Effects of extrusion parameters in the printing stability: evaluation in an innovative 3D printer containing a vertical co-rotating twin screw extrusion unit

doi:10.21203/rs.3.rs-4360109/v1

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Research Article

Effects of extrusion parameters in the printing stability: evaluation in an innovative 3D printer containing a vertical co-rotating twin screw extrusion unit

https://doi.org/10.21203/rs.3.rs-4360109/v1

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published 14 Aug, 2024

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The study of die swell phenomenon in Material Extrusion Additive Manufacturing (MEX-AM) technologies holds great importance in order to maintain the control over the extruded beads diameter to ensure surface quality, dimensional precision, adhesion between adjacent beads (intra and inter), as well mechanical properties on manufactured parts. This paper addresses an experimental procedure to analyze the influence of extrusion parameters on the die swell phenomenon on extruded beads printed from a 3D customized equipment containing a customized co-rotating vertical twin-screw extrusion unit (Co-TSE AM). In this context, an analytical estimation of shear rate in the screws and die was performed; a design of experiments (DOE) was conducted to evaluate the influence of factors as of screw rotational speed (40 rpm and 80 rpm), output rate (20 g/h and 40 g/h), and nozzle diameter (0.4 mm and 0.6 mm) on the die swell ratio (DSR); and scanning electron microscopy (SEM) was employed to assess the morphology in the cross-sectional area of the beads, as well as qualitative aspects of surface texture. Additionally, print line experiments were conducted to examine the influence of platform speed and standoff distance on bead width and bead height. It was observed that the DSR average varied between 1.28 and 1.67. Output rate and nozzle diameter are the parameters that most strongly influence DSR. Screw rotational speed has not significant influence on the thermomechanical environment that influences material swelling. The bead width and bead height are differently influenced by the standoff distance and print platform speed.

Polypropylene

Die Swell

Shear Rate Estimation

Modular Design

Parametric Analysis

Calibration Process

Analysis of the die swell phenomenon in the processing of a thermoplastic material (polypropylene) in a customized equipment with a vertical co-rotating twin-screw Co-TSE AM extrusion system;
Analysis and evaluation of rheological characteristics associated with the extrusion process applied to miniaturized and innovation equipment for additive manufacturing by single step extrusion process using feedstock in polymer-based powders where the study was led by design of experiments;
Evaluation of the beads profiles and printed basic geometry dimensions;
The results obtained on the die swell in the customized equipment presented values close to literature report using FDM 3D printers;
The CO-TSE equipment presents potential application in the single step additive extrusion processes based on powder feedstock in order to generate distributive and dispersive mixtures in the laboratory-scale to the blends formulations, a new approach to produce new filaments which will can use in desktop FDM 3D printers;
The results presented by CO-TSE additive equipment indicate the potential use on manufacturing of small parts and test specimens for research purposes.

Additive Manufacturing (AM) is a technology of fabrication where a three-dimensional (3D) computational model after being digitally sliced, it is fabricated layer upon layer, in a different paradigm compared to conventional manufacturing processes [1]. Material Extrusion Additive Manufacturing (MEX-AM) is a kind of additive processes where occurs the passage of material in a fluid or semi-solid state across a nozzle due to the application of pressure.

The MEX-AM is usually classified according to the pumping mechanism. The main categories are material extrusion based on plunger, material extrusion based on solid filament, and material extrusion based on screw [2]. The material extrusion based on screws has been applied for over eight decades in the Plastic Industry. This technology is capable of transporting, plasticizing, mixing, catalysing chemical reactions, and devolatizing systems, proving to be a good candidate for applications in AM processes [3–10].

Single screw print heads were developed in the mid-2000s as an alternative to filament-based 3D printers. Furthermore, this technology finds application in recycling [11, 12]; bio fabrication [13–17], low-cost metal and ceramic 3D printing [18, 19] and personalized medicines [20]. However, generally, the print heads based on single screw, have limited process flexibility and mixing capacity. Most recently, Justino Netto et al. (2022) [5] designed and validated an innovative small-scale 3D printer containing a co-rotating twin-screw extrusion unit. The innovative design can accept materials in either powdered or micro-pellet form. This device also offers the flexibility to configure. the output rate and screw rotational speed [3].

