Abstract
Purpose
The current analysis was conducted to investigate the quality of surfaces and geometry of tracks printed using PolyMideTM CoPA, PolymaxTM PC and PolyMideTM PA6-CF materials through fused deposition modelling (FDM). This study also examined the degree of fusion of adjacent filaments (tracks) to approximate the optimal process parameters of the three materials.
Design/methodology/approach
Images of fused adjacent filaments were acquired using scanning electron microscopy (SEM), after which, they were analysed using Image J Software and Minitab Software to determine the optimal process parameters.
Findings
The optimal process parameters for PolyMideTM CoPA are 0.25 mm, 40 mm/s, −0.10 mm, 255°C and 0.50 mm for layer thickness, printing speed, hatch spacing, extrusion temperature and extrusion width, respectively. It was also concluded that the optimal process parameters for PolymaxTM PC are 0.30 mm, 40 mm/s, 0.00 mm, 260°C and 0.6 mm for layer thickness, printing speed, hatch spacing, extrusion temperature and extrusion width, respectively.
Research limitations/implications
It was difficult to separate tracks printed using PolyMideTM PA6-CF from the support structure, making it impossible to examine and determine their degree of fusion using SEM.
Social implications
The study provides more knowledge on FDM, which is one of the leading additive manufacturing technology for polymers. The information provided in this study helps in continued uptake of the technique, which can help create job opportunities, especially among the youth and young engineers.
Originality/value
This study proposes a new and a more accurate method for optimising process parameters of FDM at meso-scale level.
Keywords
Citation
Mwania, F., Maringa, M., Nsengimana, J. and van der Walt, J.G. (2024), "Investigating surfaces, geometry and degree of fusion of tracks printed using fused deposition modelling to optimise process parameters for polymeric materials at meso-scale", Rapid Prototyping Journal, Vol. 30 No. 11, pp. 159-172. https://doi.org/10.1108/RPJ-02-2024-0069
Publisher
:Emerald Publishing Limited
Copyright © 2024, Fredrick Mwania, Maina Maringa, Joseph Nsengimana and Jacobus Gert van der Walt.
License
This article is published under the Creative Commons Attribution (CC BY 4.0) licence. Anyone may reproduce, distribute, translate and create derivative works of this article (for both commercial & non-commercial purposes), subject to full attribution to the original publication and authors. The full terms of this licence may be seen at http://creativecommons.org/licences/by/4.0/legalcode
1. Introduction
Fused deposition modelling (FDM) involves extruding semi-molten filaments to form a layer consisting of a pre-determined pattern of fused filaments (tracks, roads, beads, strands or rasters) (Li et al., 2002). The process continues where layer upon layer is deposited, resulting in formation of three-dimensional (3D) parts, as illustrated in Figure 1. Bonding of adjacent filaments can be considered a first step for developing 3D components using FDM.
Gao et al. (2021) noted that fusion of adjacent filaments is similar to welding of films that involves three steps: surface contact, neck growth and molecular diffusion and cross-linking across the interface of filaments, as summarised in Figure 2.
The quality of bonds formed between adjacent filaments and layers is very crucial as it determines the physical and mechanical properties of the finished products (Krajangsawasdi et al., 2021). Furthermore, quantifying the degree of fusion and bond property between adjacent filaments is an essential step to determine mechanical characteristics of parts printed using FDM (Tao et al., 2021). Hence, the need for investigation of bond formation to provide crucial information on FDM at the meso-structure level.
Despite being one of the most popular AM technologies, FDM is a complex process that is influenced by a myriad of parameters (Naveed, 2021). Mwema and Akinlabi (2020) broadly classified these parameters into machine or materials aspects, which include factors summarised in Figure 3.
The qualities of parts printed using FDM are subject to various process parameters, such as infill density, infill patterns, extrusion temperature, bed temperature, layer thickness, nozzle diameter, raster angle and build orientation (Syrlybayev et al., 2021). Syrlybayev et al. (2021) noted that the most crucial requirements, for finished parts, include mechanical strength, surface roughness and dimensional accuracy. The authors added that the extent of inter-layer bonding, intra-layer bonding and neck size determines the mechanical properties of printed components. Tao et al. (2021) mentioned that FDM is affected by the presence of voids and poor layer-to-layer fusion, which results in weak components with anisotropic characteristics.
Unlike powder bed fusion for polymers, where the most crucial process parameters that affect powder particle fusion have been identified, information is still missing to link different FDM process parameters to the fusion of adjacent filaments (Xia et al., 2019). Therefore, it is imperative to investigate neck formation for two adjacent filaments to gain more insights into FDM for different polymers, and to determine how different process parameters influence intra-layer bonding and neck size.
