PSI - Issue 26

N.A. Fountas et al. / Procedia Structural Integrity 26 (2020) 139–146 Fountas et al. / Structural Integrity Procedia 00 (2019) 000–000

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Shell thickness increases the outer pattern’s volume providing additional strength to the part. In combination to the layer height it is observed that it should be low enough to build a higher number of layers (Fig.3a). Infill density determines the air gap among depositing rasters. It is expected that values for air gap close to zero, i.e. 100% infill density, will increase the tensile strength of the part. For such a state for infill density, number of layers should be increased which means a low layer thickness or height (Fig.3b). Fused deposition modelling (3D printing) deposits the filament at different hatching patterns from layer to layer to increase mechanical strength of parts. Hatching patterns are built according to the orientation angle of the part with reference to X and Y axes. Orientation angle affects the number of rasters as well as their length as it occurs also to CNC machining during the tool path planning stage. Thus, when orientation angle increases the number of rasters is also increased whilst these rasters will be built with smaller lengths. It can be observed that increase in orientation angle will decrease the raster length and improve tensile strength. Fig.3c is in complete agreement with this observation. When setting high levels for orientation angle to enhance tensile strength the number of layers should be increased thus, reducing layer thickness or height. In general, FDM process is driven by the thermal energy of the almost-melted material. When printing speed is set at low levels the thickness of the deposited filament is increased and may negatively affect the already deposited material in terms of deformation owing to stress accumulation. As a result, the process may be prone to imperfections affecting the part’s mechanical strength. According to the observations depicted in Fig.3d printing speed is suggested to be set at high levels to avoid deformation owing to high thermal energy concentration. Fig.3e shows the contribution of shell thickness and infill density to tensile strength. When setting low levels for infill density, layer thickness should be increased to improve tensile strength and vice versa. Obviously, the best result is obtained by maximizing the levels for both shell thickness and infill density parameters. The same also is observed for shell thickness and orientation angle where the tensile strength is improved when setting both parameters at their high levels (Fig.3f). Shell thickness and printing speed cause an increase in tensile strength (Fig.3g). Infill density and orientation angle give the maximum tensile strength when set to their higher levels as shown in Fig.3h. The same trend of effects is noticed for the interactions among infill density-printing speed (Fig.3i) and orientation angle-printing speed (Fig.3j).