Ch 7 Manufacturing Systems

8/11/2019 Ch 7 Manufacturing Systems

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Chapter 7: Computer Integrated Manufacturing Systems

7.1 Introduction(1) In the previous chapters, we have studied various aspects of manufacturing, including- Design: engineering design, design for manufacturing, design for quality and etc.-

lanning: process planning (feature recognition, optimi!ation), and systems planning(scheduling, "ill of material, and #aterial $equirement lanning (#$))- #achine tools and control: %&%, '%, "ar code, smart card, and etc.- #aterial handling: conveyor, *, warehouse and etc.- +uality control: aguchi-s quality loss, failure mode and effect analysis (#/),

statistic quality control (0%) and etc.

() In this (last) chapter, we will study the manufacturing from a system point of view.

ig. 7.1: he correlation of the chapter to other chapters

(2) his chapter covers the following materials:- 3ust4In4ime (3I) manufacturing (%hapter 11 of the te5t"oo6),- le5i"le #anufacturing 0ystems (#0) (%hapter 1 of the te5t"oo6),- %omputer Integrated #anufacturing (%I#) (%hapter 12 of the te5t"oo6), and

-/nterprise integration (%hapter 1 of the te5t"oo6).

7.. 3ust4In4ime #anufacturing (3I)(1) 8hat is 3I9- In %hapter 2, we studied the #aterial $equirement lanning (#$) system, which

develops a "ill of material and a schedule, and releases the order to the shop.ccordingly, the manufacturing is initiated.

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customer customer

Designanalysis

rocessplanning

#aterialhandling

oolingdesign andanalysis

#achinetool andcontrol

+ualitycontrol

#anufacturing sage anddisposal

Design

#anufacturingsystem


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- s shown in igure 7., such a system is a push system, in which the materials (solidline) and information (dash line) flow in the same direction

ig. 7.: Illustration of a push system

- he push system is a open4loop system that may create following pro"lems:- It may lead to starvation or e5cessive stoc6s simultaneously at different stages

"ecause of im"alances of stoc6s "etween the stages.

-It may lead to conditions of having e5cessive equipment and surplus of wor6ers.

- In 3apan, the pro"lem is called the 2 #s pro"lems:- #uda (waste): waste for correction, waster of overproduction, waster for

processing, waste for inventory, waste of motion, waste for waiting, ;- #ura (unevenness): uneven wor6load, uneven schedule, ;- #uri (over"urden): over"urden machine, over"urden process, ;

- In order to solve these pro"lems, oyota developed a 3I manufacturing approach,which is a pull system as shown "elow.

ig.7.2:

Illustration of pull system

&ote that the information flow serves as a feed"ac6 loop that minimi!es the 2 #spro"lem.

- his approach is called the 3I manufacturing approach.

()


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- hrough the : smoothing of production- $ule ?: fine tune of production using 6an"an

4 ollowing figure illustrates how 6an"ands are wor6ed in a 3I manufacturing system.

ig. 7.>: Illustration of the paths of


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(2) AA parts- he num"er of 6an"ans:

y@ (>AA)(A.>)(1.) G (>A) @ 7- he average inventory is:

(7)(>A) @ 2>A units

his implies that we can cut down the inventory "y cut down the safety margin

- 0uppose @ A, which implies that a withdrawal 6an"an must always "e delivered

on time, whenever parts are neededH then:y@ (>AA)(A.>)(1) G (>A) @ >

at this time, the average inventory is:(>)(>A) @ >A units

his implies that we can cut down the inventory "y cut down the manufacturinglead time.

- 0uppose the production lead time is changed to 1 day, then the num"er of 6an"ansneeded is:- he num"er of 6an"ans:

y@ (>AA)(1)(1.) G (>A) @ 1at this time, the average inventory is:

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(1)(>A) @ 7AA units- /5ample (/5ample 11. in the te5t"oo6)

- =% company produces productZ, which is assem"led from two parts,Xand Y,also manufactured in the company

- he factory layout is shown in igure 7.?

ig.7.?:

factory layout of the =% company

where,


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yX@ (AAA)(1.A)(1) G 1AA @ AyY @ (AA)(A.>)(1.>) G >A @ 1A

- determining the production 6an"ans (the manufacturing process pulls from the

supplier)yX@ (AAA)(A.>)(1.) G 1AA @ 1yY @ (AA)(1)(1) G >A @ 1?

