Research

16 pages, 5934 KiB

Open AccessArticle

Overprinting of TPU onto PA6 Substrates: The Influences of the Interfacial Area, Surface Roughness and Processing Parameters on the Adhesion between Components

by Janez Slapnik, Rebeka Lorber, Irena Pulko, Miroslav Huskić and Klementina Pušnik Črešnar

Polymers 2024, 16(5), 650; https://doi.org/10.3390/polym16050650 - 28 Feb 2024

Viewed by 581

Abstract

The hybridisation of injection moulding (IM) and additive manufacturing (AM) offers the opportunity to combine the high productivity of IM and the high flexibility of AM into a single process. IM parts can be overprinted through fused filament fabrication (FFF) to allow for [...] Read more.

The hybridisation of injection moulding (IM) and additive manufacturing (AM) offers the opportunity to combine the high productivity of IM and the high flexibility of AM into a single process. IM parts can be overprinted through fused filament fabrication (FFF) to allow for the customisation of parts or to add new functionalities. However, the right material pair must be chosen, and processing parameters must be optimised to achieve suitable adhesion between the components. The present study dealt with the investigation of the influence of the interfacial area, substrate surface roughness and overprinting processing parameters on the adhesion between the polyamide 6 (PA6) substrate and thermoplastic polyurethane (TPU) rib overprinted via FFF. PA6 substrates were produced through the IM of plates into a mould with different textures to obtain substrates with three different surface roughnesses. The ribs with varied interfacial areas were overprinted onto produced substrates using a desktop FFF 3D printer. To study the effect of overprinting processing parameters, the ribs were overprinted under varying printing and substrate temperatures and printing speeds according to the Box–Behnken design of experiments (DoE). The chemical composition and thermal properties of used materials were determined via attenuated total reflectance–Fourier transform infrared spectroscopy (ATR-FTIR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The surface properties of prepared substrates were studied via digital optical microscopy (OM), through surface roughness measurements using a confocal microscope, through contact angle (CA) measurements and through the determination of free surface energy (SFE). The adhesion between the components was determined by evaluating the tear-off strength using a universal testing machine (UTM). With an increasing interfacial area, the tear-off strength decreased, while substrate surface roughness had no statistically significant effect. Overprinting parameters influenced the tear-off strength in the order of printing speed > printing temperature > substrate temperature. High values of tear-off strength were found for the lowest printing speed, while there were no important differences found between the middle and upper values. With increasing printing and substrate temperatures, the tear-off strength increased linearly. The highest value of tear-off strength (0.84 MPa) was observed at a printing temperature, substrate temperature and printing speed of 250 °C, 80 °C and 2 mm/s, respectively. Full article

(This article belongs to the Special Issue Structure and Properties of Polymeric Materials in Additive Manufacturing II)

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15 pages, 3651 KiB

Open AccessArticle

Effect of Powder Bed Fusion Laser Sintering on Dimensional Accuracy and Tensile Properties of Reused Polyamide 11

by Urvashi F. Gunputh, Gavin Williams, Marzena Pawlik, Yiling Lu and Paul Wood

Polymers 2023, 15(23), 4602; https://doi.org/10.3390/polym15234602 - 02 Dec 2023

Viewed by 864

Abstract

Polyamide 11 (PA11) is a plant-based nylon made from castor beans. Powder bed fusion laser sintering (PBF-LS) is an additive manufacturing process used for PA11 which allows for the reuse of the unsintered powder. The unsintered powder is mixed with virgin powders at [...] Read more.

Polyamide 11 (PA11) is a plant-based nylon made from castor beans. Powder bed fusion laser sintering (PBF-LS) is an additive manufacturing process used for PA11 which allows for the reuse of the unsintered powder. The unsintered powder is mixed with virgin powders at different refresh rates, a process which has been studied extensively for most semi-crystalline polyamides. However, there is lack of information on the effect of using 100% reused PA11 powder and the effect of the number of times it is reused on its own, during powder bed fusion laser sintering. This paper investigates the effect of reusing PA11 powder in PBF-LS and the effect of the number of times it is reused on the dimensional accuracy, density and thermal and tensile properties. From the 100% virgin powder to the third reuse of the powder, there is a decrease in powder wastage, crystallinity and tensile strength. These are associated with the polymerisation and cross-linking process of polymer chains, upon exposure to high temperatures. This results in a higher molecular weight and, hence, a higher density. From the fourth reuse to the tenth reuse, the opposite is observed, which is associated with an increase in high-viscosity unmolten particles, resulting in defects in the PBF-LS parts. Full article

(This article belongs to the Special Issue Structure and Properties of Polymeric Materials in Additive Manufacturing II)

