Determination of optimum printing direction of the polycarbonate parts produced by additive manufacturing

In this study, the effect of printing direction on the tensile properties of polycarbonate (PC) parts produced using a 3D printer was investigated. A total of 9 samples were produced with printing directions of 0°, 45° and 90° with infill density of 20%. Tensile tests were carried out to determine the maximum tensile strength (UTS) of the samples. As a result of the research, it was determined that the samples produced in the same direction as the tensile direction (0° printing direction) had the highest strength values; on the other hand, samples produced in the 90° printing direction have the lowest strength values. While the ultimate tensile strength values for samples produced in 0° printing direction were measured respectively as 22.4 MPa, 21.6 MPa and 20.7 MPa; as 7.1 MPa, 9.1 MPa and 9.2 MPa in 45° printing direction; it was determined as 7.2 MPa, 5.4 MPa and 5.8 MPa in the 90° printing direction. In addition, UTS/mass ratios were calculated by measuring the mass of the samples after the tensile test. According to the results obtained, samples in the 0° printing direction have the highest UTS/mass ratio compared to other printing directions, making them the most durable option for applications requiring lightweight structures. Tensile samples produced in FDM were analyzed with the finite element method (FEM) and analysis results were found to be equivalent to physical tests. This study contributes to examination of the influence of 3D printing direction, especially exposed to tensile, on material properties, and provides important information for the production of lightweight and high strength PC components in industries such as medicine, aerospace and automotive.


