Printing Path Research Articles

Stress-cognizant 3D printing of free-form concrete structures

3D printing enables engineers to design and manufacture geometrically complex structures. As 3D printing technology affords design freedom, it also brings along new challenges. One common property of classical 3D printing is the anisotropy arising from the filament-wise 3D printing process. This anisotropy reduces the load bearing capabilities of the 3D printed part when loaded in its weaker axes, that is the directions orthogonal to the filament. Conversely, by designing the 3D printing path through analyses of its mechanical constraints, the 3D printed part may be strengthened and printed such that it carries the majority of the load in its strongest axis, parallel to the filament (T1), thereby increasing its load-carrying capabilities. We experimentally investigated this idea by designing and printing several concrete samples following two strategies: (i) the classical strategy consisting of parallel rectilinear paths irrespective of the load distribution, and (ii) our proposed strategy consisting of paths that are as much parallel as possible to the principal stress lines. We then subjected the samples to mechanical testing. The test results confirmed that the proposed printing strategy significantly improved mechanical characteristics. Cracking patterns were also observed and discussed.

A dual nozzle 3D printing system for super soft composite hydrogels

Due to their inability to sustain their own weight, 3D printing materials as soft as human tissues is challenging. Hereby we describe the development of an extrusion additive manufacturing (AM) machine able to 3D print super soft hydrogels with micro-scale precision. By designing and integrating new subsystems into a conventional extrusion-based 3D printer, we obtained hardware that encompasses a range of new capabilities. In particular, we integrated a heated dual nozzle extrusion system and a cooling platform in the new system. In addition, we altered the electronics and software of the 3D printer to ensure fully automatized procedures are delivered by the 3D printing device, and super-soft tissue mimicking parts are produced. With regards to the electronics, we added new devices to control the temperature of the extrusion system. As for the software, the firmware of the conventional 3D printer was changed and modified to allow for the flow rate control of the ink, thus eliminating overflows in sections of the printing path where the direction/speed changes sharply.

Porosity in multi-axis material extrusion of short-fibre composites

Purpose This study aims to investigate the relationship between part porosity and mechanical properties of short-fibre reinforced polylactic acid printed via multi-axis material extrusion (MAMEX) to establish guidelines for optimal process configurations. Design/methodology/approach Material properties graphs provide the basis for studying the relationship between porosity and mechanical behaviour. Using the correlations found in this study, the way to improve printing strategies and filament properties can be deducted directly from an analysis of the print path and the final influence on mechanical performance. Findings Some commercial brands of short-fibre reinforced filament present inherent porosity that weakens the mechanical behaviour of MAMEX components. Originality/value Low-cost MAMEX allows the production of components that do not present anisotropic behaviour and are mechanically optimised through the alignment of the filaments along with internal stresses. This paper also addresses the effects of multi-axis deposition strategies on the resulting porosity and proposes improvements to reduce residual porosity, thus increasing the mechanical performance in the future.

Stress-oriented 3D printing path optimization based on image processing algorithms for reinforced load-bearing parts

Fibre reinforced filament fabrication is a potential additive manufacturing method for certain load-bearing parts in aerospace and automotive products. In current practice, printing paths are planned from part geometry without considering loading conditions. This paper presents a new method for optimizing printing paths to align with the principal stress field of parts in use. Because of the powerful processing capabilities, for the first time grayscale image was adopted to represent the irregular vector field, which can be robustly processed into sub-regions for generating regular printing paths. Preliminary bending test achieved promising increase in tensile strength compared with conventional methods.

Approach to an optimized printing path for additive manufacturing in construction utilizing FEM modeling

Based on experiences with common additive manufacturing processes, the application in the construction industry opens up new design freedoms and cost-effective production of complex structures. However, the time-dependent yield strength of fresh concrete leads to deformations of underlying layers during the printing process, especially when using conventional path planning methods in combination with material extrusion or jetting methods. This paper presents a finite element model based approach to minimize the resulting deviations from the target geometry by iteratively adjusting the process parameters according to simulated deformations. To achieve more detailed modelling, the utilized finite element model is derived from the printing path instead of the CAD data.

