Extrusion-based Process Research Articles

Interfacial behavior between thermoplastics and thermosets fabricated by material extrusion-based multi-process additive manufacturing

Multi-material additive manufacturing (MMAM) allows one to fabricate objects using dissimilar materials with different material properties. However, most of the existing MMAM processes are limited to the fabrication of either dissimilar thermoplastics or thermosets. To address this issue, a multi-process additive manufacturing (MPAM) technique combining two different material extrusion-based processes is developed to fabricate both thermoplastics and thermosets in a single print. To understand the interfacial behavior between a thermoplastic, polylactic acid (PLA), and a thermoset, polydimethylsiloxane (PDMS), the effect of process parameters on the surface morphology of PLA and PDMS is evaluated using an in-line 3D surface profiler. The intra-layer and interlayer adhesion between PLA and PDMS are analyzed under tensile and bending loads, respectively. The morphology of PLA and PDMS at the failure surface after mechanical tests is examined to understand the interfacial failure mechanism. Experimental results have shown that a flow rate of 80 % and a pressure of 90 kPa result in the best in-process surface quality for PLA and PDMS, respectively. The tensile strength of the PLA-PDMS specimen is 311.8 kPa, and the flexural modulus, strength, and energy absorption are 530.5 MPa, 25.3 MPa, and 2 MPa, respectively. A purely interfacial failure is observed between PLA and PDMS under both tensile and bending loads. This study provides a guideline for investigating the interfacial behavior between thermoplastics and thermosets fabricated using MPAM.

A flexible and efficient calibration method for discrete element simulations of additive manufacturing in construction

Extrusion-based 3D concrete printing (E3DCP), as one of the most advanced Additive Manufacturing processes, is a hotspot in the construction industry. Using the Discrete Element Method (DEM), the E3DCP can be investigated with reduced prototyping- and trial costs. However, DEM parameter calibration is challenging in the accurate simulation of construction materials because they are hardly typical granular matters. In addition, the introduction of a novel extrusion-based process Near-Nozzle-Mixing calls for a more flexible, efficient, and reliable calibration procedure due to the useable wide variety of material models.In this study, DEM simulation parameters of mortar and its components (e.g. Poraver® and paste) were thoroughly calibrated based on the central composite design method. Notably, the specific shape indices of related substrates were identified in the study to achieve the precise calibration of Poraver® and paste. Moreover, the European standard-based Haegermann flow table test was applied in the calibration by quantifying mortar consistency. This work provides a holistic and efficient calibration approach for three typical and physically different construction materials, which can be universally explored in the DEM simulation of most materials in E3DCP.

A Workflow for the Compensation of Substrate Defects When Overprinting in Extrusion-Based Processes

Fused granular fabrication (FGF) is used in industrial applications to manufacture complex parts in a short time frame and with reduced costs. Recently, the overprinting of continuous fibre-reinforced laminates has been discussed to produce high-performance, functional structures. A hybrid process combining FGF with Automated Fibre Placement (AFP) was developed to implement this approach, where an additively manufactured structure is bonded in situ onto a thermoplastic laminate. However, this combination places great demands on process control, especially in the first printing layer. When 3D printing onto a laminate, the height of the first printed layer is decisive to the shear strength of the bonding. Manufacturing-induced surface defects of a laminate, like thermal warpage, gaps, and tape overlaps, can result in deviations from the ideal geometry and thus impair the bonding strength when left uncompensated. This study, therefore, proposes a novel process flow that uses a 3D scan of a laminate to adjust the geometry of the additively manufactured structure to achieve a constant layer height in the 3D print and, thus, constant mechanical properties. For the above-listed surface defects, only thermal warpage was found to have a significant effect on the bonding strength.