Generally, in MEX-AM, the dimensions of the extruded material do not align effectively with the profile of the printer nozzle or die exit. This phenomenon is known as die swell, extrudate swell or the Barus effect [21]. The die swell is a complex rheological phenomenon that can be observed when the extrudate cross-section dimensional changes upon exiting the die orifice. It occurs because of the reversible elastic deformation, which leads to the reorganization of molecules as the material emerges from an extrusion die or a printer nozzle. Die swell can be evaluated by swell ratio. The die swell ratio (DSR) is defined as the radio between the extrudate diameter and the die diameter in most simple cases of capillary geometries [21, 22].

Researches on die swell in polymer flows dates back to the 1960s. Primarily, it focuses on general experimental observations and the development of analytical models aimed at understanding these observations [23, 24]. Nowadays, it is known that factors such as melt temperature, die design, volumetric output rate, shear-stress and material rheology have been identified as significant influences on the swell ratio [21].

In the MEX-AM context, studies have analysed the impacts of the parameters of the process to predict the real geometry of the extruded bead especially in a MEX-AM based on solid filament mechanism. Geng et al. (2019) [25] experimentally evaluate the effects of the extrusion speed in the die swell of polyether ether ketone (PEEK). They used a silicone fluid of dimethicone at 360°C and a glass tube at 110°C to capture the extruded bead. After that, the diameter of the beads was measured in a confocal microscope. The authors also studied the influence of the printing speed on the microstructure and surface quality of the PEEK parts.

Colon et al. (2023) [22] characterized the die swell effects in a MEX-AM based on solid filament mechanism of acrylonitrile butadiene styrene (ABS) polymer. They used a in-line instrumentation of optical and infrared cameras to estimate the swell ratio. The Tanner model was applied to fit the experimental data in different parameters of process. Wherever, Tanner model is an analytical model that the estimative of swell ratio is based on empirical constants, which limits the model's applicability to situations where experimental swelling data is available.

De Rosa, Tammaro and D’Avino (2023) [26] developed an experimental and numerical investigation of die swell in MEX-AM based on solid filament mechanism of PLA (polylactic acid). A in-line optical camera was used to estimate the swell ratio and a 4-mode Giesekus model was applied to describe the viscoelastic fluid, as a consequence of predicting the swell ratio based in rheological characterization of the material.

The investigation of die swell in MEX-AM technologies is very significant since controlling the extruded bead diameter is a critical aspect for surface quality, dimensional precision, adhesion between neighboring beads, and mechanical properties of produced parts [25; 27, 28]. However, analyses of die swell effects in 3D printing are limited especially in MEX-AM based on screw technologies. In this study, the phenomenon of die swell was analysed in a 3D printer containing a customized co-rotating vertical twin-screw extrusion unit (Co-TSE AM). The influence of the rotation of the screws, the geometry of the nozzle, and the output rate of powder are investigated in the processing and deposition of PP (polypropylene).

The innovative 3D printer equipment utilized in this investigation is composed of three primary subsystems: a) the extrusion unit, b) the drive unit, and c) the frame and positioning unit [3]. As can be seen in Fig. 1.

The extrusion unit encompasses the co-rotating twin screws, barrel, band heaters, nozzle, and screw conveyor system. The screws, characterized by a length/diameter (L/D) ratio of 11, an outer diameter of 12 mm, and a maximum channel depth of 1.8 mm, are constructed from individual elements arranged axially along a hexagonal shaft (6 mm width across flats). These elements include conveying components with various pitch/length combinations in millimetres (20/40, 20/20, 15/40, 15/20, 10/35, 10/30, and 10/20) and 3 mm thick kneading discs that can be assembled to create kneading blocks, with positives or negatives angles. The conveying elements transport the material downstream at different rates, influencing local residence times, the degree of channel fill, and heat transfer. The kneading discs, which may be staggered at positive or negative angles, introduce varying levels of distributive/dispersive mixing, as well as different residence times and viscous dissipation [3, 5].