Introduction
Increasing technological innovations in the manufacturing sector, like many other sectors, play an important role in shortening the time to market for products and enabling companies to remain competitive.Additive manufacturing (AM) methods, which emerged in the 1980s, were initially called rapid prototyping because they were used for prototype production.Nowadays, it is called additive manufacturing because of its widespread use in the production of functional parts.The general principle of this manufacturing method is to obtain a product by adding material layer by layer using 3D geometric data [1].Although the basic principle of additive manufacturing is the same, many technologies that manufacture differently from each other have been developed.Additive manufacturing, which is a modern manufacturing method, has many advantages compared to traditional manufacturing.One of these advantages is that it does not create environmental pollution.Unlike traditional manufacturing methods such as casting and turning, there is no waste or manufacturing method related environmental pollution during or after manufacturing [2].Another advantage is that it is suitable for the production of complex-shaped parts.Complex-shaped parts that are difficult to obtain with traditional manufacturing methods can be easily and quickly manufactured.Additive manufacturing has good potential to reduce both the production time and cost of a product [2,3].The use of additive manufacturing technologies is becoming increasingly widespread in many sectors such as medicine, dentistry, aerospace, automotive, and jewelry.
Additive manufacturing can be used with many methods, and the differences between the methods are generally related to how the layers are created.Stereolithography (SLA), Fused Deposition Modeling (FDM), Selective Laser Sintering (SLS), Selective Laser Melting (SLM), Direct Metal Laser Sintering (DMLS), Electron Beam Melting (EBM), Binder Jetting (BJ), Multi Jet Fusion (MJF), Laminated Object Manufacturing (LOM), and Digital Light Processing (DLP) technologies are among the most commonly used technologies for additive manufacturing.
FDM, also known as 3D printing, is widely used in industry as well as in research and academic studies.Thanks to this technology, the preliminary prototype of designs can be produced easily and quickly.In the FDM technique, thermoplastic material is used as the raw material and fed into the device as a thin plastic filament wound onto a spool.The filament fed to the nozzle with a series of controlled drive mechanisms is melted by temperature when it reaches the nozzle and brought to a semi-molten state.The melted plastic material is extruded onto the surface in a thin layer from a fine nozzle on the extrusion head that can move in two axes with computer-aided manufacturing (CAM) software, creating layers.The table moves one step down for each layer, and thus the part is built in layers.When the melted material is spread on the surface, it solidifies, and when the construction of all layers is completed, the part is removed from the table [1][2][3][4].A support structure is also created during construction when needed, and the support is removed from the part after the manufacturing is completed.Most of the additive manufacturing processes are environmentally friendly and do not require chips or molds compared to traditional manufacturing methods such as turning, milling, casting, and plastic shaping [2].This method, also known as 3D printing, allows the production of complex-shaped, low-weight parts and provides significant savings in resources.
The most commonly used materials in additive manufacturing methods are PLA, ABS, PC and PP.The 3D printer material used in the study is PC, which is also known as an engineering thermoplastic due to its durability, hardness, lightness, and transparency.PC has a high mechanical strength and high dimensional stability due to its amorphous polymer chain structure [1].
3D printing is a complex process with many parameters that affect product quality and material properties, and these parameters can be difficult to understand.Process parameters such as layer thickness, printing direction, air gap, feed rate, printing angle, printing width, and fill density have a significant effect on the quality and performance of 3D printed parts [5,6].In this technique, mechanical properties have a significant effect on functional parts, and the effects of process parameters on mechanical properties need to be investigated.Some researchers have conducted studies on the printing parameters of 3D printers, especially those related to additive manufacturing technologies.
A study was conducted focusing on the traditional use of Polymer Additive Manufacturing (PAM) technology for rapid prototyping operations.However, it notes that the use of PAM components as functional parts is still more common than injection molded components.This is due to uncertainties regarding mechanical properties and the current lack of knowledge about PAM products.In the study, a new additive manufacturing technology, inspired by injection molding technology and creating plastic parts by depositing polymer droplets in layers, was integrated into the Arburg machine in free form.In this research, the mechanical characterization of thermoplastic polymer parts obtained by Arburg plastic free forming and injection molding, a conventional process, was examined.Tensile mechanical properties were evaluated by changing some production parameters such as printing direction [5].This study investigates the application of PEEK as a high-performance material in FDM-type 3D printing, an area traditionally dominated by materials such as ABS and PLA.The reason behind the investigation of PEEK is its potential to overcome the limitations posed by materials more commonly used in FDM processes, particularly in terms of mechanical strength and performance under stress.The study results show that the average tensile strength of PEEK parts is 108% higher than that of ABS parts, their compressive strength is 114% and their bending strength is 115% [6].Samples produced using ABS P430 filament were subjected to bending, compression, and tensile tests.While no significant difference was observed in tensile strength, the compression and bending strength were highest at 0 degrees XY, with the 45 degrees XY exhibiting the lowest strength.This research contributes significantly to the understanding of how build orientation influences the mechanical properties of ABS parts in additive manufacturing [7].In experiments