基于堆积成形与去除成形的复合快速成形技术研究进展

以快速成形技术为典型代表的堆积成形(可制造的原型尺寸小、精度低、可选用材料种类有限)和数控加工为典型代表的去除成形(难于直接制造复杂形状)存在着自身难以克服的固有缺点.针对上述问题,把堆积成形和去除成形有机地结合起来,利用二者的优势克服其缺点,旨在求得精度和效率最佳组合的复合快速成形技术的研究正在兴起.本文分析了复合快速成形技术的基本原理、研究现状,探讨了存在的问题和发展趋势.     

基于无模铸型制造技术的复杂铸件快速制造

无模铸型制造技术是以树脂砂为成型材料，利用快速成型技术的离散／堆积成型原理，对三维CAD实体模型进行分层切片处理，得到不同高度截面层的信息，采用截面扫描、喷射固化工艺，直接获得树脂砂铸型或铸造模具的一种方法。在复杂铸件快速制造的实际应用中，无模铸型制造技术表现出造型材料易得、制造时间短、制造成本低、铸件质量好等优点，体现了快速敏捷制造的优势，也为快速成形技术在铸造中的应用开辟了一个新领域。     

央速成形技术在金属多孔材料制备中的应用研究现状

快速成形是一种基于离散一堆积原理的先进制造技术,它满足现代制造业高效、低成本、产品个性化的需求。采用快速成形技术进行金属多孔材料的制备是其应用发展的新趋势,根据成形工艺特点对快速成形技术进行分类,综述了各类快速成形工艺在金属多孔材料制备中的应用研究现状。     

快速成形的技术基础:选择性分离

对快速成形的技术本质进行了分析，提出快速成形的技术基础是选择性分离。认为从广义上讲，只要一种(类)物质能以一定的形态从其他物质中分离并将分离单元堆积起来，它就可应用快速成形原理进行加工。重点分析了分离／堆积的分离部分，通过对分离的尺度(从纳米到千米)、状态(固、液、气等)、使能技术(力、热、电、光等)、控制(方向、速度、精度、能量)等方面的分析，探讨了快速成形可能的努力方向，希望能为快速成形开辟新的应用领域。     

电子束快速成形Ti-6Al-4V合金的组织与性能（英文）

电子束快速成形是一种利用金属丝材沉积直接制造金属零件的新型增材制造技术。用电子束快速成形方法制备了Ti-6Al-4V合金,对其显微组织和快速成形态、退火态、热等静压态下的力学性能进行了研究。电子束快速成形Ti-6Al-4V合金的低倍组织典型特征为沿堆积高度方向生长的贯穿多层沉积层的粗大柱状晶以及分布于层间及堆积路径间的明暗相间的带状条纹。各种状态下室温拉伸性能均有明显的方向性,其中X向、Y向强度较高,Z向强度低但塑性较好;消应力退火处理对室温拉伸性能没有明显影响;热等静压处理后材料的抗拉伸强度显著降低,但具有良好的塑性与韧性,同时能够明显降低高周疲劳性能数据的分散性。快速成形态及退火态室温拉伸性能均可满足AMS4999标准的要求,但与锻件标准HB5432相比仍有差距。     

快速成形技术在金属多孔材料制备中的应用研究现状

快速成形是一种基于离散一堆积原理的先进制造技术,它满足现代制造业高效、低成本、产品个性化的需求。采用快速成形技术进行金属多孔材料的制备是其应用发展的新趋势,根据成形工艺特点对快速成形技术进行分类,综述了各类快速成形工艺在金属多孔材料制备中的应用研究现状。     

Microstructure and Mechanical Properties of Ti-6Al-4V by Electron Beam Rapid Manufacturing

