05-05-2012, 10:11 AM
Flexible Manufacturing System
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FMS Introduction and Description
1.1 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.
Fig. 1.1 Types of flexibilities
Delivery
flexibility
Volume
flexibility
Mix
flexibility
Manufacturing
flexibility
2 Flexible Manufacturing System
1.2 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.
1.3 BASIC COMPONENTS OF FMS
The basic components of FMS are:
1. Workstations
2. Automated Material Handling and Storage system.
3. Computer Control System
1. Workstations: In present day application these workstations are typically computer numerical
control (CNC) machine tools that perform machining operation on families of parts. Flexible
manufacturing systems are being designed with other type of processing equipments including
inspection stations, assembly works and sheet metal presses. The various workstations are
(i) Machining centers
(ii) Load and unload stations
(iii) Assembly work stations
(iv) Inspection stations
(v) Forging stations
(vi) Sheet metal processing, etc.
2. Automated Material Handling and Storage system: The various automated material handling
systems are used to transport work parts and subassembly parts between the processing stations,
sometimes incorporating storage into function.
The various functions of automated material handling and storage system are
(i) Random and independent movement of work parts between workstations
(ii) Handling of a variety of work part configurations
(iii) Temporary storage
(iv) Convenient access for loading and unloading of work parts
(v) Compatible with computer control
FMS Introduction and Description 3
3. 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.
Fig. 1.2 Application characteristics of FMS
Fig. 1.3 Flexible manufacturing system
Low
Low
Medium
High
Medium
Production Volume
High
Product
Variety
Stand alone NC
machines
Flexible
Manufacturing
systems
Transfer
lines
CNC 1
Tool
changer
Tool
changer
Tool
changer
Indexing
CNC 2 tables
CNC 3
As/RS
Out In Out In
Out In
Computer control
Raw material storage
(roller conveyor)
Load/unload stations
Temporary storage areas
(33 pallet spaces)
Raw material storage
(floor space)
L/U L/U
AGV 1
AGV 2
4 Flexible Manufacturing System
1.4 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.
Table 1.1 Different approaches to flexibility and their meanings
Approach Flexibility meaning
1. Manufacturing n The capability of producing different parts without major retooling
n A measure of how fast the company converts its process from
making an old line of products to produce a new product
n The ability to change a production schedule, to modify a part, or to
handle multiple parts
2. Operational n The ability to efficiently produce highly customized and unique products
3. Customer n The ability to exploit various dimension of speed of delivery
4. Strategic n The ability of a company to offer a wide variety of products to its
customers
5. Capacity n The ability to rapidly increase or decrease production levels or to shift
capacity quickly from one product or service to another
So, what is flexibility in manufacturing?
There are three levels of manufacturing flexibility.
(a) Basic flexibilities
n Machine flexibility: The ease with which a machine can process various operations
n Material handling flexibility: A measure of the ease with which different part types can be
transported and properly positioned at the various machine tools in a system
n Operation flexibility: A measure of the ease with which alternative operation sequences
can be used for processing a part type
FMS Introduction and Description 5
(b) System flexibilities
n Volume flexibility: A measure of a system’s capability to be operated profitably at different
volumes of the existing part types
n Expansion flexibility: The ability to build a system and expand it incrementally
n Routing flexibility: A measure of the alternative paths that a part can effectively follow
through a system for a given process plan
n Process flexibility: A measure of the volume of the set of part types that a system can
produce without incurring any setup
n Product flexibility: The volume of the set of part types that can be manufactured in a system
with minor setup
© Aggregate flexibilities
n Program flexibility: The ability of a system to run for reasonably long periods without
external intervention
n Production flexibility: Tthe volume of the set of part types that a system can produce without
major investment in capital equipment
n Market flexibility: The ability of a system to efficiently adapt to changing market conditions
1.5 DIFFERENT TYPES OF FMS
The different types of FMS are
n Sequential FMS
n Random FMS
n Dedicated FMS
n Engineered FMS
n Modular FMS
Sequential FMS: It manufactures one-piece part batch type and then planning and preparation is
carried out for the next piece part batch type to be manufactured. It operates like a small batch
flexible transfer line.
Random FMS: It manufactures any random mix of piece part types at any one time.
Dedicated FMS: It continually manufactures, for extended periods, the same but limited mix of
piece part batch types.
Engineered FMS: It manufactures the same mix of part types throughout its lifetime.
Modular FMS: A modular FMS, with a sophisticated FMS host, enables and FMS user to expand
their FMS capabilities in a stepwise fashion into any of the previous four types of FMS.
1.6 TYPES OF FMS LAYOUTS
The different types of FMS layouts are:
6 Flexible Manufacturing System
1. Progressive or Line Type
2. Loop Type
3. Ladder Type
4. Open field type
5. Robot centered type
1. Progressive or Line type: The machines and handling system are arranged in a line as shown in
the Fig.1.4 (a). It is most appropriate for a system in which the part progress from one workstation
to the next in a well defined sequence with no back flow. The operation of this type of system is
very similar to transfer type. Work always flows in unidirectional path as shown in Fig.1.4 (a).
2. Loop Type: The basic loop configuration is as shown in Fig. 1.4 (b). The parts usually move in
one direction around the loop, with the capability to stop and be transferred to any station. The
loading and unloading station are typically located at one end of the loop Fig.1.4 (b)
3. Ladder Type: The configuration is as shown in Fig. 1.4 ©. The loading and unloading station
is typically located at the same end. The sequence to the operation/transfer of parts from one machine
tool to another is in the form of ladder steps as shown in Fig.1.4 ©