Integration by Group Technology

8/11/2019 Integration by Group Technology

1/47

INTEGRATION BY GROUPTECHNOLOGY

CAD-CAM

UNIT III


2/47


3/47


Group technology is a way to organizeinformation to make this integration moreefficient.It can be compared to the animal kingdomclassification.

Kingdom

Phylum

Class

Order

Family

Genus

Species


4/47


Suppose the case of a plant where thousands of

part numbers are handled and where the batchsizes decrease each time, as the variety of theproducts increases.


5/47


However, if we look closely, certain products arevery similar.

This information is very useful for a designengineer that looks for similar products to the onethat is about to be designed.


6/47


In the same way, a manufacturing engineerwould like to know if there is already a product

similar to the one that is about to be produced inorder to take some references out of itsproduction process.


7/47


From this we obtain the group technology, as away to group families of products with similarcharacteristics.


8/47


The original concept of group technologies is thefollowing:

to understand that many problems are

similar, and that grouping similar problems, youcan find a single solution for a set of problemssaving that way time and effort.


9/47


An essential aspect of CAD and CAM integration

is the integration of information used byEngineering, Manufacturing and all otherdepartments in the company.


10/47


G.T. provides a medium to structure and saveinformation about parts like:

Design and manufacturing attributesCharacteristics of processesManufacturing capacities

All of these can be compatible to computarizingand analysis.


11/47


G.T. provides a common language for users.The integration of several types of related parts

information would be virtually impossible withoutG.T. As a consequence, G.T. is an important part ofCAD/CAM integration.


12/47


G.T. starts grouping parts into families basedon their attributes.

Normally these attributes are based on:1. The geometry of the part2. The characteristics of the production process


13/47


The geometric classification of the families isnormally based on:

Size Shapes

The classification of the production processes isbased on:

The type of process Sequence Number of operations


14/47


The type of operation is determined by: The process method

The method of holding the part The tool The conditions of processing


15/47


There are at least three methods that can beutilized to make parts families: Visual-manual search Production flow analysis Classification and codification


16/47


The visual manual searchis not greatly utilizedin the formal applications of group technology

due that it can lead to inconsistent results.

This is due to different reasons like theperceptions of each person regarding the

manufacturing capacity, machines and tools,and the recognition of the significant attributesof the parts.


17/47


The flow production analysis (FPA) is astructured technique to analyze the sequence of

operations (routines) through which parts passby during their fabrication.

Parts that pass through common operations aregrouped together in families of parts.


18/47


In the FPA, machines that are utilized to makethese common operations can be grouped

together in production cells.

As a consequence, this technique can be utilizedin a plant layout.


19/47


FPA Matrix

M = Number of machines

N = Number of parts

X = 1 if the part j has an operation on machine i;0 if this condition is not met.


20/47


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

A 1 1

B 1 1 1

C 1 1 1 1 1 1

D 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1

E 1 1

F 1 1 1 1G 1 1 1 1 1

H 1 1 1 1 1

I 1 1 1 1

J 1 1

K 1 1Machine

Number

Part Number

2 11 1 10 16 18 12 6 3 4 7 8 9 14 15 19 5 13 17

H 1 1 1 1

D 1 1 1 1 1

F 1 1 1 1

A 1 1

B 1 1 1

E 1 1

D 1 1 1 1 1 1 1 1 1 1

C 1 1 1 1 1 1

I 1 1 1 1 1

G 1 1 1 1

J 1 1

K 1 1

GRUPO 1

GRUPO 2

GRUPO 3

MachineNumbe

r

Part Number


21/47


If the machine-components chart is small, youcan manually group together parts with similar

operations by moving rows and columns.

However, a more correct method is to utilize acomputer procedure to make this job.


22/47


In order for this FPA technique to be successful,precise and efficient routines are required foreach part.

These routines do not exist in many companies.If they exist, frequently they are inaccuratebecause of the lack of maintenance or that they

can be inconsistent.


23/47


These inaccurate classifications normally occurrdue to the lack of a system of parts codification.

Furthermore, FPA is based on criteria, since itcould happen that some of the parts may notappear to belong to a certain family.

It must also be determined when certainmachines must be duplicated in more than onefamily.


24/47


The FPA does not consider the characteristics ofthe parts or their functions, therefore it mustnot be used for Design Engineering.

However, compared to codification technique, it

is much simpler and easy to carry on.


