Koren Y. The Global Manufacturing Revolution: Product-Process-Business Integration and Reconfigurable Systems
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In general, two basic types of reconfiguration capabilities are needed in
manufacturing systems—in their functionality (as shown in Figure 9.2) and in their
production capacity. Adjusting the system product ion capacity is needed in order
to cope with fluctuations in product demand caused by changing mark et conditions.
Figure 9.3 shows how the actual deman d for Products A and B can be different from
what was planned. This type of reconfiguration requires rapid changes in the system
production capacity, which is called system scalability.
A responsive manufacturing system is one whose production capacity is adjustable
to fluctuations in product demand, and whose functionality is adaptable to new
products.
Traditional man ufacturing systems are ill suited to meet the requirements dictated
by the new, competitive environment. Dedicated manufacturing lines (DMLs), as we
have described, are based on inexpensive fixed automation producing a company’s
core products or parts for a long time at high volume (see Figure 9.4). Each dedicated
line is typically designed to produce a single part at high production rate achieved by
the operation of all tools simultaneously. When the product dem and is high, the cost
per part is exceptionally low. DML s are cost-effective as long as they can operate at
full capacity, but with increasing pressure from global competition and over-capacity
worldwide, the norm is situations where dedicated lines do not operate at full capacity.
Flexible manufacturing systems (FMSs) can produce a variety of products, with
changeable volume and mix, on the same system. However, FMSs consist of
expensive, general-purpose computer numerically controlled (C NC) machines and
other programmable automation. Because of the single-tool operation of the CNC
machines, FMS throughput is much lower than that of a DML. The combination of
high equipment cost and low throughput makes the FMS cost per part relatively high.
Therefore, the FMS production capacity is usually lower than that of dedicated lines
as depicte d in Figure 9.4.
Figure 9.3 Projection compared to actual demand: higher initial demand than expected
for both products and Product C is introduced earlier than expected.
THE CHALLENGES OF GLOBALIZATION 231
9.2 RMS—A NEW CLASS OF SYSTEMS
A cost-effective response to market changes requires a new manufacturing approach
that not only combines the high throughput of DML with the flexibility of FMS, but
also is able to react to market changes by changing the manufacturing system and
its elements quickly and efficiently. This is a feature of an RMS whose capacity and
functionality can be changed as needed, as illustrated in Figure 9.4.
9.2.1 Japanese Flexib le Manufacturing System Complex
In 1977, Japan’s Ministry of International Trade and Industry (MITI) initiated the
development of a Flexible Manufacturing system Complex (FMC)—a test factory
consisting of modular machining units and assembly robots with functionality
adaptable to the product to be processed.
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The project was completed in 1983 with
the building of a demonstration factory in Tsukuba, Japan.
The Tsukuba FMC system was designed to produce a whole range of prism-shaped
parts within a given envelope and was completely task-driven. The FMC included
storage of machine modules in a warehouse when not in use and their assembly on
demand to accommodate the product to be produced. Upon completion of each
production exercise, the machines were broken back down into their modules and
returned to storage. The storage of so many unused machine modules is a waste and
unpractical to industry. The demonstration plant continued until 1984 and inspired
a whole generation of factory automation in Japan.
This Japanese demonstration plant was impractical and only suitable for small
volume production, although it did demonstrate machine modularity and functional
convertibility. Even so, this conversion was not done rapidly, or cost-effectively.
Figure 9.4 Both DML and FMS are static systems; the RMS is a dynamic system that can
change capacity and functionality in response to market changes
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RECONFIGURABLE MANUFACTURING SYSTEMS
Furthermore, the demo plant did not deal at all with capacity changes. By contrast,
RMS addresses changes in both functionality and capacity, as well as performing
these changes quickly and cost-effectively.
