Optimizing Dimensional Accuracy of Fused Filament Fabrication using Taguchi Design

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1 Optimizing Dimensional Accuracy of Fused Filament Fabrication using Taguchi Design ZOI MOZA 1a*, KONSTANTINOS KITSAKIS 1b, JOHN KECHAGIAS 1c, NIKOS MASTORAKIS 2d 1 Mechanical Engineering Department, Technological Educational Institute of Thessaly, Larissa, Greece 2 Department of Industrial Engineering, Technical University of Sofia, Sofia, Bulgaria. a zoigr79@yahoo.com, b kitsakis@teilar.gr, c jkechag@teilar.gr, d mastor@tu-sofia.bg Abstract: - Fused Filament Fabrication (FFF) is a manufacturing technique commonly used for 3D Printing. In order to satisfy functional requirements, FFF prototypes should have acceptable accuracy. In the current study the process parameters effects influencing the dimensional accuracy of parts produced by the low cost FFF Duplicator 4X 3D Printer are presented. Therefore nine experiments were conducted utilizing the Taguchi L 9 (3 4 ) orthogonal array. The process parameters examined included the Printing Material, Infill Rate, Number of Shells and Layer Height. Linear dimensions were measured with a 0.01 mm accuracy digital calliper. Analysis of Means (ANOM) diagrams were drawn to investigate the effect of each parameter and Analysis of Variance (ANOVA) was performed aiming in identifying the importance of each parameter variance to the performance measure as a percentage value. Key-Words: - Fused Filament Fabrication, 3D Printing, Taguchi Design, Dimensional accuracy, Optimization 1 Introduction Fused Filament Fabrication (FFF) or Fused Deposition Modeling (FDM) is a 3D printing process which generally refers to techniques that produce shaped parts by gradual creation or addition of solid material [1, 2]. The first term used to describe the creation of 3D objects is Rapid Prototyping. These techniques have been widely spread and apply to various industries, like biomedical, automotive, aerospace, etc. A wide range of rapid prototyping technologies has been developed over the last years. These technologies, which in general are referred to as Rapid Prototyping and Manufacturing, include Stereolithography, Fused Deposition Modeling, Laminated Object Manufacturing, Ballistic Particle Manufacturing and Three Dimensional Printing [2]. FFF or FDM is one of the key technologies of RP, since most of the machines existing in the market belong to this category [3]. The FFF process is in general a controllable process, since the user is able to decide on the majority of the process parameters. The quality of the part is measured by several quality indicators, most significant of which is considered the model s dimensional accuracy. Dimensional accuracy of the parts produced by using FFF technologies and the relevant factors affecting it, are major issues of investigation in the literature. The main parameters influencing dimensional accuracy were found to be layer thickness, infill rate, number of shells, printing and movement speed [4-8]. The present paper deals with the impact of various process parameters on dimensional accuracy. Such parameters involve the printing material, the infill rate, which represents the percentage that shows how much a solid model should be filled in with material when printed, the number of shells, which sets the number of outlines printed on each layer of the object and shows how dense the outside walls are and the layer height, which affects the print quality by setting the thickness of each layer that is being printed. Fig. 1. FFF process as described on RepRap [9] ISBN:

2 2 Experimental Setup An investigation of the influence of the Printing Material (PM), Infill Rate (IR), Number of Shells (NS) and Layer Height (LH) on the dimensional accuracy of parts produced by Duplicator 4X 3D Printer is presented by performing nine (9) printing operations (Fig. 2, [10]). The selected part geometry has been prepared in STL format. The Π part designed and its specifications are indicated in Fig. 3 and 4. Fig. 4. Test part dimensions Fig. 5. Test part Fig. 2. Wanhao Duplicator 4X 3D Printer Fig. 3. Experiments performed Nine experiments were carried out utilizing the Taguchi L 9 (3 4 ) orthogonal array [11, 12]. In this method, main parameters, which are assumed to have an influence on process results, are located at different rows in a designed orthogonal array. In the present case, the quality characteristic studied is dimensional accuracy and its most desirable value is the nominal dimensions (nominalthe-best characteristic). The summary statistic for the experiment, called signal-to-noise ratio, is defined in this case by the objective function: ηη ii = 10 log 10 μμ ii 2 σσ ii 2 where and μμ ii = 1 nn yy ii σσ 2 ii = 1 nn 1 (yy ii μμ ii ) 2 ii are the observed data mean and variance for the i-th experiment respectively, yy ii represents the observed data for the i-th experiment and n is the number of experiments [11]. The optimization problem here is to maximize the objective function η. The process parameters used were the Printing Material (PM), the Infill Rate (IR), the Number of Shells (NS) and the Layer Height (LH). The Printing Material is defined by the control factors Acrylonitrile Butadiene Styrene (ABS) and Polylactic Acid (PLA). For the Infill Rate, three levels equal to 20%, 50% and 70% of the solid model were selected. The Number of Shells stands for the number of outlines printed on each layer of the object and is defined by three levels equal to 1, 2 and 3. Finally, for the Layer Height three values for the thickness of each layer were considered, 0.1, 0.2 and 0.3 mm. The process parameters and their ii ISBN:

