The Design of Manufacturing Systems Part 3 pdf

and so on. Guilford and Turner [1992] identified some of the deficiencies in the tolerancing models
proposed by researchers prior to the year 1990. They reported that the committee on Shape Tolerance
Resource Model within the Standard for the Exchange of Product Model Data (STEP part 47) is attempt-
ing to define an unambiguous representation of tolerances compatible with the ANSI Y14.5 and the ISO
1101 family of standards. They identified a problem that exists in identifying locations and directions
while defining tolerances and data. In STEP, these are represented by Cartesian vectors, but the problem
of locating the part in the co-ordinate system exists. Guilford and Turner [1992] modified the approach
employed by STEP in order to overcome the problems. For example, STEP describes the direction along
which the straightness tolerance is measured as a vector in the global co-ordinate system, while the
authors described it by using some virtual geometry entities attached to the actual geometry of the part.
The authors have discussed the representation which covers almost all of the ANSI Y14.5 tolerances except
for items such as knurls, gears, and screws; equalizing data, free state variations, conical position tolerance
zones, and position tolerances on elongated holes.

Feature Data Exchange Mechanisms

Standards for Exchange of Product Data (STEP) is an international standard (designated as ISO 10303)
that deals with the computer interpretable representation and exchange of product model data. The
intent is to provide a neutral interface which is capable of describing all the life-cycle properties of a
given artifact independent of the CAD platform used for product modeling. This will also serve as a basis
for implementing and sharing product databases and archives. The various parts of ISO 10303 are divided
into the following categories: description methods, application protocols, abstract test suites, implemen-
tation methods, and conformance testing.
Application protocols (AP) provide a basis for developing implementations of STEP (ISO 10303) and
abstract test suites for conformance testing of Application Protocol (AP) implementations. AP 224 (devel-
oped by TC184/SC4/WG3) is a part of the application protocol category that defines the context, scope,
and information requirements of producing mechanical product definition for process planning appli-
cation, and it directs the integrated resources necessary to satisfy these requirements. These requirements
specify items such as part identification, shape, and material data, necessary for product definition. The
basic premise of AP 224 is that the process planning function will be greatly assisted by identifying

machining features present on the part model. Knowledge about the machining features will help in
proper identification of machining equipment, tooling, and processes to manufacture a part. AP 224
provides a schema for representation and exchange of part feature information.
ISO 10303-AP 224 employs two ways to represent the shape of part features: implicit shape represen-
tation and explicit shape representation. The explicit shape representation is specified by using a B-Rep
(boundary representation) scheme. The implicit shape representation is specified by defining parameters
(attributes) associated with each type of feature. Currently, three basic types of features are employed in
AP 224, namely, machining features (such as hole, groove, boss, thread, etc.), replicate features (such as
circular pattern, rectangular pattern, etc.), and transition features (such as chamfer, fillet, and rounded
edge). Compound features (user defined features) can be created by the union of one or more machining
features. The technical content of AP 224 provides good coverage on part features and associated
attributes. However, it can be extended in scope (though the actual approval process needs input from
representatives of several countries) to include some of the following issues.
• Multiple part mechanical parts as opposed to single piece mechanical parts
• Inclusion of features produced by manufacturing processes other than turning and milling
• Interacting features and feature relations deemed critical from the process planning standpoint
• Multiple “viewpoints” of features
• Support other CAD representation schemes than just the B-Rep scheme
• Support “redesign” product development by providing part retrieval mechanisms
• Provide definition of commonly used catalog parts such as nuts, bolts, gear, etc.
© 2001 by CRC Press LLC

3

Flexible Factory
Layouts: Issues in
Design, Modeling,

and Analysis

3.1 Introduction

3.2 Literature Review

3.3 Flexible Layout Configurations

3.4 Measuring Layout Flexibility

Geometry-Based Measures • Flow-Based Measures

3.5 A Procedure for Flexible Layout Design

Solution Procedure • A Heuristic Approach • Flexible Layout
Selection • Software Implementation and Analysis

3.6 Conclusion

In this chapter, we address several issues related to design, modeling, and analysis of flexible factory
layouts. We present a framework for defining and identifying sources of layout flexibility and for mapping
different dimensions of flexibility to specific layout configurations. We use this framework to develop
several potential measures of layout flexibility and compare the usefulness and limitations of each. We
also examine the relationship between factory layout and material handling and show that the realization
of layout flexibility largely depends on the configuration of the material handling system. Finally, we
present an integrated procedure for flexible layout design in stochastic environments. We use the pro-
cedure to highlight the desirability of disaggregating functional departments into smaller subdepartments
and distribute them throughout the factory floor. We show that increased disaggregation and distribution
can be, indeed, effective in enhancing a layout’s ability to cope with variability.

3.1 Introduction

In today’s volatile and competitive environment, manufacturing facilities must be designed with enough
flexibility to withstand significant changes in their operating requirements. The shortening of product
life cycles and the increased variety in product offerings require that facilities remain useful over many
product generations and support the manufacturing of a large number of products. Because the prolif-
eration of products makes it exceedingly difficult to produce accurate forecasts of demand volumes and
demand distribution, facilities must be able to rapidly reallocate capacity among different products
without major retooling, resource reconfiguration, or replacement of equipment. Furthermore, increased
emphasis on customer satisfaction places simultaneous requirements on shorter manufacturing lead

Saifallah Benjaafar

University of Minnesota
© 2001 by CRC Press LLC