Tolerance Graph for Tolerance Control in Process Planning

这笔资金用于开发用于数控加工中离散机械零件设置规划的自动公差控制的理论方案。提出的公差控制方案是基于图论的。零件的特征用顶点表示，特征间的参数公差和几何公差用边表示。零件的整个设计规范由一个超图或公差图表示。因此，将最优布局规划问题转化为图搜索问题。将根据各自的设置方法，基于对最小设置误差的分析来开发优化算法。公差图中包含了NC加工的特点。最后，拟议的研究将被实施为计算机程序，并将与计算机辅助设计系统集成。如果成功，这项研究将产生两大贡献：(1)为工艺设计中的公差控制奠定坚实的理论基础和科学严谨的基础；(2)开发一种公差作图技术，最终取代有限公差作图技术。借助公差图，可以有效地解决规划相关的公差控制问题。因此，可以以较低的成本生产精密零件。所提出的公差控制算法将为工艺设计和现有工艺方案的分析提供一种实用的方法。具体地说，通过使用公差图，可以(1)选择适当的设置、定位基准和操作顺序以最大限度地减少公差堆叠，(2)计算加工切割的操作尺寸和公差，以及(3)同时处理所有轴上的公差。作为一个额外的好处，本研究采用了一种基于科学的方法来解决容差控制问题。以科学为基础的方法更容易计算机化，以促进实现计算机化的公差。

This grant provides funding for the development of a theoretical scheme for automated tolerance control of discrete mechanical part setup planning in numerically controlled (NC) machining. The proposed tolerance control scheme is based on graph theory. The features of a part are represented by means of vertices while the parametric and geometrical tolerances assigned among the features are represented by edges. The entire design specifications of a part is represented by a hyper graph or tolerance graph. Hence, an optimal setup planning problem is transformed into a graph search problem. An optimization algorithm will be developed based on analysis of the minimum setup errors according to the respective setup methods. Characteristics of NC machining are incorporated within the tolerance graph. Finally, the proposed research will be implemented into a computer program and will be integrated with a computer aided design system. If successful, this research will yield two major contributions: (1) It will establish a theoretically sound foundation and scientifically rigorous base for tolerance control in process planning, and (2) It will develop a tolerance graphing technique that will eventually replace the limited tolerance charting technique. With the help of a tolerance graph, planning related tolerance control problems can be solved effectively. As a result, precision parts could be produced at reduced cost. The proposed tolerance control algorithm would provide a practical approach for process design and analyzing currently existing process plans. Specifically, by using a tolerance graph, one can (1) select appropriate setups, locating datums, and operation sequences to minimize tolerance stackup, (2) calculate operational dimensions and tolerances for machining cuts, and (3) simultaneously deal with tolerances along all axes. As an additional benefit, this research adopts a science-based approach to solving tolerance control problems. Science-based approaches are much more easily computerized to facilitate the realization of computerized tolerancing.