Technical-Economical Study on the Optimization of FDM Parameters for the Manufacture of PETG and ASA Parts

1. Introduction

Additive manufacturing consists of making components by successively adding material layer by layer, according to the instructions specified by the G-Code file, [1,2,3]. Additive manufacturing technologies have experienced continuous evolution since their inception, and due to their significant advantages over formative and subtractive technologies, these technologies are now widely used in many industrial sectors, [8,9,10,11,12,13,14,15,16,17,18,19,20]. The major advantages of additive manufacturing technologies are represented by the efficiency of the use of materials (the amount of technological residues is negligible), manufacturing of complex geometries without basing and fixing elements, low consumption of electricity, [21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41].

The additive manufacturing process represents a major innovation in the field of manufacturing, enabling the transformation of digital concepts into physical objects, [42,43,44,45,46,47,48,49,50]. This process encompasses several essential steps to ensure the transition from digital design to the final physical product:

- CAD conceptualization;

- saving the CAD model and converting it to STL format;

- generation of the G-Code file;

- equipment preparation, construction, extraction and use of parts.

In [4] innovative strategies are presented for the technical-economical optimization of the parameters of 3D printing by FDM, (L_h – the height of the deposited layer in one pass and I_d – the filling percentage). To optimize the parameters, the value analysis method was used, which consists in maximizing the ratio between the use value (V_i) and the production cost (C_p). The use value is represented by the mechanical characteristics. The results of the study show that of the two parameters considered (L_h and I_d), the height of the layer deposited at one pass decisively influences the bending resistance, and I_d categorically influences the resistance to breaking and compression, but also the hardness. The optimal parameters for printing PLA by FDM are: L_h 0.15 mm and I_d 100%, heat treated PLA: 0.20 mm and I_d 100% and ABS: L_h 0.15 mm and I_d 100%.

In [5] the authors present the study on the optimization of FDM parameters (I_d – filling percentage; L_h – height of the deposited layer in one pass; W_n – number of walls; E_t – extruder temperature; P_s – printing speed; B_t – platform temperature ; N_l – the number of lower and upper layers; I_p – the filling pattern) to minimize energy consumption, but without affecting the traction characteristics. The conclusions show that the parameters that categorically influence the energy consumption, but also the traction characteristics are: I_d, L_h, W_n, B_t, and their optimal values ​​are: I_d – 90%; L_h – 0.30 mm; W_n – 4; B_t – 60 °C.

In [6] a study is presented on the optimization of FDM parameters (N_d – extrusion nozzle diameter; W_n – number of walls; E_t – extruder temperature; I_d – filling percentage; I_p – filling pattern) to reduce the printing time, but without affecting the mechanical properties of the parts. The results of the study show that the parameters that decisively influence the printing time are: N_d, I_d, W_n. Research suggests that a larger nozzle diameter (N_d = 0.60 mm), four outer shells (W_n = 4) and a 10% infill (I_d = 10%) can reduce print time without compromising mechanical characteristics.

In [7], the impact of FDM parameters (L_h – height of the deposited layer in one pass; E_t – extruder temperature; P_s – printing speed; B_t – platform temperature) on the compression behavior of the samples made of PLA filament and used in applications is investigated biomedical and clinical. The considered FDM parameters significantly influence the mechanical properties, and statistical simulations and SEM (scanning electron microscopy) analyzes can improve the mechanical properties. The conclusions of the study show that the highest value of the compressive strength (C_s) was obtained for the samples made with the parameters: L_h = 0.10 mm; T_e = 205 °C, B_t = 60 and P_s = 50 mm/min. The ANOVA analysis certifies that the parameter that decisively influences the compressive strength (C_s) is the height of the layer deposited at one pass (L_h).

