Feature Technology

Feature Technology

Xun Xu (University of Auckland, NZ)
DOI: 10.4018/978-1-59904-714-0.ch004
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Abstract

Throughout the course of the development of CAD, CAPP, and CAM systems, unambiguous representation of a design’s geometry and topology remain an essential part of the task. Since the mid-1990’s, the technology has matured enough to enable such a representation. While geometry and topology provides a basic description of a design part, direct use of it for creation of the part and other applications, can be cumbersome. Take creation of a simple plane with four straight edges as an example. For a B-rep model to fully define the plane, four points are to be created first to be used as four vertices. They are used to define four edges, which are connected one after another to form a closed loop. Finally, a flat surface is fitted onto the loop to form the plane. When a cube is to be designed, the above process needs to be repeated five more times for the other five faces though some of the vertices and edges may be re-used. In addition, the directions of the solid have to be defined through each face. Clearly, this is not a trivial task. Users would find it helpful if the creation of geometry and topology is hidden behind them and only some meaningful parameters of the solid are provided. In the case of a simple cube, length, width, and depth would be the parameters. Hence, the concept of features (i.e. cube or block in the above example) emerged, as did the associated technologies. The same applies for other domains, such as manufacturing and engineering analysis. This chapter aims to give a succinct introduction to various feature technologies such as feature defintions, feature taxonomy, feature representation schemes, and feature-based methodologies. Several important issues are highlighted. These include the application-dependent nature of features, and surface features versus volumetric features.
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Feature Definition

Features can be thought of as ‘engineering primitives’ suited for some engineering tasks. They originate in the reasoning processes used in various design, analysis and manufacturing activities, and are therefore often strongly associated with particular application domains. This explains why there are many different definitions for features. According to Shah and Mäntylä (1995), a feature should have,

  • a physical constituent of a part;

  • a generic shape that can be mapped to;

  • engineering significance; and

  • predictable properties.

In the context of CAD/CAPP/CAM, several more specific definitions have been suggested. One of such examples is,

A feature is referred to as a distinctive or characteristic part of a workpiece, defining a geometrical shape, which is either specific for a machining process or can be used for fixturing and/or measuring purposes (Erve & Kals, 1986).

Of particular relevance in this chapter are the machining features, which are normally related to machining methods or machining operations. Thus, a machining feature can be defined as

A portion of the workpiece generated by a certain mode of metal cutting. (Choi, Barash & Anderson, 1984), or

Feature information can be considered to be about volumes of material to be removed (Anderson, 1990).

A component with four machining features is shown in Figure 1, where the slot may require an end mill, the holes may require drilling operations and the pocket may require a slotting cutter or a slotting cutter and an end mill.

Figure 1.

A component with four machining features. ©2001, Engineers Australia used with permission.

When dealing with features, there is a further complication: viewpoint dependence. That is, depending on the application domain, one could have different views towards the same, or combination of, feature(s) on a part. When a part is designed by features, the resulting model is not usually in a form convenient for other applications such as manufacturing process planning. Indeed, design features are stereotypical shapes related to a part’s function, its design intent, or the model construction methodology, whereas manufacturing features are stereotypical shapes that can be made by typical manufacturing operations (Shen & Shah, 1994). To this context, design features may also be called function features. Figure 2 illustrates a part whose different geometrical entities may be of interest for different applications.

Figure 2.

Domain specific features

Shah and Mäntylä (1995) distinguish between various types of features by using a sub-classification of features such as form features, tolerance features, assembly features, functional features and material features. Form features, tolerance features and assembly features are all closely related to the geometry of a part, and are therefore called geometric features.

Complete Chapter List

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Dedication
Table of Contents
Foreword
A.Y.C. Nee
Acknowledgment
Xun Xu
Chapter 1
Xun Xu
One of the key activities in any product design process is to develop a geometric model of the product from the conceptual ideas, which can then be... Sample PDF
Geometric Modelling and Computer-Aided Design
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Chapter 2
Xun Xu
Today, more companies than ever before are involved in manufacturing various parts of their end products using different subcontractors, many of... Sample PDF
CAD Data Exhange and CAD Standards
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Chapter 3
Xun Xu
Products and their components are designed to perform certain functions. Design specifi- cations ensure the functionality aspects. The task in... Sample PDF
Computer-Aided Process Planning and Manufacturing
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Chapter 4
Feature Technology  (pages 75-89)
Xun Xu
Throughout the course of the development of CAD, CAPP, and CAM systems, unambiguous representation of a design’s geometry and topology remain an... Sample PDF
Feature Technology
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Chapter 5
Feature Recognition  (pages 90-108)
Xun Xu
Conventional CAD models only provide pure geometry and topology for mechanical designs such as vertices, edges, faces, simple primitives, and the... Sample PDF
Feature Recognition
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Chapter 6
Feature Interactions  (pages 109-125)
Xun Xu
Feature interaction tends to have a wide range of consequences and effects on a feature model and its applications. While these may often be... Sample PDF
Feature Interactions
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Chapter 7
Xun Xu
Integrated feature technology promotes a closer connection between design and manufacturing through features. When machining features are... Sample PDF
Integrated Feature Technolog
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Chapter 8
CNC Machine Tools  (pages 165-187)
Xun Xu
The introduction of CNC machines has radically changed the manufacturing industry. Curves are as easy to cut as straight lines, complex 3-D... Sample PDF
CNC Machine Tools
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Chapter 9
Program CNCs  (pages 188-229)
Xun Xu
A CNC machine can be programmed in different ways to machine a workpiece. In addition to creating the cutting program, many other factors also need... Sample PDF
Program CNCs
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Chapter 10
Xun Xu
Technologies concerning computer-aided design, process planning, manufacturing and numerical control, have matured to a point that commercialized... Sample PDF
Integration of CAD/CAPP/CAM/CNC
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Chapter 11
Xun Xu
The integration model (Model B) as discussed in the previous chapter makes use of exchangeable neutral data formats such as IGES (1980). Neutral... Sample PDF
Integration Based on STEP Standards
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Chapter 12
Xun Xu
Function blocks are an IEC (International Electro-technical Commission) standard for distributed industrial processes and control systems (IEC... Sample PDF
Function Block-Enabled Integration
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Chapter 13
Xun Xu
In order to prepare manufacturing companies to face increasingly frequent and unpredictable market changes with confidence, there is a recognized... Sample PDF
Development of an Integrated, Adaptable CNC System
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Chapter 14
Xun Xu
A logical step after CNC machining is inspection. With inspections, Closed-Loop Machining (CLM) can be realized to maximize the efficiency of a... Sample PDF
Integrating CAD/CAPP/CAM/CNC with Inspections
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Chapter 15
Xun Xu
Today, companies often have operations distributed around the world, and production facilities and designers are often in different locations.... Sample PDF
Internet-Based Integration
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Chapter 16
Xun Xu
Companies that have been practicing CAD, CAPP, CAM, and CNC integration have now realized that there is a need to operate in a much broader scope... Sample PDF
From CAD/CAPP/CAM/CNC to PDM, PLM and Beyond
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Chapter 17
Key Enabling Technologies  (pages 354-393)
Xun Xu
While computers have proven to be instrumental in the advancement of product design and manufacturing processes, the role that various technologies... Sample PDF
Key Enabling Technologies
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About the Author