Printing Velocity Research Articles

Study of the interlayer adhesion and warping during material extrusion-based additive manufacturing of a carbon nanotube/biobased thermoplastic polyurethane nanocomposite

A thermoplastic bio-polyurethane from renewable sources (TPU) and the nanocomposite developed by mixing it with carbon nanotubes (CNT) are investigated as potentially adequate for Material Extrusion-based Additive Manufacturing (EAM). Thermal and rheological features are studied from the perspective of their liaisons with printing adequacy and conditions. As predicted by rheology, both samples show good performance in filament elaboration and flow in the nozzle. Warpage is observed for TPU, but not for the nanocomposite, which is due to the effect of CNT nanoparticles on polymer chains dynamics. At the studied printing velocities, interlayer adhesion strength is independent of printing velocity implying that there is no significant chain orientation which can induce changes in the TPU entanglements. The nanocomposite shows a lower welding strength, notwithstanding both have the same chain entanglements density. This is explained by considering that the higher viscosity of TPU/CNT, as compared to TPU, reduces the melt diffusion coefficient.

The effect of printing velocity on the temperature and viscosity of the polymer thread at the nozzle exit in 3D printers

Fused Deposition Modelling (FDM) is a powerful method for advanced additive manufacturing of polymeric materials, due to its simplicity and low cost. However, the process implies complex phenomena which are not fully understood yet. In particular, the effect of viscosity on the printed thread is a key parameter to control if good quality products are to be obtained. Experimental data of two grades of acrylonitrile-butadiene- styrene copolymer (ABS) was employed to analyse, by using ANSYS Fluent simulation package, six printing velocities at a temperature of 230°C. A drastic temperature change was observed as the printing velocity increases, confirming the effect of viscosity on the shear created on the wall of the nozzle transversal to the printing bed. The polymers analysed present different viscosity behavior even under the same angular frequency range (0.1 to 100 rad/s), and testing temperature (230°C), which could lead to inhomogeneities. Our results allow taking into account these parameters as part of the design criteria.

Print Velocity Effects on Strain-Rate Sensitivity of Acrylonitrile-Butadiene-Styrene Using Material Extrusion Additive Manufacturing.

The strain-rate sensitivity of the yield stress for Acrylonitrile-Butadiene-Styrene (ABS) tensile samples processed via material extrusion additive manufacturing (ME-AM) was investigated. Such specimens show molecular orientation and interstitial voids that affect the mechanical properties. Apparent densities were measured to compensate for the interstitial voids. Three different printing speeds were used to generate ME-AM tensile test samples with different molecular orientation. Printing velocities influenced molecular orientation and stretch, as determined from thermal shrinkage measurements. Likewise, infill velocity affected the strain-rate dependence of the yield stress. The ABS material manifests thermorheollogically simple behavior that can correctly be described by an Eyring flow rule. The changing activation volume, as a result of a varying print velocity, scales linearly with the molecular orientation, as captured in an estimated processing-induced pre-strain. Therefore, it is suggested that ME-AM processed ABS shows a deformation-dependent activation volume. This paper can be seen as initial work that can help to improve quantitative predictive numerical tools for ME-AM, taking into account the effects that the processing step has on the mechanical properties.

Food 3D printing: Effect of heat transfer on print stability of chocolate

Abstract Food 3D Printing is a novel technology which allows manufacturing three dimensional edible objects with customized shape and structure, by extruding and depositing progressively several layers. The overall process is complex since many phenomena occurs simultaneously: non-Newtonian flows, heat transfer, sintering between different layers and solidification of the printed material after deposition. This study focuses on the interplay between the rheological and thermal properties of chocolate products, and printing conditions, in order to predict the stability of 3D printed structures. The effect of printing velocity ( V p ) and environmental temperature ( T e ) on chocolate printed structure was investigated using IR thermography to characterize the local cooling dynamics.3D edible structures can be manufactured successfully only below a critical print velocity which depends on the environmental temperature. At T e = 18 ° C , V p should be lower than 16 mm/s while at 20 ° C lower than 8 mm/s. This conditions ensure a sufficient cooling and solidification of the cocoa butter, which is needed for print stability. A stability criterion based on the local yield stress is proposed to explain the stability or collapse of the 3D printed structures. The understanding provided by this work can help optimising food 3D printing conditions and product formulation.

