Supplementary treatment of FDM printed parts. Review

Wang K., Tan Q., Wang J., Liu Y., Zhai Z., Yao S., Peng Y.

3D printed structures suffered weak bead-to-bead interfacial bonding due to the layer-by-layer manufacturing process. The hot isostatic pressing (HIP) method was effective in improving the micro-structures and enhancing the mechanical properties of 3D printed structures, but it was limited due to the high-cost device and process. Inspired by the HIP method, and aimed at improving the compressive properties of 3D printed thin-walled structures, this work proposed a low-cost granular-medium hot quasi-isostatic pressing (GMHQIP) method realized by the homemade equipment. The hot quasi-isostatic ambient pressure could be produced by pressing the granular medium in the high-temperature environment. The thin-walled structures treated by the GMHQIP method showed a more regular progressive deformation mode than non-treated structures. Compared to the non-treated structure, the specific energy absorption of thin-walled structures treated at 200 °C with 2 MPa for 8 h significantly increased by 170.4 % to the value of 4.95 J/g. The results indicated that the strength and toughness of 3D printed materials improved significantly after the GMHQIP treatment. The interfacial bonding of 3D printed structures was enhanced by using the GMHQIP method. This work offered a low-cost and efficient post-processing method for 3D printed structures to improve compressive properties.

Nguyen P.Q., Panta J., Famakinwa T., Yang R.(., Ahmed A., Stapleton M., Sassaman D., Snabes S., Craff C.

This research presents an investigation of the feasibility of recycled polyethylene terephthalate (rPET) and glycol-modified polyethylene terephthalate (rPETG) thermoplastics using the fused granular fabrication (FGF) 3D printing technique. It focuses on the effects of FGF printing parameters on the mechanical properties of rPET and rPETG printed parts using a Gigabot X 3D printer. The design of experiments (DOE) was first performed considering the main FGF 3D printing parameters such as layer thickness, infill density and number of contours. The experimental studies were then carried out to study the effects of printing parameters on the tensile properties based on the DOE. The effect of interlayer bonding of printed parts on the tensile properties was also evaluated using finite element-based multiscale modelling. Scanning electron microscopy (SEM) and Fourier transformation infrared (FTIR) spectroscopy were used to observe the fracture morphology and chemical structure of post-3D printing products. The tensile test results indicate that the highest tensile strength of 26.4 MPa was obtained for rPET when using a 1.1-mm layer thickness, a 70% infill density, and 3 contours, whereas, for rPETG, the maximum tensile strength of 44.8 MPa was attained with a 1.2-mm layer thickness, a 100% infill density, and 2 contours. FTIR analysis confirms no significant changes of characteristic peaks for PET in the printed products, suggesting that rPET and rPETG are viable materials for 3D printing. Thermal stability studies also reveal that the glass transition temperature and onset degradation temperatures are not significantly affected by the printing parameters. The study demonstrates the potential of rPET and rPETG as sustainable alternatives to virgin materials and provides insights into the optimal processing conditions for achieving high-quality 3D printed parts via the FGF technique.

Hirsch P., Scholz S., Borowitza B., Vyhnal M., Schlimper R., Zscheyge M., Kotera O., Stipkova M., Scholz S.

Fused granular fabrication (FGF) is a large format additive manufacturing (LFAM) technology and focuses on cost-effective granulate-based manufacturing by eliminating the need for semifinished filaments. This allows a faster production time and a broader range of usable materials for tailored composites. In this study, the mechanical and morphological properties of FGF test structures made of polyamid 6 reinforced with 40% of short carbon fibers were investigated. For this purpose, FGF test structures with three different parameter settings were produced. The FGF printed structures show generally significant anisotropic mechanical characteristics, caused by the layer-by-layer building process. To enhance the mechanical properties and reduce the anisotropic behavior of FGF structures, continuous unidirectional fiber-reinforced tapes (UD tapes), employing automated tape laying (ATL), were subsequently applied. Thus, a significant improvement in the flexural stiffness and strength of the manufactured FGF structures was observed by hybridization with 60% glass fiber-reinforced polyamide 6 UD tapes. Since the effectiveness of UD-tape reinforcement depends mainly on the quality of the bond between the UD tape and the FGF structure, the surface quality of the FGF structure, the interface morphology, and the tape-laying process parameters were investigated.