FDM is among the most popular additive manufacturing technologies for polymers (Ismail et al., 2022). As a result, numerous commercial and research materials, such as acrylonitrile-butadiene-styrene (ABS), poly-lactic acid (PLA), nylon (PA), polypropylene (PP), polycarbonate (PC), polyethene terephthalate, thermoplastic polyurethane and polyethylene (PE) have been developed over the years for use in FDM (Patel et al., 2022). However, it is challenging to print some of the available polymeric materials because FDM is a multifactorial process, making it difficult to establish the most optimum conditions (Kristiawan et al., 2021). Considerable research has been undertaken to optimise the process parameters for different polymeric materials used in FDM to ensure a successful process and final products of high quality (Kristiawan et al., 2021). However, few studies have focused on the optimisation of these process parameters at the meso-structure level, despite bond formation (fusion between adjacent filaments) being a crucial aspect of FDM because it affects the physical and mechanical properties of printed components (Xia et al., 2019; Xia et al., 2023). The current study investigated the surfaces and geometry of adjacent filaments (tracks) printed using PolyMideTM CoPA, PolymaxTM PC and PolyMideTM PA6-CF. The study was also undertaken to examine the degree of fusion between filaments printed using the three commercial materials to establish the optimal process parameters for the materials.
2. Literature review
2.1 Types of voids present in parts printed using fused deposition modelling
Components developed using FDM are most likely to contain either of the following voids: raster gap, partial neck growth, sub-perimeter, intra-bead or infill (Tao et al., 2021). Figure 4 summarises the different types of voids common in parts printed using FDM.
A typical layer-part printed using FDM consists of a contour (shell) and rasters, as illustrated in Figure 5. Raster gap voids are formed by the spaces between adjoining filaments [Figure 4(a)]. The raster gaps can be controlled by adjusting the values of the air gap (raster gap).
The sub-perimeter voids are gaps at turning points for the filaments on the contours [Figure 4(c)]. Intra-bead voids are common in parts developed using composite materials, and occur within a bead, probably due to differing material properties [Figure 4(d)]. Infill voids are normally part of a design specification, and they are regulated through process parameters, such as infill patterns or infill density [Figure 4(e)]. Finally, partial neck growth voids are formed due to incomplete intra-layer and inter-layer bonding, as illustrated in Figure 4(b). Partial neck growth are the main contributors of voids in parts printed using FDM, and they can be avoided through 100% fusion of adjacent filaments, but this is not practically achievable. The presence of voids reduces mechanical properties of parts printed using FDM (Krajangsawasdi et al., 2021). Therefore, voids should be averted. However, this might not be achievable because parts created using FDM are most likely to contain voids. It leaves a research gap to investigate the extent to which different process parameters and material properties affect neck formation, which is the focus of this study.
2.2 Modelling of neck growth
The quality of fusion of adjoining filaments is imperative during the FDM process as it determines the mechanical integrity of a printed part (Gao et al., 2021; Ahmad et al., 2022). Gurrala and Regalla (2014) further alluded that the strength of parts printed using FDM is majorly dependent on the intra-layer bonding, inter-layer fusion and level of neck growth between filaments. According to Vanaei et al. (2021), bonding locations are points of failure when a component printed using FDM is subjected to external pressure.
Different models have been developed to describe neck growth and formation of partial neck growth voids. Early models were based on the fusion of two Newtonian fluid droplets, as represented in Figure 6(a) (Tao et al., 2021). The models assume that the droplets are identical to each other with radii of a0. The droplets coalesce after time (t), forming a resultant sphere with radius af. Figure 6(b) represents intra- and inter-layer bonding of cylindrical filaments in FDM.
Gurrala and Regalla (2014) and Frenkel (1945) developed models to describe neck growth evolution of cylindrical filaments with respect to time and viscous sintering, as illustrated by equations (1) and (2), respectively. Bhalodi et al. (2019) also developed mathematical models to relate temperature and the degree of fusion between two adjacent filaments, as summarised by equations (3) and (4):
θ= intersection angle between the filaments (°);
Γ = coefficient of surface tension;
r0= initial radius of a filament (m);
η = viscosity of the melt of a filament (kg.m−1.s−1);
t= sintering time (s);
m = mass of the filament (kg);
v= velocity of nozzle (m/s);
T = temperature at the interface of adjacent filaments (°C); and
T∞ = temperature of the build platform (°C).
Figures 6(c) and 6(d), provide an actual representation of bonding of two adjacent filaments. Tao et al. (2021) proposed a mathematical model to describe radial width of the growth of the neck with the time [based on Figures 6(b–d)], presented here as equation (5):
y(t) = radial width of neck growth (m);
H0 = raster height (m); and
θ(t) = intersection angle =
Han et al. (2022) also used the Frenkel-Eshelby model to describe the fusion of sintered particles in polymer laser sintering (PLS), resulting in formation of a melt that solidified to form a three-dimensional component. The model considers two adjacent particles that fuse together with increasing temperature as illustrated in Figure 7, where a1 and a2 are radii of two adjacent particles, y is the radius of the neck and a is the radius of resulting spherical melt.
In the current study, the Frenkel–Eshelby model could be used to explain the fusion of two adjacent threads despite the fact that FDM considers films as opposed to PLS, where powder particles are considered. One of the first models proposed by Frenkel that described coalesence of particles driven by viscous flow (Lupone et al., 2021) was modified. Equation (6) represents the Frenkel’s model which was modified in the present work due its simplicity and ease of measuring the length of the neck between two adjacent filaments from images obtained using scanning electron microscopy (SEM):
y = length of growing neck between two filaments (m);
a1 2 = initial radii of two adjacent filaments (m);
σ = surface tension of the material (N/m);
t = time (s);
a = radius of resulting fused track (m); and
η0 = viscosity of the material (kg.m−1.s−1).
