Material Extrusion Additive Manufacturing Process Research Articles

Optimization of the extrusion rate for different layer thicknesses to achieve controlled mechanical properties in MEX 3D printing of low-alloy steel

Composite extrusion modeling is an advanced material extrusion additive manufacturing process that requires fine-tuning of printing parameters for printing injection molding feedstocks. In order to achieve comparable high-quality parts at different layer thicknesses, the parameters must be optimized for the respective layer thicknesses. In this work, the printing parameters for AISI 8740 low-alloy steel injection molding material are optimized for four different layer thicknesses. The extrusion multiplier values for each layer thickness are tuned, allowing fine adjustment of the printer's screw rotation speed at every layer thickness, resulting in all final parts' maximum densities (≥ 98 %) with high accuracies. Scanning electron microscope images, surface roughness measurements, and printing precision tests proved the good and comparable high-quality of all optimized printed parts. Young's modulus, tensile and yield strengths also raised by ∼24 %, ∼16 % and ∼15 %, respectively, compared to the non-optimized printed sintered part. The achieved tensile strength range of (∼888–947) MPa and yield strength range of (∼574–586) MPa of all optimized printed sintered parts were also higher than those provided by the feedstock manufacturer. This promising approach significantly reduces printing time and manufacturing costs without compromising the printed final parts' quality and mechanical properties. The adjusting screw rotation speed methodology allows broader applicability across diverse material extrusion processes.

Tensile, flexural and fracture properties of MEX-printed PLA-based composites

Due to the continuous development of material extrusion-additive manufacturing (MEX-AM) technology, the fracture behavior of polymeric parts, and especially of their associated composites, presents some shortcomings but also a challenge in the field. In this paper, the fracture properties of non-reinforced (NR) and reinforced Polylactic Acid (PLA) samples manufactured by MEX-AM process are investigated through tensile, flexural and fracture mechanics tests. The samples are reinforced with glass fibers (GF-PLA), carbon fibers (CF-PLA) and bronze particles (BP-PLA), and tested parallel (named FLAT for all tests) and normal (named UPRIGHT for tensile test, and ON-EDGE for flexural and fracture mechanics tests) to the layer growth (LG). It was found that regardless of the type of test, the LG and the material significantly influence the mechanical properties and collapse modes of the MEX-printed samples. It was obtained that the parallel-LG load is favorable for the tensile and flexural tests, and the normal-LG for the fracture mechanics tests. Overall, the NR-PLA material gives the best strength, strain and energy absorption properties, CF-PLA stands out as the stiffest material, while BP-PLA presents the minimum performances for almost all properties. The macroscopic analyzes of the fractured samples clearly highlight distinct failure mechanisms associated with each type of test, material and LG. From the analysis of the mechanical behavior and macrostructural images, CF-PLA was identified as the most brittle material, and NR-PLA the most ductile.

Electrical conductivity upon sintering of pure Cu produced by material extrusion additive manufacturing: Effects of pore, grain size, and impurity

This study investigates the development of pores and microstructures at each processing step and sintering conditions in the material extrusion additive manufacturing process, examining their correlation with related physical properties. This is achieved by fabricating copper parts using material extrusion (MEX) and examining the primary factors that impact the electrical characteristics of the MEX parts. Initially, the application of solvent debinding to MEX-produced Cu parts effectively removes a portion of the binder, forming printing-pattern–induced pores and ineffectual pore channels. Subsequently, thermal debinding eliminates the remaining binder and promotes neck formation between the Cu particles. The process proceeds to a subsequent sintering step, where even after the final sintering, some pores remain. These pores are categorized as sintering-induced and printing-pattern–induced pores. The relatively large pore size due to the printing pattern is identified as the main reason for reduced density of MEX parts, especially those influenced by the contour pattern. As the sintering progresses, the grain size increases, with the overall grain size and shape becoming uniform during extended sintering periods. Impurities, specifically carbon and oxygen, are detected in the sintered part, and their concentrations rise with longer sintering times. After examining the variation in porosity, grain size, and impurity content with respect to sintering time, it becomes evident that porosity plays a pivotal role in influencing electrical conductivity. Consequently, the densest 48 h sintered sample, with a relative density of 95.5 %, achieves the highest electrical conductivity at 94.6 % IACS. This demonstrates that MEX can be effectively employed to craft complex-shaped Cu parts with outstanding electrical properties. In summary, densification is crucial for enhancing the electrical properties of Cu parts produced through MEX, achieved by minimizing printing-pattern–induced pores, the primary contributor to density reduction. This study is poised to advance the manufacturing of high-performance, intricate Cu components by providing insights into the development and locations of primary pores through detailed microstructural investigations.

