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The optimization of the production procedure in relation to the mechanical properties of additively manufactured parts
Available online at www.sciencedirect.com
ScienceDirect Materials Today: Proceedings 19 (2019) 1008–1013
www.materialstoday.com/proceedings
BraMat 2019
The optimization of the production procedure in relation to the mechanical properties of additively manufactured parts Camelia Gabora,*, Mihai Alin Popa, Donato Maglib, Tibor Bedoa, Sorin Ion Munteanua, Daniel Munteanua a
Transilvania University of Brasov, Material Science Department, 29 Eroilor Blvd., 500036, Brasov, Romania University of Modena and Reggio Emilia, Materials Engineering Faculty, 10 Vivarelli, 41125, Modena, Italy
b
Abstract Additive manufacturing (AM) is a type of production technology which consists of stacking and unifying individual layers, to form a three-dimensional part with complex geometry, usually unobtainable by other means of production. Due to its working principle, i.e. stacking layers, the mechanical characteristics of the built part could be influenced by the construction angle. For metallic additively manufactured parts, it was reported that the mechanical behavior, cyclic deformation and fatigue behaviors are clearly influenced by the build orientation. To date, the number of reports concerning the mechanical behavior of polymer AM parts is relatively limited. Hence, the aim of this study was to assess whether the build orientation will have an impact on the traction and compression characteristics of standard samples built by FFF (Fused Filament Fabrication), from polylactic acid filament. Samples were built at various inclination degrees. It was observed that the build orientation has a significant effect on the mechanical properties of parts, better behavior being observed for the specimens printed at 0 degrees building orientation. © 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the 11th International Conference on Materials Science & Engineering, BraMat 2019 Keywords: fused filament deposition; construction angle; precursor material.
1. Introduction Additive manufacturing (AM) is a highly flexible processing method, introduced about 30 years ago, that enables fabrication of complex structures that are otherwise difficult to obtain through forming or subtractive technologies.
* Corresponding author. Tel.: +40-732-148472. E-mail address: [email protected] 2214-7853 © 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the 11th International Conference on Materials Science & Engineering, BraMat 2019
C. Gabor et al. / Materials Today: Proceedings 19 (2019) 1008–1013
1009
The accessibility of 3D printers is continuously growing for both industrial and general public use [1] while 3D printed components can be found in automotive engineering, civil engineering, aerospace, biomedical and other applications [2-4]. As the name implies, the parts are created in a point-by-point, line-by-line or layer-by-layer additive manner from 3D CAD models [5]. 3D printing technologies offer major advantages such as fabrication without retooling, increased design freedom with complex geometries, and flexible process parameters [2]. The AM technologies have evolved continuously from the stereolithography technique (SLA), with a photopolymerization-based building approach [6], to selective laser sintering (SLS) with a large and growing palette of polymers available, or binder jetting process (the method that launched the 3D printing term, which later extended to other technologies) [1]. AM applications evolved from rapid prototype fabrication to rapid tooling and rapid manufacturing [7]. One of the most widely used techniques [8], filament fused fabrication (FFF) also known as fused deposition modeling (FDM), was developed in the early 90’s. This technique involves one or more heated nozzles that melt and distribute the extruded polymer as a fine filament in the layer-by-layer building approach, using a three-axes translatable platform [1]. The working space can be introduced within a heated chamber in order to reduce the thermal distortion that appears due to non-uniform cooling. Acrylonitrile butadiene styrene (ABS) and polylactic acid (PLA) are used on most FFF devices but the range of available materials is very wide, including polyamides, polycarbonate, polystyrene, etc. [9]. It must be mentioned that PLA is often used for biomedical 3D printing purposes [10], due to its non-toxic nature towards cells and tissues. Most of the research conducted in solid freeform fabrication technologies are related to understanding the process itself rather than modeling the mechanical properties of the resulting parts [11, 12]. Moreover, many of the studies found in the literature were conducted on ABS [12, 13-16] and even more on other AM techniques [17, 18], compared to the method presented herein, namely the FFF technique. Others focused on the change of the build