Multi-axis Additive Manufacturing Research Articles

Regularization in space–time topology optimization for additive manufacturing

In additive manufacturing, the fabrication sequence has a large influence on the quality of manufactured components. While planning of the fabrication sequence is typically performed after the component has been designed, recent developments have demonstrated the possibility and benefits of simultaneous optimization of both the structural layout and the corresponding fabrication sequence. This is particularly relevant in multi-axis additive manufacturing, where rotational motion offers enhanced flexibility compared to planar fabrication. The simultaneous optimization approach, called space–time topology optimization, introduces a pseudo-time field to encode the manufacturing process order, alongside a pseudo-density field representing the structural layout. To comply with manufacturing principles, the pseudo-time field needs to be monotonic, i.e., free of local minima. However, explicitly formulated constraints proposed in prior work are not always effective, particularly for complex structural layouts that commonly result from topology optimization.In this paper, we introduce a novel method to regularize the pseudo-time field in space–time topology optimization. We conceptualize the monotonic additive manufacturing process as a virtual heat conduction process starting from the surface upon which a component is constructed layer by layer. The virtual temperature field, which shall not be confused with the actual temperature field during manufacturing, serves as an analogy for encoding the fabrication sequence. In this new formulation, we use local virtual heat conductivity coefficients as optimization variables to steer the temperature field and, consequently, the fabrication sequence. The virtual temperature field is inherently free of local minima due to the physics it resembles. We numerically validate the effectiveness of this regularization in space–time topology optimization under process-dependent loads, including gravity and thermomechanical loads.

Topological awareness towards collision-free multi-axis curved layer additive manufacturing

We present a topology-aware computational framework that enables global collision-free and support-structure-free material extrusion for curved layer multi-axis printing of a range of high-genus and simply connected models. The nature of multi-axis additive manufacturing facilitates continuous variation of build direction, which paves the way for numerous approaches of geometry-based curved layer design. However, due to unawareness of global topological features, prevention of collision between the printer nozzle and the workpiece can either remain uncertain or demand for exhaustive algorithmic approaches, depending on the topological and geometrical complexity of a given mesh model. In this paper, we present a topological analysis framework that draws inspiration from the concepts of Reeb graph and Morse theory, to distinguish between collision-prone and collision-free regions of mesh models. We provide an exact definition for global collision-inducing features in regions of risk and optimise the nozzle orientation vector field to avoid global collisions whilst adhering to the overhang angle constraints. A new shape analysis method is then proposed to find the model orientation which maximises the manufacturability of bifurcating simply connected models. To validate our algorithmic framework, several high-genus and bifurcating simply connected models are printed using a robotic multi-axis printer. The experimental results demonstrate the feasibility and effectiveness of our framework for minimising global collisions in multi-axis curved layer additive manufacturing for a range of mesh models.

Exceptional mechanical performance by spatial printing with continuous fiber: Curved slicing, toolpath generation and physical verification

This work explores a spatial printing method to fabricate continuous fiber-reinforced thermoplastic composites (CFRTPCs), which can achieve exceptional mechanical performance. For models giving complex 3D stress distribution under loads, typical planar-layer based fiber placement usually fails to provide sufficient reinforcement due to their orientations being constrained to planes. The effectiveness of fiber reinforcement could be maximized by using multi-axis additive manufacturing (MAAM) to better control the orientation of continuous fibers in 3D-printed composites. Here, we propose a computational approach to generate 3D toolpaths that satisfy two major reinforcement objectives: (1) following the maximal stress directions in critical regions and (2) connecting multiple load-bearing regions by continuous fibers. Principal stress lines are first extracted in an input solid model to identify critical regions. Curved layers aligned with maximal stresses in these critical regions are generated by computing an optimized scalar field and extracting its iso-surfaces. Then, topological analysis and operations are applied to each curved layer to generate a computational domain that preserves fiber continuity between load-bearing regions. Lastly, continuous fiber toolpaths aligned with maximal stresses are generated on each surface layer by computing an optimized scalar field and extracting its iso-curves. A hardware system with dual robotic arms is employed to conduct the physical MAAM tasks depositing polymer or fiber reinforced polymer composite materials by applying a force normal to the extrusion plane to aid consolidation. When comparing to planar-layer based printing results in tension, up to 644% failure load and 240% stiffness are observed on shapes fabricated by our spatial printing method. We demonstrate the versatility of our approach through various complex load cases which demonstrate their successful implementation of continuous fiber printing in 3D.