In the drive unit, a specific gearbox was designed, consisting of a simple gear train followed by a belt transmission stage. This arrangement facilitates the transfer of power from a centrally positioned driving gear to two adjoining shafts. One of these shafts is linked to the initial output screw, while the other is fitted with a pulley to convey power to the second output screw. The gearbox is driven by a KTC-HT23–401 NEMA 23 stepper motor (Kalatec Automation, Brazil), connected to a PEII 050–010 planetary speed reducer (Apex Dynamics Inc., USA). This system boasts a 10:1 Nin/Nout ratio and can handle a maximum torque of 18 Nm [3, 5].

In the frame and positioning unit, the displacement in the X-Y plane is achieved through a core XY design, while vertical motion is carried out by two leadscrews. Linear ball bearings and shafts, strategically positioned at the four corners of the coreXY frame, guide the vertical motion. The coreXY mechanism improves the compactness of the positioning system and simplifies adjustments to the gantry structure. The positioning system is powered by four US17H4401 NEMA 17 stepper motors (Usongshine Inc., China). The available print volume measures 55 × 80 × 43 mm, effectively meeting the specifications for the intended benchtop applications of the Co-TSE AM system [3, 5].

The Fig. 2 shows important mechanical differences between a Co-TSE AM and a FFF 3D printer. Figure 2a presents two screw configuration possibilities. The first one (on the left) with only conveying elements correctly arranged to compress the solid bed of powder, melting and metering to the die region. The second one (on the right) with dispersing and distributive kneading elements, is especially advantageous to processing complex materials, such as polymeric blends. The Co-TSE AM exhibits significant differences when compared to the FFF AM technique, not only in terms of the extrusion mechanism but also in terms of die geometry. This is because the Co-TSE AM 3D head features a transition region between the eight-shaped section at the screw's outlet and the circular section at the nozzle's inlet, which is not present in FFF 3D printers, as can be seen in Fig. 2.

In this study, Co-TSE AM 3D printer was used only with convening elements with configurations of 20/40 15/40, 10/30, and 10/20. The choice of screws with only transport elements was based on the type of monomeric material used for the device validation. The experiments were conducted using brass 3D printing nozzles with nominal diameters of 0.4 mm and 0.6 mm. The rotational speeds and feed rates employed were 40 rpm and 80 rpm, as well as 20 g/h and 40 g/h, respectively. The band heaters were set to 180°C in the compression zone and 200°C in the metering zone.

3.1. Characterization of the feedstock

The polymer used in this study is a random polypropylene (PP), grade RP141 (Braskem®, Brazil), a high melt flow rate (MFR) copolymer. The PP-RP141 was used to validate the 3D printer used in a previous study by Justino Netto et al. 2022 [5].

The PP-RP141 in pellet form was ground in a Mikro Bantam hammer mill (Hosokawa Micron Powder Systems, USA) after immersion in liquid nitrogen, to yield powder with particle sizes ranging from 300 to 600 µm. Table 1 summarises the most important properties of PP- RP141.

Table 1

Main properties of PP- RP141
Properties	ASTM Method	Units	Values
Density	D792	g/cm³	0.902
Melt Output rate (230°C/2.16 kg)	D1238	g/10 min	40
Initial melt Temperature	D3417	°C	147
Tensile Strength at Yield	D638	MPa	1050
Tensile Elongation at Yield	D638	MPa	30

A rheometry analysis of PP-RP141 was conducted to graphically represent the material flow curve. The SR20 rheometer (Instron®, USA) and ARG2-TA rheometer (Waters Corporation, USA) were used to carry out the capilar and rotational rheometry respectively, both in the temperatures of 180°C and 200°C. Using these two rheological techniques, it was possible to investigate the rheological behavior of PP random at low (from 0.01 to 10 s^− 1) and high (from 100 to 10000 s^− 1) shear rates. The flow curves are shown in Fig. 3.

Estimating the material flow curve at the processing temperatures of the metering zone and compression zone of the twin-screw, as shown in Fig. 3, is a significant tool to discuss the die swell effects, which is influenced by rheological parameters such as temperature and shear rate.

