Polymer Additive Manufacturing Research Articles

Multiscale analysis of interlocking effects for polymer additive manufacturing on aluminum foam

AbstractHybrid structures are increasingly relevant for lightweight design and functional components. Various manufacturing techniques for creating hybrid components exist, often focusing on combining metal and polymer components. The present study examines a novel approach for manufacturing hybrid functional structures by directly printing thermoplastic onto aluminum profiles using closed‐cell aluminum foam, with the mechanical interlocking resulting in a structural bond. The filling of pores in the aluminum foam with the polymer affects the bond strength of this hybrid compound. Within a simulation‐based process design the additive manufacturing process parameters are investigated using a computational fluid dynamics (CFD) model with Fluid‐Structure Interaction for the pore‐filling process and a finite element (FE) model to evaluate the resulting bond strength. The material throughput, the nozzle distance, and the polymer temperature are the key process parameters taken into account. A parameterized, virtual foam model is used within this framework, where a linear movement of the extruder nozzle and the resulting polymer strand is investigated. This method includes the mesh conversion from the CFD results to the FE mesh for structural analysis by exporting the iso‐surface for the polymer geometry embedded in the pores of the aluminum foam structure. This approach made it possible to investigate the phenomena that occur in the process in more detail, particularly to quantify the influence of air inclusions. Thus, a decisive contribution to the hybridization of aluminum foams has been made, which opens up further potential for research and application in the long term.

Tribological Performance of Additive Manufactured PLA-Based Parts.

Polymer additive manufacturing has advanced from prototyping to producing essential parts with improved precision and versatility. Despite challenges like surface finish and wear resistance, new materials and metallic reinforcements in polymers have expanded its applications, enabling stronger, more durable parts for demanding industries like aerospace and structural engineering. This research investigates the tribological behaviour of FFF surfaces by integrating copper and aluminium reinforcement particles into a PLA (polylactic acid) matrix. Pin-on-disc tests were conducted to evaluate friction coefficients and wear rates. Statistical analysis was performed to study the correlation of the main process variables. The results confirmed that reinforced materials offer interesting characteristics despite their complex use, with the roughness of the fabricated parts increasing by more than 300%. This leads to an increase in the coefficient of friction, which is related to the variation in the material's mechanical properties, as the hardness increases by more than 75% for materials reinforced with Al. Despite this, their performance is more stable, and the volume of material lost due to wear is reduced by half. These results highlight the potential of reinforced polymers to improve the performance and durability of components manufactured through additive processes.

In situ X-ray diffraction and thermal simulation of material extrusion additive manufacturing of polymer

Material extrusion additive manufacturing (AM) has gradually become a dominant technology for the fabrication of complex-designed thermoplastic polymers that require a higher level of control over the morphological and mechanical properties. The polymer internal crystal structure formed during the AM process can present significant impacts on the mechanical properties of the individual filaments, as well as the whole structure. Currently, limited details are known about the crystal structure evolution during the material extrusion AM processes of polymers. A novel in situ synchrotron X-ray diffraction (XRD) experimental configuration was developed enabling us to capture the material evolution data throughout the extrusion AM process. The in situ time-resolved data was analysed to reveal nucleation and crystallization sequences during the continuous deposition, with the aid of both complimentary numerical simulations and post-process (ex situ) characterisations. The thermal simulations supported the prediction of the filament temperature profile over time and location during the AM process, while ex situ characterisations validated the correlation between polymer crystallinity (resulting from printing parameters) and corresponding mechanical properties. The results obtained from varied process parameters suggest that the processing temperature has a dominant influence on the crystal microstructure evolution compared to the deposition velocity. A lower processing temperature just above the melting temperature permitted favourable crystallization conditions. The overall analysis demonstrated prospects for enhancing polymer AM, to engineering mechanically hierarchical structures through correlative investigations.

Activation of additively manufactured electrodes using methanol and ethanol solutions

AbstractThe use of polymer additive manufacturing to produce electrodes is an increasingly popular area of electrochemical research. However, one downside of additively manufactured electrodes is the frequent need to remove polymer from the electrode surface to reveal a triple‐phase boundary in order for improved electrode performance to be realized. A common way to achieve this, is surface activation via chronoamperometry within an aqueous sodium hydroxide solution. However, it has not been investigated whether the same activation can be carried out effectively in solutions of sodium hydroxide in simple alcohols. Therefore, in this work, we study the effect of performing common chronoamperometric additive manufacturing electrode activation methodologies in methanolic and ethanolic solutions of 0.05 M sodium hydroxide and compare these to activation carried out in standard aqueous solutions at concentrations of both 0.05 M and 0.5 M. We show that the alcoholic solutions are more effective in removing polymer from the additive manufacturing electrode surface, but that this does not lead to any improvement in electrode currents, and furthermore appears to hinder electron transfer kinetics at the additive manufacturing electrode surface, with the latter effect shown to be related to differences in the surface functionality of the exposed carbon black filler particles. As well as being interesting chemical experiments in their own right, these results may well be of interest to electrochemists who intend for their additive manufactured electrodes to be applied in these alcohols or indeed other non‐aqueous solvents.