Mwania et al. (2023) considered that the ratio of the total height (h) of the neck to the diameter (d) of two adjacent filaments after fusion and cooling (h/d) is directly proportional to the degree of fusion [equation (7)]. The study considered that higher values represent better coalescence of filaments, which also represents better process parameters for a particular material. Figure 8 shows the total height of the neck and the diameter of two adjacent filaments after fusion and cooling:
Where:
δf= degree of fusion between adjoining filaments;
h = total height of the neck (m); and
d = diameter of two adjacent filaments after fusion and cooling.
In the current study, the degree of fusion of two adjacent tracks printed using FDM was investigated. This research aims to act as a starting point for studying degrees of fusion of tracks to establish an analytical model involving crucial process parameters used for FDM.
3. Materials and methods
3.1 Printing equipment
The specimens were built using an FDM desktop UP Mini 2 ES Printer (Figure 9).
According to the manufacturers of the equipment, the printer can be used for educational, domestic and industrial purposes. The specifications of the printing machine are outlined in Table 1.
3.2 Materials used
Two commercial polymeric filaments (PolyMideTM CoPA and PolymaxTM PC, as well as the polymer composite PolyMideTM PA6-CF) from the supplier, Polymaker, were used in this study. PolyMideTM CoPA is a copolymer consisting of nylon 6 (PA6) and nylon 6.6 (PA6.6). According to the supplier, the material has excellent strength, toughness and maximum operating temperature of 180°C. It is also suitable for printing because of limited warping. PolymaxTM PC is an engineered type of polycarbonate (PC) with good printing qualities, excellent strength, toughness and resistance to heat, as specified by the supplier. The suppliers suggest that the material is suitable for a wide range of engineering applications and can withstand temperatures up to 113°C. PolyMideTM PA6-CF is a carbon fibre-reinforced PA6. According to the supplier, the carbon fibre improves the stiffness, strength, layer adhesion and heat resistance of the parent matrix. The printing conditions specified by the supplier for the three materials, are summarised in Table 2.
3.3 Printing process
A simple parameter-printing matrix was considered for PolyMideTM PA6-CF at the onset, where one of the parameters shown in Table 3 was varied, while the others were held constant. Table 3 is a summary of the parameter-printing matrix considered for fabricating test specimens using PolyMideTM PA6-CF.
The authors used the Taguchi method to develop a matrix for the printing parameters for PolyMideTM CoPA and PolymaxTM PC. Five process-parameters [layer thickness, printing speed, hatch spacing (air gap), extrusion temperature and extrusion width] with four levels were considered, as summarised in Table 4. Table 5 is an outline of an L16 orthogonal array used in this analysis, while Table 6 is the matrix considered for the two materials. 14 samples were printed using PolymaxTM PC up to run 14 as shown in Tables 5 and 6. For the outlined process parameters, 16 samples were fabricated using PolyMideTM CoPA.
It was evident that there was a correlation between layer thickness and the extrusion width. For instance, the software displayed an error when a layer thickness of a value more than 0.25 mm was used for an extrusion width of 0.7 mm. In addition, for runs 8, 10 and 15, extrusion widths started at 0.35, 0.38 and 0.40 mm. Hence, the printing schedule had to be adjusted to accommodate these requirements of the software.
The supplier recommends annealing of PolyMideTM CoPA at 80°C for six hours because printed parts do not reach full crystallisation after printing. The suppliers further state that the material should also be dried for six hours at 100°C, in case it absorbed moisture. The suppliers observe that PolymaxTM PC can be annealed at 90°C for two hours to release internal stresses that encourage development of micro-cracks. If the parts absorbed moisture, they can be dried at 75°C for two hours. It is recommended by the suppliers that PolyMideTM PA6-CF on the other hand, can be annealed at 80°C for six hours to ensure full crystallisation of the printed parts. Moreover, the material can be dried at 100°C for eight hours, in case the printed parts absorbed moisture. The main reasons for annealing of printed parts are to minimise porosity, reduce the degree of crystallinity and relief residual stresses in the parts. However, these post-processes were not undertaken in this study, and the specimens were analysed in the as-built state, because the study was focused on the degree of fusion of adjoining built filaments that is not subject to either of these three factors, unlike the case for three-dimensional parts. The filaments were also printed in their as-received state because they were delivered in sealed bags which prevented the absorption of moisture.
Double tracks were printed on top of a support structure, as shown in Figure 10.
Different process parameters, specified in Tables 3 and 6 were considered for different test specimens. Upon completion of printing, the samples were allowed to cool to room temperature and then placed in air-tight bags to prevent them from absorbing moisture. The top surface of the tracks printed using the three materials were examined using a SEM to assess the surface roughness, as well as any other irregularities. Afterwards, the tracks were cut right through the diameter using a razor blade, and the cut surfaces then assessed using a SEM to inspect the geometry of the cross-sections. The images were analysed using (ImageJ 1.53k; Java 1.8.0_172 [64-bit]) to measure the total height (h) of the neck and the diameter (d) of two adjacent filaments after fusion and cooling. The degree of fusion for tracks, printed at different process parameters, were quantified using equation (7) and the data obtained evaluated using Minitab statistical software to determine the optimal process parameters for the different materials.