3.2. Estimation of shear rate

An analytical calculation of the average shear rate along the conveying elements of the screws, as well as in the most restrictive region of the die, is important for quickly estimating the thermomechanical environment of the material throughout processing based on geometric, process, and material parameters [29].

In this study, shear rates were calculated using two methodologies. For the conveying elements of the co-rotating twin-screw, the equations of Vergnes et al. (2021) [29] were applied, allowing the estimation of the average shear rates of the flow. The analytical average shear rates are presented in Table 2 for the experimental process parameters.

Table 2

Average shear rate on conveying elements
Conveying element	Output rate [g/h]	Screw speed [rpm]	Average shear rate [s^− 1]
15/40	20	40	31
	20	80	62
	40	40	31
	40	80	62
10/50	20	40	67
	20	80	135
	40	40	65
	40	80	133

The average shear rate calculations presented in Table 2 considered that the 20/40 elements performed solid conveyance, the 15/40 elements operated partially filled, and the 10/20 and 10/30 elements operated fully filled, as a 10/50 element only. The maximum average shear rate in the screws was 135 s^− 1, a value consistent with the expected range in extrusion operations for large-scale equipment, as reported by Alderman (1997) [30] and Carnicer et al. (2021) [31].

To the most restrictive region of the die characterized as a cylindrical tube with a diameter of 0.4 mm and 0.6 mm both with a length of 0.5 mm, the Michaeli's equations [33] were applied, allowing the estimation of the shear rate on the wall of the nozzle. The wall shear rate is present in Table 3.

Table 3

Wall shear rate
Nozzle Nominal Diameter [mm]	Output rate [g/h]	Wall shear rate [s^− 1]
0.4	20	1127
0.4	40	2255
0.6	20	353
0.6	40	707

The wall shear rates presented in Table 3 considered that PP-RP141 a power law fluid at a constant temperature of 200°C, with a pseudoplasticity index of 0.503 estimated from the flow curve generated by capillary rheometer (Fig. 3). The shear rates at the wall analytically estimated are influenced by the nozzle geometry, the pseudoplasticity index, and the output rate. The operational rotating speed of the twin screws was not considered in this calculation, however, was a parameter analyzed in the experiments of this study.

3.3. Experimental procedure

The experimental procedure was organized into two phases. The objective of the first phase was to analyze the impact of extrusion parameters on the die swell phenomenon, while the second phase aimed to assess the influence of deposition parameters on the geometry of the bead printed on the platform, both in the Co-TSE AM 3D printer. Figure 4 presents a diagram summarizing the main stages of the experimental procedure.

In the first phase, the rotational speed (40 rpm and 80 rpm), the feed rate (20 g/h and 40 g/h), and the nozzle diameter (0.4 mm and 0.6 mm) were defined as factors of design of experiments (DOE). Their influence on the swell ratio (response parameter) in the Co-TSE AM 3D printer was evaluated. For this purpose, the actual diameter of the nozzles used was measured through image analysis conducted with a confocal scanning microscope LEXT OLS 4000 (Olympus®, Japan). The nozzles were correctly cleaned with Acetone P.A. (Neon®, Brazil), and five measurements were taken for each nozzle, enabling the selection of 3D printing nozzles with the lowest standard deviation and, consequently, superior geometric quality. The 3D printing nozzles selected had 0.411 ± 0.0008 and 0.605 ± 0.0146. Figure 5 shows important aspects of 3D printing nozzle diameter measurements.

The STATISTICA software (Dell®, USA) was used for the development of the DoE. The full factorial design method with two levels per factor (2³) with one test and two replicas was applied, totaling 24 experiments in the first phase. In each experiment, three samples were collected by freeform form bead method [25]. In this method, the extrusion was performed by adding to the building platform a glass beaker filled with dimethicone (HP 20 cs, MRC Químicos, Brazil). The PP-RP141 melted was pushed through the nozzle and the extruded bead flowed into the dimethicone. The temperature of dimethicone in the glass tube was heated to 65°C and maintained by the building platform. The PP-RP141 rod was fed into dimethicone having low surface tension, low viscosity and density close to that of PP-RP141 to minimize the impact of gravity on the diameter of the semi-solidified extruded bead [32]. Figure 6 shows the free form bead process (Fig. 6a and Fig. 6b) and the beads samples shape (Fig. 6c).

