WHAT IS GROUP TECHNOLOGY? Group technology (GT) is a philosophy
that implies the notion of recognizing and exploiting similarities
in three different ways:1. By performing like activities together2.
By standardizing similar tasks3. By efficiently storing and
retrieving information about recurring problems Large manufacturing
system can be decomposed into smaller subsystems of part families
based on similarities in 1. design attributes and 2. manufacturing
features DESIGN ATTRIBUTES: part configuration (round or prismatic)
dimensional envelope (length to diameter ratio) surface integrity
(surface roughness, dimensional tolerances) material type raw
material state (casting, forging, bar stock, etc.) PART
MANUFACTURING FEATURES: operations and operation sequences
(turning, milling, etc.) batch sizes machine tools cutting tools
work holding devices processing times An essential aspect of the
integration of CAD and CAM is the integration of information used
by engineering and manufacturing and all the other departments in a
firm. Group technology emphasis on part families based on
similarities in design attributes and manufacturing, therefore GT
contributes to the integration of CAD and CAM
The Basic Key Features for a Successful Group Technology
Applications: Group Layout Short Cycle Flow Control A Planned
Machine LoadingGROUP LAYOUT:In most of todays factories it is
possible to divide all the made components into families and all
the machines into groups, in such a way that all the parts in each
family can be completely processed in one group only. The tree main
types of layout are Line Layout Group Layout Functional LayoutLine
Layout:Line Layout is used at present in simple process industries,
in continuous assembly, and for mass production of components
required in very large quantities
Functional Layout:In Functional Layout, all machines of the same
type are laid out together in the same section under the same
foreman. Each foreman and his team of workers specialize in one
process and work independently.This type of layout is based on
process specialization
Group Layout: In Group Layout, each foreman and his team
specialize in the production of one list of parts and co-operate in
the completion of common task. This type of layouts based on
component specialization.
The Difference between group and functional layout:
Families :The word Family is used as a name for any list of
similar parts. The families used with group layout are lists of
parts which are similar because they are all made on the same group
of machines. This type of family is called a Production Family.
However, not all parts which are similar in shape will appear in
the same family. The other important features that is important
choosing the families; Manufacturing tolerances Required quantities
Materials Special features, which will require the use of different
machinesGroups :A group is a list of machines, selected for layout
together in one place, because it contains all necessary facilities
to complete the processing of a given family of parts. A family of
parts can only be defined by relating it to a particular group of
machines, and a group by relating it to a family. Groups vary
greatly in type and size, widely in the number of machines and
different machines types.As group size is reduced, more types of
machine will be needed in more than one group and there is an
increased risk that some new machines must be purchased. Another
factor in choosing the size of group is the number of people who
will be employed in themGroup technology begun by grouping parts
into families, based on their attributes.
There are three methods that can be used to form part families:
Manuel visual inspection Production flow analysis Classification
and coding Manual visual inspection involves arranging a set of
parts into groups known as part families by visually inspecting the
physical characteristics of the parts.