Potapov A., Malakho A., Gnidina I., Volgin V.

Potapov A., Malakho A., Gnidina I., Volgin V.

FDM is used for printing parts from thermoplastic polymers, polymer matrix composites, biocomposites or polymer-ceramic composites, nanocomposites and fiber-reinforced composites. The main disadvantage of this method is the reduced physical and mechanical characteristics due to the presence of pores and poor adhesion of layers. The post-treatment is one of the ways to improve this properties. The heat treatment has the greatest impact among all types of post-treatment processing on the surface quality and physical and mechanical properties of finished products. The paper studies the physical and mechanical properties of samples from ABS plastic (REC brand) printed by FDM and subjected to thermal post-treatment. Two methods of thermal post-treatment were considered: in NaCl powder and in closed form with pressure. The test results of the printed samples were compared with the test results of the samples obtained by injection molding. Comparison of strength and porosity showed that the properties of printed samples after post-treatment by both methods are comparable to the properties of samples obtained by injection molding.

Erokhin Kirill S., Naumov Sergei A., Ananikov Valentine P.

Additive manufacturing technologies (or 3D printing) have emerged as powerful tools for creating a diverse array of objects, promising a paradigm shift in production methodologies across industries. In chemistry, it allows the manufacturing of reactors with complex topology. However, the benefits of these technologies can be diminished by the use of suboptimal parameters or inferior materials, leading to defects that significantly degrade the quality and functionality of the resulting products. The formulation of effective preventive strategies remains hampered by an incomplete understanding of defect formation. Given this, our review provides a comprehensive exploration of defects that arise during the Fused Filament Fabrication (FFF) — one of the most prevalent 3D printing methods. The defects are systematically classified according to several key characteristics, including size, type, mode of occurrence, and location. Each common defect is discussed in detail, describing its external manifestation, root causes, the impact on the properties of printed parts, and potential preventive measures. Our findings unveil the complex interplay between material properties, printing parameters, and cooling dynamics in the defect formation process. This classification has significant practical relevance, providing a solid basis for the development of strategies to minimize defects and improve the quality of 3D printed products. It provides valuable insights for a wide audience, including researchers investigating chemical processes and additive manufacturing technologies, 3D printing engineers, 3D printer operators, and quality assurance engineers involved in production quality control. In addition, our review points the way forward for future research in this area. There is a crucial need for the development of advanced machine learning and artificial intelligence models that can predict defect formation based on given printing parameters and material properties. Future investigations should also focus on the discovery of novel materials and refining of printing parameters to achieve superior quality of FFF 3D printed products. This is the first review on defect analysis, classification, and prevention methods in 3D printing. This review serves as a cornerstone for these future advances, promoting a deeper understanding of defect formation and prevention in additive manufacturing.The bibliography includes 180 references.

Xu Z., Zou B., Ding S., Zhuang Y., Wang X.

The use of continuous carbon fiber reinforced composites (CCFRC) in fused deposition modelling (FDM)-3D printing can significantly improve the mechanical properties of products. However, compared with the products of traditional fiber placement technology, the mechanical properties of FDM-3D printed CCFRC have a big gap. In this paper, finite element analysis (FEA) and Tsai-Wu failure criterion were used to simulate the interlaminar shear failure and tensile failure of the model with staggered arranged polyamide 6 (PA6) layers and continuous carbon fiber (CCF) layers. The post-treatment processes of CCFRC were also simulated. The FEA models were FDM-3D printed and hot isostatic pressing (HIP) post-treated with the aim of improving the mechanical properties of the CCFRC. The effects of various HIP parameters including temperature, pressure and post-treatment time on interlaminar shear strength (ILSS) and tensile strength were studied. It was found that the ILSS and tensile strength were increased maximally by 64.47 % and 27.55 % under HIP as compared to the pristine samples. The mechanical properties of CCFRC after HIP treatment can be further improved compared with annealing treatment without pressure. Studying the variations in isostatic pressure and selecting the optimal pressure level to achieve the most effective enhancement can offer a novel approach for post-treatment FDM-3D printing.

