常用快速成型系统及其选择原则

目前已经商品化的RP系统众多 ,且同一种系统又有不同的制造商 ,系统的性能价格比各不相同。因此 ,如何选择合适的RP系统 ,是用户比较头疼的一个问题。本文简要介绍了LOM、SLS、SLA和FDM四种常用RP系统的工作原理、优缺点和主要的RP系统型号及其制造商 ,从RP系统的用途、制件精度、成型材料、成型空间、成型效率、激光功率、成本和技术服务等方面出发 ,提出了一些选用常用RP系统的原则 ,并举例予以说明。     

Hybrid additive manufacturing of metal laminated forming tools

Deep drawing dies are manufactured using metal sheets. Laser metal deposition is used for bonding the sheets and smoothening the edges. The strength and surface finish of the dies are the key challenges. Milling, roller burnishing, and laser treatment are applied as post-processing for improving the surface finish. A semi-analytical model is developed for selecting the sheet combination for sufficient strength. The new rapid prototyping process offers high flexibility for complex die geometries. The evaluation by deep drawing experiments using DC06 and high-strength HC380LA blanks revealed the feasibility of the new manufacturing routes regarding deep drawability and surface finish.     

Development of a hybrid rapid prototyping system using low-cost fused deposition modeling and five-axis machining

Currently, two major processes are being used to produce prototypes, namely machining and rapid prototyping. Machining is generally more accurate and precise, but it is difficult to produce objects with certain complicated features. In contrast, rapid prototyping can produce objects with complicated features, which allows materials to be used more efficiently. However, due to the uneven shrinkage and residual stresses within rapid prototyping products, their accuracy is usually uncertain. This study attempts to integrate these two manufacturing processes and develop a hybrid rapid prototyping system in order to overcome the disadvantages associated with each process and to develop new applications. Fused deposition modeling (FDM) was used as the rapid prototyping process in this work. A spindle and a low-cost FDM extruder were designed to be placed on each end of a rotary axis in a five-axis machine tool. The proposed design allows the rotation of the axis on the five-axis machine to switch between machining and FDM, thus achieving the advantage of reducing costs for extra actuators without sacrificing working space. The case studies demonstrated that the proposed hybrid system can build FDM objects without using support materials and produce FDM parts with metal embedded to increase the stiffness. The system can also conduct five-axis machining on a completed FDM part or trim the freeform surface fabricated by FDM to achieve more accurate dimensions or better surface finish.     

Development of a welding system for 3D steel rapid prototyping process

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Concave edge-based part decomposition for hybrid rapid prototyping

As one of the solutions to the limitations of the current layered manufacturing, hybrid rapid prototyping systems that perform both machining and deposition are being introduced. In the hybrid rapid prototyping, a part of a complicated shape is realized by adding layers of a simpler shape, each of which is obtained by machining a sheet of constant thickness from its top and bottom surfaces. Thus it is desired to decompose a given part into the minimum number of layers while guaranteeing each layer to be fabricated from the given sheets using a 3-axis milling machine. To satisfy these requirements, a concave edge-based approach is proposed to decompose a part into layers by considering the tool accessibility, the total number of layers, and the allowable sheet thickness. In this approach, for a given build-up direction, the undercut edges, which cause a part to be inaccessible by a tool, are extracted and classified into two types and eliminated in two decomposition steps.     

基于金属粉末的激光快速成型技术新进展

金属粉末的激光快速成型技术是集计算机辅助设计、激光熔覆、快速成型于一体的先进制造技术,是传统加工成形方法的重要补充。本文系统介绍了金属粉末激光快速成型的原理、系统组成及最新研究进展,并对其发展前景进行了展望。     

基于超声波焊接技术的快速成型方法研究

提出了一种新的基于超声波焊接技术的快速成型方法.它是采用薄片材料,如金属、塑料片材或带材等,进行逐层加工,先采用超声波焊接,层层之间的结合实现固体连接,每一层焊接完成后,根据CAD数据信息,驱动刀具进行平面加工,然后再堆积加工成形新层,直至完成零件与模具的制造,实现了一种新的精密高效低成本加工与成形技术.使用鱼骨图分析了影响成型件产品质量的各种因素.     

基于冰上的光固化快速成型技术

为了解决快速成型技术实际应用中的精度与成本之间的矛盾,提出了基于冰上的光固化快速成型技术,该技术综合了现有的光固化(SL)和熔融沉积成形(FDM)设备的工作原理,实现了在保证原型精度的同时,大大降低了制造设备和成型的成本。     

A low cost cutter-based paper lamination rapid prototyping system

Paper lamination rapid prototyping technology has an advantage of its low overall cost due to the building materials and the processing principle. To reduce the system and its operating cost further, a cutter-based paper lamination rapid prototyping system is proposed. The cutter set employed is cheap and the cutter can turn its cutting direction automatically so as to simplify the system control. In this paper, the cutting mechanism of the cutter was studied. According to its kinetic characteristics, the motion of the cutter nose was described by a tractrix model, and its trace error can be eliminated by modifying the cutter path. Experimental study on the cutting notch was carried out, and the notch specimens were measured through a high-power microscope VH-8000. According to the analysis of the experimental results, the dimension error caused by the cutting notch was within 3 μm and the roughness average (Ra) was less than 6 μm. Two physical parts have been fabricated on the developed experimental machine, which indicates the proposed system has use value.     