Electroplating Additively Manufactured Honeycomb Structures to Increase Energy Absorption Under Quasi-Static Crush

Honeycomb (HC) has been used in energy absorption applications due to its high stiffness and low density. Metallic HC are used for energy absorption applications, however, these metallic structures can be challenging to manufacture if complex geometric features designed to improve energy absorption are used, which motivates the use of additive manufacturing (AM). Metal AM methods include powder bed fusion (PBF) and direct energy deposition (DED). In addition to capital equipment cost, these processes possess challenges that include a required inert environment, powder handling, final part porosity, residual stresses, and nonuniform surface finish. These concerns can be alleviated through the use of polymer AM, however, polymeric parts exhibit brittle failure and have a lower stiffness than metallic HC structures. In this study, a low-cost 3D polymer printing method, stereolithography (SLA), is combined with a conventional electroplating process to fabricate a metal-plastic composite HC structure with energy absorption capability much greater than of a plastic HC structures of the same nominal volume. SLA parts have a smooth surface, so that the surface finish is at least as uniform after electroplating as the SLA part. The energy absorption characteristics of the electroplated HC is studied to determine how these energy absorbing materials can be manufactured at reduced cost. Our study confirms that the metal-plastic composite HC increases both the crush strain range and the mean crush stress of these samples, resulting in metal-plastic composite HC structures with substantially increased energy absorption. This study also examines how buckling initiators (BIs), or diamond shaped holes located at 50, 75, and 100% of the height of the hexagonal cell vertices, can influence energy absorption performance. This study shows that it is feasible to fabricate electroplated HCs, using an SLA preform, to achieve a substantial increase in energy absorption over using SLA alone.

Additive Manufacturing of Head Surrogates for Evaluation of Protection in Sports.

Head impacts are a major concern in contact sports and sports with high-speed mobility due to the prevalence of head trauma events and their dire consequences. Surrogates of human heads are required in laboratory testing to safely explore the efficacy of impact-mitigating mechanisms. This work proposes using polymer additive manufacturing technologies to obtain a substitute for the human skull to be filled with a silicone-based brain surrogate. This assembly was instrumentalized with an Inertial Measurement Unit. Its performance was compared to a standard Hybrid III head form in validation tests using commercial headgear. The tests involved impact velocities in a range centered around 5 m/s. The results show a reasonable homology between the head substitutes, with a disparity in the impact response within 20% between the proposed surrogate and the standard head form. The head surrogate herein developed can be easily adapted to other morphologies and will significantly decrease the cost of the laboratory testing of head protection equipment, all while ensuring the safety of the testing process.

Integration of soft tooling by additive manufacturing in polymer profile extrusion process chain

Integrating additive manufacturing (AM) into polymer extrusion offers process chain flexibility and design freedom. It reduces the need for time-consuming iterations and trial-and-error in the die design process. Consequently, polymer AM of extrusion (i.e., soft tooling) allows for a shorter product development cycle and cost-effectiveness for small-scale production and highly customized products. In this study, carbon fibre (CF)-polyether-ether-ketone (PEEK) dies were manufactured using the fused filament fabrication (FFF) AM process, employing a streamlined die design achieved through freeform transition planes. Calibration slides were produced using masked stereolithography (MSLA), FFF, and conventional manufacturing techniques (i.e., machining) to preserve the final product’s cross-section during the cooling process. The dimensional and surface characteristics of these calibration slides were evaluated to assess the dimensional accuracy and surface topography of various materials and manufacturing processes. The dimensional evaluation reveals that MSLA-printed parts exhibit deviation from the nominal dimension closer to the conventionally manufactured part. The integrated soft tooling in the polymer extrusion line was tested with polypropylene (PP) and acrylonitrile butadiene styrene (ABS) as extruded materials. The surface topography of the CF-PEEK die displays distinctive ripple features resulting from the FFF process, identified by relatively flat peaks and deep valleys. The overall surface texture parameter values of CF-PEEK were higher due to the presence of deep valleys. Considering that the areas around the peaks interacted more with polymer molecules during the extrusion, the surface texture parameters of the extrudates were closer to the value observed in 90 µm region areas around the peaks. Notably, extrudates of AM calibration slides have lower surface texture parameters than extrudates of conventionally manufactured calibration slides, even though surface defects in the form of dimple sink marks were observed in extruded material of PP from extrudates using AM calibration slides.

