Abstract
3D printing is one of the emerging technologies in the manufacturing sector, and polymer materials play a vital role in the raw material of the additive manufacturing sector. This research explores reducing the production time by testing and analyzing the microstructure of the different polylactic acid (PLA) filament polymer samples. For this purpose, 15 pieces of ASTM (American society for testing and materials) D638 tensile samples with polylactic acid (PLA) filaments have been used exclusively with five different sets of modified process parameters in slicing software of 3D printing technology. The results of this research reveal the best PLA filament FDM production method in terms of time, mechanical strength, and FESEM analysis comparing all the results.
1. Introduction
Additive manufacturing plays a very important role in the manufacturing sector to make products with geometrical complex designs [1]. Additive manufacturing does not require huge production costs compared to conventional manufacturing, and the use of additive manufacturing in many fields is increasing day by day. An earlier literature has classified additive manufacturing into seven categories. These include vat photo polymerization, binder jetting, material jetting, material extrusion, powder bed fusion, sheet lamination, and direct energy deposition [2–4]. This allows the product to be created with multiple raw materials, especially metals, plastics, resins, etc. [5]. This research paper explores the cheapest [6] and the most widely [7] used FDM method in additive manufacturing. In particular, the PLA filament that can be used in the FDM system and how it can be used to produce better output products are explored. The FDM method is part of the extrusion process [8]. Continuous heating of a plastic filament (polylactic acid) produces a substance that is to be produced layer by layer as a thin solid-liquid form [9, 10]. Many previous researchers have studied the different filaments that can be used in FDM. Ning et al. [11] studied the mechanical properties of short carbon fiber, tensile strength, and Young’s modulus. Polyamides (PA) are made up of many nanofibers including microsphere and glass [12]. Jorge Manuel Mercado et al. explored the PLA compression uniaxial properties [13]. Fuda Ning et al. [14] and Aleksandar B Stefaniak et al. [15] explored in the carbon reinforced and nanopolymer particles. Xing Guan Zhao et al. [16] demonstrated the recycling of PLA filament with polydopamine coated.
No studies can be found on the set of printing/process parameters selected with microstructure analysis and mechanical properties analysis in the PLA material. Therefore, this paper aims at analyzing the effect of manual optimization on the set of parameters in slicing software with five ASTM D638 tensile specimens of PLA filament material and carries out the tensile test and microstructure analysis. The research paper includes the following upcoming section to obtain the main research objective. The basics of material, printing process and the entire optimization, fabrication, testing, and analysis are explored by the fabrication and testing part. At the fabrication stage, the making time of each piece has been calculated. Then, based on fabrication and time of fabrication, the result is discussed. Finally, the whole research summary and the direction of future works are detailed in the conclusion.
2. Fabrication and Testing
PLA (polylactic acid) filament material is used in this research. Generally, PLA is derived from hydroxyl acids and is considered as compostable and biodegradable. The PLA has thermoplastic properties with very high strength and high modulation, and also the thermal degradation of PLA is above 200°C [17]. It is available in the Indian market in the form of an FDM filament to INR 800 at least and is tailored to the selector in many colors. Hence, in this research, we explore 15 pieces of ASTM D638 tensile specimens made with PLA filament which is optimized by 5 different sets of printing parameters in slicing software.
This research specifically modifies the optimization parameters such as infill, printing speed, and making temperature to produce a homogeneous sample of fifteen ASTM D638 tensile specimens. Also, the production time of those fifteen fabricated specimens is calculated. This identifies the selection of which one set of parameters of the FDM is required to produce an object in the best way and in the shortest time. The famous Botzlab's Wanhao Duplicator 4S was used to fabricate these fifteen specimens. This machine can be able to use materials that have a temperature degradation of 230–250 C. Therefore, a maximum of 219°C making temperature has been used in this research paper. Also, only room temperature is used as the minimum bed/platform temperature.
