Material and Process Innovations for 3D Printing Applications

Topic Information

Dear Colleagues,

Additive manufacturing (AM), also known as 3D printing, is an innovative and emerging technology offering many advantages for various applications and industries at the design, material and processing level. AM offers many opportunities, encourages unique designs and integrates new materials, smart production methods, digitalization and advanced information technology within Industry 4.0. The contribution of AM to the circular economy is also of great importance. AM is essential as it allows the production of personalized products and lot size one with shorter lead times and less waste. Recently, AM research also has focused on the integration of certain aspects such as sustainability, recyclability and circular economy. In addition, environmental and health issues that occur when producing and applying AM are investigated.

In general, additive manufacturing can reduce inventory, make complex parts on demand, create smaller localized manufacturing environments and reduce the cost and complexity of supply chains, thus reducing logistics needs. AM technologies are very promising due to their tremendous market opportunities and multicomponent compatibility for a wide scope of materials such as polymers, composites, metals, ceramics and hybrids.

Understanding the fundamental relationship between the design, the materials and processing innovations, as well as broadening the available materials, is important for the additive manufacturing of advanced engineering (e.g., automotive and aerospace sector), medical (e.g., scaffolds and tissue engineering) and related technologies. Achieving high product quality by a combination of both material sciences and equipment/processing innovation is another main and common research challenge. For most AM technologies, the process relies on the transition of liquid phases into well-defined solid materials. This transition is influenced by many parameters that are either processing or material related.

In this Topic, there is a focus on the connection between the research fields of materials science and process innovations for additive manufacturing applications. Both theoretical and experimental contributions can be submitted.

It is our pleasure to invite you to submit a manuscript to this Special Issue, including full papers, reviews and short communications.

Prof. Dr. Ludwig Cardon
Prof. Dr. Clemens Holzer
Topic Editors

Keywords

Participating Journals

Journal Name	Impact Factor	CiteScore	Launched Year	First Decision (median)	APC
Materials materials	3.1	5.8	2008	13.9 Days	CHF 2600
Metals metals	2.6	4.9	2011	17.8 Days	CHF 2600
Applied Sciences applsci	2.5	5.3	2011	18.4 Days	CHF 2400
Polymers polymers	4.7	8.0	2009	14.5 Days	CHF 2700
Journal of Manufacturing and Materials Processing jmmp	3.3	5.1	2017	16.5 Days	CHF 1800

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Published Papers (49 papers)

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14 pages, 4917 KiB  

Open AccessArticle

Injection Molding Process Simulation of Polycaprolactone Sticks for Further 3D Printing of Medical Implants

by Krzysztof Formas, Anna Kurowska, Jarosław Janusz, Piotr Szczygieł and Izabella Rajzer

Materials 2022, 15(20), 7295; https://doi.org/10.3390/ma15207295 - 18 Oct 2022

Cited by 11 | Viewed by 2900

Abstract

The aim of the present study was a simulation of the injection molding process of polycaprolactone filament sticks for further 3D printing of osteochondral implants. Polycaprolactone data are not available in the data banks of popular injection molding simulation programs. Therefore, thermal and [...] Read more.

The aim of the present study was a simulation of the injection molding process of polycaprolactone filament sticks for further 3D printing of osteochondral implants. Polycaprolactone data are not available in the data banks of popular injection molding simulation programs. Therefore, thermal and rheological data from the literature were imported to the material database of Solidworks Plastics software to simulate the injection molding process of filament sticks. The influence of several injection molding parameters including melt temperature, injection time, and injection pressure on the geometry of filament stick (final part) was investigated. Based on the results of the performed simulation and analyses, it was possible to improve the injection process parameters. The accuracy of simulation predictions, based on the literature data, demonstrates the potential of using simulation as a tool to develop polycaprolactone parts for future implants and to optimize the injection molding process. Full article

(This article belongs to the Topic Material and Process Innovations for 3D Printing Applications)

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9 pages, 1565 KiB  

Open AccessArticle

Effect of Different Wax Pattern Manufacturing Techniques on the Marginal Fit of Lithium Disilicate Crowns

by Huda Ahmed Alshehri, Sara Mohammed Altaweel, Raghdah Alshaibani, Esraa Ahmed Alahmari, Hanan Nejer Alotaibi, Afnan Fouzan Alfouzan and Nawaf Labban

Materials 2022, 15(14), 4774; https://doi.org/10.3390/ma15144774 - 7 Jul 2022

Cited by 5 | Viewed by 2393

Abstract

Purpose: The present study evaluated the marginal gap of lithium disilicate crowns fabricated through three different wax pattern techniques; Conventional, Milling and 3D-printing. Materials and Methods: Thirty stone models were replicated from a stainless-steel model representing a prepared tooth; ten were sent to [...] Read more.

Purpose: The present study evaluated the marginal gap of lithium disilicate crowns fabricated through three different wax pattern techniques; Conventional, Milling and 3D-printing. Materials and Methods: Thirty stone models were replicated from a stainless-steel model representing a prepared tooth; ten were sent to make conventional wax patterns while the remaining were sent to a digital dental scanner. The computer aided design was completed and STL (Standard Tessellation Language) files were sent to either milling or 3D-printing machines. All wax patterns (n = 30) were pressed, and a stabilizing instrument was used to secure the crowns on the master model. The marginal gap was measured at 18 points for each crown using a digital microscope (µm) (n = 540) and compared using One-way ANOVA (p ≤ 0.05). Results: There was a significant difference in the marginal gap value between all three groups (p < 0.01) where the milled group showed the least mean gap (28.87 ± 30.18 µm), followed by 3D printed (47.85 ± 27.44 µm), while the highest mean marginal gap was found in the conventional group (63.49 ± 28.05 µm). Conclusion: Milled and 3D-printed wax patterns produced better fitting crowns compared to conventional techniques. Full article

(This article belongs to the Topic Material and Process Innovations for 3D Printing Applications)

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25 pages, 2888 KiB  

Open AccessReview

Low-Cost Cranioplasty—A Systematic Review of 3D Printing in Medicine

by Wojciech Czyżewski, Jakub Jachimczyk, Zofia Hoffman, Michał Szymoniuk, Jakub Litak, Marcin Maciejewski, Krzysztof Kura, Radosław Rola and Kamil Torres

Materials 2022, 15(14), 4731; https://doi.org/10.3390/ma15144731 - 6 Jul 2022

Cited by 28 | Viewed by 5936

Abstract

The high cost of biofabricated titanium mesh plates can make them out of reach for hospitals in low-income countries. To increase the availability of cranioplasty, the authors of this work investigated the production of polymer-based endoprostheses. Recently, cheap, popular desktop 3D printers have [...] Read more.

The high cost of biofabricated titanium mesh plates can make them out of reach for hospitals in low-income countries. To increase the availability of cranioplasty, the authors of this work investigated the production of polymer-based endoprostheses. Recently, cheap, popular desktop 3D printers have generated sufficient opportunities to provide patients with on-demand and on-site help. This study also examines the technologies of 3D printing, including SLM, SLS, FFF, DLP, and SLA. The authors focused their interest on the materials in fabrication, which include PLA, ABS, PET-G, PEEK, and PMMA. Three-dimensional printed prostheses are modeled using widely available CAD software with the help of patient-specific DICOM files. Even though the topic is insufficiently researched, it can be perceived as a relatively safe procedure with a minimal complication rate. There have also been some initial studies on the costs and legal regulations. Early case studies provide information on dozens of patients living with self-made prostheses and who are experiencing significant improvements in their quality of life. Budget 3D-printed endoprostheses are reliable and are reported to be significantly cheaper than the popular counterparts manufactured from polypropylene polyester. Full article

(This article belongs to the Topic Material and Process Innovations for 3D Printing Applications)

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13 pages, 3903 KiB  

Open AccessArticle

Carbonated 3D-Printable Polymer Composite for Thermo-Mechanically Stable Applications

by Fareed Dawan, Melvin Givens, Lakeira Williams and Patrick Mensah

J. Manuf. Mater. Process. 2022, 6(3), 66; https://doi.org/10.3390/jmmp6030066 - 15 Jun 2022

Cited by 4 | Viewed by 3285

Abstract

In this report, we investigate the infusion of carbon dioxide into a 3D-printable photosensitive polymer. The result is a carbonated polymer composite material. In use, polymer composite materials expect to succeed where ordinary polymers and metals fail. This is due to the tailorability [...] Read more.

In this report, we investigate the infusion of carbon dioxide into a 3D-printable photosensitive polymer. The result is a carbonated polymer composite material. In use, polymer composite materials expect to succeed where ordinary polymers and metals fail. This is due to the tailorability of composite materials for specific applications. Usually, micro/nano-particulates are embedded as fillers within a polymer matrix, enhancing the overall material properties. Here, carbon dioxide (CO₂) microbubbles serve as the filler within a nylon-like polymer matrix. Additive manufacturing by stereolithography (SLA) of the carbonated polymer composite proved possible using the digital light projection (DLP) 3D printing technique. Post-heat treatment using thermogravimetric analysis of the samples at elevated temperatures resulted in a 33% mass reduction, indicative of nearly complete solvent removal and curing. An initial increase in polymer carbonation duration showed a 16% increase in porosity, more stable thermal profiles, and a 40% decrease in specific heat capacity. Thermo-mechanical compressive tests on an optimal carbonated sample revealed a 70% increase in compressive strength over its neat counterpart and a peak modulus at 50 °C of 60 MPa. Such 3D-printable carbonated polymer composites may find use in applications requiring high strength-to-weight ratio thermally stable polymers and applications requiring a versatile and convenient storage medium for on-demand CO₂ deposition or supercritical fluid phase transformation. Full article

(This article belongs to the Topic Material and Process Innovations for 3D Printing Applications)

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17 pages, 8377 KiB  

Open AccessArticle

Research on 3D-Print Design Method of Spatial Node Topology Optimization Based on Improved Material Interpolation

by Xianjie Wang, Fan Zhang, Yang Zhao, Zhaoyi Wang and Guangen Zhou

Materials 2022, 15(11), 3874; https://doi.org/10.3390/ma15113874 - 29 May 2022

Cited by 3 | Viewed by 2326

Abstract

Designing a high-strength node is significant for space structures. Topological optimization can optimally allocate the material distribution of components to meet performance requirements. Although the material distribution after topology optimization is optimum, the structure becomes complicated to manufacture. By using additive manufacturing technology, [...] Read more.

Designing a high-strength node is significant for space structures. Topological optimization can optimally allocate the material distribution of components to meet performance requirements. Although the material distribution after topology optimization is optimum, the structure becomes complicated to manufacture. By using additive manufacturing technology, this problem can be well solved. At present, both topology optimization technology and additive manufacturing technology are quite mature, but their application in the design of spatial nodes is very recent and less researched. This paper involves the study and improvement of the node optimization design–manufacturing integrated method. This study used the BESO optimization algorithm as the research algorithm. Through a reasonable improvement of the material interpolation method, the algorithm’s dependence on the experience of selecting the material penalty index P was reduced. On this basis, the secondary development was carried out, and a multisoftware integration was carried out for optimization and manufacturing. The spatial node was taken as the research object, and the calculation results of the commercial finite element software were compared. The comparison showed that the algorithm used in this paper was better. Not only was it not trapped in a local optimum, but the maximum stress was also lower. In addition, this paper proposed a practical finite element geometric model extraction method and smoothing of the optimized nodes, completing the experiment of the additive manufacturing forming of the nodes. It provides ideas for processing jagged edges brought by the BESO algorithm. This paper verified the feasibility of the multisoftware integration method of optimized manufacturing. Full article

(This article belongs to the Topic Material and Process Innovations for 3D Printing Applications)

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24 pages, 3966 KiB  

Open AccessReview

A Critical Review of Additive Manufacturing Techniques and Associated Biomaterials Used in Bone Tissue Engineering

by Yanli Wu, Yongtao Lu, Ming Zhao, Sergei Bosiakov and Lei Li

Polymers 2022, 14(10), 2117; https://doi.org/10.3390/polym14102117 - 23 May 2022

Cited by 38 | Viewed by 5691

Abstract

With the ability to fabricate complex structures while meeting individual needs, additive manufacturing (AM) offers unprecedented opportunities for bone tissue engineering in the biomedical field. However, traditional metal implants have many adverse effects due to their poor integration with host tissues, and therefore [...] Read more.

