基于特征的钣金冲压零件建模研究

在分析冲压件特点的基础上提出了适合该类零件的基于特征的建模方法，建立了基于特征的零件信息模型结构，论述了形状特征信息、工艺特征信息、制造特信息等特征模块的建立原则及建立方法。     

冲压产品特征识别技术的研究

本文介绍了基于三维线框模型冲压零件的特征提取,特征推理的一些方法和原则,从零件几何模型中识别出加工特征,能提高设计评价,工艺规划,模具选择的自动化程度,针对冲压零件的形状特点,采用基于面的表达模式表示特征,利用几何推理和工艺知识相结合的方法唯一确定加工特征,特征间的关系用二叉树结构描述。     

基于特征的汽车覆盖件冲压CAPP系统研究

基于特征的冲压工艺设计是以行征作为处理的核心基本单元，通过推理确定零件的加工方法。本文描述了基于特征的覆盖件冲压ＣＡＰＰ系统的框架结构；给出了工艺特征的定义；最后，以工艺过程模型为对象描述了基于特征的冲坟工艺设计推理过程。     

钣金零件的特征建模研究

提出了一个基于特征的钣金零件模型,并运用面向对象技术来表达特征,同时利用ＡｕｔｏＣＡＤ的扩展实体数据,将特征嵌入到ＡｕｔｏＣＡＤ的图形数据库中,有效地解决了钣金零件的特征建模问题。     

基于XML的冲压零件特征建模

冲压零件信息模型是冲压工艺分析与模具设计的重要基础,对冲模CAD/CAE/CAM具有重要意义。本文引入了可扩展标识语言XM1进行冲压零件特征建模,实现了在Internet上的冲压零件信息描述,使之可用于基于Internet的CAD/CAE/CAM系统的集成研究。     

级进模CAD冲压特征工序设计自动化的研究

介绍了级进模CAD系统中，冲压工艺特征工序设计自动化方法。建立了冲压工艺特征的计算机模型和冲压工艺特征库，提出了设计零件上的冲压工艺特征和冲压工艺库的特征进行匹配的技术和算法，给出了特征参数的计算方法。探讨了这种技术在级进模CAD系统中的实现。     

汽车覆盖件冲压工艺规划建模技术

为提升工艺规划的智能化程度,应用多色集合理论建立了基于特征的汽车覆盖件的信息模型.利用多色集合建立了汽车覆盖件冲压工艺特征映射模型,实现了汽车覆盖件从设计特征到工艺特征的映射.在此基础上,提出了一种基于规则的工艺方案推理算法,并进行了汽车覆盖件冲压工艺规划的推理研究.最后,以汽车后盖板零件为例,对所提出的模型与算法进行了验证.     

一种基于特征脚本的三维零件模型描述方法

针对零件模型中参数化特征建模过程和约束等信息的描述问题，提出了一种基于特征脚本的三维CAD零件模型描述新方法，使用可扩展标记性语言(XML)描述零件特征脚本，给出了零件模型中草图和形状特征的XML脚本描述方法，针对参数依赖和几何约束信息与几何实体匹配问题，研究了几何实体的持久命名机制；以Creo系统为例，通过程序开发，生成描述零件模型的XML特征脚本文件，并导入该脚本文件，重建特征建模过程以及参数和几何依赖关系，验证了基于特征脚本CAD零件模型描述方法的可行性。     

一种基于位形空间理论的几何建模方法

基于李群李代数的位形空间理论，给出了常见特征的位形空间与基于特征原型位形表示的零件几何建模方法，建立了装配设计定位的数学模型，提出了基于零件几何模型及其位形表示的装配几何模型的建模方法。     

一种面向CAPP的零件信息输入方法

本文应用面向对象技术的思想，建立了基于特征的零件信息模型，提出了一种基于Ｗｉｎｄｅｏｗｓ环境的零件特征信息输入方法，为实现回转体零件信息的快捷输入提供了一条途径。     

An investigation of higher-order closures in the computation of the flow around a generic car