The diameters of the collected beads were analyzed using the LEXT OLS 4000 transmission confocal microscope (Olympus®, Japan), as can be seen in Fig. 6d. The diameter of each bead was measured in eight different regions. The measurements for each experimental condition were subjected to the Shapiro-Wilk test to verify the normality distribution for significance level (p) of 5%. The STATISTICA software (Dell®, USA) was employed for significance (significance level (p) of 1% and confidence interval of 99%) and desirability analysis. The parameters capable of minimizing die swell were utilized in the second phase of experiments.

After, samples of DOE beads extruded were extra collected without dimethicone and fractured following immersion in liquid nitrogen. The fractured beads were sputter-coated with gold and analyzed through scanning electron microscopy (SEM) using a LEO 440 instrument (Zeiss®, Germany).

In the second phase of experiments, the geometry of the deposited bead was analyzed under specified conditions of rotational speed, feed rate, and nozzle diameter determined by desirability analysis. The defined factors for the second phase DOE were the build platform speed (20 and 30 mm/s) and standoff distance (0.5 mm and 1 mm). The full factorial DOE with two levels per factor (2^2) was applied, with one test and two replicates, resulting in a total of 12 experiments. Two response parameters, bead width (W, mm) and bead height (H, mm), were used. The geometry of printed lines can be observed in Fig. 7.

The bead width (W, mm) and bead height (H, mm) of the samples were analyzed using the LEXT OLS 4000 transmission confocal microscope (Olympus®, Japan). Each sample was measured in ten different regions, and the STATISTICA software (Dell®, USA) was employed for significance analysis.

4.1 Parametric sensitivity analysis of the extruded beads printed

The diameter measurements for each experiment condition were subjected to the Shapiro-Wilk normality test, as could be seen in Fig. 8.

In Fig. 8, the orange graphs illustrate the distribution of bead diameter measurements with a 0.4 mm 3D printing nozzle, while the blue graphs illustrate the distribution with a 0.6 mm 3D printing nozzle. The data in Fig. 8 comprises random samples, since the p-value was greater than 0.05, therefore there is no rejection of the normality hypothesis. Table 4 presents the average and standard deviation of the bead diameter and the associated die swell for each processing condition.

Table 4 Bead diameter and DSR

Processing condition	Bead diameter (mm)	DSR
04mm_40rpm_20g/h	0.616 ± 0.004	1.50 ± 0,010
04mm_40rpm_40g/h	0.658 ± 0.005	1.60 ± 0.013
04mm_80rpm_20g/h	0.615 ± 0.007	1.49 ± 0.017
04mm_80rpm_40g/h	0.686 ± 0.006	1.67 ± 0.014
06mm_40rpm_20g/h.	0.77 ± 0.012	1.28 ± 0.020
06mm_40rpm_40g/h	0.86 ± 0.036	1.42 ± 0.060
06mm_80rpm_20g/h	0.88 ± 0.006	1.46 ± 0.001
06mm_80rpm_40g/h	0.94 ±0.002	1.57 ± 0.030

By observing the Table 4, the DSR average varied between 1.28 and 1.67, values similar to those found by Colon et al. (2023) [22] and Cheng et al. (2019) [25]. Despite different processing conditions and materials, the range remained between 1.1 and 1.7 for DSR in studies in 3D printer heads.

Next, the significance analysis was performed to verify the quantitative impact of the nozzle diameter, rotational screw speed, and output rate on the DSR of PP-RP141 in the Co-TSE AM 3D printer. In significance analysis, the vertical bars refer to the confidence interval from the mean value for the test and its replicas. The main results can be seen in Fig. 9.