Real-time Process Authentication for Additive Manufacturing Processes based on In-situ Video Analysis

Additive manufacturing (AM) processes are subject to cyber-physical attacks during all the three stages including design, slicing, and manufacturing phases. In-situ process authentication is crucial for AM to ensure that the manufacturing is performed as intended. Since most of the cyber-physical attacks aiming to alter AM processes can be manifested in the change of printing path, an in-situ optical imaging system is capable of detecting alteration in printing path in real time through texture analysis. This will prevent catastrophic geometric changes and mechanical property compromises in the AM parts, and hence improving the AM process security. In this paper, a new part authentication framework is proposed by leveraging layer-wise in-situ videos. The distribution of the segmented textures’ geometric features is extracted from the layer-wise videos, and the multilinear principal component analysis (MPCA) algorithm is used to extract low-dimensional features from the joint distribution of geometric features. A case study based on a fused filament fabrication (FFF) process is used to validate the proposed framework.

Vector field-based 3D print path generation for continuous fiber composites

Vector field-based 3D print path generation for continuous fiber composites

Multi-Axis Support-Free Printing of Freeform Parts with Lattice Infill Structures

In additive manufacturing, infill structures are commonly used to reduce the weight and cost of a solid part. Currently, most infill structure generation methods are based on the conventional 2.5-axis printing configuration, which, although able to satisfy the self-supporting condition on the infills, suffer from the well-known stair-case effect on the finished surface and the need of extensive support for overhang features. In this paper, based on the emerging continuous multi-axis printing configuration, we present a new lattice infill structure generation algorithm, which is able to achieve the self-supporting condition for both the infills and the boundary surface of the part. The algorithm critically relies on the use of three mutually orthogonal geodesic distance fields that are embedded in the tetrahedral mesh of the solid model. The intersection between the iso-geodesic distance surfaces of these three geodesic distance fields naturally forms the desired lattice of infill structure, while the density of the infills can be conveniently controlled by adjusting the iso-values. The lattice infill pattern in each curved slicing layer is trimmed to conform to an Eulerian graph so to generate a continuous printing path, which can effectively reduce the retractions of the nozzle during the printing process. In addition, to cater to the collision-free requirement and to improve the printing efficiency, we also propose a printing sequence optimization algorithm for determining a collision-free order of printing of the connected lattice infills, which seeks to reduce the air-move length of the nozzle. Ample experiments in both computer simulation and physical printing are performed, and the results give a preliminary confirmation of the advantages of our methodology.

Mechanical properties and shape memory effect of 4D printed cellular structure composite with a novel continuous fiber-reinforced printing path

Herein, a printing strategy was proposed and expended, which allows fabricating diverse geometries of cellular continuous fiber-reinforced composites (CFRCs) with fiber distribution and interlacement in the cellular structure uniformly. A class of printed triangle-filled cellular structure composites was prepared to present the detail of the printing strategy. The effects of printing and structural parameters on the mechanical properties, as well as shape memory performance of printed CFRCs, were studied precisely, and thereafter, a Finite Element (FE) model was developed on the basis of the printing path to stimulate and analyze the tensile process. Experimental results showed that introducing only 3.8% fiber content into the composite can significantly improve the tensile strength by more than 300%. An increment of cell length was capable of strengthening tensile features compellingly due to changing orientation and alignment degree of fiber in the structure. By contrast, sizing the cell length and embedding further fiber have represented a reverse pattern against the composite's shape recovery ratio, which witnessed an adverse impact on shape-changing materials. A conclusion was given that the mechanical properties and shape memory effect of the 3D-printed continuous fiber-reinforced composite can be optimized by adjusting the geometric parameters and fiber content.

Load-dependent path planning method for 3D printing of continuous fiber reinforced plastics

3D printing, to print continuous fiber reinforced plastics (CFRPs) has advantages of manufacturing complex shape and short production cycle. Due to anisotropic mechanical properties of continuous fibers, the paving direction of the fibers determines the mechanical strengths of the printed CFRPs. In this paper, a novel load-dependent path planning (LPP) method has been proposed to generate printing path for CFRPs, which exactly follows the load transmission path of the parts and could provide higher mechanical properties. A topology optimization method is applied to simplify the original disordered load distribution. In the developed Stress Vector Tracing (SVT) algorithm, the printing paths are generated along the load transmission path with the variable spacing of adjacent paths. The LPP method has been compared with the state-of-the-art printing path planning method for continuous fibers and shown better load-bearing and printability.

