Rapid Prototyping: Laser-based and Other Technologies

400 Pages·2004·11.934 MB·English

by  Patri K. Venuvinod, Weiyin Ma (auth.)

RAPID PROTOTYPING
RAPID PROTOTYPING
Laser-based and Other Technologies
Patri K. V enuvinod and Weiy in Ma
Department of Manufacturing Engineering and Engineering Management
City University of Hong Kong
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Springer Science+Business Media, LLC
Library of Congress Cataloging-in-Publication
Title: Rapid Prototyping
Laser-based and Other Technologies
Author (s): Patri K. Venuvinod and Weiyin Ma
ISBN 978-1-4419-5388-9 ISBN 978-1-4757-6361-4 (eBook)
DOI 10.1007/978-1-4757-6361-4
Copyright © 2004 by Springer Science+ Business Media New York
Originally published by Kluwer Academic Publishers in 2004
Softcover reprint of the hardcover l st edition 2004
All rights reserved. No part of this publication may be reproduced, stored in a retrieval
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Printed on acid-free paper.
Table of Contents
PREFACE xi
ACKNOWLEDGMENTS xvii
1. INTRODUCTION 1
1.1 THE IMPORTANCE OF BEING RAPID 1
1.2 THE NATURE OF RP/T 6
1.3 HISTORY OF RP 13
1.4 THE STATE OF RP/T INDUSTRY 21
2. MATERIALS BASICS 25
2.1 ATOMIC STRUCTURE AND BONDING 25
2.2 CERAMICS 31
2.3 POLYMERS 33
2.3.1 Nature ofPolymers 33
2.3.2 Free Radical Polymerization 36
2.3.3 Cationic Polymerization 38
2.3.4 Thermoplastic and Thermosetting Polymers 39
2.3.5 Polymer Structures 41
2.3 .6 Properties of Polymers 42
2.3.7 Degradation ofPolymers 47
2.4 POWDERED MATERIALS 48
2.4.1 Types ofPowders 48
2.4.2 Compaction and Sintering of Powders 49
2.5 COMPOSITES 52
vi Rapid Prototyping
3. LASERS FOR RP 57
3.1 THE PRINCIPLE OF LASER 57
3 .1.1 The Nature of Light 57
3 .1.2 Emission Radiation 59
3 .1.3 Light Amplification by Stimulated Emission Radiation 60
3.2 LASER SYSTEM 63
3.3 LASER BEAM CHARACTERISTICS 65
3.4 LASER BEAM CONTROL 69
3.5 TYPES OF LASERS USED IN RP 71
4. REVERSE ENGINEERING AND CAD MODELING 75
4.1 BASIC CONCEPT OF REVERSE ENGINEERING 75
4.2 DIGITIZING TECHNIQUES FOR REVERSE ENGINEERING 78
4.2.1 Mechanical Contact Digitizing 79
4.2.2 Optical Non-Contact Measurement 81
4.2.3 CT Scanning Method 91
4.2.4 Data Pre-processing for Surface Reconstruction 96
4.3 MODEL REPRESENTATION 98
4.3.1 Basic Geometric Features 98
4.3 .2 General Algebraic Surfaces 98
4.3.3 Parametric Surfaces 99
4.3.4 Subdivision Surfaces 101
4.3 .5 Other Approaches and Recommendations 102
4.4 B-SPLINE BASED MODEL RECONSTRUCTION 103
4.4.1 Parametrization of Measured Points 103
4.4.2 Knots Allocation 105
4.4.3 Least Squares Fitting 107
4.5 NURBS BASED MODEL RECONSTRUCTION 110
4.5.1 A Two-Step Linear Approach 112
4.5.2 Numerical Algorithms for Weights Identification 115
4.6 OTHER APPROACHES FOR MODEL RECONSTRUCTION 119
4.6.1 Basic Geometric Features 119
4.6.2 General Algebraic Surfaces 119
4.6.3 Subdivision Surface Fitting 120
4.7 SURFACE LOCAL UPDATING 121
4.7.1 Related Work and General Strategies 122
4.7.2 Pre-Processing Steps for Surface Local Updating 123
4.7.3 Computing Updated Control Points 124
4.8 EXAMPLES ON MODEL RECONSTRUCTION 125
4.8.1 Parametrization for Surface Reconstruction 126
4.8.2 B-Spline Surfaces 127
4.8.3 NURBS Surfaces 129
Table of Contents vii
4.8.4 Subdivision Surfaces 130
4.8.5 Surface Local Updating 132
5. DATA PROCESSING FOR RAPID PROTOTYPING 135
5.1 INTRODUCTION 135
5.2 CAD MODEL PREPARATION 140
5.3 DATA INTERFACING FOR RAPID PROTOTYPING 144
5.3.1 STL Interface Specification 144
5.3.2 STL Data Generation 147
5.3.3 STL Data Manipulation 149
5.3.4 Alternative RP interfaces 151
5.4 PART ORIENTATION AND SUPPORT GENERATION 152