orientation only in regards to the productivity aspects (i.e. production time, reduced waste from supporting structures) and not on the influence on the part’s mechanical properties [18, 19]. C.W. Zieman et al. studied the stiffness degradation caused by fatigue damage on ABS parts obtained by FDM (Fused Deposition Modeling). Cyclical tension fatigue tests were conducted to evaluate stiffness-based damage. The authors managed to accurately model the accumulated damage on FDM samples, excepting the last 5% of fatigue life [20]. J. F. Rodriguez also developed an analytical model for the fused deposition material stiffness and strength as a function of mesostructural parameters. A maximum 10 percent difference between the experimental and the theoretical values is reported [11]. T. McLouth et al. reported their research concerning the influence of the print orientation and raster orientation on the part’s facture toughness. However, the material they referred to is again ABS. Samples printed in the ZXY and XYZ directions contained half or more of their filaments in a direction that was orthogonal to the crack plane, which resulted in a significant obstacle to crack propagation [21]. The specific literature related to selective laser sintering, selective laser melting or powder bed fusion techniques states that a certain material will develop different mechanical properties depending on how the part is oriented and processed on a certain device, therefore the same material could exhibit different properties as function of the build orientation [1, 4, 18]. The present article aims to establish the influence of the building orientation on the mechanical properties of PLA specimens fabricated on a FFF machine, taking into consideration that the state-of-the-art on this specific area is, to date, very limited. 2. Materials and methods Polylactic acid specimens were 3D printed on a CreatBot DX FFF machine. The extrusion temperature was kept at 225 °C, with the platform surface heated at 60 °C for all samples. The printer has two nozzles extrusion system mounted on a cartesian axis setup. For this case only one of them was used. PLA filaments were mounted on a spool and processed into a heated nozzle (0.6 mm diameter) and extruded onto the heated platform. Natural PLA filament with a diameter of 2.85 mm was used, supplied by Zortrax. The printing speed was 50 mm/s while the thickness of the printing layer was 0.2 mm. Tensile strength test specimens were created as shown in figure 1, with the
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C. Gabor et al. / Materials Today: Proceedings 19 (2019) 1008–1013
following construction angle values: 0, 15, 30, 45, 60, 90 degrees on edge and flat positioning of the sample. The same printing protocol was used for the bending test specimens. The dimensions (in mm) of the specimens (presented in figure 2) were chosen according to ISO 604:2002, ISO 527:2012 and ISO 178:2019 for compressive, tensile and flexural testing, respectively. The geometry of the samples was created with the help of a computer aided design (CAD) software (SolidWorks 2016), exported as a stereolithography file (STL) and imported into a slicing software (CreatWare v.6.4.6). Tensile strength, bending strength and compressive strength were determined on a WDW – 150S universal testing machine. Tensile strength was determined according to ISO 527-2-2012 – Plastics - Determination of Tensile Properties. The three-point bending test was used to assess the flexural strength, according to ISO 178-2019 – Plastics – Determination of Flexural Properties. The presented values are the average of five measurements that were performed for each type of specimen.
a
b
Flat
Edge
Fig. 1. Printing angles and position of the specimens designated to tensile strength tests (a) and compressive tests (b).
unit: mm
Fig. 2. Samples dimensions: a) for bending tests, b) for traction tests and c) for compression tests.
C. Gabor et al. / Materials Today: Proceedings 19 (2019) 1008–1013
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3. Results and discussions The strength of the FFF printed specimens depends on several factors: part build orientation, raster angle, raster width and raster to raster gap [15]. According to the literature [15, 22], part build orientation refers to the inclination of a part in a building platform with respect to X, Y, and Z axes, while the raster angle is the direction of raster relative to the X-axis in reference to the build table. As follows, the influence of the printing angle (figure 1) on the tensile, compressive and flexural strength of the PLA specimens is analyzed. The obtained results are presented in Table 1. Table 1. Tensile, compressive and flexural strength of the specimens printed with different orientation angles. Tensile strength [MPa]
Flexural strength [MPa]
Printing angle
Compressive strength [MPa]
[degrees]
Value
St. dev.
Value
St. dev.
Value
St. dev.
Value
St. dev.
Value
St. dev.