电子束快速成形是一种利用金属丝材沉积直接制造金属零件的新型增材制造技术。用电子束快速成形方法制备了Ti-6Al-4V合金,对其显微组织和快速成形态、退火态、热等静压态下的力学性能进行了研究。电子束快速成形Ti-6Al-4V合金的低倍组织典型特征为沿堆积高度方向生长的贯穿多层沉积层的粗大柱状晶以及分布于层间及堆积路径间的明暗相间的带状条纹。各种状态下室温拉伸性能均有明显的方向性,其中X向、Y向强度较高,Z向强度低但塑性较好;消应力退火处理对室温拉伸性能没有明显影响;热等静压处理后材料的抗拉伸强度显著降低,但具有良好的塑性与韧性,同时能够明显降低高周疲劳性能数据的分散性。快速成形态及退火态室温拉伸性能均可满足AMS4999标准的要求,但与锻件标准HB5432相比仍有差距。     

金属粉末等离子熔积成形的初步工艺试验研究

等离子熔积成形是一种新型金属原型／零件(模具)快速制造技术，该技术克服了传统快速原型技术存在的问题，可用于金属原型／零件制造、表面修复工程等方面，具有十分广阔的应用前景。对等离子熔积成形技术做了初步的工艺试验研究，并采用人工神经网络对熔积层几何形貌进行了预测优化，最后成功地进行了金属零件的试制。     

激光快速成形过程中316L不锈钢显微组织的演变

对316L不锈钢在激光快速成形过程中的凝固行为和组织形成进行了考察．结果表明，成形件呈现全γ奥氏体结构，γ奥氏体从基体外延生长成柱状枝晶，并显示较强的晶体取向性，其（100）晶向基本平行沉积方向，仅在顶部出现一薄层转向枝晶层，而在成形件中出现的层带结构并未影响不同熔覆沉积层之间组织生长和取向的连续性．采用最高界面生长温度判据对激光快速成形中的相形成规律进行了分析，并结合平界面稳定性分析、枝晶生长理论和柱状晶／等轴晶转变模型讨论了成形件中的层带形成及外延柱状晶生长特性．     

基于MCT运动控制器的快速成型机数控系统研究

数控系统的合理性和可靠性是保证机床加工精度和稳定性的前提，快速成形是一种基于离散／堆积成型的快速制造工艺，对数控系统体系结构和软件有着特殊的要求。剖析了快速成形的工艺特点，提出以国产新型MCT运动控制器为控制系统核心、工业控制机为系统支撑单元的双CPU开放式数控系统，并介绍了该数控系统的功能和硬件、软件实现方法。通过该数控系统在快速成形机上的应用证明，该系统满足了快速成形技术对数控系统的要求。     

An Investigation of the Capability Profile of the Three Dimensional Printing Process with an Emphasis on the Achievable Accuracy

A benchmark procedure has been designed to assess the dimensional as well as the geometric accuracy of currently one of the most widely used rapid prototyping processes - the Three Dimensional Printing. It tests not only linear accuracy but also precision, and repeatability of the process, as well as its ability to create manufacturing features such as fillets and draft angles. The presented research results reflect the necessity to adequately respond to engineering requirements for clearly meeting dimensional and geometric tolerances and root on several in-house case studies proving the comparison with established high-end RP processes.     

A comparison of rapid prototyping technologies

Until recently, prototypes had to be constructed by skilled model makers from 2D engineering drawings. This is a time-consuming and expensive process. With the advent of new layer manufacturing and CAD/CAM technologies, prototypes may now be rapidly produced from 3D computer models. There are many different rapid prototyping (RP) technologies available. This paper presents an overview of the current technologies and comments on their strengths and weaknesses. Data are given for common process parameters such as layer thickness, system accuracy and speed of operation. A taxonomy is also suggested, along with a preliminary guide to process selection based on the end use of the prototype.     

Three-dimensional printing of metal parts for tooling and other applications

Three-Dimensional Printing is a Solid-Freeform Fabrication process that creates parts out of powder by spreading layers into which binder is ink-jet printed to define the part geometry of that layer. By repetition of the process layer-by-layer, three-dimensional components of very complex geometry can be created. This paper describes key aspects of the application of Three-Dimensional Printing to the fabrication of metal tooling where surface finish, dimensional accuracy, wear resistance, and process complexity impose challenging constraints on materials selection and processing.     

