Virtual prototypes have been appealing in the early design stage of computer aided tolerancing, because it is less expensive to evaluate and modify tolerances numerically. Derived from the machining processes, form uncertainties are simulated, controlled and analyzed in virtual prototypes using parametric and intuitive surface patches. The generation of a complete virtual prototype often involves combining surface patches with different patterns to one complete model. To overcome possible geometric defects in this process, a surface merging method is proposed in this paper. Skin Model Shapes is first introduced as the geometric foundation. The whole part surface is segmented based on the geometric shape and machining type. Then point-based patches are generated accordingly. Interpolation implicit surfaces based on radial basis function networks are constructed in patch boundaries based on spatial-constrained homogeneous transformation matrices. A feature augmentation process is then introduced to preserve processing features after resampling the blend patch. The proposed method is proved to be efficient in feature retaining as well as surface smoothing, through numerical experiments and analysis on an example mechanical part. The results show that the generated virtual prototype would become 62.5% more smooth while retaining a 91.6% feature similarity after using the proposed method. Moreover, the proposed method could preserve 174% more features at a cost of 9.0% smoothness than using a conventional modified trimmed filtering method.

虚拟原型在计算机辅助公差的早期设计阶段一直很有吸引力，因为通过数字方式评估和修改公差的成本较低。从加工过程中得出的结果，使用参数化和直观的表面补丁在虚拟原型中对形状不确定性进行了模拟，控制和分析。完整虚拟原型的生成通常涉及将具有不同图案的表面补丁组合到一个完整模型中。为了克服此过程中可能出现的几何缺陷，本文提出了一种表面合并方法。皮肤模型形状最初是作为几何基础引入的。根据几何形状和加工类型对整个零件表面进行分割。然后相应地生成基于点的补丁。在基于空间约束的齐次变换矩阵的斑块边界中构造基于径向基函数网络的内隐隐曲面。然后引入特征增强过程以在对混合补丁重新采样后保留处理特征。通过数值实验和对示例机械零件的分析，证明了该方法在特征保持和表面平滑方面是有效的。结果表明，使用所提出的方法后，生成的虚拟原型将变得更加平滑62.5％，同时保持91.6％的特征相似性。而且，与使用传统的改进的修剪滤波方法相比，所提出的方法可以以9.0％的平滑度保留174％的特征。