Analyzing Fig. 9a, Fig. 9b and Fig. 9c it is possible to observe that DSR tends to increase with a decrease in nozzle diameter, an increase in output rate, and an increase in the rotational speed of the twin-screw, for the numerical range of each factors analyzed. Additionally, by examining the Pareto chart (Fig. 9d), the significance of each factor can be quantified. The factors diameter of the 3D nozzle and the output rate statistically affected the DSR, increasing the response by 0.132 and 0.130 on average, respectively. The rotational speed influenced the DRS, increasing the response by 0.096 on average. It is worth highlighting that there was significant interaction effect between nozzle diameter and rotational speed. This interaction effect showed a reduction in the difference between mean DRS values in relation to nozzle diameter of approximately 0.06 with the increase of rotational speed.

The Fig. 9e illustrates the interaction between screw rotational speed and nozzle diameter on DSR. An increase in rotational speed results in a higher DSR for both nozzle diameters. However, with a 0.4 mm nozzle diameter, the influence of increased rotational speed on DSR is less than with the 0.6 mm nozzle. This could be a consequence of molecular orientation in the more restrictive thermomechanical environment of the 0.4 mm nozzle, as indicated by the estimated shear rates in Table 3. According to Manrich (2005) [34], there is a critical shear rate where molecules of viscoelastic materials have already achieved full orientation and, under this condition, an increase in shear rate has a diminishing impact on DSR, potentially reaching values lower than 1. Similarly, the reduced effect of rotation on the 0.4 mm nozzle can be attributed to the possibility that molecules are already highly oriented and closer to the critical shear rate condition. Consequently, they experience a lesser influence from the screw rotational speed.

Before performing the desirability analysis, the beads were examined under processing conditions both longitudinally and transversely. The objective was to qualitatively evaluate the surface texture and morphology. The Fig. 10 presents the SEM results.

As can be observed in Fig. 10, the surface quality of the extruded beads without silicone and their respective morphologies exhibits minimal discrepancies when comparing Fig. 10a to Fig. 10h. The surface texture of all samples demonstrates favorable characteristics, without depressions or damages. The bead's morphology, observed in the cross-sectional view, reveals an absence of empty or contaminants, even when the Co-TSE AM 3D printer operates in an unenclosed environment. The acquired surface texture and morphology in the samples suggest that all processing conditions could potentially be suitable for 3D printing print lines experiments.

Since all samples exhibit suitable surface quality and morphology for be printed in trajectory experiments, a desirability analysis was conducted for all conditions to determine which processing parameters would minimize DSR. Fig. 11 shows the desirability chart.

By observing Fig. 11, it can be noted that the desirable outcome (1) is achieved when the diameter is the largest (0.6 mm), the output rate is the lowest (20 g/h), and the rotational speed is the lowest (40 rpm). Additionally, it is observed that the desirable conditions (0.6 mm, 20 g/h, and 40 rpm) align with analytical expectations, as these circumstances tend to minimize the shear rate developed during the extrusion of PP-RP 141.

4.2 Analyses of the trajectories and profiles of the extruded beads

The printed lines of the extruded beads samples were analyzed at LEXT OLS 4000 transmission confocal microscope (Olympus®, Japan), the main images were showed in Fig. 12.

By observing Fig. 12, it could be notice that the surface texture of the print lines trajectories is different, especially influenced by the standoff distance. The textures of Fig. 12a and Fig. 12b are more similar to each other and exhibit greater geometric conformity with the trajectory of the G code when compared to Fig. 12c and Fig. 12d. Fig. 13 presents the Pareto chart for H and W parameters, respectively.

Analyzing Fig. 13, it can be observed that for the H, the standoff distance has a greater influence, whereas for W, the platform speed parameter has a greater effect. Additionally, it is noteworthy that the interaction between standoff distance and platform speed is significant only for H under the investigated printing conditions. Fig. 13 provides an analysis of the influence of the platform speed and standoff distance on bead height (H, mm) and bead width (W, mm).

