Printing Path Research Articles

Vector field-based curved layer slicing and path planning for multi-axis printing

• A new vector field-based curved layer slicing and printing path planning method is proposed. • A quantitative optimization model is established to find the optimal filament orientation and printing orientation vector fields. • Multi-factors including support-free requiement, collision-free condition, and mechanical performance are considered. • A continuous printing path planning algorithm is developed to reduce the number of nozzle retractions. The emergence of multi-axis printing systems provides a new solution to print complex parts. However, the current process planning methods fail to balance the support-free requirement, the collision-free condition, as well as the mechanical performance at the same time when printing parts with complicated features. This paper proposes a new curved layer slicing and continuous printing path planning method that considers these factors. The proposed method makes use of two mutually orthogonal unit vector fields embedded on the tetrahedral mesh of the part: the filament orientation vector field and the printing orientation vector field, which indicate the filament orientation and the nozzle orientation at each position during the printing process respectively. A quantitative optimization model is established to compute the two optimal unit vector fields. Then a monotonically increasing scalar distance field is generated by integrating along the optimal printing orientation vector field, and the isosurfaces of the distance field can be used to naturally slice the part into curved layers. Finally, at each isosurface, a continuous printing path is planned along the optimal filament orientation field by interpolating isolines of a surface embedded scalar distance field. Both the simulation and physical experiments were conducted to confirms the effectiveness of the proposed method and its advantage over the existing methods in balance different factors including support-free condition, collision-free requirement, and mechanical performance.

Topology optimization of 3D-printed continuous fiber-reinforced composites considering manufacturability

This work presented an orthogonal-element solid orthotropic material with penalization (SOMP) topology optimization method incorporating with 3D printing manufacturability of continuous carbon fiber reinforced composites (CCFRCs), together with a printing path planning strategy. Topological optimizations were performed with a shear beam and a bending beam to demonstrated the effectiveness of the proposed method. The optimal structure was also determined by a traditional density-based SOMP topology optimization method with an offset path planning method for comparison. The results showed that the printing paths of the optimal structure were consistent with the fiber orientation distribution of the optimal results by the proposed orthogonal-element SOMP method. Correspondingly, the stiffness and the stiffness-to-weight ratio of the optimal specimen by the presented orthogonal-element SOMP method were increased by 30.0% and 26.3%, respectively, compared with those by the traditional SOMP method. In addition, the low void contents inside the optimal specimens also confirmed the effectiveness of the proposed orthogonal-element SOMP method with the consideration of the manufacturability.

Direct-write 3D printing of UV-curable composites with continuous carbon fiber

Continuous fiber-reinforced polymer composites, with their superior combinations of high stiffness, high strength, lightweight, and corrosion resistance, have been leading contenders in various applications ranging from aerospace to ground transportation. The integration with 3D printing allows the composite products to be customized quickly and fabricated inexpensively to meet unique specifications. However, the material-process-property relationships of 3D printed thermoset composites with continuous fiber are insufficiently explored in the field. In this work, a cost-effective 3D printing method is developed based on the direct ink writing method to print UV-curable composites reinforced with continuous carbon fiber. During the printing, the fiber tow is impregnated with an acrylate ink inside the printer head and then extruded onto the printer bed, where it is cured upon UV irradiation. The influences of different material and processing variables, such as the resin viscosity, nozzle size, printing speed, and substrate temperature, on the quality and mechanical properties of composites, are investigated. The porosity, stiffness, and strength of printed symmetric laminate are also examined. Finally, the 3D printing of composite structures and the conformal coating of curved surfaces along a defined printing path are demonstrated. The findings reported in this work could contribute to the rapid design and manufacturing of composite components with unprecedented mechanical properties and emerging functionalities for the automotive, defense, and aerospace industries.