With the ability to fabricate complex structures while meeting individual needs, additive manufacturing (AM) offers unprecedented opportunities for bone tissue engineering in the biomedical field. However, traditional metal implants have many adverse effects due to their poor integration with host tissues, and therefore new material implants with porous structures are gradually being developed that are suitable for clinical medical applications. From the perspectives of additive manufacturing technology and materials, this article discusses a suitable manufacturing process for ideal materials for biological bone tissue engineering. It begins with a review of the methods and applicable materials in existing additive manufacturing technologies and their applications in biomedicine, introducing the advantages and disadvantages of various AM technologies. The properties of materials including metals and polymers, commonly used AM technologies, recent developments, and their applications in bone tissue engineering are discussed in detail and summarized. In addition, the main challenges for different metallic and polymer materials, such as biodegradability, anisotropy, growth factors to promote the osteogenic capacity, and enhancement of mechanical properties are also introduced. Finally, the development prospects for AM technologies and biomaterials in bone tissue engineering are considered. Full article

(This article belongs to the Topic Material and Process Innovations for 3D Printing Applications)

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15 pages, 3407 KiB  

Open AccessArticle

3D Printing Manufacturing of Polydimethyl-Siloxane/Zinc Oxide Micro-Optofluidic Device for Two-Phase Flows Control

by Giovanna Stella, Matteo Barcellona, Lorena Saitta, Claudio Tosto, Gianluca Cicala, Antonino Gulino, Maide Bucolo and Maria Elena Fragalà

Polymers 2022, 14(10), 2113; https://doi.org/10.3390/polym14102113 - 22 May 2022

Cited by 6 | Viewed by 2764

Abstract

Tailored ZnO surface functionalization was performed inside a polydimethyl-siloxane (PDMS) microchannel of a micro-optofluidic device (mofd) to modulate its surface hydrophobicity to develop a method for fine tuning the fluid dynamics inside a microchannel. The wetting behavior of the surface is [...] Read more.

Tailored ZnO surface functionalization was performed inside a polydimethyl-siloxane (PDMS) microchannel of a micro-optofluidic device (mofd) to modulate its surface hydrophobicity to develop a method for fine tuning the fluid dynamics inside a microchannel. The wetting behavior of the surface is of particular importance if two different phases are used for system operations. Therefore, the fluid dynamic behavior of two immiscible fluids, (i) air–water and (ii) air–glycerol/water in PDMS mofds and ZnO-PDMS mofds was investigated by using different experimental conditions. The results showed that air–glycerol/water fluid was always faster than air–water flow, despite the microchannel treatment: however, in the presence of ZnO microstructures, the velocity of the air–glycerol/water fluid decreased compared with that observed for the air–water fluid. This behavior was associated with the strong ability of glycerol to create an H-bond network with the exposed surface of the zinc oxide microparticles. The results presented in this paper allow an understanding of the role of ZnO functionalization, which allows control of the microfluidic two-phase flow using different liquids that undergo different chemical interactions with the surface chemical terminations of the microchannel. This chemical approach is proposed as a control strategy that is easily adaptable for any embedded micro-device. Full article

(This article belongs to the Topic Material and Process Innovations for 3D Printing Applications)

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15 pages, 3169 KiB  

Open AccessArticle

The Anisotropic Electrochemical Machinability of Laser Cladding Deposited Ti6Al4V Alloy in NaCl Solution

by Jiaqiang Li, Yuan Yang, Gangxian Zhu, Chengfeng Sun, Yiyang Chen, Kejun Wang and Shihong Shi

Materials 2022, 15(10), 3642; https://doi.org/10.3390/ma15103642 - 19 May 2022

Cited by 4 | Viewed by 1926

Abstract

The hybrid manufacturing method of laser cladding deposition (LCD) additive manufacturing and electrochemical machining (ECM) is a promising approach to advanced manufacturing technology for difficult machined materials. The anisotropic electrochemical performance of LCD-produced Ti6Al4V alloy was studied in 15 wt.% NaCl solution by [...] Read more.

The hybrid manufacturing method of laser cladding deposition (LCD) additive manufacturing and electrochemical machining (ECM) is a promising approach to advanced manufacturing technology for difficult machined materials. The anisotropic electrochemical performance of LCD-produced Ti6Al4V alloy was studied in 15 wt.% NaCl solution by polarization curve measurements and ECM tests. The horizontal-plane (X0Y plane) exhibits a more stable passive film in both static electrolyte and low current density ECM processes than the vertical-plane (X0Z plane). Additionally, the horizontal-plane exhibits a higher material removal rate and more consistent dissolved surface roughness in comparison with the vertical-plane during the high current density ECM process. The microstructure of the LCD-produced Ti6Al4V alloy on the horizontal-plane consisted of equiaxed-like prior-β grains and slightly finer α-laths but was composed by columnar prior-β grains and coarser α-laths on the vertical-plane. These differences in the microstructural characteristics produce the distinctions observed in the electrochemical dissolution behavior and electrochemical machinability on the horizontal- and vertical-planes. Full article

(This article belongs to the Topic Material and Process Innovations for 3D Printing Applications)

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23 pages, 23693 KiB  

Open AccessArticle

Multi-Layer Simulation of the Powder Bed Selective Laser Processing of Alumina for Residual Stress and Distortion Evaluation

by Mohamed Abdelmoula and Gökhan Küçüktürk

Materials 2022, 15(10), 3498; https://doi.org/10.3390/ma15103498 - 13 May 2022

Cited by 5 | Viewed by 2760

Abstract

A numerical model was developed to simulate the real process of alumina powder bed selective laser processing (PBSLP) to thoroughly investigate the residual stress and distortion experienced in printed parts when multi-layer scanning with a CO₂ laser source is considered. The model [...] Read more.

A numerical model was developed to simulate the real process of alumina powder bed selective laser processing (PBSLP) to thoroughly investigate the residual stress and distortion experienced in printed parts when multi-layer scanning with a CO₂ laser source is considered. The model contains a user-defined function (UDF) for the laser source, temperature-dependent material properties, scanning strategies, and build orientations, and it is solved using ANSYS 2020R2. In addition, the model’s validation was confirmed with experimental results. The results revealed that a high scanning speed (up to 1200 mm/s) and low laser power are effective for the PBSLP of alumina, owing to alumina’s high absorptivity for CO₂ lasers, and a high manufacturing rate can be achieved. During the multi-layer printing simulation, the accumulated heat inside the part increased gradually with an increased number of printed layers. Additionally, the calculated residual stress exceeded the yield limit for all the studied build orientations due to the printed part’s high-temperature difference. When preheating was applied, the residual stress decreased by 23% and the distortion decreased by 54%. For the successful PBSLP of ceramics, commercial printers cannot be used effectively. A particular printer equipped with a temperature controller and a preheating system is required for ceramics. Full article

(This article belongs to the Topic Material and Process Innovations for 3D Printing Applications)

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13 pages, 7468 KiB  

Open AccessArticle

Innovation Process for Optical Face Scanner Used to Customize 3D Printed Spectacles

by Cristian Gabriel Alionte, Liviu Marian Ungureanu and Tudor Mihai Alexandru

Materials 2022, 15(10), 3496; https://doi.org/10.3390/ma15103496 - 13 May 2022

Cited by 5 | Viewed by 3055

Abstract

Many people for different reasons end up wearing glasses to correct their vision. From time immemorial, there has been an unquestionable ability to associate people with glasses. Designing the glasses according to the physiognomy of each person opens a new path for a [...] Read more.

Many people for different reasons end up wearing glasses to correct their vision. From time immemorial, there has been an unquestionable ability to associate people with glasses. Designing the glasses according to the physiognomy of each person opens a new path for a completely new optical experience. The frames are designed to fit perfectly on the face, are comfortable on the nose, and are positioned at an optimal distance from the cheeks and eyelashes. Three-dimensional printing technology offers the possibility to customize any form of glasses at a low cost with average quality. In this type of technology, the printer receives a digitized model of the spectacle frame (usually in STL file format) that must meet the parameters related to the wearer’s anatomy. Therefore, this paper presents an innovative process, an optical method used to scan the wearer’s face to design a parameterized design of the spectacle frames. The procedure has a measurement phase for quantifying the anatomical features of the wearer’s face, a para-metric design phase of the glasses for adjusting the design parameters according to the anatomical characteristics, and a manufacturing phase in which the custom eyeglass frame will be manufactured using 3D printing technology. The aim of this study was to create an innovative process that could be tested as an educational 3D printing system that could be used by undergraduate students (studying under an optometry program), a process that would begin at optometric prescription stage and can be used in the educational laboratory of the Department of Mechatronics and Precision Mechanics from the Politehnica University of Bucharest. Using this method we obtained a custom spectacle frame that can be prototyped using 3D printing. The 3D-printed polylactic acid (PLA) frames are lightweight, flexible, durable, and the innovative photogrammetry process gives designers the ability to create custom designs that cannot be created with traditional manufacturing techniques. Full article

(This article belongs to the Topic Material and Process Innovations for 3D Printing Applications)

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13 pages, 5615 KiB  

Open AccessArticle

Production of Dense Cu-10Sn Part by Laser Powder Bed Fusion with Low Surface Roughness and High Dimensional Accuracy

by Flaviana Calignano, Diego Manfredi, Silvia Marola, Mariangela Lombardi and Luca Iuliano

Materials 2022, 15(9), 3352; https://doi.org/10.3390/ma15093352 - 7 May 2022

Cited by 3 | Viewed by 2125

Abstract

Tin-bronze alloys with a tin content of at least 10 wt% have excellent mechanical properties, wear resistance, and corrosion resistance. Among these alloys, Cu-10Sn was investigated in this study for production with the laser powder bed fusion process with a 500W Yb:YAG laser. [...] Read more.

Tin-bronze alloys with a tin content of at least 10 wt% have excellent mechanical properties, wear resistance, and corrosion resistance. Among these alloys, Cu-10Sn was investigated in this study for production with the laser powder bed fusion process with a 500W Yb:YAG laser. In particular, a design of experiment (DoE) was developed in order to identify the optimal process parameters to obtain full density, low surface roughness, and high dimensional accuracy. Samples were characterized with Archimedes’ method and optical microscopy to determine their final density. It was shown that the first method is fast but not as reliable as the second one. A first mechanical characterization was performed through microhardness tests. Finally, a set of process parameters was identified to produce fully dense samples with low surface roughness and high accuracy. The results showed that the volumetric energy density could represent an approach that is too simplified, therefore limiting the direct correlation with the physical aspects of the process. Full article

(This article belongs to the Topic Material and Process Innovations for 3D Printing Applications)

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16 pages, 5513 KiB  

Open AccessArticle

Manufacturing of a Magnetic Composite Flexible Filament and Optimization of a 3D Printed Wideband Electromagnetic Multilayer Absorber in X-Ku Frequency Bands

by Christophe Vong, Alexis Chevalier, Azar Maalouf, Julien Ville, Jean-François Rosnarho and Vincent Laur

Materials 2022, 15(9), 3320; https://doi.org/10.3390/ma15093320 - 5 May 2022

Cited by 14 | Viewed by 2602

Abstract

With the multiplication of electronic devices in our daily life, there is a need for tailored wideband electromagnetic (EM) absorbers that could be conformed on any type of surface-like antennas for interference attenuation or military vehicles for stealth applications. In this study, a [...] Read more.

