摘要
随着快速成形技术的发展，人们对制件的精度越来越重视。通过不断改进成形工艺和成形材料的性能，其精度已有很大的提高。然而在快速成形技术中，目前普遍采用基于STL文件的数据处理方式，再加上在成形过程中难以克服的阶梯效应，这就在一定程度上限制了制件精度的进一步提高。此外，现有快速成形系统中的CAD、数据处理和监控加工软件彼此独立，使得其前处理过程想当繁琐，要求操作人员必须具有较高的素质。针对上述问题，本文在深入研究直接分层和自适应分层方法的基础上，基于MDT软件环境，开发了RP数据处理软件。所作的主要工作如下：
(1) 提出一种基于网格划分的参数曲面与平面求交算法。这种算法简单、实用，已成功地应用于基于CAD模型直接分层的RP数据处理软件中。
(2) 提出一种综合考虑法线与面积的自适应分层算法，并针对同一模型对自适应分层和等厚分层的误差分布作了比较。结果表明，在相同的尖峰误差条件下，自适应分层能明显提高加工效率。
(3) 在深入研究MDT(Mechanical Desktop)中三维模型表示方法的基础上，运用Autodesk公司提供的MDT二次开发工具ObjectARX和MDT API，成功地实现了对MDT模型信息的提取，进而使直接自适应分层算法得以实现。
(4) 对直接分层得到的数据进行了工艺规划。实现了对层片轮廓线段的排序、拟合、刀具补偿以及轮廓内部填充和扫描路径优化等。
(5) 根据RP数据处理系统的功能需求，对整个软件进行系统设计，并对各个功能模块进行集成。该系统不但提供了目前RP系统普遍采用的CLI文件输出接口，而且还自定义了一种新的由直线和圆弧组成的CLA文件接口，从而为后续监控加工模块的实现和整个CAD/CAPP/RP系统的集成奠定了基础。
本课题的研究，对提高快速成形制件质量、简化数据前处理过程、促进RP设备的重新定位具有重要的理论意义和实用价值。
With the development of rapid prototyping (abbreviated as RP hereinafter) technology, the part precision issue is becoming more and more important. And the prototyping precision has been greatly improved by ameliorating the processing skills and material properties. In the present rapid prototyping technologies, however, the STL file based data processing method and the staircase effect, which is inevitable during rapid prototyping process, restricts the further improvement of the part precision. Also, the existing RP-related software, including CAD system, the data processing system, and the monitoring and controlling system, are independent of one another. The preprocessing procedure of RP is so complicated that it requires the operators to be well-educated. Considering the above issues, this paper deals with the direct and adaptive slicing methods of CAD model, and develops the RP data processing software based on the Mechanical Desktop (MDT) software. The main work may be summarized as follows.
(1) Presents a grid-based intersection algorithm of parametric surface and plane, which is characterized by effectiveness and conciseness, and has been successfully implemented in the RP data processing software.
(2) After discussing all kinds of the existing algorithms, this paper presents a new kind of adaptive slicing algorithm by comprehensively considering the surface normal and the cross-section area. And for the same part, a comparison of the cusp height error distributions between the adaptive slicing and the equal-thickness slicing methods is given. The results show that the adaptive slicing method can greatly improve the manufacturing efficiency in the same cusp height error.
(3) Based on a close research of the CAD model representation in MDT, this paper picks up the model information expressed in the boundary representation (B-Rep) using the development kits of ObjectARX and MDT API offered by Autodesk Inc.
(4) The direct slicing data are processed so as to realize the sorting and fitting of short lines, the cutting tool compensation, the layer contour filling and the optimization of the scanning paths, etc.
(5) Designs the architecture of RP data processing software according to the functional requirement of RP, and integrates all the functional modules. The software not only provides CLI file interface applied in the current RP systems, but also provides a initiatively-defined CLA file interface consisting of lines and arcs in order to lay a solid foundation for the forthcoming realization of monitoring and controlling modules and for the integration of CAD, CAPP and RP.
The work in this paper will be beneficial to improving the part quality and simplifying the preprocessing procedures of RP. It might lead the rapid prototyping apparatus to be re-oriented to a new member of the modern CAD system family.
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