The ability of non-linear eddy-viscosity and second-model-closure models to predict the flow around a simplified three-dimensional car body, known as the “Ahmed body,” is investigated with a steady RANS scheme. The principal challenge is to predict the separation from and reattachment onto the slanted rear roof portion at the slant angle 25°, which is close to the critical value at which separation is just provoked from the roof surface. At these conditions, it has been conjectured that separation is intermittent, with periodic flapping being a highly influential process. This is thus an exceptionally challenging case, especially for low-Re models, as the geometrical complexity occurs together with high-Re conditions (Re = 768,000) and highly complex flow features in the wake of the body. A 1.89M-node mesh containing 44-blocks was employed for one half of the spanwise symmetric body. The results demonstrate that the Reynolds-stress-transport model employed is able to reproduce, in contrast to all other models, the reattachment of the flow on the slanted rear surface. As a consequence, the strong streamwise vortices emanating from the sides of the body and associated with lift and circulation are also reproduced in good agreement with experimental data. The physical processes at play and the reasons for the predictive differences are discussed.     

A History-Independent Modelling-Oriented Approach to Solve Geometric Constraints Between Features in 3D Space

History-independent modelling systems are more flexible than history-based ones. They let designers manipulate the model in a more associative, rather than prescribed, way. In this paper, an approach based on 2D geometric constraint solving and a topological entity naming mechanism (TENM) is presented to solve the geometric constraints between features in 3D space. Firstly, in order to break the unidirectional dependency between features in a history-based modelling system, a data structure named feature constraint graph(FCG) is adopted to represent the geometric constraints between features in 3D space. Then a solving sequence is obtained using degree-of-freedom (DOF) based graph analysis. And finally, during the evaluation of the solving sequence, the dimensions in 3D space are mapped to 2D space, the dimensions in 3D space are satisfied indirectly by solving the corresponding 2D geometric constraint system. An example is given to illustrate the process of our approach.     

Conversion of wireframe to ACIS solid models for 2 1/2-D engineering components

Wireframe models need to be converted to solid models as the latter tend to become more widespread, consistent and affordable. A conversion algorithm for manifold objects was defined to obtain ACIS, thede facto standard B-rep model from a neutral IGES wireframe model and was implemented in C++ in successive stages as follows. All potential surfaces are found first. The entities lying on the same surface are examined in order to form closed profile-loops. Loop nesting is examined according to a ray casting algorithm. Adjacency and nesting of loops is used in order to assign traversal directions to all edges according to the Möbius rule. Invalid profiles (those containing edges belonging to more than two loops) are searched for and successively removed. The final test is that of edge type. If the majority of edges turn out to be concave, the traversal sign of all edges is reversed, so that the body is solid in empty space and not the other way around. For engineering components the algorithm adequately resolves all singular cases.     

Shape Representation and Interoperability for Virtual Prototyping in a Distributed Design Environment

Internet technology opens up another domain for building a future CAD/CAM environment. The environment will be global, network-centric, and spatially distributed. In this paper, we present an approach to network-centric virtual prototyping (NetVP) in a distributed design environment. The presented approach combines the current virtual assembly modelling and analysis technique with distributed computing and communication technology for supporting virtual prototyping activities over the network. This paper focuses on shape representation and interoperability of product models for distributed virtual prototyping. STEP standard and CORBA-based interfaces allow bi-directional communication between the CAD model and the virtual prototyping model, which makes it possible to solve the problems of interoperability, heterogeneity of platforms, and data sharing. STEP AP203 is used as a means of transferring and sharing product models. In addition, Attributed Abstracted B-rep (AAB) is introduced as 3D shape abstraction for trans-parent transmission of 3D models and for the maintenance of naming consistency between CAD models and virtual prototyping models over the network.     

支持设计和工艺过程的装配模型

产品装配建模是对产品进行设计评价的基础,ＳＴＥＰ是支持产品整个生命周期的产品信息数据交换标准;本文提出了反映设计过程和装配过程的二叉树装配模型。采用面向对象的技术,用ＳＴＥＰ的ＥＸＰＲＥＳＳ－Ｇ 对装配单元进行描述,便于产品的可装配性评价及与其它应用领域如ＣＡＤ、ＣＡＭ 等的集成。     

基于组件的三维CAD系统开发的关键技术研究

研究子组件技术和特征造型技术 ,并以“金银花”系统的开发为实例对基于组件开发三维 CAD系统的相关技术和实现方法进行了深入研究 ,给出了实现系统的框架结构和组件结构。     