5 .4.1 Factors Affecting Part Orientation 152
5.4.2 Various Models for Part Orientation Determination 153
5.4.3 The Functions ofPart Supports 158
5.4.4 Support Structure Design 159
5.4.5 Automatic Support Structure Generation 162
5.5 MODEL SLICING AND CONTOUR DATA ORGANIZATION165
5.5.1 Model Slicing and Skin Contour Determination 165
5.5.2 Identification of Internal and External Contours 169
5.5.3 Contour Data Organization 171
5.6 DIRECT AND ADAPTNE SLICING 173
5.6.1 Identification of Peak Features 174
5 .6.2 Adaptive Layer Thickness Determination 178
5.6.3 Skin Contours Computation 180
5.7 ASELECTNEHATCHINGSTRATEGYFORRP 185
5.8 TOOL PATH GENERATION 188
6. STEREOLITHOGRAPHY (SL) 195
6.1 THE STEREOLITHOGRAPHY (SL) PROCESS 195
6.1.1 Part Building Using SL 195
6.1.2 Post-build Processes 197
6.1.3 Pre-build Processes 198
6.2 PHOTO-POLYMERIZATION OF SL RESINS 199
6.2.1 SL Polymers 199
6.2.2 Radical Photo-polymerization 200
6.2.3 Cationic Polymerization 204
6.2.4 Vinylethers and Epoxies 204
6.2.5 Developments in SL Resins 205
6.3 ABSORPTION OF LASER RADIATION BY THE RESIN 207
6.3.1 Beam Size and Positioning over the Resin Surface 207
6.3 .2 Laser Scanning Patterns 208
V111 Rapid Prototyping
6.3.3 Total Exposure from a Single Laser Scan 208
6.3 .4 Total Exposure of Interior Resin Layers 210
6.3.5 Shape of a Cured Strand 211
6.3.6 Cure Depth and Width 212
6.3.7 Multi-layer Part Building, Overcure, and Undercure 214
6.4 RECOATING ISSUES 216
6.4.1 Recoating Cycle 216
6.4.2 Resin Level Control 220
6.4.3 Gap Control 221
6.5 CURING AND ITS IMPLICATIONS 222
6.5.1 Degree of Curing and 'Green Strength' 222
6.5.2 Effects During Post-curing 225
6.6 PART QUALITY AND POCESS PLANNING 227
6.6.1 Shrinkage, Swelling, Curl and Distortion 227
6.6.2 Surface Deviation and Accuracy 231
6.6.3 Build Styles and Decisions 235
6.6.4 Build-time and Build-cost 238
6.6.5 Functional Prototyping using SL 240
6. 7 OTHER LASER LITHOGRAPHY SYSTEMS 242
7. SELECTIVE LASER SINTERING (SLS) 245
7.1 THE PRINCIPLE OF SLS 245
7.2 INDIRECT AND DIRECT SLS 249
7 .2.1 Powder Structures 249
7.2.2 Indirect SLS using Coated Powders 250
7.2.3 Direct SLS using Mixed Powders and LPS 254
7.3 MODELING OF SLS 258
7.3.1 Modeling ofMaterial Properties 258
7.3.2 Energy Input Sub-model 263
7.3.3 Heat Transfer Sub-model 266
7.3.4 Sintering Sub-model and Solution 268
7.4 POST-PROCESSING 272
7.5 PROCESS ACCURACY 275
8. OTHER RP SYSTEMS 279
8.1 SELECTIVE LASER CLADDING (SLC) 279
8.2 LAMINATED OBJECT MANUFACTURING (LOM) 281
8.3 FUSED DEPOSITION MODELING (FDM) 288
8.4 3D PRINTING AND DESKTOP PROCESSES 294
8.5 SHAPE DEPOSITION MANUFACTURING (SDM) 300
8.6 VACUUM CASTING 303
8.7 ELECTROFORMING 304
Table of Contents lX
8.8 FREEZE CASTING 305
8.9 CONTOUR CRAFTING 306
8.10 3D WELDING 307
8.11 C NC MACHINING AND HYBRID SYSTEMS 308
9. RAPID TOOLING 311
9.1 CLASSIFICATION OF RT ROUTES 312
9.2 RP OF PATTERNS 313
9.3 INDIRECT RT 316
9.3.1 Indirect Methods for Soft and Bridge Tooling 316
9.3.2 Indirect Methods for Production Tooling 322
9.3.3 Direct RT Methods for Soft and Bridge Tooling 324
9.3.4 Direct RT Methods for Production Tooling 325
9.4 OTHERRT APPROACHES 327
lO.APPLICATIONS OF RP 329
10.1 HETEROGENEOUS OBJECTS 330
10.2 ASSEMBLIES 332
10.3 MEMS AND OTHER SMALL OBJECTS 333
10.4 MEDICINE 337
10.5 MISCELLANEOUS AREAS INVOLVING ART 340
REFERENCES 345
INDEX 377
Preface
Since the dawn of civilization, mankind has been engaged in the
conception and manufacture of discrete products to serve the functional
needs of local customers and the tools (technology) needed by other
craftsmen. In fact, much of the progress in civilization can be attributed to
progress in discrete product manufacture.
