Table Of ContentMANUFACTURING RESEARCH AND TECHNOLOGY
Volume 1. Flexible Manufacturing: Recent developments in FMS, Robotics
CAD/CAM, CIM (edited by A. Raouf and S. I. Ahmad)
Volume 2. Computer-Aided Design, Selection and Evaluation of Robots (B. O. Nnaji)
Volume 3. Modelling and Design of Flexible Manufacturing Systems (edited by
A. Kusiak)
Volume 4. Flexible Manufacturing: Integrating technological and social innovation
(P. T. Bolwijn, J. Boorsma, Q. H. van Breukelen, S. Brinkman and
T. Kumpe)
Volume 5. Proceedings of the Second ORSA/TIMS Conference on Flexible
Manufacturing Systems: Operations research models and applications
(edited by Κ. E. Stecke and R. Suri)
Volume 6. Recent Developments in Production Research (edited by A. Mital)
Volume 7A. Intelligent Manufacturing Systems I (edited by V. R. Milacic)
Volume 7B. Intelligent Manufacturing Systems II (edited by V. R. Milacic)
Volume 8. Proceedings of the Third ORSA/TIMS Conference on Flexible
Manufacturing Systems: Operations research models and applications
(edited by Κ. E. Stecke and R. Suri)
Volume 9. Justification Methods for Computer Integrated Manufacturing Systems:
Planning, design justification, and costing (edited by H. R. Parsaei,
Τ L. Ward and W. Karwowski)
Volume 10. Manufacturing Planning and Control - A Reference Model
(F. P. M. Biemans)
Volume 11. Production Control - A Structural and Design Oriented Approach
(J.W. M. Bertrand, J. C. Wortmann and J. Wijngaard)
Volume 12. Just-in-Time Manufacturing Systems-Operational planning and control
issues (edited byA.Satir)
Volume 13. Modelling Product Structures by Generic Bills-of-Materials
(E. A. van Veen)
Volume 14. Economic and Financial Justification of Advanced Manufacturing
Technologies (edited by H.R. Parsaei, T.R. Hanley and W.G. Sullivan)
Volume 15. Integrated Discrete Production Control: Analysis and Synthesis -
A View based on GRAI-Nets (L. Pun)
Volume 16. Advances in Factories of the Future, CIM and Robotics (edited by
M. Cotsaftis and F. Vernadat)
Volume 17. Global Manufacturing Practices-A Worldwide Survey of Practices in
Production Planning and Control (edited by D.C. Whybark and G. Vastag)
Volume 18. Modern Tools for Manufacturing Systems (edited by R. Zurawski
and T.S.Dillon)
Volume 19. Solid Freeform Manufacturing-Advanced Rapid Prototyping
(D. Kochan)
Volume 20. Advances in Feature Based Manufacturing (edited by J. J. Shah,
M. Mantyla and D. S. Nau)
MANUFACTURING RESEARCH AND TECHNOLOGY 20
Advances in Feature
Based Manufacturing
Edited by
Jami J. Shah
Department of Mechanical and Aerospace Engineering
Arizona State University, Tempe, AZ, USA
Martti Mantyla
Department of Computer Science
Helsinki University of Technology, Espoo, Finland
Dana S. Nau
Department of Computer Science and Institute for Systems Research
University of Maryland, College Park, MD, USA
ELSEVIER
Amsterdam - London - New York - Tokyo 1994
ELSEVIER SCIENCE B.V.
Sara Burgerhartstraat25
P.O. Box 211,1000 AE Amsterdam, The Netherlands
Library of Congress Catalog1ng-1n-PublIcatlon Data
Advances in feature based manufacturing / edited by Jam1 J. Shah,
Martti Mantyla, Dana S. Nau.
p. ct. — (Manufacturing research and technology ; 20)
Includes bibliographical references.
ISBN 0-444-81600-3 (add-free paper)
1. Production planning—Data processing. 2. CAD/CAM systems.
I. Shah, Jan J. II. Mantyla, Martti, 1955- . III. Nau, Dana S.
IV. Series.
TS183.3.A38 1994
658.5—dc2C 94-44
CIP
ISBN: 0 444 81600 3
© 1994 Elsevier Science B.V. All rights reserved.
No part of this publication may be reproduced, stored in a retrieval system or transmitted in any
form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the
prior written permission of the publisher, Elsevier Science B.V., Copyright & Permissions
Department, P.O. Box 521,1000 AM Amsterdam, The Netherlands.