General geometric modelling approach for machining process simulation

Machining process simulation systems can be used to verify NC (numerically controlled) programs as well as to optimise the machining phase of the production. These systems contribute towards improving the reliability and efficiency of the process as well as the quality of the final product. Such systems are particularly needed by industries dealing with complex cutting operations, where the generation of NC code represents a very complex and error-prone task. A major impediment to implementing these systems is the lack of a general and accurate geometric method for extracting the required geometric information. In this paper, a novel approach to performing this task is presented. It uses a general and accurate representation of the part shape, removed material, and cutting edges, and can be used for any machining process. Solid models are used to represent the part and removed material volume. Bezier curves (in 3D space) are used to represent cutting edges. It is shown that by intersecting the removed material volume with the Bezier curves, in-cut segments of the tool cutting edges can be extracted. Using these segments, instantaneous cutting forces as well as any other process parameters can be evaluated. It is also shown that by using B-rep (Boundary representation) polyhedral models for representing solids, and cubic Bezier curves for representing cutting edges, efficient, generic procedures for geometric simulation can be implemented. The procedure is demonstrated and verified experimentally for the case of ball end-milling. A very good agreement was found between simulated cutting forces and their experimental counterparts. This proves the validity of the new approach.Notation cx ₃,cx ₂,cx ₁,cx ₀ parameters of cubic polynomialx(t) - cy ₃,cy ₂,cy ₁,cy ₀ parameters of cubic polynomialy(t) - cz ₃,cz ₂,cz ₁,cz ₀ parameters of cubic polynomialz(t) - bx _i ,by _i ,bz _i x-,y-, andz-coordinates of ith control point, respectively - b _i ith control point - R tool radius (m) - angular position of point on cutting edge measured from positivex-axis in case of flat end mill (°) - helix angle of cutting edge on flat end mill (°) - A, B, C, D parameters of the equation of a plane - td _i ,tu _i lower end and upper end of theith in-cut segment (before updating) - n number of in-cut segments (before updating) - td _j ,tu _j lower end and upper end of theith in-cut segment (after updating) - m number of in-cut segments (after updating) - dF _t , dF _r tangential and radial components of the infinitesimal cutting force (N) - K _t ,K _r empirical constants in tangential force and radial force equations (N/m²) - b thickness of axial infinitesimal element of cutting edge (m) - h instantaneous chip thickness of axial infinitesimal element of cutting edge (m) - _s shear strength of workpiece (N/m²) - dA _c cross-section area of undeformed chip on the infinitesimal element of cutting edge (m²) - shear angle (°) - _e effective rake angle (°) - friction angle (°) - or (t) angular position of point on cutting edge of ball nose of ball end mill (rad) - u _j , d _j lower end and upper end ofjth in-cut segment (rad) - t parameter     

A stochastic tessellation for modelling and simulating colour aluminium grain images

The work described in this article is motivated by the need for modelling and simulating some colour aluminium grain images. One possible approach for modelling these colour aluminium grain images is to approximate the images by trivariate piecewise constant functions corrupted by additive and correlated noise. Such a piecewise constant function modelling approach is naturally divided into three parts: shape, colour and noise. The main focus of this article is to present a new tessellation model which can be applied to model the shape characteristics of the aluminium grain images. One special feature of the new tessellation model is that it is capable of generating tessellation patterns having rough boundaries. Some empirical properties and variants of the tessellation model are also described. Then, as a secondary focus, this article describes models and methods for modelling the observable colour values and noise of the aluminium grain images. Both visual and empirical comparisons between real and simulated images suggest that our modelling is reasonable.     

Identification of a friction model—Application to the context of dry cutting of an AISI 1045 annealed steel with a TiN-coated carbide tool

The characterization of friction coefficients at the tool-chip-workpiece interface remains an issue. This paper aims to identify a friction model able to describe the friction coefficient at this interface during the dry cutting of an AISI1045 with TiN coated carbide tools. A new tribometer has been designed in order to reach relevant values of pressures and sliding velocities. This set-up is based on a modified pin-on-ring system. Additionally a numerical model simulating the frictional test has been associated in order to quantify average friction coefficients around the spherical pin, from the standard macroscopic data provided by the experimental system. A range of cutting speeds has been investigated. It has been shown that the friction coefficient is very much dependant on the sliding velocity. A new friction model has been identified based on the average local sliding velocity.     

产品造型设计要重视和运用价值工程

在市场经济条件下,价值工程对产品造型设计的指导作用尤为重要.该文作者结合价值工程概念与功能分析等因素探讨了这一问题.