD stress analysis and slicer orientation selection means most users never connect the two, and functional parts ship with preventable structural weaknesses.