In [12] a study is presented on the influence of the filling pattern (I_p) on the compressive strength of parts manufactured by FDM from PLA. In this context, 28 samples were manufactured on the Anycubic 4 Max Pro 2.0 3D printer using 7 filling patterns (Grid, Tri-hexagon, Octet, Triangles, Cubic subdivision, Gyroid, Cross 3D). The dimensions of the specimens were measured before and after the compression test using a DeMeet 3D coordinate measuring machine. The results show a minimum printing accuracy of 98.98% and a maximum deformation value of 57.70% for the specimens with the Triangles fill pattern. The highest values ​​of compressive strengths were obtained for the specimens with the Triangles filling pattern. To establish the optimal option from a technical-economical point of view, the maximization of the ratio between the use value (V_i) and the production cost (C_p) was used, this ratio being one of the fundamental technical-economical principles of the value analysis. Cubic subdivision fill pattern is the most efficient method for FDM fabrication of PLA compression specimens using lattice structures.

Additive manufacturing technologies have significant potential to contribute to sustainability in various industries, with the main benefits being: waste reduction, optimizing the use of materials, reducing energy consumption, the use of sustainable materials, integration of the production and consumption model based on circularity, [23,24,25,26,27,28,29,30,31,32,33].

Table 1 details the main additive manufacturing technologies, including the components, operating principles, materials used, and advantages and disadvantages of each technology.

In the following we will focus on additive manufacturing technology through thermoplastic extrusion, this is one of the most widespread additive manufacturing technologies due to its ease of use, but also the low costs of equipment and materials, (see Table 1).

This paper presents a technical-economical study regarding the optimization of the FDM parameters (L_h – the height of the layer deposited in one pass and I_d – the filling percentage) for the manufacture of tensile and compression specimens from PETG and ASA. The novelty of the study consists in the application of the fundamental principle of value analysis (AV), which aims to maximize the ratio between the use value (V_i) and the production cost (C_p). Thus we will establish the optimal FDM parameters for the manufacture of tensile and compression specimens from PETG and ASA.

2. Materials and Methods

The variable parameters of FDM used in the manufacture of tensile and compression specimens from PETG and ASA are: the height of the deposited layer in one pass, L_h = (0.10/0.15/0.20) mm and the filling percentage I_d = (50/75/100) %. The mechanical properties of tensile and compression specimens were previously determined by the authors in works [43,44], respectively [41,42].

Using the parameters in Table 2, 54 tensile specimens (27 of PETG and 27 of ASA) according to the ASTM D638-14 standard and 90 compression specimens (45 of PETG and 45 of ASA) were manufactured on the Anycubic Pro Max 2.0 3D printer (Figure 1) according to ISO 604:2002. Tensile and compression specimens made from Everfil brand PETG and ASA filament on the Anycubic Pro Max 2.0 3D printer were tested on the Barrus White 20 kN universal testing machine.

Table 3 shows the technical specifications of the Everfil filament used in the manufacture of tensile and compression specimens from PETG and ASA.

Following the realization of the experimental determinations for the two types of mechanical tests (tension and compression), as well as the calculation of the production cost for each set of samples, the technical-economical study on the optimization of the FDM parameters was carried out. To establish the optimal variant, the fundamental principle of value analysis was used, presented in relation 1 and which consists in maximizing the ratio between the use value (V_i) and the production cost (C_p), [4,12,57,58,59,60].

$${\displaystyle \frac{V_i}{C_p}}\to max$$

(1)

Where, V_i represents the value in use (mechanical characteristic), and C_p represents the production cost expressed in monetary units.

Minitab 19 software was used to optimize the ratio between V_i and C_p. To calculate the production cost, the following relationships were used [4,12,57,58,59,60]:

$$C_p=C_{mat}+C_{en}$$

(2)

$$C_{mat}=Q_{mat}\times P_{mat}$$

(3)

$$C_{en}=P_t\times E_c\times P_{en}$$

(4)

Where, $C_p$ represent production cost (euro); $C_{mat}$ – cost of material (euro); $C_{en}$ – energy cost (euro); $Q_{mat}$ – quantity of used material (g); $P_{mat}$– material price (euro/g); $P_t$ – printing time (h); $E_c$ – energy consumption (kW); $P_{en}$ – price of electrical energy (euro/ kWh).

The following constant values ​​were used to perform the economical calculations: $P_m$ = 0.22 Euro/g (for PETG); $P_m$ = 0.23 Euro/g (for ASA); $P_{en}$ = 0.25 kW/h; $E_c$ = 0.23 kW/h, [37,38]. The material consumption and print time values ​​for each set of samples were generated by Cura Slicer.

