A feasible approach to the integration of CAD and CAPP

Although current CAD systems are declared to be feature-based, in fact, the so-called feature is just a modeling macro or menu name such as Protrusion, Revolution, Cutout, Block, etc., instead of a design feature or manufacturing feature in accordance with engineering practice. Consequently, product model data insufficiency and incompatibility between varieties of application systems are still the major barriers to system integration, especially the integration of design and process planning. This paper proposes a practical solution for a bi-directional integration of CAD and CAPP on the platform of commercial CAD systems. The key techniques such as feature recognition and conversion, feature parameter and constraint extraction, feature tree reconstruction, technical information processing, process planning, automatic process drawing marking and 3D material stock CAD model generating are discussed. And the extracted features and their related technical information and knowledge are encapsulated together with the geometry-oriented CAD model to form an integrated product information model to facilitate effective integration with the downstream activities. The integrated CAD/CAPP system is implemented on a commercial CAD package, UGS/SolidEdge. A case study and industry implementation illustrate the feasibility of the approach proposed.     

并行工程下基于特征的零件可制造性及其评价方法研究*

结合并行工程的思想,对零件可制造性进行较详细的分析,提出并行工程环境下基于特征的可制造性分析方法,研究建立基于特征的可制造性零件定义模型及评价体系。阐述了基于特征的可制造性的评价方法,认为可制造性评价是一个多层次的决策问题,建立了基于制造约束规则的加工可行性定性评价和基于模糊综合评判的加工可行性定量评价两种评价方法,并给出了解法。利用上述研究方法,全面合理地对零件的可制造性进行评价和反馈,从而指导产品设计。最后以涡轮叶片榫头特征的可制造性分析为应用实例,说明了该方法的有效性和实用性。     

面向概念设计的实体草绘建模

提出了一种简单、快速、高效的基于草绘设计的概念模型创建方法.该方法模仿传统的纸笔草绘设计方式,允许用户自由地在笔式用户界面上勾画特征笔划,然后根据笔划的形状和位置关系采用基于特征的实体建模方法构造不同的扫描特征体素.在此基础上,采用了基于意图捕捉的特征添加及切削机制创建复杂的实体模型,给出了一些关键算法的实现过程.实验结果表明:该方法能够较好地应用到联机三维概念模型快速创建过程中.     

A road map to solid modeling

The objective of solid modeling is to represent, manipulate and reason about the 3D shape of solid physical objects by computer. Such representations should be unambiguous. Solid modeling's major application areas include design, manufacturing, computer vision, graphics and virtual reality. The field draws on diverse sources, including numerical analysis, symbolic algebraic computation, approximation theory, applied mathematics, point set topology, algebraic geometry, computational geometry and databases. In this article, we begin with some mathematical foundations of the field. We next review the major representation schemata of solids. Then, major layers of abstraction in a typical solid modeling system are characterized. The lowest level of abstraction comprises a substratum of basic service algorithms. At an intermediate level of abstraction there are algorithms for larger, more conceptual operations. Finally, a yet higher level of abstraction presents to the user a functional view that is typically targeted towards solid design. We look at some applications and at user interaction concepts. The classical design paradigms of solid modeling concentrated on obtaining one specific final shape. Those paradigms are becoming supplanted by feature-based, constraint-based design paradigms that are oriented more toward the design process and define classes of shape instances. These new paradigms venture into territory that has yet to be explored systematically. Concurrent with this paradigm shift, there is also a shift in the system architecture towards modularized confederations of plug-compatible functional components     

A feature-based fixture design methodology for the manufacturing of aircraft structural parts

In fixture design for the manufacturing of aircraft structural parts, there are various challenges and serious problems in industry, such as difficulty in design knowledge capture and reuse, and the arbitrary or non-standard nature of design, which influence the efficiency and quality of fixture design. This paper proposes a feature-based fixture design methodology in which previous fixture design cases and design rules are described in association with features and thus the design knowledge is integrated with geometric information of aircraft structural parts, which are the main concern of this project. In this methodology, machining features of the structural parts and their associated attributes are identified by feature recognition technique from the 3 dimensional (3D) part models defined based on model-based definition (MBD) technique. The feature-based part information models are then established and are used to retrieve previous fixture design cases and design rules stored in the knowledge base. Fixture designers will choose the appropriate retrieved design cases as the starting point for new fixture design or use previous designs to assess his/her current design. In this way the process of new fixture design can be improved. In the current stage of the research, a prototype feature-based fixture design system based on CATIA for the manufacturing of aircraft structural parts has been developed and used by a large airplane manufacturer.     