- now, let us assume that the assem"ly process is shipped to mainland. s a result, thelead time increases to days. he withdrawal 6an"ans will "e:

yX@ (AAA)()(1) G 1AA @ AyY @ (AA)()(1.>) G >A @ A

"ut the production 6an"ans remain the same. his implies that in order to 6eep thesame supply, we must increase the process capa"ility a, which in turn, will increase

the total production cause.

() pro"a"ilistic cost model for determining optimal num"er of 6an"ans- In practice, it is inevita"le that the manufacturing systems are affected "y various

JrandomK distur"ances, such as machine "rea6down, supply shortage, la"or a"sent,and etc. Lence, it is more realistic to develop a pro"a"ilistic 6an"an model for 3Isystems.

- Denote:- n@ num"er of 6an"ans- p(x) @ pro"a"ility mass function for the num"er of 6an"ans required- ch@ holding cost per container per unit time at a wor6 center- cs@ cost of shortage per container per unit time at a wor6 center

- here are two possi"ilities:- he actual requirement for the 6an"ans, 5, is less than n, and the e5pected cost is:

/5pected holding cost @ =

n

x

h xpxncA

)()(

- he actual requirement for the 6an"ans, 5 is more than n, and the e5pected cost is:

/5pected shortage cost @

+=

1

)()(nx

s xpnxc

- Lence, the total e5pected cost, TC(n), is:

==

+=nx

s

n

x

h xpnxcxpxncnTC )()()()()(A

- It can "e shown (in the te5t"oo6) that the optimal value ncan "e o"tained fromthe following equation:

)()1( nPCC

CnP

sh

s

ro"a"ility A A. A.2 A.2> A.1 A.A>

- the holding cost and shortage cost per container per unit time are M>A andMAA respectively

- 0olution:- he cost ratio: (cs) G (csB ch) @ (AA) G (AA B >A) @ A.- he pro"a"ility function:

P(A) @ A,P(1) @ A.,P() @ A.>,P(2) @ A.>,P() @ A.N>,P(>) @ 1

4 hence, the optimal num"er of 6an"an is n@ 2.

(>) 0ignal illustrates the process of signal 6an"ans.- In general, signal 6an"ans can "e further divided into two types:

- raw material ordering 6an"an: used to withdraw material from the preceding stage(represented "y a rectangular in igure 7.7).

- production ordering 6an"an: used to trigger the production of a lot at the wor6center (represented "y a triangular in igure 7.7).

- 0ignal 6an"ans are different from standard 6an"ans. comparison "etween standard6an"an and signal 6an"an is as follows:- In the standard 6an"an process, a production 6an"an is sent "ac6 to trigger

production after every withdrawal of a container- In the signal 6an"an process, the production 6an"an is not sent "ac6. Instead, a

production ordering signal 6an"an is used to minimi!e the setup time.- here are two important aspects of a signal 6an"an system:

- he determination of lot si!e- he position of "oth production4ordering as well as material4ordering signal

6an"anshe calculations in determining these parameters are the same as the withdraw6an"and and production 6an"an.

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ig.7.7:

Illustration of flow of signal 6an"an

-n e5ample- stamping plant runs two shifts: 5 @ 1? hrs. G day- he press utili!ation is AO: 1? 5 A. @ 1. hrs. G day- he rest of the time (AO) is used for setup (die changes): 1? 5 A. @ 2. hrs. G day- verage setup (die change) time is 2 min.: 2 G ?A hrs.- he ma5imum num"er of possi"le setup is - he demand for the parts,D: 1AA G day

- he safety factor: @ A.

