Large-scale Additive Manufacturing Research Articles

Development of efficient distortion prediction numerical method for laser additive manufactured parts

Part distortion is a technical bottleneck in the field of laser solid forming additive manufacturing (AM). Finite element modeling has shown great power in analyzing and predicting thermal distortion during laser AM process. However, as the global size of the manufactured component increases, the conventional numerical method appears limited due to the long computation time. In this paper, the temperature distribution and the evolution of a Ti-6Al-4V thin wall during the AM process were investigated first via the transient heat transfer analysis. “Quasi-steady state” characteristic of the temperature distribution was observed after depositing several layers. Based on this, an efficient equivalent temperature field (ETF) method was developed to predict thermal distortion by extracting the quasi-steady temperature field and applying it as a thermal boundary during mechanical analysis. The developed ETF method was validated by the good agreement in the predicted distortion distribution pattern and magnitude compared with that predicted by the conventional move heat source numerical method. The developed ETF method in this paper significantly saved computation time by above 90% during mechanical analysis. Furthermore, the distortion of laser additive manufactured thin wall with 266 layers was successfully predicted by the ETF method within several hours. The maximum deviation is 29.3% compared with the experimental results. The proposed method provides the possibility to predict distortion for large-scale AM parts, which may have the potential application in engineering.

Control of Process Settings for Large-Scale Additive Manufacturing With Sustainable Natural Composites

We present a system for 3D printing large-scale objects using natural biocomposite materials, which comprises a precision extruder mounted on an industrial six-axis robot. This paper highlights work on controlling process settings to print filaments of desired dimensions while constraining the operating point to a region of maximum tensile strength and minimum shrinkage. Response surface models relating the process settings to the geometric and physical properties of extruded filaments are obtained through face-centered central composite designed experiments. Unlike traditional applications of this technique that identify a fixed operating point, the models are used to uncover dimensions of filaments obtainable within the operating boundaries of our system. Process-setting predictions are then made through multi-objective optimization of the models. An interesting outcome of this study is the ability to produce filaments of different shrinkage and tensile strength properties by solely changing process settings. As a follow-up, we identify optimal lateral overlap and interlayer spacing parameters to define toolpaths to print structures. If unoptimized, the material’s anisotropic shrinkage and nonlinear compression characteristics cause severe delamination, cross-sectional tapering, and warpage. Finally, we show the linear scalability of the shrinkage model in 3D space, which allows for suitable toolpath compensation to improve the dimensional accuracy of printed artifacts. We believe this first-ever study on the parametrization of the large-scale additive manufacture technique with biocomposites will serve as reference for future sustainable developments in manufacturing.

Wire Arc Additive Manufacturing by Robot Manipulator: Towards Creating Complex Geometries

Abstract Additive manufacturing (AM) is the umbrella term that covers a variety of techniques that build up structures layer-by-layer as opposed to machining and other subtracting methods. It keeps evolving as an important technology in prototyping and the development of new devices. However, using AM on a larger scale is still challenging, as traditional methods require the AM machines to be larger than the manufactured structure. The research presented in this paper is a continuation of our work on assessing the possibility of large-scale robotic AM. The focus in this paper is the feasibility of large-scale AM of metallic materials by arc welding. A series of experiments with robotic arc welding using an ABB IRB2400/10 robot are presented and discussed. These experiment will help map some of the challenges that need to be addressed in future work.

Integrating digital image correlation in mechanical testing for the materials characterization of big area additive manufacturing feedstock

To enable the advancement of large-scale additive manufacturing processes, it is necessary to establish and standardize methodologies to characterize the mechanical properties of printed test coupons. Due to the large size of the print beads, conventional test standards are inadequate. The focus of this study was to determine the feasibility of using Digital image correlation (DIC) technology as a key enabler for robust data collection of strain measurements of large 3D printed parts. To incorporate the DIC measurements, a novel method was developed to prepare large 20% (by wt.) glass filled ABS test coupons for adequate contrast. Through this technique, Poisson's ratio and elastic modulus were measured and stress strain curves were generated. The data produced by DIC correlated well with failure analysis performed on spent test coupons. Additionally, fracture surface analysis of the specimens revealed poor adhesion among the ABS matrix and glass fibers. This matrix/fiber debonding demonstrated the need for improved printing parameters to maximize tensile strength. Finally, critical length analysis of the fibers revealed them to be dimensionally inadequate.