2.1. Design and Optimization Parameters
This research paper explores the tensile specimen ASTM D638 and is the standard used by previous researchers, especially for polymer materials [18, 19]. Then, type 5 in particular has been used in this research. Its basic geometrical shape is shown in Figure 1. Its design is as follows: overall length (lo) is 63.5 mm, distance (d) between grip is 25.4 mm, length of the narrow section is 9.53 mm, width (Wn) of the narrow section is 3.18 mm, and width (Wo) of the narrow section is 19 mm [20]. Also, in this research paper, the ASTM D638 design.STL (Standard Triangle Language) file is sliced by flash print Magic 5.0 slicing software. Of these, 7 fabrication parameters of each set like extruder temperature, layer height, printing speed [21], travel speed, and infill (density/pattern) [22] were modified and production started separately. Table 1 describes all the modified set of printing parameters. The image taken during production can be seen in Figure 2. Moreover, the product make time of each specimen is calculated during production. The time of the calculated specimen can be seen in Table 2. Also, the optimized .STL (standard triangle language) file is converted to G-code and fabrication started.
2.2. Tensile Test
The breaking point, tensile strain, tensile stress, Young's modulus, and elongation of the presently manufactured specimen are calculated one after the other by the Instron 8801 testing system. An experiment’s gauge length, width, and weakness are 7.62 mm, 3.18 mm, and 3 mm, respectively. During the process, a constant load was applied automatically for fitting both the gripper parts of the specimen to the tensile testing piston. Then, the initial area of cross section and the load helps to estimate the nominal stress (S). Similarly, other specimens were tested, and we found the breaking point, tensile strain, tensile stress, Young's modulus, and elongation of the fifteen pieces of the modified parameters specimens produced by the PLA filament. In previous literature, only the composite and one or two optimization parameters were modified and tested. The most notable aspect of this research is the infill parameters. All of the significant infill percentages and infill parameters in the slicing software have been tested in this research. All these can be seen in Table 2.
2.3. Field Emission Scanning Electron Microscope (FESEM)
The slicing parameters of each specimen produced in this research are of different types. In particular, the infill parameter is specified in Section 2.2. Infill patterns such as line, hexagonal, triangle 45°, infill 3D, and triangle 65° are used in this research. During production, the 3D printer produces specimen according to the infill pattern method mentioned above. Also, the tensile specimen produced in this way has different braking points and production times. Therefore, the tensile fracture surface of the five specimens being produced and the surface of the other specimen was detected by Quanta™ 250 FEG machine with the help of high magnification topography. Prior to this test, the sputter coating was applied to each specimen. Polishing is not mandatory as it comes in the form of PLA polymer and plastic [24]. Moreover, below are the FESEM images of all the found specimens.
3. Results and Discussion
3.1. Fabrication Time
Table 1 describes the modified set of parameters and the production time required. The extruder temperature used is a minimum of 195°C for specimen I and a maximum of 220°C for specimen V. Similarly, the bed/platform temperature used is a minimum of 0°C and a maximum of 50°C, where 0°C is the base bed/platform temperature at which specimen is produced. Instead, the fabricating machine will automatically use room temperature as bed temperature. The layer height is known as the first form of an initial outline of a specimen that can be produced [25]. The minimum first layer of specimen I is 0.12 mm, and the maximum specimen V is 0.21 mm. The printing speed is used to produce specimen at a minimum speed of 35 mm/s in specimen II and a maximum of 80 mm/s in specimen IV. Then, the travel speed is the interval between producing one layer and producing the next layer [26]. A minimum speed of 60 mm/s in specimen II and a maximum speed of 85 mm/s in specimen III are applied in this research
Moreover, infill is known as “how the filament fills and how much it fills” when the material is produced. The most common infill parameters are hexagonal line, triangle, and 3D infill pattern [27]. It also has many angles on the line and triangle patterns. Of these, triangle 45° and triangle 65° of specimens III and V were used to produce the tensile specimen in this research [28].
Finally, the shell count is used as a minimum of 2 and a maximum of 3. Thus, when optimization is perfectly fabricated, the production time of specimen I is 10 minutes, the production time of specimen II is 17 minutes, the production time of specimen III is 11 minutes, the production time of specimen IV is 9 minutes, and the production time of specimen V is estimated at 10 minutes. In terms of time, specimen IV is rated at a minimum of 8 minutes and specimen II at a maximum of 18 minutes [29]. Nevertheless, this research provides an excellent PLA FDM production technique based on tensile test and field emission scanning electron microscope results [30]. Moreover, Figure 1 illustrates the geometrical parameter of the specimen. Similarly, Figures 2 and 3 illustrate photos taken during production [31]. Figure 4 shows a photograph taken after a tensile test of the main types of modified specimen is produced.