With the multiplication of electronic devices in our daily life, there is a need for tailored wideband electromagnetic (EM) absorbers that could be conformed on any type of surface-like antennas for interference attenuation or military vehicles for stealth applications. In this study, a wideband flexible flat electromagnetic absorber compatible with additive manufacturing has been studied in the X-Ku frequency bands. A multilayer structure has been optimized using a genetic algorithm (GA), adapting the restrictions of additive manufacturing and exploiting the EM properties of loaded and non-loaded filaments, of which the elaboration is described. After optimization, a bi-material multilayer absorber with a thickness of 4.1 mm has been designed to provide a reflectivity below −12 dB between 8 and 18 GHz. Finally, the designed multilayer structure was 3D-printed and measured in an anechoic chamber, achieving −11.8 dB between 7 and 18 GHz. Thus, the development of dedicated materials has demonstrated the strong potential of additive technologies for the manufacturing of thin wideband flexible EM absorbers. Full article

(This article belongs to the Topic Material and Process Innovations for 3D Printing Applications)

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15 pages, 6356 KiB  

Open AccessArticle

Wear Resistance and Biocompatibility of Co-Cr Dental Alloys Fabricated with CAST and SLM Techniques

by Wenqi Fu, Shuang Liu, Jun Jiao, Zhiwen Xie, Xinfang Huang, Yun Lu, Huiying Liu, Shuhai Hu, Enjun Zuo, Ni Kou and Guowu Ma

Materials 2022, 15(9), 3263; https://doi.org/10.3390/ma15093263 - 2 May 2022

Cited by 28 | Viewed by 3957

Abstract

Cobalt–chromium (Co-Cr) alloys have been widely used as dental-restoration materials for many years. This study sought to investigate whether selective laser melting (SLM) is a more appropriate process than traditional casting (CAST) for fabricating dental Co-Cr alloys. Metallurgical microscopy, X-ray photoelectron spectroscopy (XPS), [...] Read more.

Cobalt–chromium (Co-Cr) alloys have been widely used as dental-restoration materials for many years. This study sought to investigate whether selective laser melting (SLM) is a more appropriate process than traditional casting (CAST) for fabricating dental Co-Cr alloys. Metallurgical microscopy, X-ray photoelectron spectroscopy (XPS), Vickers hardness and nanoindentation tests, and friction and wear tests were used to evaluate the microstructure, surface compositions, mechanical properties, and wear resistance, respectively. Additionally, the biocompatibilities and cell adhesion of the alloys were evaluated with L-929 fibroblasts via CCK-8 assay, Live/Dead staining, flow cytometric analysis, scanning electron microscopy (SEM) observation and real-time PCR (RT-PCR) assay. The XPS results showed that the two alloys were all mainly comprised of Co, Cr, and O. The hardness in the CAST group equaled 7.15 ± 0.48 GPa, while in the SLM group, it equaled 9.06 ± 0.49 GPa. The friction coefficient of SLM alloys remained at approximately 0.46, but the CAST specimens fluctuated significantly. SLM alloys exhibited shallower wear scars and less wear debris compared with CAST alloys, simultaneously. Additionally, there were higher survival and expression of cell-adhesion-related genes on SLM alloys of L-929 cells, which meant that the deleterious effect on L-929 cells was significantly reduced compared with that for the CAST alloys. Overall, the wear resistances and biocompatibilities of the Co-Cr dental alloys were dramatically affected by the fabrication technique. The SLM technique is advantageous over the CAST technique for fabricating Co-Cr dental alloys. Full article

(This article belongs to the Topic Material and Process Innovations for 3D Printing Applications)

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16 pages, 4578 KiB  

Open AccessArticle

3D-Printed Poly (P-Dioxanone) Stent for Endovascular Application: In Vitro Evaluations

by Junlin Lu, Xulin Hu, Tianyu Yuan, Jianfei Cao, Yuanli Zhao, Chengdong Xiong, Kainan Li, Xun Ye, Tao Xu and Jizong Zhao

Polymers 2022, 14(9), 1755; https://doi.org/10.3390/polym14091755 - 26 Apr 2022

Cited by 8 | Viewed by 3343

Abstract

Rapid formation of innovative, inexpensive, personalized, and quickly reproducible artery bioresorbable stents (BRSs) is significantly important for treating dangerous and sometimes deadly cerebrovascular disorders. It is greatly challenging to give BRSs excellent mechanical properties, biocompatibility, and bioabsorbability. The current BRSs, which are mostly [...] Read more.

Rapid formation of innovative, inexpensive, personalized, and quickly reproducible artery bioresorbable stents (BRSs) is significantly important for treating dangerous and sometimes deadly cerebrovascular disorders. It is greatly challenging to give BRSs excellent mechanical properties, biocompatibility, and bioabsorbability. The current BRSs, which are mostly fabricated from poly-l-lactide (PLLA), are usually applied to coronary revascularization but may not be suitable for cerebrovascular revascularization. Here, novel 3D-printed BRSs for cerebrovascular disease enabling anti-stenosis and gradually disappearing after vessel endothelialization are designed and fabricated by combining biocompatible poly (p-dioxanone) (PPDO) and 3D printing technology for the first time. We can control the strut thickness and vessel coverage of BRSs by adjusting the printing parameters to make the size of BRSs suitable for small-diameter vascular use. We added bis-(2,6-diisopropylphenyl) carbodiimide (commercial name: stabaxol^®-1) to PPDO to improve its hydrolytic stability without affecting its mechanical properties and biocompatibility. In vitro cell experiments confirmed that endothelial cells can be conveniently seeded and attached to the BRSs and subsequently demonstrated good proliferation ability. Owing to the excellent mechanical properties of the monofilaments fabricated by the PPDO, the 3D-printed BRSs with PPDO monofilaments support desirable flexibility, therefore offering a novel BRS application in the vascular disorders field. Full article

(This article belongs to the Topic Material and Process Innovations for 3D Printing Applications)

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24 pages, 10623 KiB  

Open AccessArticle

An Improved Point Clouds Model for Displacement Assessment of Slope Surface by Combining TLS and UAV Photogrammetry

by He Jia, Guojin Zhu, Lina Guo, Junyi He, Binjie Liang and Sunwen He

Appl. Sci. 2022, 12(9), 4320; https://doi.org/10.3390/app12094320 - 25 Apr 2022

Cited by 3 | Viewed by 2214

Abstract

TLS can quickly and accurately capture object surface coordinates. However, TLS point clouds cannot cover the entire surface of the target object, due to block of view and limitation of measurement condition. Thus, using it to monitor deformation of slope reduces the detection [...] Read more.

TLS can quickly and accurately capture object surface coordinates. However, TLS point clouds cannot cover the entire surface of the target object, due to block of view and limitation of measurement condition. Thus, using it to monitor deformation of slope reduces the detection accuracy of slope surface deformation. To overcome the drawbacks, a method to improve TLS point clouds by UAV photogrammetric point clouds is proposed. The two kinds of point clouds are registered as the new multi-view point clouds by PCA and ICP. The locations of monitoring points are extracted based on HSL color space recognition method from the new multi-view point clouds to analyze the surface displacement. At present, the proposed method has applied in a highway slope in Yunnan Province, and complete point clouds were successfully constructed. A RTK survey was used to compare and verify the proposed method. The verification result demonstrate that the difference of displacement between two measurement methods is less than 10 mm. Comprehensive experiments demonstrate that the proposed method is reliable and meets the slope displacement monitoring standard. Full article

(This article belongs to the Topic Material and Process Innovations for 3D Printing Applications)

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19 pages, 22993 KiB  

Open AccessArticle

Influencing the Size and Shape of High-Energy Ball Milled Particle Reinforced Aluminum Alloy Powder

by Maik Trautmann, Husam Ahmad and Guntram Wagner

Materials 2022, 15(9), 3022; https://doi.org/10.3390/ma15093022 - 21 Apr 2022

Cited by 7 | Viewed by 3159

Abstract

High-energy ball milling represents an efficient process for producing composite powders consisting of ceramic particles dispersed in a metallic matrix. However, collision events, plastic deformations, and cold welding during the milling lead to a flake or block-like shape of the resulting composite powders. [...] Read more.

High-energy ball milling represents an efficient process for producing composite powders consisting of ceramic particles dispersed in a metallic matrix. However, collision events, plastic deformations, and cold welding during the milling lead to a flake or block-like shape of the resulting composite powders. Further consolidation of such irregularly shaped powders by powder bed-based additive manufacturing technologies can be challenging because of their low flowability and low bulk density. In this work, different approaches, including milling process parameters (speed, process control agent atmosphere) and post-treatments (mechanical and thermal), are investigated on their suitability to influence the particle shape, especially concerning the roundness of the composite powders consisting of the aluminum alloy AlSi10Mg with 5 vol% SiC and Al₂O₃ reinforcement. It is found that milling with menthol as a process control agent leads to the finest composite powder compared to other milling parameters, with the lowest particle roundness of 0.39 (initial powders 0.84). No success in rounding the milled composite powder could be achieved through mechanical post-treatment in a planetary ball mill. On the other side, the thermal spraying of, e.g., SiC reinforced AlSi10Mg powder resulted in a 77–82% relative roundness. A remarkable change in the microstructure and the shape of the composite powders could also be observed after heat treatment in tube furnaces at a temperature above the melting point of AlSi10Mg. The best result in terms of improved roundness (relative to around 85%) was obtained for Al₂O₃ reinforced at 600 °C. A further increase of the temperature to 700 °C resulted in a moderate coarsening of powders with Al₂O₃ and extensive sintering of powders with SiC, presumably due to a different distribution inside the matrix. Full article

(This article belongs to the Topic Material and Process Innovations for 3D Printing Applications)

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15 pages, 6779 KiB  

Open AccessArticle

3D Printing Application in Wood Furniture Components Assembling

by Antoniu Nicolau, Mihai Alin Pop and Camelia Coșereanu

Materials 2022, 15(8), 2907; https://doi.org/10.3390/ma15082907 - 15 Apr 2022

Cited by 24 | Viewed by 4953

Abstract

Additive manufacturing (AM) is used in many fields and is a method used to replace wood components or wood-jointed furniture components in the furniture industry. Replacing wood joints by 3D printed connectors would be an advantage, considering the fact that during the process [...] Read more.

Additive manufacturing (AM) is used in many fields and is a method used to replace wood components or wood-jointed furniture components in the furniture industry. Replacing wood joints by 3D printed connectors would be an advantage, considering the fact that during the process of assembling furniture, the execution technology of the joints is difficult, time-consuming, and labor-intensive. Advanced technology of AM applied in furniture manufacturing helps the designers to create new concepts of product design, with no limits of shape, number of joints, color, or size. The diversity of 3D printers and AM technologies provides the selection of materials in relation with the applicability of the 3D printed object. In this respect, the objective of the present research is to design a 3D printed connector to be used for jointing three chair components, namely the leg and two stretchers made from larch (Larix decidua Mill.) wood, and to use reinforced polylactic acid (PLA) fiberglass (20 wt. %) filament for 3D printing this connector using AM with fused filament fabrication (FFF) technology. The design of the connector, the possibility of using this type of material, and the deposition method of filament were investigated in this research. For this purpose, several evaluation methods were applied: microscopic investigation with 50×, 100×, and 200× magnifications, both of the filament and of the 3D printed connector; mechanical testing of corner joint formed with the help of connector between chair leg and the two stretchers; and a microscopic investigation of the connectors’ defects that occurred after applying the compression and tensile loads on the diagonal direction of the L-type joint. The microscopic investigation of the composite filament revealed the agglomerations of glass fibers into the core matrix and areas where the distribution of the reinforcements was poor. The heterogeneous structure of the filament and the defects highlighted in the 3D printed connectors by the microscopic investigation contributed to the mechanical behavior of L-type connecting joints. The bending moments resulting from compression and tensile tests of the 3D printed connectors were compared to the results recorded after testing, under the same conditions, the normal mortise–tenon joint used to assemble the abovementioned chair components. The larch wood strength influenced the mechanical results and the conclusions of the microscopic investigations, as well as the analysis of the broken connectors after testing recommended the change of connector design and filament deposition direction. Full article

(This article belongs to the Topic Material and Process Innovations for 3D Printing Applications)

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24 pages, 23969 KiB  

Open AccessArticle

Embedded Optical Fibre with Fibre Bragg Grating Influence on Additive Manufactured Polymeric Structure Durability

by Magdalena Mieloszyk, Katarzyna Majewska and Artur Andrearczyk

Materials 2022, 15(7), 2653; https://doi.org/10.3390/ma15072653 - 4 Apr 2022

Cited by 3 | Viewed by 2215

Abstract

Additive manufacturing (AM) polymers are applied in many branches of the industry due to the possibility of fast and accurate production of elements with various and complex shapes. Fibre Bragg grating sensors (FBG) are widely applied in structural health monitoring (SHM) systems. The [...] Read more.