9.2.2 Cost of Capacity
Three features—capacity, functionality, and cost—define the difference between the
three types of manufacturing systems—RMS, DML, and FMS. While DML and FMS
are usually fixed at the capacity-f unctionality plane as shown in Figure 9.4, the RMS is
not constrained by capacity or functionality and can change over time as the system
reacts to changing market circumstances.
In the system-cost versus capacity plane, the DML is a constant at its maximum
planned capacity; a whole additional line must be built when greater capacity is
needed. The pure-parallel FMS is scalable at a constant rate (adding machines in
parallel), as depicted in Figure 9.5. The RMS is scalable, but at a non-constant rate that
depends on the initial design of the RMS and market circumstances.
A critical question is: When is the Right Time to Consider Building a New
RMS? It is when planning a new manufacturing system for a part family or a product
family line with several variants that are expected to change in the next 10–15 years,
and the market is volatile, so it is hard to forecas t demand. The new RMS should be
designed at the outset for reconfiguration, which will be achieved through:
.
Design of the system and its machines for adjustable structure that enable
system scalability in response to market demands and system/machine con-
vertibility to new products. Structure may be adjusted (1) at the system level
(e.g., adding machines), (2) at the machine level (e.g., adding spindles and
axes or changing angles between axes), and (3) at the control software (e.g.,
integrating easily advanced controllers).
Figure 9.5 Manufacturing system cost versus capacity.
RMS—A NEW CLASS OF SYSTEMS 233
.
Design of the manufacturing system around the part family, with the custom-
ized flexibility required for producing all parts of this part family.
Manufacturing equipment is reconfigurable, and not just flexible, if the answer to
the following two questions is positive.
1. Is this manufacturing system or equipment was designed for possible easy
changes in its physical structure?
2. Is this manufacturing system or equipment was designed for production or
inspection of a particular part family?
9.2.3 RMS—The Best of Both
As we have seen an FMS posse ss the flexibility needed to switch between the
manufacturing of product variants, but is not as cost-effective as DML. By contrast,
the DML has high productivity but no flexibility. An RMS embraces the best qualities
from both types: a system that not only possesses cost-effective, flexible production,
but als o has changeable structure (at both the system level and the machine level) so it
can handl e unexpected market changes.
The DML design focuses on the produced part. If the part is not defined, you cannot
design a DML. By contras t, a typical FMS is composed of CNC machines. I was at a
technology exhibition in which a small FMS with five CNCs was demonstrated. It was
not built to produce any particular part. “You bring the part” they told me “and we will
do the process-planning to machine it.” Their design focus was to produce multi-axis
precise machines. This focus on the machine rather than on the part is one reason for
the waste and low production rates of FMS technology.
Borrowing from dedicated lines that are designed around a single part/product,
RMS focuses on families of parts, like cylinder heads. Between four-, six-, and eight-
cylinder models there are many differences, but they also have many more common
features. Focusing on the part family enables the designer to plan a system that
accommodates different variations of the same part family with minimum alteration
to the production scheme. This approach utilizes the high productivity of DML
machine design, and is much more economical than the general functionality of FMS.
An artist’s view of the three systems is depicted in Appendix B. As summarized
in Table 9.1, a system with adjustable structure and a design focus on a part family
constitutes a new class of system—an RMS.
Building a system with changeable structure provides scalability and customized
flexibility is focused on a part family and creates a responsive reconfigurable system.
The flexibility of RMS, although it is really just “customized flexibility,” provides all
the flexibility needed to process that whole part family.
9.2.4 RMS Definition
Highly productive, cost-effective systems are created by (i) part-family focus and
(ii) customized flexibility that enables the operation of simultaneous tools. The
234 RECONFIGURABLE MANUFACTURING SYSTEMS
invention of the RMS is documented in a U.S. Patent (by Y. Koren and G. Ulsoy).
3
The
RMS is designed to cope with situations where both productivity and the ability of the
system to react to changes are of vital importance.