不同类型多孔结构生物材料支架制备及其性能优化

多孔支架是组织工程应用中的关键环节,类似细胞外基质的作用,支撑细胞的粘附和随后细胞向组织的衍化。虽然目前已采用多种制备技术研发出大量的多孔支架,但是多孔生物材料支架的制备和性能优化,仍然是组织工程支架领域的研究热点。结合实验室工作,综述了多种制备不同类型多孔结构生物材料支架的制备技术,主要包括颗粒和纤维堆积型支架、泡沫浸渍法支架和颗粒制孔支架等的制备技术,并阐述了这些制备技术对多孔结构支架的孔结构、贯通性和力学性能的改善效果。其目的旨在提供满足组织工程需求的多孔生物材料支架。     

Fabrication of Bioceramic Bone Scaffolds for Tissue Engineering

In this study, microhydroxyapatite and nanosilica sol were used as the raw materials for fabrication of bioceramic bone scaffold using selective laser sintering technology in a self-developed 3D Printing apparatus. When the fluidity of ceramic slurry is matched with suitable laser processing parameters, a controlled pore size of porous bone scaffold can be fabricated under a lower laser energy. Results shown that the fabricated scaffolds have a bending strength of 14.1 MPa, a compressive strength of 24 MPa, a surface roughness of 725 nm, a pore size of 750 μm, an apparent porosity of 32%, and a optical density of 1.8. Results indicate that the mechanical strength of the scaffold can be improved after heat treatment at 1200 °C for 2 h, while simultaneously increasing surface roughness conducive to osteoprogenitor cell adhesion. MTT method and SEM observations confirmed that bone scaffolds fabricated under the optimal manufacturing process possess suitable biocompatibility and mechanical properties, allowing smooth adhesion and proliferation of osteoblast-like cells. Therefore, they have great potential for development in the field of tissue engineering.     

Regenerative engineering and bionic limbs

Amputations of the upper extremity are severely debilitating, current treatments support very basic limb movement, and patients undergo extensive physiotherapy and psychological counseling. There is no prosthesis that allows the amputees near normal function. With increasing number of amputees due to injuries sustained in accidents,natural calamities, and international conflicts, there is a growing requirement for novel strategies and new discoveries. Advances have been made in technological, material,and in prosthesis integration where researchers are now exploring artificial prosthesis that integrate with the residual tissues and function based on signal impulses received from the residual nerves. Efforts are focused on challenging experts in different disciplines to integrate ideas and technologies to allow for the regeneration of injured tissues,recording on tissue signals and feedback to facilitate responsive movements and gradations of muscle force. A fully functional replacement and regenerative or integrated prosthesis will rely on interface of biological process with robotic systems to allow individual control of movement such as at the elbow, forearm, digits, and thumb in the upper extremity. Regenerative engineering focused on the regeneration of complex tissue and organ systems will be realized by the cross-fertilization of advances over the past 30 years in the fields of tissue engineering, nanotechnology, stem cell science, and developmental biology. The convergence of toolboxes crated within each discipline will allow interdisciplinary teams from engineering, science, and medicine to realize new strategies, mergers of disparate technologies,such as biophysics, smart bionics, and the healing power of the mind. Tackling the clinical challenges, interfacing the biological process with bionic technologies, engineering biological control of the electronic systems, and feedback will be the important goals in regenerative engineering over the next two decades.     