0
81.50
2.30
45.00
1.00
49.80
2.17
230.00
0.00
208.40
11.72
15
79.00
4.16
37.25
3.59
44.80
5.45
166.00
0.00
234.00
8.94
30
76.50
4.55
30.25
8.85
42.60
4.04
135.80
12.40
211.40
17.67
45
78.50
6.16
38.80
1.30
38.00
3.92
142.60
18.90
214.75
12.66
60
85.00
1.83
32.33
11.85
25.25
8.26
145.80
18.21
165.80
11.67
90
78.00
1.83
21.50
1.29
21.50
1.29
159.20
9.31
159.20
9.31
Flat
Edge
Flat
Edge
The printing angle of the specimens allows one to obtain different transverse isotropic planes, taking into account the layer-by-layer construction type method used to manufacture the samples. Therefore, in the case of tensile strength, one should consider that the printing angle is in fact the angle between the direction of applied force and the vertical growth direction of the specimens during the printing process. Figure 3 shows the variation of the tensile strength values as a function of the build orientation angle. The obtained results show that for both flat and edge printed specimens the best behavior is obtained for 0 degrees construction angle, while the lowest value of the tensile strength is obtained for the specimens build at 90 degrees. Thus, for the flat printed specimens a 45 MPa tensile strength at break value is obtained for 0 degrees and the values decrease while the orientation angle evolves from 0 to 90 degrees, down to 21.5 MPa. A similar evolution can be noticed for the edge printed specimens. This behavior is explainable since the situation when the force acting along the longitudinal axis of the specimens is perpendicular on the printed layers is clearly the most favorable.
Fig. 3. Tensile strength as a function of the build orientation.
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C. Gabor et al. / Materials Today: Proceedings 19 (2019) 1008–1013
As expected, compressive strength was also influenced by the printing parameters, build orientation respectively. The variation of the compressive strength values is depicted in figure 4. The general tendency of the obtained results is similar to the one noticed in the case of tensile and flexural strength. Thus, the values of the compressive strength are decreasing from 81.5 to 76.5 MPa while the build orientation angle increases from 0 to 90 degrees. However, for the 60 degrees build orientation the obtained value of the compressive strength is relatively higher, namely 85 MPa. The higher compressive strength value might be influenced by a combination of factors, like the area of the isotropic planes and the value of the construction angle.
Fig. 4. Compressive strength as a function of the build orientation.
The results of the bending tests, graphically presented in figure 5, exibit a similar evolution with the tensile strength values. This behaviour is somehow expected since the orientation of the isotropic planes can work as a significant obstacle for crack propagation/breaking of the specimens when they are 3D printed at 0 degrees angle orientation. For both flat and edge printed specimens, a general decreasing tendency of the obtained flexural strength values (flat: from 230.0 to 159.2 MPa; edge: from 234.0 to 165.8 MPa ) can be noticed while the orientation angle is increasing from 0 to 90 degrees.
Fig. 5. Bending strength as a function of the build orientation.
C. Gabor et al. / Materials Today: Proceedings 19 (2019) 1008–1013
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4. Conclusions The interest regarding the development of additive manufacturing technologies shows a dramatic growth, considering that 3D printing use is shifting from rapid prototyping to part production. The printing parameters seem to have a great influence on the obtained part’s properties. The influence of the building orientation angle on the mechanical properties of 3D printed specimens from polylactic acid (PLA) with the help of a filament fusion fabrication (FFF) machine were evaluated in this study. For this purpose, multiple specimens were printed with 0, 15, 30, 45, 60, and 90 degrees angle orientation and tested afterwards for tensile, compressive and flexural strength. As expected, the mechanical properties of the specimens were influenced by the printing parameters. Thus, the specimens printed at 0 degrees angle orientation