with ABS material, samples with a printing angle of 45°were found to have higher tensile strength, while samples with a 0°/ 90°angle had a higher elastic modulus.This research highlights that PLA produced by open source RepRap 3D printers has higher values than ABS in terms of tensile strength and hardness [8].A study focused on determining the mechanical properties of maraging steel produced by laser additive manufacturing for two printing directions (0°and 90°) revealed that the tensile properties were higher in the 90°printing direction.Additionally, microstructural analyses using scanning electron microscopy were conducted on the fracture surface to observe material defects and pores.This work facilitates to provide a better understanding of the selection of scan direction patterns for fabrication of better quality MS parts using the DMLS AM process [9].The effects of printing orientation on PLA material were examined, and in a comparison between 0/90°and ± 45°, the tensile strength value for the 0/90°printing orientation was approximately 17% stronger.This paper aims to determine the influence of 3D printing parameters [10].Investigating samples produced at different printing angles using 3D printing technology, it was found that mechanical properties varied depending on these printing angles, with the 0°printing orientation demonstrating higher strength compared to 45°and 90°.The research suggests a practical approach to recycling PLA materials, enhancing the sustainability of 3D printing practices [11].PLA filaments were produced in three different orientations: flat, on edge, and upright, and subjected to tensile and three-point bending tests.According to the test results, the tensile test values were on edge (66.5 MPa), flat (49.5 MPa), and upright (26.1 MPa), while the bending test values were on edge (98.6 MPa), flat (93.5 MPa), and upright (42.3 MPa).Due to the layer-by-layer process, 3D printed samples exhibit anisotropic behaviour.Upright orientation shows the lowest mechanical properties.On the other hand, on-edge and flat orientation show the highest strength and stiffness.From a layer thickness and feed rate point of view, it is observed that ductility decreases as layer thickness and feed rate increase.In addition, the mechanical properties increase as layer thickness increases and decrease as the feed rate increases for the upright orientation.However, the variations in mechanical properties with layer thickness and feed rate are of slight significance for on-edge and flat orientations, except in the particular case of low layer thickness [12].To confirm the effect of moisture content in PLA material on mechanical properties, production was carried out with three different printing angles (0°, 45°, and 90°).It was determined that samples with a 90°printing angle and 10% moisture content exhibited optimal strength and strain mechanical properties.This study sheds light on the importance of manufacturing parameters in the FDM process, demonstrating that both raster angle and moisture content significantly impact the mechanical properties of PLA materials [13].Studies have also investigated the microstructure and fatigue behavior of samples produced with different printing angles (0°, 45°, 90°) using the SLM method.By identifying the significant impact of post heat treatment and the relatively minor influence of build orientation on fatigue performance, the study offers practical guidelines for enhancing the durability of additive manufactured components [14].In addition to printing orientation, it is known that other parameters such as nozzle size, thickness, and positioning can significantly influence the mechanical properties of PC parts produced through additive manufacturing.Additionally, a finite element method (FEM) simulation was performed in the research.It was concluded that the results obtained were equivalent to physical tests [15].While layer thickness has little effect on the mechanical performance of PP samples, the fill degree has a noticeable and linear impact on the mechanical properties of the samples.The results showed the potential of the FDM to compete with conventional techniques, especially for the production of small series of parts/components; also, it was showed that this technique allows the production of parts with adequate mechanical performance and, therefore, does not need to be restricted to the production of mockups and prototypes [16].In another study, PC filament was manufactured and utilized to 3D print tensile test specimens for the optimization of two 3D printing parameters (temperature and layer height) in relation to the UTS and the elastic modulus.The maximum value for UTS and E, which are 3D printer operating parameters, was obtained at a layer height of 0.2 mm and a nozzle temperature of 270 °C [17].Experimental techniques and results for the mechanical characterization of ABS and PC 3D printed parts to determine the anisotropy of sliding properties were examined.Because of the anisotropy, tensile material properties cannot be used to determine shear properties.Iosipescu shear specimens were manufactured at various print raster ([+ 45/−45], [+ 30/−60], [+ 15/−75], and [0/90]) and build orientations (flat, on-edge, and upright) to determine the directional properties of both ABS and PC samples.The ABS samples exhibited strong anisotropy as a function of build orientation while the PC samples exhibited strong anisotropy as a function of raster orientation [18].
The aim of the study is to provide accurate and precise information to determine the optimum printing direction of the PC produced with infill density of 20% in the 3D printer.In this context, the effect of printing orientation (0°, 45°, 90°) on the tensile mechanical properties of PC filament is investigated, keeping other process parameters constant.
When the above literature is examined, while most studies focus on different printing directions and parameters of more commonly used materials such as ABS and PLA, this study focuses on PC material, which has an important place in industrial applications and has higher mechanical properties.In addition, the study provides important information for the production of parts with high UTS/mass ratio, especially for use in sectors such as medicine, aerospace and automotive that require lightweight structures.By comparing FEM analyzes with physical test results, the study also confirms the effects of 3D printing technology and material selection on mechanical performance.This increases the accuracy of engineering decisions in design processes.

