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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Fig. 3. Response surface plots for FDM parameters effect on load ( kN ) for tensile strength.

4. Conclusions and future perspectives This work studied the effect of five additive manufacturing parameters to the fabrication of parts with fused deposition modelling (FDM / 3D printing). The parameters were shell thickness, layer height, infill density, orientation angle and printing speed. Experiments were conducted according to L 16 fractional factorial design to obtain results for load at break ( kN ) and further investigate the effect on the tensile strength of standard ASTM 638-10 type I specimens being fabricated using fused deposition modelling. The fractional factorial design was converted to a customized response surface one, in order to investigate the non-linear behaviour of the control parameters on the response of load ( kN ) for tensile strength evaluation. The material tested was PLA. Statistical analysis followed the experiments resulted in a regression model capable of explaining the experimental variability of parameters in the response, up to 96.95% and exploring the design space for further research. Owing to the complexity of the problem investigated, the parameters were examined as interactions between two independent variables rather than as single factors. Experimental observations as well as statistical outputs suggest that infill density is a dominant parameter to affect the tensile strength of PLA fabricated specimens. Orientation angle should be high enough to reduce raster length and increase their number; thus, contributing to the improvement of tensile strength. The same also goes for shell thickness. The higher the thickness, the stronger the outer pattern of fabricated parts. Printing speed strongly affects thermal energy and its absorption from neighbouring deposited layers. Printing speed should be set to middle and high levels to avoid thermal deformations of fabricated parts which in turn may negatively affect tensile strength. In the case of tensile strength, the number of layers should be increased meaning that the layer height or thickness should be set at low levels. Moreover, observation it is indicated that the curvature exhibited in response surface analysis of results, shows high non-linearity; suggesting the complex relationship between fused deposition modelling parameters and load at break ( kN ) as a tensile strength indicator. Looking further ahead, the research will involve more experiments under an original response surface design i.e., L 32 to clearly examine the results of factorial points, center points and star points to investigate the experimental error. Moreover, the regression model presented in this study or another yet to be generated after conducting new experiments will serve as the objective function to optimize the FDM process with the use of genetic algorithms. If another objective is to be introduced, i.e. fabrication time or material consumption, a multi-objective problem will be solved using several algorithms for comparison. In addition, other materials than PLA such as ABS and Nylon will be tested to examine their mechanical strength under several destructive tests such as tension, compression, flexural and impact. Wear is also under question to examine the effect of FDM parameters for different materials.