Assembled design and compressive performance simulation of mine waterproof wall based on concrete 3D printing

With the increase of mining depth, the deep mine waterproof wall project faces the test of worse construction environment and higher risk of water damage. With the development of intelligent construction technology, it is necessary to introduce concrete 3D printing technology for the construction of coal mine waterproof walls, so as to adapt to more complex construction environment and engineering needs. Through uniaxial compression tests, the compressive properties of 3D printed concrete were tested under different printing methods and force directions. The results showed that the compressive strength of the 3D printed concrete was higher under the conditions of printing path B and loading along the direction parallel to the bonding layer. According to test results, the mine waterproof wall structure based on concrete 3D printing was designed. Then, ABAQUS was used to simulate the compressive strength and deformation of the 3D printed waterproof wall. The results showed that the ultimate load of the 3D printing module was 6.697e4kN and the deformation range was controllable, which meet the engineering requirements. The advantages of 3D printing mine waterproof walls are more flexible in design, faster in manufacturing, and more intelligent in operation. This work provides new ideas for the design and construction of waterproof walls in deep mines.

Ginkgo biloba Ketone Ester Tablets with different release rates prepared by fused deposition modeling 3D printing technology

The present study prepared a new type of Ginkgo biloba ketone ester(GBE50) preparation from polyethylene glycol and croscarmellose sodium with good biocompatibility and a certain viscosity by fused deposition modeling(FDM)-type 3D printing technique. Firstly, a cylindrical 3D printing model with a diameter of 9.00 mm and a height of 4.50 mm was established. Subsequently, the 3D-GBE50 preparations with three paths(concentric, zigzag, and grid), different layer heights, and different filling gaps were designed and prepared after the optimization of the proportions of excipients. The morphology, size, chemical properties, and dissolution activity of the 3D-GBE50 preparations were fully characterized and investigated. The results showed that 3D-GBE50 preparations had smooth appearance, clear texture, standard friability, good thermal stability, and stable chemical properties. Moreover, the printing path, layer height, and filling gap were directly related to the release rate of 3D-GBE50 preparations. The dissolution of 3D-GBE50 tablets with zigzag printing path was the fastest, while the dissolution rates of 3D-GBE50 tablets with concentric circle and grid-shaped printing paths were slower than that of commercially available G. biloba Ketone Ester Tablets. In addition, the dissolution of 3D-GBE50 tablets was faster with higher layer height and wider filling gap. As revealed by the results, th FDM-type 3D printing technique can flexibly regulate the drug release activity via controlling the printing parameters, providing effective ideas and methods for the pre-paration of personalized pharmaceutical preparations.

Toolpath-based design for 3D concrete printing of carbon-efficient architectural structures

The paper presents a data-informed toolpath-based design approach for 3D Concrete Printing (3DCP) for the fabrication of architectural horizontal structures in one continuous printing process. 3DCP has inherent advantages resulting from shaping concrete without formwork and from placing material only where functionally required. However, to date, only a few examples and applications of efficient design solutions through 3DCP exist at the construction scale. Building on the advantages of the technique, the presented work introduces a novel approach for reducing the amount of material employed in structural beams through a high-resolution stress-based optimisation of their material layout in the longitudinal section. The paper presents an innovative workflow for the design and fabrication of 3DCP structures which provides design flexibility by implementing a set of geometric optimisation routines tailored to the concrete extrusion process, and which integrates Finite Element (FE) analysis at multiple stages of the development, for the definition of the printing path, the optimisation of the layer design through speed variation, and the informed placement of the reinforcement bars. The workflow was verified through the design, fabrication and testing of three beam designs which progressively integrates the developed methods. The strength-to-weight ratio of the three designs shows the impact of the proposed workflow, which increases the performance to almost three times between a full beam and the lightest tested beam. The potential for material saving through a design workflow tailored for 3DCP opens to more carbon-efficient and environmental production processes and structures.