Spherical path planning for multi axis support free additive manufacturing of truss structures

Multi-axis additive manufacturing systems are gaining increasing attention due to their potential for unsupported manufacturing and reduced stair-stepping effects. In response to the challenges of unsupported printing for truss structures, a five-axis path planning method based on spherical slicing has been proposed. Leveraging the implicit expression equation based on cylinders, this study has effectively achieved the generation of efficient surface slicing and five-axis spherical path. The employed path planning method demonstrates significant advantages in both generation efficiency and stability. In the testing experiments, various unsupported path planning schemes are generated for different truss cells and truss structures, including configurations such as the “bridge” and cross-cylinder truss cells. To validate and extend the applicability of this method, two types of five-axis additive manufacturing devices are utilized: one based on a five-axis CNC system and the other employing a UR10 robot. The manufacturing experiments have effectively verified the feasibility of the spherical slicing algorithm in manufacturing various truss unit types, which provides a new technical way for the unsupported manufacturing of truss structures in the future.

Topology Optimization for Multi-Axis Additive Manufacturing

Topology Optimization for Multi-Axis Additive Manufacturing

Design of optimal truss components for fabrication via multi-axis additive manufacturing

Additive manufacturing (AM) has developed rapidly in recent years and has the potential to enable fabrication of structurally optimized components that have hitherto been impossible to manufacture. When the degree of design freedom is high it can be observed that structurally optimized components are often truss-like in form, such that truss topology (or ‘layout’) optimization methods can be used to rapidly and directly identify optimal forms. However, these forms are often geometrically complex, and the presence of overhanging elements means that they generally need to be manufactured with support structures when traditional 3-axis AM machines are employed. To reduce, or even completely eliminate, the need for support structures, multi-axis AM machines with 5 or more axes can instead be used. In this contribution a novel process-aware truss layout optimization strategy tailored for multi-axis AM machines is proposed, which involves combining curved printing surface identification with truss layout and geometry optimization. Due to the non-linear and non-convex nature of the resulting optimization formulation, two strategies are proposed: (i) performance-based, to obtain highly materially-efficient structures, though which have as little need for support structures as possible; (ii) printability-based, to obtain fully self-supportable structures, though which consume as little material as possible. Several examples are presented to demonstrate the effectiveness of the proposed approach. It is shown that fully self-supporting optimized structures can often be identified, with little or no sacrifice in terms of structural performance.

Partition-based Print Sequence Planning and Adaptive Slicing for Scalar Field-based Multi-axis Additive Manufacturing

While multi-axis additive manufacturing is found to be a good solution to the inherent limitations of conventional 2.5D additive manufacturing, it is a much more sophisticated process. Among different existing multi-axis process planning algorithms, we are interested in those based on a scalar field, in which print slices are the iso-surfaces of a scalar field embedded in the 3D model. In this paper, we propose a partitioned-based print sequence planning algorithm and an adaptive slicing algorithm, which together determine a complete multi-axis printing process for an arbitrary solid model. The first algorithm iteratively subdivides the model into a set of components such that a collision-free print sequence can be established among the components. The second algorithm then extracts print slices from each component such that all these slices satisfy the self-support condition. Since an arbitrary model may not satisfy both the self-support and collision-free requirements, we also define certain critical printability rules at the beginning to check whether a given input model with its associated scalar field is printable. The generated print slices and print sequence by the proposed two algorithms are guaranteed to be printable. Furthermore, a shorter total fabrication time and a better surface quality are achieved. Physical experiments of four test models are performed on a homebuilt multi-axis FDM printer, whose results verify the capabilities of the proposed algorithms.

