Progress in Additive Manufacturing

Das, Arit; McIlroy, Claire; Bortner, Michael J.

doi: 10.1007/s40964-020-00137-3pmid: N/A

Material-extrusion (MatEx) additive manufacturing involves layer-by-layer assembly of extruded material onto a printer bed and has found applications in rapid prototyping. Both material and machining limitations lead to poor mechanical properties of printed parts. Such problems may be addressed via an improved understanding of the complex transport processes and multiphysics associated with the MatEx technique. Thereby, this review paper describes the current (last 5 years) state of the art modeling approaches based on momentum, heat and mass transfer that are employed in an effort to achieve this understanding. We describe how specific details regarding polymer chain orientation, viscoelastic behavior, and crystallization are often neglected and demonstrate that there is a key need to couple the transport phenomena. Such a combined modeling approach can expand MatEx applicability to broader application space, thus we present prospective avenues to provide more comprehensive modeling and therefore new insights into enhancing MatEx performance.

Longhitano, Guilherme Arthur; Nunes, Guilherme Bitencourt; Candido, Geovany; da Silva, Jorge Vicente Lopes

doi: 10.1007/s40964-020-00159-xpmid: 38624444

The coronavirus disease 2019 (COVID-19) pandemic, caused by severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), has spread through more than 180 countries, leading to diverse health systems overload around the world. Because of the high number of patients and the supply chain disruption, it generated a shortage of medical devices and personal protective equipment. In this context, initiatives from the additive manufacturing community emerged to fight the lack of devices. Diverse designs were produced and are currently being used in hospitals by patients and health workers. However, as some devices must follow strict standards, these products may not fulfill these standards. Therefore, to ensure the user’s health, there is a need for understanding each device, their usage, and standards. This study reviews the use of additive manufacturing during COVID-19 pandemic. It gathers the source of several 3D printed devices such as face shields, face masks, valves, nasopharyngeal swabs, and others, discussing their use and regulatory issues. In this regard, the major drawbacks of the technology, addressed for the next pandemic scenario, are highlighted. Finally, some insights of the future of additive manufacturing during emergency are given and discussed.

Balla, Vamsi Krishna; Tadimeti, Jogi Ganesh Dattatreya; Sudan, Kavish; Satyavolu, Jagannadh; Kate, Kunal H.

doi: 10.1007/s40964-020-00138-2pmid: N/A

The United States is world’s largest producer of soybeans and significant amount of residual soybean hulls is generated during soybean processing. Soymeal and animal feed are the two current low-value outlets for the disposal of the hulls. To enhance the value of the soy hulls, we have made an attempt to use soybean hull-derived fibers as reinforcement in polymer matrix composite filaments for fused filament fabrication (FFF)-based additive manufacturing. In our approach, the soybean hulls were pre-treated with dilute acid hydrolysis followed by defibrillation of the hydrolyzed hulls. Both chemically treated soybean hull fibers (CTSHF) and untreated soybean hull fibers (UTSHF) with 5 and 10 wt.% concentrations were mixed within a thermoplastic copolyester (TPC) elastomer matrix to prepare composite filaments for FFF 3D printing. Studies were performed to understand the influence of CTSHF and UTSHF on the rheological, microstructural, and mechanical properties of these composite filaments. The results indicated improved fiber defibrillation with high-shear mixing and dilute acid hydrolysis. Interestingly, the addition of 5 and 10 wt.% CTSHF to TPC matrix decreased the viscosity when compared to virgin TPC. Furthermore, the CTSHF reduced the amount of porosity, enhanced fiber distribution, and fiber–matrix interfacial adhesion in TPC-CTSHF composites, resulting in enhanced mechanical properties compared to TPC-UTSHF composites. We expect that our study will lead to further investigations on soybean hull fiber-reinforced polymer composites for variety of applications.

Lopez, Alix; Marquette, Christophe A.; Courtial, Edwin-Joffrey

doi: 10.1007/s40964-020-00143-5pmid: N/A

Soft material 3D printing through liquid deposition modelling (LDM) is a challenging manufacturing process where yield stress control is mandatory. Indeed, the higher the yield stress value, the more complex the 3D printed structure can be. In a bid to go one step further, this report proposes a new approach enabling the prediction of soft material 3D printability as a function of the material’s properties and shape. The prediction consists in numerical simulation to anticipate, in silico, the collapse of a voxelised 3D design, called FingerMap. To do so, a calibration of the program using three silicone formulations (with increasing yield stress value) was first performed to define a printability domain according to mass/surface ratio, overhang angle and the z-position of each voxel. Then, two anatomical 3D models (ear and aortic valve) were used to demonstrate the capacity of the tool to predict printability. Good correlations between theoretical and experimental results were obtained. The proposed in silico simulation tool was then proven to be useful for LDM, even if some limitations were identified, particularly in the case of materials exhibiting complex rheological behaviours such as time-dependent rheological properties.

Kamaal, M.; Anas, M.; Rastogi, H.; Bhardwaj, N.; Rahaman, A.

doi: 10.1007/s40964-020-00145-3pmid: N/A

This paper presents the effect of process parameters of the fused deposition modelling (FDM) method on mechanical properties of 3D-printed carbon fibre (CF)-reinforced polylactic acid (PLA) composite. Building direction, infill percentage, and layer height are the process variables considered for studies due to their high influencing factor in mechanical properties of product. Tensile strength and impact strength are the response parameters considered in the study. Multi-optimisation is done using TOPSIS (Technique for Order Preferences by Similarity to Ideal Solution) analysis to find the best set of parameters that would provide the maximum strength using minimum material. The material used is CF-reinforced PLA composite filament (1.75-mm diameter) for 3D printing.

