“材料成型”专业CAX课程体系探索与实践

文章介绍了CAD／CAE／CAM课程体系教改实施意义、实施过程与实践效果，阐述了CAD／CAE／CAM课程体系强调理论与实操并重的教学目标，让学生掌握信息集成的制造思想的教育模式。并对CAD／CAE／CAM课程体系教改后进一步完善提出了建议。     

Global parameterization of a topological surface defined as a collection of trimmed bi‐parametric patches: Application to automatic mesh construction

We describe a new geometric algorithm to map surfaces into a plane convex area. The mapping transformation is bijective; it redefines the whole surface as a unique bi‐parametric patch. Thus this mapping provides a global parametrization of the surface. The surfaces are issued from industrial CAD software; they are usually described by a large number of patches and there are many shortcomings. Indeed, the decomposition into patches depends on the algorithm of the geometric modelling system used for design and usually has no meaning for any technological application. Moreover, in many cases, the surface definition is not compatible, i.e. patches are not well connected, some patches are self‐intersecting or intersect each other. Many applications are hard to address because of these defects. In this paper we show how patch‐independent meshing techniques may be easily automated using a unique metric in a plane parametric space. Thus we provide an automatic procedure to build valid meshes over free‐form surfaces issued from industrial CAD software (Computer Aided Design: this terminology should refer to a large amount of software. For the scope of this paper we only refer to geometric modelling systems. Indeed geometric modelling systems remain the kernel of many CAD software). Copyright © 2002 John Wiley & Sons, Ltd.     

Product data quality validation system for product development processes in high-tech industry

Among various product data, 3D CAD data plays a key role in current product design and manufacturing processes including industrial design, detail design, CAE, inspection, mould-making, production, and so on. If 3D CAD data has geometrical or topological errors by user mistakes or modelling software bugs and those errors are not cleaned by the data creator in an early stage, the data will be transferred to the downstream operators and they have to fix the errors before starting their own work. Because 3D data is quite complex, it is very difficult to recognise the data errors manually in a modelling system before a big problem is encountered which blocks the next operation. In this case, it generally causes time delay and high cost for data correction and the effect will be bigger when the process is close to the back-end. In this research, we develop a fully automated product data quality validation and management system to support the product development processes of high-tech products like televisions, camcorders, mobile telephones, home appliances, etc. The system automatically validates the 3D data in real time and gives 3D error reports to the creator to correct modelling failures in their steps. Also, project managers can check or control the data delivery based on the data quality for each step.     

An evolutionary approach for cooling system optimization in plastic injection moulding

The cooling process is of great importance in plastic injection moulding as it has a direct impact on both productivity and product quality. Cooling process optimization is a sophisticated task which includes not only the design of cooling channels but also the selection of process parameters. Most existing optimization systems focus on either cooling channel design or process parameter selection but not both. This paper explores an approach to optimize both cooling channel design and process condition selection simultaneously through an evolutionary algorithm. The prototype system proposed in this paper is an integration of the genetic algorithm and CAE (Computer-Aided Engineering) technology. The aim is to launch a computerized system that can guide the optimization of the cooling process in plastic injection moulding. The objective is to achieve the most uniform cavity surface temperature to assure product quality.     

选材系统的设计与实现

介绍一个基于材料科学数据库的选材系统。该系统按照开放性的原则设计，将材料科学数据分为三大部分：仅与材料成分有关的基本材料数据，材料加工和应用过程中产生的材料加工工艺和性能数据，材料产品的生产供应等商业信息。     

Machine planning in a product model environment

In recent years the integration of computer-based design and manufacture activities has received significant research effort as it has major potential to improve industrial performance. Product modelling is becoming accepted as the mechanism by which a central source of product data can be captured to provide an integrating mechanism between a range of design and manufacture functions. This paper describes the use of activity and data modelling methods to define an integrated planning system. From this an experimental system has been produced, building and integrating machine planning functions in a CAE system, employing a product modelling environment. The software implementation of this concentrates on planning and NC code generation functions for the machining of 2½-dimensional prismatic components from solid stock on a three-axis vertical machining centre.     