Tensile and Bending Strength Improvements in PEEK Parts Using Fused Deposition Modelling 3D Printing Considering Multi-Factor Coupling.

Compared with laser-based 3D printing, fused deposition modelling (FDM) 3D printing technology is simple and safe to operate and has a low cost and high material utilization rate; thus, it is widely used. In order to promote the application of FDM 3D printing, poly-ether-ether-ketone (PEEK) was used as a printing material to explore the effect of multi-factor coupling such as different printing temperatures, printing directions, printing paths, and layer thicknesses on the tensile strength, bending strength, crystallinity, and grain size of FDM printed PEEK parts. The aim was to improve the mechanical properties of the 3D printed PEEK parts and achieve the same performance as the injection molded counterparts. The results show that when the thickness of the printed layer is 0.1 mm and the printing path is 180° horizontally at 525 °C, the tensile strength of the sample reaches 87.34 MPa, and the elongation reaches 38%, which basically exceeds the tensile properties of PEEK printed parts reported in previous studies and is consistent with the tensile properties of PEEK injection molded parts. When the thickness of the printed layer is 0.3 mm, the printing path is 45°, and with vertical printing direction at a printing temperature of 525 °C, the bending strength of the sample reaches 159.2 MPa, which exceeds the bending performance of injection molded parts by 20%. It was also found that the greater the tensile strength of the printed specimen, the more uniform the size of each grain, and the higher the crystallinity of the material. The highest crystallinity exceeded 30%, which reached the crystallinity of injection molded parts.

Analyzing the effects of 3D printing process per se on the microstructure and mechanical properties of cereal food products

3D Food Printing has gaining interest to create food with personalized properties. In order to customize the texture it is necessary to explore whether and how 3D printing process per se has consequences on the mechanical features. As test case, a cubical cereal-based structure was manufactured by traditional processing and 3D printing. Microstructure properties and mechanical attributes were analyzed. Here we show that 3D printing clearly affects the microstructure generating bigger pores, less in number and like-round in shape. Also, we have observed that the positions of the pores are greatly driven by the printing movements. These features significantly affect the mechanical properties of 3D samples showing high hardness, chewiness and cohesiveness. The obtained data have been linked and interpreted on the basis of three main key-points: 1. the printing path; 2. the imbalance between speed printing and extrusion rate; 3. the compression of the food formula in the extrusion system. These findings should be considered for creating food with innovative texture perceptions.Industrial relevance: The creation of 3D printed food with programmed texture has the ambitions of getting personalized properties improving industry competitiveness by novel texture perceptions and also helping to mitigate swallowing or mastication problems of vulnerable peoples. Here we show that 3D Printing process per se – intrinsically – modifies the morphology and the distribution of pores in 3D structure thereby affecting the texture of cereal-based snacks. All these because pores generation is not ‘randomly’ distributed as for traditional manufacturing methods but driven by printing movements previously planned during the slicing of digital model. With the aim to get personalized food texture the intimate relationship between the movements of printing and the food texture shall taken into account by interested industries and producers.

Calculating Filament Feed in the Fused Deposition Modeling Process to Correctly Print Continuous Fiber Composites in Curved Paths.

Fused deposition modeling (FDM) is a popular additive manufacturing (AM) method that has attracted the attention of various industries due to its simplicity, cheapness, ability to produce complex geometric shapes, and high production speed. One of the effective parameters in this process is the filament feed presented in the production G-code. The filament feed is calculated according to the layer height, the extrusion width, and the length of the printing path. All required motion paths and filling patterns created by commercial software are a set of straight lines or circular arcs placed next to each other at a fixed distance. In special curved paths, the distance of adjacent paths is not equal at different points, and due to the weakness of common commercial software, it is not possible to create curved paths for proper printing. The creation of a special computer code that can be used to make various functions of curved paths was investigated in this study. The filament feed parameter was also studied in detail. Next, by introducing a correction technique, the filament feed was changed on the curved path to uniformly distribute the polymer material. Variable-stiffness composite samples consisting of curved fibers can be produced with the proposed method. The high quality of the printed samples confirms the suggested code and technique.

