gtawad

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Computer Aided Manufacturing

2Dr. Mohamed Ahmed Awad

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GROUP TECHNOLOGY

• Group technology is a manufacturing • Technique and philosophy to increase

production efficiency by exploiting the “underlying sameness” of component

• Shape, Dimensions, Process Route, Etc.


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• Group Technology is 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.


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• GT is the beginning stage of Computer-Aided Process Planning


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Why Group Technology

• Average lot size decreasing

• Part variety increasing

• Increased variety of materials

• With diverse properties

• Requirements for closer

• tolerances

Dr. Mohamed Ahmed Awad 6

FLEXIBILITY

PRODUCTION CAPACITY

TRANSFERLINE

SPECIAL SYSTEM

FLEXIBLEMANUFACTURING

SYSTEM

MANUFACTURINGCells

STD. AND GEN.MACHINERY

VO

LU

ME

HIGH

VARIETYLOW HIGH


Everyday Examples• 1. Fast food chains• 2. Doctors, dentists and also manufacturing


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Production Family


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Benefits Of Group Technology

Reduction In • Throughput time• Set-up time• Overdue orders• Production floor space• Raw material stocks• In-process inventory• Capital expenditures• Tooling costs• Engineering time and costs• New parts design• New shop drawings• Total number of drawings


GT affects most every operating and staff function. It is more than merely a technique, but a total

Manufacturing philosophy.

GT

DESIGNENGINEERI

NGDATA

PROCESSING

MAINTENANCE

TOOL ENGINEERING

ESTIMATING

INDUSTRIALRELATIONS

QUALITYCONTROL

R & D

COSTACCOUNTING

SALES

INVENTORY

PLANNING

PURCHASING

ASSEMBLY

MANAGEMENT

MFG.ENGINEERING

SHIPPING &RECEIVING


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Techniques To Form Part Families

• 1. Tacit judgment or visual inspection

• 2. Production Flow Analysis

• 3. Classification And Coding


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1. Tacit judgment or visual inspection

• May use photos or part prints

• Utilizes subjective judgment


Visual MethodVisual Method

Parts grouped into families using a visual method

Parts are grouped according to their similarities in the geometric shape

Dependent on personal preference ( 주관적 ) Applicable when the number of parts is

rather limited13


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2. Production Flow Analysis

• Uses information contained on the route sheet (therefore only mfg. Info)

• Parts grouped by required processing


Cluster analysis 15


Cluster Analysis MethodCluster Analysis Method

Grouping objects into homogeneous Grouping objects into homogeneous clusters(groups) based on the object clusters(groups) based on the object featuresfeatures

Grouping : parts into part families (PFs) Grouping : parts into part families (PFs)

machines into machine cells machines into machine cells (MCs)(MCs)

To model the GT problem, To model the GT problem, threethree clustering formulation are usedclustering formulation are used Matrix formulation Matrix formulation Mathematical programming formulation Mathematical programming formulation Graph formulationGraph formulation

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Result of groupingResult of grouping

Physical cell vs Logical Physical cell vs Logical (virtual) cell(virtual) cell

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3. Classification And Coding

• Codes geometry/design and mfg. Info about a component

• Codes are alphanumeric strings

• Easier to use for other analyses


Coding MethodCoding Method

Parts are first classified based on Parts are first classified based on featuresfeatures (characteristics) (characteristics)

Using a coding system : numerical or Using a coding system : numerical or alphanumerical codealphanumerical code

Three basic Three basic typestypes of coding systems of coding systems Monocode (tree structure)Monocode (tree structure) PolycodePolycode HybridHybrid

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Types Of Classification And Coding Systems

GT coding can benefit many facets of the Firm and fall into one of 3 categories:

• 1. Systems based on part design Attributes

• 2. Systems based on part mfg. Attributes

• 3. Systems based on design and mfg. Attributes


Examples:

Part Mfg. Attributes• Major processes• Minor operations• Fixtures needed

Part Design Attributes• Basic external shape• Basic internal shape• Material


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Major GT Code structures

• 1. Monocode (or hierarchical structure)

• 2. Polycode (Or Chain-type Structure)

• 3. Mixed Code


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1. Monocode (or hierarchical structure)

A code in which each digit amplifies the

information given in the previous digit

• Difficult to construct

• Provides a deep analysis

• Usually for permanent information


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2. Polycode (Or Chain-type Structure)

Each digit is independent of all others, presents information not dependent On previous ones

Easier to accommodate Change


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3. Mixed Code

Has some digits forming monocodes, but

strings them together in the general

Arrangement of a polycode


UN

F t

hre

ad

Tra

nsm

issi

on

Hierarchical Structure

Hydraulic Electrical

Mechanical

32XX

321X

322X

No

thre

adU

NC

thread

3222

323X

Power

Receiving

3232

3231 3233

3221 3223


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3. Mixed Code

• Has some digits forming monocodes, but strings them together in the general

• Arrangement of a polycode

Dr. Mohamed Ahmed Awad 31MonocodePolycode Polycode

Hybrid Structure


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Proliferation Of Parts

Selection of optical instrument parts in one company, Illustrating the similarity between certain components


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Conceptual design

Coding (rough model)

Retrieval existing designs

Existing designs

Design modification

New Design

Design archive

Retrieve designs of similarshape or function and usethem as the examples.

Design concept can be coded.

Code is a rough model of theconceptual design.


Technique:

1. Determine part and machine requirements

2. Numerically code each partGeometry (& size)MaterialOther specifications (tolerance, Surface finish)

3. Form a family of similar parts which use (Largely) the same set of machine tools

4. Lay out of each cell (a group of machine Tools) to make a family of parts

5. Design group tooling


Example:

Thirteen parts with similar manufacturing Process requirements but different Design attributes


Functional Layouts Are Inefficient

PROCESS-TYPE LAYOUT

Lathe Milling Drilling

Grinding

Assembly

Receiving andShipping

L

L L

L

L

L

L

L M

MM

M M

M

A A

A A

D

D D

D

G

G

G

G G

G


Group Technology Layout

Shipping

L L M D

L M D

G

L M GG

A A

Receiving


Department #2

Department #3

Department #1

D D M I

D ML L I

D

M

LM

I

Cellular Layout


1st Digitpart class

Positionswith adigit

2nd Digitmain shape

3rd Digitrotationalmachining

4th Digitplane surface

matching

5th Digitadditional

holes teeth &forming

Form Code

Opitz coding and classification system.

(Reprinted with permission from H. Opitz, A Classification System to Describe Workpieces, Pergamon Press.)

Special

Non

-rot

atio

nal

Special

Rot

atio

nal

9

8

7

6

5

4

3

2

1

0Internal

shapeelement

Rotationalmachining

Main bore & rotationalmachining

Other holesand teeth

Other holesteeth andforming

Other holesteeth andforming

Machiningof planesurfaces



External shape

element

Main shape

Main shape

Main shape

Main shape

Supplim-entarycode

Digit6 7 8 9

Dim

ensi

ons

Mat

eria

lO

rigi

nal s

hape

of

raw

mat

eria

lsA

ccu

racy


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Examining Opitz Code:


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This Form code is the Opitz Code Solution on this shaft- like part


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• GT schemes are developed for specific applications.

• GT coding is basically a case analysis of possible part shapes.

Digit Meaning Code

1Rotational part, L/D ratio > 0.5

1

2 Step to one end 1

3Internal bore w/o

shape element1

4No external plane

surface0

5 Gear teeth 6

Sample part for GT coding “11106”

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