4. Results and discussion
4.1 Top surfaces of tracks printed using PolyMideTM CoPA, PolymaxTM PC and PolyMideTM PA6-CF
Figure 11 (Magnification X110) shows the top surface of tracks printed using PolyMideTM CoPA, PolymaxTM PC and PolyMideTM PA6-CF for process parameters suggested as optimal from this analysis.
It is essential to establish the surface roughness of components printed using FDM, to ensure that they meet the requirements of tolerance and roughness, as was noted by Boschetto et al. (2016). A visual inspection of the printed parts shows that PolyMideTM PA6-CF had more surface irregularities (roughness) as compared to tracks printed using PolyMideTM CoPA and PolymaxTM PC. This is supported by observations of the images in the foregoing figure. Parts fabricated using PolymaxTM PC appeared to have the smoothest surface for all the three materials used, as is evident in Figure 11. Assuming that the surface roughness of the printed tracks reflects the surface roughness of finished parts, it can be deduced that for the three materials, PolymaxTM PC is the best material suitable for FDM printing, followed by PolyMideTM CoPA, for applications that require a smooth surface. This foregoing analysis suggests that PolyMideTM PA6-CF will present challenges when printed using FDM, for applications requiring smooth surfaces. This is because of notable surface roughness, as represented by the considerable irregularities on the surfaces on the tracks.
Notable research has been undertaken to investigate how different process parameters, such as layer thickness, spreading speed and raster angle, affect surface roughness of parts printed using FDM (Sukindar et al., 2024; Bintara et al., 2021; Alsoufi and Elsayed, 2018). However, few studies have focused on the impacts of different feedstock materials on surface roughness of printed parts. The current study, illustrates that the source of printing material will affect the surface roughness of components printed using FDM.
4.2 Geometry of the tracks printed using PolyMideTM CoPA, PolymaxTM PC and PolyMideTM PA6-CF
Figure 12 shows that parts printed using PolymaxTM PC and PolyMideTM CoPA have double tracks that were not fully fused, as opposed to tracks fabricated using PolyMideTM PA6-CF. It can be assumed by this, that parts printed using PolyMideTM PA6-CF are denser compared to parts built using PolymaxTM PC and PolyMideTM CoPA because the former material results in better fusion of filaments, which can be seen through visual inspection. On the other hand, it was difficult to remove tracks printed using PolyMideTM PA6-CF from the support structure because the tracks fused with the support structure to form a single entity as illustrated in Figure 12(a). Parts printed from materials that are suitable for the FDM process should be easy to remove from the support structure to prevent damaging the components (Joseph et al., 2023). The tracks printed using PolyMideTM CoPA also fused with the support structure, but the outline of the track was visible, thus making it possible to investigate the degree of fusion of the tracks, while still attached to the support structure [Figure 12(b)]. The filaments printed using PolymaxTM PC were easy to remove from the support structure [Figure 12(c)], thus allowing the inspection of the level of fusion of the tracks separately from the support structure. Therefore, this study only considered bond formation and degree of fusion for tracks printed using PolyMideTM CoPA and PolymaxTM PC.
4.3 Bond formation and degree of fusion of filaments printed using PolyMideTM CoPA and PolymaxTM PC
Numerous process parameter optimisation studies have been undertaken, but most of them have focused on ABS, PLA and PC (Dey and Yodo, 2019). The current study optimises process-parameters for two new commercial materials (PolyMideTM CoPA, PolymaxTM PC). The obtained results were analysed using Minitab software to determine the optimum process parameters of layer thickness, printing speed, hatch spacing and extrusion width for PolyMideTM CoPA and PolymaxTM PC polymeric materials. The analysis was undertaken using the Taguchi method (a modelling strategy embedded into the software) to optimise and determine the parameters with the most significant impact. The larger is better feature was considered in this analysis, as recommended by Atakok et al. (2022). Table 7 presents data on the degree of fusion for specimens printed using different process parameters.
4.3.1 Bond formation and degree of fusion of filament-parts printed using PolyMideTM CoPA
Table 8 summarises the average values of the degree of fusion of PolyMideTM CoPA for different levels of layer thickness, printing speed, hatch spacing, extrusion temperature and extrusion width. Table 8 also ranks the significance of these process parameters based on the degree of fusion of two adjacent filaments.
The order of the significance of the selected process parameters, for PolyMideTM CoPA, in the foregoing table in order of the most to the least critical is as follows: extrusion temperature, layer thickness, extrusion width, hatch spacing and printing speed.
Figure 13 is a representation of plots for the mean values of the degree of fusion for adjacent filaments printed using PolyMideTM CoPA for the selected process parameters.
