一种基于STEP的CAD模型直接分层方法

提出了一种基于产品模型数据交换标准的3维计算机辅助设计实体模型直接分层方法,零件的原始计算机辅助设计模型以产品模型数据交换标准中性文件的格式输入分层系统,系统提取其几何拓扑信息并重建计算机内部几何模型。用户选择零件的制作方向并指定分层厚度后,系统自动对计算机辅助设计模型进行直接分层,分层结果可直接送到各种快速成型系统加工。基于产品模型数据交换标准的计算机辅助设计模型直接分层不依赖任何特定的计算机辅助设计系统,通用性、灵活性好,而且产品模型数据交换标准文件的数据量大大小于STL文件,有利于网络化设计与制造环境下的数据传输与交换。     

Parasolid数据的STL变换研究

为满足CAD软件与快速成形领域的数据交换需要,提出了一种Parasolid数据的STL变换方法。利用Parasolid建模核心的PK-TOPOL-facet()函数将Parasolid模型按STL文件规则进行三角网格化,通过返回的拓扑信息构建三角面片与它的顶点和法向量的拓扑关系,并由此生成了STL文件。应用实例和Solidworks软件诊断表明,采用该方法可以将Parasolid文件变换为STL文件,生成的STL模型中无错误面和缝隙存在。     

自由曲面的反求工程与快速原形技术

反求工程与ＲＰ技术相结合的可以为快速产品开发提供关键技术技术;数据获取技术和曲面重建技术。本文首先对这两方面的关键技术的原理与方法进行了分析;然后分析了ＲＰ机驱动数据文件－ＳＴＬ文件格式。提出了不经过格式转换,直接从ＣＡＤ模型以ＳＴＥＰ或ＳＴＬ格式进行切片处理来研究如何提高精度的新思路。     

STL File Generation with Data Reduction by the Delaunay Triangulation Method in Reverse Engineering

Reverse engineering has been widely used for the shape reconstruction of an object without CAD data and typical steps include the scanning of a clay or wood model and the generation of manufacturing data such as an STL file. A new approach to remove point data with Delaunay triangulation is introduced to deal with the size problems of the STL file and the difficulties in the operation of the rapid prototyping (RP) process. The selection of a group of triangles, based on the angle, is used for a robust and reliable implementation of the Delaunay triangulation method. The developed software enables the user to specify the criteria for the selection of the group of triangles by the angle between triangles, the percentage of reduced triangles, and the allowable area. This approach can be used to reduce the measuring data from the laser scanner, thus save the handling time of point data during the modelling process and is useful for verifying and slicing the STL model during the RP process.     

基于Magics的激光快速成型三维CAD模型数据处理

Magics软件是快速成型行业中数据处理的通用软件.本文介绍了激光快速成型中基于Magics的三维CAD模型的数据处理技术,包括STL文件修复、产品的位置放置和支撑生成等.从而快速地获得精确的制造数据,并快速制得所需原型.     

CS File – An Improved Interface Between CAD and Rapid Prototyping Systems

The STL file, which is de facto standard for the rapid prototyping industries, has too large a file size. This paper proposes an improved interface between CAD and rapid prototyping systems, i.e. a CS (compressed STL) file that has very low data storage redundancies and is completely compatible with the STL file. The CS file is about a quarter of the size of the original binary STL file, without any model information loss. This is very suitable for file transferring via the Internet. Removing coordinate data of duplicate vertices, bit-compression technology, and a comparison of the size and compressed performance of the STL and the CS are also discussed. ID="A1"Correspondance and offprint requests to: Dr Li-Chao Zhang, Rapid Prototyping Building, State Key Laboratory of Plastic Forming Simulation and Die and Mould Technology, Huazhong University of Science and Technology, Wuhan, Hubei, 430074, PR China. E-mail: elegantteac@yahoo.com     

Adaptive direct slicing of a commercial CAD model for use in rapid prototyping

Slicing a 3D graphic model into layers of 2D contour plots is an essential step for all rapid prototyping (RP) machines. Various methods are available, such as stereo lithography (STL) file slicing, direct slicing and adaptive direct slicing. Amongst these, adaptive direct slicing is the most advanced for its capability of adapting the slicing thickness according to the curvature of any contour. In this study, an adaptive direct slicing method complete with the algorithm for calculating the thickness of each layer is proposed. As an illustration of the method, the algorithm was programmed within the commercial CAD software package, PowerSHAPE. The method was shown to be fast and accurate in comparison with STL file slicing and direct slicing, which both used a constant layer thickness. An erratum to this article can be found at     

STL file generation from digitised data points based on triangulation of 3D parametric surfaces

For the current generation of rapid-prototyping models, laser scanners are currently being used more frequently due to rapid first measuring speed and high precision. Direct generation of an STL file from the digitised points has a great of advantage in that it can reduce time and error during the modelling process. A reduction in the number of point data is important while generating the STL file directly from the measured point data and maintaining precision. A new approach is developed in this paper to generate an STL file directly from point clouds by indicating a tolerance ε to maintain precision. The STL file can be generated directly from scattered points using a new algorithm that reduces and triangulates digitised point data based on triangulation of 3D parametric surfaces. Two experimental examples are presented to demonstrate the effectiveness and efficiency of the proposed algorithm.     