Mechanical Evaluation of PET-G 3D-Printed Wrist-Hand Orthosis: An Integrated Experimental and Numerical Approach.

Limb injuries frequently necessitate orthotic bracing, and the utilization of material extrusion (MEX) additive manufacturing (AM) or 3D printing offers a rapid and cost-effective means of producing orthoses. These characteristics are highly sought after in today's orthotic market. The study focused on the mechanical strength analysis of the wrist-hand orthosis (WHO) made of PET-G filament. Experimental testing and simulation were employed to assess the properties of individualized wrist orthoses fabricated through the MEX AM process. Standard three-point bending samples were manufactured using PET-G filament on a low-cost MEX 3D printer, alongside orthotic fragments and complete orthosis. Experimental testing was performed using a universal testing machine, and results were juxtaposed with those from a finite element simulation model created in the Abaqus environment. This comprehensive research approach facilitates the comparison of the modulus of elasticity of the fabricated components, enabling a comparison between the mechanical properties of the complete wrist-hand orthosis (WHO) product and those of a conventional bending sample.

Direct relationship between crystalline structure and part deformation of polypropylene copolymer parts fabricated by material extrusion additive manufacturing

AbstractThe high crystallinity and fast crystallization rate of polypropylene (PP) often result in severe warpage of final parts prepared by means of material extrusion additive manufacturing (MEAM). In this work, the effect of bed temperature (Tb) and nozzle temperature (Tn) on the dimensional accuracy and mechanical property of MEAM‐printed PP copolymer parts was investigated. It is found that raising Tb and Tn could significantly reduce the warpage of PP parts by regulating the crystallization behavior of PP. Specially, the amount of γ‐crystal grows obviously while the total crystallinity remains unchanged, as Tb or Tn increases. Moreover, the more the content of γ‐crystal, the lower the warpage height of PP samples is. Hence, a close correlation between the content of γ‐crystal and part deformation of MEAM‐printed PP parts is successfully established. This is mainly related to the large rigidity of γ‐crystal, which significantly reduces the volume shrinkage of PP during MEAM process. Besides, the raise of Tb or Tn also enhances the tensile strength, modulus and the elongation at break of PP parts. This wok provides an effective and convenient method for the manufacture of PP parts with good dimensional accuracy and excellent mechanical properties by means of MEAM techniques.

Nanocomposites with Optimized Polytetrafluoroethylene Content as a Reinforcement Agent in PA12 and PLA for Material Extrusion Additive Manufacturing.

Herein, polytetrafluoroethylene (PTFE) is evaluated as a reinforcement agent in material extrusion (MEX) additive manufacturing (AM), aiming to develop nanocomposites with enhanced mechanical performance. Loadings up to 4.0 wt.% were introduced as fillers of polylactic acid (PLA) and polyamide 12 (PA12) matrices. Filaments for MEX AM were prepared to produce corresponding 3D-printed samples. For the thorough characterization of the nanocomposites, a series of standardized mechanical tests were followed, along with AFM, TGA, Raman spectroscopy, EDS, and SEM analyses. The results showed an improved mechanical response for filler concentrations between 2.0 and 3.0 wt.%. The enhancement for the PLA/PTFE 2.0 wt.% in the tensile strength reached 21.1% and the modulus of elasticity 25.5%; for the PA12/PTFE 3.0 wt.%, 34.1%, and 41.7%, respectively. For PLA/PTFE 2.0 wt.%, the enhancement in the flexural strength reached 57.6% and the modulus of elasticity 25.5%; for the PA12/PTFE 3.0 wt.%, 14.7%, and 17.2%, respectively. This research enables the ability to deploy PTFE as a reinforcement agent in the PA12 and PLA thermoplastic engineering polymers in the MEX AM process, expanding the potential applications.