Continuous and adaptable printing path based on transfinite mapping for 3D concrete printing

Three-dimensional (3D) concrete printing is an advanced and promising construction method that shows great development potential in the field of construction engineering owing to its highly flexible and intelligent characteristics. The printing path design that is directly related to the 3D printing process is usually limited by the time-dependent rheological properties of concrete composites and the nozzle opening of the print head. Improper path design is liable to disruption, interfacial defects, self-intersection, and even a certain amount of unfilled areas. This paper proposes a flexible and adaptive transfinite mapping method for the path planning of 3D concrete printing by properly mapping a predetermined continuous-type path to the digital model to be printed. This method combines the morphological features of the digital model and path types to achieve a high-quality and high-continuity adaptive printing path. Meanwhile, the relationship between the extrusion process parameters of cementitious composites is experimentally measured and subsequently incorporated into the path design program to realize zero-gap printing by in-process controlling the extrusion parameters. The advantages of this method in adapting to the diversity of morphological features and path types are verified by a set of free-form structures, and the applicability is experimentally validated.

Deposition Offset of Printed Foam Strands in Direct Bubble Writing.

Direct Bubble Writing is a recent technique to print shape-stable 3-dimensional foams from streams of liquid bubbles. These bubbles are ejected from a core-shell nozzle, deposited on the build platform placed at a distance of approximately 10 cm below the nozzle, and photo-polymerized in situ. The bubbles are ejected diagonally, with a vertical velocity component equal to the ejection velocity and a horizontal velocity component equal to the motion of the printhead. Owing to the horizontal velocity component, a discrepancy exists between the nozzle trajectory and the location of the printed strand. This discrepancy can be substantial, as for high printhead velocities (500 mm/s) an offset of 8 mm (in radius) was measured. Here, we model and measure the deviation in bubble deposition location as a function of printhead velocity. The model is experimentally validated by the printing of foam patterns including a straight line, a circle, and sharp corners. The deposition offset is compensated by tuning the print path, enabling the printing of a circular path to the design specifications and printing of sharp corners with improved accuracy. These results are an essential step towards the Direct Bubble Writing of 3-dimensional polymer foam parts with high dimensional accuracy.

Improved Modeling of Kinematics-Induced Geometric Variations in Extrusion-Based Additive Manufacturing Through Between-Printer Transfer Learning

For extrusion-based additive manufacturing, the variation in material deposition can significantly affect printed material distribution, causing infill nonuniformity and defects. These variations are induced by kinematic variations of the printer extruder. Such infill nonuniformity is more significant in an application of collaborative printing systems by which multiple printers’ extrudes co-create the same structure since more accelerate–decelerate kinematic cycles are involved. There is a lack of a quantitative understanding of the impact of printing kinematics on such variations to guide the printing process control. This article deals with the challenge by establishing a mathematical model that quantifies the printing width variations along the printing paths induced by printing speed and acceleration. The model provides vital information for predicting infill pattern nonuniformity and potentially enables using G-code adjustment to compensate for the infill errors in future research. In addition, since the model captures the mechanism of kinematics-induced variations, it provides a way of between-printer knowledge transfer on estimating printing errors. This article further proposes an informative-prior-based transfer learning algorithm to improve the quality prediction model for a printer with limited historical data by leveraging the shared data from interconnected 3-D printers. A case study based on experiments validated the effectiveness of the proposed methodology. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Note to Practitioners</i> —This article quantitatively studies the impact of extruder kinematics on geometric variations and printing quality in extrusion-based 3-D printing processes. The model can help predict the geometric printing quality and related defects, such as overfill or underfill problems given kinematics setup by G-code. This study can expedite the learning process of printing variations induced by kinematics for new printers to set up monitoring and G-code adjustment for process control in the early stage of production when the data are limited. In the long run, such between-printer transfer learning has the potential to enable the transfer learning for interconnected collaborative 3-D printing systems with improved printing efficiency and quality.

3D printing of continuous carbon fibre reinforced powder-based epoxy composites

This paper presents an experimental study on 3D printing of continuous carbon fibre reinforced thermoset epoxy composites. Powder-based solid epoxy was electrostatically flocked on the 1K continuous carbon fibre tow and then melted to fabricate composite filaments. The produced filament was printed using a modified extrusion-based printer which melted and deposited the filament following designed printing paths, to form multilayer preforms with complex geometries. After vacuum bagging and oven curing, high tensile strength (1372.4 MPa) and modulus (98.2 GPa) were obtained in the fibre direction due to the good wettability of epoxy and the consequent high fibre volume fraction (56%). The tensile tests of open-hole composites were also conducted, in which the sample with designed stress-lines fibre paths was seen to improve the ultimate strength by 95% compared with the mechanically-drilled sample. Other case studies, such as a spanner and a lattice structure, further demonstrated the design freedom of produced filaments for complex geometries.