FDM (fused deposition modeling) technology
Among 3D printing technologies, additive manufacturing is the most preferred in terms of durability, dimensional stability, and applicability.Initially, a CAD model of the part to be produced is created in a computer-aided design (CAD) environment.To transfer the CAD model to the 3D printer, it needs to be converted to the .STL format.Once converted to this format, the model undergoes a slicing technique to generate G codes.The 3D printer then constructs the part layer by layer according to the specified G codes [15,16].This technique is commonly applied to thermoplastic materials and is also known as FDM.
The thermoplastic material, in the form of filament produced from granules, is transferred to the nozzle with the help of an extruder (feeding head).The filament, reaching the glassy transition temperature at the nozzle, accumulates on the heated build platform, gradually forming the part [1]. Figure 1 shows a schematic of the FDM technology, which is one of the additive manufacturing technologies used in this study.

Material and method
In the scope of this study, Ultimaker brand PC printing filament is preferred for its high hardness, low density, resistance to temperature, and strong interlayer adhesion properties, with the aim of supporting the internal structure of machine elements subjected to tension.The mechanical and physical properties of the PC filament to be used in the study are provided in table 1.
The tensile specimens within the scope of the study were produced according to the ASTM D638-14 standard, which is applicable to plastic materials, with the aim of determining the optimum printing direction for the strength of PC material.Figure 2 shows the technical drawing used for this standard.Other processing parameters were kept constant to investigate their impact on the mechanical properties during the 3D printing of tensile specimens.
The specimens were produced using the Raise3D brand Pro 2 Plus model 3D printer with 0.4 mm diameter nozzle as shown in figure 3. FDM printing technology was chosen to be compatible with the selected 3D printing technique.The filament transferred from the spool to the extruder creates the desired specimen layer by layer, depending on the defined working parameters.
During the production of the part, nozzle temperature and bed temperature are important parameters that affect efficiency.The nozzle temperature should be higher than the glass transition temperature of the transferred filament.Additionally, the optimum bed temperature needs to be determined for the filament to adhere to the bed and create support.Table 2 provides the selected 3D printer technical specifications, taking these parameters into account.In this study, printing direction has been changed while preserving other parameters such as infill pattern and density, print speed, layer height, printing and bed temperature.The dimensions of the device used in the study are 620 mm × 590 mm × 1105 mm, and the print bed size is 305 mm × 305 mm × 605 mm.
The printing orientations of the tensile specimens were created in three different directions (0°, 45°, 90°) with infill density 20% and grid pattern, as shown in figure 4, and as seen in figure 5, three samples were produced for each printing direction.
In order to determine the mechanical properties of PC specimens produced in different printing directions according to ASTM-D638-14 standard, tensile tests were conducted.For the experiment, an Alarge brand AL-UN 100 model with a 100 kN capacity tensile testing machine was used.The tests were conducted at room temperature (23 ± 2 °C) with a test speed of 1 mm min −1 .
After the tensile test, the mass of the samples was measured to determine the stability of the manufacturing method.The mass values of each sample were measured with an SF 400C Plus digital precision balance (with a precision of 0.001 grams) at 23 ± 2 °C room temperature and 45 ± 10% relative humidity.FEM simulation was performed to model the behavior of PC tensile samples, as shown in figure 6.A geometrically simple tensile was designed in order to present a complex stress state mesh when tested.The auto mesh was created during the analysis of static stresses.Using the Solidworks simulation system, a simple loading analysis was performed using static structural analysis to evaluate whether the printed tensile specimens can withstand the load of 1000 N in the X direction operated on them.The model considered was for maximum size

Results and discussions
In this study, tensile specimens with different printing directions (0°, 45°, 90°) with of 20% were produced using an FDM type 3D printer, and the effects of the printing direction on the tensile strength of the specimens were investigated.The tensile diagrams of the specimens produced with a 0°printing direction are shown in figure 7.
The maximum tensile stress values of the specimens produced with a 0°printing direction are obtained as 22.4 MPa, 21.6 MPa, and 20.7, as shown in table 3. Since this printing direction is in the same direction as the   tensile force, it can be interpreted as the direction where the interlayer bond is strongest and the material shows the best performance under load.These results emphasize that the stress direction should be chosen strategically in the design of load-bearing parts.
The tensile diagrams of the specimens produced with a 45°printing direction are shown in figure 8.The maximum tensile stress values of the specimens produced with a 45°printing direction are obtained as 7.1 MPa, 9.1 MPa, and 9.2 MPa, as shown in table 4.These values are significantly lower than in the 0°direction, but ductile behavior is still observed in these samples.This indicates that they may undergo some plastic deformation under load but still elastic before sudden fracture occurs.
The tensile diagrams of the specimens produced with a 90°printing direction are shown in figure 9.
The maximum tensile stress values of the specimens produced with a 90°printing direction are obtained as 7.2 MPa, 5.4 MPa ve 5.8 MPa, as shown in table 5.This direction, especially in the tensile direction, shows the lowest strength and brittle material behavior due to the absence of filaments.The weak bond between layers leads to direct separation of layers under tensile force.
The best results in terms of maximum tensile strength were obtained from specimens with a 0°printing direction.Samples with 0°and 45°printing directions exhibited ductile material behavior, while samples with a 90°printing direction showed brittle material behavior.This is because, in samples with a 90°printing direction, there are no filaments in the tensile direction, leading to the direct fracture of filament layers.
The fractured states of the specimens produced with 0°, 45°, and 90°printing directions after the tensile test are showed in figure 10, and the mass values are presented in table 6.It was observed that the mass values of the specimens did not differ significantly.However, it was determined that the tensile strength (UTS)/mass ratio varied with the printing directions of the specimens.A higher (UTS)/ mass ratio indicates that a material is stronger relative to its weight.In this case, the 0°printing direction has the highest (UTS)/mass ratio, indicating that it is the most durable among the three printing directions.
Two output responses, stress and displacement have been analyzed in static analysis with FEM for 0°, 45°a nd 90°printing direction, shown in figures 11, 12 and 13 respectively.The blue color region represents the area of low stress and the red region represents the area of high stress.The maximum stress coincided with the node on the support and was 78.03 MPa, 61.31 MPa and 44.08 MPa respectively for 0°, 45°and 90°printing direction.
The blue color region represents the less displacement and the greater displacement is the red region.The maximum displacement occurred as 1.663 mm, 1.568 mm and 1.221 mm respectively for 0°, 45°and 90°p rinting direction on the surfaces where the tension occurred respectively for 0°, 45°and 90°printing direction.The results of FEM simulation shows the displacement of the part from its original position is much lesser than the 2 mm in the direction of the force exerted was noticed.It means the applied maximum is also safe for the design of the part.