Understanding the process-microstructure-property relationships in material extrusion additive manufacturing of polylactic acid microcellular foams

Process-microstructure-property relationships are reported for microcellular foams printed via material extrusion (MEX) additive manufacturing (AM) process. Polylactic acid and thermally expandable microspheres were mixed and extruded to prepare the filament. In situ foaming during MEX AM process was then conducted to investigate the impact of nozzle temperature, flow rate, and print speed on the cellular morphology, mesostructure, part density, and the mechanical behavior of the foams. The temperature and the residence time were identified as the two key factors governing the foaming behavior and thus the resultant microstructure and properties. Too excessive temperature and residence time resulted in the deformed, wrinkled, or collapsed microspheres due to gas loss and contraction. On the other hand, too low temperature and residence time caused limited number of microspheres to expand, due to insufficient energy and time. Both overly activated and partially unexpanded microspheres provided nonuniform cellular morphologies and higher densities and thus adversely affected the tensile properties. The foam expansion/shrinkage behavior during the MEX AM process was demonstrated as a function of a combined process variable that unifies temperature, flow rate, and print speed. Upon the utilization of the optimum process variables, foam samples with uniform morphology, low density, and high toughness were achieved. The results shed light on the understanding and advancing of MEX AM process as a novel manufacturing approach to produce quality foams.

Optimizing the Rheological and Thermal Behavior of Polypropylene-Based Composites for Material Extrusion Additive Manufacturing Processes.

In this study, composites based on a heterophasic polypropylene (PP) copolymer containing different loadings of micro-sized (i.e., talc, calcium carbonate, and silica) and nano-sized (i.e., a nanoclay) fillers were formulated via melt compounding to obtain PP-based materials suitable for Material Extrusion (MEX) additive manufacturing processing. The assessment of the thermal properties and the rheological behavior of the produced materials allowed us to disclose the relationships between the influence of the embedded fillers and the fundamental characteristics of the materials affecting their MEX processability. In particular, composites containing 30 wt% of talc or calcium carbonate and 3 wt% of nanoclay showed the best combination of thermal and rheological properties and were selected for 3D printing processing. The evaluation of the morphology of the filaments and the 3D-printed samples demonstrated that the introduction of different fillers affects their surface quality as well as the adhesion between subsequently deposited layers. Finally, the tensile properties of 3D-printed specimens were assessed; the obtained results showed that modulable mechanical properties can be achieved depending on the type of the embedded filler, opening new perspectives towards the full exploitation of MEX processing in the production of printed parts endowed with desirable characteristics and functionalities.

Towards optimization of polymer filament tensile test for material extrusion additive manufacturing process

Material extrusion (MEX) is a popular additive manufacturing (AM) method that can process a wide range of feedstock materials, most commonly in filament form. Currently, there is no standardized testing method for filament tensile properties, and researchers resort to 3D-printed dog-bone specimens, which necessarily include the effects of the printing process. In this study, the impact of the strain measurement device, knife-edge type, gage length, testing speed, and oven treatment on filament tensile properties was explored using an off-the-shelf fixture. It was observed that an extensometer with blunt knife edges, a filament gage length of 165 mm, and a 6.35 mm/min (0.25 in./min) testing speed could accurately evaluate the tensile properties of acrylonitrile butadiene styrene (ABS) filaments. In addition, an optimized raster path, 3D printing design, and process parameters were used to manufacture dog bone tensile specimens according to ASTM D638-22 from the same ABS filament spool. The tensile properties of the filaments were validated using the results of 3D-printed dog-bone specimens. Young's modulus, stress at yield, and stress at break for the optimum filament test set (2.20 GPa, 43.9 MPa, and 39.1 MPa) were very similar to those of the 3D-printed specimens (2.26 GPa, 44.9 MPa, and 37.3 MPa). The optimum filament tensile testing parameters determined in this study for ABS can be used for the initial test setup for other filament materials to provide baseline values that can serve as the foundation for AM process development.