Chaste: using agile programming techniques to develop computational biology software

Cardiac modelling is the area of physiome modelling where the available simulation software is perhaps most mature, and it therefore provides an excellent starting point for considering the software requirements for the wider physiome community. In this paper, we will begin by introducing some of the most advanced existing software packages for simulating cardiac electrical activity. We consider the software development methods used in producing codes of this type, and discuss their use of numerical algorithms, relative computational efficiency, usability, robustness and extensibility. We then go on to describe a class of software development methodologies known as test-driven agile methods and argue that such methods are more suitable for scientific software development than the traditional academic approaches. A case study is a project of our own, Cancer, Heart and Soft Tissue Environment, which is a library of computational biology software that began as an experiment in the use of agile programming methods. We present our experiences with a review of our progress thus far, focusing on the advantages and disadvantages of this new approach compared with the development methods used in some existing packages. We conclude by considering whether the likely wider needs of the cardiac modelling community are currently being met and suggest that, in order to respond effectively to changing requirements, it is essential that these codes should be more malleable. Such codes will allow for reliable extensions to include both detailed mathematical models--of the heart and other organs--and more efficient numerical techniques that are currently being developed by many research groups worldwide.     

基于HyperMesh的立式加工中心结构拓扑优化

应用CAD/CAE系统建立XH786A立式加工中心的整机模型,并进行动态分析.找出机床薄弱环节,利用优化软件HyperMesh对薄弱环节进行优化设计,得到优化结果和优化前相比较,表明拓扑优化结果具有理论指导意义,为后续详细的设计提供理论依据.     

Environmental conscious product design using CAD and CAE

Environmental consciousness has been regarded as an important concept for survival in the contemporary scenario. Modern design engineers are in need of approaches for creating environmentally friendlier products. In this context, this article reports a case study carried out in an Indian rotary switches manufacturing organization. The existing components of rotary switch have been modelled using computer-aided design (CAD). Then, the sustainability analysis has been carried out for determining the environmental impact. This is followed by the optimisation of the components using computer-aided engineering (CAE). The environmental impact has been measured in terms of carbon footprint, energy consumption and air/water impacts. It has been found that the optimized components possess minimal environmental impact. The sustainability improvement after the implementation of the proposed approach has been computed. It could be inferred from the results of the case study that CAD and CAE could lead to the development of environmental conscious product designs with minimal impact to the environment.     

A methodology for structural optimisation with damage tolerance constraints

This paper presents recent developments in the optimal design of structural components with fracture constraints. To minimise the computational effort it is suggested that an initial “near optimum” shape be used. One approach could be to begin with the optimal shape for the non-cracked geometry. This initial near optimum shape would then be used in conjunction with the alternating finite element method, for multiple cracks, which builds on existing CAD based finite element models and the resultant formulation then linked to available optimisation codes. This approach is illustrated by considering the problem of an optimum cut-out geometry for a square plate subjected to a 4:1 and a 2:1 biaxial stress field. When considering the problem of shape optimisation with static fracture constraints it was found that an initial “near optimal” shape, based on the optimal shape for the uncracked geometry, was in fact an excellent approximation to the optimal solution for the cracked problem. It was also found that, in each case, for a given crack length the stress intensity factors, for cracks emanating at any arbitrary point around the hole, were essentially constant along most of the circumference. This behaviour is intuitively expected for an optimised geometry, where it would be hoped that all locations around the hole would be equally critical. A similar behaviour was found when considering shape optimisation with durability, i.e. crack growth, constraints. In this case it was hypothesised that the optimum shape would be such that all locations around the cut-out would be equally fatigue critical. However, in this case it is believed that the final optimal shape will depend on: the initial flaw size, the critical crack length, the load spectrum and the overall geometry of the structure. The analysis also reveals that, as the geometry of the cut-out or hole changes, the location of the crack which determines the minimum fatigue life can also change. This makes it necessary to consider flaws at a range of locations around the hole.     