Influence of droplet velocity, spacing, and inter-arrival time on line formation and saturation in binder jet additive manufacturing

Binder Jetting (BJ) is a low-cost Additive Manufacturing (AM) process that uses inkjet technology to selectively bind particles in a powder bed. BJ relies on the ability to control, not only the placement of binder on the surface but also its imbibition into the powder bed. This is a complex process in which picoliter-sized droplets impact powder beds at velocities of 1–10 m/s. However, the effects of printing parameters such as droplet velocity, size, spacing, and inter-arrival time on saturation level (fraction of pore space filled with binder) and line formation (merging of droplets to form a line) are unknown. Prior attempts to predict saturation levels with simple measurements of droplet primitives and capillary pressure assume that droplet/powder interactions are dominated by static equilibrium and neglect the impact of printing parameters. This study analyzes the influence of these parameters on the effective saturation level and conditions for line formation when printing single lines into powder beds of varied materials (316 stainless steel, 420 stainless steel, and alumina) and varied particle size (d50=10–47 µm). Results show that increasing droplet velocity or droplet spacing decreases effective saturation while droplet spacing, velocity, and inter-arrival time affect line formation. At constant printing velocity, the conditions for successful line printing are shown to be a function of droplet spacing and square root of the droplet inter-arrival time analogous to the Washburn model for infiltration into a porous media. The results have implications to maximizing build rates and improving quality of small features in BJ.

Comparative study of the flexural properties of ABS, PLA and a PLA–wood composite manufactured through fused filament fabrication

PurposeThe aim of this paper is to analyze the mechanical properties of acrylonitrile-butadiene-styrene (ABS) parts manufactured through fused filament fabrication and compare these results to analogous ones obtained on polylactic acid (PLA) and PLA–wood specimens to contribute for a wider understanding of the different materials used for additive manufacturing.Design/methodology/approachWith that aim, an experimental based on an L27 Taguchi array was used to combine the specific parameters taken into account in the study, namely, layer height, nozzle diameter, infill density, orientation and printing velocity. All samples were subjected to a four-point bending test performed according to the ASTM D6272 standard.FindingsYoung’s modulus, elastic limit, maximum stress and maximum deformation of every sample were computed and subjected to an analysis of variance. Results prove that layer height and nozzle diameter are the most significant factors that affect the mechanical resistance in pieces generated through additive manufacturing and subjected to bending loads, regardless of the material.Practical implicationsThe best results were obtained by combining a layer height of 0.1 mm and a nozzle diameter of 0.6 mm. The comparison of materials evidenced that PLA and its composite version reinforced with wood particles present more rigidity than ABS, whereas the latter can experience further deflection before break.Originality/valueThis study is of interest for manufacturers that want to decide which is the best material to be applied for their application, as it derives in a practical technical recommendation of the best parameters that should be selected to treat the material during the fused filament fabrication process.

Thermal analysis of the fused filament fabrication printing process: Experimental and numerical investigations

A 3d printing of a thin wall is achieved by a fused filament fabrication process. The influence of the printing velocities on the filament morphology is studied using optical microscopy. The strand morphology is approximated to different geometries and compared to experimental data. The oblong cross-section is a good approximation to estimate the strand’s height and width. A local temperature is recorded by introducing a thermocouple during the printing of a thin wall. The polymer undergoes successive heating and cooling. Their magnitudes decrease with time while the filament deposition occurs farther from the thermocouple location. A steady-state cooling is observed after an extended period of time due to the surrounding air cooling. The influence of the strand’s cross-section area on its cooling kinetics is investigated experimentally. The printing of a thin wall with the same geometry is also numerically computed by solving the heat transfer equation with a finite element method. The thermal conductivity takes into account the porosity of the printed wall. An estimation of the heat transfer coefficients between the wall and the surrounding air is done by comparison with a particular experiment. The numerical computation reproduces very well the amplitudes and the periods of heating and cooling observed experimentally. Moreover, the changes in the morphology of the melted filament show the reliability of the numerical tool to obtain a thermal history in agreement with experimental data.