Geometric reasoning for mill-turn machining process planning

An integrated system to support both product and manufacturing process design should be such that (1) the part design can be evaluated and redesigned based on manufacturability analysis and (2) the manufacturing processes can be selected efficiently and flexibly exploiting product information provided by part design representations.

In this paper, we describe the feature-based geometric reasoning system for part modeling and process planning as applied to mill-turn machined parts. The feature recognition system based on convex decomposition and the mapping method to relate the negative feature volumes to machining process classes are applied to mill-turn parts. Also, the geometry-based machining precedence relations have been generated for various alternative machining feature decompositions. The above geometric information is input to mill-turn machining process planning to determine machining process sequences and assignment to multiple spindles and turrets.     

基于特征的三维变量设计模型及形体重构

本文提出了一个适用于微机的基于特征的三维变量设计模型及形体重构方法。通过引入特征及约束的概念使变量设计成为可能而特征树的应用克服了以往利用CSG树进行三维变量设计的不足。该方法保存的信息还能用于后序加工。     

Feature-based modeling for automatic mesh generation

Automatic meshing algorithms for finite element analysis are based on a computer understanding of the geometry of the part to be discretized. Current mesh generators understand the part as either a boundary representation, an octree, or a point set. A higher-level understanding of the part can be achieved by associating engineering significance and engineering data, such as loading and boundary conditions, with generic shapes in the part. This technique, called feature-based modeling, is a popular approach to integrating computer-aided design (CAD) and computer-aided manufacturing through the use of machinable shapes in the CAD model. It would seem that feature-based design also could aid in the finite element mesh generation process by making engineering information explicit in the model.This paper describes an approach to feature-based mesh generation. The feature representation of a fully functioning feature-based system that does automatic process planning and inspection was extended to include finite element mesh generation. This approach is based on a single feature representation that can be used for design, finite element analysis, process planning, and inspection of prismatic parts. The paper describes several advantages that features provide to the meshing process, such as improved point sets and a convenient method of simplifying the geometry of the model. Also discussed are possible extensions to features to enhance the finite element meshing process.     

融合意图捕捉的笔式草绘特征建模

实现了一种基于笔式草绘特征建模方法.该方法模仿传统的纸笔草绘交互设计方式,利用意图捕捉机制揣测用户的设计意图,并采用基于特征的建模方法构造出三维实体概念模型.支持在模型表面上直接草绘截面和轨迹线,并通过特征切削或添加操作构造复杂物体模型;初步实现了基于手势的模型编辑操作.实验结果表明,该方法简单、高效,适合于快速表达不精确的概念模型.     

Development of a feature-based and object-oriented concurrent engineering system

Product information modeling is critical to the integration of mechanical CAD/CAM systems and to the implementation of a concurrent engineering system. This paper presents a recent development of a feature-based and object-oriented concurrent engineering system with its focus on a product information modeling technique implemented in the system. The technique was developed to capture product definition data including form features and their spatial relationships and to store them as an object-oriented information model during the design process. The paper also describes the implementation of the information modeling technique and its application to manufacturing process planning in an object-oriented environment.     

A general model for machinable features and its application to machinability evaluation of mechanical parts

This paper is intended to reveal the rationale in the machinability evaluation and to present an effective, systematic approach to the assessment of the machined parts in the early stage of design. By examining the inherent shaping mechanism of machining processes, a geometric feature model, termed ‘machining volume’, resulting from the cutter's movement that mimics the cutter's real motion trajectory in machining, is proposed with which a set of feature derivatives can be affiliated. The geometric and topological patterns of machining volume permit to capture and convey machinability constraints on a part shape, leading to a new, simple machinability evaluation method centered on machining volume. This method is dedicated to two kinds of inspection on the geometry of a part in design: one is to search for unmachinable surfaces that are beyond the capability of machining processes, and the other to detect machining interference between a cutter and a part. It shows a more useful means to characterize machinable features that result in the machinability evaluation with ease and efficiency.     