Development of an architecture-property model for triply periodic minimal surface structures and validation using material extrusion additive manufacturing with polyetheretherketone (PEEK)

Additively manufactured structures designed from triply periodic minimal surfaces (TPMSs) have been receiving attention for their potential uses in the medical, aerospace, and automobile industries. Understanding how these complex geometries can be designed to achieve particular architectural and mechanical properties is essential for tuning their function to certain applications. In this study, we created design tools for visualizing the interplay between TPMS design parameters and resulting architecture and aimed to validate a model of the relationship between structure architecture and Young's modulus. A custom MATLAB script was written to analyze structural properties for families of Schoen gyroid and Schwarz diamond structures, and a numerical homogenization scheme was performed to predict the effective Young's moduli of the structures based on their architecture. Our modeling methods were validated experimentally with polyetheretherketone (PEEK) structures created using material extrusion additive manufacturing. The architectural characteristics of the structures were determined using micro-computed tomography, and compression testing was performed to determine yield strength and Young's modulus. Two different initial build orientations were tested to determine the behavior both perpendicular and parallel to the layer deposition direction (referred to as z-direction and xy-direction, respectively). The z-direction Young's modulus ranged from 289.7 to 557.5 MPa and yield strength ranged from 10.12 to 20.3 MPa. For the xy-direction, Young's modulus ranged from 133.8 to 416.4 MPa and yield strength ranged from 3.8 to 12.2 MPa. For each initial build orientation, the mechanical properties were found to decrease with increasing porosity, and failure occurred due to both strut bending and interlayer debonding. The mechanical properties predicted by the modeling agreed with the values found for z-direction samples (difference 2–11%) but less so for xy-direction samples (difference 27–62%) due to weak interlayer bonding and print path irregularities. Ultimately, the findings presented here provide better understanding of the range of properties achievable for additive manufacturing of PEEK and encouraging results for a TPMS architecture-property model.

Orientation behavior and thermal conductivity of liquid crystal polymer composites based on Three-Dimensional printing

Liquid Crystal Polymer (LCP) / hexagonal boron nitride (BN) composites are manufactured bythree-dimensional (3D)printing approach. The results confirm that 3D printing can build up LCP bulk material with highly aligned nematic domains along the printing path. Also, BN can be orderly arrangement in matrix, exhibiting the same oriented direction as LCP molecules. The degree of orientation of BN is relevant to its lateral dimension. BN with a lateral size of 50 um in LCP matrix has a much higher degree of orientation compared with BN with a lateral size of 0.5 um and 5um. The well-ordered arrangement of BN and aligned LCP result that all of the printed sample has high thermal conductivity. The printed neat LCP bulk has a thermal conductivity 0.74 W m−1 K−1 parallel to the printing path direction, being filled with 20% mass fraction of BN, it can reach to 1.77 W m−1 K−1.

Thermal conductivity of 3D printed concrete with recycled fine aggregate composite phase change materials

In this study, a novel shape-stabilization phase change materials (PCM) for 3D printed concrete have been generated by impregnating paraffin into the recycled fine aggregates. Based on both steady state hot plate method and transient hotwire method, the impact of printing parameters, including printing layers, path, extrusion rate and materials on thermal conductivity of the 3D printed concrete was investigated. The relationship among thermal conductivity, dry density and porosity of the 3D printed concrete was analyzed. The results showed that recycled fine aggregates can be successfully used as a support material for paraffin. The melting temperature and latent heat is 36.52 °C and 40.65 J/g, respectively. The thermal conductivity of 3D printed concrete was significantly influenced by the multi-layer structure and with thermal anisotropy. Under the same size, density class or mix design, the thermal conductivity of the 3D printed concrete can reach up to 31.04% lower than that of mould cast concrete. The results also indicate that impregnating paraffin into the recycled fine aggregate can improve its thermal properties so as to upgrade the overall performance of 3D printed concrete.