Structural-Functional Mathematical Modeling of Additive Manufacturing Polymers

Structural-Functional Mathematical Modeling of Additive Manufacturing Polymers

A cyber-physical production system for autonomous part quality control in polymer additive manufacturing material extrusion process

A cyber-physical production system for autonomous part quality control in polymer additive manufacturing material extrusion process

Comparative study on tensile and morphological properties of resin and rice husk reinforced polymer composite gyroid lattice structures

This study aims to compare the tensile behaviour of 3d printed resin and rice husk-reinforced resin-based gyroid lattice structures. The work was completed in two phases, firstly a resin gyroid lattice structure with two design configurations of unit cell sizes (3, 4, 5, and 6) and solidity percentages (30, 40, and 50) was developed according to the ASTM638 (4) standard. The 12 designs were manufactured using VAT polymerization additive manufacturing and investigated for tensile strength. In the second phase, the poorest tensile testing results were chosen to develop the rice husk-reinforced resin samples with a mixing proportion of 10–20%–30%. The experiment results revealed that the fracture is localized inside the gauge length according to the standard. Remarkably, the rice husk composite-based gyroid lattice samples exhibit 4.29, 6.55, and 9.35 times higher tensile strength than the selected resin sample (U3–30). Additionally, a homogeneous distribution of rice husk particles has been observed in the micrograph analysis (SEM).

Influence of Build Height on Quality of Additively Manufactured Thermoplastic Polyurethane Parts

Due to geometrical degrees of freedom, low cost, and ease of realizing complex structures, polymer additive manufacturing (AM) has emerged exceptionally well. Even with rapid evolutionary growth, AM lacks sound quality mainly including inherent porosity and surface roughness compared to their counterparts (conventional manufacturing processes) due to the involvement of several printing parameters in AM processes. This quality‐based comparative assessment presents the influence of build/layer height on the porosity (using micro‐X‐ray computed tomography) and surface roughness (in build direction) of additively manufactured thermoplastic polyurethane (due to its versatile properties in applications like wearable electronics and biomedical) using three different polymer AM processes namely selective laser sintering, fused deposition modeling, and stereolithography. Along with porosity, an in‐depth pore characterization is also performed to understand the geometrical feature and severity of pores present in each sample of the AM process. Results are compared finally to make concluding remarks.

Exploring Conductive Filler‐Embedded Polymer Nanocomposite for Electrical Percolation via Electromagnetic Shielding‐Based Additive Manufacturing

AbstractThis review delves into the progress made in additive manufacturing through the incorporation of conductive fillers in nanocomposites. Emphasizing the critical role of percolation and conductivity, the study highlights advancements in material selection, particularly focusing on carbon nanotubes with low percolation thresholds. The practical applications of these nanocomposites in additive manufacturing polymer composites are explored, emphasizing the understanding of percolation thresholds. Furthermore, the present review paper investigates the potential of these materials as lightweight alternatives for electromagnetic interference shielding (EMI), particularly in key sectors such as automotive and aerospace industries. The integration of advanced materials, modeling techniques, and standardization is discussed as pivotal for successful implementation. Overall, the review underscores the significant strides in enhancing electrical properties and electromagnetic interference shielding capabilities through the strategic use of conductive filler nanocomposites in additive manufacturing.

High pressure salt water and low temperature effects on the material performance characteristics of additive manufacturing polymers

