Efficient calculation of trapped volumes in the layered manufacturing process

Prototypes of a design are always needed for the purposes of visualisation and evaluation for manufacturability, functionality, and aesthetic appearance. Since the prototyping process requires a significant amount of cost and time, various rapid prototyping processes have recently been introduced. However, it is usually necessary for a part built up by a rapid prototyping system to be finished by a post-processing process, in which the stair steps on the surfaces, the support structures (if they exist), and the unprocessed material are eliminated. This post-processing is usually done manually and is a time-consuming task. Eliminating the trapped volumes (the volume of the unprocessed material entrapped by the solidified portion) is sometimes impossible in some processes.This study provides a designer with a tool to detect the existence of trapped volumes and to calculate the quantity in a given build-up direction, so that a suitable build-up direction is chosen or the part is built in pieces to avoid the problems caused by the trapped volumes. Since the proposed algorithm can efficiently calculate the amount of the trapped volumes in any build-up direction, it has the potential for such applications as optimising the build-up direction to minimise the trapped volumes.     

形状沉积制造及其应用

文章在分析了常规的快速原型制造所存在的缺点后，详细地介绍了形状沉积制造区别于快速原型制造过程中单纯地添加材料的过程——添加／去除零件材料方法，正是由于这一差别使得该方法制造的零件精度不受分层厚度的影响，并且可以采用多种材料制造零件。介绍了形状沉积法的具体工艺过程、可采用的材料沉积工艺方法、沉积制造的设备构成、分层技术、特点及基于形状沉积制造的新方法——模具形状沉积制造，最后介绍了形状沉积制造在功能零件、模具及预装配机构快速制造中的应用实例。     

Integrated simulation of the injection molding process with stereolithography molds

Functional parts are needed for design verification testing, field trials, customer evaluation, and production planning. By eliminating multiple steps, the creation of the injection mold directly by a rapid prototyping (RP) process holds the best promise of reducing the time and cost needed to mold low-volume quantities of parts. The potential of this integration of injection molding with RP has been demonstrated many times. What is missing is the fundamental understanding of how the modifications to the mold material and RP manufacturing process impact both the mold design and the injection molding process. In addition, numerical simulation techniques have now become helpful tools of mold designers and process engineers for traditional injection molding. But all current simulation packages for conventional injection molding are no longer applicable to this new type of injection molds, mainly because the property of the mold material changes greatly. In this paper, an integrated approach to accomplish a numerical simulation of injection molding into rapid-prototyped molds is established and a corresponding simulation system is developed. Comparisons with experimental results are employed for verification, which show that the present scheme is well suited to handle RP fabricated stereolithography (SL) molds.     

阻抗套密封在离心压缩机中的应用介绍

对阻抗套密封的工作原理、密封结构特点、密封可靠性作了详细的说明。通过密封性能计算以及试验数据证实了阻抗套密封的优点(同浮环密封相比)。最后介绍了阻抗套密封在生产使用中应注意的事项。     

<Emphasis Type="Italic">Rapid Moulding Using Epoxy Tooling Resin</Emphasis>

Rapid prototyping (RP) is fast becoming a standard tool in today’s product design and manufacturing environment. Significant benefits in terms of lead time and cost savings have been reported with the use of RP technology. However, these benefits can be derived only during the design and planning stages of a new product where RP parts are produced in small quantities for design evaluation, form fitting, and marketing analysis. The high cost of raw material stock used in current RP systems makes them economically unsuitable even for small-batch production during the product evaluation and manufacturing stages. Further to this, the difference between the mechanical and physical properties of RP and traditional manufacturing materials limits the functionality of RP end products. Rapid tooling (RT) technology has opened up new cost-effective solutions for small-batch production. In this paper, a technique using a rapid soft-tooling approach, namely, aluminium filled epoxy resin tooling for injection mould preparation is successfully explored. An aluminium filled epoxy resin mould is evaluated and the characteristics of the injection-moulded end products are presented.     

