Technical University – Berlin
Department of Information Technology

MASTER’S THESIS

Framework for a Structure Oriented
Exchange of CAD Data

Analytical Master’s Thesis on the subject
Industrial Information Technology

Submitted by: 

Lubomir Krastev

in partial fulfilment of requirements of the
Master of Engineering Science in
Global Production Engineering

Preface
Engineering Product Data Exchange (EPDE) is still in the Research and Development stage. It has been necessary to exchange data which describe a product – often, its geometric shape – since computers were first used for design and analysis in 1950s. That necessity still exists today. The data must to be available throughout the life cycle of the product and among all of the different enterprises.

This thesis will introduce the development of a framework for a structure-oriented exchange of CAD model data (CAD model data is a sub-data of Engineering Product Data).

The major tasks of this thesis are:

1. The analysis of CAD modelling capabilities regarding feature modelling and structural representation.
2. A survey of existing scientific and commercial strategies for an exchange of CAD model data.
3. The specification of an overall framework solving central technical problems.
4. Illustration of the framework’s functionality in a use case.

Acknowledgements

[in Downloaddatei enthalten]

Contents
Preface ...  iii
Acknowledgements  ...  iv
Contents ...  v

I. Introduction  ...  1
1. Problem analysis and requirements definition  ...  1
2. Review state of the art of exchange strategies  ...  1
3. Analysis of modelling capabilities regarding feature modelling and structure representation  ...  1
4. Needs-identification  ...  2
5. Requirement definitions  ...  2
6. Outline of the thesis  ...  2

II. Approaches to the Exchange of CAD Data  ...  3
1. Outline  ...  3
2. General Classification of Exchange Approaches  ...  3
2.1. Direct and Standard-based exchange Approaches  ...  3
2.2. Horizontal and Vertical Exchange Approaches  ...  5
2.3. Classification of exchange strategies  ...  8
3. Capabilities of Scientific Exchange Strategies  ...  8
3.1. On the Implicit Exchange of Feature-Based Product Model Data  ...  8
3.2. Exchange of CAD Part Models Based on the Macro-Parametric Approach  ...  10
3.3. The Unified Approach to Modelling Multidisciplinary Interaction  ...  12
3.4. An exchange Approach in Conceptual-Based Design System  ...  15
3.5. Open CAD Environment  ...  16
4. Capabilities of Exchange Strategies in Commercial Areas  ...  18
4.1. Vendor Exchange Method  ...  18
4.2. Native Exchange Method  ...  18
4.3. Neutral Exchange Method  ...  19
4.3.1. IGES  ...  19
4.3.2. VDA-FS  ...  21
4.3.3. SET  ...  22
4.3.4. XBF  ...  23
4.3.5. PDDI  ...  23
4.3.6. Projects Related to Neutral Exchange Methods  ...  24
4.3.7. STEP (ISO-10303)  ...  25
5. Further technologies  ...  31
5.1. Parts Library  ...  31
5.2. CAD – Services  ...  34
5.3. ProSTEP  ...  35
6. Conclusion  ...  36

III. Analysis of today’s CAD systems – concepts and capabilities  ...  36
1. Outline  ...  36
2. Feature modelling definitions  ...  37
2.1. Feature definitions  ...  37
2.2. Feature model definition  ...  37
2.3. Feature modelling definition  ...  38
2.4. Feature attributes definition  ...  38
2.5. Types of features  ...  38
2.6. Feature properties  ...  38
2.7. Feature properties classification  ...  39
2.8. Generic and composite features  ...  39
2.9. Feature taxonomies  ...  39
2.10. Feature mapping  ...  40
3. Analysis of feature modeling methods  ...  40
3.1. Basic feature creation methods  ...  40
3.2. Analysis of specific features modeling methods  ...  41
3.2.1. Interactive feature modeling  ...  41
3.2.2. Automatic (recognition) feature recognition  ...  42
3.2.3. Design by feature modeling  ...  43
3.3. Analysis of structural representation regarding feature modeling methods  ...  44
3.3.1. Automatic feature recognition  ...  44
3.3.2. Design by feature modelling  ...  47
4. Major benefits of feature modelling methods  ...  48
4.1. Design Intent  ...  48
4.2. Multilevel structure  ...  49
4.3. Feature-Kernel  ...  49
5. Deficiencies as a result of feature data exchange  ...  49
6. Analysis of commercial systems  ...  50
6.1. Scope and process of analysis  ...  50
6.1.1. Analysis of basic feature creation methods  ...  50
6.1.2. Analysis of modelling kernel  ...  51
6.1.3. Scope and process of model representation  ...  52
6.2. Pro/Engineer’s analysis  ...  54
6.3. I-DEAS’s analysis  ...  63
6.4. Unigraphic’s analysis  ...  69
7. Conclusions  ...  76

