Multi-material sandwich panel produced with desktop 3D printer

Fused Deposition Modelling (FDM) has gained important segment in the market of consumer goods in recent years. With the expiration of the existing patents more and more producers have started constructing their own 3D printer with different qualities and different capabilities. For example, ASTRA (Additive manufacturing for Systems and_sTRuctures in Aerospace) group at Politecnico Di Torino uses a Desktop 3D printer with FDM technology to construct structural part of a multifunctional UAV in order to have an easy to access platform open to researchers and consumers. The advantage of the patented solution is that it is possible to reconfigure the aerial vehicle printing just 8 different components in more than twelve versions. In this manner, not only the spare part logistics is dramatically simplified but also the overall cost of the drone itself is reduced. Constructing a part with FDM means to add several filaments of semi-melted material that glues each other layer after layer. This technology obviously introduces anisotropy due to the technique of fabrication itself: different properties have been found along the fibres respect to the crossing direction; moreover, along the construction direction there are again other mechanical properties. This anisotropy seems to suggest a design approach similar to the one already validated for composites for the ply orientation. Technologically this is quite easy to apply using open FDM machines where the strategy of deposition (raster orientation) can be changed easily. Another problem that will be faced in this work is related to solve a disadvantage of this constructing technique: after the deposition that is at high temperature (245 °C for the ABS (Acrylonitrile Butadiene Styrene)) the fibre cool down rapidly and the thermal deformation introduced between different layers a traction tension. This inconvenience can lead to separation from the building platform of the component or, also, the delamination of the part itself. Different materials, with different melting temperatures and different thermal expansion coefficients give different responses to this bad phenomena. For example, PLA (PolyLactic Acid), a natural fibre derived from Corn, gives less distortion respect to ABS or Nylon but has got lower mechanical properties. In this work this technical disadvantage will be overcome introducing multi-material structures: complex part made with an internal core of PLA (easy to manufacture) and strong external skin in ABS or Nylon. this strategy opens the design scenario to multiple possibilities: in fact, is not only possible to change the internal core material but also the shape of the core from honeycombs to square etcetera. Also, the raster orientation explained above and the density of the fibres deposited for the skins will be investigated. In this manner, it will be possible for the designed application (e.g., the proposed multifunctional UAV called Polidrone) to have stiffener and lighter structures easy to be manufactured with a low-cost 3D printer