- he minimal lot si!e per setup is:#inimum lot si!e per setup @ (Demand)(safety) G (time of setup)

or

#inimum lot si!e per setup @ (1AA)(1.) G () @ A.- 0uppose the si!e of the container is 1AA parts, then the num"er of containers

needed is:

A G 1AA N

- he position of the production4order signal 6an"an is determined "y the 6an"ancycle time. he 6an"an cycle time, Tc, consists of several elements such aswaiting time, transfer time, and lot processing time. he formula to calculate theposition of the production4order signal 6an"an is as follows:

roduction signal 6an"an positiona

TD c)1( +=

- 0uppose the 6an"an cycle time is 2 hrs.: 2 G 1? days

-he production signal 6an"an is:

roduction signal 6an"an position @ (1AA)(1.)(2G1?) G (1AA) @ 2.1>

containers.- 0imilarly, we can calculate the material4ordering signal 6an"an.

(?) Pther related issues

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$awmaterialinventorystorage

8or6center 'ot si!e

=

0tandard 6an"anprocess

0ignal 6an"an process


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- he concept of 6an"an has "een e5tended greatly to carry out various Jfeed"ac6Kcontrol functions in the manufacturing systems. hey all use 6an"ans, such as- /5press 6an"an- /mergency 6an"an- ;

-

It is interesting to 6now that in additional to push and pull, there are other types ofmanufacturing models such as:- eriodic pull- %onstant wor64in4process- 'ong pull- ;

- inally, there has "een effort to com"ine 3I in purchasing.

7. roup echnology(1) 8hat is roup echnology ()- is a philosophy that recogni!ing and e5ploiting similarities in three different ways

-

=y performing li6e activities together- =y standardi!ing similar tas6s- =y efficiently storing and retrieving information a"out recurring pro"lems

- has a num"er of advantages, such as- family of products can "e manufactured with minimum changes- complicated product can "e decomposed into a num"er of standard parts (or

systems) and manufactured with minimum additional facilities- would result in significant cost saving. It is a "asis of cellular manufacturing,

which will "e discussed in the su"sequent section.

() art features: design features and manufacturing features- In %hapter 2 (process planning), we have discussed the fact that parts have design

features (e.g., a hole), and manufacturing features (e.g., drilling). is "ased onrecogni!ing and using these features.

- num"er of approaches have "een developed to decompose a largemanufacturing activity into smaller, managea"le system "ased on similarities ofdesign features and manufacturing features.

- approaches can "e divided into two categories- *isual inspection method- %oding method

- *isual inspection method is relatively simple. n e5perienced engineer can e5amine apart and determine its "asic design features (e.g., a hole) and manufacturing features(e.g., drilling). fter all, this was the only approach used in the past, and is stilleffectively used.

- In this section, however, we will focus on the coding method.

(2) %oding methods- %oding refers to the process of assigning sym"ols to the parts. he sym"ols represent

the features ("oth the design features and manufacturing features) of the parts.

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- %oding is for classification Q the process of categori!ation of a set of parts into partfamilies.

- *arious coding systems have "een developed and these systems can "e grouped intothree types:- #onocode or hierarchical code: the structure of these codes is li6e a tree in which

each sym"ol amplifies the information provided in the previous digit.- olycode: also 6nown as chain code in which each digit is independent and

descri"es a specific information- #i5ed4mode code: a com"ination of monocode and polycode.

- 8e will present a few commonly used codes "elow.

() Ppti! classification system- he Ppti! classification system is developed at the echnical niversity of achen

for erman #achine ool ssociation- he Ppti! system is one of the oldest systems and you can use it a "ase to develop

your own.-

It is a mi5ed code system (and hence, rather representative)- he system consists of the following sequence of digits:

12> ?7N =%Dorm code 0upplementary code 0econdary code

- he code structure and the definition are shown in igure 1.2 (in the te5t"oo6).- n e5ample

orm code 1 2 1 A ?

Interpretation:- irst digit @ 1: it is a rotation part with A.> RLGDR 2 (N.? G > 1.N)

- 0econd digit @ 2: the e5ternal shape has a functional groove- hird digit @ 1: the internal shape has a through hole- ourth digit @ A: the plain surface does not e5ist- ifth digit @ ?: there are spur gear teeth on the part.- he part is shown in igure 7.

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ig. 7.: spur gear with Ppti! code 121A?- &ote that the code does not contain detailed engineering design information. Instead,

it shows the design features. =ased on the design features, the manufacturing plan can"e determined.