Fluid Flow-inspired Curvature-aware Print-paths from Hexahedral Meshes for Additive Manufacturing

Thanks to recent improvements, computational methods are able to produce high-quality hexahedral meshes, whose hexahedrons are arranged along the principal curvature directions of the input surfaces. Curvature-aware print-paths following these curvature directions have been recently proposed by Gunpinar and enable reduction in stair-stepping effect in the printed parts. However, crosswise contacts can exist between the print-paths (i.e., print-paths are quasi-perpendicular to each other), which is undesirable as failures may occur particularly at those contact regions. Therefore, the present work aims at generation of curvature-aware print-paths without crosswise contacts between them. To solve this problem, we inspire from fluid flow and imitate (laminar) streamlines for an inlet and an outlet of a duct for designing print-paths. A hexahedral mesh is decomposed into blocks (cuboid-like sub-volumes), each of which is covered with fluid flow-inspired print-paths. A multi-axis (collision-free) additive manufacturing (AM) planning technique is also proposed. As a proof of concept, fluid flow-inspired curvature-aware print-paths are validated using a multi-axis AM simulator and machine.

Fabrication sequence optimization for minimizing distortion in multi-axis additive manufacturing

Additive manufacturing of metal parts involves phase transformations and high temperature gradients which lead to uneven thermal expansion and contraction, and, consequently, distortion of the fabricated components. The distortion has a great influence on the structural performance and dimensional accuracy, e.g., for assembly. It is therefore of critical importance to model, predict and, ultimately, reduce distortion. In this paper, we present a computational framework for fabrication sequence optimization to minimize distortion in multi-axis additive manufacturing (e.g., robotic wire arc additive manufacturing), in which the fabrication sequence is not limited to planar layers only. We encode the fabrication sequence by a continuous pseudo-time field, and optimize it using gradient-based numerical optimization. To demonstrate this framework, we adopt a computationally tractable yet reasonably accurate model to mimic the material shrinkage in metal additive manufacturing and thus to predict the distortion of the fabricated components. Numerical studies show that optimized curved layers can reduce distortion by orders of magnitude as compared to their planar counterparts.

Method for the Calculation of Local Bead Volume in Multi-Axis Additive Manufacturing

In recent history, Multi-Axis Additive Manufacturing enjoys increasing attention for both industrial and research application. In comparison to traditional processes, the additional rotation axes enable parts to be printed with greater design flexibility, while reducing the need for support structures. The multi-axis motion additionally allows for optimization of structural properties of the parts. However, curved-layer printing requires significantly higher effort for planning and computation, as the layers exhibit curvature in their shape and feature local variations of the layer height and bead width. Consideration of these properties is often neglected in the development of path planning methods, although they pose a significant influence to the optical and structural quality of the printed parts. Local over- or under-extrusion can result in material accumulation or voids within the part and need to be avoided. Additionally, some Multi-Axis Additive Manufacturing processes like Directed Energy Deposition are especially prone to errors in practice, as the melt-pool behavior is hard to model and predict accurately. This paper introduces a method for the precise calculation and adjustment of local bead volume, as a possible solution to these problems. The method processes existing Cartesian paths and uses a model of the bead geometry to simulate the extrusion by rasterization. The method considers printing head orientation, as well as neighborhood information of adjacent beads and builds a volumetric map of the paths. Local extrusion volume is then determined for each waypoint of the path from this volume map and provided to the printer along with the G-Code, enabling adjusted volume deposition both in advance and during the process by iterative path-adaptation. The provided implementation is able to achieve favorable results for both use-cases but proves especially beneficial for the latter.

