The University of Southampton School of Engineering Sciences 11. GROUP TECHNOLOGY 11.1 Shipbuilding Background The relevance and use of group technology in shipbuilding is perhaps best explained against a backdrop of various types of production organisations. These can be classified as below. (A) Craft Organisation (Job Shop): Organisation using well trained and experienced workers to perform many activities in one or a few locations. Most production decisions are left to the craftsmen, who may approach each job in a different way. The required engineering data may be minimum and it could be lacking in accuracy. Craft organisations are difficult to schedule and control. (B) Semi-Process Organisation: Organisation using well trained and experienced workers, but attempting better planning and control by routing similar work processes to specific work areas. This required more planning effort, but scheduling and some production control is attainable. The engineering has to be more detailed to enable planning to break down the work into task packages. (C) Process Organisation (Batch): This is the complete use of specific work areas to perform specialised activities. This enables workers to be trained only in the special activity they are selected to perform. Planning becomes more complex regarding scheduling and material control. Engineering is prepared for specialised process rather than total product. (D) Product or Group Organisation: This type of organisation focuses on a type of product, such as flat panels, and links all the processes together to complete the product. It then combines a number of products to make a new larger product, such as an erection module and ultimately the ship’s hull. Planning is simpler as it follows a logical sequence of events. Again, the Professor R A Shenoi Part II - Ship Production Technology 11-1
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The University of Southampton School of Engineering Sciences
11. GROUP TECHNOLOGY
11.1 Shipbuilding Background
The relevance and use of group technology in shipbuilding is perhaps best
explained against a backdrop of various types of production organisations. These
can be classified as below.
(A) Craft Organisation (Job Shop): Organisation using well trained and
experienced workers to perform many activities in one or a few locations.
Most production decisions are left to the craftsmen, who may approach each
job in a different way. The required engineering data may be minimum and
it could be lacking in accuracy. Craft organisations are difficult to schedule
and control.
(B) Semi-Process Organisation: Organisation using well trained and
experienced workers, but attempting better planning and control by routing
similar work processes to specific work areas. This required more planning
effort, but scheduling and some production control is attainable. The
engineering has to be more detailed to enable planning to break down the
work into task packages.
(C) Process Organisation (Batch): This is the complete use of specific work
areas to perform specialised activities. This enables workers to be trained
only in the special activity they are selected to perform. Planning becomes
more complex regarding scheduling and material control. Engineering is
prepared for specialised process rather than total product.
(D) Product or Group Organisation: This type of organisation focuses on a type
of product, such as flat panels, and links all the processes together to
complete the product. It then combines a number of products to make a new
larger product, such as an erection module and ultimately the ship’s hull.
Planning is simpler as it follows a logical sequence of events. Again, the
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extent of worker training is limited to those processes utilised in a given
work station. Engineering is prepared to show the product to be processed
at a given work station. Control can be precise due to the many available
data points.
(E) Mass Production Organisation: This type of organisation maximises the use
of mechanisation, continuous flow lines and the specialisation of activities
at sequential work stations. Material handling is decided at the time of
facility design. Engineering is more involved in machine instructions, jog
and tooling and quality control data.
The differences and relative effort for each type of organisation are summarised in
Figure 11.1. It shows the productivity gap existing between organisation currently
producing one-off products and mass production organisations. One way to close
the productivity is through improved planning and production control (see Chapter
12) of activities. Yet another is to properly organise the shop layout and streamline
production.
11.2 Clarification of Terminology
Group technology is an approach to batch manufacture which aims to increase
productivity by allowing such techniques as flow-line and more automated methods
of production to be used.
In a typical factory organised for small-batch or one-off production, the machines
are by tradition usually arranged according to their function – see Figure 11.2a. So,
for a factory in the metal cutting industry, there might be a twinning section, in
which all the metal cutting machines are assembled. There may also be milling,
grinding and drilling sections. Each functional type is a self-contained unit with its
own supervision, and a component during manufacture may need to visit all or
some of these functional units – frequently more than once. This results in heavy
losses of time due to the resetting of machines, in particular, as largely dissimilar
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parts may be loaded successively causing large queues of parts awaiting processing
on each machine.
A further inevitable condition with small batch or one-off manufacture is large
variety, and the result is one of a seemingly infinite variety of components
threading their way somehow between the functionally laid-out machine sections,
until they emerge from the final process as a finished component.
An alternative approach is to organise the machines in a group-based layout as
shown in Figure 11.2b. Group technology is a technique for identifying and
bringing together related or similar components in a production process in order to
take advantage of their similarities by making use of, for example, the inherent
economies of flow-production methods. The aim is to reduce substantially the
work-in-progress and improve delivery performance by reducing throughput times.
This is achieved by organised what may appear to be a large number of diverse
components into facilities which require similar manufacturing facilities for groups
of families.
The relationship between products and components is shown in Figure 11.3. While
final assembled products may bear little relation to each other, the sub-assemblies
for which they are constructed will exhibit some like features. It is by exploiting
the similarities which are known to exist among such a population of components,
that group technology attempts to reduce the time and cost of component
manufacture. Cells will be created to manufacture defined typed and size ranges of
components. Groups of machines, chosen for each family, are situated in a group
layout (Figure 11.2b) in such a way that components flow from one machine to the
next in sequence of operation. It is not necessary for every component to pass to
each machine, but the machines within the cell should ideally be capable of
carrying out all the operations required in the family.
Figure 11.4 illustrated and contrasts a group layout with product, process and fixed
position layouts.
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Figure 11.1: Transition from craft to mass production
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Figure 11.2: Functional and group layouts
Figure 11.3: Groupings of similar components for manufacture
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11.3 Applications in Shipyard Context
Most of the reported applications of group technology to shipbuilding have been in
the area of ship structure. It has been used to group structural parts by both their
geometry and processing characteristics for interim products such as subassemblies,
assemblies and modules. The varieties of parts in ships’ structure are large whereas
the varieties of assemblies and modules are relatively small. The differences in size
and work content of the interim products result in work not being suitable for
normal continuous flow processing. Group technology can partially overcome this
problem by grouping the interim products into similar geometry and/or processing
requirement groups, so that the effective individual group volume increases to the
extent that some of the benefits of continuous flow can be obtained.
The first and most important task in this context is to devise a classification and
coding system which identifies product variety and similarities. It is only after
similarities are established that processes can be designed and layouts established.
Two such classification systems are outline below.
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Figure 11.4: Types of Processes Figure 11.4: Types of Processes
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Figure 11.6: Examples of first digit shape code – B.S.R.A system
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The basic features of this system are shown in Figure 11.5. The
classification/coding system in nine digits long and is of the “fixed” digital
significance type. The first six digits describe the geometric shape of the
component in a way which provide useful data to the planning and production
engineers. The general allocation of digits is as follows:
Digit 1 – General Classification Subdivision into sections and plates, and major variations within these groups. Digit 2 – Shape before forming Defines the geometric profile of the cut component. Digit 3 – Forming Defines the forming to be carried out – bends, flanges, corrugations. Digit 4 - Material Material specification and quality Digit 5 – Size classification Length
The sixth through tenth digits are used for different classification depending on the
first two digits as follows.
Digit 6 – For plate: width For sections: depth Digit 7 – For plate: thickness For sections: flange width Digit 8 – For plate: shape For sections: web thickness Digit 9 – For plate: holes and slots For sections: flange thickness Digit 10 – For plate: edge preparation For sections: end cut.
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