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18 pages, 11336 KiB

Open AccessArticle

Mechanical Performance and Failure Analysis of a 3D-Printed “Continuous Layer–Lattice Layer–Continuous Layer” Sandwich Structure

by Daming Nie, Lingyu Kong, Yu Zhang, Xingyu Qiu, Yili Fu and Jason Gu

Polymers 2023, 15(21), 4283; https://doi.org/10.3390/polym15214283 - 31 Oct 2023

Cited by 1 | Viewed by 992

Abstract

Sandwich structures are engineered with continuous layers surrounding the inner lattices, which combines the advantages of the high strength of the continuous layer and the light weight of the lattice layer. They are widely employed in weight-critical energy-absorbing engineering fields such as aerospace, [...] Read more.

Sandwich structures are engineered with continuous layers surrounding the inner lattices, which combines the advantages of the high strength of the continuous layer and the light weight of the lattice layer. They are widely employed in weight-critical energy-absorbing engineering fields such as aerospace, automobile, and robotics. However, the application of sandwich structures made of polymer matrix composites is still limited due to lack of essential performance investigation and adequate reference data. The following innovative works are accomplished in this paper: (i) Continuous long glass fiber (CGF) is employed within the continuous layer of the sandwich structure, with composite short carbon fiber/polyamide (SCF/N) applied within the lattice layer. (ii) Sandwich structures with different cell types and orientations of the lattice infills are designed and prepared by additive manufacturing. (iii) The basic mechanical properties of the sandwich structures, i.e., the bi-directional tension/compression compound performance, failure modes and mechanisms in characteristic directions, are analyzed systematically. (iv) The effects of geometric features on the three-point bending properties of L-shaped sandwich structures are investigated and compared with those of pure SCF/N structures. The results show that the bending resistance per unit weight was up to 54.3% larger than that of pure SCF/N, while the weight could be decreased by 49%, and the bending flexibility before fracture could be increased by 44%. These studies contribute fundamental research data to the application of sandwich structures prepared by fiber reinforced polymer matrix composites. Full article

(This article belongs to the Special Issue Structure and Properties of Polymeric Materials in Additive Manufacturing II)

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14 pages, 9817 KiB

Open AccessArticle

Photocurable High-Energy Polymer-Based Materials for 3D Printing

by Dmitrii Tkachev, Yana Dubkova, Alexander Zhukov, Yanis Verkhoshanskiy, Alexander Vorozhtsov and Ilya Zhukov

Polymers 2023, 15(21), 4252; https://doi.org/10.3390/polym15214252 - 28 Oct 2023

Viewed by 1311

Abstract

Digital light processing (DLP) or stereolithography is the most promising method of additive manufacturing (3D printing) of products based on high-energy materials due to, first of all, the absence of a high-temperature impact on the material. This paper presents research results of an [...] Read more.

Digital light processing (DLP) or stereolithography is the most promising method of additive manufacturing (3D printing) of products based on high-energy materials due to, first of all, the absence of a high-temperature impact on the material. This paper presents research results of an ultraviolet (UV)-cured urethane methacrylate polymer containing 70 wt.% of high-energy solid powder based on ammonium salts, which is intended for digital light processing. Polymerization of the initial slurry is studied herein. It is shown that the addition of coarse powder transparency for the UV radiation to resin increases its curing depth. The thickness of the layer, which can polymerize, varies from 600 µm to 2 mm when the light power density ranges from 20 to 400 mJ/cm², respectively. In DLP-based 3D printing, the obtained material density is 92% of the full density, while the compressive strength is 29 ± 3 MPa, and the ultimate tensile strength is 13 ± 1.3 MPa. The thermogravimetric analysis shows the decrease in the thermal decomposition temperature of UV-cured resin with high-energy additives compared to the thermal decomposition temperatures of the initial components separately. Thermal decomposition is accompanied by intensive heat generation. The burning rate of obtained samples grows from 0.74 to 3.68 mm/s, respectively, at the pressure growth from 0.1 to 4 MPa. Based on the results, it can be concluded that DLP-based 3D printing with the proposed UV photocurable resin is rather promising for the fabrication of multicomponent high-energy systems and complex profile parts produced therefrom. Full article

(This article belongs to the Special Issue Structure and Properties of Polymeric Materials in Additive Manufacturing II)

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16 pages, 3930 KiB

Open AccessArticle

Joining of Aluminum and CFRP via Laser Powder Bed Fusion: Influence of Experimental Set-Up and Laser Processing on Microstructure and Mechanical Properties

by Sara Nester, Dieter Meinhard, Jochen Schanz, Markus Rettenberger, Iman Taha, Harald Riegel and Volker Knoblauch

Polymers 2023, 15(18), 3839; https://doi.org/10.3390/polym15183839 - 21 Sep 2023

Cited by 1 | Viewed by 1054

Abstract

Additive-manufacturing-based joining methods enable tailored or even functionalized joints and allow for hybridization at small scales. The current study explored an innovative joining method for aluminum cast alloys (AlSi12) with thermoset carbon-fiber-reinforced polymers (CFRPs) via laser powder bed fusion (LPBF). The direct build-up [...] Read more.