Effects of redispersible polymer powders on the structural build-up of 3D printing cement paste with and without hydroxypropyl methylcellulose

This paper studies the effects of polyvinyl acetate-ethylene (VAE) based redispersible polymer powder (RPP) and polyvinyl acetate-vinyl versatate-ethylene (VVE) based RPP on the structural build-up of 3D printing cement paste within several hours of hydration. At the same time, two cases of the presence or absence of hydroxypropyl methylcellulose (HPMC) were considered. The build-up performance of cement paste was assessed by the hysteresis area, dynamic yield stress ratio, static yield stress, shear modulus and ultrasonic plus velocity from the dynamic shear test, static shear test and ultrasonic wave transmission test. In addition, the limit layer thickness and printing velocity were calculated by dynamic and static yield stresses to quantitatively characterize shape stability and printing efficiency of cement paste. Results indicate that both VAE with higher ethylene content (VAE1) and VVE decrease the structural build-up rate of cement paste, independent of shear test modes. However, VAE with lower ethylene content (VAE2) increases the structural build-up rate of cement paste under dynamic shear test whereas decreases the growth rate of static yield stress. The dynamic yield stress ratio of cement paste containing 2% VAE2 is 0.57, which is 83.9% higher than that of pure cement paste. In addition, HPMC alters the effects of VAE2 on the structural build-up of cement paste. VAE1 and VVE decrease the shape stability of cement pastes with and without HPMC, while VAE2 is beneficial to the shape stability of cement paste. Limit layer thicknesses of cement pastes with 4% VAE2 are 7.3 mm and 14 mm in the absence and presence of HPMC, which are about 3.0 and 5.8 times that of pure cement paste. In the absence of HPMC, VVE decreases the limit printing velocity of cement paste in the first tens of minutes. VAE1 and VAE2 can improve the printing efficiency due to the increase of limit printing velocity in the first tens of minutes. In the presence of HPMC, only VAE2 significantly improves the limit printing velocity of cement paste.

Processing of Highly Filled Polymer-Metal Feedstocks for Fused Filament Fabrication and the Production of Metallic Implants.

Fused filament fabrication (FFF) is a new procedure for the production of plastic parts, particularly if the parts have a complex geometry and are only needed in a limited quantity, e.g., in specific medical applications. In addition to the production of parts which are purely composed of polymers, fused filament fabrication can be successfully applied for the preparation of green bodies for sintering of metallic implant materials in medical applications. In this case, highly filled polymer–metal feedstocks, which contain a variety of polymeric components, are used. In this study, we focus on various polymer-metal feedstocks, investigate the rheological properties of these materials, and relate them to our results of FFF experiments. Small amplitudes of shear oscillations reveal that the linear range of the polymer–metal feedstocks under investigation is very small, which is caused by elastic and viscous interactions between the metallic particles. These interactions strongly influence or even dominate the flow properties of the feedstock depending on the applied shear stress. The magnitude of the complex viscosity strongly increases with decreasing angular frequency, which indicates the existence of an apparent yield stress. The viscosity increase caused by the high powder loading needed for sintering limits the maximum printing velocity and the minimum layer height. The apparent yield stress hinders the formation of smooth surfaces in the FFF process and slows down the welding of deposited layers. The influence of composition on the processing parameters (suitable temperature range) and part properties (e.g., surface roughness) is discussed on the basis of rheological data.

Investigation on shape recovery of 3D printed honeycomb sandwich structure

Lightweight sandwich panels have been used in various industry sectors due to their unique properties as well as a high ratio of stiffness‐to‐weight and energy absorption. Three‐dimensional (3D) printing process provides a unique opportunity to fabricate highly complex shapes of sandwich panels and also the application of smart materials, such as shape memory polymers, can create unique functionality for the 3D printed sandwich structure so that they can change their shape in response to external stimuli and give a new dimension to the printing process called four‐dimensional (4D) printing. Polylactic acid is a biodegradable and compostable polymer with a good shape memory effect that can be printed easily with an inexpensive fused deposition modeling. This study investigated the effect of printing and activation parameters on the functionality, in particular shape recovery, of the deformed sandwich structure with honeycomb out‐of‐plane tailored core. The input parameters were the activation temperature, the nozzle temperature, and the printing velocity. The results showed that the optimum recovery ratio can be achieved using a higher activations and nozzle temperatures and lower printing speed.