The values of process parameters corresponding to the highest degree of fusion were considered as the optimal process parameters. From Figure 13, the optimum process parameters for filaments printed using PolyMideTM CoPA are 0.25 mm, 40 mm/s, −0.10 mm, 255°C and 0.50 mm for layer thickness, printing speed, hatch spacing, extrusion temperature and extrusion width, respectively.
4.3.2 Bond formation and degree of fusion of filament-parts printed using PolymaxTMPC
Table 9 outlines the average values of the degree of fusion of PolymaxTMPC for different levels of layer thickness, printing speed, hatch spacing, extrusion temperature and extrusion width. Table 9 also ranks the significance of these process parameters based on the degree of fusion of two adjacent filaments.
The order of the significance of the selected process parameters, for PolymaxTM PC, in the foregoing table in order of the most to the least critical is as follows: hatch spacing, extrusion width, layer thickness, printing speed and extrusion temperature.
The plots for the mean values of the degree of fusion for adjacent filaments printed using PolymaxTM PC is as shown in Figure 14.
The optimal process parameters for PolymaxTM PC, that would yield the highest degree of fusion of adjacent filaments, are 0.30 mm, 40 mm/s, 0.00 mm, 260°C and 0.6 mm for layer thickness, printing speed, hatch spacing, extrusion temperature and extrusion width respectively.
4.3.3 Linear regression models
Equations (8) and (9) are linear regression models that were developed in the present work using the regression module embedded in the Minitab Software. They show the relationship between the degree of fusion between two adjacent filaments with different process parameters (layer thickness, printing speed, hatch spacing, extrusion temperature and extrusion width) for PolyMideTM CoPA and PolymaxTM PC, respectively. The models can be used to predict the optimal process parameters for the two materials or other closely related polymers based on the degree of fusion between two adjacent filaments:
δf = degree of fusion;
t = layer thickness (m);
s = sprinting speed (mm/s);
h = hatch spacing (m);
T = extrusion temperature (°C); and
w = extrusion width (m).
Table 10 compares the values of degree of fusion between two adjacent filaments printed using PolyMideTM CoPA and PolymaxTM PC, based on the experimental data and calculated using equations (8) and (9), respectively.
The use of equation (8) on PolyMideTM CoPA resulted in an average difference in the degree of fusion of 15.57% between experimental and linear regression model. Similarly, applying equation (9) to PolymaxTM PC, led to an average difference in the degrees of fusion of 16.85%. Clearly, the two respective linear regression models can be used to predict the degree of fusion between two adjacent filaments printed using PolyMideTM CoPA and PolymaxTM PC, noting the determined percentage differences.
5. Conclusions and recommendations
This study was conducted to investigate the surface and geometry of tracks printed using PolyMideTM CoPA, PolymaxTM PC and PolyMideTM PA6-CF. The study also examined the degree of fusion of adjacent filaments for PolyMideTM CoPA and PolymaxTM PC, to determine the optimal process parameters that would yield the highest degree of fusion between two adjacent filaments. The following conclusions can be drawn from the results presented and discussed here:
PolyMideTM PA6-CF is most likely to present challenges when used in the FDM process to fabricate components as it was difficult to separate printed tracks from the support structure. The tracks also had noticeable surface irregularities that might limit the applications of final components due to the high probability of building parts with rough surfaces.
Moderate irregularities were observed on the surfaces of tracks printed using PolyMideTM CoPA. Post-process operations such as cutting and grinding might be required to remove components that have been fabricated using this material from the support structure as there was some level of fusion between the printed tracks and the support structures.
PolymaxTM PC might be considered the most suitable material, of all the three materials considered, for use in FDM here, because the printed tracks showed the smoothest surface, and it was easy to remove them from the support structures.
The study results suggested the optimal process parameters for PolyMideTM CoPA as 0.25 mm, 40 mm/s, −0.10 mm, 255°C and 0.50 mm for layer thickness, printing speed, hatch spacing, extrusion temperature and extrusion width, respectively.
The analysis carried out here came up with optimal process parameters for PolymaxTM PC of 0.30 mm, 40 mm/s, 0.00 mm, 260°C and 0.6 mm for layer thickness, printing speed, hatch spacing, extrusion temperature and extrusion width, respectively.
It is suggested that three dimensional samples be fabricated using the materials considered in this analysis to ascertain their utility in FDM. An evaluation should also be undertaken to examine the physical and mechanical properties of printed samples. Moreover, the influence of other process parameters (bed temperature, feed rate, printing time) on bond formation should also be investigated.