The functionality of a discrete object depends on two entities: form, and
material composition. For instance, the aesthetic appearance of a sculpture
depends upon its form whereas its durability depends upon the material
composition. An ideal manufacturing process is one that is able to
automatically generate any form (freeform) in any material. However,
unfortunately, most traditional manufacturing processes are severely
constrained on all these counts.
There are three basic ways of creating form: conservative, subtractive,
and additive. In the first approach, we take a material and apply the needed
forces to deform it to the required shape, without either adding or removing
material, i.e., we conserve material. Many industrial processes such as
forging, casting, sheet metal forming and extrusion emulate this approach. A
problem with many of these approaches is that they focus on form
generation without explicitly providing any means for controlling material
composition. In fact, even form is not created directly. They merely
duplicate the external form embedded in external tooling such as dies and
molds and the internal form embedded in cores, etc. Till recently, we have
had to resort to the 'subtractive' approach to create the form of the tooling.
The production of such tooling can be quite expensive and time consuming,
thus making unit costs highly sensitive to production volume.
Xll Rapid Prototyping
The subtractive approach involves taking a block of material and
chipping away unwanted segments. This is the way Michelangelo had
created his brilliant sculptures. In modem industry, CNC machines work on
the subtractive principle. An advantage of CNC is that it can utilize
information embedded in a CAD model of the part. Further, form generation
depends on the relative motion between the subtractive tool (e.g., an end
mill) and the blank. In other words, it is not necessary to have tooling
embedded with the required form, so small-volume production becomes
possible. As a result, much of the tooling industry today depends upon CNC
machining. However, when applied to the direct manufacture of products,
CNC machining is not economical for high production volumes. Further,
only those form features accessible by the subtractive tools can be created.
This means that reentrant comers and internal form cannot be created.
Another problem is that, although the machine is computer controlled, the
physical side of machining requires manual attention. Lastly, like the
conservative approach, the subtractive approach merely focuses on the
generation of form without providing a means of controlling material
composition.
The 'additive' approach starts with nothing and builds an object
incrementally by adding material. The material added each time can be the
same or different. Thus, one is able to address the problems of form
generation and material composition at once through the same process. The
smaller the volume of each material increment, the greater are the form
accuracy achievable and the degree of control on material composition. In
the ultimate, the principle is capable of even achieving the dream of "from
bits to atoms". The immediate advantage, however, is that, in principle, any
solid 3D freeform can be generated without the aid of external tooling with
embedded form, so most of the problems associated with the conservative
and subtractive methods are totally sidestepped.
Unfortunately, till recently, the additive principle could not be
implemented in industry owing to the lack of suitable materials and
supporting technologies. However, by the 1980s, progress in photopolymers,
laser technologies, CAD modeling, etc. had matured sufficiently to enable
layer-wise additive creation of 3D physical objects through selective
polymerization of a photosensitive resin. The first commercially available
equipment based on this principle was StereoLithography Apparatus-1
(SLA-1) released by 3D Systems, Inc. in 1987. This started a new revolution
in manufacturing. The revolution is still in progress as evident from the
growing number of commercially available SFF technologies: selective laser
sintering (SLS), fused deposition modeling (FDM), layered object
manufacturing (LOM), 3D Printing (3DP), etc.