Tensile and compression characterization of 3D printed ABS specimens for UAV applications

Desktop 3D printers based on the Fused Deposition Modelling (FDM) technique are usually employed for the production of non-structural objects. The innovative idea of the present work is the use of this technology to produce structural elements employed in the construction of Unmanned Aerial Vehicles (UAVs). Mechanical stresses are not excessive for small UAVs such as multirotor drones. In this case, FDM technique combined with polymers, such as the ABS (Acrylonitrile Butadiene Styrene), can be successfully employed to produce structural components. In order to achieve this target, the work is devoted to the statistical study of the performance of a desktop 3D printer to understand the process development and its boundary limits of acceptance. Mechanical and geometrical properties of ABS specimens are evaluated by means of a capability analysis which allows both mechanical and dimensional performance identifications. Experimental collected data are used to determine statistically stable limits. The ABS specimens are produced using appropriate geometries for tensile and compression experimental tests, respectively. Moreover, such tests are conducted for several specimens produced using different directions for the deposition of the material via the 3D FDM technology. In the preliminary projects of small UAVs, ABS is chosen as the structural material because of its high mechanical properties combined with a reduced weight. In order to use the 3D FDM technology and the ABS material, it is necessary to know the mechanical properties and the dimensional accuracy of specimens obtained via FDM. The mechanical properties are fundamental for a correct structural analysis and optimization of the drone for the actual loads and employed material. This study is necessary because the filling percentage of ABS and the manufacturing process influence the mechanical properties of the finished pieces. The dimensional accuracy is necessary to provide essential information on the tolerances to use in the project. The dimensional behaviour is strictly dependent on the specific used 3D-printer. Furthermore, a capability study is proposed to understand the statistical behaviour of 3D printers. Therefore, this work is focused on both the mechanical and dimensional characterization and on the capability analysis based on the Six Sigma process. The proposed capability analysis is set up and preliminary mechanical and dimensional information are evaluated to understand if a desktop 3D printer is suitable for the self-production of aeronautic components. It will be verified that almost all the measurements have a good fit with the normal distribution; the boundary limits are established to have a stable process. For both tensile and compressive tests, Young Modulus, maximum stress at rupture and stress at proportional limit are determined. These values can be used with confidence as inputs in the UAV project. Considering the dimensional parameters, it is clear how a scale effect influences the dimension of the specimens; this feature must be evaluated and corrected during the production process. Although, further satisfying analysis must be carried on to understand if the scale effect is constant or if it is related to the dimension of the part. Future studies will also consider bending tests combined with different directions of deposition for the construction of ABS specimens via the 3D FDM printing.