Elastic buckling and plastic collapse during 3D concrete printing

This contribution studies failure by elastic buckling and plastic collapse during 3D concrete printing of wall structures. Four types of experiments were performed, which demonstrate the circumstances under which elastic buckling and plastic collapse occur, the effect of geometrical imperfections on the buckling response, the influence by the curing rate of the concrete material on the buckling stability, and the conditions leading to the successful printing of a complex, practical structure (a picnic table). The experimental results are compared to those computed by the parametric 3D printing model recently developed by Suiker (Int. J. Mech Sci, 137: 145–170, 2018), showing a very good agreement. The design formulas and design graphs deduced from the parametric model serve as a useful tool for accurately designing wall structures against failure during 3D concrete printing. Furthermore, they may be applied to optimize the process conditions during 3D printing, by providing the maximal printing velocity, the optimal geometrical characteristics, or the minimal amount of material required for adequately printing the structure.

Study of the manufacturing process effects of fused filament fabrication and injection molding on tensile properties of composite PLA-wood parts

The present study evaluates the effects of manufacturing parameters on the tensile properties of a commercial composite material based upon polylactic acid (PLA) with wood fibers known as Timberfill. The specimens are built through fused filament fabrication (FFF), and the influence of four printing parameters (layer height, fill density, printing velocity, and orientation) is considered through a L27 Taguchi orthogonal array. Tensile tests are applied to obtain the response variable used as output results to perform the ANOVA calculations. Results show that fill density is the most influential parameter on the tensile strength, followed by building orientation and layer height, whereas the printing velocity shows no significant influence. The optimal set of parameters and levels is found, being 75% fill density, 0○Z-axis orientation, 0.4 mm layer height, and 40 mm/s velocity as the best combination. Applying this combination, a 9.37-MPa maximum strength is the highest value obtained for the material. Additionally, five solid injection molded Timberfill specimens were tested as well and the results compared with the FFF samples. The values of the elastic modulus, elastic limit, and maximum strength of the injected samples were almost twofold of those were obtained for the FFF samples, but the maximum elongation of the injected specimens fell sharply.

Process-Structure-Quality Relationships of Three-Dimensional Printed Poly(Caprolactone)-Hydroxyapatite Scaffolds.

Bone defects are common and, in many cases, challenging to treat. Tissue engineering is an interdisciplinary approach with promising potential for treating bone defects. Within tissue engineering, three-dimensional (3D) printing strategies have emerged as potent tools for scaffold fabrication. However, reproducibility and quality control are critical aspects limiting the translation of 3D printed scaffolds to clinical use, which remain to be addressed. To elucidate the factors that yield to the generation of defects in bioprinting and to achieve reproducible biomaterial printing, the objective of this article is to frame a systematic approach for optimizing and validating 3D printing of poly(caprolactone) (PCL)-hydroxyapatite (HAp) composite scaffolds. We delineate the effect of PCL-to-HAp ratio, print velocity, print temperature, and extrusion pressure on the architectural and mechanical properties of the 3D printed scaffold. Furthermore, we present an in situ image-based monitoring approach to quantify key quality-related aspects of constructs, such as the ability to deposit material consistently and print elementary shapes with fewer flaws. Our results show that small defects generated during the printing process have a significant role in lowering the mechanical properties of 3D printed polymeric scaffolds. In addition, the in vitro osteoinductivity of the fabricated scaffolds is demonstrated. Impact statement Identifying quality control measures is essential in the translation of three-dimensional (3D) printed scaffolds into clinical practice. In this article, we highlighted the importance of selected printing parameters on the quality of the 3D printed scaffolds. We also demonstrated that flaws, such as voids, significantly lower the mechanical properties (compressive modulus) of 3D printed polymeric scaffolds.