The effects of salt water exposure at deep ocean depth pressures when coupled with low temperatures on the material characteristics of three unique additively manufactured polymers has been investigated through a detailed experimental approach. The polymers in the study were manufactured utilizing both Vat Photopolymerization and Material Extrusion printing techniques. The Material Extrusion process was utilized to produce material specimens of Stratasys ULTEM 9085 and Markforged Onyx while the Vat Photopolymerization process was used to produce specimens of Accura ClearVue. The ULTEM 9085 and Markforged Onyx are filament based polymers and the ClearVue is a liquid based resin. The specimens were first submerged in a high pressure, salt water bath of 3.5% NaCl solution at 34.5 MPa (5000 lb/in2) for a total exposure time of 60 days to determine the water absorption characteristics. Subsequent to the salt water exposure at high pressure, the specimens were evaluated to determine changes in tension, compression, flexure, and in-plane fracture properties. To determine the effects of water saturation and low temperature coupling, the mechanical testing was performed at temperatures of 20 °C, 0 °C and −20 °C in both dry and saturated conditions. Additionally, non-destructive testing in the form of TeraHertz and FIRT imaging was conducted to analyze the physical material changes through the thickness of the material due to the saline water absorption. To quantify the change in material storage and loss moduli properties, Dynamic Mechanical Analysis (DMA) characterization was performed on each of the AM polymers in dry and saturated states. The DMA testing also quantified changes in the Glass Transition Temperature because of salt water exposure. In summary, The current study investigates the effects of coupled long term/high pressure salt water exposure with low temperatures on the mechanical and material characteristics of three unique AM polymers by: (1) immersing the materials in a salt water solution at 34.5 MPa for 60 days, (2) Conducting post exposure mechanical testing on the materials at 0 °C and −20 °C with comparisons to 20 °C testing on dry specimens, and quantifies changes in material properties through DMA experiments. The results from all testing in the study show that high pressure salt water exposure when coupled with low temperatures has unique effects on each of the materials considered in the study and careful consideration to each parameter must be given based on the material type when components will be employed in marine operations.

Mechanical investigation of compositing by resin filling in lattice structures manufactured with fused deposition modelling

Fused Deposition Modeling (FDM) is a widely used polymer additive manufacturing technique for polymer part manufacturing and prototyping. However, manufacturing speed, mechanical properties, and high costs, limit its suitability for industrial applications. In this study, researchers blended polyester and polyurethane resins with lattice structures to achieve a remarkable 70% reduction in production time and a 75% decrease in manufacturing costs. They explored five lattice structure geometries relevant to common literature applications. Lattice structures were manufactured using PA, PLA, PA-CF, and TPU filaments. The composite samples underwent comprehensive analysis, including SEM microscopic inspections, density measurements, and compression tests. Parameters such as density, yield strength, compressive strength, specific stress, modulus of elasticity, and toughness were evaluated. The findings revealed that polyester-based composites exhibited a remarkable 131% enhancement in mechanical properties, with toughness values increasing up to 12-fold. The results revealed significant mechanical advantages that the developed composites can offer in applications.

Biomechanical Behavior of a 3D-Printed Denture Base Material.

To evaluate relevant material properties (flexural strength [σf], elastic modulus [E], water sorption [Wsp] and solubility [Wsl], and biocompatibility) of an additive manufacturing (AM) polymer vs a heat-curing acrylic resin (AR; control) for the manufacture of complete dentures, testing the hypothesis that fabrications from both materials would present acceptable material properties for clinical use. The σf, E, Wsp, and Wsl were evaluated according to the ISO 20795-1:2013 standard, and the biocompatibility was evaluated using MTT and SRB assays. Disk-shaped specimens were fabricated and used for Wsp (n = 5), Wsl (n = 5), and biocompatibility (n = 3) testing. For assessment of σf and E, bar-shaped specimens (n = 30) were fabricated and stored in 37°C distilled water for 48 hours or 6 months before flexural testing in a universal testing machine with a constant displacement rate (5 ± 1 mm/minute). Data from σf, E, Wsp, Wsl, and biocompatibility tests were statistically analyzed using Student t test (α = .05). Weibull analysis was also used for σf and E data. Significant differences between the two materials were found for the evaluated material properties. Water storage for 6 months did not affect the flexural strength of the AM polymer, but this material showed inadequate σf and Wsl values. Despite adequate biocompatibility and strength stability after 6 months of water storage, the AM polymer recommended for complete dentures needs further development to improve the material properties evaluated in this study.

Accurate additive manufacturing of lightweight and elastic carbons using plastic precursors

Despite groundbreaking advances in the additive manufacturing of polymers, metals, and ceramics, scaled and accurate production of structured carbons remains largely underdeveloped. This work reports a simple method to produce complex carbon materials with very low dimensional shrinkage from printed to carbonized state (less than 4%), using commercially available polypropylene precursors and a fused filament fabrication-based process. The control of macrostructural retention is enabled by the inclusion of fiber fillers regardless of the crosslinking degree of the polypropylene matrix, providing a significant advantage to directly control the density, porosity, and mechanical properties of 3D printed carbons. Using the same printed plastic precursors, different mechanical responses of derived carbons can be obtained, notably from stiff to highly compressible. This report harnesses the power of additive manufacturing for producing carbons with accurately controlled structure and properties, while enabling great opportunities for various applications.

Electrically Conductive Polymers for Additive Manufacturing.