The dimensions and test conditions of the tensile and compression specimens are shown in Table 4.

3. Results and Discussion

3.1. Applications of Value Analysis for Analyzing the Mechanical Behavior of PETG and ASA 3D Printed Samples

3.1.1. Tensile Testing

Table 5 and Table 6 show the results obtained from the application of relations (2 - 4) and the determination of the production cost for the tensile specimens manufactured by FDM from PETG and ASA.

FDM parameters impact the mechanical behavior of parts made of PETG and ASA, but also the consumption of electricity [5]. The results of the V_i/C_p ratio are shown in Table 7 and Table 8.

Figure 2 shows graphically the values ​​of the ratios between V_i (ultimate tensile strength) and C_p (production cost) of the samples manufactured by FDM from PETG and ASA.

Analyzing Figure 2 we notice that the highest value of the ratio between V_i (ultimate tensile strength) and C_p (production cost) was obtained for the set of specimens made of ASA with the layer height deposited at a pass L_h = 0.20 mm and the percentage of filling I_d = 100%. In the case of specimens made of PETG, the highest value of the ratio between V_i and C_p was obtained for the set of specimens with the layer height deposited at a pass Lh = 0.20 mm and the filling percentage I_d = 100%. Comparing the minimum and maximum results of the V_i/C_p ratios of the ASA samples with those obtained for the PETG samples, it is found that for the ASA samples the results are higher by (13.94 – 37.23) % compared to the results of the V_i/C_p ratios of the samples from PETG.

Using the Minitab 19 software, we performed the ANOVA analysis, through which we evaluated the relationship between the FDM parameters (L_h and I_d) and the result of the ratio between V_i (ultimate tensile strength) and C_p (production cost), [36]. Figure 3 shows the result of the ANOVA analysis.

Analyzing Figure 3 we observe how the two considered parameters (L_h and I_d) affect the result of the V_i/C_p ratio of the tensile specimens made of PETG (Figure 3a) and ASA (Figure 3b). According to Figure 3a, the layer height deposited in one pass (L_h) is the parameter that significantly influences the result of the V_i/C_p ratio of the tensile specimens made of PETG. Analyzing Figure 3b, we notice that the filling percentage (I_d) is the parameter that decisively influences the result of the V_i/C_p ratio of the tensile specimens in ASA. The same conclusions are suggested by the Pareto charts shown in Figure 4.

3.1.1. Compressive Testing

Table 9 and Table 10 present the results obtained following the application of relations (2 - 4) and the determination of the production cost for the compression specimens manufactured by FDM from PETG and ASA.

Table 11 and Table 12 show the V_i/C_p results for the compression specimens manufactured by FDM from PETG and ASA.

Figure 5 shows graphically the values ​​of the ratios between V_i (compressive strength) and C_p (cost of production) of the samples manufactured by FDM from PETG and ASA.

Analyzing Figure 5, we notice that the highest value of the ratio between V_i (compressive strength) and C_p (cost of production) was obtained for the set of samples made of ASA with the height of the layer deposited at a pass L_h = 0.20 mm and the filling percentage I_d = 100%. In the case of specimens made of PETG, the highest value of the ratio between V_i and C_p was obtained for the set of specimens with the layer height deposited at a pass L_h = 0.20 mm and the filling percentage I_d = 100%. Comparing the minimum and maximum results of the V_i/C_p ratios of the ASA samples with those obtained for the PETG samples, it is found that for the ASA samples the results are higher by (12.47 - 20.42) % compared to the results of the V_i/C_p ratios of the samples from PETG.

Figure 6 shows the result of the ANOVA analysis, where the relationship between the FDM parameters (L_h and I_d) and the result of the ratio between V_i (compressive strength) and C_p (production cost) is studied.