Conclusions
This study shows the impact of 3D printing orientation on tensile properties.According to the results, tensile strength is most influenced by the printing orientation compared to tensile stress.The highest tensile strength of the PC printing material was achieved with a 0°printing orientation.The highest tensile was observed to be 21.583MPa in the 0°printing direction.This is because the printing orientation along the loading stress direction can transfer stress at the highest level.As the printing orientation increases, tensile strength significantly decreases from 61% to 72%; the lowest tensile strength was determined to be 5.439 MPa at 90°.The reason for this is the significant reduction or absence of filaments subjected to tension in the loading direction.In addition, it is observed that the tensile strength values obtained in the study are lower than the tensile strength of the standard PC material.This is related to the filling rates of the samples printed on the 3D printer.Standard values were determined for samples printed with infill density of 100%, and the values obtained in the study were printed with infill density of 20%.In addition, specimens with 0°and 45°printing orientations behave like   ductile materials, while specimens with a 90°printing orientation exhibit brittle material behavior.The reason for this is to be the elongation of filaments in the tensile direction for specimens with 0°and 45°p rinting orientations, while specimens with a 90°printing orientation break due to the absence of filaments in the tensile direction.The 0°printing direction has the highest (UTS)/mass ratio, indicating that it is the most durable among the three printing directions.There is a clear agreement between the physical test results and FEM analysis results.Both methods showed that the 0°printing direction had the highest mechanical strength (78.03 MPa), the 45°direction showed intermediate performance (61.31MPa), and the 90°direction had the lowest strength (44.08 MPa) and displacement (12.21 mm).FEM analysis results support physical test results, especially in terms of stress and displacement, and can serve as an important tool in engineering design and material selection.This agreement confirms that FEM analysis is a reliable method for optimizing material and structural design.
It also emphasizes that in 3D printing, the printing direction has a decisive impact on the mechanical properties of the parts and that this parameter must be chosen carefully.This study reveals the importance of 3D printing parameters in the use of materials such as PC, especially for applications requiring light weight and high strength such as medical, aerospace, and automotive.
The study can be further expanded to investigate other mechanical performances of PC and other printing material.The match between FEM analysis and physical testing encourages future research to integrate simulation driven design to predict and improve part performance early in the development process.Apart from this, dynamic force analysis needs to be carried out in future by considering the various dynamics load to detect the dynamic behavior.

Figure 2 .
Figure 2. The technical drawing of the tensile test specimens.

Figure 4 .
Figure 4.The printing orientations of the tensile specimens.

Figure 6 .
Figure 6.Load state of solid model.

Figure 7 .
Figure 7. Tensile diagram of the specimens with a 0°printing direction.

Figure 8 .
Figure 8. Tensile diagram of the specimens with a 45°printing direction.

Figure 9 .
Figure 9. Tensile diagram of the specimens with a 90°printing direction.

Figure 10 .
Figure 10.Specimens of mass measurements after the tensile test.

Figure 11 .
Figure 11.(a) Stress distribution on the part, (b) Displacement distribution on the part for 0°printing direction.

Figure 12 .
Figure 12.(a) Stress distribution on the part, (b) Displacement distribution on the part for 45°printing direction.

Figure 13 .
Figure 13.(a) Stress distribution on the part, (b) Displacement distribution on the part for 90°printing direction.

Table 2 .
[20]rinter technical properties.During part meshing, 174.289 nodes and 94.514 elements were identified.The von mises stress result for baseline accuracy is used to estimate content yielding under complicated loading from the results of uniaxial tensile testing[20].

Table 3 .
The tensile test results of the specimens with a 0°printing direction.

Table 4 .
The tensile test results of the specimens with a 45°printing direction.

Table 5 .
The tensile test results of the specimens with a 90°printing direction.

Table 6 .
Mass measurements after the tensile test.