Additive manufacturing (AM) polymers are applied in many branches of the industry due to the possibility of fast and accurate production of elements with various and complex shapes. Fibre Bragg grating sensors (FBG) are widely applied in structural health monitoring (SHM) systems. The main objective of this research is to perform analyses of the influence of embedded FBG sensors on AM polymer elements’ durability. Two polymers (M3 X and M3 Crystal) with different mechanical properties were analysed. The tests were performed on samples with FBG sensors embedded in (different alignment) and attached to the surfaces of the elements. Firstly, the samples were exposed to elevated or sub-zero temperatures under stable relative humidity levels. The strain in the samples was measured using fibre Bragg grating (FBG) sensors. The achieved results allow us to determine the relationships between strain and temperature for both materials and the differences in their mechanical response to the thermal loading. Then, the samples were subjected to a tensile test. A comparison of the tensile strength values was performed for the samples without and with embedded FBG sensors. The samples after the tensile tests were compared, showing differences in the mechanisms of failures related to the polymers and the thermal treatment influence on the material internal structure. Additionally, strain values measured by the FBG sensors were compared to the strain values achieved from the testing machine showing a good agreement (especially for M3 X) and indicating the differences in the materials’ mechanical properties. The achieved results allow us to conclude there is a lack of influence of embedded FBG sensors on the mechanical durability of AM polymers. Full article

(This article belongs to the Topic Material and Process Innovations for 3D Printing Applications)

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9 pages, 1646 KiB  

Open AccessArticle

3D Printing of Tooth Impressions Based on Multi-Detector Computed Tomography Images Combined with Beam Hardening Artifact Reduction in Metal Structures

by Yeon Park and Seung-Man Yu

Appl. Sci. 2022, 12(7), 3339; https://doi.org/10.3390/app12073339 - 25 Mar 2022

Cited by 1 | Viewed by 2178

Abstract

We investigated the role of metal artifact reduction by taking 3D print impressions using 3D data of Computed Tomography (CT) images based on the algorithm applied. We manufactured a phantom of a human mandible tooth made of gypsum and nickel alloy to measure [...] Read more.

We investigated the role of metal artifact reduction by taking 3D print impressions using 3D data of Computed Tomography (CT) images based on the algorithm applied. We manufactured a phantom of a human mandible tooth made of gypsum and nickel alloy to measure the metal artifacts. CT images were obtained by changing the phantom tube voltage and tube current. The signal intensity of the image generated by the metal artifacts before and after the iterative metal artifact reduction algorithm (iMAR) was measured. A 3D printing process was performed after converting the images, before and after iMAR application, into STL files using InVesalius version 3.1.1 by selecting the conditions that minimized the effect of the artifact. Regarding metal artifacts, the Hounsfield unit (HU) value showed low as the tube voltage increased. The iMAR-applied images acquired under the same conditions showed a significantly lower HU. The artifacts, in the form of flashes, persisted in the 3D-printed product of the image not subjected to iMAR, but were largely removed in the 3D-printed product following iMAR application. In this study, the application of iMAR and data acquired using high tube voltage eliminated a significant portion of the metal artifacts, resulting in an impression shape that was consistent with the human body. Full article

(This article belongs to the Topic Material and Process Innovations for 3D Printing Applications)

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20 pages, 3331 KiB  

Open AccessArticle

Reorientation of Suspended Ceramic Particles in Robocasted Green Filaments during Drying

by Bastien Dietemann, Larissa Wahl, Nahum Travitzky, Harald Kruggel-Emden, Torsten Kraft and Claas Bierwisch

Materials 2022, 15(6), 2100; https://doi.org/10.3390/ma15062100 - 12 Mar 2022

Cited by 4 | Viewed by 3299

Abstract

This work considers the fabrication of ceramic parts with the help of an additive manufacturing process, robocasting, in which a paste with suspended particles is robotically extruded. Within the final part, the material properties depend on the orientation of the particles. A prediction [...] Read more.

This work considers the fabrication of ceramic parts with the help of an additive manufacturing process, robocasting, in which a paste with suspended particles is robotically extruded. Within the final part, the material properties depend on the orientation of the particles. A prediction of the particle orientation is challenging as the part usually undergoes multiple processing steps with varying contributions to the orientation. As the main contribution to the final particle orientation arises from the extrusion process, many corresponding prediction models have been suggested. Robocasting involves, however, further processing steps that are less studied as they have a smaller influence on the orientation. One of the processing steps is drying by natural convection, which follows directly after the extrusion process. A quantification of the reorientation that occurs during drying is mostly unknown and usually neglected in the models. Therefore, we studied the amount of reorientation of suspended particles in robocasted green filaments during drying in detail. For our study, we applied the discrete element method, as it meets various requirements: The exact particle geometry can be resolved precisely; particle–particle interactions can be described; the paste composition is reproduced exactly; the initial particle orientation can be set in accordance with the prediction from the analytical models for the extrusion part; macroscopic force laws exist to represent capillary forces due to the remaining fluid phase that remains during drying. From our study, we concluded that the magnitude of particle reorientation during drying is small compared to the orientation occurring during the extrusion process itself. Consequently, reorientation during drying might further be neglected within analytical orientation prediction models. Full article

(This article belongs to the Topic Material and Process Innovations for 3D Printing Applications)

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14 pages, 6957 KiB  

Open AccessArticle

Polypropylene Random Copolymer Based Composite Used for Fused Filament Fabrication: Printability and Properties

by Zhiyao Zhang and Xueqin Gao

Polymers 2022, 14(6), 1106; https://doi.org/10.3390/polym14061106 - 10 Mar 2022

Cited by 16 | Viewed by 3219

Abstract

Fused filament fabrication (FFF) is one of the most commonly used additive manufacturing technologies. However, the applied material for commercial FFF is limited. Presently, though being one of the most used polymer materials, polypropylene (PP) is rarely used in FFF because of its [...] Read more.

Fused filament fabrication (FFF) is one of the most commonly used additive manufacturing technologies. However, the applied material for commercial FFF is limited. Presently, though being one of the most used polymer materials, polypropylene (PP) is rarely used in FFF because of its serious warpage and shrinkage problems. This study investigated the impact of addition of short glass fibers (GF) and ethylene propylene diene monomer (EPDM) on the printability of polypropylene random copolymer (PPR) based FFF and mechanical properties of the printed samples, as well as other properties including rheology, thermal behaviors, and morphology. The results show that the modified PPR has excellent printability, as the printed samples are of good geometrical accuracy. The addition of GF can significantly improve the strength and modulus of the composite, but it also leads to serious decrease in toughness. EPDM addition can effectively improve the toughness of the composite, showing a complementary effect with GF. This work has important meaning in expanding the FFF applicable material and in broadening the application of PP. Full article

(This article belongs to the Topic Material and Process Innovations for 3D Printing Applications)

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13 pages, 9940 KiB  

Open AccessArticle

Performance of High-Layer-Thickness Ti6Al4V Fabricated by Electron Beam Powder Bed Fusion under Different Accelerating Voltage Values

by Hongxin Li, Xiaoyu Liang, Yang Li and Feng Lin

Materials 2022, 15(5), 1878; https://doi.org/10.3390/ma15051878 - 3 Mar 2022

Cited by 13 | Viewed by 2561

Abstract

The electron beam powder bed fusion (EB-PBF) process is typically carried out using a layer thickness between 50 and 100 μm with the accelerating voltage of 60 kV for the electron beam. This configuration ensures forming accuracy but limits building efficiency. The augmentation [...] Read more.

The electron beam powder bed fusion (EB-PBF) process is typically carried out using a layer thickness between 50 and 100 μm with the accelerating voltage of 60 kV for the electron beam. This configuration ensures forming accuracy but limits building efficiency. The augmentation of the accelerating voltage enlarges the molten pool due to the rise in penetrability, suggesting that a higher layer thickness can be used. Therefore, the effects of layer thickness and accelerating voltage were investigated simultaneously in this study to explore the feasibility of efficiency improvement. Ti6Al4V was fabricated by EB-PBF using layer thicknesses of 200 and 300 μm. Two accelerating voltage values of 60 and 90 kV were used to study their effects under expanded layer thickness. The results reveal that dense parts with the ultimate tensile strength higher than 950 MPa and elongation higher than 9.5% could be fabricated even if the layer thickness reached 300 μm, resulting in a building rate of up to 30 mm³/s. The expansion of the layer thickness could decrease the minimum bulk energy density needed to fabricate dense parts and increase the α platelet thickness, which improved the energy efficiency. However, expanding layer thickness had a significant negative effect on surface roughness, but it could be improved by applying augmented accelerating voltage. Full article

(This article belongs to the Topic Material and Process Innovations for 3D Printing Applications)

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17 pages, 7475 KiB  

Open AccessArticle

Design and Characterization of Asymmetric Cell Structure of Auxetic Material for Predictable Directional Mechanical Response

by Rodrigo Valle, Gonzalo Pincheira, Víctor Tuninetti, Eduardo Fernandez and Esmeralda Uribe-Lam

Materials 2022, 15(5), 1841; https://doi.org/10.3390/ma15051841 - 1 Mar 2022

Cited by 14 | Viewed by 3743

Abstract

A three-dimensional auxetic structure based on a known planar configuration including a design parameter producing asymmetry is proposed in this study. The auxetic cell is designed by topology analysis using classical Timoshenko beam theory in order to obtain the required orthotropic elastic properties. [...] Read more.

A three-dimensional auxetic structure based on a known planar configuration including a design parameter producing asymmetry is proposed in this study. The auxetic cell is designed by topology analysis using classical Timoshenko beam theory in order to obtain the required orthotropic elastic properties. Samples of the structure are fabricated using the ABSplus fused filament technique and subsequently tested under quasi-static compression to statistically determine the Poisson’s ratio and Young’s modulus. The experimental results show good agreement with the topological analysis and reveal that the proposed structure can adequately provide different elastic properties in its three orthogonal directions. In addition, three point bending tests were carried out to determine the mechanical behavior of this cellular structure. The results show that this auxetic cell influences the macrostructure to exhibit different stiffness behavior in three working directions. Full article

(This article belongs to the Topic Material and Process Innovations for 3D Printing Applications)

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15 pages, 6207 KiB  

Open AccessArticle

Coupling Analysis on Microstructure and Residual Stress in Selective Laser Melting (SLM) with Varying Key Process Parameters

by Peiying Bian, Chunchang Wang, Kewei Xu, Fangxia Ye, Yongjian Zhang and Lei Li

Materials 2022, 15(5), 1658; https://doi.org/10.3390/ma15051658 - 23 Feb 2022

Cited by 13 | Viewed by 2809

Abstract

With the application of Selective Laser Melting (SLM) technology becoming more and more widespread, it is important to note the process parameters that have a very important effect on the forming quality. Key process parameters such as laser power (P), scan [...] Read more.