Analyzing Figure 6, we observe how the two considered parameters of FDM (L_h and I_d) affect the result of the V_i/C_p ratio of compression specimens made of PETG (Figure 6a) and ASA (Figure 6b). According to Figure 6a, the filling percentage (I_d) is the parameter that significantly influences the V_i/C_p ratio result of compression specimens made of PETG. Analyzing Figure 3b, we notice that the filling percentage (I_d) is the parameter that decisively influences the result of the V_i/C_p ratio of the ASA compression specimens. The same conclusions are suggested by the Pareto charts shown in Figure 7.

3.2. Optimization of FDM parameters based of Value Analysis for improve the 3D printing efficiency for samples made by PETG and ASA

Using Minitab 19, the FDM parameters presented in Table 2 and the results obtained by applying the fundamental principle of value analysis by maximizing the V_i/C_p ratio, we optimized the FDM parameters with the aim of achieving technical-economical efficiency.

To optimize the FDM parameters, we used the desirability method, where the goal was to maximize the values ​​of the ratios between V_i/C_p for each type of mechanical test (tension and compression) and each type of material (PETG and ASA). Table 13 presents optimization objectives for each studied material.

For the desirability study, we used the following relationships, [3]:

$$D={(d_1·d_2·\dots {·d}_n)}^{1/n}$$

(5)

$$d_i=0,if{y}_i<L_i$$

(6)

Where, $D$ – is the composite desirability; n – number of responses; $d_i$– represent the desirability for each individual response, $y_i,L_i,T_i$ – represent the predicted value, target value, and lowest value, respectively, of the analyzed response of response.

Table 14 shows the composite desirability for each printing parameters and each type of material.

Figure 8 shows the plots of FDM parameter optimizations for the manufacture of PETG and ASA samples.

Analyzing Figure 8 we observe how each factor (column) influences the composite desirability response (row). The vertical solid red lines indicate the current setting of the factors, and the red numbers on each column indicate the current level of the factors. The blue horizontal dashed lines indicate the responses corresponding to the current factor settings, and the blue numbers indicate the response corresponding to the current factor settings.

According to Figure 8a, following the optimization process of the FDM parameters for PETG, the following optimal settings resulted: layer height (L_h) = 0.20 mm and infill density (I_d) = 100%. Analyzing Figure 8b, we notice that following the optimization process of the FDM parameters for ASA, the following optimal settings resulted: layer height (L_h) = 0.20 mm and infill density (I_d) = 100%. Increasing the layer height per pass (L_h) has a significant impact on print time, and this leads to lower power consumption, thus lower production costs. The decrease in the height of the layer deposited at a pass (L_h) has a direct impact on production costs, but also on maintenance costs, which increase considerably.

4. Conclusions

The paper presents the results of the technical-economical study regarding the optimization of FDM parameters for the manufacture of PETG and ASA parts. In this context, we have carried out a multi-objective optimization with the aim of finding the optimal FDM parameters (L_h - the height of the deposited layer in one pass and I_d - the filling percentage) for the manufacture of PETG and ASA parts. Following the determination of the mechanical characteristics (tensile and compression) of the specimens manufactured by FDM from PETG and ASA, but also the determination of the production cost for each set of specimens, using the fundamental principle of value analysis by maximizing the V_i/C_p ratio, we achieved the technical-economical optimization of the FDM parameters.

The results of the ANOVA analysis show that the two FDM parameters considered (L_h - the height of the layer deposited in one pass and I_d - the filling percentage) influence the results of the V_i/C_p ratios. For tensile specimens made of PETG, the parameter that significantly influences the results of the V_i/C_p ratios is L_h - the height of the layer deposited in one pass, and in the case of compression specimens made of PETG, the parameter that significantly influences the results of the V_i/C_p ratios is I_d – the filling percentage.

In the case of specimens manufactured by FDM from ASA, the parameter that decisively influences the results of the V_i/C_p ratios of the tensile and compression specimens is I_d – the filling percentage.

Using the results of the V_i/C_p ratios for the tensile and compression specimens made of PETG and ASA, we found the optimal FDM parameters: L_h = 0.20 mm and I_d = 100%.

The results of the study have applicability for the efficient exploitation of the 3D printer for the manufacture of PETG and ASA parts by FDM.

We propose to extrapolate the study to other types of materials, but also to other types of mechanical tests.