Manual visual inspection incorrect results human error different
judgment by different people inexpensive least sophisticated good
for small companies having smaller number of parts Production flow
analysis: Parts that go through common operations are grouped into
part families. The machines used to perform these common operations
may be grouped as a cell, consequently this technique can be used
in facility layout (factory layout)
Coding methods: are employed in classifying parts into part
families Coding refers to the process of assigning symbols to the
parts The symbols represent design attributes of parts or
manufacturing features of part families The variations in codes
resulting from the way the symbols are assigned can be grouped into
three distinct type of codes: Monocode or hierarchical code
Polycode or attribute Hybrid or mixed code MONOCODE (HIERARCHICAL
CODE) This coding system was originally developed for biological
classification in 18th century. The structure of monocode is like a
tree in which each symbol amplifies the information provided in the
previous digit. The following figure illustrates the structure of a
monocode: A monocode (hierarchical code) provides a large amount of
information in a relatively small number of digits useful for
storage and retrieval of design-related information such as part
geometry, material, size, etc. it is difficult to capture
information on manufacturing sequences in hierarchical manner, so
applicability of this code in manufacturing is rather limited
POLYCODE (ATTRIBUTE CODE): The code symbols are independent of each
other Each digit in specific location of the code describes a
unique property of the workpiece it is easy to learn and useful in
manufacturing situations where the manufacturing process have to be
described the length of a polycode may become excessive because of
its unlimited combinational features
Differences in information storage capacity between monocode and
polycode: Assume that a code consists of a five symbols and that in
each of the five code fields the digits 0 to 9 are used. Determine
how many mutually exclusive characteristics can potentially be
stored in the monocode and the polycode Number of characteristics
may be stored in a monocode: 101 + 102 + 103 + 104 + 105 =111110
Number of characteristics may be stored in a polycode: 10 + 10 + 10
+ 10 + 10 = 50 MIXED CODE (HYBRID CODE):It is the mixture of both
monocode and polycode systems. Mixed code retains the advantages of
both systems. Most coding systems use this code structure. MIXED
CODE (HYBRID CODE): The first digit for example, might be used to
denote the type of part, such as gear. The next five position might
be reserved for a short attribute code that would describe the
attribute of the gear. The next digit (7th digit) might be used to
designate another subgroup, such as material, followed by another
attribute code that would describe the attributes. A code created
by this manner would be relatively more compact than a pure
attribute code while retaining the ability to easily identify parts
with specific characteristics. The OPITZ classification system: it
is a mixed (hybrid) coding system developed by Opitz, Technical
University of Aachen, 1970 it is widely used in industry it
provides a basic framework for understanding the classification and
coding process it can be applied to machined parts, non-machined
parts (both formed and cast) and purchased parts it considers both
design and manufacturing information The Opitz coding system
consists of three groups of digits: FormSupplementarySecondary
codecodecode 123456789ABCDpart geometry and features relevant to
part design .information relevant to manufacturing.(polycode)
Production processes and production sequences .
PART FAMILY FORMATION: One of the primary uses of coding systems
is to develop part families. Example: Consider the family of
ferrous parts formed by first three digits of Opitz form code; 131.
This implies that the attributes associated with the family members
are length/diameter ratio in the range 0.5 to 3.0, all parts
stepped to one end and internal shape elements with threads. A
number of mathematical approaches have also been developed to form
part families using classification and coding system.
SELECTION OF CLASSIFICATION AND CODING SYSTEMS For the purpose
of selecting or developing your own code, it is important to
understand the attributes of classification and coding systems.
SELECTION OF CLASSIFICATION AND CODING SYSTEMS Some of the
important classification and coding system attributes include: 1.
Flexibility for various applications such as part family formation,
process planning, costing, and purchasing 2. Accuracy, to provide
correct information on parts 3. Expandability, to accommodate
information on more part attributes deemed important later on 4.
Ease of learning 5. Ease of retrieval 6. Reliability and
availability of software 7. Suitability for specific
applicationsSELECTION OF CLASSIFICATION AND CODING SYSTEMS Matching
these attributes with the objectives of an organization would be
helpful in selecting or developing a coding system to meet
organizational needs.BENEFITS OF GROUP TECHNOLOGY Group technology
is a management strategy to help eliminate waste caused by
duplication of effort. BENEFITS OF GROUP TECHNOLOGYIt affects all
areas of a company, including: engineering equipment specification
facilities planning process planning production control quality
control tool design purchasing service Some of the well-known
tangible and intangible benefits of implementing GT : 1.
Engineering design Reduction in new parts design Reduction in the
number of drawings through standardization Reduction of drafting
effort in new shop drawings Reduction of number of similar parts,
easy retrieval of similar functional parts, and identification of
substitute parts 2. Layout planning Reduction in production floor
space required Reduced material-handling effort 3. Specification of
equipment, tools, jigs, and fixtures Standardization of equipment
Implementation of cellular manufacturing systems Significant
reduction in up-front costs incurred in the release of new parts
for manufacture 4. Manufacturing: process planning Reduction in
setup time and production time Alternative routing leading to
improved part routing Reduction in number of machining operations
and numerical control (NC) programming time 5. Manufacturing:
production control Reduced work-in-process inventory Easy
identification of bottlenecks Improved material flow and reduced
warehousing costs Faster response to schedule changes Improved
usage of jigs, fixtures, pallets, tools, material handling, and
manufacturing equipment 6. Manufacturing: quality control Reduction
in number of defects leading to reduced inspection effort Reduced
scrap generation Better output quality Increased accountability of
operators and supervisors responsible for quality production,
making it easier to implement total quality control concepts. 7.