A robotic 3D printing system for supporting-free manufacturing of complex model based on FDM technology

Purpose3D printing technology has the characteristics of fast forming and low cost and can manufacture parts with complex structures. At present, it has been widely used in various manufacturing fields. However, traditional 3-axis printing has limitations of the support structure and step effect due to its low degree of freedom. The purpose of this paper is to propose a robotic 3D printing system that can realize support-free printing of parts with complex structures.Design/methodology/approachA robotic 3D printing system consisting of a 6-degrees of freedom robotic manipulator with a material extrusion system is proposed for multi-axis additive manufacturing applications. And the authors propose an approximation method for the extrusion value E based on the accumulated arc length of the already printed points, which is used to realize the synchronous movement between multiple systems. Compared with the traditional 3-axis printing system, the proposed robotic 3D printing system can provide greater flexibility when printing complex structures and even realize curved layer printing.FindingsTwo printing experiments show that compared with traditional 3D printing, a multi-axis 3D printing system saves 47% and 79% of materials, respectively, and the mechanical properties of curved layer printing using a multi-axis 3D printing system are also better than that of 3-axis printing.Originality/valueThis paper shows a simple and effective method to realize the synchronous movement between multiple systems so as to develop a robotic 3D printing system that can realize support-free printing and verifies the feasibility of the system through experiments.

Controls and process planning strategies for 5-axis laser directed energy deposition of Ti-6Al-4V using an 8-axis industrial robot and rotary motion

Interest in multi-axis additive manufacturing has grown significantly in recent years due to associated benefits that range from improved quality to support for greater geometric complexity. A method of 5-axis Laser Hot-Wire Directed Energy Deposition is developed and demonstrated in this study using an 8-axis industrial robot, comprised of a 6-axis serial link robot and a 2 degree‐of‐freedom positioner. Coordinated 5-axis motion is used to print Ti-6Al-4V objects predominantly through build plate rotation. Methods of slicing and toolpath generation are presented, including the use of an alternating toolpath direction philosophy and the manipulation of the CAD model surface normal vectors for determining the required build plate tilt angles for maintaining consistent deposition orientations relative to gravity. Another objective of the study was to determine the limits of conventional slicing and layer height control techniques for printing geometries with significant unsupported overhangs. A comparison is made between the behavior of normal and conformal bead alignment in this regard, and the performance of the layer height controller is reported as it relates to process stability and the limits of printing overhang geometries. Unsupported overhangs were successfully printed at 35° without build plate tilt and 45° with build plate tilt. Toolpath velocity and net-shape printing performance are reported as well, with 3D scans of the printed surfaces used for net-shape characterization. In all, the printing of three geometries is presented, including the overhang geometry, a 5-axis toolpath geometry, and a large-scale, multi-bead demonstrator part, which exceeded 500 mm in height and weighed 44 kg (97 lbs).

A Set of Novel Procedures for Carbon Fiber Reinforcement on Complex Curved Surfaces Using Multi Axis Additive Manufacturing

There has been considerable research in recent years on the additive manufacturing (AM) of carbon fiber reinforced polymer (CFRP) parts based on the process of fused deposition modeling (FDM). The currently-applied steps within the manufacturing pipeline, such as slicing and path planning, consider only the planar case of filament deposition and mostly make no use of the possibility to place single pre-impregnated (prepreg) filaments. Classical methods such as tape-laying and laminating struggle with highly curved and complex geometries and require the costly production of molds, whereas when using AM, these geometries can be realized more easily and molds can be created using the same process. In this paper, a set of algorithms is presented that aims to resolve these problems. Criteria are formulated which enable the goal oriented development and evaluation of the presented methods and represent metrics for future methods. The developed algorithms enable the use of both continuous and discontinuous fiber patches in a much wider range of applications in designing and manufacturing of CFRPs. This opens up new possibilities in this promising field. The developed metrics and infrastructure further constitute progress in the field of multi-axis non-planar path planning for slicing algorithms in general and the conducted evaluation proves the formal applicability of the developed algorithms.