Experimental analysis of manufacturing parameters’ effect on the flexural properties of wood-PLA composite parts built through FFF

This paper aims to determine the flexural stiffness and strength of a composite made of a polylactic acid reinforced with wood particles, named commercially as Timberfill, manufactured through fused filament fabrication (FFF). The influence of four factors (layer height, nozzle diameter, fill density, and printing velocity) is studied through an L27Taguchi orthogonal array. The response variables used as output results for an analysis of variance are obtained from a set of four-point bending tests. Results show that the layer height is the most influential parameter on flexural strength, followed by nozzle diameter and infill density, whereas the printing velocity has no significant influence. Ultimately, an optimal parameter set that maximizes the material’s flexural strength is found by combining a 0.2-mm layer height, 0.7-mm nozzle diameter, 75% fill density, and 35-mm/s velocity. The highest flexural resistance achieved experimentally is 47.26 MPa. The statistical results are supported with microscopic photographs of fracture sections, and validated by comparing them with previous studies performed on non-reinforced PLA material, proving that the introduction of wood fibers in PLA matrix reduces the resistance of raw PLA by hindering the cohesion between filaments and generating voids inside it. Lastly, five solid Timberfill specimens manufactured by injection molding were also tested to compare their strength with the additive manufactured samples. Results prove that treating the wood-PLA through additive manufacturing results in an improvement of its resistance and elastic properties, being the Young’s module almost 25% lower than the injected material.

Multi-Response optimization of a light guide plate printing process using Taguchi based super ranking method

Light guide plate (LGP) printing process includes the demand for both illumination and homogeny as it directly influences the quality of liquid crystal display (LCD) display. Various process parameters such as mixed rate of ink, printing velocity, printing pressure etc. critically affect the light refraction that incurs manufacturing cost along with it. Hence, selection of best parametric combination is very much essential to achieve desired outcomes. Thus, this paper shows the effectiveness of Taguchi based super ranking method in finding the best parametric combination of printing velocity, mixed rate of ink, printing pressure, angle of scrapper, and hardness of scrapper in simultaneous optimization of illumination, homogeny, printing ink thickness and VAR of illumination, as responses. Based on the obtained optimal parametric combination, the response values are estimated with the aid of developed regression equations that shows that the derived optimal parametric combination results in better response values by a percentage of 3.93%, 7.45%, 4.34%, and 6.13% for homogeny, illumination, VAR of illumination and printing ink thickness when compared to that with past researchers. Lastly, ANOVA analysis identified mixed rate of ink as the most influential process parameters that significantly affect the response values.

Mechanical Properties of 3D-Printing Polylactic Acid Parts subjected to Bending Stress and Fatigue Testing.

This paper aims to analyse the mechanical properties response of polylactic acid (PLA) parts manufactured through fused filament fabrication. The influence of six manufacturing factors (layer height, filament width, fill density, layer orientation, printing velocity, and infill pattern) on the flexural resistance of PLA specimens is studied through an L27 Taguchi experimental array. Different geometries were tested on a four-point bending machine and on a rotating bending machine. From the first experimental phase, an optimal set of parameters deriving in the highest flexural resistance was determined. The results show that layer orientation is the most influential parameter, followed by layer height, filament width, and printing velocity, whereas the fill density and infill pattern show no significant influence. Finally, the fatigue fracture behaviour is evaluated and compared with that of previous studies’ results, in order to present a comprehensive study of the mechanical properties of the material under different kind of solicitations.

Volumetric Bioprinting of Complex Living-Tissue Constructs within Seconds.