With the application of Selective Laser Melting (SLM) technology becoming more and more widespread, it is important to note the process parameters that have a very important effect on the forming quality. Key process parameters such as laser power (P), scan speed (s), and scanning strategy (μ) were investigated by determining the correlation between the microstructure and residual stress in this paper. A total of 10 group 316L specimens were fabricated using SLM for comprehensive analysis. The results show that the key process parameters directly affect the morphology and size of the molten pool in the SLM deposition, and the big molten pool width has a direct effect on the larger grain size and crystal orientation distribution. In addition, the larger grain size and misorientation angle also affect the size of the residual stress. Therefore, better additive manufacturing grain crystallization can be obtained by reasonably adjusting the process parameter combinations. The transfer energy density can synthesize the influence of four key process parameters (P, v, the hatching distance (δ), and the layer thickness (h)). In this study, it is proposed that the accepted energy density will reflect the influence of five key process parameters, including the scanning trajectory (μ), which can reflect the comprehensive effect of process parameters more accurately. Full article

(This article belongs to the Topic Material and Process Innovations for 3D Printing Applications)

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14 pages, 7416 KiB  

Open AccessArticle

Hybrid Printing Method of Polymer and Continuous Fiber-Reinforced Thermoplastic Composites (CFRTPCs) for Pipes through Double-Nozzle Five-Axis Printer

by Haiguang Zhang, Xu Lei, Qingxi Hu, Shichao Wu, Mohamed Aburaia, Joamin Gonzalez-Gutierrez and Herfried Lammer

Polymers 2022, 14(4), 819; https://doi.org/10.3390/polym14040819 - 20 Feb 2022

Cited by 13 | Viewed by 3911

Abstract

The most widely used 3D process, fused deposition modeling (FDM), has insufficient interlayer adhesion due to its layer-by-layer forming method. A support material is also essential for the hollow parts and cantilevers. Moreover, the polymer materials used have limited mechanical properties. These issues [...] Read more.

The most widely used 3D process, fused deposition modeling (FDM), has insufficient interlayer adhesion due to its layer-by-layer forming method. A support material is also essential for the hollow parts and cantilevers. Moreover, the polymer materials used have limited mechanical properties. These issues have restricted the application of FDM in high-performance fields. Continuous fiber-reinforced thermoplastic composites (CFRTPCs) have high mechanical properties and have recently become the focus of research in the field of 3D printing. This paper, using pipe parts as an example, proposes a hybrid of pure polymer (pure PLA used) and CFRTPC (flax fiber pre-impregnated filament) material to develop a printing method based on the outstanding mechanical properties of CFRTPC material. After studying the printing path planning algorithm, the CFRTPC filament is laid along the axial and radial directions on the surface of the polymer base to improve the printed parts’ properties. The method feasibility and algorithm accuracy are verified through the development of five-axis printing equipment with a double nozzle. Through the printed sample’s tensile, compression and bending tests, the results show that the tensile, compressive and bending properties of PLA pipe can be significantly enhanced by laying CFRTPC filament along the axial and radial directions of the pipe. To summarize, the introduction of CFRTPCs greatly improved the mechanical properties of the printed parts, and the implementation of our method provides an effective way to solve the defects of the FDM process. Full article

(This article belongs to the Topic Material and Process Innovations for 3D Printing Applications)

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24 pages, 12351 KiB  

Open AccessArticle

Restoration and Possible Upgrade of a Historical Motorcycle Part Using Powder Bed Fusion

by Lukas Kudrna, Quoc-Phu Ma, Jiri Hajnys, Jakub Mesicek, Radim Halama, Frantisek Fojtik and Lukas Hornacek

Materials 2022, 15(4), 1460; https://doi.org/10.3390/ma15041460 - 16 Feb 2022

Cited by 8 | Viewed by 2445

Abstract

Reverse engineering is the process of creating a digital version of an existing part without any knowledge in advance about the design intent. Due to 3D printing, the reconstructed part can be rapidly fabricated for prototyping or even for practical usage. To showcase [...] Read more.

Reverse engineering is the process of creating a digital version of an existing part without any knowledge in advance about the design intent. Due to 3D printing, the reconstructed part can be rapidly fabricated for prototyping or even for practical usage. To showcase this combination, this study presents a workflow on how to restore a motorcycle braking pedal from material SS316L with the Powder Bed Fusion (PBF) technology. Firstly, the CAD model of the original braking pedal was created. Before the actual PBF printing, the braking pedal printing process was simulated to identify the possible imperfections. The printed braking pedal was then subjected to quality control in terms of the shape distortion from its CAD counterpart and strength assessments, conducted both numerically and physically. As a result, the exterior shape of the braking pedal was restored. Additionally, by means of material assessments and physical tests, it was able to prove that the restored pedal was fully functional. Finally, an approach was proposed to optimize the braking pedal with a lattice structure to utilize the advantages the PBF technology offers. Full article

(This article belongs to the Topic Material and Process Innovations for 3D Printing Applications)

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15 pages, 10136 KiB  

Open AccessArticle

Polymer–Nickel Composite Filaments for 3D Printing of Open Porous Materials

by Ewelina Mackiewicz, Tomasz Wejrzanowski, Bogusława Adamczyk-Cieślak and Graeme J. Oliver

Materials 2022, 15(4), 1360; https://doi.org/10.3390/ma15041360 - 12 Feb 2022

Cited by 14 | Viewed by 3818

Abstract

Catalysis has been a key way of improving the efficiency-to-cost ratio of chemical and electrochemical processes. There have been recent developments in catalyst materials that enable the development of novel and more sophisticated devices that, for example, can be used in applications, such [...] Read more.

Catalysis has been a key way of improving the efficiency-to-cost ratio of chemical and electrochemical processes. There have been recent developments in catalyst materials that enable the development of novel and more sophisticated devices that, for example, can be used in applications, such as membranes, batteries or fuel cells. Since catalytic reactions occur on the surface, most catalyst materials are based on open porous structures, which facilitates the transport of fluids (gas or liquid) and chemical (or electrochemical) specific surface activity, thus determining the overall efficiency of the device. Noble metals are typically used for low temperature catalysis, whereas lower cost materials, such as nickel, are used for catalysis at elevated temperatures. 3D printing has the potential to produce a more sophisticated fit for purpose catalyst material. This article presents the development, fabrication and performance comparison of three thermoplastic composites where PLA (polylactic acid), PVB (polyvinyl butyral) or ABS (acrylonitrile butadiene styrene) were used as the matrix, and nickel particles were used as filler with various volume fractions, from 5 to 25 vol%. The polymer–metal composites were extruded in the form of filaments and then used for 3D FDM (Fused Deposition Modeling) printing. The 3D printed composites were heat treated to remove the polymer and sinter the nickel particles. 3D printed composites were also prepared using nickel foam as a substrate to increase the final porosity and mechanical strength of the material. The result of the study demonstrates the ability of the optimized filament materials to be used in the fabrication of high open porosity (over 60%) structures that could be used in high-temperature catalysis and/or electrocatalysis. Full article

(This article belongs to the Topic Material and Process Innovations for 3D Printing Applications)

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17 pages, 6080 KiB  

Open AccessArticle

Influence of Silicon Carbide on Direct Powder Bed Selective Laser Process (Sintering/Melting) of Alumina

by Asif Ur Rehman, Muhammad Ahsan Saleem, Tingting Liu, Kai Zhang, Fatih Pitir and Metin Uymaz Salamci

Materials 2022, 15(2), 637; https://doi.org/10.3390/ma15020637 - 15 Jan 2022

Cited by 11 | Viewed by 3756

Abstract

The powder bed selective laser process (sintering/melting) has revolutionised many industries, including aerospace and biomedicine. However, PBSLP of ceramic remains a formidable challenge. Here, we present a unique slurry-based approach for fabricating high-strength ceramic components instead of traditional PBSLP. A special PBSLP platform [...] Read more.

The powder bed selective laser process (sintering/melting) has revolutionised many industries, including aerospace and biomedicine. However, PBSLP of ceramic remains a formidable challenge. Here, we present a unique slurry-based approach for fabricating high-strength ceramic components instead of traditional PBSLP. A special PBSLP platform capable of 1000 °C pre-heating was designed for this purpose. In this paper, PBSLP of Al₂O₃ was accomplished at different SiC loads up to 20 wt%. Several specimens on different laser powers (120 W to 225 W) were printed. When the SiC content was 10 wt% or more, the chemical interaction made it difficult to process. Severe melt pool disturbances led to poor sintering and melting. The structural analysis revealed that the micro-structure was significantly affected by the weight fraction of SiC. Interestingly, when the content was less than 2 wt%, it showed significant improvement in the microstructure during PBSLP and no effects of LPS or chemical interaction. Particularly, a crack pinning effect could be clearly seen at 0.5 wt%. Full article

(This article belongs to the Topic Material and Process Innovations for 3D Printing Applications)

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18 pages, 6918 KiB  

Open AccessArticle

Theoretical and Experimental Investigation on the 3D Surface Roughness of Material Extrusion Additive Manufacturing Products

by Shijie Jiang, Ke Hu, Yang Zhan, Chunyu Zhao and Xiaopeng Li

Polymers 2022, 14(2), 293; https://doi.org/10.3390/polym14020293 - 11 Jan 2022

Cited by 16 | Viewed by 2603

Abstract

Material extrusion (ME), one of the most widely used additive manufacturing technique, has the advantages of freedom of design, wide range of raw materials, strong ability to manufacture complex products, etc. However, ME products have obvious surface defects due to the layer-by-layer manufacturing [...] Read more.

Material extrusion (ME), one of the most widely used additive manufacturing technique, has the advantages of freedom of design, wide range of raw materials, strong ability to manufacture complex products, etc. However, ME products have obvious surface defects due to the layer-by-layer manufacturing characteristics. To reveal the generation mechanism, the three-dimensional surface roughness (3DSR) of ME products was investigated theoretically and experimentally. Based on the forming process of bonding neck, the 3DSR theoretical model in two different directions (vertical and parallel to the fiber direction) was established respectively. The preparation of ME samples was then completed and a series of experimental tests were performed to determine their surface roughness with the laser microscope. Through the comparison between theoretical and experimental results, the proposed model was validated. In addition, sensitivity analysis is implemented onto the proposed model, investigating how layer thickness, extrusion temperature, and extrusion width influence the samples’ surface roughness. This study provides theoretical basis and technical insight into improving the surface quality of ME products. Full article

(This article belongs to the Topic Material and Process Innovations for 3D Printing Applications)

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15 pages, 4762 KiB  

Open AccessArticle

Force and Microstructure Variation of SLM Prepared AlMgSc Samples during Three-Point Bending

by Daming Nie, Ruilong Du, Pu Zhang, Fangyan Shen, Jason Gu and Yili Fu

Materials 2022, 15(2), 437; https://doi.org/10.3390/ma15020437 - 7 Jan 2022

Cited by 2 | Viewed by 1874

Abstract

Lightweight parts manufactured by metal selective laser melting (SLM) are widely applied in machinery industries because of their high specific strength, good energy absorption effect, and complex shape that are difficult to form by mechanical machining. These samples often serve in three-dimensional stress [...] Read more.

Lightweight parts manufactured by metal selective laser melting (SLM) are widely applied in machinery industries because of their high specific strength, good energy absorption effect, and complex shape that are difficult to form by mechanical machining. These samples often serve in three-dimensional stress states. However, previous publications mainly focused on the unidirectional tensile/compressive properties of the samples. In this paper, AlMgSc samples with different geometric parameters were prepared by the SLM process, and the variation of force and microstructure during three-point bending were systematically investigated. The results demonstrate that the deformation resistance of these samples has good continuity without mutation in bending, even for brittle materials; the bending force-displacement curves exhibit representative variation stages during the entire bending process; the equivalent bending strength deduced from free bending formula is not applicable when compactability is less than 67%. The variations of grain orientation and size of the three representative bending layers also show regularity. Full article

(This article belongs to the Topic Material and Process Innovations for 3D Printing Applications)

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18 pages, 2608 KiB  

Open AccessArticle

Setting the Optimal Laser Power for Sustainable Powder Bed Fusion Processing of Elastomeric Polyesters: A Combined Experimental and Theoretical Study

by Ruben Vande Ryse, Mariya Edeleva, Ortwijn Van Stichel, Dagmar R. D’hooge, Frederik Pille, Rudinei Fiorio, Patrick De Baets and Ludwig Cardon

Materials 2022, 15(1), 385; https://doi.org/10.3390/ma15010385 - 5 Jan 2022

Cited by 11 | Viewed by 2909

Abstract

Additive manufacturing (AM) of polymeric materials offers many benefits, from rapid prototyping to the production of end-use material parts. Powder bed fusion (PBF), more specifically selective laser sintering (SLS), is a very promising AM technology. However, up until now, most SLS research has [...] Read more.