It can be observed in Fig. 14a that H tends to decrease as the speed increases. As well as, an examination of Fig. 14b reveals that, at higher speeds, W tends to decrease at both the 0.5 mm and 1 mm distances. Moreover, it is worth mentioning that, at a speed of 30 mm/s, the influence of speed on width is minimized. One possible explanation is that, at the higher speed (30 mm/s), the heated nozzle spends less time influencing the thermomechanical environment of the polymer adhering to the bed, likely resulting in quicker bead cooling. This stands in contrast to the scenario at a speed of 20 mm/s. At 20 mm/s, W for 0.5 mm of standoff distance tends to be larger than for 1 mm of standoff distance, which could be linked to the extended duration the heated nozzle interacts with the polymer during adhesion, leading to slower cooling and potentially greater susceptibility to height influence due to the increased moldability permitted by the thermomechanical environment.

In this study, extrusion parameters in the printing stability related to die swell phenomenon were investigated from an innovative additive manufacturing equipment, based on miniaturized Co-TSE printhead to direct fabrication.

Analytical estimation of shear rates was presented for different processing conditions of PP-RP 141. Additionally, an experimental procedure was conducted to investigate the influence of twin-screw extrusion parameters on the die swell of the extrudate. Based on the presented results, the following conclusions can be drawn:

• It can be observed that the average of DSR varied between 1.28 and 1.67, meaning that the filament swelled by approximately 28–67%.
• Output rate and nozzle diameter are the parameters that most strongly influence on DSR (as seen in industrial extrusion equipment);
• Despite screw rotational speed being a crucial aspect that analytically affects shear rates during processing, in the matrix region, these rates have low influence on the thermomechanical environment that influences material swelling.
• For this equipment, the movement speeds of the print platform need to be low to allow for the structuring of a printing line.
• Standoff distances of 0.5 mm in a nozzle of 0.6 mm being more suitable for both 20 mm/s and 30 mm/s speeds.
• The results also indicate the potential of the equipment in personalized printing applications using powdered material as feedstock.

At this point, it's important to emphasize that, beyond minimizing swelling, the ability to track and estimate it is of greater significance. This is particularly pertinent given that the examined equipment serves dual purposes as both a 3D printer and a benchtop extruder, capable of processing diverse polymer blends on a miniature scale in a more sustainable manner than larger-scale devices. In this context, future endeavors will focus on performing a numerical analysis of the equipment using the data collected in this study to validate the model and also introducing a temperature and pressure melt microsensor into the matrix region to adequately track the thermomechanical environment of the polymers.

Funding

This study was supported by the Coordination for the Improvement of Higher Education Personnel (CAPES), grand number 88887.817119/2023-00. The Author DML Silva has received research support from CAPES.

This study was supported by National Council for Scientific and Technological Development, grand number (CNPq) grand number 302131/2023-0. The Author ZC Silveira has received research support from CNPq.

Competing interests

On behalf of all authors, the corresponding author states that there is no competing of interest.

Author Contributions

All authors contributed to the study conception. Material preparation and experimental data collection was performed by Dávila Moreira Lopes Silva and Patrícia Alves Barbosa. Microscopic analyzes and statistical analyzes was performed by Patrícia Alves Barbosa, Zilda de Castro Silveira, and Marcelo Aparecido Chinelatto. The first draft of the manuscript was written by Dávila Moreira Lopes Silva and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.

Acknowledgements

The authors acknowledge Ph.D. Joaquim Manoel Justino Netto for his support and guidance during the calibration process of the 3D printer equipment, and the Structural Characterization Laboratory (LCE, in Portuguese) at the Federal University of Sao Carlos for their assistance the acquisition of images.

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Effects of extrusion parameters in the printing stability: evaluation in an innovative 3D printer containing a vertical co-rotating twin screw extrusion unit

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Abstract

Figures

Highlights

1. Introduction

2. Co-TSE AM 3D printer equipment

3. Materials and Method

3.1. Characterization of the feedstock

3.2. Estimation of shear rate

3.3. Experimental procedure

4. Results and Discussions

4.1 Parametric sensitivity analysis of the extruded beads printed

4.2 Analyses of the trajectories and profiles of the extruded beads

5. Conclusion

6. Future Works

Declarations

References

Supplementary Files

Status:

Journal Publication

Version 1