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A model for self-support evaluation of 3D-printed structures with inclined surfaces

University of British Columbia

Additive manufacturing (AM) is renowned for its flexibility and low upfront costs. Amongst the variety of AM technologies, fused filament fabrication (FFF) is by far the most prevalent. FFF printers work by extruding molten polymer in a series of planar layers according to directions derived from computer-aided design (CAD) data. While FFF provides a low-cost alternative to conventional manufacturing for small-batch prototyping, it’s hindered by its time-intensive nature and high unit cost of production. One contributing factor to the manufacturing time and material costs of FFF is the requirement to print additional supporting structures in order to facilitate the construction of inclined surfaces. In absence of these structures, the forces acting on the unsupported (overhanging) portion of the molten extrusions are liable to cause deformation or collapse. As per the universally-quoted heuristic, any surface that is inclined by more than 45 degrees from the vertical should be supported. However, to date, there has been little justification provided to support this heuristic and, in fact, components with surface angles exceeding 45 degrees are routinely produced without support using FFF printers. In this work we present a theory to explain the limiting phenomena in the printing of inclined surfaces via FFF. We also develop a model to predict a component’s printability based on its geometry, the process parameters and the material properties of the filament. Experimental validation is provided to verify the appropriateness of the model. The results indicate that the phenomena limiting the maximum surface angle are scale-dependent. For large-scale FFF printing, the angle is limited by gravity, which tends to cause the extruded filament to deflect downwards, limiting the vertical progression of the structure. For small-scale printing, the angle is limited by surface tension, which tends to cause the extruded filament to contract, limiting the structure’s horizontal progression. At small scales the maximum surface angle was found to depend solely on the geometry of the print bead and the number of perimeters, whereas at large scales it also depends on the process parameters and material properties.

Text

2019-12-11

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/72692

Mechanical Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/