Biofabrication technologies, including stereolithography and extrusion-based printing, are revolutionizing the creation of complex engineered tissues. The current paradigm in bioprinting relies on the additive layer-by-layer deposition and assembly of repetitive building blocks, typically cell-laden hydrogel fibers or voxels, single cells, or cellular aggregates. The scalability of these additive manufacturing technologies is limited by their printing velocity, as lengthy biofabrication processes impair cell functionality. Overcoming such limitations, the volumetric bioprinting of clinically relevant sized, anatomically shaped constructs, in a time frame ranging from seconds to tens of seconds is described. An optical-tomography-inspired printing approach, based on visible light projection, is developed to generate cell-laden tissue constructs with high viability (>85%) from gelatin-based photoresponsive hydrogels. Free-form architectures, difficult to reproduce with conventional printing, are obtained, including anatomically correct trabecular bone models with embedded angiogenic sprouts and meniscal grafts. The latter undergoes maturation in vitro as the bioprinted chondroprogenitor cells synthesize neo-fibrocartilage matrix. Moreover, free-floating structures are generated, as demonstrated by printing functional hydrogel-based ball-and-cage fluidic valves. Volumetric bioprinting permits the creation of geometrically complex, centimeter-scale constructs at an unprecedented printing velocity, opening new avenues for upscaling the production of hydrogel-based constructs and for their application in tissue engineering, regenerative medicine, and soft robotics.

Perfusive and osmotic capabilities of 3D printed hollow tube for fabricating large-scaled muscle scaffold

PurposeThe purpose of this paper is to present a new method for the fabrication of a large-scaled muscle scaffold containing an artificial hollow tube network, which may solve the problems of nutrient supply, oxygen exchange and metabolic waste removal.Design/methodology/approachIn this paper, a ferric chloride structural strength-enhanced sodium alginate hollow tube was used to build the hollow tube network. Gelatin infill was then added to make a large alginate/gelation gel soft tissue scaffold. A pilot experiment was performed and an osmotic test platform was built to study the perfusion and osmotic ability of the 3D printed hollow tube. The essential fabrication parameters (printing velocity and gap) for building the vascular (i.e., hollow tube) network-contained scaffold were investigated. Moreover, cells in culture were spread within the gelation scaffold, and the circulation characteristics of the hollow tube network were studied.FindingsThe printed large-scaled scaffold that contained a ferric chloride structural strength-enhanced sodium alginate hollow tube had good perfusion ability. The osmotic distance of the hollow tube reached 3.7 mm in 8 h in this experiment.Research limitations/implicationsThe osmotic distance was confirmed by perfusing a phenol solution; although it is more reliable to test for cell viability, this will be investigated in our later research.Practical implicationsThis research may provide new insights in the area of tissue engineering for large-scaled vascularized scaffold fabrication.Originality/valueThis paper presents a new method for fabricating large-scaled scaffolds, and the perfusion ability and osmotic distance of a ferric chloride structural strength-enhanced sodium alginate hollow tube are shown.

Nanosilica particles as structural buildup agents for 3D printing with Portland cement pastes

This work presents a comparative study of the effects of nanosilica particles on the fresh state properties of a Portland cement paste designed for 3D printing. Cement pastes were prepared with different solid substitutions of cement by pozzolanic particles and their yield stress was measured after different resting times. Rheological results were used to obtain the rate of thixotropic buildup of each paste, which was used to compute the parameters of an ideal 3D printing process (layer height, time to extrude one layer, and horizontal velocity). Results obtained for nanosilica were compared with results from other three commonly used pozzolanic nano and micro particles (microsilica, metakaolin and nanoclay). All pozzolanic particles studied were capable of increasing both the initial yield stress and the rate of thixotropic buildup of cement paste through different mechanisms; nevertheless, these increases did not translate directly into a more efficient 3D printing process due to the limitations imposed by the need to avoid cold joints between layers. It was concluded that even though nanosilica particles are more efficient thickeners for cement paste than the other particles studied, their effect is constrained by the maximum and minimum printing velocities. Additional chemical accelerators should be considered to reach the full potential of nanosilica as a structural buildup agent.

Control of morphological and electrical properties of flexographic printed electronics through tailored ink rheology

Abstract Functional model inks were formulated and printed using flexography in order to assess the influence of ink extensional elasticity and print velocity on the morphological and electrical properties of printed layers. Increased extensional elasticity and higher print velocity resulted in the printing of more isotropic prints, both morphologically and electronically. Furthermore, a correlation between the prints’ morphological and electrical anisotropy strongly suggests that print uniformity has a considerable influence on functionality and that ink rheology may be used to control such characteristics.