IE 590 INTEGRATED MANUFACTURING
GROUP TECHNOLOGY
J Cecil IE 590 NMSU
CAM-I Automated Process Planning System
• One of the most well-known systems is the CAM-I
Automated Process Planning (CAPP) system
• DO NOT CONFUSE THE CONCEPTUAL
TERM ‘CAPP’ (COMPUTER AIDED PROCESS
PLANNING) WITH THE system‘CAPP’,
WHICH IS FOR THE PROCESS PLANNING
SYSTEM BUILT BY CAM-I
• CAM-I stands for Computer Aided Manufacturing
- International, which is a non profit industrial
research organization
J Cecil IE 590 NMSU
CAM-I Automated Process Planning System
In CAPP, previously prepared process plans are
stored in a database
When a new component needs to be planned,
a process plan for a similar component is retrieved
AND
subsequently modified by a human process
planner to satisfy specific requirements
J Cecil IE 590 NMSU
VARIANT PROCESS PLANNING SYSTEMS (VPPS)
• Variant process planning
– uses similarity among parts or components to
retrieve existing process plans
• Standard Plan (SP):
– A process plan that can be used by a family of
parts
– SP is usually stored permanently in the DB
– Each SP has a FAMILY NUMBER as its KEY
– No Limitation on the level of detail in an SP
– AT A MINIMUM, AT LEAST A SEQUENCE OF
OPERATIONS
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VARIANT PROCESS PLANNING SYSTEMS (VPPS)
• When an SP is retrieved, a certain min
degree of modification is usually required to
use the plan to manufacture a part
• The retrieval method and the logic used in
Variant Systems depend on the grouping of
parts into families
• Common manufacturing methods can be
then identified for each family
– Such common manuf methods can be rep
by SPs
J Cecil IE 590 NMSU
VPPS ......contd
• Mechanism of standard plan retrieval is
based on part families
• A family can be rep by a family matrix,
which includes all possible members
• VPPS HAVE 2 OPERATIONAL STAGES:
– PREPARATORY STAGE
– PRODUCTION STAGE
J Cecil IE 590 NMSU
VPPS ......contd
• PREPARATORY STAGE:
• Preparatory work is reqd when a company
first starts implementing a VPPS
• During this stage:
– existing parts are coded
– classified
– then grouped into families
• FIRST STEP IS TO CHOOSE AN
APPROPRIATE CODING SYSTEM
J Cecil IE 590 NMSU
PART CODING SYSTEMS AND ISSUES
• CODING SYSTEM must cover the entire
spectrum of parts produced in your shop
• it must be UNAMBIGUOS and easy to
understand
• Special features on the parts MUST BE
CLEARLY IDENTIFIED BY THE
CODING SYSTEM
• An Existing Coding system can be adopted
and then modifications can be made for the
specific manufacturing shop or facility
J Cecil IE 590 NMSU
PART CODING SYSTEMS AND ISSUES
• CODING REQUIRES DETAILED STUDY OF
INVENTORY OF DRAWINGS / MODELS AND
PROCESS PLANS
• PERSONNEL INVOLVED IN CODING MUST BE
TRAINED
– they must have a precise understanding of the
coding system
– test: they must generate identical code for the
same part, when they work independently
– Note: inconsistent coding will result in redundant
and erroneous data in the DATABASE DBJ Cecil IE 590 NMSU
PART FAMILIES
• After coding is completed, PART
FAMILIES can be formed
• Our interest is in grouping parts which may
require similar manufacturing processes or
operations
• NOT NECESSARILY SIMILAR IN SHAPE
J Cecil IE 590 NMSU
PART FAMILIES
– Such a Set of similar parts can be called a
PRODUCTION FAMILY
– Since SIMILAR PROCESSES are needed for
ALL FAMILY MEMBERS, A MACHINE
CELL can be built or used to manufacture this
family of parts
– This makes production planning and control far
easier.
– Such a cell oriented layout is called a Group
Technology layout or CELL LAYOUT.