KARTAL F., KAPTAN A.

This study aims to investigate the effect of annealing temperature and duration on the mechanical properties of PLA (polylactic acid) plastics produced by a 3D (three-dimensional) printer. For this purpose, PLA samples were annealed at 70 °C, 85 °C, and 100 °C temperatures and for 30, 60, and 90-minute durations. As a result of the study, it was shown that the annealing process has a significant effect on the mechanical properties of PLA plastics. Compared to the control sample, an increase of 48% in tensile stress, 78% in the modulus of elasticity, 28% in Shore D hardness value, and 41% in bending stress was observed. In particular, the highest mechanical properties of PLA plastics were reached after applying the annealing process at 85 °C temperature and for 90 minutes. These results demonstrate the advantages of using 3D printers in the production of products requiring high durability in industrial applications. Moreover, the study findings provide an important method for optimizing the mechanical properties of materials produced with 3D printer technology.

Mushtaq R.T., Wang Y., Khan A.M., Rehman M., Li X., Sharma S.

In this paper, the laser polishing method has been used to alleviate the asperities on the printed surface. The proposed laser polishing method is specifically used to solve industrial problems such as improving mechanical properties (flexural strength and tensile strength), surface roughness, and eco-friendly polishing of 3D-printed novel nylon-6 polymers. A series of experimentations were conducted using response surface methodology to see how changing the laser parameters affected the surface finish and the mechanical qualities of the test materials. Mechanical properties and scanning electron microscope-based surface analysis were compared with the pre-polishing workpiece. After multi-optimization, optimal laser scanning parameters resulted in a 20.2 % reduction in surface roughness, 8.27 % increment in flexural strength, and a 1.45 % increase in tensile strength. The optimum laser scanning time for samples was 0.23 min, and the energy consumption was 1.58E−05 kWh for one experiment. These findings prove that the relatively new post-processing laser polishing method improves the mechanical and surface properties of a 3D-printed nylon-6 polymer material. This new method is highly useful in the 3D printing industry to provide sustainable products.

Singh G., Kumar R., Sandhu K., Pei E., Singh S.

Lyu Y., Wu J., Zhang H., Brádaigh C.M., Yang D.

This study investigates the thermal behaviour of discontinuous carbon fibre reinforced polyphenylene sulphide (CF/PPS), additively manufactured by material extrusion, with a focus on the effects of thermal process conditions on the degree of crystallinity, oxidation crosslinking and mechanical properties of CF/PPS from filament fabrication, material extrusion to annealing treatment. The screw extrusion parameters are optimised by performing a thermal analysis of the fabricated filaments. The effect of crosslinking reactions on the crystallinity process in determining the mechanical properties of the printed samples is illustrated by investigating the influence of the printing conditions. Furthermore, the effect of annealing treatment on the semi-crystalline polyphenylene sulphide (PPS) is studied by measuring the degree of crystallinity and viscoelasticity behaviours. Results demonstrate that the flexural properties of the printed CF/PPS composites at elevated processing temperatures are determined by the oxidation crosslinking between PPS chains. These enhance the crystallisation process of semi-crystalline polymers by acting as the nucleating agent first but negatively affect the mechanical properties at higher temperatures because of the detrimental effects of the polymer inter-chain bonding. The maximum flexural strength of printed CF/PPS reached 164.65 MPa when processing at an extrusion temperature of 280°C, a printing temperature of 320°C, and an annealing temperature of 130°C for 6 h. By adjusting the thermal treatment conditions, the degree of the crystallinity and the mechanical properties of the printed CF/PPS composites can be designed, controlled and tailored.

Seok W., Jeon E., Kim Y.