Improved intermediate point curve model for integrating reverse engineering and rapid prototyping

Direct integration of reverse engineering and rapid prototyping removes two intermediate steps of surface fitting from point cloud data and STL file generation from CAD models. Therefore errors introduced due to surface fitting and triangulations are eliminated and also the process of STL data validation and repair is avoided. Intermediate point based curve model (IPCM) method is one of the promising approaches for direct integration of reverse engineering and rapid prototyping however this approach has the limitation that it cannot handle objects, which result in multiple contoured slices. Moreover, IPCM based method is implemented with layers of constant thickness slices, and adaptive slicing with this method is not attempted. The present work is an attempt towards improving the capabilities of IPCM based method by overcoming the above-mentioned two limitations. The new system developed here has been tested on many parts, which demonstrates the capability of the proposed system. An erratum to this article can be found at     

SL快速成型中支撑自动生成技术研究

针对 SL快速成型技术加工时需要对零件加支撑的要求 ,通过对 CAD模型和 STL模型文件特点的分析 ,采用直接从 STL 模型文件提取信息找到 CAD模型的待加支撑面、线、点 ,并按待加支撑面、线、点的特征给其加二维支撑 ,再确定支撑空间高度的方案 ,实现了支撑自动生成。应用表明 :该技术节省了 SL加工时的数据预处理时间 ,避免了利用人工加支撑时的人为错误 ,提高了快速成型的效率     

义齿加工模型STL文件的数据读取技术研究

STL文件是一种在快速成型加工中经常使用的文件格式。采用Oracle数据库技术读取STL文件中的数据,并对STL中的数据点进行了有效的冗余去除,减小了数据存储量,便于对有用的数据进行加工后处理,提高了处理效率。同时,Oracle技术的使用增强了编程的灵活性和效率。     

快速成型的切片数据优化

在目前的快速成型系统中，普遍采用STL格式文件来表达CAD模型，因而在切片后截面轮廓含有大量的数据冗余点，影响了插补加工的精度和效率。文章针对直接插补算法，在分析STL文件及切片数据的组成基础上，提出了一种数据冗余点过滤算法，在保证加工精度的条件下，有效地滤除了冗余点。该方法算法简单，运算时间短，有效地提高了后续插补过程的稳定性，在数据优化后仍采用直线插补，既保证了加工精度，又加快了插补速度。     

基于CT数据及快速成型技术的牙列三维重建研究

通过CT扫描,获得牙列图像的原始数据,再通过医用处理软件Mimics对所得的数据进行处理与转换,对牙列进行三维重建.然后再在Geomagic软件对模型进行修补,光顺等处理,使之尽量与病人的组织完全贴合,并转化为快速成型机能够识别的STL文件格式.最后在快速成型机上做出病人的组织模型.     

Part decomposing algorithm based on STL solid model used in shape deposition manufacturing process

Shape deposition manufacturing is an innovative rapid prototyping technology combining CNC machining and deposition processes and in which if a surface of the part is visible from the build direction it can be directly shaped into desired geometry on part material; if the part features are undercut or face away from the build direction, these part features will be sculptured into the support material in order to form a negative cavity at first, then the part material is deposited into this negative cavity in order to replicate these features into part material. This process is cyclically repeated until all segments have been built. Finally, the sacrificial material is removed, and the finished part is left. This innovative technology has the benefits of commercial rapid prototyping technology; meanwhile, it inherits the accuracy and high surface quality of traditional machining process. For this process to be realized, it is essential to decompose the CAD solid model into a series of manufacturable segments which have no undercut surfaces at the data pretreatment step. In this paper, a solid decomposing strategy is proposed with a detailed discussion on the classification of the segments based on the value of triangle face normal vector, and then an algorithm for auto-decomposing a CAD solid model in STL data format is developed.     

面向快速成形的复杂曲面重建技术研究

针对快速成形工艺特点,提出了一种基于实物的复杂曲面几何重 建的方法。由此直接生成的快速成形机优化STL接口文件,实现了反求容差与模型网格数的 最佳匹配,避免了由通用软件转换存在的错误和繁复,提高了成形设备的前处理效率,并为 反求工程与快速成形技术的有机集成提供了可靠途径。     

The computer-aided design and rapid prototyping fabrication of removable partial denture frameworks

This study explores the application of computer-aided design and manufacture (CAD/CAM) to the process of electronically surveying a scanned dental cast as a prior stage to producing a sacrificial pattern for a removable partial denture (RPD) metal alloy framework. These are designed to retain artificial replacement teeth in the oral cavity. A cast produced from an impression of a patient's mouth was digitally scanned and the data converted to a three-dimensional computer file that could be read by the computer-aided design (CAD) software. Analysis and preparation were carried out in the digital environment according to established dental principles. The CAD software was then used to design the framework and generate a standard triangulation language (STL) file in preparation for its manufacture using rapid prototyping (RP) methods. Several RP methods were subsequently used to produce sacrificial patterns, which were then cast in a chromium-cobalt alloy using conventional methods and assessed for accuracy of fit. This work demonstrates that CAD/CAM techniques can be used for electronic dental cast analysis, preparation, and design of RPD frameworks. It also demonstrates that RP-produced patterns may be successfully cast using conventional methods and that the resulting frameworks can provide a satisfactory fit.     

Multiresolution Hybrid Mesh for Rapid Prototyping

Stereolithography (STL) is the prevailing technology in rapid prototyping (RP) applications. The STL process involves mesh triangulation of a sculptured object from a CAD model and then the extraction of cross-sections from the mesh model. In most current systems, the resulting model suffers from topological problems, such as degenerate facets, undesired holes, or flipped normals, which lead to invalid cross-sections that cannot be manufactured as layers. This paper proposes a hybrid system that takes advantage of structured and unstructured mesh geometry in order to optimise the RP process and make it more robust and accurate. The system has been developed as part of a joint project between the 3S Laboratory at Grenoble University, France and the Laboratory for Computer Graphics and CAD at the Technion, Israel. Within the system, a constrained mesh simplification model (3S Lab) is integrated with a multilevel model (CAD Lab).