Additive manufacturing (AM) of polymeric materials offers many benefits, from rapid prototyping to the production of end-use material parts. Powder bed fusion (PBF), more specifically selective laser sintering (SLS), is a very promising AM technology. However, up until now, most SLS research has been directed toward polyamide powders. In addition, only basic models have been put forward that are less directed to the identification of the most suited operating conditions in a sustainable production context. In the present combined experimental and theoretical study, the impacts of several SLS processing parameters (e.g., laser power, part bed temperature, and layer thickness) are investigated for a thermoplastic elastomer polyester by means of colorimetric, morphological, physical, and mechanical analysis of the printed parts. It is shown that an optimal SLS processing window exists in which the printed polyester material presents a higher density and better mechanical properties as well as a low yellowing index, specifically upon using a laser power of 17–20 W. It is further highlighted that the current models are not accurate enough at predicting the laser power at which thermal degradation occurs. Updated and more fundamental equations are therefore proposed, and guidelines are formulated to better assess the laser power for degradation and the maximal temperature achieved during sintering. This is performed by employing the reflection and absorbance of the laser light and taking into account the particle size distribution of the powder material. Full article

(This article belongs to the Topic Material and Process Innovations for 3D Printing Applications)

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19 pages, 8954 KiB  

Open AccessArticle

Piston-Based Material Extrusion of Ti-6Al-4V Feedstock for Complementary Use in Metal Injection Molding

by Lennart Waalkes, Jan Längerich, Philipp Imgrund and Claus Emmelmann

Materials 2022, 15(1), 351; https://doi.org/10.3390/ma15010351 - 4 Jan 2022

Cited by 14 | Viewed by 3872

Abstract

Piston-based material extrusion enables cost savings for metal injection molding users when it is utilized as a complementary shaping process for green parts in small batch sizes. This, however, requires the use of series feedstock and the production of sufficiently dense green parts [...] Read more.

Piston-based material extrusion enables cost savings for metal injection molding users when it is utilized as a complementary shaping process for green parts in small batch sizes. This, however, requires the use of series feedstock and the production of sufficiently dense green parts in order to ensure metal injection molding-like material properties. In this paper, a methodological approach is presented to identify material-specific process parameters for an industrially used Ti-6Al-4V metal injection molding feedstock based on the extrusion force. It was found that for an optimum extrusion temperature of 95 °C and printing speed of 8 mm/s an extrusion force of 1300 N ensures high-density green parts without under-extrusion. The resulting sintered part properties exhibit values comparable to metal injection molding in terms of part density (max. 99.1%) and tensile properties (max. yield strength: 933 MPa, max. ultimate tensile strength: 1000 MPa, max. elongation at break: 18.5%) depending on the selected build orientation. Thus, a complementary use could be demonstrated in principle for the Ti-6Al-4V feedstock. Full article

(This article belongs to the Topic Material and Process Innovations for 3D Printing Applications)

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13 pages, 7138 KiB  

Open AccessArticle

Model of the Temperature Influence on Additively Manufactured Carbon Fibre Reinforced Polymer Samples with Embedded Fibre Bragg Grating Sensors

by Torkan Shafighfard and Magdalena Mieloszyk

Materials 2022, 15(1), 222; https://doi.org/10.3390/ma15010222 - 28 Dec 2021

Cited by 13 | Viewed by 2300

Abstract

This study investigates the thermo-mechanical behaviour of additively manufactured Carbon Fiber Reinforced Polymer (CFRP) with embedded Fibre Bragg Grating (FBG) sensors with respect to their feasibility for utilising them under thermal loading. This was conducted through the Finite Element Method (FEM) inside an [...] Read more.

This study investigates the thermo-mechanical behaviour of additively manufactured Carbon Fiber Reinforced Polymer (CFRP) with embedded Fibre Bragg Grating (FBG) sensors with respect to their feasibility for utilising them under thermal loading. This was conducted through the Finite Element Method (FEM) inside an ABAQUS environment. Numerical simulation was complemented by several experimental investigations in order to verify the computational results achieved for the specimens exposed to thermal loading. FBG sensors, incorporated into the material by embedding technique, were employed to measure the strains of the samples subjected to elevated temperatures. It was shown that the strains given by numerical simulation were in good agreement with the experimental investigation except for a few errors due to the defects created within the layers during Additive Manufacturing (AM) process. It was concluded that the embedding FBG sensors were capable of identifying thermo-mechanical strain accurately for 3D-printed composite structures. Therefore, the findings of this article could be further developed for other types of material and loading conditions. Full article

(This article belongs to the Topic Material and Process Innovations for 3D Printing Applications)

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13 pages, 4294 KiB  

Open AccessArticle

Antimicrobial Activity of 3D-Printed Acrylonitrile Butadiene Styrene (ABS) Polymer-Coated with Silver Nanoparticles

by Isabel Tse, Atishay Jay, Ina Na, Sean Murphy, Nereida Niño-Martínez, Gabriel Alejandro Martínez-Castañon, Jamie Magrill and Horacio Bach

Materials 2021, 14(24), 7681; https://doi.org/10.3390/ma14247681 - 13 Dec 2021

Cited by 16 | Viewed by 3802

Abstract

Medical devices with antimicrobial properties are a potential long-term solution to the high rate of multi-drug-resistant healthcare-associated infections. Silver nanoparticles (AgNPs) are an established agent for effectively eliminating a wide range of microbial strains. AgNPs have been commonly incorporated into traditional plastic materials; [...] Read more.

Medical devices with antimicrobial properties are a potential long-term solution to the high rate of multi-drug-resistant healthcare-associated infections. Silver nanoparticles (AgNPs) are an established agent for effectively eliminating a wide range of microbial strains. AgNPs have been commonly incorporated into traditional plastic materials; however, recently, there has been increased interest in using AgNPs combined with 3D-printing technology for medical devices due to the accessibility and customizability of 3D-printed products. This study reports a novel method of utilizing acetone to partially dissolve 3D-printed polymer acrylonitrile butadiene styrene (ABS) plastic to attach a layer of AgNPs. The antimicrobial properties of this AgNP-coated surface were tested against several microbial strains prevalent in healthcare-associated infections. AgNP-coated ABS (AgNP-ABS) plastic demonstrated significant elimination of viable bacteria within 4 h for all tested bacterial species (Acinetobacter baumannii, non-pathogenic and pathogenic Escherichia coli, Pseudomonas aeruginosa, and methicillin-resistant Staphylococcus aureus) and within 19 h for the tested fungus Candida albicans. The longevity of adhesion of AgNPs to the ABS plastic was assessed by checking antibacterial activity against A. baumannii after repeat use cycles. AgNP-ABS plastic showed decreased antibacterial efficacy with repeated use but maintained the ability to eliminate microbes within 3 h for up to eight use cycles. The AgNP-coated ABS plastic showed efficacy as an antimicrobial surface, and future studies will consider its applicability in the production of medical devices. Full article

(This article belongs to the Topic Material and Process Innovations for 3D Printing Applications)

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18 pages, 9528 KiB  

Open AccessArticle

Vat Photopolymerization of Cemented Carbide Specimen

by Thomas Rieger, Tim Schubert, Julian Schurr, Andreas Kopp, Michael Schwenkel, Dirk Sellmer, Alexander Wolff, Juliane Meese-Marktscheffel, Timo Bernthaler and Gerhard Schneider

Materials 2021, 14(24), 7631; https://doi.org/10.3390/ma14247631 - 11 Dec 2021

Cited by 6 | Viewed by 4788

Abstract

Numerous studies show that vat photopolymerization enables near-net-shape printing of ceramics and plastics with complex geometries. In this study, vat photopolymerization was investigated for cemented carbide specimens. Custom-developed photosensitive WC-12 Co (wt%) slurries were used for printing green bodies. The samples were examined [...] Read more.

Numerous studies show that vat photopolymerization enables near-net-shape printing of ceramics and plastics with complex geometries. In this study, vat photopolymerization was investigated for cemented carbide specimens. Custom-developed photosensitive WC-12 Co (wt%) slurries were used for printing green bodies. The samples were examined for defects using quantitative microstructure analysis. A thermogravimetric analysis was performed to develop a debinding program for the green bodies. After sintering, the microstructure and surface roughness were evaluated. As mechanical parameters, Vickers hardness and Palmqvist fracture toughness were considered. A linear shrinkage of 26–27% was determined. The remaining porosity fraction was 9.0%. No free graphite formation, and almost no η-phase formation occurred. WC grain growth was observed. 76% of the WC grains measured were in the suitable size range for metal cutting tool applications. A hardness of 1157 HV10 and a Palmqvist fracture toughness of 12 $\mathrm{MPa}\sqrt{\mathrm{m}}$ was achieved. The achieved microstructure exhibits a high porosity fraction and local cracks. As a result, vat photopolymerization can become an alternative forming method for cemented carbide components if the amount of residual porosity and defects can be reduced. Full article

(This article belongs to the Topic Material and Process Innovations for 3D Printing Applications)

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12 pages, 2168 KiB  

Open AccessArticle

A 3D Bioprinted Human Meniscus Shape Enriched with Mesenchymal Cells

by Mihai Hurmuz, Mihai Ionac, Carmen Tatu, Daniela Puscasiu, Catalin Adrian Miu, Sergiu Galatanu and Fabian Tatu

Appl. Sci. 2021, 11(24), 11733; https://doi.org/10.3390/app112411733 - 10 Dec 2021

Viewed by 2725

Abstract

Background and objectives: Regenerative medicine, with its massive development over the years, has the potential to solve some of the most problematic medical issues, such as functional organ transplantation. The aim of this study was to create a human meniscal shape 3D-printed enriched [...] Read more.

Background and objectives: Regenerative medicine, with its massive development over the years, has the potential to solve some of the most problematic medical issues, such as functional organ transplantation. The aim of this study was to create a human meniscal shape 3D-printed enriched with human adipose-derived mesenchymal cells. Materials and Methods: Human infrapatellar fat pad was harvested, and mesenchymal cells were isolated. The mesenchymal stem cells were differentiated to the chondrocite lineage and a hydrogel (a nanofibrillar cellulose, sodium alginate, D-mannitol, and Hepes buffer solution combination) cell mixture was bioprinted to create three human-size meniscus structures. The obtained structures were evaluated regarding the cell viability, appropriate size in relation to a native meniscus, and some mechanical characteristics. Results: The human meniscal shape created respected the anatomic characteristic of a native structure. Cell viability of approximately 97% and extracellular matrix formation after the printing process were observed. The mean maximum force for the meniscus with mesenchymal cells was 6.5 N (+/−0.5 N) compared to the mean maximum force for the native meniscus of 10.32 N (+/−0.7 N), which is statistically relevant (p < 0.01). Conclusion: This paper presents the potential of bioprinting viable cell structures that could in the future present enough mechanical strength to replace a human organ, such as a meniscus. There are still limitations regarding the ink and the printing process, but we are confident that these problems will soon be solvable. Full article

(This article belongs to the Topic Material and Process Innovations for 3D Printing Applications)

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13 pages, 4053 KiB  

Open AccessArticle

Finite Element Analysis on Initial Crack Site of Porous Structure Fabricated by Electron Beam Additive Manufacturing

by Meng-Hsiu Tsai, Chia-Ming Yang, Yu-Xuan Hung, Chao-Yong Jheng, Yen-Ju Chen, Ho-Chung Fu and In-Gann Chen

Materials 2021, 14(23), 7467; https://doi.org/10.3390/ma14237467 - 6 Dec 2021

Cited by 4 | Viewed by 2591

Abstract

Ti6Al4V specimens with porous structures can be fabricated by additive manufacturing to obtain the desired Young’s modulus. Their mechanical strength and deformation behavior can be evaluated using finite element analysis (FEA), with various models and simulation methodologies described in the existing literature. Most [...] Read more.