exhibit the highest values of tensile, compressive and flexural strength, due to the resulted array of the transverse isotropic planes. The strength values of the tested specimens are decreasing while the printing orientation angle is increasing from 0 to 90 degrees. Thus, in practice, in order to obtain parts with the optimal characteristics, the printing angle should be chosen depending on the loads that occur during parts operation. Acknowledgements This work was supported by a grant of the Romanian National Authority for Scientific Research and Innovation, CNCS/CCCDI - UEFISCDI, project number PN-III-P3-3.6-H2020-2016-0077, within PNCDI III. The authors also acknowledge the structural founds project PRO-DD (POS-CCE, O.2.2.1., ID 123, SMIS 2637, ctr. No 11/2009) for providing the infrastructure used in this work. References [1] J. Stansbury, M. Idacavage, 3D printing with polymers: Challenges among expanding options and opportunities, Dent. Mater. 32 (2016) 54– 64. [2] A. Ambrosi, M. Pumera, 3D-printing technologies for electrochemical applications, Chem. Soc. Rev., 45 (2016) 2740-2755. [3] L.E. Murr, Frontiers of 3D printing/additive manufacturing: from human organs to aircraft fabrication, J. Mater. Sci. Technol. 32 (2016) 987– 995. [4] E. Lepowsky, S. Tasoglu, 3D printing for drug manufacturing: A perspective on the future of pharmaceuticals, Int J Bioprint 4 (2018). [5] Z. Chen, Z. Li, J. Li, C. Liu, C. Lao, Y. Fu, C. Liu, Y. Li, P. Wang, Y. He, 3D printing of ceramics: A review, J. Eur. Ceram. Soc. 39 (2019) 661-687. [6] DC. Neckers, Stereolithography – an introduction, Chemtech 20 (1990) 615–619. [7] D.T. Pham, S.S. Dimov, Rapid prototyping and rapid tooling – the key enablers for rapid manufacturing. Proc. Inst. Mech. Eng. C: J. Mech. Eng. Sci. 217 (2003) 1-23. [8] C. Balletti, M. Ballarin, F. Guerra, 3D printing: State of the art and future perspectives. J. Cult. Herit. 26 (2017) 172–182. [9] N. Guo, M. C. Leu, Additive manufacturing: technology, applications and research needs, Front. Mech. Eng. 8 (2013) 215–243. [10] T. Serra, MA. Mateos-Timoneda, JA. Planell, M. Navarro, 3Dprinted PLA-based scaffolds: a versatile tool in regenerative medicine, Organogenesis 9 (2013) 239–244. [11] J. Rodriguez, J. Thomas, J. Renaud, Mechanical behavior of acrylonitrile butadiene styrene fused deposition materials modeling, Rapid Prototyp. 9 (2003) 219–230. [12] M. Hebda, C. McIlroy, B. Whiteside, F. Caton-Rose, P. Coates, A method for predicting geometric characteristics of polymer deposition during fused-filament-fabrication, Additive Manufacturing 27 (2019) 99–108. [13] C. Ziemian, M. Sharma, S. Ziemian, Anisotropic Mechanical Properties of ABS Parts Fabricated by Fused Deposition Modelling, M. Gokcek (Ed.), Mechanical Engineering, InTech, 2012, ISBN: 978–953–51-0505-3. [14] S. Ahn, M.Montero, D. Odell, S. Roundy, P.Wright, Anisotropicmaterial properties of fused deposition modeling ABS, Rapid Prototyp. J. 8 (2002) 248–257. [15] A. Sood, R. Ohdar, S. Mahapatra, Parametric appraisal of mechanical property of fused deposition modelling processed parts, Mater. Des. 31 (2010) 287–295. [16] S.N. Ziemian, M.N. Okwara, C.W. Ziemian, Tensile and fatigue behavior of layered acrylonitrile butadiene styrene, Rapid Prototyp. J. 21 (2015) 270–278. [17] A. Leicht, U. Klement, E. Hryha, Effect of build geometry on the microstructural development of 316L parts produced by additive manufacturing, Mater. Charact. 143 (2018) 137–143. [18] M. Zwier, W. Wits, Design for additive manufacturing: Automated build orientation selection and optimization, Procedia CIRP 55 (2016) 128 – 133. [19] B. Leutenecker-Twelsiek, C. Klahn, M. Meboldt, Considering Part Orientation in Design for Additive Manufacturing, Procedia CIRP 50 (2016) 408 – 413. [20] C.W. Ziemian, R.D. Ziemian, K.V. Haile, Characterization of stiffness degradation caused by fatigue damage of additive manufactured parts, Mater. Design 109 (2016) 209–218. [21] T. McLouth, J. Severino, P. Adams, D. Patel, R. Zaldivar, The impact of print orientation and raster pattern on fracture toughness in additively manufactured ABS, Additive Manufacturing 18 (2017) 103–109. [22] Stratasys. FDM vantage user guide version 1.1. Minnesota: Stratasys; 2004.