Figures
Figure 1
Schematic representation of the process of developing parts in FDM
Figure 2
The steps of bond formation between adjoining filaments
Figure 3
Key machine parameters and material properties influencing the FDM process
Figure 4
Types of voids common in parts printed using FDM
Figure 5
Schematic representation of a typical layer-part
Figure 6
Schematic representation of neck growth evolution for two spherical droplets (a), intra- and inter-layer bonding of filaments in FDM (b), and cylindrical filaments (c, d)
Figure 7
Schematic representation of the Frenkel–Eshelby model, which is used to describe fusion of two adjacent particles in PLS
Figure 8
Schematic representation of the total height of the neck and the diameter of two adjacent filaments after fusion and cooling
Figure 9
The UP Mini 2 ES Printer that was used in this study
Figure 10
A sample of a fabricated test specimen with the support structure and dual tracks
Figure 11
Top surfaces of tracks printed using PolyMideTM CoPA, PolymaxTM PC, and PolyMideTM PA6-CF
Figure 12
Cross-sectional view of tracks printed using PolyMideTM PA6-CF, PolyMideTM CoPA, and PolymaxTM PC
Figure 13
Plots for mean values of degree of fusion for adjacent filaments printed using PolyMideTM CoPA
Figure 14
Plots for the mean values of degree of fusion for adjacent filaments printed using PolymaxTM PC
Specifications of up mini 2 ES mini printer
| # | Description and parameter | Specification |
|---|---|---|
| 1 | Printing technology | Melted extrusion modelling (MEM) |
| 2 | Extruder | 1 |
| 3 | Nozzle diameter | 0.4 mm |
| 4 | Maximum extruder temperature | 299°C |
| 5 | Maximum extruder travel speed | 200 mm/sec |
| 6 | Accuracy in X, Y and Z directions | 5 microns |
| 7 | Build volume | 120 × 120 × 120 mm3 |
| 8 | Accuracy of printed parts | ± 0.1 /100 mm |
| 9 | Layer resolutions | 0.15/0.2/0.25/0.3/0.35 mm |
| 10 | Maximum temperature of the build plate | 70°C |
| 11 | Recommended filament materials | ABS, PLA, TPU and others |
| 12 | Filament diameter | 1.75 mm |
| 13 | Software | UP Studio version 2.5 or above |
| 14 | Supported operating system | Windows 7 or higher (32 or 64 bits) Mac OS 10.10 |
| 15 | Hardware | OpenGL 2.0 with at least 4GB of RAM |
Source: Table by authors
Recommended printing parameters
| # | Printing parameters | PolyMideTM CoPA | PolymaxTM PC | PolyMideTM PA6-CF |
|---|---|---|---|---|
| 1 | Printing temperature (°C) | 250–270 | 250–270 | 280–300 |
| 2 | Bed temperature (°C) | 25–50 | 90–105 | 25–50 |
| 3 | Printing speed (mm/s) | 30– 50 | ||
| 4 | Fan | Off | ||
Source: Table by authors
Parameter matrix for test specimens printed in PolyMideTM PA6-CF
| Layer thickness (mm) |
Infill density (%) | Printing speed (mm/s) | Extrusion width (mm) | Air gap (mm) | Extrusion temperature (°C) |
|---|---|---|---|---|---|
| Printing matrix with variation of the layer thickness | |||||
| 0.05 | 99 | 45 | 0.58 | 0 | 245 |
| 0.20 | 99 | 45 | 0.58 | 0 | 245 |
| 0.25 | 99 | 45 | 0.58 | 0 | 245 |
| 0.30 | 99 | 45 | 0.58 | 0 | 245 |
| 0.35 | 99 | 45 | 0.58 | 0 | 245 |
| Printing matrix with variation of the infill density | |||||
| 0.20 | 15 | 45 | 0.58 | 0 | 245 |
| 0.20 | 20 | 45 | 0.58 | 0 | 245 |
| 0.20 | 65 | 45 | 0.58 | 0 | 245 |
| 0.20 | 80 | 45 | 0.58 | 0 | 245 |
| 0.20 | 99 | 45 | 0.58 | 0 | 245 |
| Printing matrix with variation of the printing speed | |||||
| 0.20 | 99 | 35 | 0.58 | 0 | 245 |
| 0.20 | 99 | 40 | 0.58 | 0 | 245 |
| 0.20 | 99 | 45 | 0.58 | 0 | 245 |
| 0.20 | 99 | 55 | 0.58 | 0 | 245 |
| 0.20 | 99 | 60 | 0.58 | 0 | 245 |
| Printing matrix with variation of the air gap | |||||