快速成形转向快速生产的主要障碍

快速成形制造 (RPM)技术是国外 80年代后期发展起来的一门新兴综合技术。它使直接从概念设计迅速转为产品设计的生产模式成为可能 ,工业界正在探索使用快速成形机器生产最终要制造的零件的问题。但是 ,它面临诸如材料性能、表面质量、零件的尺寸规格和成形速度等许多挑战。一旦克服了这些障碍 ,快速成形就将转向快速生产 ,并将促进大量定制生产模式的加快实现     

Optimizing process parameters for selective laser sintering based on neural network and genetic algorithm

Selective laser sintering (SLS) is an attractive rapid prototyping (RP) technology capable of manufacturing parts from a variety of materials. However, the wider application of SLS has been limited, due to their accuracy. This paper presents an optimal method to determine the best processing parameter for SLS by minimizing the shrinkage. According to the nonlinear and multitudinous processing parameter feature of SLS, the theory and the algorithms of the neural network are applied for studying SLS process parameters. The process is modeled and described by neural network based on experiment. Moreover, the optimum process parameters, such as layer thickness, hatch spacing, laser power, scanning speed, work surroundings temperature, interval time, and scanning mode are obtained by adopting the genetic algorithm based on the neural network model. The optimum process parameters will be benefit for RP users in creating RP parts with a higher level of accuracy.     

Al2O3 Ceramics Preparation by LOM (Laminated Object Manufacturing)

Al2 O3 ceramics green tape of 0.7 mm thickness was fabricated by a roll-forming technique. Ceramic green parts were formed by LOM (laminated object manufacturing), a kind of RP (rapid prototyping) technique. Final products were produced by a pressureless sintering process. Thermal analysis and SEM microstructure analysis of green tape were carried out to decide on the best process for removing the binder. Using a SEM, the microstructure of the ceramic parts was analysed. The mechanical properties of the parts were also analysed.     

Rapid Prototyping Applications in Medicine. Part 1: NURBS-Based Volume Modelling

Rapid prototyping (RP) technology has extended traditional manufacturing applications in areas other than product engineering. Using RP to fabricate custom implants and prostheses for surgical planning and education is now an important area of research. Although, in theory, RP is capable of producing objects of any complexity, designing freeform shapes is difficult using current CAD systems. These CAD systems are geared toward the design of parts manufactured by traditional methods; they do not help designers exploit the extended opportunities offered by RP technology. Medical data cannot be input into these CAD systems directly for further modification and manipulation. The purpose of this project is to explore a new approach for modelling and prototyping biomedical objects. The work extends from volume modelling to RP and medicine. In this paper, Part 1 of two papers, a new approach to modelling complex objects, NURBS-based volume modelling, is proposed. A NURBS representation of volumes is developed to represent not only the surface boundary but also the interior of a 3D object. NURBS-based volume modelling inherits advantages from both NURBS modelling and voxel-based modelling. The key idea of the NURBS-based volume modelling is to exploit the flexibility of NURBS modelling and use the voxelised NURBS volumes as components for constructing complex objects. Part 2 deals mainly with issues of interfacing volume models to RP systems. A new approach to generate STL files through volume modelling and iso-surface extraction is proposed. This approach guarantees the validity of the final STL file inherently. Software development and case studies are also given.     

Process chain development for the rapid prototyping of microstructured polymer, ceramic and metal parts: composite flow behaviour optimisation, replication via reaction moulding and thermal postprocessing

Different variants of reaction moulding techniques exploiting the rapid light-induced photopolymerisation of reactive resins are widely used in microsystem technologies for the fabrication of plastic components or for rapid prototyping (RP) purposes. In this paper, the further development of micro reaction moulding with respect to a rapid prototyping of ceramic and metal parts will be described. As in powder injection moulding, the process sequence binder–filler–formulation, replication, debinding and sintering has to be passed. The mould filling and, hence, the accurate reproduction of surface details depend strongly on the composite’s viscosity, which is a function of the filler load. Especially, an improved process control of the composite formation prior to moulding and the thermal debinding is crucial for the realisation of microstructured ceramic or metal parts. The development of the whole process chain and some examples will be presented. This paper was originally presented at the International Conference on Multi-Material Micro Manufacture (4M), Karlsruhe, Germany, 29 June 2005 to 1st July 2005, and is extended for publication in this journal.     