Surface Preparation and Treatment for Large-Scale 3D-Printed Composite Tooling Coating Adhesion

Recent advances in large-scale thermoplastic additive manufacturing (AM), using fused deposition modelling (FDM), have shown that the technology can effectively produce large aerospace tools with common feed stocks, costing 2.3 $/kg, such as a 20% carbon-filled acrylonitrile butadiene styrene (ABS). Large-scale additive manufacturing machines have build-volumes in the range of cubic meters and use commercially available pellet feedstock thermoplastics, which are significantly cheaper (5–10 $/kg) than the filament feedstocks for desktop 3D printers (20–50 $/kg). Additionally, large-scale AM machines have a higher material throughput on the order of 50 kg/h. This enables the cost-efficient tool production for several industries. Large-scale 3D-printed tooling will be computerized numerical control (CNC)-machined and -coated, to provide a surface suitable for demolding the composite parts. This paper outlines research undertaken to review and improve the adhesion of the coating systems to large, low-cost AM composite tooling, for marine or infrastructure composite applications. Lower cost tooling systems typically have a lower dimensional accuracy and thermal operating requirements than might be required for aerospace tooling. As such, they can use lower cost commodity grade thermoplastics. The polymer systems explored in the study included polypropylene (PP), styrene-maleic anhydride (SMA), and polylactic acid (PLA). Bio-based filler materials were used to reduce cost and increase the strength and stiffness of the material. Fillers used in the study included wood flour, at 30% by weight and spray-dried cellulose nano-fibrils, at 20% by weight. Applicable adhesion of the coating was achieved with PP, after surface treatment, and untreated SMA and PLA showed desirable coating adhesion results. PLA wood-filled composites offered the best properties for the desired application and, furthermore, they have environment-friendly advantages.

Defect Identification and Mitigation Via Visual Inspection in Large-Scale Additive Manufacturing

Defect identification and mitigation is an important avenue of research to improve the overall quality of objects created using additive manufacturing (AM) technologies. Identifying and mitigating defects takes on additional importance in large-scale, industrial AM. In large-scale AM, defects that result in failed prints are extremely costly in terms of time spent and material used. To address these issues, researchers at Oak Ridge National Laboratory’s Manufacturing Demonstration Facility investigated the use of a laser profilometer and thermal camera to collect data concerning an object as it was constructed. These data provided feedback for an in situ control system to adjust object construction. Adjustments were made in the form of automated height control. This paper presents results for both a polymer- and metal-based system. Object construction for both systems was improved significantly, and the resulting objects were more geometrically identical to the ideal 3D representation.

Case Studies in Topological Design and Optimization of Additively Manufactured Cable-nets

Advances in additive manufacturing technologies have availed new modes of design and production across the design and engineering disciplines. While lightweight cable-net structures have long captured the imagination of engineers and architects, there has so far been little research on the opportunities afforded by large-scale additive manufacturing of cable-net structures for form-active or performative tensile surfaces. Additive manufacturing opens up the possibility of manufacturing tensile surfaces beyond knitted, woven nets, or mechanically fastened nets, and expands the types of materials that can be used in such systems. This paper discusses research in novel approaches to the topological design and optimization of cable-nets enabled by the additive manufacturing of elastomeric materials. Through three realized case studies, the topological structure is used to determine the formal, behavioral, and performance-based properties of the cable-net system. This is achieved through the reorientation of a standard quad-grid topology, through a material programming method that embeds non-natural three-dimensional forms into two-dimensional patterns, and through a new meso-scale density-based topological optimization method.

Evaluating the relationship between deposition and layer quality in large-scale additive manufacturing of concrete

ABSTRACTScaling up additive manufacturing (AM) for automated building construction requires expertise from different fields of knowledge, including architecture, material science, engineering, and manufacturing to develop processes that work for practical applications. While concrete is a viable candidate for printing due to its common use in building, it raises important challenges in deposition due to the material deformation that occurs as concrete transitions from fresh to hardened states. This study aims to experimentally quantify the deformation of printed concrete layers under the influence of different processing variables, including layer thickness, printing orientation, and direction. A mixer-pump extrudes the material and an industrial 6-axis robotic arm, which provides various ranges of movement in different axes, layers the material. The results of this study can be used to develop a tool for predicting and accounting for the deformation of concrete layers during the AM process.

Rheology, crystal structure, and nanomechanical properties in large-scale additive manufacturing of polyphenylene sulfide/carbon fiber composites

Extrusion based high-throughput Additive Manufacturing (AM) provides a rapid and versatile approach for producing complex structures by using a variety of polymer materials. An underexplored aspect of this technique is concerned with the formation of interfaces between successively deposited layers. This is particularly important for large-scale additive manufacturing of semi-crystalline polymers because of the highly non-isothermal conditions involved, which influence both nucleation and crystal growth. The objective of this work is to investigate the microstructure and the corresponding viscoelastic properties of carbon fiber (CF) reinforced polyphenylene sulfide (PPS) resulting from extrusion-based high-throughput AM process. Questions on development of morphology focus on polymer crystal structure and carbon fiber orientation in the vicinity of the interface between successive layers. This study attempts to establish a fundamental understanding of the role of the AM has in transferring a set of intrinsic material properties to the macroscopic properties of the final AM structure.

Plasma transferred arc additive manufacturing of Nickel metal matrix composites

This paper analyzes the geometric stability and microstructure characteristics of metal additive manufacturing parts using plasma transferred arc with Metal Matrix Composites. The technology used to enhance the capabilities of a plasma system to create an additive manufacturing system is described. Geometric stability, microstructure porosity and cross-sectional hardness analysis of the additive manufacturing parts are discussed. This work confirms that the new capabilities of the system allow building a 3D printed part of nickel-base metal matrix with tungsten carbide particles for wear resistance. The results will lead to the development of large-scale additive manufacturing parts for industrial purposes.

Large-scale additive manufacturing with bioinspired cellulosic materials

Cellulose is the most abundant and broadly distributed organic compound and industrial by-product on Earth. However, despite decades of extensive research, the bottom-up use of cellulose to fabricate 3D objects is still plagued with problems that restrict its practical applications: derivatives with vast polluting effects, use in combination with plastics, lack of scalability and high production cost. Here we demonstrate the general use of cellulose to manufacture large 3D objects. Our approach diverges from the common association of cellulose with green plants and it is inspired by the wall of the fungus-like oomycetes, which is reproduced introducing small amounts of chitin between cellulose fibers. The resulting fungal-like adhesive material(s) (FLAM) are strong, lightweight and inexpensive, and can be molded or processed using woodworking techniques. We believe this first large-scale additive manufacture with ubiquitous biological polymers will be the catalyst for the transition to environmentally benign and circular manufacturing models.

Microstructure and mechanical properties of Al-Mg-Zr alloys processed by selective laser melting

Gas-atomized powders of two ternary alloys, Al-3.60Mg-1.18Zr and Al-3.66Mg-1.57Zr (wt.%), were densified via laser powder bed fusion. At energy densities ranging from 123 to 247 J/mm3, as-fabricated components are near-fully densified (relative density 99.2–99.9%) as verified by X-ray tomography. While Mg acts a solid-solution strengthener, Zr creates two types of metastable L12 Al3Zr precipitates, each playing dual roles: (a) sub-micrometer Al3Zr particles form in the melt upon solidification and act as grain refining agents, nucleating fine aluminum grains, which (i) prevent hot-tearing during the rapid solidification inherent to laser melting and (ii) enhance tensile strength (Hall-Petch strengthening) and ductility (influence a heterogenous grain structure) after fabrication; (b) Al3Zr nano-precipitates form in the solid alloy during subsequent aging, which (i) precipitation-strengthen the alloy leading to an increase of >40% in strength over the as-fabricated value, and (ii) promote thermal stability of the fine grain size (and the associated Hall-Petch strengthening) after exposure to high temperature due to the slow kinetics of Al3Zr coarsening (from the sluggish diffusivity of Zr in solid Al-Mg). While the Zr-richer alloy shows higher yield and ultimate tensile strength in the as-fabricated state, both alloys have identical mechanical properties after peak aging. Interconnected bands of fine (∼0.8 μm), equiaxed, isotropic grains and coarser (∼1 × 10 μm), columnar, textured grains – both containing oxide particles and Al3Zr precipitates - provide a combination of high yield strength and high ductility (e.g., ∼354 MPa, and ∼20%, respectively) with isotropic values in both as-fabricated and peak-aged samples, unlike Al-Si alloys processed via laser fusion of commercial Al-Si-based powders. The pre-alloyed, gas-atomized Al-Mg-Zr powders do not contain expensive alloying elements such as Sc, nor do they require blending with a second powder to nucleate fine grains, making them excellent candidates for economical, large-scale additive manufacturing applications.

Rapid fabrication of hybrid aerogels and 3D printed porous materials

In this manuscript, methods will be reviewed that alleviate or solve processing issues of aerogels. Techniques will be described that allow one-pot, rapid synthesis of both native-aerogels and mechanically reinforced-aerogels, as well as porous oxide monoliths with hierarchical pore size distribution. Farther, techniques will be reviewed that allow fabrication of inhomogeneous/anisotropic porous monoliths. Techniques will be described that allow to reinforce or functionalize selected regions of monoliths. These techniques are photolithographic in nature and allow to fabricate a wide variety of structures, including honeycombs and functionally graded materials. These materials consist of functionalized and/or mechanically reinforced regions embedded into an otherwise native aerogels and they will be termed as “hybrid”. Finally, techniques will be reviewed that alleviate or solve geometrical constraints. Typically, porous materials are produced by pouring a sol into a mold. Techniques will be presented that allow additive manufacturing of porous materials. It will be shown that technical issues likely prevent large-scale additive manufacturing of oxide aerogels. However, techniques are available and will be discussed which allow additive manufacturing of porous polymeric structures.

Rheology Effects on Predicted Fiber Orientation and Elastic Properties in Large Scale Polymer Composite Additive Manufacturing

Short fiber-reinforced polymers have recently been introduced to large-scale additive manufacturing to improve the mechanical performances of printed-parts. As the short fiber polymer composite is extruded and deposited on a moving platform, velocity gradients within the melt orientate the suspended fibers, and the final orientation directly affects material properties in the solidified extrudate. This paper numerically evaluates melt rheology effects on predicted fiber orientation and elastic properties of printed-composites in three steps. First, the steady-state isothermal axisymmetric nozzle melt flow is computed, which includes the prediction of die swell just outside the nozzle exit. Simulations are performed with ANSYS-Polyflow, where we consider the effect of various rheology models on the computed outcomes. Here, we include Newtonian, generalized Newtonian, and viscoelastic rheology models to represent the melt flow. Fiber orientation is computed using Advani–Tucker fiber orientation tensors. Finally, elastic properties in the extrudate are evaluated based from predicted fiber orientation distributions. Calculations show that the Phan–Thien–Tanner (PTT) model yields the lowest fiber principal alignment among considered rheology models. Furthermore, the cross section averaged elastic properties indicate a strong transversely isotropic behavior in these composites, where generalized Newtonian models yield higher principal Young’s modulus, while the viscoelastic fluid models result in higher shear moduli.

A Computationally Efficient Finite Element Framework to Simulate Additive Manufacturing Processes

Macroscale finite element (FE) models, with their ability to simulate additive manufacturing (AM) processes of metal parts and accurately predict residual stress distribution, are potentially powerful design tools. However, these simulations require enormous computational cost, even for a small part only a few orders larger than the melt pool size. The existing adaptive meshing techniques to reduce computational cost substantially by selectively coarsening are not well suited for AM process simulations due to the continuous modification of model geometry as material is added to the system. To address this limitation, a new FE framework is developed. The new FE framework is based on introducing updated discretized geometries at regular intervals during the simulation process, allowing greater flexibility to control the degree of mesh coarsening than a technique based on element merging recently reported in the literature. The new framework is evaluated by simulating direct metal deposition (DMD) of a thin-walled rectangular and a thin-walled cylindrical part, and comparing the computational speed and predicted results with those predicted by simulations using the conventional framework. The comparison shows excellent agreement in the predicted stress and plastic strain fields, with substantial savings in the simulation time. The method is then validated by comparing the predicted residual elastic strain with that measured experimentally by neutron diffraction of the thin-walled rectangular part. Finally, the new framework's capability to substantially reduce the simulation time for large-scale AM parts is demonstrated by simulating a one-half foot thin-walled cylindrical part.

Additively-manufactured lightweight Metamaterials for energy absorption

Recent developments in architectural design and additive manufacturing (AM) techniques have led to advances in the design and fabrication of metamaterials. We demonstrate that by precisely designing the architecture of a lattice structure and implementing the accurate and cost-effective capabilities of polymer-based AM, it is possible to create lightweight and strong structures that are highly energy absorbing, able to recover their shape after extreme deformation, and have a high strength-over-weight ratio. Largescale AM lattices with various densities of unit cells were fabricated from two different polymers. The densities of the structures ranged from 66kg/m3 to 192kg/m3. Compression experiments established the scaling of their strength and stiffness with their relative density and revealed that the structures were able to recover their original shape after a compression up to 70% strain. The energy absorption efficiency of the structures was 11% higher than Duocel® aluminum foam and comparable to that of aluminum honeycomb, expanded polystyrene (EPS) foams, and Skydex twin hemispheres. These unconventional mechanical properties substantiate the potential of architectural design along with additive manufacturing in various applications, not only at laboratory scale, but also at industrial level.

Additive manufacturing of geopolymer for sustainable built environment

This paper evaluates the potential of fly ash based geopolymer cement for large scale additive manufacturing (AM) of construction elements. Geopolymer is considered as a green construction material and its use in AM may contribute towards sustainable environment since in AM process material is only deposited whereby it is necessary. As part of this research, an industrial robot was employed to print geopolymer mortar in layer-by-layer manner directly from 3D computer-aided design (CAD) model. The characteristic of raw materials and fresh properties were examined by rheology, x-ray diffraction (XRD), and scanning electron microscopy (SEM). Mechanical tests such as compression, flexural and tensile bond strength were conducted on the printed geopolymer in different printing directions and their performance was compared with casted samples. It was found, from the experimental results, that the mechanical properties of 3D printed geopolymer are mostly dependent of loading directions due to anisotropic nature of the printing process and retains intrinsic performance of the material.

Large scale additive manufacturing of eco-composites

The evolution of additive manufacturing processes is enabling the production of parts with improved dimensional accuracy, mechanical, physical and chemical properties [1]. New materials also contribute to this trend, and in this scope, eco-composites, materials with environmental and ecological advantages, which include natural polymers, have been acquiring increased relevance [2]. The purpose of this study is to develop composite material parts manufactured from recycled thermoplastics and natural fibres, in this case, wood residues. Additive manufacturing (fused deposition modelling) will be accomplished using a robot combined with extrusion unit. The objective is to access the influence of the main manufacturing parameters, such as temperature, distance between layers or deposition speed, on the final part characteristics, especially dimensional accuracy. Reverse engineering and several material analysis techniques will be employed to achieve this goal.

Excision robotique d’un grand schwannome rétropéritonéal (avec vidéo)

In the present paper a new additive manufacturing processing route is introduced for ultra-high performance concrete. Interdisciplinary work involving materials science, computation, robotics, architecture and design resulted in the development of an innovative way of 3D printing cementitious materials. The 3D printing process involved is based on a FDM-like technique, in the sense that a material is deposited layer by layer through an extrusion printhead mounted on a 6-axis robotic arm. The mechanical properties of 3D printed materials are assessed. The proposed technology succeeds in solving many of the problems that can be found in the literature. Most notably, this process allows the production of 3D large-scale complex geometries, without the use of temporary supports, as opposed to 2.5D examples found in the literature for concrete 3D printing. Architectural cases of application are used as examples in order to demonstrate the potentialities of the technology. Two structural elements were produced and constitute some of the largest 3D printed concrete parts available until now. Multi-functionality was enabled for both structural elements by taking advantage of the complex geometry which can be achieved using our technology for large-scale additive manufacturing.

Development of a range-extended electric vehicle powertrain for an integrated energy systems research printed utility vehicle

Rapid vehicle and powertrain development has become essential to for the design and implementation of vehicles that meet and exceed the fuel efficiency, cost, and performance targets expected by today’s consumer while keeping pace with reduced development cycle and more frequent product releases. Recently, advances in large-scale additive manufacturing have provided the means to bridge hardware-in-the-loop (HIL) experimentation and preproduction mule chassis evaluation. This paper details the accelerated development of a printed range-extended electric vehicle (REEV) by Oak Ridge National Laboratory, by paralleling hardware-in-the-loop development of the powertrain with rapid chassis prototyping using big area additive manufacturing (BAAM). BAAM’s ability to accelerate the mule vehicle development from computer-aided design to vehicle build is explored. The use of a hardware-in-the-loop laboratory is described as it is applied to the design of a range-extended electric powertrain to be installed in a printed prototype vehicle. The integration of the powertrain and the opportunities and challenges it presents are described in this work. A comparison of offline simulation, HIL and chassis rolls results is presented to validate the development process. Chassis dynamometer results for battery electric and range extender operation are analyzed to show the benefits of the architecture.