Numerical predictions and experimental validation on the effect of material properties in filament material extrusion

The numerical prediction of dimensional accuracy and mechanical performance of 3D-printed structures can eliminate or reduce the need to perform trial-and-error experimentation to achieve the desired part quality quickly and at a reduced cost. Therefore, this study focuses on experimental and numerical investigations of the effect of material properties on dimensional control of the material extrusion additive manufacturing process. A thermomechanical model is utilized, validated, and used to predict the part deflections, warpages, and residual stresses in 3D-printed components for two different materials (i.e., polyamide-6 (PA6) and acrylonitrile butadiene styrene (ABS)). In addition, numerical simulations for mechanical testing were performed and validated through experimental investigations. The numerical model considered the effect of material on final product quality and was in close agreement with experimental results. It was concluded that the materials with a lower thermal expansion coefficient (CTE) would provide better dimensional accuracy of 3D-printed parts. In addition, the lower thermal conductivity and temperature variations within the 3D-printed part will further produce precise parts. The controlled ambient environment using a closed chamber can also assist in maintaining desired thermal gradient and avoid non-uniform cooling during the process. Finally, the numerical model accurately predicted the mechanical behavior of 3D-printed samples as validated via experimentation.

Tensile behavior of individual fibers and films made via material extrusion additive manufacturing

The mechanical behavior of thermoplastic materials processed via material extrusion additive manufacturing (MEAM) is a topic of great interest in several disciplines. Most of the material behavior characterization that has been done on the materials produced by material extrusion has been on macro-scale (“bulk”) parts. In order to better model and understand the process effects and take advantage of these during design, it is necessary to study the meso-scale material elements extruded by the process used to build the part geometry. While modeled effectively in previous works, full mechanical characterization at the meso-scale is yet to be accomplished. At this level, the essential material elements are known as “beads” or “roads”, the sum of which comprise each layer of the part. These elements are approximately uniform in cross-section and are defined by their dimensions, length, and placement angle. Therefore, they are effectively fibers and a set of them together constitute a layer, which can be built as a film (usually but not always flat). To further progress on this topic, this article explored the manufacturing and testing of these elements (fibers) and layers (films) at the meso-scale. The dimensional consistency was measured for each case in order to determine the process repeatability, followed by tensile tests on the fibers and films made from three common thermoplastic materials: Acrylonitrile butadiene styrene (ABS), polylactic acid (PLA), and polycarbonate (PC). For the fibers, both extruded (round, as produced) and deposited (rectangular, after printing on a surface) fibers were tested. Films were tested in single- and double-layer configurations with several different element layout patterns. The results and potential process sensitivities were discussed in detail, providing recommendations for use and future development of design rules when using these materials. These results will be useful in driving design decisions (for both macro-scale products and structured materials) and providing characterization data for further modeling and simulation of the MEAM process. These results will also help ensure the manufacturability of designed parts and materials built of these deposited thermoplastic fibers and films. This article also introduced and described mechanical testing methods that are useful for thermoplastic MEAM parts and have not yet been utilized elsewhere.

Production of an Office Stapler by Material Extrusion Process, using DfAM as Optimization Strategy

For the last few decades, the rapid growth of Additive Manufacturing (AM) technologies has been seeable. It is expected to keep maturing continuously due to its advantages compared to conventional manufacturing technologies: flexibility, reliability, energy consumption, and material efficiency. This research article addresses the development and production of a stapler using the Material Extrusion AM process. It is intended to show the development steps to redesign an everyday stapler, into an added-value tool, from the selection and fixture of the CAD model and generative design through Fusion 360 to its optimization on nTopology, simulation, and plot of the part in Eiger.

Experimental validation of numerical model for thermomechanical performance of material extrusion additive manufacturing process: Effect of infill design & density

The optimum selection of process parameters, materials, and product design is essential to achieve the desired response of 3D-printed structures, especially in functional components. The current practices of the experimental optimization process require significant resources, which can be limited through numerical modeling and simulation techniques. In this study, a thermomechanical numerical model is used to predict the performance of the additive manufacturing (AM) process, i.e., fused filament fabrication (FFF). 3D printing (3DP) process simulations were performed for tensile testing coupons using carbon fiber-reinforced polyamide-6 (PA6-CF) material. The numerical model predicted the effect of infill patterns and densities on the deflections and distortions during the FFF process. The numerical model predictions were validated via experiments performed under similar conditions. The results conclude that the numerical model can adequately predict the process-induced deflections and distortions during the FFF process. Generally, higher dimensional control was observed for rectangular infill patterns and increased infill density. However, the numerical model overestimates the shrinkage as the stress-relaxation effect is not considered in the numerical model and underestimates the warpages as perfect build plate adhesion is assumed.

