16-01-2013, 04:29 PM
Flexible Manufacturing System
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INTRODUCTION
In the middle of 1960s, market competition became more intense. During 1960 to 1970 cost was the
primary concern. Later quality became the priority. As the market became more and more complex,
speed of delivery became something customer also needed.
A new strategy was formulated (Customizability). The companies have to adapt to the
environment in which they operate, to be more flexible in their operations and to satisfy different
market segments. Thus the innovation of FMS became related to the effort of gaining competitive
advantage.
First of all, FMS is a manufacturing technology. Secondly, FMS is a philosophy. “System” is
the key word. Philosophically, FMS incorporates a system view of manufacturing. The buzzword
for today’s manufacturer is “agility”. An agile manufacturer is one who is the fastest to the market,
operates with the lowest total cost and has the greatest ability to “delight” its customers. FMS is
simply one way that manufacturers are able to achieve this agility.
DEFINITION
A flexible manufacturing system (FMS) is an arrangement of machines ... interconnected by a
transport system. The transporter carries work to the machines on pallets or other interface units so
that work-machine registration is accurate, rapid and automatic. A central computer controls both
machines and transport system.
Or
“FMS consists of a group of processing work stations interconnected by means of an automated
material handling and storage system and controlled by integrated computer control system.”
FMS is called flexible due to the reason that it is capable of processing a variety of different part
styles simultaneously at the workstation and quantities of production can be adjusted in response to
changing demand patterns.
Computer Control System:
It is used to coordinate the activities of the processing stations and
the material handling system in the FMS. The various functions of computer control system are:
(i) Control of each work station
(ii) Distribution of control instruction to work station
(iii) Production control
(vi) Traffic control
(v) Shuttle control
(vi) Work handling system and monitoring
(vii) System performance monitoring and reporting
The FMS is most suited for the mid variety, mid value production range.
THE SIGNIFICANCE OF FMS IN THE 1990s
The installed worldwide FMS base in 1989 was estimated to be around 500 to 1200 systems, the
higher figure arising when a system is defined as having 2 or more CNC machine tools connected
by a materials handling system, and controlled by a central computer. Ranta and Tchijov suggest
that this number will rise to around 2500–3500 by the year 2000. This led them to suggest that “the
strategic majority of production of the metal-working industries in the industrialized countries will
be produced by FMS or similar systems [by the year 2000].”
Kelley’s empirical research in 1987 strongly contradicts this. In a large (>1000 firms) survey of
US metal working firms, she found that less than 5 per cent of those plants with computerized
automation have an FMS and that FMS constituted only 1.5 per cent of the total number of installations
of computerized automation. Why are there still so few FMS in the world given that small-batch
engineering production is a significant proportion of manufacturing output?
There are significant practical reasons for the disparity between the promise of FMS in the
1980s and its narrowness and scarcity of application in the early 1990s. These reasons are outlined
below separately, though they are very much interdependent. Different approaches to flexibility
and their meanings are shown Table 1.1.
Seeking Benefits on Flexibility
Today’s manufacturing strategy is to seek benefits from flexibility. This is only feasible when a
production system is under complete control of FMS technology. Having in mind the Process-
Product Matrix you may realize that for an industry it is possible to reach for high flexibility by
making innovative technical and organizational efforts. See the Volvo’s process structure that makes
cars on movable pallets, rather than an assembly line. The process gains in flexibility. Also, the
Volvo system has more flexibility because it uses multi-skill operators who are not paced by a
mechanical line. So we may search for benefits from flexibility on moving to the job shop structures.
Actually, the need is for flexible processes to permit rapid low cost switching from one product
line to another. This is possible with flexible workers whose multiple skills would develop the
ability to switch easily from one kind of task to another.
As main resources, flexible processes and flexible workers would create flexible plants as plants
which can adapt to changes in real time, using movable equipment, knockdown walls and easily
accessible and re-routable utilities.
FMSAN EXAMPLE OF TECHNOLOGY AND AN ALTERNATIVE LAYOUT
The idea of an FMS was proposed in England (1960s) under the name “System 24”, a flexible
machining system that could operate without human operators 24 hours a day under computer
control. From the beginning the emphasis was on automation rather than the “reorganization of
workflow”.
Early flexible manufacturing systems were large and very complex, consisting of dozens of
Computer Numerical Controlled machines (CNC) and sophisticated material handling systems.
DIRECT REAL TIME SCHEDULE CONTROL
The major functions of an FMS host are illustrated in the Fig. 1.9
Planned work is only allocated to a specific machine when the individual piecepart has been
setup in a fixture on a pallet and a machine is available, with all its necessary equipment and
programs, to process it. The object of the host is to keep the expensive capital equipment utilized by
supplying with it with work. This is best achieved when preparatory work is carried out simultaneously
whilst the machine is still working. The host organizes the preparation and transportation of the
work so that it is readily available to the machine when it next requests some work. The best
machine utilization can be obtained when a machine’s layout includes an internal machine buffer.
The host can then organize this internal buffer to be always loaded with work. If this buffer is
always loaded with work there will always be work available for the machine to transfer immediately
into the spindle’s work area. Piece parts are moved from a machine under the organization of the
host to other machines, or to a system buffer station, if the next machine in a piecepart’s process
route is busy and cannot accept a piecepart into its buffer.