Each RMS is designed to produce a particular family of parts. The main
components of RMS for machining are CNC machines and Reconfigurable Mach ine
Tools (RMTs)
4
—see Chapter 8. To coordinate and operate the CNCs and RMTs,
reconfigurable controls integrated in an open-architecture environment are critical to
the success of an RMS.
The definition of an RMS is, therefore:
An RMS is designed at the outset for rapid change in structure, as well as in
hardware and software components, in order to quickly adjust production capacity
and functionality within a part family in response to sudden changes in market or
regulatory requirements.
If the system and its machin es are not designed at the outset for reconfigurability,
the reconfiguration process will prove lengthy and impractical.
9.3 CHARACTERISTICS AND PRINCIPLES OF RECONFIGURATION
In 1996, the National Science Foundation established an Engineering Research
Center for RMSs to explore and describe the enabling technologies that underlay
TABLE 9.1 RMS Combines Features of Dedicated and Flexible Systems
Dedicated RMS/RMT FMS/CNC
System structure Fixed Changeable Changeable
Machine structure Fixed Changeable Fixed
System focus Part Part family Machine
Scalability No Yes Yes
Flexibility No Customized (around
a part family)
General
Simultaneously
operating tools
Yes Yes No
Productivity High High Low
Lifetime cost Low Medium Reasonable
For a single part,
when fully
utilized
For production at
medium-to-high
volume parts with
variable demand
during system
lifetime
For simultaneous
production of
many parts (at
low volume)
Otherwise—High
CHARACTERISTICS AND PRINCIPLES OF RECONFIGURATION 235
reconfigurable manufacturing. The NSF supported the Center until 2007. The Center
has defined a number of principles and characteristics for RMS, and a range of
patented innovations that provide the basis for developing new reconfiguration
technologies and processes. These enabling technologies and characteristics are
discussed below.
9.3.1 RMS Enabling Technologies
FMS and its CNC machines allow flexibility i n the production o f a variety of parts.
The RMS allows flexibility not only in producing a variety of parts, but also in
changing the s ystem itself. N ote that not only dedicated lines but a lso flexible
systems use fixed hardware and fixed software. In recent years, however, two
technologies have emerged that are enablers for reconfiguration: In software—
open-architecture controls that allow reconfiguration of the machine controller;
5
and in machine hardware—modular machine too ls that offer the customer more
machine options. These emerging technologies enable the design of vastly more
responsive systems with reconfigurable hardware and software, as depicted in
Figure 9.6.
Reconfigurable hardware and software are necessary but they are not, by them-
selves, sufficient conditions for a cost-effective RMS. RMS design must also include
an advanced systems perspective that forecasts possible reconfigurations during
the operational life of the system with their ongoing economic modeling. Future
reconfiguration planning should include system design options combined with
possible upcoming reconfigurations of the machines, and the automated part handling
and tooling systems, as well as open-architecture controllers. RMS design, therefore,
engenders a whole new approach to the design of manufacturing systems—design to
meet current needs, but with future perspective.
With such design, the system capacity and functionality can be changed in
response to market demand. When the production plan of a new product is added,
the system functionality can be adjusted to handle it. We summarize these attributes as:
Exactly the functionality and capacity needed. ... Exactly when needed.
Figure 9.6 Classes of machines and manufacturing systems.
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RECONFIGURABLE MANUFACTURING SYSTEMS
Both the systems and their reconfigurable machines mus t be designed at the outset
to be reconfigurable by applying the characteristics discussed below.
9.3.2 Reconfiguration Core Characteristics
Reconfigurable systems must be designed from the outset with hardware and software
modules that can be integrated quickly and reliably. Otherwise, the reconfiguration
process will be lengthy and impractical. And, like reconfigurable machines, achieving
this goal requires an RMS that possesses much the same six key characteristics:
Customization, Scalability, Convertibility, Modularity, Integrability, and Diagnosa-
bility. These system-level characteristics apply to the design of the whole production
system. Ultimately they may even be applied to the ente rprise as a whole. We
elaborate below on these key characteristics.