Additive-manufacturing-based joining methods enable tailored or even functionalized joints and allow for hybridization at small scales. The current study explored an innovative joining method for aluminum cast alloys (AlSi12) with thermoset carbon-fiber-reinforced polymers (CFRPs) via laser powder bed fusion (LPBF). The direct build-up of AlSi12 on a CFRP substrate proved to be challenging due to the dissimilar thermal properties of the considered materials, which led to substrate damage and low joint adhesion. These effects could be overcome by introducing an AlSi12 foil as an interlayer between the two joining partners, acting as a thermal barrier and further improving the AlSi12 melt wettability of the substrate. Within LPBF, the energy input in the form of volumetric laser energy density influenced both the porosity of the fused layers and the formation of thermally induced stresses due to the high cooling rates and different thermal expansion properties of the materials. While the AlSi12 volume density increased with a higher laser energy input, simultaneously increasing thermal stresses caused the debonding and deformation of the AlSi12 foil. However, within a narrow processing window of laser parameters, the samples achieved remarkably high shear strengths of τ > 20 MPa, comparable to those of conventional joining methods. Full article

(This article belongs to the Special Issue Structure and Properties of Polymeric Materials in Additive Manufacturing II)

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22 pages, 7780 KiB

Open AccessArticle

Influence of the Print Envelope Temperature on the Morphology and Tensile Properties of Thermoplastic Polyolefins Fabricated by Material Extrusion and Material Jetting Additive Manufacturing

by Lukas Hentschel, Sandra Petersmann, Frank Kynast, Ute Schäfer, Clemens Holzer and Joamin Gonzalez-Gutierrez

Polymers 2023, 15(18), 3785; https://doi.org/10.3390/polym15183785 - 16 Sep 2023

Viewed by 950

Abstract

Additive manufacturing (AM) nowadays has become a supportive method of traditional manufacturing. In particular, the medical and healthcare industry can profit from these developments in terms of personalized design and batches ranging from one to five specimens overall. In terms of polymers, polyolefins [...] Read more.

Additive manufacturing (AM) nowadays has become a supportive method of traditional manufacturing. In particular, the medical and healthcare industry can profit from these developments in terms of personalized design and batches ranging from one to five specimens overall. In terms of polymers, polyolefins are always an interesting topic due to their low prices, inert chemistry, and crystalline structure resulting in preferable mechanical properties. Their semi-crystalline nature has some advantages but are challenging for AM due to their shrinkage and warping, resulting in geometrical inaccuracies or even layer detaching during the process. To tackle these issues, process parameter optimization is vital, with one important parameter to be studied more in detail, the print envelope temperature. It is well known that higher print envelope temperatures lead to better layer adhesion overall, but this investigation focuses on the mechanical properties and resulting morphology of a semi-crystalline thermoplastic polyolefin. Further, two different AM technologies, namely material jetting (ARBURG plastic freeforming—APF) and filament-based material extrusion, were studied and compared in detail. It was shown that higher print envelope temperatures lead to more isotropic behavior based on an evenly distributed morphology but results in geometrical inaccuracies since the material is kept in a molten state during printing. This phenomenon especially could be seen in the stress and strain values at break at high elongations. Furthermore, a different crystal structure can be achieved by setting a specific temperature and printing time, also resulting in peak values of certain mechanical properties. In comparison, better results could be archived by the APF technology in terms of mechanical properties and homogeneous morphology. Nevertheless, real isotropic part behavior could not be managed which was shown by the specimen printed vertically. Hence, a sweet spot between geometrical and mechanical properties still has to be found. Full article

(This article belongs to the Special Issue Structure and Properties of Polymeric Materials in Additive Manufacturing II)

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17 pages, 5058 KiB

Open AccessArticle

Acquiring Process Knowledge in Extrusion-Based Additive Manufacturing via Interpretable Machine Learning

by Lukas Pelzer, Tobias Schulze, Daniel Buschmann, Chrismarie Enslin, Robert Schmitt and Christian Hopmann

Polymers 2023, 15(17), 3509; https://doi.org/10.3390/polym15173509 - 23 Aug 2023

Viewed by 723

Abstract

Additive manufacturing (AM), especially the extrusion-based process, has many process parameters which influence the resulting part properties. Those parameters have complex interdependencies and are therefore difficult if not impossible to model analytically. Machine learning (ML) is a promising approach to find suitable combinations [...] Read more.