J Cecil IE 590 NMSU
GROUP TECHNOLOGY
Please refer to chapter 13 of CAM book
J Cecil IE 590 NMSU
GROUP TECHNOLOGY (GT)
• In 1958, Mitrofanov (Russian engineer)
formalized this concept in his book, The
Scientific Principles of Group Technology
• GT can be defined as:
• “ the realization that many problems are similar,
and that by grouping similar problems, a single
solution can be found to a set of problems thus
saving time and effort”
• This definition is broad; however, usually
engineers relate GT only to manufacturing or
production applications
J Cecil IE 590 NMSU
PART FAMILIES
• Design families: In part design, many parts may
have similar shape (FIGURE 12.1)
– similar parts can be grouped into design families
– new design can be created by modifying existing
part design from the same family
– using this concept, composite parts can be
developed
– These parts embody all the design features of a
design family
– See FIGURE 12.1
J Cecil IE 590 NMSU
GROUP TECHNOLOGY (GT)
• Production families :
– are families formed because they require similar
mfg operations to be produced
– SEE FIGURE 12.3
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Coding and Classification
• Three types: Hierarchical, chain and hybrid
codes
• Hybrid is widely used
– Eg: Opitz code
• Other examples are Vuoso-Praha and KK-3
(Japan) coding systems
J Cecil IE 590 NMSU
HIERARCHICAL OR MONOCODE
In a monocode, each code number is qualified
by the preceding characters
• SEE FIGURE 12.4
• The fourth digit indicates threaded or not
threaded for family 322X
• Advantage: large amount of info with few
code positions
• Disadvantage: potential complexity of
coding system
–all branches in hierarchy must be
defined
–hence, difficult to develop
J Cecil IE 590 NMSU
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•
•
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Chain or PolyCode
Every digit in the code position rep. a distinct bit of
info, regardless of previous digit
In Table 12.1, a chain coding scheme is given
A ‘1’ in the 3rd digit position always means an
axial hole (no matter what numbers are assigned to
digits 1 and 2)
Advantage: Compact and easy to construct / use
Disadvantage: They cannot be as detailed as
hierarchical structures with same number of coding
digits
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Hybrid Code
• mixture of chain and hierarchical code structures
eg. Opitz code
• Will discuss Opitz code in next section
• Advantages of both can be obtained
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FURTHER READINGS
• Read the Vuoso Praha system (short code),
KK-3 system (long code)
• OPITZ CODE is most widely used and will
be discussed
• Also review MICLASS and DCLASS
Systems
J Cecil IE 590 NMSU
THE OPITZ CODE
• BEST KNOWN AND MOST WIDELY USED
• has 2 sections
– geometric code
– supplementary code
• Geometric code
– rep. Parts of following variety
– Rotational, flat, long, cubic
– Dimension ratio used to classify geometry
• l/d ratio (for rotational)
• l/width or l/height ratios (for non rotational /
prismatic)
J Cecil IE 590 NMSU
GEOMETRIC CODE
• 5 Digits
• Digits:
– 1 - component class
– 2 - basic shape
– 3 - rotational surface machining
– 4 - plane surface machining
– 5 - auxiliary holes, gear teeth and forming
• see table 12.4 (pages 483 and 484)
J Cecil IE 590 NMSU
SUPPLEMENTAL CODE
• 4 Digits APPENDED TO GEOMETRIC CODE
• DIGITS:
– 1- major dimension (dia or edge length)
• range: 0.8 to 80 inches
• < 0.8 rep by 0 and > 80 rep by 9
– 2 - material type
– 3 - raw material shape
– 4- accuracy
• clearance tolerances or surface quality (eg: 32
microinches)
• see pages 485
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OPITZ CODE EXAMPLE
• SEE FIGURE 12.7
• CODE: 1 1 1 0 2
• Supplementary code: review part given
– code:?
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GT BENEFITS
• Coding/classification provide few benefits if it ends
there
• coding:a means to quantify part geometry, content
• One use: to code potential designs before formally
designing them
– designers sketches a concept, then codes it
– using code, similar designs are retrieved from DB
– if existing part can be used to satisfy design new
design needs, then process ends and time saved
– if existing part cant be used, perhaps a variant can
be used (simply modify existing design)
J Cecil IE 590 NMSU
GT BENEFITS
• In both cases, no or minimal changes in process plan
and production plans may be needed
• Many companies have found that they produce
identical parts with different names
– duplicate tooling, fixtures and engineering time
are required when this occurs
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OTHER PROBLEMS
• Common characteristic of US industry (Chang) is
under-utilization of expensive processing equipment
• Takes 2 forms:
– Much of the machine time is idle and
unproductive
– Many of the parts assigned to a specific machine
are far below the capacity of the machine
• Approach: By grouping closely matched parts into
a part family, machines can be more fully utilized
from both a scheduling as well as a capacity
standpoint
J Cecil IE 590 NMSU
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•
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Application of GT concepts
Major benefit includes part family formation for
efficient workflow
Efficient workflow can result from grouping
machines logically so that:
– material handling and setup can be MINIMIZED
Parts can frequently be grouped so that the same
tooling and fixtures can be used:
– this enables a major reduction in setup times
Machines can be grouped so that the amount of
handling time between machining operations can
be minimized
J Cecil IE 590 NMSU
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LAYOUT ISSUES
See figures 12.6 and 12.7 : Process type layout
Versus GT based layout
M/c’s are clustered by function Vs M/cs that
produce part family form a cell
BASIS FOR GT LAYOUT is part family formation
– family formation is based on part features viz.
manufacturing features.
No rigid rules for part families ; user sets own
definition
– General rule: all parts in a family must be related
J Cecil IE 590 NMSU
Part families
• For production flow analysis, all parts in a family
must have similar routings
• Family size will change depending on criteria
• If criteria is: only those parts having exactly the
same routing
• then few parts will qualify for this family
• If criteria is: group all parts requiring a common
machine into a family
• large part families will result
• Before grouping can start, collect info of design and
processing of all parts
J Cecil IE 590 NMSU
Part families
• Each part is then rep as a coded form, called an
Operation Plan code (OP code)
• OP code rep a sequence of operations on a machine
and/or a workstation
• Eg: DRL01 can rep the sequence:
–load the workpiece onto a drill press
–attach a drill
–drill holes
–change the drill to reamer
–ream hole & unload workpiece from drill
J Cecil IE 590 NMSU
Part families
• An Operation Plan (OP Plan) is a plan where
operations are rep using OP codes
• OP codes SIMPLIFIES REPRESENTATION
OF PROCESS PLANS
• see table 12.7
• Next Focus: Clustering Approach
J Cecil IE 590 NMSU