模具制造中的窄深特征自动识别
Automatic Narrow-Deep Feature Recognition for Mould Manufacturing
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摘要: 模具中通常存在一些细长窄深的凹区域，该区域很难、甚至无法用刀具加工，通常需要电火花加工或使用镶块等特殊加工方法。然而目前模具中镶块拆分和电火花加工设计大多还是利用CAD工具交互进行，非常耗时费力。为了自动确定这些窄深细小区域，本文分析了窄深细小区域的特点，利用特征技术，提出了一种基于痕迹和体分解特征识别方法相结合的窄深特征自动识别方法。该方法能在模具的设计模型中自动识别提取窄深细小区域信息，将有效提高模具镶块件和电火花加工设计效率，进而提高模具生产效率。
面向模具区域加工需求，结合窄深区域形状、几何特性，提出窄深特征的概念，再根据窄深特征形状进行归类，将窄深特征划分为基本窄深特征和组合窄深特征，基本窄深特征又进一步分为平面、圆柱、拉伸、梯形、圆锥形、锥形拉伸等不同类型。根据窄深特征加工特点，提出了窄深特征要求符合特征痕迹和拔模方向、刀具的最小直径、适合用刀具加工的区域的最小宽度阈值和最小宽深比条件。窄深特征识别方法首先确定窄深特征痕迹，以窄深区域近似平行面对为痕迹，通过扩展面对使之能完全切割毛坯；然后，通过几何推理识别特征组成面，以扩展痕迹面切割毛坯得到在包含特征体的特征扩展体中的基本组成面；最后，生成基本窄深特征的特征体，用扩展面对切割基本组成面和组成面切割扩展面对后，将切割的组成面缝合后生成特征扩展体，找出该基本特征的阻挡面，扩展阻挡面并切割特征扩展体得到特征体。为了得到尽可能大的组合特征，提出用启发式策略进行特征组合，生成组合特征的特征体。在特征组合时，相交、接触或近距离的窄深特征需要组合在一起可能大，同类型的窄深特征组合的可能性大。
本方法主要特点有：把特征识别技术应用到了模具非机加工领域；利用细小窄深区域特性确定特征痕迹以及进行相交特征处理；同时利用特种加工工艺要求和实体模型的几何性质进行几何推理识别基本窄深特征，由基本特征组合成复杂的组合特征；窄深特征的组成面可由平面或圆柱或曲面组成，曲面主要由扫描曲面和特定自由曲面等组成，部分拓展了现有特征识别方法的识别范围。实例验证了所提出方法的可行性。然而，针对含有复杂的旋转曲面和其它自由曲面构成窄深特征，对其面对的确定要复杂和困难得多，需要进一步研究；同时，由于近似面对的确定中采用采样技术、几何推理过程中涉及许多布尔运算，算法的效率有待提高。
所提出的窄深细小特征自动识别方法，将自动特征识别技术应用于模具非机加工领域，为窄深特征EDM加工和镶块生成提供一个计算机辅助设计与计算机辅助工艺规划连接的智能接口，也为模具CAD/CAM集成、提高模具特种加工效率提供了有效方法。Abstract: There usually exist narrow-long-deep areas in mould needed to be machined in special machining. To identify the narrow-deep areas automatically, an automatic narrow-deep feature (NF) recognition method is put forward accordingly. First, the narrow-deep feature is defined innovatively in this field and then feature hint is extracted from the mould by the characteristics of narrow-deep feature. Second, the elementary constituent faces (ECF) of a feature are found on the basis of the feature hint. By means of extending and clipping the ECF, the feature faces are obtained incrementally by geometric reasoning. As a result, basic narrow-deep features (BNF) related are combined heuristically. The proposed NF recognition method provides an intelligent connection between CAD and CAPP for machining narrow-deep areas in mould.-
Keywords:
- narrow-deep feature /
- feature recognition /
- face-pair /
- mould
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