ScienceDirect Materials Today: Proceedings 19 (2019) 1008–1013
www.materialstoday.com/proceedings
BraMat 2019
The optimization of the production procedure in relation to the mechanical properties of additively manufactured parts Camelia Gabora,*, Mihai Alin Popa, Donato Maglib, Tibor Bedoa, Sorin Ion Munteanua, Daniel Munteanua a
Transilvania University of Brasov, Material Science Department, 29 Eroilor Blvd., 500036, Brasov, Romania University of Modena and Reggio Emilia, Materials Engineering Faculty, 10 Vivarelli, 41125, Modena, Italy
b
Abstract Additive manufacturing (AM) is a type of production technology which consists of stacking and unifying individual layers, to form a three-dimensional part with complex geometry, usually unobtainable by other means of production. Due to its working principle, i.e. stacking layers, the mechanical characteristics of the built part could be influenced by the construction angle. For metallic additively manufactured parts, it was reported that the mechanical behavior, cyclic deformation and fatigue behaviors are clearly influenced by the build orientation. To date, the number of reports concerning the mechanical behavior of polymer AM parts is relatively limited. Hence, the aim of this study was to assess whether the build orientation will have an impact on the traction and compression characteristics of standard samples built by FFF (Fused Filament Fabrication), from polylactic acid filament. Samples were built at various inclination degrees. It was observed that the build orientation has a significant effect on the mechanical properties of parts, better behavior being observed for the specimens printed at 0 degrees building orientation. © 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the 11th International Conference on Materials Science & Engineering, BraMat 2019 Keywords: fused filament deposition; construction angle; precursor material.
1. Introduction Additive manufacturing (AM) is a highly flexible processing method, introduced about 30 years ago, that enables fabrication of complex structures that are otherwise difficult to obtain through forming or subtractive technologies.
* Corresponding author. Tel.: +40-732-148472. E-mail address: [email protected] 2214-7853 © 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the 11th International Conference on Materials Science & Engineering, BraMat 2019
C. Gabor et al. / Materials Today: Proceedings 19 (2019) 1008–1013
1009
The accessibility of 3D printers is continuously growing for both industrial and general public use [1] while 3D printed components can be found in automotive engineering, civil engineering, aerospace, biomedical and other applications [2-4]. As the name implies, the parts are created in a point-by-point, line-by-line or layer-by-layer additive manner from 3D CAD models [5]. 3D printing technologies offer major advantages such as fabrication without retooling, increased design freedom with complex geometries, and flexible process parameters [2]. The AM technologies have evolved continuously from the stereolithography technique (SLA), with a photopolymerization-based building approach [6], to selective laser sintering (SLS) with a large and growing palette of polymers available, or binder jetting process (the method that launched the 3D printing term, which later extended to other technologies) [1]. AM applications evolved from rapid prototype fabrication to rapid tooling and rapid manufacturing [7]. One of the most widely used techniques [8], filament fused fabrication (FFF) also known as fused deposition modeling (FDM), was developed in the early 90’s. This technique involves one or more heated nozzles that melt and distribute the extruded polymer as a fine filament in the layer-by-layer building approach, using a three-axes translatable platform [1]. The working space can be introduced within a heated chamber in order to reduce the thermal distortion that appears due to non-uniform cooling. Acrylonitrile butadiene styrene (ABS) and polylactic acid (PLA) are used on most FFF devices but the range of available materials is very wide, including polyamides, polycarbonate, polystyrene, etc. [9]. It must be mentioned that PLA is often used for biomedical 3D printing purposes [10], due to its non-toxic nature towards cells and tissues. Most of the research conducted in solid freeform fabrication technologies are related to understanding the process itself rather than modeling the mechanical properties of the resulting parts [11, 12]. Moreover, many of the studies found in the literature were conducted on ABS [12, 13-16] and even more on other AM techniques [17, 18], compared to the method presented herein, namely the FFF technique. Others focused on the change of the build orientation only in regards to the productivity aspects (i.e. production time, reduced waste from supporting