Tolerance Graph for Tolerance Control in Process Planning

该补助金为数控（NC）加工中离散机械零件设置规划的自动公差控制理论方案的开发提供资金。 提出的公差控制方案是基于图论。 零件的特征用顶点表示，而特征之间的参数公差和几何公差用边表示。 零件的整个设计规格由超图或公差图表示。 因此，一个最佳的安装规划问题转化为一个图搜索问题。 根据各自的设置方法，将基于最小设置误差的分析开发优化算法。 数控加工的特点是纳入公差图。 最后，建议的研究将实施到一个计算机程序，并将与计算机辅助设计系统集成。 如果成功的话，这项研究将产生两个主要的贡献：（1）它将建立一个理论上健全的基础和科学严谨的基础公差控制在工艺规划，（2）它将开发一个公差图技术，最终将取代有限的公差图表技术。 借助公差图，可以有效地解决与规划相关的公差控制问题。 结果，可以以降低的成本生产精密部件。 提出的公差控制算法将为工艺设计和分析现有工艺方案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，以使公差叠加最小化，（2）计算加工切削的操作尺寸和公差，以及（3）同时处理沿沿着所有轴的公差。 作为一个额外的好处，这项研究采用了基于科学的方法来解决公差控制问题。 基于科学的方法更容易计算机化，以促进计算机化公差的实现。

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.