Gebrehiwot, Silas Z.; Espinosa Leal, L.; Eickhoff, J. N.; Rechenberg, L.

doi: 10.1007/s40964-020-00146-2pmid: N/A

We used finite element analyses (FEA) on Abaqus to study flexural properties of additive manufactured beams using polylactic acid (PLA) polymer. Experimental stress–strain data from flexural testing are used to define elastic–plastic properties of the material in the computation software. The flexural experiments are used to validate the FEA approach suggested. The method provides good results of deflection and stress with errors well below 10% in most of the cases. Therefore, by using the proposed approach, costs related to repeated experimental works can be avoided. In addition, the flexural rigidities of the additive manufactured beams are studied. Five different beam stiffener designs (diamond, honeycomb, square, triangular and wiggle) are studied based on beam bending theory. The force–deflection data from the flexural tests are used to determine the area moments of inertia of the beams. The honeycomb stiffener showed the highest force–deflection behaviour that led to the highest calculated area moment of inertia. However, with the lowest force–deflection behaviour, the square stiffener had the lowest calculated area moment of inertia.

Slapnik, Janez; Pulko, Irena

doi: 10.1007/s40964-020-00147-1pmid: N/A

This study illustrates the application of the principles of the design of experiments for the development of photocurable resins for additive manufacturing with easily adjustable mechanical and thermal properties. Photocurable resins were prepared using a combination of various oligomers and monomers, cured in a UV-curing system, and characterized in terms of mechanical and thermal properties. Photocurable resins for stereolithography were prepared using varying concentrations of photoinitiator and pigment, 3D printed and characterized in terms of processability as well as mechanical and thermal properties. Multi objective optimization was performed to obtain the compositions with the highest desirability. The proposed approach enables convenient tailoring properties of photocurable resins by varying just four basic components.

El Jai, Mostapha; Saidou, Nourddin; Zineddine, M’hamed; Bachiri, Housseine

doi: 10.1007/s40964-020-00148-0pmid: N/A

In this study, the authors propose a new design of a novel class of lattice structures. The new design is based on two main geometrical properties, the “volume” and the “surface to volume ratio”. It takes advantage of the strongest column designed against buckling proposed by Keller (Arch Ration Mech Anal 5:275–285, 1960) and Seiranyan (J Appl Math Mech 51(2):272–275, 1987). The Schoen minimal gyroid is used as a reference to establish the necessary lightweight property of the proposed design. This is to say, the surface to volume ratio and the volume of the new class of structures and their gyroid equivalent are equal. Models are built using CAD software and printed with UP mini 2.0 using acrylonitrile butadiene styrene (ABS) copolymer. Moreover, compression tests are conducted, using “MTS Criterion—Model 45”. The results show that after the phases of elasticity, relaxation and plasticity, the structure (three samples) is stable in the sense that it did not buckle nor collapse. Furthermore, reaching 7.35 mm of platen displacement (14.7% of strain) and 7.5 kN of resistance (3 MPa of equivalent stress), an additional progressive hardening is observed due to material densification and friction phenomena. A normalized comparison between the proposed structure and several lattice structures is conducted, showing a higher competitive behavior of the new design. The results of this study could possibly be a major contribution in the fields of biomechanics, aeronautic, and mechanical parts design.

Rajpurohit, Shilpesh R.; Dave, Harshit K.

doi: 10.1007/s40964-020-00150-6pmid: N/A

Fused filament fabrication (FFF) has been used to manufacturing customizable products, which offers tremendous advantages due to its ability to create end-use products having any complex geometry in shorter lead-time. However, the application of the FFF process in functional parts is restricted due to the poor mechanical performance because of the nature of the process to form the object in a layer-by-layer manner. The mechanical properties of the FFF-printed object are largely influenced by the selection of the build parameters. Hence, in this study, the impact strength of the FFF fabricated PLA has been evaluated as a function of three build variables viz. raster angle, layer height, and raster width. The impact test specimen was fabricated at varying build conditions and tested as per the ASTM D256 standard. Results showed that the raster angle was found to be the most significant build parameter that affects the impact strength of a printed specimen. The higher impact strength was achieved at 0° raster angle with 300 µm layer height and 700 µm raster width. However, the results obtained may be effective only within the limit of parameters and ranges tested in this work. Furthermore, SEM analysis of fracture surface reveals that failure mode is influenced mainly by the raster angle. Apart from that, voids have also been displayed on the fractured surface that may act as stress concentration and reduce the strength.

Terry, Shane; Fidan, Ismail; Tantawi, Khalid

doi: 10.1007/s40964-020-00151-5pmid: N/A

Additive manufacturing (AM) technologies provide a method of fabrication that minimizes the production of waste and maximizes part customization. The most common form of this technology is material extrusion (ME) in which material is deposited layer-by-layer to produce a highly customized part. However, this additive production method has experienced difficulty in widespread adoption in metal fabrication due to the inability to produce metallic parts with strong mechanical properties. This study presents some innovations on a new metal-fabrication technique for ME printing that allows for low-cost metal printing. A metal powder polymer composite filament, with a high metal composition, can be printed and sintered to yield a part that is completely metal. Overall, this study provides the initial investigation of the microstructural behavior and the resulting hardness levels. This study found that the metal powder in finished parts is fused by approximately 90% derived from the percent area porosity on a microstructural level. The final hardness of the processed parts is reduced by approximately 60%. Characterizing these properties is the initial step in incorporating ME technology in the field of metal 3D printing.