基于特征模型的铸件毛坯自动生成方法

针对毛坯模型设计问题,提出一种由先铸造后加工零件的设计特征模型来自动生成毛坯模型的方法.首先消除设计特征模型中由草图和变换特征形成的多重解释;然后根据特征的设计历史提取材料移除体,再利用预先制定的可铸造性规则对材料移除体逐一进行可铸造性分析;最后根据拓扑元素父子关系还原修饰特征并增加加工余量,生成铸件毛坯模型.实验结果表明,该方法是有效的.     

形状特征中的拓扑元素编码体系

在基于特征的参数化造型系统中,根据特征历史记录进行特征重建是特征编辑的重要实现手段。在特征编辑中,维护设计者的设计意图,其关键问题是维护模型修改前后拓扑结构的对应关系,拓扑元素编码是维护模型修改前后拓扑结构对应关系的基础。依据模型的几何拓扑关系提出一种简洁、高效的拓扑元素编码体系,较好地实现了拓扑元素的编码,为特征编辑和重建打下了良好的基础,提高了特征设计的灵活性。     

一个标识子系统的设计与实现

特征造型的关键是合理地确定新旧模型拓扑元素之间的对应关系，文中提出一个基于特征的标识子系统，使得产品模型中每个拓扑元素都对应一个唯一的标识，标识匹配算法可以建立新旧模型拓扑元素之间的对应关系，标识子系统是作者开发的特征造型系统GDS的重要线成部分，为特征编辑、语义操作，二三维约束统一求解等奠定了基础。     

基于ACIS/HOOPS的特征造型系统设计与实现

为了探索CAD/CAM领域中的特征造型关键技术,研发一个特征造型系统。该系统分别以ACIS和HOOPS为几何造型引擎和渲染引擎,能够实现常用特征的创建、特征历史的管理、基本约束的管理和特征模型与几何模型的存取等功能,并且支持一些自由曲面特征造型以及参数化设计。为了维护用户的隐含设计意图,系统采用了一种新的拓扑元素命名与辨识机制。最后,给出了使用该系统进行特征建模、自由曲面特征参数化设计以及设计意图有效维护等实例,验证了本系统的可行性和有效性。     

渐开线齿轮实体建模与模板研究

基于Pro/ENGINEER的参数化设计,是指先用一组参数定义零件的三维实体模型并确定参数关系,包含几何关系和拓扑关系,然后提供给设计人员进行零件三维造型使用,设计结果的修改由尺寸驱动.设计时不必考虑零件中几何元素的准确位置或数值,而是通过向图形添加适当的约束条件定义零件形状.零件的参数化模型就是带有参数名的草绘,用户通过编辑参数,零件几何模型的拓扑信息不变,而尺寸自动改变.每一个约束形成一个代数关系式,通过约束推理确定需要修改的尺寸参数,系统将自动检索此尺寸参数对应的数据结构,找出相关参数的方程组并计算出参数,驱动参数化模型形状的改变,从而形成新的零件三维实体模型.     

混合加工特征识别方法

介绍一种集成了自动特征识别和用户交互特征定义的混合特征识别方法，该方法采用基于广义痕迹的特征识别建立零件的加工特征模型，通过交互特征定义对已建立的加工特征模型进行局部修改和再解释，在交互特征定义中，用户只需通过选取要修改的特征面定义自己的特征，剩余的面则调用自动特征识别算法处理，特征参数由系统提供的统一算法计算，从而减少了交互的工作量，这种混合特征识别方法有助于提高加工特征识别系统的实用性和健壮性。     

基于草图交互的个性化服装生成方法

以建立和交互修改三维服装草图为设计手段,提出在三维人体模型上生成三维个性化服装的参数化造型方法．服装草图由2种基本几何元素组成：体现人体围度信息的封闭样条曲线和体现人体在高度方向上曲面形状过渡的不封闭样条曲线．将服装草图约束分为2类4种：一类是体现服装宽松程度的人体与服装曲面之间的间隙约束;另一类是服装几何元素本身之间的共点、共面与对称约束．从人体的特征点出发,通过间隙约束生成服装草图的几何元素;在共点、对称和共面约束下,由服装草图几何元素建立拓扑结构为四边网格的服装草图．服装草图的交互修改是草图约束维护的过程,构建侧视图、正视图、断面图3个视图组成草图修改平台,在平台上交互编辑特征曲线．服装曲面则以三维草图为框架,通过对四边网格双线性Coons曲面插值生成．提供的设计方法使服装的造型变得简洁、灵活．     