Ceramic additive manufacturing and microstructural analysis of tricalcium phosphate implants using X-ray microcomputed tomography

Additive manufacturing (AM) of ceramic bone implants from tricalcium phosphate (TCP) offers several benefits for bone regeneration and defect treatment. TCP scaffolds, e.g. featuring lattice or gyroid geometries, can effectively induce bone ingrowth and integration, showing a high potential in the treatment of large bone defects, e.g. as filler material for large bone defects. A major advantage of TCP is its osteoconductivity making it an effective choice for a broad range of orthopedic and dental applications. In addition, AM allows for the possibility to create precise, patient-specific implants with controllable mechanical properties. Those properties can be controlled by the implants' microstructure, e.g. in relation to bulk density and internal porosity. In this contribution, eleven resorbable bone implants were produced from β-tricalcium phosphate (β-TCP) in order to quantify the internal porosity in three dimensions using microcomputed tomography (μ CT). All components were manufactured using an extrusion-based process and scanned using an industrial μCT system at a voxel size of 10 μm. Two samples were physically prepared to allow a high-resolution μCT analysis at a voxel size of 1 μm. Results show that post-processed image data enables the non-destructive inspection of highly complex ceramic AM implants. Using μCT we were able to quantify internal porosity in β-TCP bone implant and quantify the geometry and distribution of wall thicknesses in the gyroid geometry. However, a detailed microstructural analysis is only possible using high-resolution μCT volume data, e.g. in relation to internal porosity. The findings emphasize that ceramic AM is able to produce complex components. However, NDT using μCT is crucial in the development of new materials and geometries. μCT provides high-resolution insights into the internal and external structure of ceramic AM components. It plays a critical role in detecting internal features, including small-scale porosity and delamination which are crucial for the integrity and functionality of medical implants. Moreover, μCT provides volumetric data that supports the design and manufacturing process at various stages, enabling an iterative approach of continuous improvement in mechanical performance and osseointegration.

Development approach of a workflow for 3D printing of living mycelium materials and their growth manipulation

As a viscous mycelium-substrate-composite, mycelia can be processed into more complex geometries in generative extrusion-based processes, even without molding tools. Biological transformation can also affect the properties of a printed object such that the mycelium still lives and grows after the 3D-build-process and changes the object over time. Depending on the substrate composition, type of fungus and growth conditions, different properties of the object can be manipulated. Different test geometries with corresponding preliminary characterization tests are shown. The present results demonstrate that test geometries could be successfully 3D printed with living mycelium material and manipulated during cultivation.

A screw extrusion-based system for additive manufacturing of wood: Sodium silicate thermoset composites

The aims of this work were to investigate the printability of high-fraction wood and sodium-silicate composites (WSSC) for additive manufacturing and to develop a screw extrusion-based process to demonstrate this approach for building construction applications. A custom additive manufacturing system was fabricated, and mixtures of 40%–60% wood fiber and 60%–40% sodium silicate were printed. The printability of these formulations was determined by observing their viscosity, extrudability, print-bed and layer adhesion, and curing characteristics. Fiber to resin ratios of 45:55 to 50:50 were the most suitable for printing. The printability was also affected by printing temperature and nozzle travel speed. The mechanical properties of printed and cured WSSC, were determined by three-point bending, tensile, and compression testing. Tensile strength, bending strength, and elastic modulus were found to be comparable to those of 3D printed concrete and other wood-plastic composites reported in the literature. The WSSC was successfully printed into a panel indicating promise for use in additive manufacturing.

Advancing bovine in vitro fertilization through 3D printing: the effect of the 3D printed materials.