用于人工骨制造的喷射成形技术

近年来,应用组织工程材料的人工骨因能适时降解并诱导成形人骨,而成为最理想的骨组织人工替代方法和治疗手段。介绍采用多喷射成形制造骨组织工程材料的人工骨,指出用此法得到的人工骨的材料种类及微观组织结构均与人骨高度相似,而采用骨水泥,或含有烧结等步骤,将不具有这种相似性;此人工骨具有与人骨的功能梯度上相一致的材料结构、几何结构和生理功能;人骨生长因子（ＢＭＰ）通过特殊处理,使这达到多维复合,并且具有缓释     

BP神经网络在RP/RT集成制造系统误差控制中的应用

用RP/RT集成制造系统以往生产过程的工程记录数据作为样本对来训练一个改进的BP神经网络,把要加工制件的理想尺寸输入已训练好的神经网络的输入层,以该神经网络的输出层数据作为RP/RT集成制造系统的三维CAD输入数据,能有效地降低集成制造系统的误差,是提高RP/RT集成制造精度的一条新途径。     

Rapid Prototyping Applications in Medicine. Part 2: STL File Generation and Case Studies

Rapid prototyping (RP) technology has extended traditional manufacturing applications in areas other than product engineering. Using RP to fabricate custom implants and prosthesis for surgical planning and education is now an important area of research. Although, in theory, RP is capable of producing objects of any complexity, designing freeform shapes is difficult using current CAD systems. These CAD systems are geared toward the design of parts manufactured by traditional methods; they do not help designers exploit the expanded opportunities offered by RP technology. Medical data cannot be input into these CAD systems directly for further modification and manipulation. The purpose of this project is to explore a new approach for modelling and prototyping biomedical objects. The work extends from volume modelling to RP and medicine. In Part 1 of two papers, a new approach to modelling complex objects, NURBS-based volume modelling, is proposed. A NURBS representation of volumes is developed to represent not only the surface boundary but also the interior of a 3D object. NURBS-based volume modelling inherits advantages from both NURBS modelling and voxel-based modelling. The key idea of the NURBS-based volume modelling is to exploit the flexibility of NURBS modelling and use the voxelised NURBS volumes as components for constructing complex objects. This paper, Part 2, deals mainly with issues of interfacing volume models to RP systems. A new approach to generate STL files through volume modelling and iso-surface extraction is proposed. This approach guarantees the validity of the final STL file inherently. Software development and case studies are also given.     

A study of the relationship between stick-slip and micro-scratches generation during chemical-mechanical polishing process

An observation on the relationship between stick-slip phenomena and chatter scratch generation during chemical-mechanical polishing (CMP) was made using finite element analysis. The motivation for this work is based on the questions about the possibility of the stick-slip phenomena in the CMP process and the quantitative relation between the stick-slip behaviors and the formation characteristics of the scratch. The finite element simulation results showed that stick-slip friction could occur during CMP and it could be seen only in the case of the interactions with the particles trapped inside pad surface. Also, the stick-slip period increased with the density of interacting wafer surface material and the particle size had a significant effect on the stick-slip period and magnitude. It is expected that this work will aid the development of chatter scratch reduction technology.     