| 0.20 | 99 | 45 | 0.58 | −0.10 | 245 |
| 0.20 | 99 | 45 | 0.58 | −0.05 | 245 |
| 0.20 | 99 | 45 | 0.58 | 0.00 | 245 |
| 0.20 | 99 | 45 | 0.58 | +0.05 | 245 |
| 0.20 | 99 | 45 | 0.58 | +0.01 | 245 |
| Printing matrix with variation of the extrusion temperature | |||||
| 0.20 | 99 | 45 | 0.58 | 0 | 215 |
| 0.20 | 99 | 45 | 0.58 | 0 | 225 |
| 0.20 | 99 | 45 | 0.58 | 0 | 245 |
| 0.20 | 99 | 45 | 0.58 | 0 | 255 |
| 0.20 | 99 | 45 | 0.58 | 0 | 260 |
Source: Table by authors
Process parameters and levels for printing test specimens in PolyMideTM CoPA and PolymaxTM PC
| # | Process parameter | Levels of each process parameter | |||
|---|---|---|---|---|---|
| Level 1 | Level 2 | Level 3 | Level 4 | ||
| 1 | Layer thickness (mm) | 0.15 | 0.2 | 0.25 | 0.30 |
| 2 | Printing speed (mm/s) | 30 | 35 | 40 | 50 |
| 3 | Hatch spacing (mm) | −0.10 | 0.00 | 0.10 | 0.15 |
| 4 | Extrusion temperature (°C) | 250 | 255 | 260 | 270 |
| 5 | Extrusion width (mm) | 0.30 | 0.40 | 0.50 | 0.60 |
Source: Table by authors
L16 Orthogonal array
| Run# | Layer thickness | Printing speed | Hatch spacing | Extrusion temperature | Extrusion width |
|---|---|---|---|---|---|
| 1 | 1 | 1 | 1 | 1 | 1 |
| 2 | 1 | 2 | 2 | 2 | 2 |
| 3 | 1 | 3 | 3 | 3 | 3 |
| 4 | 1 | 4 | 4 | 4 | 4 |
| 5 | 2 | 1 | 2 | 3 | 4 |
| 6 | 2 | 2 | 1 | 4 | 3 |
| 7 | 2 | 3 | 4 | 1 | 2 |
| 8 | 2 | 4 | 3 | 2 | 1 |
| 9 | 3 | 1 | 3 | 4 | 2 |
| 10 | 3 | 2 | 4 | 3 | 1 |
| 11 | 3 | 3 | 1 | 2 | 4 |
| 12 | 3 | 4 | 2 | 1 | 3 |
| 13 | 4 | 1 | 4 | 2 | 3 |
| 14 | 4 | 2 | 3 | 1 | 4 |
| 15 | 4 | 3 | 2 | 4 | 1 |
| 16 | 4 | 4 | 1 | 3 | 2 |
Source: Table by authors
Process-parameter matrix for printing test specimens in PolyMideTM CoPA and PolymaxTM PC
| Run# | Layer thickness (mm) |
Printing speed (mm/s) |
Hatch spacing (mm) |
Extrusion temperature (°C) |
Extrusion width (mm) |
|---|---|---|---|---|---|
| 1 | 0.15 | 30 | −0.10 | 250 | 0.30 |
| 2 | 0.15 | 35 | 0.00 | 255 | 0.40 |
| 3 | 0.15 | 40 | 0.10 | 260 | 0.50 |
| 4 | 0.15 | 50 | 0.15 | 270 | 0.60 |
| 5 | 0.20 | 30 | 0.00 | 260 | 0.60 |
| 6 | 0.20 | 35 | −0.10 | 270 | 0.50 |
| 7 | 0.20 | 40 | 0.15 | 250 | 0.40 |
| 8 | 0.20 | 50 | 0.10 | 255 | 0.35 |
| 9 | 0.25 | 30 | 0.10 | 270 | 0.40 |
| 10 | 0.25 | 35 | 0.15 | 260 | 0.38 |
| 11 | 0.25 | 40 | −0.10 | 255 | 0.60 |
| 12 | 0.25 | 50 | 0.00 | 250 | 0.50 |
| 13 | 0.30 | 30 | 0.15 | 255 | 0.50 |
| 14 | 0.30 | 35 | 0.10 | 250 | 0.60 |
| 15 | 0.30 | 40 | 0.00 | 270 | 0.40 |
| 16 | 0.30 | 50 | −0.10 | 260 | 0.40 |
Source: Table by authors
Degree of fusion for tracks printed using PolyMideTM CoPA and PolymaxTM PC at different process parameters
| Run# | Layer thickness (mm) |
Printing speed (mm/s) |
Hatch spacing (mm) |
Extrusion temperature (°C) |
Extrusion width (mm) |
Degree of fusion for tracks printed using PolyMideTM CoPA | Degree of fusion for tracks printed using PolymaxTM PC |
|---|---|---|---|---|---|---|---|
| 1 | 0.15 | 30 | −0.10 | 250 | 0.30 | 0.23 | 0.22 |
| 2 | 0.15 | 35 | 0.00 | 255 | 0.40 | 0.32 | 0.21 |
| 3 | 0.15 | 40 | 0.10 | 260 | 0.50 | 0.30 | 0.26 |
| 4 | 0.15 | 50 | 0.15 | 270 | 0.60 | 0.22 | 0.31 |
| 5 | 0.20 | 30 | 0.00 | 260 | 0.60 | 0.38 | 0.41 |
| 6 | 0.20 | 35 | −0.10 | 270 | 0.50 | 0.30 | 0.27 |
| 7 | 0.20 | 40 | 0.15 | 250 | 0.40 | 0.18 | 0.15 |
| 8 | 0.20 | 50 | 0.10 | 255 | 0.35 | 0.29 | 0.00 |
| 9 | 0.25 | 30 | 0.10 | 270 | 0.40 | 0.24 | 0.00 |
| 10 | 0.25 | 35 | 0.15 | 260 | 0.38 | 0.35 | 0.23 |
| 11 | 0.25 | 40 | −0.10 | 255 | 0.60 | 0.58 | 0.44 |
| 12 | 0.25 | 50 | 0.00 | 250 | 0.50 | 0.44 | 0.34 |
| 13 | 0.30 | 30 | 0.15 | 255 | 0.50 | 0.51 | 0.48 |
| 14 | 0.30 | 35 | 0.10 | 250 | 0.60 | 0.33 | 0.20 |
| 15 | 0.30 | 40 | 0.00 | 270 | 0.40 | 0.32 | 0.35 |