Additive manufacturing (AM), especially the extrusion-based process, has many process parameters which influence the resulting part properties. Those parameters have complex interdependencies and are therefore difficult if not impossible to model analytically. Machine learning (ML) is a promising approach to find suitable combinations of process parameters for manufacturing a part with desired properties without having to analytically model the process in its entirety. However, ML-based approaches are typically black box models. Therefore, it is difficult to verify their output and to derive process knowledge from such approaches. This study uses interpretable machine learning methods to derive process knowledge from interpreted data sets by analyzing the model’s feature importance. Using fused layer modeling (FLM) as an exemplary manufacturing technology, it is shown that the process can be characterized entirely. Therefore, sweet spots for process parameters can be determined objectively. Additionally, interactions between parameters are discovered, and the basis for further investigations is established. Full article

(This article belongs to the Special Issue Structure and Properties of Polymeric Materials in Additive Manufacturing II)

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17 pages, 5937 KiB

Open AccessArticle

Investigating the Mechanical Properties of Annealed 3D-Printed PLA–Date Pits Composite

by Ahmed Fouly, Thamer Albahkali, Hany S. Abdo and Omar Salah

Polymers 2023, 15(16), 3395; https://doi.org/10.3390/polym15163395 - 13 Aug 2023

Cited by 1 | Viewed by 1179

Abstract

Biomedical applications are crucial in rehabilitation medicine, assisting individuals with disabilities. Nevertheless, materials failure can sometimes result in inconvenience for users. Polylactic Acid (PLA) is a popular 3D-printed material that offers design flexibility. However, it is limited in use because its mechanical properties [...] Read more.

Biomedical applications are crucial in rehabilitation medicine, assisting individuals with disabilities. Nevertheless, materials failure can sometimes result in inconvenience for users. Polylactic Acid (PLA) is a popular 3D-printed material that offers design flexibility. However, it is limited in use because its mechanical properties are inadequate. Thus, this study introduces an artificial intelligence model that utilizes ANFIS to estimate the mechanical properties of PLA composites. The model was developed based on an actual data set collected from experiments. The experimental results were obtained by preparing samples of PLA green composites with different weight fractions of date pits, which were then annealed for varying durations to remove residual stresses resulting from 3D printing. The mechanical characteristics of the produced PLA composite specimens were measured experimentally, while the ANSYS model was established to identify the composites’ load-carrying capacity. The results showed that ANFIS models are exceptionally robust and compatible and possess good predictive capabilities for estimating the hardness, strength, and Young’s modulus of the 3D-printed PLA composites. The model results and experimental outcomes were nearly identical. Full article

(This article belongs to the Special Issue Structure and Properties of Polymeric Materials in Additive Manufacturing II)

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16 pages, 8718 KiB

Open AccessArticle

Adaptive Neuro-Fuzzy-Based Models for Predicting the Tribological Properties of 3D-Printed PLA Green Composites Used for Biomedical Applications

by Thamer Albahkali, Hany S. Abdo, Omar Salah and Ahmed Fouly

Polymers 2023, 15(14), 3053; https://doi.org/10.3390/polym15143053 - 15 Jul 2023

Viewed by 962

Abstract

Tribological performance is a critical aspect of materials used in biomedical applications, as it can directly impact the comfort and functionality of devices for individuals with disabilities. Polylactic Acid (PLA) is a widely used 3D-printed material in this field, but its mechanical and [...] Read more.

Tribological performance is a critical aspect of materials used in biomedical applications, as it can directly impact the comfort and functionality of devices for individuals with disabilities. Polylactic Acid (PLA) is a widely used 3D-printed material in this field, but its mechanical and tribological properties can be limiting. This study focuses on the development of an artificial intelligence model using ANFIS to predict the wear volume of PLA composites under various conditions. The model was built on data gathered from tribological experiments involving PLA green composites with different weight fractions of date particles. These samples were annealed for different durations to eliminate residual stresses from 3D printing and then subjected to tribological tests under varying normal loads and sliding distances. Mechanical properties and finite element models were also analyzed to better understand the tribological results and evaluate the load-carrying capacity of the PLA composites. The ANFIS model demonstrated excellent compatibility and robustness in predicting wear volume, with an average percentage error of less than 0.01% compared to experimental results. This study highlights the potential of heat-treated PLA green composites for improved tribological performance in biomedical applications. Full article

(This article belongs to the Special Issue Structure and Properties of Polymeric Materials in Additive Manufacturing II)

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