2D stationary computational printing of cement-based pastes

An efficient computational strategy has been developed for modeling additively manufactured cement-based materials which captures the dynamics of 2D slices at a stationary location along a print path, i.e. 2-D stationary computation printing (2D-SCP). Flow rheometry was used to experimentally establish the fluid properties of cement pastes of various water contents and to calibrate the computational model. The model was validated using mini conical slump flow tests. A hollow cylinder geometry was used as a benchmark for printed objects. Deformations and rates of deformation for the free-surface flow were then simulated for like 2-D geometries. The relative importance of yield stress and structuration rates were quantified by comparing the 2D-SCP model outcomes with cut cross-sections of the 3D printed cylinders. Good agreement between printed objects and model outcomes were found in all cases. Quantification of print fidelity shows that 2D-SCP is a strong predictor of actual printed object outcomes.

Bending properties and failure behavior of 3D printed fiber reinforced resin T‐beam

AbstractFiber‐reinforced resin T‐beams have a wide range of applications. The forming of T‐beams based on the fused deposition process provides a new method for its manufacture. This paper studied the key process parameters of 3D printing continuous fiber and short fiber reinforced resin T‐beams. The results show that continuous fiber reinforced resin T‐beams with similar fiber volume fractions have better bending performance than shorter fiber reinforced resin T‐beams. When the printing layer thickness is 0.7 mm, 0.8 mm and 0.9 mm, the flexural strength and modulus of the continuous fiber reinforced resin T‐beam are obviously lower with the increase of the layer thickness. Under the printing path 0°, ±45°, 90°, the short fiber reinforced resin T‐beam with the 0°path has the highest flexural strength and modulus. Furthermore, T‐beam with different printing path have significantly different bending failure behavior. The work provided a new approach to the production of beam structures of the actual engineering application.

Effects of printing paths and recycled fines on drying shrinkage of 3D printed mortar

3D printing process poses great impacts on the properties of mortar, especially on the shrinkage behavior of 3D printed mortar (3DPM) prepared with recycled fine aggregate (RFA) and recycled powder (RP). This study focuses on the effects of printing paths on the flowability and the drying shrinkage of 3DPM. RFA and RP, together with their contents, are used as variables in 3DPM. The results show that the flow loss of mortar during the first 30 mins increased with the incorporation of recycled fines due to the high water-absorption of RFA and the low hydration reactivity of RP. The drying shrinkage development of 3DPM was higher than that of cast mortar during the first 28 days, but exhibited a deceleration in shrinkage increasing rate after 28 days. Printing path showed a limited effect on the mass loss of 3DPM during the test period, but had significant impacts on the drying shrinkage and the shrinkage development trend. An increase in drying shrinkage of 3DPM was caused by 50 ∼ 100% RFA replacement (29.1 ∼ 57.9% in 60 days), while 10 ∼ 20% RP content decreased the drying shrinkage of 3DPM (3.3 ∼ 12.4% in 60 days). Additionally, the incorporation of recycled fines delayed the development of 3DPM drying shrinkage.

Tribological properties of flexible composite surfaces through direct ink writing for durable wearing devices

Polydimethylsiloxane (PDMS), as a polymer material with excellent mechanical properties and flexibility, is widely used in flexible wearable devices, soft robots and other fields. Commonly, the Mold-flipping is used to produce PDMS based samples, while it is time-consuming and impractical for the large-scale fabrication. With the additive manufacturing, printing pastes can be freely configured thanks to direct ink writing (DIW) technology, enabling rapid and high precision manufacturing. Herein, we have improved the rheology of Sylgard-184 by adding crosslinkers and silica nanoparticles to make it printable. By adjusting the printing path, flexible surfaces with textures were created. Ball-on-disc dry friction experiments were carried out on the specimens. Results show that the texture produced by the print path can effectively reduce the coefficient of friction (COF) compared to samples produced by the conventional molding. When the print path is at 60° to the sliding direction, COFs for samples are reduced by 23.2% to 32.9%. Our findings provide a new strategy for preparing flexible and wearable devices through significantly enhancing the wear resistance of substantiable usage and prolonging the lifespan.