Orientation smoothing in multi-axis additive manufacturing

In multi-axis processes, such as material extrusion like Fused Filament Fabrication (FFF), the orientation of the tool relatively to the workspace is usually set by the CAM software to an angle that is locally constant relative to the manufacturing surface. However, in the case of large curvature gradients or small curvature radius of the surface or the path, this method leads to significant variations of the tool orientation. These variation require large compensating movements of the axes to maintain the desired deposition tool orientation along the path. Kinematic constraints such as acceleration or jerk limits can lead to a reduction of the path velocity or noticeable positioning errors along the movement, as well as unwante vibrations, which means poor process conditions and defects in the parts. The paper presents a post path planning algorithm that allows smooth in of the tool orientation to avoid jerky compensation motion of the CNC system by varying the orientation within a defined tolerance. This tolerance depends on the deposition process, and is determined experimentally for a FFF process. The proposed methodology was successfully validated b the manufacturing of two sample parts using a robotic additive manufacturing cell.

Singularity-Aware Motion Planning for Multi-Axis Additive Manufacturing

Multi-axis additive manufacturing enables high flexibility of material deposition along dynamically varied directions. The Cartesian motion platforms of these machines include three parallel axes and two rotational axes. Singularity on rotational axes is a critical issue to be tackled in motion planning for ensuring high quality of manufacturing results. The highly nonlinear mapping in the singular region can convert a smooth toolpath with uniformly sampled waypoints defined in the model coordinate system into a highly discontinuous motion in the machine coordinate system, which leads to over-extrusion/ under-extrusion of materials in filament-based additive manufacturing. The problem is challenging as both the maximal and the minimal speeds at the tip of a printer head must be controlled in motion. Moreover, collision may occur when sampling-based collision avoidance is employed. In this letter, we present a motion planning method to support the manufacturing realization of designed toolpaths for multi-axis additive manufacturing. Problems of singularity and collision are considered in an integrated manner to improve the motion therefore the quality of fabrication.

A parametric study and characterization of additively manufactured continuous carbon fiber reinforced composites for high-speed 3D printing

High-speed 3D printing has recently gained much interest due to its potentials in improving efficiency of fabricating complex geometry components and applications in large-scale additive manufacturing (AM). In this study, a parametric study is performed experimentally to investigate factors affecting high-speed 3D printing of continuous carbon fiber reinforced composites (CFRCs), including material deposition rate, print (nozzle traverse) speed, and nozzle tilt angle based on a novel multi-axis AM approach. The method uses thermoplastic pellets and continuous carbon fiber tows as feedstock materials. The obtained sample quality and mechanical properties are investigated with respect to deposition rate, print speed, and nozzle tilt angle. The fiber impregnation quality is examined through microstructure analysis and correlated with the process conditions and mechanical properties. Increasing deposition rate and tilt angle both improve fiber impregnation quality, enabling implementation of higher print speed and yielding improved mechanical properties. This, combined with demonstrations of printed complex geometry components, shows the great potentials of the proposed method for AM of continuous CFRCs at high speeds. The results of this study also provide further guidance on design and manufacturing of large-volume, high-strength CFRCs through 3D printing.

Investigation of Parameter Spaces for Topology Optimization With Three-Dimensional Orientation Fields for Multi-Axis Additive Manufacturing