基于子图的草图设计和约束求解

提出了一种基于子图的拟序列化草图设计方法。基于标识的约束模型统一了二维、三维约束,使得每个几何元素对应唯一的标识,几何元素之间的约束关系表示为标识之间的约束,这些约束被分为结构约束和尺寸约束。提出了基于序列化设计过程的约束求解方法。实验表明,该技术可快速有效地进行参数化草图设计和特征编辑。     

基于细胞元模型拓扑约束求解

在模型制造领域,对于拓扑约束的求解是一个比较新的课题,以往的研究一直局限在拓扑优化方面。而且对其应用也仅限于模型的定义方面,在模型的声明与约束求解方面却没有得到应用。文章提出一种基于细胞元模型拓扑约束求解方法,通过该方法可以确定模型拓扑声明的关系,文章假设一个模型是由一个或多个细胞元组成的,并且能够用这些细胞元的组合来表示,对模型进行拓扑约束求解就是用来确定细胞模型中的每个细胞元是否是全约束的。要做到这点,文章将每个细胞元用一个布尔变量表示,把拓扑约束问题映射成为布尔可满足性问题。再对新的问题进行求解,从而解决了模型的拓扑约束求解问题。     

参数化特征造型中拓扑结构变异的一种解决方法

文中首先分析了基于边界表示的特征模型用于参数化特征变动设计所存在的问题,指出了以边界表示中的几何边为形状特征定位约束基准无法满足拓拟结构变异的局限性,分析了基于草图的特征造型方法在变动设计中的重要性。在此基础上,提出了将基于实体模型边界表示的特征模型与基于草图的特征模型结合起来的新思想,并给出了该思想的实现方法,该方法使特征定位基准在特征造型过程中保持不变,且不随特征定位约束参数的改变而变化,能很好地满足参数化变动设计与拓扑结构变异的要求。     

A knowledge base model for complex forging die machining

Recent evolutions on forging process induce more complex shape on forging die. These evolutions, combined with High Speed Machining (HSM) process of forging die lead to important increase in time for machining preparation. In this context, an original approach for generating machining process based on machining knowledge is proposed in this paper. The core of this approach is to decompose a CAD model of complex forging die in geometrical features. Technological data and topological relations are aggregated to a geometrical feature in order to create machining features. Technological data, such as material, surface roughness and form tolerance are defined during forging process and dies design. These data are used to choose cutting tools and machining strategies. Topological relations define relative positions between the surfaces of the die CAD model. After machining features identification cutting tools and machining strategies currently used in HSM of forging die, are associated to them in order to generate machining sequences. A machining process model is proposed to formalize the links between information imbedded in the machining features and the parameters of cutting tools and machining strategies. At last machining sequences are grouped and ordered to generate the complete die machining process. In this paper the identification of geometrical features is detailed. Geometrical features identification is based on machining knowledge formalization which is translated in the generation of maps from STL models. A map based on the contact area between cutting tools and die shape gives basic geometrical features which are connected or not according to the continuity maps. The proposed approach is illustrated by an application on an industrial study case which was accomplished as part of collaboration.     

Exact Recognition of Compound Features by Feature Adjacency Matrix Elimination Algorithm

Aiming at the axiom of design for manufacture (DFM), this paper describes a recognition method for abstracting compound features from a part model and discloses the basic mechanism of compounding, also builds the corresponding 2D-simulation model. The inner association between feature neighboring and feature compounding is deeply discussed and, based on the essential transforming rule of two neighboring features, the corresponding feature adjacency matrix (FAM) of multi - feature entities are generated. For the manufacturing feature converted from the pure design feature; an innovative concept-homogenous compounding is presented to clarify the architecture of machining domain. Then, the FAM recurrence elimination algorithm is developed to determine all the compound features, and according to machining sequence, outputs a group of machining domains.     