Ti6Al4V specimens with porous structures can be fabricated by additive manufacturing to obtain the desired Young’s modulus. Their mechanical strength and deformation behavior can be evaluated using finite element analysis (FEA), with various models and simulation methodologies described in the existing literature. Most studies focused on the evaluation accuracy of the mechanical strength and deformation behavior using complex models. This study presents a simple elastic model for brittle specimens followed by an electron beam additive manufacturing (EBAM) process to predict the initial crack site and threshold of applied stress related to the failure of cubic unit lattice structures. Six cubic lattice specimens with different porosities were fabricated by EBAM, and compression tests were performed and compared to the FEA results. In this study, two different types of deformation behavior were observed in the specimens with low and high porosities. The adopted elastic model and the threshold of applied stress calculated via FEA showed good capabilities for predicting the initial crack sites of these specimens. The methodology presented in this study should provide a simple yet accurate method to predict the fracture initiation of porous structure parts. Full article

(This article belongs to the Topic Material and Process Innovations for 3D Printing Applications)

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15 pages, 8721 KiB  

Open AccessArticle

A Simple Method of Reducing Coolant Leakage for Direct Metal Printed Injection Mold with Conformal Cooling Channels Using General Process Parameters and Heat Treatment

by Chil-Chyuan Kuo and Shao-Xuan Qiu

Materials 2021, 14(23), 7258; https://doi.org/10.3390/ma14237258 - 27 Nov 2021

Cited by 28 | Viewed by 2548

Abstract

Direct metal printing is a promising technique for manufacturing injection molds with complex conformal cooling channels from maraging steel powder, which is widely applied in automotive or aerospace industries. However, two major disadvantages of direct metal printing are the narrow process window and [...] Read more.

Direct metal printing is a promising technique for manufacturing injection molds with complex conformal cooling channels from maraging steel powder, which is widely applied in automotive or aerospace industries. However, two major disadvantages of direct metal printing are the narrow process window and length of time consumed. The fabrication of high-density injection molds is frequently applied to prevent coolant leakage during the cooling stage. In this study, we propose a simple method of reducing coolant leakage for a direct-metal-printed injection mold with conformal cooling channels by combining injection mold fabrication with general process parameters, as well as solution and aging treatment (SAT). This study comprehensively investigates the microstructural evolution of the injection mold after SAT using field-emission scanning electron microscopy and energy-dispersive X-ray spectroscopy. We found that the surface hardness of the injection mold was enhanced from HV 189 to HV 546 as the Ni-Mo precipitates increased from 12.8 to 18.5%. The size of the pores was reduced significantly due to iron oxide precipitates because the relative density of the injection mold increased from 99.18 to 99.72%. The total production time of the wax injection mold without coolant leakage during the cooling stage was only 62% that of the production time of the wax injection mold fabricated with high-density process parameters. A significant savings of up to 46% of the production cost of the injection mold was obtained. Full article

(This article belongs to the Topic Material and Process Innovations for 3D Printing Applications)

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12 pages, 4017 KiB  

Open AccessArticle

3D Printed In Vitro Dentin Model to Investigate Occlusive Agents against Tooth Sensitivity

by Shiva Naseri, Megan E. Cooke, Derek H. Rosenzweig and Maryam Tabrizian

Materials 2021, 14(23), 7255; https://doi.org/10.3390/ma14237255 - 27 Nov 2021

Cited by 5 | Viewed by 2474

Abstract

Tooth sensitivity is a painful and very common problem. Often stimulated by consuming hot, cold, sweet, or acidic foods, it is associated with exposed dentin microtubules that are open to dental pulp. One common treatment for tooth hypersensitivity is the application of occlusive [...] Read more.

Tooth sensitivity is a painful and very common problem. Often stimulated by consuming hot, cold, sweet, or acidic foods, it is associated with exposed dentin microtubules that are open to dental pulp. One common treatment for tooth hypersensitivity is the application of occlusive particles to block dentin microtubules. The primary methodology currently used to test the penetration and occlusion of particles into dentin pores relies upon dentin discs cut from extracted bovine/human teeth. However, this method is limited due to low accessibility to the raw material. Thus, there is a need for an in vitro dentin model to characterize the effectiveness of occlusive agents. Three-dimensional printing technologies have emerged that make the printing of dentin-like structures possible. This study sought to develop and print a biomaterial ink that mimicked the natural composition and structure of dentin tubules. A formulation of type I collagen (Col), nanocrystalline hydroxyapatite (HAp), and alginate (Alg) was found to be suitable for the 3D printing of scaffolds. The performance of the 3D printed dentin model was compared to the natural dentin disk by image analysis via scanning electron microscopy (SEM), both pre- and post-treatment with occlusive microparticles, to evaluate the degree of dentinal tubule occlusion. The cytocompatibility of printed scaffolds was also confirmed in vitro. This is a promising biomaterial system for the 3D printing of dentin mimics. Full article

(This article belongs to the Topic Material and Process Innovations for 3D Printing Applications)

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19 pages, 6392 KiB  

Open AccessArticle

Requirements for Processing High-Strength AlZnMgCu Alloys with PBF-LB/M to Achieve Crack-Free and Dense Parts

by Steffen Heiland, Benjamin Milkereit, Kay-Peter Hoyer, Evgeny Zhuravlev, Olaf Kessler and Mirko Schaper

Materials 2021, 14(23), 7190; https://doi.org/10.3390/ma14237190 - 25 Nov 2021

Cited by 11 | Viewed by 2785

Abstract

Processing aluminum alloys employing powder bed fusion of metals (PBF-LB/M) is becoming more attractive for the industry, especially if lightweight applications are needed. Unfortunately, high-strength aluminum alloys such as AA7075 are prone to hot cracking during PBF-LB/M, as well as welding. Both a [...] Read more.

Processing aluminum alloys employing powder bed fusion of metals (PBF-LB/M) is becoming more attractive for the industry, especially if lightweight applications are needed. Unfortunately, high-strength aluminum alloys such as AA7075 are prone to hot cracking during PBF-LB/M, as well as welding. Both a large solidification range promoted by the alloying elements zinc and copper and a high thermal gradient accompanied with the manufacturing process conditions lead to or favor hot cracking. In the present study, a simple method for modifying the powder surface with titanium carbide nanoparticles (NPs) as a nucleating agent is aimed. The effect on the microstructure with different amounts of the nucleating agent is shown. For the aluminum alloy 7075 with 2.5 ma% titanium carbide nanoparticles, manufactured via PBF-LB/M, crack-free samples with a refined microstructure having no discernible melt pool boundaries and columnar grains are observed. After using a two-step ageing heat treatment, ultimate tensile strengths up to 465 MPa and an 8.9% elongation at break are achieved. Furthermore, it is demonstrated that not all nanoparticles used remain in the melt pool during PBF-LB/M. Full article

(This article belongs to the Topic Material and Process Innovations for 3D Printing Applications)

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18 pages, 19040 KiB  

Open AccessArticle

Influence of Metallic Powder Characteristics on Extruded Feedstock Performance for Indirect Additive Manufacturing

by Cyril Santos, Daniel Gatões, Fábio Cerejo and Maria Teresa Vieira

Materials 2021, 14(23), 7136; https://doi.org/10.3390/ma14237136 - 24 Nov 2021

Cited by 13 | Viewed by 2834

Abstract

Material extrusion (MEX) of metallic powder-based filaments has shown great potential as an additive manufacturing (AM) technology. MEX provides an easy solution as an alternative to direct additive manufacturing technologies (e.g., Selective Laser Melting, Electron Beam Melting, Direct Energy Deposition) for problematic metallic [...] Read more.

Material extrusion (MEX) of metallic powder-based filaments has shown great potential as an additive manufacturing (AM) technology. MEX provides an easy solution as an alternative to direct additive manufacturing technologies (e.g., Selective Laser Melting, Electron Beam Melting, Direct Energy Deposition) for problematic metallic powders such as copper, essential due to its reflectivity and thermal conductivity. MEX, an indirect AM technology, consists of five steps—optimisation of mixing of metal powder, binder, and additives (feedstock); filament production; shaping from strands; debinding; sintering. The great challenge in MEX is, undoubtedly, filament manufacturing for optimal green density, and consequently the best sintered properties. The filament, to be extrudable, must accomplish at optimal powder volume concentration (CPVC) with good rheological performance, flexibility, and stiffness. In this study, a feedstock composition (similar binder, additives, and CPVC; 61 vol. %) of copper powder with three different particle powder characteristics was selected in order to highlight their role in the final product. The quality of the filaments, strands, and 3D objects was analysed by micro-CT, highlighting the influence of the different powder characteristics on the homogeneity and defects of the greens; sintered quality was also analysed regarding microstructure and hardness. The filament based on particles powder with D₅₀ close to 11 µm, and straight distribution of particles size showed the best homogeneity and the lowest defects. Full article

(This article belongs to the Topic Material and Process Innovations for 3D Printing Applications)

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13 pages, 3975 KiB  

Open AccessArticle

A Novel Additive Manufacturing Method of Cellulose Gel

by Hossein Najaf Zadeh, Daniel Bowles, Tim Huber and Don Clucas

Materials 2021, 14(22), 6988; https://doi.org/10.3390/ma14226988 - 18 Nov 2021

Cited by 5 | Viewed by 2791

Abstract

Screen-additive manufacturing (SAM) is a potential method for producing small intricate parts without waste generation, offering minimal production cost. A wide range of materials, including gels, can be shaped using this method. A gel material is composed of a three-dimensional cross-linked polymer or [...] Read more.

Screen-additive manufacturing (SAM) is a potential method for producing small intricate parts without waste generation, offering minimal production cost. A wide range of materials, including gels, can be shaped using this method. A gel material is composed of a three-dimensional cross-linked polymer or colloidal network immersed in a fluid, known as hydrogel when its main constituent fluid is water. Hydrogels are capable of absorbing and retaining large amounts of water. Cellulose gel is among the materials that can form hydrogels and, as shown in this work, has the required properties to be directly SAM, including shear thinning and formation of post-shearing gel structure. In this study, we present the developed method of SAM for the fabrication of complex-shaped cellulose gel and examine whether successive printing layers can be completed without delamination. In addition, we evaluated cellulose SAM without the need for support material. Design of Experiments (DoE) was applied to optimize the SAM settings for printing the novel cellulose-based gel structure. The optimum print settings were then used to print a periodic structure with micro features and without the need for support material. Full article

(This article belongs to the Topic Material and Process Innovations for 3D Printing Applications)

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21 pages, 4763 KiB  

Open AccessArticle

Geometrical Scaling Effects in the Mechanical Properties of 3D-Printed Body-Centered Cubic (BCC) Lattice Structures

by Alia Ruzanna Aziz, Jin Zhou, David Thorne and Wesley James Cantwell

Polymers 2021, 13(22), 3967; https://doi.org/10.3390/polym13223967 - 17 Nov 2021

Cited by 13 | Viewed by 3275

Abstract

This paper investigates size effects on the mechanical response of additively manufactured lattice structures based on a commercially available polylactic acid (PLA) polymer. Initial attention is focused on investigating geometrical effects in the mechanical properties of simple beams and cubes. Following this, a [...] Read more.