structures) and not on the influence on the part’s mechanical properties [18, 19]. C.W. Zieman et al. studied the stiffness degradation caused by fatigue damage on ABS parts obtained by FDM (Fused Deposition Modeling). Cyclical tension fatigue tests were conducted to evaluate stiffness-based damage. The authors managed to accurately model the accumulated damage on FDM samples, excepting the last 5% of fatigue life [20]. J. F. Rodriguez also developed an analytical model for the fused deposition material stiffness and strength as a function of mesostructural parameters. A maximum 10 percent difference between the experimental and the theoretical values is reported [11]. T. McLouth et al. reported their research concerning the influence of the print orientation and raster orientation on the part’s facture toughness. However, the material they referred to is again ABS. Samples printed in the ZXY and XYZ directions contained half or more of their filaments in a direction that was orthogonal to the crack plane, which resulted in a significant obstacle to crack propagation [21]. The specific literature related to selective laser sintering, selective laser melting or powder bed fusion techniques states that a certain material will develop different mechanical properties depending on how the part is oriented and processed on a certain device, therefore the same material could exhibit different properties as function of the build orientation [1, 4, 18]. The present article aims to establish the influence of the building orientation on the mechanical properties of PLA specimens fabricated on a FFF machine, taking into consideration that the state-of-the-art on this specific area is, to date, very limited. 2. Materials and methods Polylactic acid specimens were 3D printed on a CreatBot DX FFF machine. The extrusion temperature was kept at 225 °C, with the platform surface heated at 60 °C for all samples. The printer has two nozzles extrusion system mounted on a cartesian axis setup. For this case only one of them was used. PLA filaments were mounted on a spool and processed into a heated nozzle (0.6 mm diameter) and extruded onto the heated platform. Natural PLA filament with a diameter of 2.85 mm was used, supplied by Zortrax. The printing speed was 50 mm/s while the thickness of the printing layer was 0.2 mm. Tensile strength test specimens were created as shown in figure 1, with the
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C. Gabor et al. / Materials Today: Proceedings 19 (2019) 1008–1013
following construction angle values: 0, 15, 30, 45, 60, 90 degrees on edge and flat positioning of the sample. The same printing protocol was used for the bending test specimens. The dimensions (in mm) of the specimens (presented in figure 2) were chosen according to ISO 604:2002, ISO 527:2012 and ISO 178:2019 for compressive, tensile and flexural testing, respectively. The geometry of the samples was created with the help of a computer aided design (CAD) software (SolidWorks 2016), exported as a stereolithography file (STL) and imported into a slicing software (CreatWare v.6.4.6). Tensile strength, bending strength and compressive strength were determined on a WDW – 150S universal testing machine. Tensile strength was determined according to ISO 527-2-2012 – Plastics - Determination of Tensile Properties. The three-point bending test was used to assess the flexural strength, according to ISO 178-2019 – Plastics – Determination of Flexural Properties. The presented values are the average of five measurements that were performed for each type of specimen.
a
b
Flat
Edge
Fig. 1. Printing angles and position of the specimens designated to tensile strength tests (a) and compressive tests (b).
unit: mm
Fig. 2. Samples dimensions: a) for bending tests, b) for traction tests and c) for compression tests.
C. Gabor et al. / Materials Today: Proceedings 19 (2019) 1008–1013
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3. Results and discussions The strength of the FFF printed specimens depends on several factors: part build orientation, raster angle, raster width and raster to raster gap [15]. According to the literature [15, 22], part build orientation refers to the inclination of a part in a building platform with respect to X, Y, and Z axes, while the raster angle is the direction of raster relative to the X-axis in reference to the build table. As follows, the influence of the printing angle (figure 1) on the tensile, compressive and flexural strength of the PLA specimens is analyzed. The obtained results are presented in Table 1. Table 1. Tensile, compressive and flexural strength of the specimens printed with different orientation angles. Tensile strength [MPa]
Flexural strength [MPa]
Printing angle
Compressive strength [MPa]
[degrees]
Value
St. dev.
Value
St. dev.
Value
St. dev.
Value
St. dev.
Value
St. dev.