Special regulations for readers in the U.S.A. - This publication has been registered with the
Copyright Clearance Center Inc. (CCC), Salem, Massachusetts. Information can be obtained from
the CCC about conditions under which photocopies of parts of this publication may be made in the
U.S.A. All other copyright questions, including photocopying outside of the U.S.A., should be
referred to the copyright owner, Elsevier Science B.V., unless otherwise specified.
No responsibility is assumed by the publisher for any injury and/or damage to persons or property
as a matter of products liability, negligence or otherwise, or from any use or operation of any
methods, products, instructions or ideas contained in the material herein.
pp. 399-422: Copyright not transferred.
This book is printed on acid-free paper.
Printed in The Netherlands
This book is dedicated to
Alan Grayer, Lycourgas Kyprianou, Charles Lang, and Ian Braid
in recognition of their contributions to geometric modeling
and their pioneering efforts in the development of features technology
vii
PREFACE
Smooth and effective integration of computer-aided design (CAD) and computer
aided manufacturing (CAM) systems is vital for companies striving for survival in the present
increasingly competitive marketplace. Features are generally regarded as a key component in
this integration effort. In the design realm, features provide a means for capturing, explicitly,
the engineering attributes and relationships between product definition entities. This richer
product database is an essential requirement for automating analyses and various design
tasks. In the manufacturing realm, features can be linked to manufacturing knowledge of
various types. Hence, it is possible to automate manufacturing process planning and to
generate the detailed operating instructions required by modern production systems such as
CNC machines, flexible manufacturing systems, robots, and CMM inspection equipment.
The goal of this book is to present a comprehensive picture of the present stage of
development of Features Technology from the point of view of applications in
manufacturing. The book is aimed at several audiences. First, it provides the research
community an overview of the present state-of-the-art of features in manufacturing, along
with references in the literature. Second, the book should be useful as supporting material for
a graduate-level course on product modeling and realization. Last but not least, the book
should also be useful to industrial companies who are assessing the significance of features
for their business.
Well known researchers in all areas related to feature based manufacturing have
contributed chapters to this book. Some of the chapters are surveys, while others review a
specific technique. All contributions, including those from the editors, were thoroughly
refereed. The introduction provides a brief account of the development of feature concepts
and enumerates some key issues of applying features technology in manufacturing. This
creates a framework for viewing the various contributions included in the book. The book
contains twenty chapters organized into six parts, as follows:
Part 1 - Manufacturing feature recognition
Part 2 - Feature mapping
Part 3 - Process planning for machining
Part 4 - Planning for non-machining processes
Part 5 - Inspection planning
Part 6 - Prototype systems
All manufacturing applications require the specification of the product in terms of
manufacturing features, which may be obtained from a solid model (Feature Recognition) or
by transforming a design feature model (Feature Mapping). Chapters on feature recognition
and mapping have been placed in Parts 1 and 2, respectively. The next three Parts contain
chapters on manufacturing planning. Parts 4 and 5 have fewer contributions than Part 3; this
reflects the level of activity in each of these areas. Machining process planning has received
far greater attention than that given to other processes. This may also be due to the fact that
features on formed or cast products are more complex and often involve sculptured surfaces.
Chapters that describe integrated feature based systems have been put in Part 6, under
Prototype Systems.
viii
We have purposely omitted the subject of feature data exchange standards. Even
though several STEP resource models and application protocols will have a major impact on
feature based manufacturing, the situation is not stable enough, both with respect to these
models, and their interpretation. It is our feeling that a chapter on standards will be outdated
by the time this book is published.
We want to thank all contributors, many of who also provided reviews for the articles
submitted. We also thank additional external reviewers, who will remain anonymous. We
enjoyed working with the Publishing Editors at Elsevier: Eefke Smit, who initiated the
project, and Amanda Shipperbottom, who saw it to completion. Finally, we thank Joyce
Arambula and Julie Skonord of Arizona State for handling all the correspondence, reviews,
checking formats, and taking care of other administrative details throughout this project
J and Shah Martti Mantyla Dana Nau
Tempe, Arizona Espoo, College Park, Maryland
USA FINLAND USA
October, 1993
Advances in Feature Based Manufacturing
JJ. Shah, M. Mantyla and D.S. Nau (Editors)
© 1994 Elsevier Science B.V. All rights reserved. 1
CHAPTER 1
Introduction To Feature Based Manufacturing
JamiShaha, Martti Mantylab, DanaNauc
aMechanical and Aerospace Engineering, Arizona State University, USA
^Laboratory for Information ProcessingScience, Helsinki University of Technology,
Finland
cComputer Science Department and Institute for Systems Research,
University of Maryland, USA
1. BACKGROUND
The purpose of this Chapter is to introduce the reader to some basic concepts,
definitions, and terminology used in feature based manufacturing. Also, we present a brief
overview of the contributions included in this book. We hope that this helps the reader before
he/she tackles the more specialized subjects covered in the rest of the book.