| 16 | 0.30 | 50 | −0.10 | 260 | 0.40 | 0.42 | 0.24 |
Source: Table by authors
Levels and corresponding average values of process parameters used for PolyMideTM CoPA
| Levels | Average values of the degree of fusion after analysis | ||||
|---|---|---|---|---|---|
| Layer thickness (mm) | Printing speed (mm/s) | Hatch spacing (mm) | Extrusion temperature (°C) | Extrusion width (mm) | |
| 1 | 0.27 | 0.34 | 0.38 | 0.30 | 0.30 |
| 2 | 0.29 | 0.33 | 0.37 | 0.43 | 0.29 |
| 3 | 0.40 | 0.35 | 0.29 | 0.36 | 0.39 |
| 4 | 0.40 | 0.34 | 0.32 | 0.27 | 0.38 |
| Rank | 2 | 5 | 4 | 1 | 3 |
Source: Table by authors
Levels and corresponding average values of degree of fusion for five process parameters used for PolymaxTM PC
| Average values of the degree of fusion after analysis | |||||
|---|---|---|---|---|---|
| Level | Layer thickness (mm) | Printing speed (mm/s) | Hatch spacing (mm) | Extrusion temperature (°C) | Extrusion width (mm) |
| 1 | 0.25 | 0.28 | 0.29 | 0.23 | 0.20 |
| 2 | 0.21 | 0.23 | 0.33 | 0.28 | 0.15 |
| 3 | 0.25 | 0.30 | 0.12 | 0.29 | 0.34 |
| 4 | 0.32 | 0.22 | 0.29 | 0.23 | 0.34 |
| Delta | 0.11 | 0.08 | 0.21 | 0.06 | 0.19 |
| Rank | 3 | 4 | 1 | 5 | 2 |
Source: Table by authors
Degree of fusion between two adjacent filaments printed using PolyMideTM CoPA and PolymaxTM PC based on the experimental data and the proposed linear regression models
| Run# | Degree of fusion for tracks printed using PolyMideTM CoPA (based on the experimental results) | Degree of fusion for tracks printed using PolyMideTM CoPA (Based on the linear regression model results) | % difference between experimental and linear regression model results (%) |
Degree of fusion for tracks printed using PolymaxTM PC (based on the experimental results) | Degree of fusion for tracks printed using PolymaxTM PC (based on the linear regression model results) | % difference between experimental and linear regression model results (%) |
|---|---|---|---|---|---|---|
| 1 | 0.23 | 0.28 | 21.74 | 0.22 | 0.20 | 09.09 |
| 2 | 0.32 | 0.27 | 15.63 | 0.21 | 0.21 | 0.00 |
| 3 | 0.30 | 0.26 | 13.33 | 0.26 | 0.23 | 11.53 |
| 4 | 0.22 | 0.24 | 09.09 | 0.31 | 0.25 | 19.35 |
| 5 | 0.38 | 0.37 | 02.63 | 0.41 | 0.37 | 09.76 |
| 6 | 0.30 | 0.34 | 13.33 | 0.27 | 0.33 | 22.22 |
| 7 | 0.24 | 0.29 | 20.83 | 0.15 | 0.18 | 20.00 |
| 8 | 0.29 | 0.26 | 10.34 | 0.00 | 0.14 | 14.00 |
| 9 | 0.24 | 0.29 | 20.83 | 0.00 | 0.23 | 23.00 |
| 10 | 0.35 | 0.27 | 22.86 | 0.23 | 0.20 | 13.04 |
| 11 | 0.58 | 0.47 | 18.97 | 0.44 | 0.40 | 09.09 |
| 12 | 0.44 | 0.42 | 04.55 | 0.34 | 0.30 | 11.76 |
| 13 | 0.51 | 0.40 | 21.57 | 0.48 | 0.31 | 35.42 |
| 14 | 0.33 | 0.47 | 42.42 | 0.25 | 0.38 | 27.57 |
| 15 | 0.32 | 0.34 | 06.25 | 0.35 | 0.27 | 22.86 |
| 16 | 0.42 | 0.44 | 4.76 | 0.24 | 0.29 | 20.83 |
| Overall (mean) difference = 15.57 |
Overall (mean) difference = 16.85 |
Source: Table by authors
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Acknowledgements
The authors would like to thank Product Development Technology Station at the Central University of Technology (CUT), Free State, for their assistance with the printing of the filament-parts using FDM. Special gratitude is also extended to the Department of Geology, University of the Free State, South Africa, for their assistance with the SEM experiments.
Funding: This research was funded by CPAM programme (Collaborative Program in Additive Manufacturing), grant number CSIRNLC-CPAM-18-MOA-CUT-03. The APC was funded by CPAM.
Data availability statement: All the information will be available on request.
Conflicts of interest: The authors declare no conflict of interest.