拉伸类特征的高效实现

在特征造型系统中，对于复杂零件的造型，特征实现的效率问题越来越突出。对于拉伸类特征：孔、槽、凸台等，通常将其特性轮廓线拉伸形成标准特征体，然后用布尔操作与基本体结合。但是，由于布尔操作存在效率低、操作的可预见性差等问题，效果并不令人满意。针对这些问题，我们提出了布操作的一种替代，将轮廓线直接拉伸到实体的边界。该算法作为一种有效的造型手段。已在特征造型系统ZD－MCADⅡ中用于拉伸类特征的实现。

AN EFFICIENT IMPLEMENTATION FOR PROTRUSION FEATURES

In the feature based modelling system, the efficiency of feature implementation is especially emphasized for complex part in engineering applications. The conventional method is to generate evaluated boundary representation by converting features into solid primitives and corresponding Boolean operations. For the protrusion features, such as hole,slot,pocket, the protofeature is obtained by sweeping it's characteristic profile, and merged to the base part using Boolean operation. For the thinking of efficiency, we propose an algorithm, which directly sweep the 2D profile into the surface of the base solid.This algorithm is efficient and robust, and had been applied in a feature - based modeling system ZD - MCADII for the implementation of protrusion features.