Customization: This characteristic distinguishes RM S drastically from that of
FMS and DML, and allows for substantial efficiencies in system cost. It enables
the design of systems for the production of part families, rather than for single
parts (as those produced by DML) or any part (FMS). In the context of RMS,
a part family is defined as all parts (or products) that have similar geometric
features and shapes, the same level of tolerances, require the same production
processes, and are within the same range of cost. From a systems point of view,
this definition also assumes that most manufacturing system resources are
utilized for the production of every member part.
Customization, or customized flexibility, delivers substantial economic
benefit by enhancing productivity at low cost. Customized flexibility means
that the RMS configuration must accommodate the full range of dominant
features of the whole part family. It allows for the greatest commonality of
application of multiple tools (e.g., spindles in machining or nozzles in injection
molding) on the same machine, thereby increasing productivity at reduced cost
without compromising flexibility. When properly designed, the RMS provides
the rig ht balance between productivity and general flexibility.
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Convertibility: System convertibility is the ability to quickly change system
functionality to produce (or inspect) all members of the product family. System
convertibility includes also machine conversion. For example, conversion may
require switching spindles on a milling machine from a low-torque high-speed
spindle for aluminum to a high-torque low-speed spindle for titanium, or
manual adjustment of passive degrees-of-freedom changes when switching
production between two members of a part family within the same day. System-
level conversion includes integrating new machines and extending reach of
gantries to expand the range of a system functionality to produce new parts.
Scalability: It is increasingly difficult to predict product demand, providing a
compelling reason for why manufacturing systems need to be scalable.
Scalability of the system’s produc tion capacity is the ability to quickly and
efficiently change the maximum production volume possible, and is the
CHARACTERISTICS AND PRINCIPLES OF RECONFIGURATION 237
counterpart of Convertibility. The Scalability characteristic may require adding
spindles at the machine level to increase its productivity, and at the system level
changing part routing or adding machines to expand the overall system capacity
as the market grows.
Modularity: RMSs need a modular overall structure
7
to meet the requirements
of changeability.
8
At the system level, every machine is a module, and many
material-handling systems (conveyors, gantries, etc.) are built in a modular
structure to facilitate future reconfigurations. In addition, components at the
machine level may be modular (e.g., structural elements, axes, controls, soft-
ware, and tooling). When necessary, modular components, at any level, can be
replaced or upgraded to better suit new applications and new market demand.
Integrability: At the machine level, spindles and axes of motions can be
integrated to form new machines. At the system level, the machines are the
modules to be integrated via material transport systems to form a reconfigurable
system. In addition, machine controllers can be integrated into a factory-level
control system.
Diagnosability: Diagnosability has two goals in RMSs: noticing machine failures
and detecting unacceptable part quality. The second aspect is critical in RMS. As
production systems are made more reconfigurable, and their layouts are modified
more frequently, it becomes essential to rapidly tune the newly reconfigured
system so that it quickly produces quality parts. To this end, reconfigurable
systems must also include product quality measurement systems as an integral
part. These measurement systems are intended to help identify product quality
problems in the production system rapidly, so they can be corrected utilizing
control technologies, statistics, and signal processing techniques.
The six core reconfigurable system characteristics are summarized in Table 9.2.
Customization, Scalability, and Convertibility are necessary characteristics for
reconfiguration. Modularity, Integrability, and Diagnosability are sufficient char-
acteristics for reco nfiguration. The six key RMS characteristics reduce the time and
effort of reconfiguration, and thereby enhance system responsiveness. These char-
acteristics can reliably reduce lifetime cost by enablin g the system to constantly
change during its lifetime, “staying alive” despite changes in markets, consumer
demand, and process technology.