25/47


Parts Classification is the process ofcategorizing parts into groups, which are alsocalled families, according to a set of rules orprinciples.


26/47


Codificationis the process of assigning symbols

to the part.

The objectives are to group together similarparts and to separate parts that are different toeach other.


27/47


The symbols inside the Codification must havemeanings that reflect the attributes of the part,making it easier the analysis or informationprocessing.


28/47


Many classification and codification systems

have been developed, and many people havetried to improve them.

But no system has ever had a universalacceptance.


29/47


This is mainly due to two things:

1. The information that is represented in theclassification and codification varies from onecompany to another.

2. The two biggest usages of G.T. are the

recovery of the design and the cell production,hence each company has its own needs forthese functions.


30/47


A reason for a design engineer to classify and

codificate parts is to reduce the design effort byidentifying similar parts that already exist.

Some of the most significant attributes in which

it can be identified are the shape, material andthe size.


31/47


If the parts classification and codification is

successful, it must be able to identify someadditional attributes:

1. Tolerances2. Materials manufacturability

3. Process requirements4. Machine tools requirements


32/47


The classification and codification helps thecompanies to improve the communicationbetween design and manufacturing.

This way, CIM will also be facilitated.


33/47


Even though exist more than 100 classificationand codification systems, all of them can begrouped together in three different basic types:

1. Hierarchical or monocode2. By attributes or polycode3. Hybrid or mixed


34/47


On the Hierarchical Code the meaning of eachcharacter depends on the previous character.

This means that each character amplifies theinformation according to the previouscharacter.


35/47


The Hierarchical Code delivers a lot ofinformation in a relatively small number ofdigits.

To find the meaning of each digit in this type ofsystem can be complicated, even though theapplication of the defined system is relatively

simple.


36/47


Attributes code: is also called polycode, chaincode, discrete code or fixed digit code.

The meaning of each character in an attributescode, in contrast with a hierarchical code, isthat they are independent to each other.


37/47


Therefore, each attribute of a part can beassigned a specific position in an attribute code.


38/47


POSSIBLE DIGIT VALUE

DIGIT CHARACTERISTIC TYPE 1 2 3 4

1 External Shape

Cylindrical or

without

deviations

Cylindrical with

deviation

s

Box type ___

2 Internal Shape None Center hole Other hole ___

3 Number of Holes 0 1-2 3-5 ___

4 Type of Holes Axial Crossed Axial crossed ___

5 Gear Teeth Worm Internal spur External spur ___


39/47


On this example, this type of gear would have

the code 22213, where digit 3 of the fifthposition means that the part has an externalspur, regardless of the values of the digits onthe previous positions of the code.


40/47


If this attribute code had been used for several

parts and we would want to retrieveinformation about all the parts with externalspurs, we would just have to identify all theparts with a 3on the 5th position of the code.


41/47


Consequently, an attributes code is popular

among the manufacturing organizations duethat it makes easier the identification of partsthat have similar characteristics and thatrequire similar processes.


42/47


A disadvantage of an attributes code is that anyposition in the code must be reserved for eachdifferent attribute; therefore, the resulting codecan be too long.


43/47


Hybrid code: is the combination of the twotypes of codes previously reviewed.

(hierarchical and by attributes).

With this type of code, the advantages of eachsystem are taken into account.


44/47


Hybrid code: In this case, the code for a part is a mixture ofpolycodes and monocodes. Such coding methods usemonocodes where they can, and use polycodes for the other

digits -- in such a way as to obtain a code structure thatcaptures the essential information about a part shape. This isthe most commonly used method of coding and classification.


45/47


In this system, the first digit, for instance, canbe used to identify the type of the part, like agear.

The following 5 positions can be reserved for ashort attributes code that describes theattributes of the gear.

B 3 2 6 4 1

1st position toindicate the type

of part

The following 5 positions toindicate the attributes (color,

size, type of teeth, etc.)


46/47


The following digit, in the 7th position, can beused to designate another subgroup, like the

type of material, followed by another attributescode that describes its attributes.

B 3 2 6 4 1 D 3 9

7th position to indicateanother subgroup, like

the type of material.

The following positions toindicate other attributes.


47/47


With this system, a hybrid code can be created,and is able to be relatively more compact than

just only an attributes code, without loosing theability to easily identify the parts with specificcharacteristics.

Integration by Group Technology

Documents