IV. Exchange strategy – concept  ...  80
1. Problem discussion  ...  80
2. Needs identification on a Feature Model-Tree exchange methodology  ...  82
3. Requirements definition - sequence of needs identification  ...  82
3.1. Openness - neutral type of exchange data  ...  83
3.2. Modularity – structure oriented data  ...  83
3.3. Optimal Completeness – optimal density of exchange data  ...  83
4. Requirements list  ...  83
5. Established and new exchange strategies  ...  84
6. Concept details  ...  87
6.1. Fundamental ideas  ...  87
6.2. General framework  ...  87
6.3. Detail of the framework  ...  88
6.4. Translation process  ...  89

V. Evaluation and outlook  ...  90

References  ...  . 91

I. Introduction

1. Problem analysis and requirements definition

Integration of a CAx (Computer Aided x) system throughout the product life cycle and among different enterprises is a major issue for industrial competitiveness and collaboration. One of the main successful factors for CAx system integration is efficient methodology for EPDE (Engineering Product Data Exchange). Data exchange is the totality of establishing the approach for and the successful achievement of the transfer of data between two distinct CAx systems.

Problem Statement:

• Why does an exchanged CAD (Computer Aided Design) model lose some modelling properties? – Especially losses such as model tree (design intent) and features.
• What reasons influence that phenomenon?
• How can these losses be minimized?

2. Review state of the art of exchange strategies

The review of exchange strategies is focused on which existing approaches are in use today, which capabilities are supported by them, which deficiencies they have, an understanding of state of the art is a precondition for beginning to deal with of the problem statement.

3. Analysis of modelling capabilities regarding feature modelling and structure representation

The analysis begins with a short review of existing feature modelling techniques, which will build up a framework for the analysis process. Three CAD systems are analysed – Pro/Engineering, I-DEAS and UniGraphics. Typical models, with the frequently occurring features, are reviewed depending on the feature modelling method and structural representation.

4. Needs-identification

The results of the analysis of modelling capabilities lead to the improvement of new methods and techniques. This defines the essential basis for the building of a concept framework.

5. Requirement definitions

• How can the model-tree to be exchanged?
• How will the exchanged model-tree act?

6. Outline of the thesis

The material is organized in three major sections. The first one, the state of the art, examines the fundamentals of exchange approaches, the current state of scientific and commercial exchange approaches and further related technologies.

The second one, presents the current state of feature modelling techniques and analyses of three commercial CAD systems according to feature modelling capabilities and structural representation.
The next section, the concept framework, designs a concept framework fitting the requirement definitions.

II. Approaches to the Exchange of CAD Data

1. Outline

The state of the art is discussed in this section according to existing approaches to the exchange of CAD data. Engineering Product Data Exchange (EPDE) refers to the task of expressing and transferring information about a given engineering product in digital format. This section will first outline the general classification of exchange approaches, such as direct and standard-based also horizontal-based and vertical-based. Furthermore, the classification of exchange strategies as a scientific and commercial. Review of capabilities on both approaches. Further technologies review additional exchange techniques. All these will be elaborated later in the next sections of the thesis.

2. General Classification of Exchange Approaches

2.1. Direct and Standard-based Exchange Approaches

The information generated during the design phase - the definition of the product - is the first precondition for data exchange. Basically, there are two types of CAD-product definition. One contains the data of a drafting and a solid model. The first one is composed of the vectors data for lines as solid lines, dotted lines, centre lines and extension lines together with annotation data for the dimension values, notes and symbols in the drafting. The second type of product definition data consists of a solid model with some annotation data.

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