Development of transfer type variable lamination manufacturing (VLM- ) process

RP technologies have been widely used to reduce the lead-time and development cost of new products. However, most of the developed RP technologies have disadvantageous characteristics, due to their working principle: a large building time, a stair-stepped surface of a part and additional post-processing. In addition, it requires a high cost to install, operate and maintain the RP apparatus.The objective of this paper is to propose a new rapid prototyping system, transfer type variable lamination manufacturing process using expandable polystyrene foam (VLM- ), to overcome the disadvantages. VLM- has various technical novelties such as a thick layer with thickness of less than 4 mm, a sloped surface with the first order approximation between the top and bottom surfaces of each layer, a stacking method using the pilot pin and building board, a concept of unit shape layer (USL), and a synchronized four-axis hotwire cutter with linear heat source and a parallelogram mechanism.In this paper, the characteristics and the key features of VLM- are discussed. In order to investigate the applicability of the new RP process, various prototypes, such as an extruded shape, son-o-kong shape, a world-cup logo, and a human head shape, are manufactured by the prototype of the VLM- apparatus. All shapes are manufactured within one hour. In addition, the efficiency of the new RP process is examined by comparing the world-cup logo shape and the human head shape with those of Laminated Object Manufacturing (LOM) from the viewpoint of geometrical conformity, total building time, building cost, and dimensional accuracy.     

Development of transfer type variable lamination manufacturing (VLM-st) process

RP technologies have been widely used to reduce the lead-time and development cost of new products. However, most of the developed RP technologies have disadvantageous characteristics, due to their working principle: a large building time, a stair-stepped surface of a part and additional post-processing. In addition, it requires a high cost to install, operate and maintain the RP apparatus.The objective of this paper is to propose a new rapid prototyping system, transfer type variable lamination manufacturing process using expandable polystyrene foam (VLM-st), to overcome the disadvantages. VLM-st has various technical novelties such as a thick layer with thickness of less than 4 mm, a sloped surface with the first order approximation between the top and bottom surfaces of each layer, a stacking method using the pilot pin and building board, a concept of unit shape layer (USL), and a synchronized four-axis hotwire cutter with linear heat source and a parallelogram mechanism.In this paper, the characteristics and the key features of VLM-st are discussed. In order to investigate the applicability of the new RP process, various prototypes, such as an extruded shape, son-o-kong shape, a world-cup logo, and a human head shape, are manufactured by the prototype of the VLM-st apparatus. All shapes are manufactured within one hour. In addition, the efficiency of the new RP process is examined by comparing the world-cup logo shape and the human head shape with those of Laminated Object Manufacturing (LOM) from the viewpoint of geometrical conformity, total building time, building cost, and dimensional accuracy.     

An inverse approach to the numerical design of the process sequence of tailored heat treated blanks

While in industries lightweight construction gain an increasingly significant role and as weight reduction is often done with aluminum sheets, advanced production technologies have to be developed to be competitive for this evolution. Since steel sheet metal parts cannot be substituted directly with aluminum due to its minor formability, the usage of so called tailored heat treated blanks (THTB) is presented in this work. THTB are locally heat treated aluminum blanks from the 6,000-series alloy which exhibit a specific strength pattern optimized to the forming operation leading to a significantly improved formability for the manufacturing of complex aluminum car body parts. The enhancement of the formability is reached by a local heat treatment before the forming process. Due to the strong interdependency of heat treatment and forming operation, a numerical investigation of the process sequence is a prerequisite for a cost-effective usage of the THTB. An inverse approach on basis of a finite element simulation enables the determination of process parameters for an optimized THTB, thus having an effective and efficient engineering method for this technology. The investigations presented in this paper were carried out within the project CRC 396 B4 “Robust, shortened process sequences for lightweight sheet parts” sponsored by the German Research Foundation (DFG).     

Representation of surface roughness in fused deposition modeling

Most rapid prototyping (RP) technologies apply a layered manufacturing (LM) process to efficiently fabricate 3D physical models. However, a critical drawback that reduces the surface quality of the RP parts occurs by utilizing LM. Hence, topics related to surface roughness have been a key issue in RP. In this paper, a new approach to model surface roughness in fused deposition modeling (FDM) is proposed. Based on actual surface roughness distributions of FDM parts, a theoretical model to express surface roughness distribution according to changes in surface angle is presented by considering the main factors that crucially affect surface quality. The proposed expression is verified by implementation and comparison with empirical data. Also, the effectiveness of the main factors is analyzed and discussed.