Nowadays there is an increasing demand for assisted reproductive technologies due to the growth of infertility problems. Naturally, fertilization occurs in the oviduct, where the oviductal epithelial cells (OECs) secrete many molecules that affect the embryo's metabolism and protect it from oxidative stress. When the OECs are grown in 3D culture systems, they maintain a great part of their functional characteristics, making them an excellent model for in vitro fertilization (IVF) studies. In this work, we aimed to evaluate the suitability of different 3D-printing processes in conjunction with the corresponding set of commercially available biomaterials: extrusion-based processing using polylactic acid (PLA) and polycaprolactone (PCL) and stereolithography or digital-light processing using polyethylene-glycol-diacrylate (PEGDA) with different stiffness (PEGDA500, PEGDA200, PEGDA PhotoInk). All the 3D-printed scaffolds were used to support IVF process in a bovine embryo assay. Following fertilization, embryo development and quality were assessed in terms of cleavage, blastocyst rate at days 7 and 8, total cell number (TCN), inner cell mass/trophectoderm ratio (ICN/TE), and apoptotic cell ratio (ACR). We found a detrimental effect on cleavage and blastocyst rates when the IVF was performed on any medium conditioned by most of the materials available for digital-light processing (PEGDA200, PEGDA500). The observed negative effect could be possibly due to some leaked compound used to print and stabilize the scaffolds, which was not so evident however with PEGDA PhotoInk. On the other hand, all the extrusion-based processable materials did not cause any detrimental effect on cleavage or blastocyst rates. The principal component analysis reveals that embryos produced in presence of 3D-printed scaffolds produced via extrusion exhibit the highest similarity with the control embryos considering cleavage, blastocyst rates, TCN, ICN/TE and ACR per embryo. Conversely, all the photo-cross linkable materials or medium conditioned by PLA, lead to the highest dissimilarities. Since the use of PCL scaffolds, as well as its conditioned medium, bring to embryos that are more similar to the control group. Our results suggest that extrusion-based 3D printing of PCL could be the best option to be used for new IVF devices, possibly including the support of OECs, to enhance bovine embryo development.

Simulation-Based Identification of Operating Point Range for a Novel Laser-Sintering Machine for Additive Manufacturing of Continuous Carbon-Fibre-Reinforced Polymer Parts.

Additive manufacturing using continuous carbon-fibre-reinforced polymer (CCFRP) presents an opportunity to create high-strength parts suitable for aerospace, engineering, and other industries. Continuous fibres reinforce the load-bearing path, enhancing the mechanical properties of these parts. However, the existing additive manufacturing processes for CCFRP parts have numerous disadvantages. Resin- and extrusion-based processes require time-consuming and costly post-processing to remove the support structures, severely restricting the design flexibility. Additionally, the production of small batches demands considerable effort. In contrast, laser sintering has emerged as a promising alternative in industry. It enables the creation of robust parts without needing support structures, offering efficiency and cost-effectiveness in producing single units or small batches. Utilising an innovative laser-sintering machine equipped with automated continuous fibre integration, this study aims to merge the benefits of laser-sintering technology with the advantages of continuous fibres. The paper provides an outline, using a finite element model in COMSOL Multiphysics, for simulating and identifying an optimised operating point range for the automated integration of continuous fibres. The results demonstrate a remarkable reduction in processing time of 233% for the fibre integration and a reduction of 56% for the width and 44% for the depth of the heat-affected zone compared to the initial setup.

Mechanical Properties and Fatigue Performance of 17-4 PH Stainless Steel Manufactured by Atomic Diffusion Additive Manufacturing Technology

Additive Manufacturing (AM) is gaining importance as an alternative and complementary technology to conventional manufacturing processes. Among AM technologies, the Atomic Diffusion Additive Manufacturing (ADAM) technology is a novel extrusion-based process involving metallic filaments. In this work, the widely used 17-4 PH stainless steel filament was selected to study the effect of different deposition strategies of ADAM technology on mechanical properties. The printed parts had mechanical properties comparable to those obtained by other more developed AM technologies. In the case of tensile and fatigue tests, obtained values were in general greatly affected by deposition strategy, achieving better results in horizontal built orientation specimens. Interestingly, the effect was also considered of machining post-process (turning), which in the case of the tensile test had no remarkable effect, while in fatigue tests it led to an improvement in fatigue life of two to four times in the tested range of stresses.