Methodology to assess interlayer quality in the material extrusion process: A temperature and adhesion prediction on a high performance polymer

The material extrusion additive manufacturing process consists in extruding a molten polymer along a path with trajectories defined from a 3D definition of the part. One of the major drawbacks of this process is the reduction of the mechanical properties of the parts compared with those made by conventional manufacturing methods such as injection molding. On the one hand, this reduction of properties is linked to the presence of macroporosities in the part and, on the other hand, to the limited adhesion between the deposited layers. These two phenomena strongly depend on the thermal history of the polymer. This work proposes to determine the thermal conditions leading to sufficient adhesion, and to the manufacture of parts with sufficient final interfilament strength. An instrumented bench was developed from a 3D printer in order to investigate the cooling, at the filament scale, of parts printed in PEKK material. In parallel, heat transfers in the material extrusion process were simulated using a model, which was validated with the experimental data obtained using the bench. The adhesion was also modeled by describing the phenomena of coalescence and healing of the interface. The physical properties necessary for the models were characterized taking into consideration their thermodependency. A parametric study then quantifies the influence of each parameter on the temperature of the polymer, as well as on the interlayer adhesion, thus contributing to the definition of the process window.

A Review on Microstructural Formations of Discontinuous Fiber-Reinforced Polymer Composites Prepared via Material Extrusion Additive Manufacturing: Fiber Orientation, Fiber Attrition, and Micro-Voids Distribution.

A discontinuous fiber-reinforced polymer composite (DFRPC) provides superior mechanical performances in material extrusion additive manufacturing (MEAM) parts, and thus promotes their implementations in engineering applications. However, the process-induced structural defects of DFRPCs increase the probability of pre-mature failures as the manufactured parts experience complicated external loads. In light of this, the meso-structures of the MEAM parts have been discussed previously, while systematic analyses reviewing the studies of the micro-structural formations of the composites are limited. This paper summarizes the current state-of-the-art in exploring the correlations between the MEAM processes and the associated micro-structures of the produced composites. Experimental studies and numerical analyses including fiber orientation, fiber attrition, and micro-voids are collected and discussed. Based on the review and parametric study results, it is considered that the theories and numerical characterizations on fiber length attrition and micro-porosities within the MEAM-produced composites are in high demand, which is a potential topic for further explorations.

Physical-mechanical behaviors of stainless steel plate-lattice built by material extrusion additive manufacturing

Additive manufacturing (AM) technology has been widely adopted for the fabrication of metal lattices due to its freeform design capability over traditional manufacturing methods. However, the prevalent laser-based AM technologies possess high energy and investment consumption, and relatively low manufacturing speed, hampering their widespread adoption in building metal lattice components. In this study, an integrated approach of material extrusion AM, debinding, and sintering was introduced to produce 17–4 PH stainless steel plate-lattice structures in a time-efficient and cost-effective way. Three types of plate-lattice structures, namely body-centered cubic (BCC), face-centered cubic (FCC) and their combination (BCC-FCC), were successfully fabricated. Physical-mechanical behaviors, including physical deformation and compressive properties, were investigated through modeling, simulation, and experiments. Specifically, the shrinkage of the final sintered parts was predicted by the analytical modeling and characterized by experimental observation, the results of which showed a good consistency. The plate-lattice structure exhibited equiaxed grains on each surface, with a small portion of lath martensite observed at the top surface. Numerical simulation and compression test were conducted to reveal the compressive modulus, yield strength, and the fractural response at large compressive strains. All three types of plate-lattices possessed a lower compressive modulus than the simulated value, but still exhibited extraordinary yield strength under the compressive force compared to the truss-based or triply periodic minimal surface lattices. The successfully built metal plate-lattice structure verifies the great potential of material extrusion AM process, showing a great promise to fabricate complex metal lattice for large scale applications.