This paper investigates size effects on the mechanical response of additively manufactured lattice structures based on a commercially available polylactic acid (PLA) polymer. Initial attention is focused on investigating geometrical effects in the mechanical properties of simple beams and cubes. Following this, a number of geometrically scaled lattice structures based on the body-centered cubic design were manufactured and tested in order to highlight size effects in their compression properties and failure modes. A finite element analysis was also conducted in order to compare the predicted modes of failure with those observed experimentally. Scaling effects were observed in the compression response of the PLA cubes, with the compression strength increasing by approximately 19% over the range of scale sizes investigated. Similar size-related effects were observed in the flexural samples, where a brittle mode of failure was observed at all scale sizes. Here, the flexural strength increased by approximately 18% when passing from the quarter size sample to its full-scale counterpart. Significant size effects were observed following the compression tests on the scaled lattice structures. Here, the compression strength increased by approximately 60% over the four sample sizes, in spite of the fact that similar failure modes were observed in all samples. Finally, reasonably good agreement was observed between the predicted failure modes and those observed experimentally. However, the FE models tended to over-estimate the mechanical properties of the lattice structures, probably as a result of the fact that the models were assumed to be defect free. Full article

(This article belongs to the Topic Material and Process Innovations for 3D Printing Applications)

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36 pages, 18190 KiB  

Open AccessArticle

Laser Powder Bed Fusion (LPBF) of In718 and the Impact of Pre-Heating at 500 and 1000 °C: Operando Study

by Asif Ur Rehman, Fatih Pitir and Metin Uymaz Salamci

Materials 2021, 14(21), 6683; https://doi.org/10.3390/ma14216683 - 5 Nov 2021

Cited by 16 | Viewed by 4989

Abstract

The morphology of a melt pool has a critical role in laser powder bed fusion (LPBF). Nevertheless, directly characterizing the melt pool during LPBF is incredibly hard. Here, we present the melt pool flow of the entire melt pool in 3D using mesoscopic [...] Read more.

The morphology of a melt pool has a critical role in laser powder bed fusion (LPBF). Nevertheless, directly characterizing the melt pool during LPBF is incredibly hard. Here, we present the melt pool flow of the entire melt pool in 3D using mesoscopic simulation models. The physical processes occurring within the melt pool are pinpointed. The flow patterns throughout the same are exposed and measured. Moreover, the impact of pre-heating at 500 and 1000 °C has been described. The study findings offer insights into LPBF. The findings presented here are critical for comprehending the LPBF and directing the establishment of improved metrics for process parameters optimization. Full article

(This article belongs to the Topic Material and Process Innovations for 3D Printing Applications)

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14 pages, 2997 KiB  

Open AccessArticle

Titania Nanotube Architectures Synthesized on 3D-Printed Ti-6Al-4V Implant and Assessing Vancomycin Release Protocols

by H-thaichnok Chunate, Jirapon Khamwannah, Abdul Azeez Abdu Aliyu, Saran Tantavisut, Chedtha Puncreobutr, Atchara Khamkongkaeo, Chiraporn Tongyam, Krittima Tumkhanon, Thanawat Phetrattanarangsi, Theerapat Chanamuangkon, Torlarp Sitthiwanit, Dechawut Decha-umphai, Pharanroj Pongjirawish and Boonrat Lohwongwatana

Materials 2021, 14(21), 6576; https://doi.org/10.3390/ma14216576 - 1 Nov 2021

Cited by 15 | Viewed by 3367

Abstract

The aim of this study is to synthesize Titania nanotubes (TNTs) on the 3D-printed Ti-6Al-4V surface and investigate the loading of antibacterial vancomycin drug dose of 200 ppm for local drug treatment application for 24 h. The antibacterial drug release from synthesized nanotubes [...] Read more.

The aim of this study is to synthesize Titania nanotubes (TNTs) on the 3D-printed Ti-6Al-4V surface and investigate the loading of antibacterial vancomycin drug dose of 200 ppm for local drug treatment application for 24 h. The antibacterial drug release from synthesized nanotubes evaluated via the chemical surface measurement and the linear fitting of Korsmeyer–Peppas model was also assessed. The TNTs were synthesized on the Ti-6Al-4V surface through the anodization process at different anodization time. The TNTs morphology was characterized using field emission scanning electron microscope (FESEM). The wettability and the chemical composition of the Ti-6Al-4V surface and the TNTs were assessed using the contact angle meter, Fourier transform infrared spectrophotometer (FTIR) and the X-ray photoelectron spectroscopy (XPS). The vancomycin of 200 ppm release behavior under controlled atmosphere was measured by the high-performance liquid chromatography (HPLC) and hence, the position for retention time at 2.5 min was ascertained. The FESEM analysis confirmed the formation of nanostructured TNTs with vertically oriented, closely packed, smooth and unperforated walls. The maximum cumulative vancomycin release of 34.7% (69.5 ppm) was recorded at 24 h. The wetting angle of both Ti-6Al-4V implant and the TNTs were found below 90 degrees. This confirmed their excellent wettability. Full article

(This article belongs to the Topic Material and Process Innovations for 3D Printing Applications)

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22 pages, 21292 KiB  

Open AccessArticle

Comparison of Different Additive Manufacturing Methods for 316L Stainless Steel

by Javier Bedmar, Ainhoa Riquelme, Pilar Rodrigo, Belen Torres and Joaquin Rams

Materials 2021, 14(21), 6504; https://doi.org/10.3390/ma14216504 - 29 Oct 2021

Cited by 50 | Viewed by 6340

Abstract

In additive manufacturing (AM), the technology and processing parameters are key elements that determine the characteristics of samples for a given material. To distinguish the effects of these variables, we used the same AISI 316L stainless steel powder with different AM techniques. The [...] Read more.

In additive manufacturing (AM), the technology and processing parameters are key elements that determine the characteristics of samples for a given material. To distinguish the effects of these variables, we used the same AISI 316L stainless steel powder with different AM techniques. The techniques used are the most relevant ones in the AM of metals, i.e., direct laser deposition (DLD) with a high-power diode laser and selective laser melting (SLM) using a fiber laser and a novel CO₂ laser, a novel technique that has not yet been reported with this material. The microstructure of all samples showed austenitic and ferritic phases, which were coarser with the DLD technique than for the two SLM ones. The hardness of the fiber laser SLM samples was the greatest, but its bending strength was lower. In SLM with CO₂ laser pieces, the porosity and lack of melting reduced the fracture strain, but the strength was greater than in the fiber laser SLM samples under certain build-up strategies. Specimens manufactured using DLD showed a higher fracture strain than the rest, while maintaining high strength values. In all the cases, crack surfaces were observed and the fracture mechanisms were determined. The processing conditions were compared using a normalized parameters methodology, which has also been used to explain the observed microstructures. Full article

(This article belongs to the Topic Material and Process Innovations for 3D Printing Applications)

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16 pages, 1729 KiB  

Open AccessEditor’s ChoiceArticle

FFF 3D Printing in Electronic Applications: Dielectric and Thermal Properties of Selected Polymers

by David Kalaš, Karel Šíma, Petr Kadlec, Radek Polanský, Radek Soukup, Jan Řeboun and Aleš Hamáček

Polymers 2021, 13(21), 3702; https://doi.org/10.3390/polym13213702 - 27 Oct 2021

Cited by 37 | Viewed by 5075

Abstract

The present study is a focused and comprehensive analysis of the dielectric and thermal properties of twenty-four 3D printed polymers suitable for fused filament fabrication (FFF) in electronic applications. The selected polymers include various thermoplastic elastomers, such as thermoplastics based on polycarbonate (PC), [...] Read more.

The present study is a focused and comprehensive analysis of the dielectric and thermal properties of twenty-four 3D printed polymers suitable for fused filament fabrication (FFF) in electronic applications. The selected polymers include various thermoplastic elastomers, such as thermoplastics based on polycarbonate (PC), polyethylene terephthalate glycol (PETG), and acrylonitrile butadiene styrene (ABS-T). Their overall thermal behavior, including oxidation stability, glass transition, and melting temperature, was explored using simultaneous thermal analysis (STA) and differential scanning calorimetry (DSC). Considering their intended usage in electronic applications, the dielectric strength (E_p) and surface/volume resistivity (ρ_s/ρ_v) were comprehensively tested according to IEC 60243-1 and IEC 62631-3, respectively. The values of the dielectric constant (ε’) and loss factor (ε”) were also determined by broadband dielectric spectroscopy (BDS). While, on the one hand, exceptional dielectric properties were observed for some thermoplastic elastomers, the materials based on PCs, on the other hand, stood out from the others due to their high oxidation stability and above average dielectric properties. The low-cost materials based on PETG or ABS-T did not achieve thermal properties similar to those of the other tested polymers; nevertheless, considering the very reasonable price of these polymers, the obtained dielectric properties are promising for undemanding electronic applications. Full article

(This article belongs to the Topic Material and Process Innovations for 3D Printing Applications)

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15 pages, 6429 KiB  

Open AccessArticle

Experimental Study on Time-Dependent Changes in Rheological Properties and Flow Rate of 3D Concrete Printing Materials

by Hojae Lee, Eun-A Seo, Won-Woo Kim and Jae-Heum Moon

Materials 2021, 14(21), 6278; https://doi.org/10.3390/ma14216278 - 21 Oct 2021

Cited by 10 | Viewed by 2575

Abstract

Three-dimensional concrete printing (3DCP) materials require a relatively low water-to-binder ratio (W/B) of 0.3 or less to ensure their buildability and flow properties are sufficiently maintained after mixing. In this study, the rheological properties of 3DCP materials with W/B 0.28 were evaluated up [...] Read more.

Three-dimensional concrete printing (3DCP) materials require a relatively low water-to-binder ratio (W/B) of 0.3 or less to ensure their buildability and flow properties are sufficiently maintained after mixing. In this study, the rheological properties of 3DCP materials with W/B 0.28 were evaluated up to 60 min after mixing, and the yield stress and plastic viscosity were analyzed over time. A gradual decrease in flow rate with time was observed during the transport of 200 kg of material per batch through a 20 m hose. To examine the time-dependent changes in flow rate and layer volume, a 2200 mm × 1000 mm test specimen was printed. The dependence of the layer width over time during the printing process was measured and analyzed. The experimental analyses showed that the flow rate and layer volume of the 3DCP material gradually decreased with time after mixing, which was correlated with the rheological properties. Full article

(This article belongs to the Topic Material and Process Innovations for 3D Printing Applications)

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19 pages, 4105 KiB  

Open AccessArticle

A Combined Experimental and Modeling Study for Pellet-Fed Extrusion-Based Additive Manufacturing to Evaluate the Impact of the Melting Efficiency

by Andrea La Gala, Rudinei Fiorio, Daniel V. A. Ceretti, Mustafa Erkoç, Ludwig Cardon and Dagmar R. D’hooge

Materials 2021, 14(19), 5566; https://doi.org/10.3390/ma14195566 - 25 Sep 2021

Cited by 14 | Viewed by 3078

Abstract

To improve the product quality of polymeric parts realized through extrusion-based additive manufacturing (EAM) utilizing pellets, a good control of the melting is required. In the present work, we demonstrate the strength of a previously developed melt removal using a drag framework to [...] Read more.

To improve the product quality of polymeric parts realized through extrusion-based additive manufacturing (EAM) utilizing pellets, a good control of the melting is required. In the present work, we demonstrate the strength of a previously developed melt removal using a drag framework to support such improvement. This model, downscaled from conventional extrusion, is successfully validated for pellet-based EAM—hence, micro-extrusion—employing three material types with different measured rheological behavior, i.e., acrylonitrile-butadiene-styrene (ABS), polylactic acid (PLA) and styrene-ethylene-butylene-styrene polymer (SEBS). The model’s validation is made possible by conducting for the first time dedicated EAM screw-freezing experiments combined with appropriate image/data analysis and inputting rheological data. It is showcased that the (overall) processing temperature is crucial to enable similar melting efficiencies. The melting mechanism can vary with the material type. For ABS, an initially large contribution of viscous heat dissipation is observed, while for PLA and SEBS thermal conduction is always more relevant. It is highlighted based on scanning electron microscopy (SEM) analysis that upon properly tuning the finalization of the melting point within the envisaged melting zone, better final material properties are achieved. The model can be further used to find an optimal balance between processing time (e.g., by variation of the screw frequency) and material product performance (e.g., strength of the printed polymeric part). Full article

(This article belongs to the Topic Material and Process Innovations for 3D Printing Applications)

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