Tuning pharmaceutically active zein-based formulations for additive manufacturing

Zein, a biopolymer from corn, was plasticized by glycerol and an Active Pharmaceutical Ingredient-Ionic Liquid (API-IL) for its melt processing at 130 °C. In order to enhance the rheological properties of the formulation for 3D printing, the ratio of glycerol to API-IL was adjusted while maintaining a consistent addition of 20% plasticizer. A 50/50 ratio allowed obtaining an initial melt viscosity suitable for extrusion-based processes, at approximately 1 kPa.s at a shear rate of 10 s−1, with a shear thinning behavior. This viscosity remained stable during a processing window of about 6 min, before zein proteins start to aggregate, leading to an apparent gelation phenomenon for long residence times. The processability of this formulation containing API-IL for the printing of tablets for potential therapeutic applications was confirmed by tests on a 3D printer. Nonetheless, in comparison to a reference formulation containing only glycerol, the printing accuracy experienced a decrease. This was ascribed to slower viscous sintering kinetics in presence of API-IL, evidenced by monitoring fusion-bonding during dynamic X-ray tomography trials carried out at Synchrotron SOLEIL.

Tensile and Compression Strength Prediction and Validation in 3D-Printed Short-Fiber-Reinforced Polymers.

In the current study, a methodology is validated for predicting the internal spatially varying strength properties in a single 3D-printed bead composed of 13%, by weight, carbon-fiber-filled acrylonitrile butadiene styrene. The presented method allows for the characterization of the spatially varying microstructural behavior yielding a local anisotropic stiffness and strength that can be integrated in a finite element framework for a bulk estimate of the effective stiffness and strength. The modeling framework is presented with a focus on composite structures made from large area additive manufacturing (LAAM). LAAM is an extrusion-based process yielding components on the order of meters, with a typical raster size of 10 mm. The presented modeling methods are applicable to other short-fiber-reinforced polymer processing methods as well. The results provided indicate the modeling framework yields results for the effective strength and stiffness that align with experimental characterization to within ∼1% and ∼10% for the longitudinal compressive and tensile strength, respectively, and to within ∼3% and ∼50% for the longitudinal compressive and tensile stiffness, respectively.

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

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

The study of screw extrusion-based additive manufacturing of eco-friendly aliphatic polyketone

Aliphatic polyketone is a new-age eco-friendly, high-performance engineering thermoplastic. However, its potential for replacing other polymers depends on its ability to be processed. Considering that the first aliphatic polyketone suitable for processing was developed relatively recently (2015), the material gained new research potential. In this paper screw extrusion-based process was developed for additive manufacturing of aliphatic polyketone. A detailed characterisation of the process and printed samples was done. It was shown that the extruder-base process can produce stable additive-manufactured parts depending on printing speed (process parameters). The interpass temperature has a significant influence on printing properties and it depends on printing speed (travel speed of building platform and extruder rotational speed). With the increase in the printing speed, the interpass temperature increases as well. If it is low causes insufficient heat for diffusion to occur causing delamination and if it is too high causes geometrical deviation of workpieces which leads to defects causing a reduction in inter-road strength. The tensile strength of specimens with raster angle 0° was 62.7 ± 1.4 MPa, which is slightly higher than the tensile strength of base material guaranteed by the supplier (60 MPa) while the elongation up to the first crack was 32.8 ± 4.6%. Iinter-road strength in specimens with a raster angle of 90° was 37.2 ± 0.8 MPa which is 62% of the base material while interpass temperature was 189 ± 3.3 °C.

Experimental Analysis and Optimisation of a Novel Laser-Sintering Process for Additive Manufacturing of Continuous Carbon Fibre-Reinforced Polymer Parts

Additive manufacturing of continuous carbon fibre-reinforced polymer (CCFRP) parts enables the production of high-strength parts for aerospace, engineering and other industries. Continuous fibres allow for parts to be reinforced along the load path, multiplying their mechanical properties. However, current additive manufacturing processes for producing CCFRP parts do not optimally meet the requirements of the matrix. With resin- and extrusion-based processes, the time-consuming and costly post-processing required to remove support structures severely limits design freedom, and producing small batches requires increased effort. In contrast, laser sintering has proven to be a promising alternative in an industrial environment, allowing the production of robust parts without support structures in a time-efficient and economical manner for single and small-batch production. Based on a novel laser-sintering machine with the automated integration of continuous fibres, a combination of the advantages of the laser-sintering process and the advantages of continuous fibres is to be achieved. This paper describes an experimental analysis and optimisation of this laser-sintering machine using design of experiments. The processing time for fibre integration could be reduced by a factor of three compared to the initial state.