Manufacturing of micro thin-walled metal parts by micro-droplet deposition

Metal micro-droplet deposition manufacturing technique is a novel direct metal rapid prototyping for building the miniaturized parts. In this paper, the novel direct metal rapid prototyping was proposed to fabricate micro thin-walled metal parts. A direct droplet fabrication experimental system was developed based on the forming principle of micro-droplet deposition manufacture. Several deposition experiments were conducted to investigate the influences of process parameters on the formed wall thickness and deposition accuracy of droplets. The experimental results show that the proper deposition distance Hs for obtaining high deposition accuracy of droplet ranges from 1 mm to 20 mm; the formed wall thickness W can be controlled by selecting different nozzle diameters D and formed angle of deposited droplet θ. According to the experiment results, a micro thin-walled structure with wall thickness of 400 μm was fabricated by adjusting the process parameters. The above research works show that it is feasible to fabricate the micro thin-walled metal parts by micro-droplet deposition manufacturing technique.     

Three-dimensional finite element analysis of thermal stress in single-pass multi-layer weld-based rapid prototyping

The complex thermal stress and residual stress distributions in the weld-based rapid prototyping process could cause large deformation and even cracking. In this paper, the thermal stress evolution, and the residual stress distribution in a single-pass multi-layer weld-based rapid prototyping are examined, and the effect of depositing directions on the residual stress and residual strain is studied by numerical simulation, after experimental verifications of the finite element model. The results show that the predicted residual stress variation trends are generally in agreement with the experimental results. The deposition of the last layer dominated the residual stress of whole component. This is due to the stress release effect of the rear layers on the fore layers. Besides, depositing directions have significant influence on the residual stress and equivalent plastic strain distributions of components, where the deposition in the reverse direction acquires the better result.     

基于激光诱导化学液相沉积的快速成型方法

对当前常用的RP工艺,如立体光刻、分层实体制造、熔融挤压成型、选区激光烧结等的原理、工艺和优缺点进行了简单评述,认为上述工艺均存在一些固有缺陷,距离企业的需求(如金属模具直接成型等)还有比较大的差距。在介绍激光诱导化学液相沉积(LCLD)技术的基础上,本文提出了一种基于该技术的新型快速成型方法,给出了其成型系统原理图,并详细介绍了系统的工作过程。分析表明,该种RP系统能够较好地弥补现有系统的不足之处,具有极其广阔的应用前景。     

Fine lattice structures fabricated by extrusion freeforming: Process variables

This paper describes the main factors affecting the rapid prototyping of fine lattices by extrusion freeforming of powder, notably equipment accuracy, paste preparation, extrusion and post-processing and their effects on filament deposition and the defects that might be caused. Effective methods were devised in order to reduce the incidence of these defects. The results provide guidance for fabrication of very fine lattices from powder extrusion (comprising <100 μm diameter filaments) and improvement of sample quality.     

Reverse engineering for rapid prototyping of 3D compound surfaces using edge detection and delaunay triangulation method

The objective of this research is to develop an efficient reverse engineering method of 3-dimensional compound surfaces for rapid prototyping processes. As a first step, the image-processing techniques were applied to scanned data obtained using a laser scanner for edge detection. Based on the detected edges, the boundary information of the compound surface was extracted in order to divide the surface into several separate regions. As a next step, the Delaunay triangulation method was applied in order to independently reconstruct the surface on the basis of the scanned data and the boundary information. Finally, STL files were created for the rapid prototyping process. Required simulations and experiments were performed and the results were analyzed to show the effectiveness of the proposed methods.     

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.     

A 3D dynamic analysis of thermal behavior during single-pass multi-layer weld-based rapid prototyping

Weld-based rapid prototyping enables the capacity of forming 3D complex parts. In rapid prototyping there exists the particular thermal cycling, being repeatedly heated at the same place, which is the basic cause of complex thermal stress. In this paper experiments are carried out to investigate the thermal characters of single-pass ten-layer deposition. Meanwhile a 3D transient heat transfer numerical simulation with temperature-dependent material properties is conducted to investigate temperature field evolution, thermal cycling character, temperature gradient and the effects of depositing directions on the thermal process of single-pass ten-layer rapid prototyping. The calculated results match the experimental measurements well. The research results show that the heat diffusion condition of molten pool becomes worse as the depositing height increases. With other parameters being constant, the heat diffusion condition can be significantly improved by optimizing the depositing directions. The heat diffusion condition of component with the same depositing directions is better than reverse directions.     

基于极坐标下的FDM快速成型机的插补算法的设计

插补作为FDM成型中的关键环节,在FDM快速成型机中具有重要的作用,直接影响着加工成型的速度和精度,而采用极坐标的插补算法成本低、控制原理简单。鉴于极坐标下插补的优点,在对普通的直角坐标系插补算法的分析的基础上,对FDM快速成型机的极坐标插补算法进行了分析与设计,并且通过Delphi可视化软件的设计验证了该插补算法的可行性。为了使基于极坐标系下的插补算法更满足FDM快速成型机工作时对速度稳定性的要求,在此基础上,提出了时间分割的方法来优化该算法,从而保证了在一个周期内进给速度的稳定,熔滴成型的均匀性,大大提高了加工的精度。     

Windows操作系统下快速成型控制系统研究

本文根据快速成型技术的特点设计了适合多种快速成型技术的主从式控制系统，介绍了其系统组成结构，并重点介绍了Windows环境下多线程程序的优先级控制方法和32位并行通讯协议的实现方法。     

三维快速成型打印机成型材料

三维快速成型打印技术作为新兴技术,具有很大潜力.简述了三维快速成型打印技术的发展和现状,描述了三维打印技术的成型原理,材料的选择后处理过程,并提出了展望.