1.1 History
The earliest work related to features goes back to Grayer's Ph.D. dissertation at
Cambridge in 1976 [1]. The objective of his work was to automate the link between CAD
and NC part programming. Several other researchers in the CAD group at Cambridge
contributed to both solid modeling and feature modeling. It is for this reason that the book is
dedicated to this group of pioneers. Significant contributions of the group include well
known solid modeling systems BUILD, ROMULUS 1, PARASOLID1, and ACIS2.
Kyprianou's Ph.D. work laid down the foundations for feature recognition from Boundary
Models [2]. Feature recognition research then appears to have spread to several Universities
in the U.S., particularly Purdue and Illinois [3-7]. In the mid-1980s CAM-I proposed the
design-by-feature approach [8] and several prototype systems began appearing [9-13]. By the
late 1980s commercial CAD systems started supporting parametric and feature based on
approaches. Throughout this period there was also considerable research in automating
process planning and NCpart programming [14].
1.2 Definition of a Feature
There are many published definitions of the concept of a feature. Even though these
definitions seem to be dissimilar, they all consider features as entities which are of
1. Trademark of Shape Data Ltd/Electronic Data Systems
2. Trademark of Spatial Technology Inc/Three Space Ltd.
2
semantically higher level than the pure geometric elements typically used in solid modeling
systems. Geometric elements are solid primitives in constructive solid geometry (CSG) type
solid models (blocks, cylinders spheres, tori) or boundary elements used in boundary
representation (BRep) type solid models (faces, edges, vertices). Almost universally, the
concept of generic feature classes is used, and models are built from instances of generic
features. The generic types may be organized into a feature taxonomy, often realized as a
collection of classes with inheritance of information according to the principles of object-
oriented programming.
In the type-instance approach, feature instances are represented in terms of various
feature attributes. Common attributes include the intrinsic geometric attributes of the shape
corresponding to the feature (length, width, depth, radius, etc.), the position and orientation of
the feature with respect to some global coordinate frame, geometric tolerances, material
properties, and references to adjacent and other features. Types contain information shared by
all instances of the type. In the object-oriented approach to features, this information often is
in the form of procedures for computing interesting properties of the instances, such as
volume and cost.
A useful categorization of the various definitions is the separation of "top-down"
definitions and "bottom-up" definitions. Top-down definitions emphasize the designer's view
of features as elementary entities of a part definition; part geometry is considered as a
property of a feature-based part definition which can be computed on the basis of the feature
definition. Bottom-up definitions emphasize features as abstractions of recurring
combinations of geometric elements.
The above categorization typically reflects the primary feature creation method used
by feature-based modeling systems. Thus, top-down definitions correspond with systems
utilizing primarily design-by-features method, where models are originally defined in terms of
their constituent features. Similarly, bottom-up definitions correspond with systems utilizing
feature recognition, where features are extracted from a previously generated geometric
model.
1.3 Manufacturing Features
Features can be defined from different viewpoints, such as design, analysis, assembly,
and function. Because of this, there may be several co-existing feature models of the same
product design. This gives rise to the problem of feature mapping, i.e. conversion among the
various viewpoints. For the purposes of this book, the main viewpoint of interest is
manufacturing, and therefore, features in this book are typically defined from the
manufacturing point of view. A manufacturing feature is commonly defined as a collection of
related geometric elements which correspond to a particular manufacturing method or
process, or which can be used to reason about the suitable manufacturing methods or
processes for creating that geometry.
The link between manufacturing features and manufacturing knowledge is typically
realized through manufacturing process models. For machining, process models can be
organized into a taxonomy containing elementary processes such as milling, drilling, facing,
and turning. Process models are expressed in terms of the manufacturing resources which can
be used to realize the process (machines, tools, fixtures, auxiliary materials), process
parameters related to the use of the resource (for machining, feed and speed), and attribute
information which can be used to guide the choice of a particular process (such as time and
3
cost). Often, procedural knowledge is included, such as procedures for computing the
process parameters on the basis of feature attribute information. An important aspect of a
process model is representation of the tool kinematics, such as access direction, and possible
technological constraints.