Purchasing Coding of purchased part leading to standardized rules
for purchasing Economies in purchasing possible because of accurate
knowledge of raw material requirements Reduced number of part and
raw materials Simplified vendor evaluation procedures leading to
just-in-time purchasing 8. Customer service Accurate and faster
cost estimates Efficient spare parts management, leading to better
customer service
CELLULAR MANUFACTURINGCellular manufacturing is an application
of group technology in manufacturing in which all or a portion of a
firms manufacturing system has been converted into cells. CELLULAR
MANUFACTURING:A manufacturing cell is a cluster of machines or
processes located in close proximity and dedicated to the
manufacture of a family of parts. The parts are similar in their
processing requirements, such as operations, tolerances, and
machine tool capacities The primary objectives in implementing a
cellular manufacturing system are to reduce: setup times (by using
part family tooling and sequencing) flow times (by reducing setup
and move times and wait time for moves and using smaller batch
sizes) reduce inventories market response times In addition, cells
represent sociological units that have more tendency to teamwork.
This means that motivation for process improvements often arises
naturally in manufacturing cells. Manufacturing cells are natural
candidates for just-in-time (JIT) implementation. Functional and
cellular layouts of an electronics plant:
I
Introduction to Cellular Manufacturing: Cellular Manufacturing
is an application of group technology in which dissimilar machines
or processes have be aggregated into cells, each of which is
dedicated to the production of a part or product family or a
limited group of families.Benefits of Cellular Manufacturing:
Composite Part Concept: A Composite Part for a given family,
which includes all of the design and manufacturing attributes of
the family. In general, an individual part in the family will have
some of the features that characterize the family but not all of
them. The composite part possesses all of the features
Machine Cell Design: Design of the machine cell is critical in
cellular manufacturing. The cell design determines to a great
degree the performance of the cell.Types of machine cells and
layouts: GT manufacturing cells can be classified according to the
number of machines and the degree to which the material flow is
mechanized between machines. Four common GT cell configurations:1.
Single machine cell (Type I M)2. Group machine cell with manual
material handling (Type II M generally, Type III M less common)3.
Group machine cell with semi-integrated handling (Type II M
generally, Type III M less common).4. Flexible manufacturing cell
or flexible manufacturing system (Type II A generally, Type III A
less common)Machine Cell Design: Single machine cell consists of
one machine plus supporting fixtures and tooling. This type of cell
can be applied to workparts whose attributes allow them to be made
on one basis type of process, such as turning or milling.
Machine Cell Design: Group machine cell with manual handling is
an arrangement of more than one machine used collectively to
produce one or more part families. There is no provision for
mechanized parts movement between the machines in the cell.
Instead, the human operators who run the cell perform the material
handling function. The cell is often organized into a U-shaped
layout.
U shaped layout,Machine Cell Design: Group machine cell with
semi-integrated handling uses a mechanized handling system, such as
a conveyor, to move parts between machines in the cell.
(a)in-line layout(b)loop layout(c)rectangular layoutMachine Cell
Design: Flexible manufacturing system combines a fully integrated
material handling system with automated processing stations. The
FMS is the most highly automated of the Group Technology machine
cells.
Machine Cell Design:2- Types of part movements Determining the
most appropriate cell layout depends on the routings of parts
produced in the cell. Four types of part movement can be
distinguished in a mixed model part production system.
1. Repeat Operation, in which a consecutive operation is carried
out on the same machine, so that the part does not actually move.2.
In-sequence move, in which the part move from the current machine
to an immediate neighbor in the forward direction.3. By-passing
move, in which the part moves forward from the current machine to
another machine that is two or more machines ahead.4. Backtracking
move, in which the part moves from the current machine in the
backward direction to another machine.