A potential field based multi-axis printing path generation algorithm

ABSTRACT Robotic multi-axis curved layer additive manufacturing has drawn more attention recently owing to its unique ability of printing complex shapes while avoiding the stair-step effect and the usage of support structure. However, as the robotic manipulator is an open serial structure and the printing layer now is no longer planar but a free-form surface, the shape and pattern of a printing path now have a huge impact on the mechanical behaviour of the printer – an arbitrarily planned printing path could cause severe angular fluctuations of the joints of the robotic manipulator which in turn would lead to poor printing quality and prolonged printing time. In this paper, a potential field based algorithm is proposed for automatically generating a printing path for printing an arbitrary free-form curved layer on a robotic multi-axis printer. By considering both the printing efficiency and the joints’ kinematics, the potential field identifies the local optimal feed direction on the curved layer. Then, by employing the iso-cusp height expansion method, a printing path is generated to best fit this potential field. Both computer simulations and physical printing experiments are carried out to assess the proposed methodologies and the results give a positive confirmation on their advantages.

Improved co-scheduling of multi-layer printing path scanning for collaborative additive manufacturing

Additive manufacturing processes, especially those based on fused filament fabrication mechanism, have a low productivity. One solution to this problem is to adopt a collaborative additive manufacturing system that employs multiple printers/extruders working simultaneously to improve productivity by reducing the process makespan. However, very limited research is available to address the major challenges in the co-scheduling of printing path scanning for different extruders. Existing studies lack: (i) a consideration of the impact of sub-path partitions and simultaneous printing of multiple layers on the multi-extruder printing makespan; and (ii) efficient algorithms to deal with the multiple decision-making involved. This article develops an improved method by first breaking down printing paths on different printing layers into sub-paths and assigning these generated sub-paths to different extruders. A mathematical model is formulated for the co-scheduling problem, and a hybrid algorithm with sequential solution procedures integrating an evolutionary algorithm and a heuristic is customized to multiple decision-making in the co-scheduling for collaborative printing. The performance was compared with the most recent research, and the results demonstrated further makespan reduction when sub-path partition or the simultaneous printing of multiple layers is considered. This article discusses the impacts of process setups on makespan reduction, providing a quantitative tool for guiding process development.

Development of a new additive manufacturing platform for direct freeform 3D printing of intrinsically curved flexible membranes

The wearable technology market has been expanding from wearable medical devices for non-invasive continuous monitoring of patient vital signs to wearable devices for tracking fitness activities that any person can access. Regardless of their form or function, desirable characteristics of wearable devices are the ability to be flexible, conformal, and easily attachable to the human body. However, as the human body is intrinsically curved and irregular, flat devices often have poor interfacial adhesion with the human body. This often leads to interfacial delamination and eventual detachment of the device. Therefore, a new additive manufacturing (AM) platform, a direct freeform 3D printing process (DF3DP), is proposed to allow direct construction of intrinsically curved 3D surfaces during the material deposition phase without the need for any pre-shaped supporting molds or templates. This 3D freeform printing process involves a supporting matrix made up of calcium alginate microgels, printing material made from silicone ink, and freeform printing paths derived from customized G-codes that conform exactly to the scanned human surface profile. Curved meshes mimicking the human elbow were used as a demonstration. A static contact stability test showed that the printed 3D silicone mesh was highly conformal to the model elbow surface as compared to a 2D flat mesh. A dynamic contact stability test was also conducted by subjecting both meshes to 100 cycles of mechanical flexion and extension, proving that intrinsically curved surfaces can provide better contact stability for complex human body surfaces undergoing motion than can flat surfaces. These results have proven that intrinsically curved membranes or structures fabricated by DF3DP can reduce the interfacial shear stress and occurrence of cracks and delamination while maintaining structural integrity and stability during use without compromising the comfort of the users. Our approach can resolve interfacial issues in flexible substrates and has great potential for epidermal devices or soft robotics via its long-term sustainable performance.

Melt Electrowritten In Vitro Radial Device to Study Cell Growth and Migration.