Influence of aging treatments on 17–4 PH stainless steel parts realized using material extrusion additive manufacturing technologies

The most relevant criticalities of parts produced by material extrusion additive manufacturing technologies are lower mechanical properties than standard material performances, the presence of pores caused by the manufacturing method, and issues related to the interface between layers and rods. In this context, heat treatments can be considered an effective solution for tailoring the material behavior to different application fields, especially when using precipitation hardening stainless steels. In this work, aging treatments were conducted on parts realized using three different extrusion-based processes: Atomic Diffusion Additive Manufacturing, bound metal deposition, and fused filament fabrication. Two conditions of direct aging (H900 and H1150) were considered with the aim of comparing the response of properties in the opposite conditions of peak-aged and overaged. The hardness tests revealed that H900 aging significantly influenced hardness (max increase of 52%), and porosity (− 34.3% with respect to the as-sintered condition). On the other hand, the H1150 aging decreased the hardness (− 18% max) and porosity (− 32.2% max). Substantial differences among the microstructures due to grain size and δ-ferrite were illustrated. A statistical test was included to better highlight the influence of the heat treatment on the investigated properties.

Adhesion dynamics under time-varying deposition: A study on robotic assisted extrusion

Recent advances in robotic assisted-additive manufacturing (RA-AM) have enabled rapid material extrusion-based processing with comprehensive data collection. The following study investigates the adhesion dynamics of the initial printed layer across parameters such as surface energies, stand-off heights, and extrusion speeds of up to 100 mm/s, using an applied in-situ thermal analysis technique. Observations indicate that the characteristic length parameter, Lc < 0.05 mm, is adequate in anchoring the thermal melt, which adheres to the substrate when the nozzle proximity to the surface increases. Up to 100% molten area is contacting the surface prior to translation, and a final eccentricity over 0.85 has been observed. Through an analysis of variance, operational parameters of lower nozzle heights, printing speeds, and higher surface energy were statistically significant. The resultant in-situ characterization-driven data, was used to train a convolutional neural network (CNN). The model tested at an accuracy of 90.9%, and was able to distinguish between failed prints and initially adhered structures.

Additive manufacturing of complexly shaped SiC with high density via extrusion-based technique – Effects of slurry thixotropic behavior and 3D printing parameters

Additive manufacturing of dense SiC parts was achieved via an extrusion-based process followed by electrical-field assisted pressure-less sintering. The aim of this research was to study the effect of the rheological behavior of SiC slurry on the printing process and quality, as well as the influence of 3D printing parameters on the dimensions of the extruded filament, which are directly related to the printing precision and quality. Different solid contents and dispersant- Darvan 821A concentrations were studied to optimize the viscosity, thixotropy and sedimentation rate of the slurry. The optimal slurry was composed of 77.5 wt% SiC, Y2O3 and Al2O3 powders, 0.25 wt% dispersant and 0.01 wt% defoamer. The printing parameters studied included extrusion pressure, nozzle size, layer height and printing speed; the one that had the most prominent effect on filament width and height was indicated as layer height. The nozzle inner diameter of 1.04 mm, speed of 350 mm/min, layer height of 0.7 mm and extrusion air pressure of 0.31 MPa were the optimal printing parameters. Furthermore, the relationship between the printing parameters and the filament dimensions was successfully predicted by using machine learning and grey system theory. Finally, the relative density of the printed SiC parts sintered at 1900 oC reached 94.7±1.5%.