汽车制造业中的CAD/CAE/CAM集成应用

以研究院所和企业的合作事例为基础,将汽车车身覆盖件拉深模具CAE分析模型的几何信息到通用CAD/CAM平台的顺畅传递,以及应用CAM系统对模具进行数控加工建模与仿真的实现过程做实例,表明了在国内汽车设计制造企业中实现CAD/CAE/CAM集成应用的可行性和有效性.     

Globally optimal tool paths for sculptured surfaces with emphasis to machining error and cutting posture smoothness

Global optimisation for manufacturing problems is mandatory for obtaining versatile benefits to facilitate modern industry. This paper deals with an original approach of globally optimising tool paths to CNC-machine sculptured surfaces. The approach entails the development of a fully automated manufacturing software interface integrated by a non-conventional genetic/evolutionary algorithm to enable intelligent machining. These attributes have been built using already existing practical machining modelling tools such as CAM systems so as to deliver a truly viable computer-aided manufacturing solution. Since global optimisation is heavily based on the formulation of the problem, emphasis has been given to the definition of optimisation criteria as crucial elements for representing performance. The criteria involve the machining error as a combined effect of chord error and scallop height, the tool path smoothness and productivity. Experiments have been designed considering several benchmark sculptured surfaces as well as tool path parameters to validate the aforementioned criteria. The new approach was implemented to another sculptured surface which has been extensively tested by previous research works. Results were compared to those available in the literature and it was found that the proposed approach can indeed constitute a promising and trustworthy technique for the global optimisation of sculptured surface CNC tool paths.     

Module partition for 3D CAD assembly models: a hierarchical clustering method based on component dependencies

Reusing previous CAD assembly models directly in new product development is almost impossible in One-of-a-Kind Production (OKP) in which customer requirements vary from one to another. As such, modularisation of CAD assembly models is required to facilitate modular design for OKP. However, to the authors’ best knowledge, there has been no research carried out on modularisation of CAD assembly models so far. To bridge this gap and make the best use of existing CAD models, this paper proposes a novel module partition approach, to group existing CAD assembly models into modules based on component dependencies. In this approach, an extraction algorithm was developed to extract assembly information from a given assembly model directly, by using automated programmable interfaces of CAD software tools. The extracted information is processed to generate the component design structure matrix (DSM) representing hierarchical relations and dependency strengths between components. Four popular hierarchical clustering methods were used to work with the component DSM to produce results of module partition. A case study was carried out to illustrate the proposed methods and demonstrate their feasibility. It enables OKP companies to respond rapidly to changing customer requirements and develop customised products in a short period.     

具有复杂内腔和外形的斗齿快速逆向设计

为了获得某型挖掘机斗齿点云逆向造型的实体化模型和CAD工程图样,研究了斗齿点云快速实体化的方法.采用基于“曲面重构-实体化-工程图”的逆向设计途径,提出把对精度要求高的内腔和销孔部位及对精度要求一般的斗齿外形分别用Imageware及Geomagic Studio软件完成曲面重构和基于Pro/E软件完成曲面合并和实体化的逆向策略,介绍了斗齿点云的数据分割、曲面重构与合并、实体化以及其工程图获取过程中的主要过程和方法.研究结果表明：对于型面数量多而复杂的斗齿,曲面逆向工具的选取及点云的数据分割方法是否得当是决定曲面和实体模型重建效率和成败的关键,通过恰当选择逆向策略和工具,合理简化点云的分割、曲面重构与合并以及实体模型的建立等,可显著提高逆向设计效率.     