3.2. Tensile Test
Figures 5(a)–5(e) show the load versus extension of specimen I to specimen V plotted, and each specimen has a separate load withstand and extension. Figure 5(a) shows the 730 N load and 0.23206 mm extension of specimen I. Figure 5(b) shows the 660 N load and 0.22772 mm extension of specimen II [32]. Figure 5(c) shows the 280 N load withstand and 0.0904 2 mm extension of specimen III. Similarly, Figures 5(d) and 5(e) illustrate the 240 N load withstand and 0.16210 mm extension of specimen IV and 330 N load and 0.14127 mm extension of specimen V. All these can be seen in Table 2.
(a)
(b)
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(d)
(e)
Optimum tensile test results were found in the ANOVA interaction plot using Minitab software [33]. This is because each specimen has different load and extension. Figure 6 illustrates the ANOVA interaction plot. The high load-bearing specimen I can be seen in blue. Thus, the parameters of specimen I are considered as the best set of parameters, that is, the extrusion temperature is 200°C, the bed temperature is 50°C, the layer height is 0.18 mm, the printing speed is 60 mm/s, the travel speed is 80 mm/s, and the tensile density is 15%, and the hexagonal pattern and shell count 2 are the best PLA manufacturing printing parameters.
However, the purpose of this research paper is to reach a final conclusion based on the microstructure results and production time also. Hence, the FESEM test and the final results are as follows [34].
3.3. Field Emission Scanning Electron Microscope
The microstructure of each specimen can be seen in Figure 7. Figure 7(a) illustrates the microstructure of specimen I, and it detects distances between the two layers ranging from 441.6 μm to 468.4 μm, and also, some subtle cracks can be seen. However, the closed microstructure can be also found.
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(b)
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Figure 7(b) illustrates the microstructure of specimen II. Layer distance spacing was found from 821.8 µm to 826.0 µm in Figure 7(b). Figure 7(c) illustrates the microstructure of specimen III. The spacing of the inbetween layers is estimated to be 606.1 μm to 623.6 μm. Figure 7(d) illustrates the microstructure of specimen V. It is calculated in the range of 536.3 μm to 558.3 μm. The research did not reveal the microstructure of specimen IV. This is because in the slicing parameter of specimen IV the 3D infill is used. Thus, higher density and moisture are found in specimen IV. The microstructure could not be detected due to high moisture and density.
This research paper also reveals that when an object is manufactured using the 3D infill pattern, its internal structure cannot be found out. Specimen I includes slightly more optimized parameters than other specimens in terms of time and available data. Also, FESEM-based specimen I has a very close microstructure compared to other specimens. Therefore, the results of FESEM also ensured the slicing parameters of specimen I have the most optimum.
In terms of time, specimen IV, specimen I, specimen V, and specimen III, have the shortest time. However, there is one minute time difference for specimen IV and specimen I. Therefore, specimen I set of parameters is the best production parameters for PLA.
4. Conclusion
In this research, the main objective is selecting the optimum set of process parameters for PLA filament in the FDM fabrication method. For this, five types of ASTM D638 tensile specimens were produced by modifying the seven set of process parameters. The tensile test and FESEM analysis were performed on all 15 specimens being produced. Based on the results obtained, the process parameters of specimen I were found to be the best. Specimen I withstands high load and extension based on the tensile test, and it also has a very close microstructure in terms of FESEM. Furthermore, the process parameters of specimen I are considered as the best production parameters for PLA filament as they are close to the average production time in terms of total production time. An additional novelty of this research is that the microstructure cannot be detected using the 3D infill pattern from that modern slicing software infill options. This research ensures the quality of the product with less time with modifying set of printing parameters for the manufacturers who want high productivity.[23].
Data Availability
The data used to support the findings of this study are included in the article. Further data or information required are available from the corresponding author upon request.
Conflicts of Interest
The authors declare that there have no conflicts of interest regarding the publication of this paper.
Acknowledgments
The authors thank and acknowledge the management of Vellore Institute of Technology, Vellore, for their support to carry out this research work, and they specially thank Additive Manufacturing Laboratory (DIGI-MAN) incharge and technician staff. The authors also express their sincere thanks to Tensile and FESEM laboratories staffs.