Analyses of mechanical properties and morphological behavior of additively manufactured ABS polymer, ABS/PBT blend, and ABS/PBT /CNT nanocomposite parts

Fused filament fabrication (FFF) and Fused deposition modeling (FDM) are among the most common methods of additive manufacturing technology for a variety of industries. However, the extrusion-based process of these technologies has qualified the usable materials to thermoplastics with inherently limited mechanical properties. Augmenting the properties of these materials by blending them with other polymers or their reinforcement with various additives are among the solutions to overcome this issue. This study examines the result of the introduction of Polybutylene Terephthalate (PBT) to acrylonitrile butadiene styrene (ABS), as one of the most common thermoplastics used in FDM/FFF processes, and explores the effects of the incorporation of Multi-Walled Carbon Nanotubes (MWCNT) to ABS/PBT blend with different filler fractions (0.1, 0.3, and 0.5 wt.%) on the mechanical properties of the printed specimens. In order to assess the mechanical behavior of the printed parts, standard melt flow index (MFI), tensile, three-point flexural, and notched impact tests have been performed on the produced parts. The morphological analyses through Scanning Electron Microscopy (SEM) micrographs have been conducted to inspect the distribution of impregnated MWCNTs and the fracture behavior of the specimens. The most satisfactory improvement has been observed in printed parts of the ABS/PBT/CNT nanocomposites containing 0.3 wt.% of MWCNTs.

Additive Manufactured Poly(ε-caprolactone)-graphene Scaffolds: Lamellar Crystal Orientation, Mechanical Properties and Biological Performance.

Understanding the mechano–biological coupling mechanisms of biomaterials for tissue engineering is of major importance to assure proper scaffold performance in situ. Therefore, it is of paramount importance to establish correlations between biomaterials, their processing conditions, and their mechanical behaviour, as well as their biological performance. With this work, it was possible to infer a correlation between the addition of graphene nanoparticles (GPN) in a concentration of 0.25, 0.5, and 0.75% (w/w) (GPN0.25, GPN0.5, and GPN0.75, respectively) in three-dimensional poly(ε-caprolactone) (PCL)-based scaffolds, the extrusion-based processing parameters, and the lamellar crystal orientation through small-angle X-ray scattering experiments of extruded samples of PCL and PCL/GPN. Results revealed a significant impact on the scaffold’s mechanical properties to a maximum of 0.5% of GPN content, with a significant improvement in the compressive modulus of 59 MPa to 93 MPa. In vitro cell culture experiments showed the scaffold’s ability to support the adhesion and proliferation of L929 fibroblasts (fold increase of 28, 22, 23, and 13 at day 13 (in relation to day 1) for PCL, GPN0.25, GPN0.5, and GPN0.75, respectively) and bone marrow mesenchymal stem/stromal cells (seven-fold increase for all sample groups at day 21 in relation to day 1). Moreover, the cells maintained high viability, regular morphology, and migration capacity in all the different experimental groups, assuring the potential of PCL/GPN scaffolds for tissue engineering (TE) applications.

Particle Loading Effects on Additively Manufactured and Laser Cured Medical Grade Silicone

Abstract A proposed benefit to additive manufacturing (AM) silicone components is the ability to selectively add fillers such as agents to make drug delivery devices. Laser curing silicones have benefits such as selective or graded curing of specific locations in the part. A challenge with high-temperature extrusion-based AM processes is understanding how particles of various thermal sensitivities, sizes, and loading amounts may affect the AM build parameters, polymer crosslink densities, and final products produced. This article investigates the effect of particle loading on laser-cured medical-grade silicone. Die swelling of silica gel-loaded silicone, chosen as a relatively nonthermally sensitive representative filler for drug agents, was evaluated as a function of extrusion speed, particle size, and particle loading amount. A design of experiments (DoE) on silica gel-loaded samples through tetrahydrofuran (THF) swell studies was done to explore how layer height, particle size, and particle loading amount may affect crosslink density. Last, the AM process with the female hormone 2-methoxyestradiol (2-Me2) and the drug Cyclosporin was investigated using nuclear magnetic resonance (NMR) spectroscopy and high-performance liquid chromatography (HPLC) elution to observe potential alterations of the final product. The results show promise for drug-loaded silicone samples fabricated using an extrude and laser curing AM technique.