Integrated CAx-Chain for the Production of Subperiosteal Implants

In recent years, the development of modern technologies, especially that of additive manufacturing, has led to the renewal and renaissance of a subperiosteal implant. The purpose of the development was to elaborate a reliable CAx process chain to produce a subperiosteal implant with connections corresponding accurately to the designed ones by the combination of additive manufacturing and CNC milling. First part of the CAx chain consists of CT scanning, segmentation of the DICOM file to a 3D model, 3D analysis, planning, and design of the implant. A key element to achieve an absolute correspondence between the final implant connection and the planned design is the overlap between the 3D printed semi-product and the subsequent milling phase. Therefore, in the second part of the CAx chain, software developed primarily for abutments and bars was applied. It generates a modified design consisting of a centering system that makes it possible to position the implant inside the milling machine, and the implant with modified connection parts. This new design serves as the basis for the generation of the printing path for the metal 3D printer and the milling path for the milling machine. The integrated CAx-chain makes possible the production of the subperiosteal implant with accurate implant connections. The CAx-chain reduces manual interactions and adjustment requirements by adopting a unified system of referencing. The elaborated CAx chain can successfully be used for the preparation of accurate subperiosteal implants.

Infrared Heating for Rapid and Localized Shape Transformations of Additively Manufactured Polymer Parts

Four-dimensional (4D) printing is an advanced application of additive manufacturing which enables additional shape transformations over time in response to external stimuli. For appropriate shape transformation, dedicated materials such as shape memory polymers or 3D printers supporting multi-material printing have been used. Recently, a facile 4D printing method was developed which used a fused filament fabrication type 3D printer and a plain thermoplastic filament. This method used the anisotropic thermal deformation of the FFF-printed part to intentionally impose anisotropy by programming orthogonal printing paths, which resulted in thermoresponsive shape transformation upon a thermal stimulation. While the previous studies used convective heating as the thermal stimulus and thus required a long heating time of more than 10 min, this study uses an infrared (IR) heating to enable rapid thermoresponsive shape transformation. An infrared heating system was developed which included an optical focusing unit, a masking unit and a movable heating stage. To investigate the speed of shape transformation, IR heating was performed on a rectangular strip (60 × 6 × 1.6 mm) and the relevant shape transformation time was compared with the previous convective heating result. The shape transformation proceeded rapidly, and after 70 s formed a fully-closed circular shape, corresponding to the 1/10 reduction compared with the convection type heating (more than 13 min). The IR heating was further applied to 2D-to-3D shape transformations of 2D star-shape and flower-shape specimens. For each specimen, a profiled mask was used to selectively irradiate IR on predefined regions and thus to localize the relevant thermoresponsive shape transformation. The global and local IR irradiations were then compared in terms of heating capability and the variability in shape transformations.

Adhesion Analysis between Concrete Layers Generated by a 3D Printing

On 3DPC, the layers are made through a process where the cement mortar is extruded through a nozzle that follows a predetermined circuit. The classic method of formwork generates a uniform element, while 3D printing generates a non-homogeneous element. Such an innovative process offers new horizons to explore. One of these is the cohesion between the two printed layers and all their mechanical properties. The objective of this work is to study the shear action of two printed layers. To understand the mechanisms, the tested specimens were made in four different ways. The first using a formwork made for the occasion. The second way involves the creation of a printed specimen with a continuous printing path. The third has a time interval of about an hour between the second and third layer. The fourth also has an interval of one hour between the same layers with the addition of a special additive mortar used for the casting recovery. The results obtained reflect on the differences between different specimens and regulations. The differences between the specimens that are studied concern the single printed specimens, the formwork specimens and the printed ones. At a regulatory level, the results of the printed specimens are compared with the regulations concerning the same tests carried out on specimens made of masonry and mortar.