工程布局CAD系统设计与实现

针对工程布局设计的复杂性,提出了开放式的工程布局设计CAD系统的结构框架,讨论了实现该系统的关键方法,包括自动化设计进程建模、基于功能特征的待布物和布局空间几何近似建模、布局知识和布局约束的表达、布局方法应用.基于该系统框架,实现了计算机辅助工程布局设计原型系统,并以车辆动力舱布局设计为背景,对原型系统的有效性进行了验证.     

Design and implementation of a relational data base for automated process planning

The function of process planning in a manufacturing facility is to identify the processes and the machines required to convert a design into its final form. Majority of the process plans are still made manually. The degree of the process plan detail varies with the shop environment. A feature-based process planning system which interacts with the SDRC I-DEAS solid modeling software is presented. The system operates under the UNIX environment. A relational database model which incorporates manufacturing details including the operation selection, machine selection, tool selection, fixture selection, etc. was developed and implemented. This relational database was structured using Microsoft SQL SERVER for the PC multi-user environment. This database is part of an ongoing research project on automated process planning and scheduling and primarily focuses on prismatic parts. The developed routines generate the Overall Removable Volume (ORV) graphically by comparing the desirable design to the blank work piece. The routines then decompose the ORV into various General Manufacturing Features (GMF) based on concave edges. The recognition routine captures geometrical and topological information and identifies the shape of each GMF. An expert system (using CLIPS expert system shell) analyzes the GMFs and determines appropriate operation(s) for the designed part. The developed expert system is capable of recommending the suitable machines, tools, fixtures, etc.     

Parametric feature constraint modeling and mapping in product development

This paper presents the exploration and application of a feature-based design methodology within mechanical product development cycles. Based on a review of the feature technology and previous research work, this paper focuses on the modeling of intricate relations among features of different design aspects. A concept of feature parameter map that leads to a constraint mapping method is proposed. Further, features are classified into different levels; and information management for product lifecycle support is considered. The application of this method is demonstrated with the conceptual design and optimization of a gearbox as the study case. In addition, an extended feature system for product development was explored. With a spreadsheet package and a computer aided design (CAD) tool, the product model generation, change management and final optimization of the case assembly including its bulk shape, have been achieved. Two important information chains were used to address the aspect of “design for post-manufacture services” with concurrent engineering consideration, i.e. a field installation pattern and a set of wrapping dimensions for product transport packaging. In order to demonstrate the feasibility of change management, a different product derivative model was regenerated by adopting and changing the values of a main conceptual feature. The result is promising.     

基于结构树的产品制造质量信息建模

为了给面向制造质量的设计提供全面支持,需要对制造质量信息进行有效管理。制造质量信息的组织在其管理中具有重要作用,考虑到结构树作为产品生命周期信息载体的特点,提出了制造质量信息的结构树建模方法。分析了产品构成以及通用信息树的结构,构建了制造质量信息的结构树模型。分析了制造质量信息树的结构、节点、节点及其属性操作,给出了制造质量信息树的构建方法与步骤。以某重型汽车的变速箱为实例,建立了变速箱制造质量信息的结构树模型。     

Similarity comparison of mechanical parts to reuse existing designs

In actual practice, many new mechanical parts are designed by modifying existing ones. In this way, time and effort can be saved by not having to design parts from scratch. Design time would be further reduced if there were an efficient way to search for existing similar designs. Furthermore, a new part design can be very efficiently generated by modifying the dimensions on the features of the existing part if a part with a similar feature set and the corresponding modeling history can be easily searched from the existing part library.In this paper, a two-step similarity comparison method for B-rep files is proposed. Overall appearances are compared first, and then detailed features are compared. In this way, existing parts with similar feature set in addition to similar overall shape can be identified from the part library. Once the similar part is identified, its modeling history can also be used for parametric modeling if the existing part was designed by a feature-based modeler.     

钣金件自动展开新方法

在对钣金件特征研究和"零厚度"假设的基础上,提出一种钣金件自动展开新方法.对钣金件进行特征分类,基于特征设计进行钣金件特征造型,并通过特征树的形式存储特征之间的关系,最后对特征树进行中序遍历得到钣金件的展开图.并将上述方法应用在SMCAD(Sheet-Metal CAD)系统中.结果表明,该方法能方便快捷的实现钣金件自动展开,并使钣金件设计和展开摆脱了对三维平台的依赖,展开过程更为简洁.