Experimental Validation of Numerical Model for Thermomechanical Performance of Material Extrusion Additive Manufacturing Process: Effect of Process Parameters.

The material extrusion additive manufacturing (MEAM) process for polymers seems straightforward. However, several controlled and uncontrolled factors affect the 3D printed product quality, e.g., MEAM process parameters, thermomechanical properties of the material, and part design. Therefore, it is crucial to understand these interlinked factors of part geometry, material properties, and 3D printing (3DP) process parameters to optimize 3D printed product quality. The numerical models and simulation tools can predict the thermomechanical performance of the MEAM process under given input parameters (material, design, and process variables) and reduce the research and development costs significantly. However, the numerical models and tools need further exploration and validation of simulation predictions for their adaptability and reliability. Therefore, in this study, numerical simulations were performed to observe the impact of process parameters on the part quality of MEAM 3D printed components. The two crucial process parameters (i.e., extrusion temperature and layer resolution) were varied while keeping the other process parameters, part geometry (tensile testing coupon), and material properties (acrylonitrile butadiene styrene (ABS)) constant. These two process parameters were sequentially optimized for optimum part quality, first by varying the extrusion temperature and secondly by changing the printing resolution using the optimum printing temperature. The 3DP process quality was evaluated in terms of dimensional accuracy, distortions, and residual stresses. Finally, the specimens were 3D printed under similar process conditions to validate the numerical model predictions.

In Situ Foam 3D Printing of Microcellular Structures Using Material Extrusion Additive Manufacturing.

A facile manufacturing method to enable the in situ foam 3D printing of thermoplastic materials is reported. An expandable feedstock filament was first made by incorporation of thermally expandable microspheres (TEMs) in the filament during the extrusion process. The material formulation and extrusion process were designed such that TEM expansion was suppressed during filament fabrication. Polylactic acid (PLA) was used as a model material, and filaments containing 2.0 wt % triethyl citrate and 0.0-5.0 wt % TEM were fabricated. Expandable filaments were then fed into a material extrusion additive manufacturing process to enable the in situ foaming of microcellular structures during layer deposition. The mesostructure, cellular morphology, thermal behavior, and mechanical properties of the printed foams were investigated. Repeatable foam prints with highly uniform cellular structures were successfully achieved. The part density was reduced with an increase in the TEM content, with a maximum reduction of 50% at 5.0 wt % TEM content. It is also remarkable that the interbead gaps of mesostructure vanished due to the local polymer expansion during in situ foaming. The incorporation of TEM and plasticizer only slightly lowered the critical temperatures of PLA, that is, glass-transition, melting, and decomposition temperatures. Moreover, with the introduction of foaming, the specific tensile strength and modulus decreased, whereas the ductility and toughness increased severalfold. The results unveil the feasibility of a novel additive manufacturing technology that offers numerous opportunities toward the manufacturing of specially designed structures including functionally graded foams for a variety of applications.

Fabrication of Metal Gas Filter by Material Extrusion Additive Manufacturing Process

Fabrication of Metal Gas Filter by Material Extrusion Additive Manufacturing Process

Development of a Material Extrusion Additive Manufacturing Process of 1.2083 steel comprising FFF Printing, Solvent and Thermal Debinding and Sintering

In recent years, Fused Filament Fabrication (FFF) of feedstock comprising metal powder and a polymer binder system attracted more and more attention as an extrusion-based Additive Manufacturing method. Allowing for the production of intricate geometries at reasonably low cost, FFF and subsequent debinding and sintering is an attractive solution for producing complex parts made of metals or ceramics. This study investigates the FFF, debinding and sintering process chain for 1.2083 (AISI 420) tool steel. The effect of printing temperature, printing speed and filament feed rate on the density of the green body was evaluated. With regard to the subsequent solvent debinding the required time for complete binder removal was determined as a function of the maximum part thickness. Based on a thermogravimetric analysis (TGA) the decomposition behavior of the remaining insoluble binder was monitored and accordingly a temperature program for the thermal debinding was derived. The sintering curve was determined by dilatometry. Finally, the capability of the process is demonstrated by manufacturing an impeller geometry and examining the resulting microstructure and hardness of the material.