T样条曲面计算机辅助制造方法与关键技术研究

发布时间：2018-04-18 01:27

本文选题：T样条曲面 + 计算机辅助制造　；参考：《浙江大学》2014年博士论文

【摘要】：为了在计算机辅助制造过程中更方便地表达形状复杂的零件,尤其是便于对自由曲面生成多轴加工刀路,学术界和工业界一直在寻求合适的数学表达方法。多面体模型和多片张量积曲面复合模型是当前最流行的两种数学模型,但是它们在表达复杂工件和刀具路径生成方面各自有不足之处。而在另一方面,T样条曲面突破了张量积结构的桎梏,发展了局部控制域的概念,减少了曲面控制顶点数量并使其自由地排列。由于其出色的曲面表达能力,T样条已经在计算机辅助设计、造型、有限元分析等领域得到了广泛应用。针对上述CAM业界由来已久的问题,本文提出了一整套解决方案。将T样条引入CAM过程中,用于表达自由曲面。利用T样条曲面参数域原像特殊的拓扑结构,直接对其完成刀具路径规划。该项工作为解决自由曲面的计算机辅助制造提供了新思路,同时也拓展了新型曲面的应用,增强了CAD/CAM领域的交叉发展。本文完成了以下几项工作：一、经过比较和总结CAM系统自由曲面的常见数学表达方法,提出使用T样条曲面作为计算机辅助制造的数学模型。建立了T样条节点／控制顶点一体化数据结构,发展了局部控制域的概念,完善了T样条曲面点求值与局部几何性质的计算方法。在此基础上,结合刀具路径参数与误差标准,直接在T样条曲面上生成加工刀路。连通了复杂形状零件的CAD造型设计与CAM加工规划之间的鸿沟。二、针对传统等高度分层加工的加工余量不均匀、引发刀具颤振、损害成形表面等缺点,提出一种渐进型分层加工方法(Morphing machining strategy, MMS)。利用了T样条曲面自由的参数域拓扑结构,将复杂的工件和毛坯形状表达于单一曲面。以切削深度和工序余量等加工参数作为约束条件,基于能量最小化方法调整控制顶点,使T样条曲面从设计形状向毛坯形状整体变形,生成一系列变形曲面。然后,将按逆序把这些曲面作为加工层,从毛坯开始逐层加工,最终得到工件的设计形状。三、提出了一种基于改进型空间填充曲线(Improved space-filling curve, ISFC)的精加工刀路生成方法。为了克服传统空间填充曲线无法在非矩形域上生成刀具路径的缺点,针对T样条曲面不规则的参数原像以及带孔洞的拓扑结构,调整网格点安排策略,保证形成合法胞腔,防止边界附近区域出现欠切削材料。另外,针对刀具路径拐角容易引起切削不足的问题,添加Hermite补偿曲线,使刀具在拐角平滑过渡并且清除多余材料。四、整合上述T样条曲面点及几何性质计算方法,渐进型分层加工方法,ISFC精加工刀路生成算法,开发了一套针对T样条曲面的CAM原型系统。该系统能够读取和查看T样条曲面,结合用户输入的加工参数,生成加工分层,并在各曲面层内规划单连通刀具路径。对于生成的刀路,系统可以进行线框走刀仿真。然后根据五轴机床配置,进行刀路后处理,输出用于实际切削加工的数控NC代码。为了验证刀路算法和软件性能,在实验章节选用了包括鼠标凸模、变速箱端盖、人造指骨模型等传统机械零件以及生物医疗器件,进行了刀路生成、软件仿真以及实际机床加工。实验成果表明了本文算法的可行性,高效性,以及软件系统的可靠性。进一步说明了T样条曲面在表达复杂零件和刀路规划方面具有优秀的性质,适合应用于自由曲面的计算机辅助制造。
[Abstract]:In order to facilitate the expression of complex shape parts in computer aided manufacturing process, especially for the generation of multi axis machining tool path on the free surface, academia and industry have been expressed in seeking appropriate mathematical methods. Polyhedral model and multi chip tensor product surface two kinds of mathematical models of composite model is the most popular, but they the expression of complex workpiece and tool path generation of their own shortcomings. On the other hand, T spline surface breaks the shackles of the tensor product structure, the development concept of local control domain, reduce the number of control points and the amount of surface free arrangement. Because of its excellent surface expression ability, T spline have been in the computer aided design, modeling, finite element analysis has been widely used. In the CAM industry long-standing problems, this paper puts forward a set of solutions. The T spline The introduction of the CAM process, for the expression of the free-form surface. Using topological structure of T spline surface parameter domain preimage special, complete tool path planning on it. This work provides a new way to solve the computer aided manufacturing of freeform surface, but also opens a new surface should be used, enhance the cross development in the field of CAD/CAM in this paper. The following work has been finished:
First, through the common mathematical comparison and summary of CAM system for free surface expression method is proposed using the T spline surface as a mathematical model for computer aided manufacturing. Established T spline node / control points of the unified data structure, the development of the concept of local control domain, improve the calculation method of T spline surface and local geometric point evaluation nature. On this basis, combined with the tool path parameter and standard error, direct generation of tool path in T spline surface. The gap between the connected parts with complex shape CAD design and CAM machining programming.
Two, the traditional machining allowance highly stratified processing is not uniform, causing damage to the surface forming tool chatter, and other shortcomings, put forward a kind of incremental hierarchical processing method (Morphing machining strategy, MMS). By using the parameter domain topology T spline surface free, the workpiece and the blank shape complex expressed on a single surface with the cutting depth and the process allowance and other processing parameters as constraint conditions, energy minimization method to adjust the control points based on T spline surface deformation from the design to the overall shape of the blank shape, generating a series of deformation surface. Then, according to the reverse surface as the processing layer, from the rough start step by step processing, final design the shape of the workpiece.
Three, the paper proposes an improved based on space filling curves (Improved space-filling curve, ISFC) of the precision machining tool path generation method. In order to overcome the traditional space filling curve cannot generate the tool path in the non rectangular domain shortcomings, for the parameter preimage of T spline surface and irregular topology with holes, adjust the grid arrange strategy, ensure the formation of legal cell, prevent the emergence of less cutting material area near the boundary. In addition, the tool path is easy to cause the problem of insufficient corner cutting, adding Hermite compensation curve, so that the tool in the corner smooth transition and remove excess material.
Four, the integration of the T spline method to calculate the surface point and geometric properties, incremental hierarchical processing method, ISFC machining tool path generation algorithm developed for T spline surface CAM prototype system. The system can read and view the T spline surface, combined with the processing of user input parameters, generate hierarchical processing, and in the surface layer planning single connected tool path. For the generation of the tool path, the system can take the knife frame simulation. Then according to the five axis machine tool configuration, road postprocessing, output for the actual machining NC NC code.
In order to verify the tool path algorithm and software performance, in the experiment section were selected including the mouse punch, gearbox cover, artificial phalangeal model of the traditional mechanical parts and biomedical devices, the tool path generation, software simulation and actual machining. The experimental results show the feasibility of this algorithm, the efficiency and reliability of the software. The system is further illustrated. T spline surface has excellent properties in the expression of complex parts and tool path planning, suitable for computer aided manufacturing of freeform surface.

【学位授予单位】：浙江大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TH164

【参考文献】