3 respective levels are summarized in Table 1. Based on robust design, the standard L 9 (3 4 ) orthogonal array has been selected in order to perform the matrix experiment (Table 2). The results obtained from ANOM are summarized in Fig. 6 and 7, whereas the respective results obtained from ANOVA are presented in Tables 3 and 4. No Process Parameter Printing Material (PM) ABS PLA - 2 Infill Rate (IR) 20% 50% 70% 3 Number of Shells (NS) Layer Height (LH) 0.1mm 0.2mm 0.3mm Table 1: Parameter Design Dimensional No Process Parameters Performance (η of i ) XY Z Exp. PM IR NS LH Plane Height average Table 2: Orthogonal experiment Linear dimensions in XY plane and Z direction for each experiment have been measured with a 0.01 mm accuracy digital caliper. The effect of each parameter was analyzed by Analysis of Means (ANOM) and Analysis of Variance (ANOVA). The best parameter levels were detected and the optimized combination was built and evaluated. 3 Discussion of the results Based on the values obtained by the nine experiments for the dimensions investigated, the Analysis of Means (ANOM) and Analysis of Variance (ANOVA) have been conducted to determine the factors influencing the dimensional accuracy. The optimum level for a factor based on the ANOM was determined as the one that gives the higher value of the objective function η in the experimental region. Fig. 6. Plots of factor effects (ANOM) for XY plane Fig. 7. Plots of factor effects (ANOM) for Z height DoF SoS MS % PM % IR % NS % LH % Total Table 3. ANOVA for XY plane DoF SoS MS % PM % IR % NS % LH % Total Table 4. ANOVA for Z direction ISBN:

4 4 Conclusions The process parameters influencing the dimensional accuracy of the FFF Duplicator 4X 3D printer were investigated. The experimental results obtained indicate that the process parameters influencing the dimensional accuracy in the XY plane don t follow the same pattern as in Z direction. From Fig. 3 and 4 we can determine the optimum level for each factor and from Tables 3, and 4 we determine the relative magnitude of each factor in the dimensional accuracy. The experimental results indicate that the dimensional accuracy in XY plane is mainly affected by the printing material, followed by the infill rate and number of shells. The results obtained in the Z direction indicate that all factor parameters have a significant influence in the dimensional accuracy, with dominant factor the layer height and the number of shells. The results are summarized in Table 5. PM IR NS LH XY plane PLA 20% mm Z direction PLA 20% mm Table 5. Best parameters levels Taking the above into account the combination of parameters resulting in the most desirable dimensional accuracy is PLA for printing material. The XY plane and Z direction are both optimized by an infill rate of 20%. The optimum level for the number of shells is 1 in the XY plane, and 3 in the Z direction. Finally, layer height of 0.3 mm gives better results on XY plane, whereas the best value for the Z direction is obtained with a layer height of 0.2 mm. Further process parameters and their effect on the dimensional accuracy optimization of each printing material will be investigated in future work. Fig. 8. Percentage of factors importance for XY plane Fig. 9. Percentage of factors importance for Z direction Acknowledgements The authors express special thanks to the undergraduate student Alexandros Kakaroumpas for his support on the developed laboratory activities. References: [1] J.-P. Kruth, M.-C. Leu, and T. Nakagawa, "Progress in additive manufacturing and rapid prototyping," CIRP Annals-Manufacturing Technology, vol. 47, pp , [2] X. Yan and P. Gu, "A review of rapid prototyping technologies and systems," Computer-Aided Design, vol. 28, pp , [3] R. Anitha, S. Arunachalam, and P. Radhakrishnan, "Critical parameters influencing the quality of prototypes in fused deposition modelling," Journal of Materials Processing Technology, vol. 118, pp , [4] G. Ambrogio, I. Costantino, L. De Napoli, L. Filice, L. Fratini, and M. Muzzupappa, "Influence of some relevant process parameters on the dimensional accuracy in incremental forming: a numerical and experimental investigation," Journal of Materials Processing Technology, vol , pp , 11/10/ [5] D. Dimitrov, W. v. Wijck, K. Schreve, and N. d. Beer, "Investigating the achievable accuracy of three dimensional printing," Rapid Prototyping Journal, vol. 12, pp , [6] J. Kechagias, "Investigation of LOM process quality using design of experiments approach," Rapid Prototyping Journal, vol. 13, pp , [7] J. Kechagias, P. Stavropoulos, A. Koutsomichalis, I. Ntintakis, and N. Vaxevanidis, "Dimensional Accuracy ISBN:

5 Optimization of Prototypes produced by PolyJet Direct 3D Printing Technology," in Proceedings of the 18th International Conference on Circuits, Systems, Communications and Computers, pp [8] J. G. Zhou, D. Herscovici, and C. C. Chen, "Parametric process optimization to improve the accuracy of rapid prototyped stereolithography parts," International Journal of Machine Tools and Manufacture, vol. 40, pp , 2// [9] reprap.org/wiki/fused_filament_fabrication [10] Wanhao Duplicator 4X. Available: [11] M. S. Phadke, Quality engineering using robust design: Prentice Hall PTR, [12] Tsui, K.-L., An overview of Taguchi method and newly developed statistical methods for robust design. IIE Transactions, (5): p ISBN: