Algorithm for converting 3D objects into rolls using spiral coordinate system

The article reports about the algorithm of converting objects into a flat ribbon in the process of roll powder sintering (RPS) additive manufacturing technology. The main idea of the author is to conform the transformation of spiral of Archimedes to 3D space. This algorithm is based on linear rolling effect. It is well known that any plane can be transformed into a roll and, in this way, the third dimension appears. Thus, two-dimensional space and height provide the conformity between (x, y, z) and (l, z) coordinates. This work describes how the algorithm of precise transformation of a 3D object to a flat ribbon, using the spiral coordinate system, has been designed and implemented with a varied layer thickness, a winding axle and resolution. The algorithm has been extensively tested with the help of several parts of computer aided design models based on the RPS process.     

Multiphase topology design with optimal material selection using an inverse p‐norm function

We present an original mathematical formulation for optimizing structural topology while simultaneously identifying an optimal set of design materials that are selected from a larger set of candidate materials. This design task is analogous to that, which is commonly encountered in additive manufacturing applications in which the 3D printer can print parts containing up to 3 distinct materials that can be selected from a larger suite of usable materials. The material distribution is parameterized via the shape functions with penalization formulation in which a set of activation functions, which are derived from a partition of the unit hypercube, is used to determine the effective local elasticity modulus within a single finite element. Additionally, we introduce an inverse p‐norm function, which is used to ensure that the optimized material properties converge to a set of discrete values corresponding to the available candidate materials. The algorithm has been implemented on a set of 2D benchmark problems. Numerical results show that the formulation combining the inverse p‐norm function with the activation functions successfully produces optimized multimaterial solutions containing no more than the prescribed number of distinct materials.     

(2-RPU/RPS)&R混联机构的工作空间及其分拣应用

目的 针对包装生产线上需对食品、电子元器件等产品进行分拣的功能需求,提出一种新颖的(2-RPU/RPS)&R混联机构.方法 基于螺旋理论建立2-RPU/RPS并联机构的螺旋矩阵,并用修正的Kutzbach-Grübler公式对所得自由度数进行验证.通过机构的结构特征建立约束方程,并采用闭环矢量法求出机构的位置逆解.然后利用粒子群优化(PSO)算法分析机构的位置正解.最后采用数值搜索法求解机构的可达工作空间.结果 (2-RPU/RPS)&R混联机构具有4个自由度(3R1T).在PSO算法实例中,分析得到了动平台位置正解的数值解和适应度曲线,工作空间连续且无空洞,满足分拣活动范围的需求,在给出的应用实例中表明(2-RPU/RPS)&R混联机器人能很好地应用于手机包装生产线中物体的分拣和抓取等工作.结论 (2-RPU/RPS)&R混联机构运动学性能良好、工作空间大、运行平稳,适用于包装生产线上具有不同方位的物品的分拣功能需求.     

电弧增材制造技术及其应用的研究进展

电弧增材制造是近年来发展最为迅速的增材制造技术之一,其以电弧为热源,通过熔化金属丝材,在规划的路径上层层堆积成形三维实体金属构件,具有制造成本低、制造自由度与成形效率高等优点,尤其适用于大型尺寸及中低结构复杂度金属构件的形性一体化成形.近年来,电弧增材制造技术在国内外得到了广泛研究与长足发展,在电弧增材制造装备、过程控...     

增材制造金属玻璃的研究进展

金属玻璃(即非晶合金)具有较高的强度、硬度和耐磨性,优异的耐腐蚀性能等,目前已被广泛应用于制备棒球杆、传感器、电磁铁芯、变压器等。增材制造(即3D打印)技术集节约材料、可个性化定制复杂几何件优点于一身,现被广泛研究和应用。目前已掀起了3D打印金属玻璃的研究热潮。本文主要综述了3D打印金属玻璃的研究进展,在此基础上探讨了其存在的问题以及解决办法。采用优化的工艺参数和扫描策略可部分避免这些问题,对热影响区的温度分布与工艺参数之间的关系模拟研究是解决3D打印成形致密块体金属玻璃问题的关键。     

Hopping Light Vat Photopolymerization for Multiscale Fabrication

3D objects with features spanning from microscale to macroscale have various applications. However, the fabrication of such objects presents challenges to additive manufacturing (AM) due to the tradeoffs among manufacturable feature resolution, maximum build area, and printing speed. This paper presents a projection-based AM process called hopping light vat photopolymerization (HL-VPP) to address this critical barrier. The key idea of HL-VPP is to synchronize linear scanning projection with a galvo mirror's rotation. The projector moves continuously at a constant speed while periodically rotating a one-axis galvo mirror to compensate for the projector's linear movement so synchronized hopping motion can be achieved. By this means, HL-VPP can simultaneously achieve large-area (over 200 mm), fast-speed (scanning speed of 13.5 mm s^-1), and high-resolution (10 µm pixel size) fabrication. The distinguishing characteristic of HL-VPP is that it allows for hundreds of times lower refresh rates without motion blur. Thus, HL-VPP decouples the fabrication efficiency limit imposed by the refresh rate and will enable super-fast curing in the future. This work will significantly advance VPP's use in applications that require macroscale part size with microscale features. The process has been verified by fabricating multiple multiscale objects, including microgrids and biomimetic structures.     

基于搅拌摩擦的金属固相增材制造研究进展EI北大核心CSCD

基于搅拌摩擦的固相增材制造是大型轻质合金构件成形制造的新技术,已成为国内外先进成形制造领域研究的热点之一。本文对目前国内外基于搅拌摩擦的金属固相增材制造技术及其相关工艺机理的研究现状进行了分析和总结。常见的基于搅拌摩擦的固相增材制造技术可分为三类:基于搅拌摩擦搭接焊原理,使板材逐层堆积,从而获得增材构件的搅拌摩擦增材制造(friction stir additive manufacturing,FSAM)技术;采用中空搅拌头,通过添加剂(粉末或丝材)进行固相搅拌摩擦沉积的增材制造(additive friction stir deposition,AFSD)技术;采用消耗型棒材,通过棒材的摩擦表面处理,形成增材层的摩擦表面沉积增材制造(friction surfacing deposition additive manufacturing,FSD-AM)技术。重点分析了金属材料基于搅拌摩擦的固相增材制造技术的国内外研究与应用现状,对比了三类基于搅拌摩擦的固相增材制造技术的特征及其工艺优缺点。最后指出增材工艺机理、形性协同控制、外场辅助工艺改型、新材料应用和人工智能优化是基于搅拌摩擦的固相增材制造技术未来研究的重点方向。     

Static assessment of plain/notched polylactide (PLA) 3D‐printed with different infill levels: Equivalent homogenised material concept and Theory of Critical Distances

A novel approach based on the equivalent homogenised material concept and the theory of critical distances is formulated to perform static assessment of plain/notched objects of polylactide (PLA) when this polymer is additively manufactured with different infill levels. The key idea is that the internal net structure resulting from the 3D‐printing process can be modelled by keeping treating the material as linear elastic, continuum, homogenous, and isotropic, with the effect of the internal voids being taken into account in terms of change in mechanical/strength properties. This idea is initially used to assess the detrimental effect of the manufacturing voids on the static strength of the plain (ie, unnotched) material. This is done by addressing this problem in a Kitagawa‐Takahashi setting via the Theory of Critical Distances. Subsequently, this approach is extended to the static assessment of notched components of 3D‐printed PLA; ie, it is used to take into account simultaneously the effect of both manufacturing voids and macroscopic geometrical features. The accuracy and reliability of this design methodology were checked against a large number of experimental data generated by testing, under axial loading, plain specimens, as well as notched samples (including open notches) of PLA. These specimens were manufactured by making the infill level vary in the rage 10% to 90%. This validation exercise allowed us to demonstrate that the proposed approach is highly accurate, returning estimates falling within an error interval of ±20%. This remarkable level of accuracy strongly supports the idea that static assessment of 3D‐printed materials with complex geometries and manufactured with different infill levels can be performed by simply post‐processing conventional linear elastic finite element (FE) solid models, ie, without the need for modelling explicitly the detrimental effect of the manufacturing voids.     

金属选区激光熔化的研究现状

金属3D打印是目前增材制造技术中最具发展潜力和最前沿的技术。选区激光熔化(SLM)是金属3D打印的重要分支,在传统方法无法制造的复杂异型结构件及工件制造的快速响应上具有极大优势,可解决传统方法加工过程中存在的长周期、高成本、难加工等技术难题,加工出传统制造方式无法加工的复杂金属零件。主要分析总结了目前选区激光熔化所涉及的基本原理、成型设备、材料特性、工艺参数和制造过程中常见的孔隙、球化、应力应变等问题,最后对金属3D打印的发展前景进行了展望。     

Image-based adaptive crosshatch toolpath generation for laminated object manufacturing

The adaptive crosshatching concept has been introduced for better waste material removal process in Laminated Object Manufacturing. However, the existing approaches that involve a STereoLithography model require additional information from other sources for determining adaptive crosshatch patterns, and for determining the toolpath from intersection points between these customised patterns and cross-sectional contours on their associated layers. Visual representation, on the other hand, seems to be more logical in practice for generating an adaptive crosshatch toolpath. Therefore, the image processing technique has been applied in this research for ease of adaptive crosshatch toolpath generation. For this approach, a uniform crosshatch pattern is created first as a common platform for the entire model. The pattern is modified next for each layer before being mapped onto the layer to determine the toolpath. An algorithm has been developed, and successfully implemented in the LabVIEW program. Some examples are illustrated in this paper to demonstrate the proposed approach.     

Material characterisation and process development for chocolate additive layer manufacturing

This paper describes the development of a novel fabrication method known as chocolate additive layer manufacture (ChocALM). The system has been developed for the layer-by-layer manufacture of creative and personalised three dimensional (3D) chocolate products. This study investigates the material and property behaviour of a commercial chocolate. Deposition experiments have been carried using the newly developed ChocALM system to illustrate the effects of the deposition parameters on the geometrical accuracy and dimension of the deposited chocolates. The results revealed that process parameters such as extrusion rate, nozzle velocity and nozzle height are critical for successful deposition of chocolate and the optimisation of these parameters enables the ChocALM system to create 3D chocolates with appropriate quality.     

A scalable parallel finite element framework for growing geometries. Application to metal additive manufacturing

This work introduces an innovative parallel fully-distributed finite element framework for growing geometries and its application to metal additive manufacturing. It is well known that virtual part design and qualification in additive manufacturing requires highly accurate multiscale and multiphysics analyses. Only high performance computing tools are able to handle such complexity in time frames compatible with time-to-market. However, efficiency, without loss of accuracy, has rarely held the centre stage in the numerical community. Here, in contrast, the framework is designed to adequately exploit the resources of high-end distributed-memory machines. It is grounded on three building blocks: (1) hierarchical adaptive mesh refinement with octree-based meshes; (2) a parallel strategy to model the growth of the geometry; and (3) state-of-the-art parallel iterative linear solvers. Computational experiments consider the heat transfer analysis at the part scale of the printing process by powder-bed technologies. After verification against a three-dimensional (3D) benchmark, a strong-scaling analysis assesses performance and identifies major sources of parallel overhead. A third numerical example examines the efficiency and robustness of (2) in a curved 3D shape. Unprecedented parallelism and scalability were achieved in this work. Hence, this framework contributes to take on higher complexity and/or accuracy, not only of part-scale simulations of metal or polymer additive manufacturing but also in welding, sedimentation, atherosclerosis, or any other physical problem where the physical domain of interest grows in time.     

Additive layered manufacturing: sectors of industrial application shown through case studies

In modern industry, mass production has migrated to third world countries. To be competitive, European companies are forced to rapidly switch towards manufacturing of short series of customised products with added value. In European industry, a great effort has been made in order to customise products and give them an added value by developing new fabrication technologies. Additive layered manufacturing (ALM), also known as rapid manufacturing (RM), is a powerful tool that offers the necessary competitiveness to European companies. ALM comprises the use of layer-by-layer manufacturing in order to build a part by addition of material. Fabrication is performed directly from the 3D CAD model, which is sliced into layers that are printed one upon the other. Also known as free form fabrication, additive fabrication ‘unlocks’ design potential since part design obeys functionality, pushing the limits of manufacturability. In this paper, the authors review ALM technologies and the state-of-the-art of ALM applications in tooling, biomedicine and lightweight structures for the automotive and aerospace sectors. The authors present their experience in industrial application of additive fabrication through various industrial technology transfer projects made to transfer ALM technology to SMEs. Various case studies are presented and the achieved benefits of ALM are shown.     

Development of Bioimplants with 2D, 3D,and 4D Additive Manufacturing Materials

Over the past 30 years, additive manufacturing (AM) has developed rapidly and has demonstrated great potential in biomedical applications. AM is a materials-oriented manufacturing technology, since the solidification mechanism, architecture resolution, post-treatment process, and functional application are based on the materials to be printed. However, 3D printable materials are still quite limited for the fabrication of bioimplants. In this work, 2D/3D AM materials for bioimplants are reviewed. Furthermore, inspired by Tai Chi, a simple yet novel soft/rigid hybrid 4D AM concept is advanced to develop complex and dynamic biological structures in the human body based on 4D printing hybrid ceramic precursor/ceramic materials that were previously developed by our group. With the development of multi-material printing technology, the development of bioimplants and soft/rigid hybrid biological structures with 2D/3D/4D AM materials can be anticipated.     

Three-dimensional printing of tungsten structures by directed energy deposition

Although three-dimensional (3D) printing of tungsten parts by Powder Bed Fusion (PBF) has been demonstrated by multiple research groups, a directed energy deposition (DED) process for fabricating pure tungsten structures has never been reported. This work reports successful fabrication of pure tungsten structures by DED, revealing the required process conditions. The effect of laser power, scan speed, powder feed rate and carrier gas velocity on the stability and properties of the structures is first analyzed, based on which the proper process condition for effective 3D printing of tungsten parts is proposed. Fabrication of a rectangular tube of 110 mm in height is demonstrated using an in-house DED printing system. Analyses of the fabricated samples show that the density and the hardness can be as high as 18.9 g/cm³ (98.4% of the theoretical value) and 3.9 GPa, respectively. The results indicate that the optimal condition for 3D printing of tungsten is 400 ~ 530 J/mm² in terms of specific energy and that high-speed or high-mass injection of powder can induce waviness on the surface. This work suggests that DED can be a promising alternative to produce pure tungsten parts in various applications.     

Analytic formulations for calculating nearly singular integrals in two-dimensional BEM

There exist the nearly singular integrals in the boundary integral equations when a source point is close to an integration element but not on the element, such as the field problems with thin domains. In this paper, the analytic formulations are achieved to calculate the nearly weakly singular, strongly singular and hyper-singular integrals on the straight elements for the two-dimensional (2D) boundary element methods (BEM). The algorithm is performed after the BIE are discretized by a set of boundary elements. The singular factor, which is expressed by the minimum relative distance from the source point to the closer element, is separated from the nearly singular integrands by the use of integration by parts. Thus, it results in exact integrations of the nearly singular integrals for the straight elements, instead of the numerical integration. The analytic algorithm is also used to calculate nearly singular integrals on the curved element by subdividing it into several linear or sub-parametric elements only when the nearly singular integrals need to be determined. The approach can achieve high accuracy in cases of the curved elements without increasing other computational efforts. As an application, the technique is employed to analyze the 2D elasticity problems, including the thin-walled structures. Some numerical results demonstrate the accuracy and effectiveness of the algorithm.     

Investigation of microstructure in additive manufactured Inconel 625 by spatially resolved neutron transmission spectroscopy

Non-destructive testing techniques based on neutron imaging and diffraction can provide information on the internal structure of relatively thick metal samples (up to several cm), which are opaque to other conventional non-destructive methods. Spatially resolved neutron transmission spectroscopy is an extension of traditional neutron radiography, where multiple images are acquired simultaneously, each corresponding to a narrow range of energy. The analysis of transmission spectra enables studies of bulk microstructures at the spatial resolution comparable to the detector pixel. In this study we demonstrate the possibility of imaging (with ~100 μm resolution) distribution of some microstructure properties, such as residual strain, texture, voids and impurities in Inconel 625 samples manufactured with an additive manufacturing method called direct metal laser melting (DMLM). Although this imaging technique can be implemented only in a few large-scale facilities, it can be a valuable tool for optimization of additive manufacturing techniques and materials and for correlating bulk microstructure properties to manufacturing process parameters. In addition, the experimental strain distribution can help validate finite element models which many industries use to predict the residual stress distributions in additive manufactured components.     

High‐Performance Materials for 3D Printing in Chemical Synthesis Applications

3D printing has emerged as an enabling technology for miniaturization. High‐precision printing techniques such as stereolithography are capable of printing microreactors and lab‐on‐a‐chip devices for efficient parallelization of biological and biochemical reactions under reduced uptake of reactants. In the world of chemistry, however, up until now, miniaturization has played a minor role. The chemical and thermal stability of regular 3D printing resins is insufficient for sustaining the harsh conditions of chemical reactions. Novel material formulations that produce highly stable 3D‐printed chips are highly sought for bringing chemistry up‐to‐date on the development of miniaturization. In this work, a brief review of recent developments in highly stable materials for 3D printing is given. This work focuses on three highly stable 3D‐printable material systems: transparent silicate glasses, ceramics, and fluorinated polymers. It is further demonstrated that 3D printing is also a versatile technique for surface structuring of polymers to enhance their wetting performance. Such micro/nanostructuring is key to selectively wetting surface patterns that are versatile for chemical arrays and droplet synthesis.     

Highly Tunable Thiol-Ene Photoresins for Volumetric Additive Manufacturing

Volumetric additive manufacturing (VAM) forms complete 3D objects in a single photocuring operation without layering defects, enabling 3D printed polymer parts with mechanical properties similar to their bulk material counterparts. This study presents the first report of VAM-printed thiol-ene resins. With well-ordered molecular networks, thiol-ene chemistry accesses polymer materials with a wide range of mechanical properties, moving VAM beyond the limitations of commonly used acrylate formulations. Since free-radical thiol-ene polymerization is not inhibited by oxygen, the nonlinear threshold response required in VAM is introduced by incorporating 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) as a radical scavenger. Tuning of the reaction kinetics is accomplished by balancing inhibitor and initiator content. Coupling this with quantitative measurements of the absorbed volumetric optical dose allows control of polymer conversion and gelation during printing. Importantly, this work thereby establishes the first comprehensive framework for spatial–temporal control over volumetric energy distribution, demonstrating structures 3D printed in thiol-ene resin by means of tomographic volumetric VAM. Mechanical characterization of this thiol-ene system, with varied ratios of isocyanurate and triethylene glycol monomers, reveals highly tunable mechanical response far more versatile than identical acrylate-based resins. This broadens the range of materials and properties available for VAM, taking another step toward high-performance printed polymers.