0
81.50
2.30
45.00
1.00
49.80
2.17
230.00
0.00
208.40
11.72
15
79.00
4.16
37.25
3.59
44.80
5.45
166.00
0.00
234.00
8.94
30
76.50
4.55
30.25
8.85
42.60
4.04
135.80
12.40
211.40
17.67
45
78.50
6.16
38.80
1.30
38.00
3.92
142.60
18.90
214.75
12.66
60
85.00
1.83
32.33
11.85
25.25
8.26
145.80
18.21
165.80
11.67
90
78.00
1.83
21.50
1.29
21.50
1.29
159.20
9.31
159.20
9.31
Flat
Edge
Flat
Edge
The printing angle of the specimens allows one to obtain different transverse isotropic planes, taking into account the layer-by-layer construction type method used to manufacture the samples. Therefore, in the case of tensile strength, one should consider that the printing angle is in fact the angle between the direction of applied force and the vertical growth direction of the specimens during the printing process. Figure 3 shows the variation of the tensile strength values as a function of the build orientation angle. The obtained results show that for both flat and edge printed specimens the best behavior is obtained for 0 degrees construction angle, while the lowest value of the tensile strength is obtained for the specimens build at 90 degrees. Thus, for the flat printed specimens a 45 MPa tensile strength at break value is obtained for 0 degrees and the values decrease while the orientation angle evolves from 0 to 90 degrees, down to 21.5 MPa. A similar evolution can be noticed for the edge printed specimens. This behavior is explainable since the situation when the force acting along the longitudinal axis of the specimens is perpendicular on the printed layers is clearly the most favorable.
Fig. 3. Tensile strength as a function of the build orientation.
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C. Gabor et al. / Materials Today: Proceedings 19 (2019) 1008–1013
As expected, compressive strength was also influenced by the printing parameters, build orientation respectively. The variation of the compressive strength values is depicted in figure 4. The general tendency of the obtained results is similar to the one noticed in the case of tensile and flexural strength. Thus, the values of the compressive strength are decreasing from 81.5 to 76.5 MPa while the build orientation angle increases from 0 to 90 degrees. However, for the 60 degrees build orientation the obtained value of the compressive strength is relatively higher, namely 85 MPa. The higher compressive strength value might be influenced by a combination of factors, like the area of the isotropic planes and the value of the construction angle.
Fig. 4. Compressive strength as a function of the build orientation.
The results of the bending tests, graphically presented in figure 5, exibit a similar evolution with the tensile strength values. This behaviour is somehow expected since the orientation of the isotropic planes can work as a significant obstacle for crack propagation/breaking of the specimens when they are 3D printed at 0 degrees angle orientation. For both flat and edge printed specimens, a general decreasing tendency of the obtained flexural strength values (flat: from 230.0 to 159.2 MPa; edge: from 234.0 to 165.8 MPa ) can be noticed while the orientation angle is increasing from 0 to 90 degrees.
Fig. 5. Bending strength as a function of the build orientation.
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4. Conclusions The interest regarding the development of additive manufacturing technologies shows a dramatic growth, considering that 3D printing use is shifting from rapid prototyping to part production. The printing parameters seem to have a great influence on the obtained part’s properties. The influence of the building orientation angle on the mechanical properties of 3D printed specimens from polylactic acid (PLA) with the help of a filament fusion fabrication (FFF) machine were evaluated in this study. For this purpose, multiple specimens were printed with 0, 15, 30, 45, 60, and 90 degrees angle orientation and tested afterwards for tensile, compressive and flexural strength. As expected, the mechanical properties of the specimens were influenced by the printing parameters. Thus, the specimens printed at 0 degrees angle orientation exhibit the highest values of tensile, compressive and flexural strength, due to the resulted array of the transverse isotropic planes. The strength values of the tested specimens are decreasing while the printing orientation angle is increasing from 0 to 90 degrees. Thus, in practice, in order to obtain parts with the optimal characteristics, the printing angle should be chosen depending on the loads that occur during parts operation. Acknowledgements This work was supported by a grant of the Romanian National Authority for Scientific Research and Innovation, CNCS/CCCDI - UEFISCDI, project number PN-III-P3-3.6-H2020-2016-0077, within PNCDI III. The authors also acknowledge the structural founds project PRO-DD (POS-CCE, O.2.2.1., ID 123, SMIS 2637, ctr. No 11/2009) for providing the infrastructure used in this work. References [1] J. Stansbury, M. Idacavage, 3D printing with polymers: Challenges among expanding options and opportunities, Dent. Mater. 32 (2016) 54– 64. [2] A. Ambrosi, M. Pumera, 3D-printing technologies for electrochemical applications, Chem. Soc. Rev., 45 (2016) 2740-2755. [3] L.E. 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