The development of in vitro assays for 3D microenvironments is essential for understanding cell migration processes. A 3D-printed in vitro competitive radial device is developed to identify preferred Matrigel concentration for glioblastoma migration. Melt electrowriting (MEW) is used to fabricate the structural device with defined and intricate radial structures that are filled with Matrigel. Controlling the printing path is necessary to account for the distance lag in the molten jet, the applied electric field, and the continuous direct-writing nature of MEW. Circular printing below a diameter threshold results in substantial inward tilting of the MEW fiber wall. An eight-chamber radial device with a diameter of 9.4 mm is printed. Four different concentrations of Matrigel are dispensed into the radial chambers. Glioblastoma cells are seeded into the center and grow into all chambers within 8 days. The cell spreading area demonstrates that 6 and 8 mg mL-1 of Matrigel are preferred over 2 and 4 mg mL-1 . Furthermore, topographical cues via the MEW fiber wall are observed to promote migration even further away from the cell seeding depot. Previous studies implement MEW to fabricate cell invasive scaffolds whereas here it is applied to 3D-print in vitro tools to study cell migration.

A postprocessing and path optimization based on nonlinear error for multijoint industrial robot-based 3D printing

Multijoint industrial robots can be used for 3D printing to manufacture the complex freeform surfaces. The postprocessing is the basis of the precise printing. Due to the nonlinear motion of the rotational joint, nonlinear error is inevitable in multijoint industrial robots. In this article, the postprocessing and the path optimization based on the nonlinear errors are proposed to improve the accuracy of the multijoint industrial robots-based 3D printing. Firstly, the kinematics of the multijoint industrial robot for 3D printing is analyzed briefly based on product of exponential (POE) theory by considering the structure parameters. All possible groups of joint angles for one tool pose in the joint range are obtained in the inverse kinematics. Secondly, the nonlinear error evaluation based on the interpolation is derived according to the kinematics. The nonlinear error of one numerical control (NC) code or one tool pose is obtained. The principle of minimum nonlinear error of joint angle is proposed to select the appropriate solution of joint angle for the postprocessing. Thirdly, a path smoothing method by inserting new tool poses adaptively is proposed to reduce the nonlinear error of the whole printing path. The smooth level in the smoothing is proposed to avoid the endless insertion near the singular area. Finally, simulation and experiments are carried out to testify the effectiveness of the proposed postprocessing and path optimization method.

Effects of infill characteristics and strain rate on the deformation and failure properties of additively manufactured polyamide-based composite structures

Additive manufacturing is one of the advanced manufacturing methods for producing cellular composites with desired infill patterns. Previous studies of the influence of the printing infill characteristics on the material mechanical properties have mainly focused on stiffness and strength. Limited work revealed that printing infill patterns also influenced the plastic deformation and failure mechanisms of composite structures. The present work aimed to systematically investigate the effects of infill parameters and tensile strain rate on the elastoplastic deformation and failure behaviors of polyamide-based composite structures, built by fused deposition modeling (FDM) process. The mechanical investigations were conducted combined with the capture of morphological evolution. The effects of infill pattern, infill density, and tensile strain rate on the mechanical properties and relative energy absorption of the composite structures were analyzed. The infill pattern was one of the deterministic factors for the deformation and failure modes, mainly due to the defects caused by the printing path. Besides, higher infill densities produced more imperfections, causing lower elongation at break of the composite structures. However, the strain rate has a limited influence on deformation and failure properties for the composite structures.

A skeleton-based process planning framework for support-free 3+2-axis printing of multi-branch freeform parts

Continuous 3+2-axis additive manufacturing (AM) is an emerging AM technology that overcomes the signature problems of the need of support structures and the staircase effect of the traditional 3-axis AM. This paper presents a novel process planning framework for automatically generating a multi-axis support-free printing path for continuous 3+2-axis AM of an arbitrary freeform part. The framework is based on the geometric processing of skeletonization and decomposition and is particularly suitable for a part with distinct multiple trunk-branch structures. The physical printing experimental results carried out by the authors indicate that the proposed framework has performed well and fabricated some challenging models with large overhangs and twisty spatial topologies.