9.3.3 Reconfiguration Principles
RMSs operate according to three Reconfiguration Principles that have been intro-
duced by the author. These principles are intended to improve its speed of recon-
figuration and consequently its speed of responsiveness to (i) unpredictable
external occurrences (e.g., market changes), (ii) planned product model changes,
and (iii) unexpected intrinsic system events (such as unexpected long machine
failure). The more these principles are applicable to a given manufacturing system,
the more reconfigurable that system is.
238 RECONFIGURABLE MANUFACTURING SYSTEMS
9.3.3.1 Design Principles of Reconfigurable Manufacturing Systems
1. The RMS provides adjustable production resources to respond to unpre-
dictable market changes and system intrinsic occurrences:
.
RMS capacity can be rapidly scalable in small increments.
.
RMS functionality can be rapidly adaptable to new products.
.
RMS inbuilt adjustment capabilities enable rapid response to unexpected
equipment failures.
2. The RMS is designed around a part or a product family, with just enough
customized flexibility needed to produce all members of that family.
3. The RMS core characteristics should be embedded in the whole system as
well as in its components (mechanical, communications, and control).
The environment of many manufacturing companies is characterized by unpre-
dictable market changes. Changing orders requires altering the output capacity and
the processing functions of the manufacturing system. RMSs meet these requirements
by rapidly adapting both their capacity and functionality to new situations.
TABLE 9.2 Reconfigurable System Core Characteristics
Customization
Flexibility limited
to part family
The design of system or machine flexibility limited to just a product
family, thereby obtaining customized-flexibility
Convertibility
Design for
functionality
changes
The ability to easily transform the functionality of existing systems,
machines, and controls to suit new production requirements
Scalability
Design for capacity
changes
The ability to easily modify production capacity by adding or
subtracting manufacturing resources (e.g., machines) and/or
changing the reconfigurable components of the system
Modularity
Components are
modular
The compartmentalization of operational functions into units that
can be manipulated between alternate production schemes to
achieve the most optimal arrangement
Integrability
Interfaces for rapid
integration
The ability to integrate modules rapidly and precisely by a set of
mechanical, informational, and control interfaces that enable
integration and communication
Diagnosability
Design for easy
diagnostics
The ability to automatically read the current state of a system and
controls to detect and diagnose the root causes of output product
defects, and quickly correct operational defects
CHARACTERISTICS AND PRINCIPLES OF RECONFIGURATION 239
Implementing the RMS characteristics and principles in the system design enables
achievement of the ultimate goal—to create a “living factory” that is able to rapidly
adjust its production capacity while maintaining high levels of quality from one part
to the next. This adaptability guarantees a high long-term benefit-to-cost-ratio on
investment in RMSs.
9.4 INTEGRATED RMS CONFIGURATIONS
This section deals with two issues: (a) designing RM S systems that have all six core
characteristics and (b) designing RMS systems that incorporate innovative RMTs
and reconfigurable inspection machines (RIMs) – both were introduced in Chapter 8 –
into the configuration. These two innovations make the RMS more productive and
responsive.
Our starting point is the RMS configuration depicted in Figure 9.7. It represents
a system already being utilized in the powertrain industry. It is a system of t hree
stages that can produce two different parts simultaneously. A cell gantry serves all
machines in a particular stage; it brings parts and loads them on the machines, and
takes t he finished pa rt s and tran s fer them to a buffer (the circle in Figure 9.7)
located next to the main material handling system. The latter is usually a gantry
(called the spine gantry), but it can be a lso a conveyor, or several AGVs. To
balance the system sequence, all stages should have almost the same cycle time. In
this figure, the cycle time of each of the two machines in Stage 2 is approximately
1.5 times shorter than the cycle time for the three machines in Stages 1 and 3. (In
industry, the set of all machining tasks assigned to a stage is called an “Operation.”
Usually operations are numbered 10, 20, 30, etc., allowing for the addition of
intermediate operations as needed over time, for example, adding Operation 15.
However, we prefer the term “stage.”)
Figure 9.7 Practical RMS configuration with three stages.
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RECONFIGURABLE MANUFACTURING SYSTEMS