大型原型快速制造中的并行加工技术

认为分层实体制造工艺（ＬＯＭ）是目前较成熟的几种快速成形工艺中加工效率最高的一种,最适合用于制造大型原型。提出了基于ＬＯＭ工艺的分区并行加工的思想,即将加工平面分为加工区域,并将被加工零件的数据进行分割,控制系统驱动多台扫描仪并行加工。对其关键技术进行了分析。采用分区并行加工技术可大幅度提高ＬＯＭ工艺的成形效率。     

基于CNC的自适应直接分层制造方法研究

将RP技术的增材制造理念与数控铣削加工技术相结合,提出了基于CNC机床的金属零件分层制造方法。为解决等厚分层方法存在的缺陷,提出了基于相邻层面积变化比率和轮廓法向矢量的自适应直接分层算法,并在Pro/E软件平台上,利用Pro/TOOLKIT进行了系统的开发。该方法采用定厚板材作为造型材料,在等厚分层的基础上对分层板进行自适应分层切削,有利于保证成型精度和提高成型效率,为复杂形面功能零件的快速成型制造提供了一种有效的方法。     

On-Line Layer Profile Dimensions Measurement of Model Maker Rapid Prototyping Using Vision Technology

The key principle of rapid prototyping (RP) is to fabricate a 3D object, layer by layer, which is a 2D fabrication process. Vision technology is being successfully applied in general industry to inspect object dimensions on-line, but most of the applications are limited to objects with 2D patterns. Hence, it should be possible to apply vision technology to inspect RP layer profile dimensions on-line. A CCD camera was employed to capture the layer profile image of the Model Maker (MM) RP system layer by layer. The captured image was processed to identify the RP profiles and further to calculate the real profile dimensions of the fabricated layer. The experimental results demonstrate that the dimensions of an RP part could be measured in situ, layer by layer, and could, potentially, be real-time monitored. This paper presents the vision calibration and the detailed image processing algorithms for the single layer profile identification and dimensions measurement. The results show that the measurement accuracy of the layer profile was about 98%.     

A Generic Part Orientation System Based on Volumetric Error in Rapid Prototyping

The paper presents the development of a generic part orientation system for rapid prototyping by considering the issue of volumetric error encountered in parts during the layer by layer building process in a rapid prototyping (RP) system. An algorithm is developed that slices the part with horizontal planes and computes the volumetric error in the part at different orientations by rotation about user-specified axes. The system recommends the best orientation based on the least amount of volumetric error in the part. The system has been tested using several examples of simple and complex parts. The generic part orientation system is believed to be first of its kind based on a volumetric error approach and will be useful for RP users in creating RP parts with a higher level of accuracy and surface finish, and also for intelligent process planning in rapid prototyping. RID=" ID=" <E5>Correspondence and offprint requests to</E5>: Assoc. Prof. S. H. Masood, CAD/CAM/CAE Group, Industrial Research Institute Swinburne, Swinburne University of Technology, Hawthorn, Melbourne, 3122 Australia. E-mail: smasood&commat;swin.edu.au     

Analysis of vacuum melting, ultrasonic, and radiographic techniques for gas porosity evaluation in die castings

Parts manufactured using die-casting processes may have significant limitations, mainly due to the tendency for air to be trapped during die-cavity filling. The detection and accurate measurement of porosity due to trapped air are essential issues for improving the quality of manufactured parts. This paper focuses on a comparison of radiographic, ultrasonic inspection, and vacuum melting techniques for analyzing the porosity level due to trapped air in parts manufactured using die-casting processes. To this end, aluminum alloy parts manufactured in a horizontal cold chamber die-casting machine using different injection velocities and mold configurations are analyzed. For the radiographic and ultrasonic techniques, a methodology is established to determine the level of porosity in the part, while, for the vacuum melting technique, a test procedure is established and an expression is obtained to relate the quantity of gas trapped in the part with the pressure increments measured as the part is melted in a vacuum furnace. The advantages and limitations of these techniques to evaluate porosity levels in die-cast parts are discussed in detail. Finally, the possibilities of using these techniques to select operating conditions that reduce the amount of trapped air during the filling stage are analyzed.