Dimension and tolerance modeling and transformations in feature based design and manufacturing

This paper describes the development and application of a geometric dimension and tolerance (GD&T) model for use in both design and process planning. The model meets criteria for computability and compatibility with the Y14.5M standard. The model is first used to capture the designers GD&T scheme on a feature based design model, validate its completeness, and then transfer the GD&T to machining features extracted automatically by feature recognition. The model is based on relative degrees of freedom of geometric entities: feature axes, edges, faces and features-of-size. Dimension graphs are created based on the degrees of freedom for each control direction. Datum reference frames and standard tolerance classes are incorporated into the graph. The model allows dimension specification, dimension scheme modification, and dimension scheme validation. A methodology to automatically determine the GD&T of machining volumes obtained by feature recognition is also described.     

Recognizing manufacturing features from a design-by-feature model

This paper presents a methodology for recognizing manufacturing features from a design feature model. The common feature-feature interacting relationships are categorized. A feature recognition processor first translates the design feature model of a part into an intermediate manufacturing feature tree by handling design features according to their properties and the interacting relationships between features. Through combination, decomposition, and (tool approach direction) TAD-led operations, alternative interpretations of manufacturing feature model for the part are then generated, and the manufacturing feature tree is updated and extended with AND/OR operators to store these interpretations. Finally, a single interpretation with the lowest machining cost will be selected in the manufacturing feature tree. The proposed processor can support a dynamic and effective recognition process of manufacturing features during the design stage of a part. By defining the interactions between volumetric features elaborately, and utilizing design features and auxiliary information, the processor can recognize manufacturing features from complex parts. The processor recognizes not only some essential manufacturing features but also replicate, compound and transition features defined in STEP. The alternative interpretations can be used for a generic manufacturing application environment.     

特征的自动识别规则与提取

在对箱体类零件的加工特征及特征参数进行了分析,归纳和总结,在特征实体造型进行了研究的基础上,制定了各类特征的合理的识别规则和 识别算法,及提取的信息模型,实现了对复杂箱体类零件的加要特征信息自动提取,及CAD／CAPP系统的信息自动传递。     

一种拓扑元素的命名和辨识方法

在基于历史的参数化特征造型系统中,拓扑元素的命名和特征模型重新生成时拓扑元素的正确辨识是一个关键问题。该文提出了一种拓扑元素命名和辨识的新方法,此方法基于两个新概念－－影响特征和影响面,通过检查被引用元素和被辨识元素间的影响特征集、影响面集以及非影响集是否存在子集关系进行拓扑元素的辨识,其主要创新点在于依据导致一拓扑元素产生和产生变化的特征和特征面的信息进行拓扑元素辨识。该方法的主要优点是在特征模型编辑后物体的拓扑结构发生变异时能够更合理地辨识出设计历史中的引用拓扑元素。     

设计特征模型到分析特征模型的自动转换方法

针对有限元分析建模的需求,提出一种将工程零件的设计特征模型自动转换为相应的分析特征模型的方法.首先将设计特征模型分解为所有正特征剩余体的集合,然后从各正特征剩余体中分解出一组扫成体和非扫成体,再采用基于二维轮廓的方法从各扫成体中确定出候选分析特征区域,最后通过合成候选分析特征区域得到真正的分析特征区域,并在此基础上生成分析特征和分析特征模型.实验结果表明该方法是有效的.     

设计特征向加工特征转换的扫体重构法

针对同时需要铣削和车削加工的零件,提出一种基于扫体的从设计特征向加工特征转换的统一方法.采用扫体方式重构零件和毛坯模型,并将毛坯与零件之间的差体沿着这些扫体扫掠路径拆分出各种新的加工扫体,最后将这些加工扫体依照它们之间的邻接关系和加工特征形状结构选择合并成加工特征.该方法实现了同一零件中直扫体和回转扫体2种特征的统一转换,能够产生对应各种不同加工方法和方向的加工特征,有利于工艺优化.文中方法已应用于一个CAPP系统,其结果证明了该方法的可靠性.