The use of electrically conductive polymers (CPs) in the development of electronic devices has attracted significant interest due to their unique intrinsic properties, which result from the synergistic combination of physicochemical properties in conventional polymers with the electronic properties of metals or semiconductors. Most conventional methods adopted for the fabrication of devices with nonplanar morphologies are still challenged by the poor ionic/electronic mobility of end products. Additive manufacturing (AM) brings about exciting prospects to the realm of CPs by enabling greater design freedom, more elaborate structures, quicker prototyping, relatively low cost, and more environmentally friendly electronic device creation. A growing variety of AM technologies are becoming available for three-dimensional (3D) printing of conductive devices, i.e., vat photopolymerization (VP), material extrusion (ME), powder bed fusion (PBF), material jetting (MJ), and lamination object manufacturing (LOM). In this review, we provide an overview of the recent research progress in the area of CPs developed for AM, which advances the design and development of future electronic devices. We consider different AM techniques, vis-à-vis, their development progress and respective challenges in printing CPs. We also discuss the material requirements and notable advances in 3D printing of CPs, as well as their potential electronic applications including wearable electronics, sensors, energy storage and conversion devices, etc. This review concludes with an outlook on AM of CPs.

Development of EN AW-6082 Metal Foams and Stochastic Foam Modeling for the Individualization of Extruded Profiles

AbstractLightweight design and hybrid components enable innovative and new component concepts, especially when combining structurally reliable metal components with individualized polymer components. In this research, a process for additive manufacturing polymers on the surface of extruded aluminum profiles is examined. The extrusion process is adapted to produce foamable aluminum profiles, which can be utilized to enable a form fit between the two materials and ensures sufficient bond strength. For this purpose, a novel aluminum block material based on the standard wrought alloy EN AW-6082 was developed. It consists of a solid EN AW-6082 core and powder metallurgically produced outer layer, which allows local foaming of the aluminum profile surface. The main objective of this study was to optimize the bond strength of the hybrid aluminum-polymer components. The methods employed include fabricating aluminum test specimens, performing mechanical tests, x-ray microscopy to analyze the pore structure and evaluating the 3D pore distribution and the wall thickness. Virtual foam models were created to numerically investigate suitable pore sizes and foam geometries for form-fit with the polymer. The porosity achieved as a function of the processing of the components are discussed and a comparison is made between the real and virtual pore structures.

Effect of recycled powder and gear profile into the functionality of additive manufacturing polymer gears

PurposePolymer laser powder bed fusion (PBF-LB/P) is an additive manufacturing technology that is sustainable due to the possibility of recycling the powder multiple times and allowing the fabrication of gears without the aid of support structures and subsequent assembly. However, there are constraints in the process that negatively affect its adoption compared to other additive technologies such as material extrusion to produce gears. This study aims to demonstrate that it is possible to overcome the problems due to the physics of the process to produce accurate mechanism.Design/methodology/approachTechnological aspects such as orientation, wheel-shaft thicknesses and degree of powder recycling were examined. Furthermore, the evolving tooth profile was considered as a design parameter to provide a manufacturability map of gear-based mechanisms.FindingsResults show that there are some differences in the functioning of the gear depending on the type of powder used, 100% virgin or 50% virgin and 50% recycled for five cycles. The application of a groove on a gear produced with 100% virgin powder allows the mechanism to be easily unlocked regardless of the orientation and wheel-shaft thicknesses. The application of a specific evolutionary profile independent of the diameter of the reference circle on vertically oriented gears guarantees rotation continuity while preserving the functionality of the assembled mechanism.Originality/valueIn the literature, there are various studies on material aging and reuse in the PBF-LB/P process, mainly focused on the powder deterioration mechanism, powder fluidity, microstructure and mechanical properties of the parts and process parameters. This study, instead, was focused on the functioning of gears, which represent one of the applications in which this technology can have great success, by analyzing the two main effects that can compromise it: recycled powder and vertical orientation during construction.

Application of machine learning in polymer additive manufacturing: A review

AbstractAdditive manufacturing (AM) is a revolutionary technology that enables production of intricate structures while minimizing material waste. However, its full potential has yet to be realized due to technical challenges such as the dependence of part quality on numerous process parameters, the vast number of design options, and the occurrence of defects. These complications may be magnified by the use of polymers and polymer composites due to their complex molecular structures, batch‐to‐batch variations, and changes in final part properties caused by small alterations in process settings and environmental conditions. Machine learning (ML), a branch of artificial intelligence, offers approaches to tackle these challenges and significantly reduce the experimental and computational time and expense. This review provides a comprehensive analysis of existing research on integrating ML techniques into polymer AM. It highlights the challenges involved in adopting ML in polymer AM, proposes potential solutions, and identifies areas for future research.