This study investigates the effect of annealing on the mechanical properties of fused deposition modeling (FDM) 3D-printed recycled carbon fiber (rCF)-reinforced composites. In this study, filaments for FDM 3D printers are self-fabricated from pure acrylonitrile butadiene styrene (ABS) and ABS reinforced with fiber content of 10 wt% and 20 wt% rCF. This study explores the tensile and flexural properties as a function of the annealing temperature and time for the three different fiber content values. In addition, dimensional measurements of the shape changes are performed to determine the suitability of applying annealing in practical manufacturing processes. The results show that annealing improves the mechanical properties by narrowing the voids between the beads, which occur during the FDM process, and by reducing the gaps between the fibers and polymer. Following annealing, the largest tensile and flexural strength improvements are 12.64% and 42.33%, respectively, for the 20 wt% rCF content samples. Moreover, compared with the pure ABS samples, the annealing effect improves the mechanical properties of the rCF-reinforced samples more effectively, and they have higher dimensional stability, indicating their suitability for annealing. These results are expected to expand the application fields of rCF and greatly increase the potential use of FDM-printed parts.

Morfini L., Guerra M.G., Lavecchia F., Spina R., Galantucci L.M.

Engineering polymers are widely used in aerospace, automotive, aviation, and biomedical industries. They can be processed with different technologies and Additive Manufacturing. Polyether ether ketone (PEEK) is a semi-crystalline polymer that exhibits excellent mechanical properties and resistance to high temperatures. Being a semi-crystalline polymer, heat treatments can be used to improve its properties. They can be conducted in the oven or through a direct annealing system included in the Fused Filament Fabrication (FFF) machine. This study aims to provide more information on the correlation between annealing and the flexural properties of PEEK specimens made by FFF technology. A direct annealing process, performed during the printing, was carried out and compared with a traditional oven annealing with similar duration. The flexural properties were analyzed as a function of the annealing type and temperature.

Jayakumar N., Arumugam H., Albert Selvaraj A.D.

FDM, being the most popular AM technology, has a wide user base across the globe. The process makes use of a layer-by-layer approach, causing a staircase effect on the material’s printed surface. Though it affects several mechanical properties, its effect on surface integrity is highly detrimental and needs to be addressed. Chemical vapour dip and immersion techniques can provide a rapid solution using solvents. The solvents employed in the current study were the polar solvents- acetone and ethyl acetate, the mid-polar solvent- tetrahydrofuran (THF), and the non-polar solvents- chloroform and dichloromethane (DCM). The superior surface finish obtained during the post processing of 3D printed parts was having mean roughness value (Ra) of 0.67 µm, originally 11.42 µm. It was obtained when experimentation was carried out with the chemical vapour technique using THF. The optimum surface finish was readily achieved with mid- and non-polar solvents, whereas the polar solvents were slow to react with the surface of the PLA. A number of variables, including the solvent's polarity, boiling point, vapour pressure, and water miscibility, have an impact on the final surface's appearance and strength. During vapour treatment, the tensile strength of the 3D printed parts got reduced between 11.6% (THF) to 43.78% (DCM). On the other hand, the chemical immersion technique has a even more impact on the material’s strength and hardness. It reduces hardness to the maximum of 44.41% (THF), whereas the vapour evaporation technique reduces hardness by only up to 14.64% (chloroform).

Park S.J., Kim D.H., Ju H.G., Park S.J., Hong S., Yong son, Ahn I.H.

Recently, short carbon fiber-reinforced plastic (SFRP) has been selected as a filament material to improve the strength of components fabricated by material extrusion (ME). However, despite the improved material properties, the weak interlayer bonding and voids present in the microstructure constitute defects that cause anisotropy in the SFRP composite and deteriorate its mechanical properties such as the tensile, compressive, and flexural strengths. In this study, warm isostatic pressing (WIP) was investigated as a means to increase the interlayer bonding force and reduce the voids. To increase the efficiency of WIP, vacuum packing was investigated as a means to promote interfacial strength and diffusion between the layers. The WIP process improved the tensile, compressive, and flexural properties, and the anisotropy decreased with increasing interlayer bonding force. In addition, the thermal properties improved with an increase in the degree of crystallinity, and the voids in the microstructure were effectively reduced. These results indicate that WIP is a promising post-processing treatment for ME-fabricated SFRP parts.

Ishigeev R.S., Potapov V.A.

This microreview summarizes the literature data over the past 10 years on methods of synthesis of condensed heterocycles based on pyridine-2-selanyl chloride. The material is systematized by reagents which pyridine-2-selanyl chloride reacts with such as reactions with nitriles, isocyanates, cyanamides, and alkenes.