基于有限元分析的高精密柔性夹具优化方案设计

针对高精密加工过程中柔性夹具的变形问题进行理论计算和实验分析.首先应用CAE软件对现有柔性夹具进行有限元分析,分析夹具变形问题.然后通过CAD软件改变该夹具模型的结构参数和尺寸参数,优化夹具构造,以减少定位过程的夹具变形,并再次通过CAE软件进行分析,验证优化效果.通过增加夹具体主平面刚度、增加夹具体肋板刚度和改变夹具定位点位置等方法,实现夹具体的最大变形量满足加工精度的要求.实验分析以定位点变形为研究对象,测量得到4个定位点在夹具装夹过程中的变形量.实验结果基本符合理论计算结果,得到最终优化方案的4个定位点变形量均小于001 mm,满足了该高精密加工中对夹具体的精度要求.优化方案在实际生产中得到实施,效果良好.     

Applying the topological relationships of form features to retrieve part files from a CAD system

The efficient retrieval of stored CAD files is an area that has received significant attention in recent years. Several Product Data Management products have been developed, most of which are based on the use of coding concepts to retrieve designs. However, the limited number of codes that can be used limits the flexibility of part shape representation and also versatility in retrieving existing drawings. In this paper, an integrated approach using topological relationships among form features as the search indices is proposed. The use of a feature adjacency graph and also a feature topological relation graph that acts as the interface enables this approach to translate the feature-based B-Rep model of a part that is stored in the CAD system into topological relationships that are stored in a relational database. In addition, five types of queries based on topological relationships an; used to aid the retrieval of designs. The proposed technique for design retrieval is more convenient than traditional coding based methods:     

Methods for rating directly buried high voltage cable circuits

To manage a cable network effectively it is desirable to rate cable assets precisely. To investigate the conservatism of cable ratings provided by accepted modelling approaches several models have been employed to provide comparative continuous ratings for a directly buried cable group arrangement. Operational ratings are performed using expedient cable rating calculations, typically employing analytical or one dimensional (ID) finite difference (FD) methods. The case for a directly buried cable group is considered; ratings are obtained using three methods including the international standard analytical approach (IEC 60287), ID FD and a 2D finite element analysis (FEA) approach. A continuous equation for resultant heat-flux has been derived to more precisely model the dielectric loss in 2D and 3D FEA models. Comparing results shows that all the models have good agreement when modelling an isothermal ground surface condition and validate the 2D FEA model against established approaches. The FEA model developed has been used to investigate more realistic ground surface boundary conditions. Results for different cable burial depths and ground surface boundary conditions show that using the established methods can lead to overestimation of cable ratings in the case of shallow buried cables.     

A performance evaluation method to compare the multi-view point cloud data registration based on ICP algorithm and reference marker

Registration of range images of surfaces is a fundamental problem in three-dimensional modelling. This process is performed by finding a rotation matrix and translation vector between two sets of data points requiring registration. Many techniques have been developed to solve the registration problem. Therefore, it is important to understand the accuracy of various registration techniques when we decide which technique will be selected to perform registration task. This paper presents a new approach to test and compare registration techniques in terms of accuracy. Among various registration methods, iterative closest point-based algorithms and reference marker methods are two types of commonly applied methods which are used to accomplish this task because they are easy to implement and relatively low cost. These two methods have been selected to perform a comprehensively quantitative evaluation by using the proposed method and the registration results are verified using the calibrated NPL freeform standard.     

Automatic segmentation and approximation of digitized data for reverse engineering

Reverse engineering is the process of developing a computer-aided design (CAD) model and a manufacturing database for an existing object. This process is used in CAD modelling of part prototypes, in designing moulds and in automated inspection of parts with a complex surface. This paper reports on the automatic segmentation and approximation of three-dimensional digitized points for reverse engineering. Based on an innovation that uses the properties of a non-uniform rational B-spline (NURBS) or B-spline and makes ordered digitized points be control points directly to construct a NURBS or B-spline surface, which takes less computation time than traditional algorithms in calculating surface normals and curvatures at digitized points, an algorithm was developed for automatic segmentation and NURBS surfaces fitting for digitized points.