To implement the link, manufacturing feature types refer to a collection of possible
process models which can be used to generate instances of the feature type. Thus, for
instance, a hole feature would be linked with the process models related to drilling and
milling processes.
2. PRODUCT DEFINITION FOR MANUFACTURING
There are essentially two ways by which product data is prepared for feature based
manufacturing applications:
• recognition of manufacturing features from a solid model
• mapping a design feature model to manufacturing features
Considerable research has been done in feature recognition over the last two decades
[15, 16]. On the other hand, feature mapping (also known as feature conversion,
transformation, transmutation) came about recently, only after the design by feature approach
became popular. In feature recognition, the solid model is created first, and the
manufacturing features recognized, either interactively by the process planner, or
automatically. Some hybrid methods have also been devised to combine interactive and
automatic recognition [17, 18]. In feature mapping one has the benefit, at least in theory, of
extracting manufacturing information from a richer database. Solid models are only capable
of providing the nominal geometry, which is all that is available in feature recognition.
Manufacturing planning requires knowledge of tolerances, datums, surface attributes, and
material specifications. All of these may be available in a design feature model. However, a
close scrutiny of feature mapping methods does not reveal any evidence that feature level
information is being used to any significant degree. Consequently, the boundary between
feature recognition and feature mapping is rather fuzzy.
3. MANUFACTURING FEATURE RECOGNITION
A large variety of techniques have been developed for feature recognition. We do not
intend to give a comprehensive survey here; the reader should refer to Chapters 2-4. We give
a brief overview of the following popular recognition techniques used in manufacturing:
- Sectioning methods
- Convex hull decomposition
- Boundary based methods
- Cellular decomposition
The main characteristics of each of these are given below:
4
3.1 Sectioning Methods
These are typically used to generate tool paths for 2 1/2D milling. Before this method
can be applied, one needs to determine (automatically or manually) that the part is
manufacturable by 2 1/2 milling. The path is oriented such that its principal feature directions
coincide with the three milling axes. The part volume is sliced with planes parallel to X-Y at
fixed ΔΖ values, representing a series of tool positions. This results in one or more
intersection profiles, representing the part's boundaries. These profiles are classified as
"material" or "void" and offset curves generated to form the basis for NC tool path generation.
Chapter 9 describes some of the techniques used in this methodology.
3.2 Convex Hull Decomposition
Originally developed by Woo [4] this algorithm decomposes a volume by subtracting
it from its convex hull and repeating the process for all the resulting volumes. The
decomposition for each sub-volume terminates when a null object results. Thus, a volume is
decomposed into an alternating sum of volumes (ASV). The original algorithm had the
problem of non-convergence in many cases, and often resulted in volumes that did not bear
resemblance to common manufacturing features. Kim extended the ASV method by
introducing partitioning of non-extremal faces in order to solve the problem of non-
convergence [19]. For recognizing machining features the positive volumes are converted to
equivalent negative volumes. The method is limited to polyhedral solids so far. Chapter 3
presents convex decomposition techniques in detail.
3.3 Boundary Based Methods
All methods that operate primarily on Β-Rep models and use geometric and
topological relations between boundary entities have been lumped under this category. For
each feature, the geometric and topological conditions that need to be satisfied are identified.
To find features in a solid model, the database is searched to see if the conditions
corresponding to each feature are present. Sometimes it is more convenient to build a
separate data structure, such as a face adjacency graph, to facilitate the search. Another key
concept in feature recognition is entity classification, which specifies the geometric relation
between two entities. For example, if two faces meet at an angle of under 180°, the edge at
which they meet is classified as convex. It is common to see data structures combining
topology (face adjacency graph) with geometry (edge classification) for feature recognition
(see, for example, Chap. 2, Figure 5).
The actual mechanics of representing and matching geometric and topological
relations may vary considerably. Rule based procedures, graph grammar, syntactical
methods, algebraic representations, and neural nets have all been employed in specific
implementations. Chapter 2 gives further details of these methods.
Despite their popularity, boundary based feature recognition methods have suffered
from the lack of robust algorithms, particularly when feature interactions are present. Laakko
and Mantyla (Chapter 19) have resolved this problem by a strategy of incremental recognition
of interacting features. Another method for overcoming interaction problems is presented in
Chapter 5, where Vanderbrande and Requicha describe a method called feature completion to
reconstruct portions of features destroyed by interactions.