Abstract The layer-by-layer deposition process used in material extrusion (ME) additive manufacturing results in inter- and intra-layer bonds that reduce the mechanical performance of printed parts. Multi-axis (MA) ME techniques have shown potential for mitigating this issue by enabling tailored deposition directions based on loading conditions in three dimensions (3D). Planning deposition paths leveraging this capability remains a challenge, as an intelligent method for assigning these directions does not exist. Existing literature has introduced topology optimization (TO) methods that assign material orientations to discrete regions of a part by simultaneously optimizing material distribution and orientation. These methods are insufficient for MA–ME, as the process offers additional freedom in varying material orientation that is not accounted for in the orientation parameterizations used in those methods. Additionally, optimizing orientation design spaces is challenging due to their non-convexity, and this issue is amplified with increased flexibility; the chosen orientation parameterization heavily impacts the algorithm’s performance. Therefore, the authors (i) present a TO method to simultaneously optimize material distribution and orientation with considerations for 3D material orientation variation and (ii) establish a suitable parameterization of the orientation design space. Three parameterizations are explored in this work: Euler angles, explicit quaternions, and natural quaternions. The parameterizations are compared using two benchmark minimum compliance problems, a 2.5D Messerschmitt–Bölkow–Blohm beam and a 3D Wheel, and a multi-loaded structure undergoing (i) pure tension and (ii) three-point bending. For the Wheel, the presented algorithm demonstrated a 38% improvement in compliance over an algorithm that only allowed planar orientation variation. Additionally, natural quaternions maintain the well-shaped design space of explicit quaternions without the need for unit length constraints, which lowers computational costs. Finally, the authors present a path toward integrating optimized geometries and material orientation fields resulting from the presented algorithm with MA–ME processes.

Spherical slicing method and its application on robotic additive manufacturing

This article presents a spherical slicing method for additive manufacturing (AM) which is used to lay additive layers on a spherical surface, thus removing the stair stepping effect, increasing structural integrity and tensile strength. A toolpath is required to guide the extruder in the three-dimensional space and deposit the material in the desired locations. These tool paths are computed using slicing algorithms. The well-established method in AM industry is the planar slicing. In this method, the Computer Aided Design model is sliced using planes and as a result, two-dimensional tool paths are formed. With the introduction of multi-axis AM machines, development of new non-planar slicing algorithms has started. In this article, a novel non-planar, spherical slicing, is introduced. In the proposed spherical slicing method, the model is sliced by spherical shells such as that of an onion. These spherical slices are then used to generate the appropriate tool paths for guiding the robotic manipulator in three-dimensional space together with the corresponding orientation to lay the spherical layers on top of the previously manufactured planar base. Results are verified by manufacturing a model using a six-axis robotic serial manipulator by fused deposition modeling.

A software architecture for a multi-axis additive manufacturing path-planning tool

Direct-deposition Additive Manufacturing technologies like Fused Deposition Modeling suffer from several drawbacks such as anisotropic mechanical properties which impair part quality. Multi-Axis Additive Manufacturing (MAAM) promises to significantly reduce these drawbacks. However, path-planning for the complex kinematics still poses a problem which has only been solved partly and for very specific applications. This paper proposes a software architecture for a general purpose path-planning tool for MAAM technologies enabling the simultaneous implementation of different strategies. The architecture is designed to be extensible, largely machine independent and enables granular multi-scale optimizations. First implementation results and illustrating examples demonstrate the modularity and extensibility.

Curved layer based process planning for multi-axis volume printing of freeform parts

The traditional 2.5-axis volume printing process purely relies on planar and parallel slicing layers, which imperatively requires the support structure when dealing with overhanging features on the part. The advent of multi-axis additive manufacturing inaugurates a brand new type of printing process with an adjustable build direction, based on which the support structure can be successfully reduced (if not completely eliminated) upon a proper process planning. Presented in this paper is a curved layer based process planning algorithm for multi-axis printing of an arbitrary freeform solid part. Given a freeform solid model represented as a watertight mesh surface, our algorithm starts with the establishment of a surface embedded field, whose value at any particular point is exactly the geodesic distance to the specified bottom of the model. Any iso-level contour induced from this field is first flattened, filled by a Delaunay triangular mesh, and then mapped back to 3D space through the Harmonic mapping to interpolate the original 3D contour, thus generating a curved layer. After the entire model is decomposed into curved layers by the proposed adaptive slicing strategy, the multi-axis printing paths are then generated on these layers in a contour-parallel fashion. Finally, following the strict increasing order of iso-levels, the contours are printed one by one till the final formation of the part. Preliminary tests in both computer simulation and physical printing of our algorithm have given a positive validation on its effectiveness and feasibility in eliminating the need of support structure.