- he "enefit of :-

Lelp engineering design- Lelp layout planning- Lelp design G selection of equipment, tools, Cigs and fi5tures- Lelp manufacturing process planning- Lelp production control- Lelp quality control- Lelp purchasing- Lelp customer services

(>) and %ellular #anufacturing- %ellular manufacturing is an application of in manufacturing, in which

manufacturing facilities are organi!ed as cells. he parts are similar in theirprocessing requirement, such as operations, tolerances, and machine tool capa"ilitiesare manufactured together.

- he o"Cectives of cellular manufacturing are- $educe setup time- $educe flow time- $educe inventories and- $educe mar6et response time

- #anufacturing cells are natural candidates for 3I implementation.- %ell design is rather complicated in which the following issues must "e addressed:

- 0election of part families and grouping of parts in families- 0election of machines and processes and grouping them together

- 0election of tools, fi5tures and pallets- 0election of material4handling equipment- %hoice of equipment layout- Detailed design of Co"s- Prgani!ation of supporting personnel- ormulation of maintenance and inspection policies- Design of operation procedures- #odification of cost control

(?) %ell formation approach- here are several cell formation approaches. he most commonly used one is the

#achine4%omponent roup nalysis (#%) approach.- he procedure of #%

0tage 1: machine classification0tage : chec6ing parts list and production route information0tage 2: factory flow analysis0tage : machine4component group analysis.

8e will focus on 0tages 2 and using an e5ample.

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- /5ample: he machines and components information (the output of 0tages 1 and ) isas follows.

a"le : n e5ample of machine4part production information ta"le

%omponents

#achines 1 2 > ? 7 N 1A#1 1 1 1 1 1 1 1 1 1# 1 1 1 1 1#2 1 1 1 1# 1 1 1 1 1 1#> 1 1 1 1 1 1 1 1

where, an J1K implies the correlation "etween the machines and components.

- 8e use the $an6 Prder %lustering ($P%) algorithm for factory flow analysis anduse 0ingle4'in6age %luster nalysis (0'%) algorithm for machine4componentgroup analysis.

-0tep 1 ($P%): assign "inary weight and calculate a decimal weight for each rowand column using the formula "elow:

Decimal weight for row =

=m

p

pm

ipbi1

Decimal weight for column =

=

n

p

pn

pjbj1

where, bip(and bpj) are "inary weights. If thejth machine is used to processpthcomponent, bip@ 1H else bip@ A. or the data shown a"ove, the resulting decimalequivalents are as follows.

a"le 2: he $P% column weighting of the e5ample a"ove%omponents1 2 > ? 7 N 1A

Decimal =inary weight#achines equivalent N 7 ? > 2 1 A

#1 1AA7 1 1 1 1 1 1 1 1 1# >1 1 1 1 1 1#2 >? 1 1 1 1# >> 1 1 1 1 1 1#> 1AA 1 1 1 1 1 1 1 1

+uestion: suppose the order of the components is changed (e.g., instead of 1, , 2,;, 1A, we have 1A, N, , ;, 1), will the result "e the same9 Eou are encouraged tothin6 a"out it.

- 0tep ($%P): re4arrange rows "y sorting the decimal weights in decreasing orderand then calculate the column decimal equivalent. or the data a"ove, the result isthe following matri5:

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a"le : he $P% row weighting of the e5ample a"ove

%omponents1 2 > ? 7 N 1A

=inary =inary weight#achines weight N 7 ? > 2 1 A

#>

1 1 1 1 1 1 1 1#1 2 1 1 1 1 1 1 1 1 1#2 1 1 1 1# 1 1 1 1 1 1 1# A 1 1 1 1 1

%olumn decimalequivalent

7 7 7 A ? 11 11

- 0tep 2 ($%P): re4arrange the columns "y sorting the column decimal weights indecreasing order. or the data a"ove, the resulting matri5 is as follows:

a"le >: he resulting machine grouping in the a"ove e5ample%omponents

1 > 7 2 ? N 1A

=inary =inary weight#achines 8eight N 7 ? > 2 1 A

#> 1 1 1 1 1 1 1 1#1 2 1 1 1 1 1 1 1 1 1#2 1 1 1 1# 1 1 1 1 1 1 1# A 1 1 1 1 1

-0tep ($%P): repeat steps and 2 until there are no changes in row and columnpositions. his completes the factory flow analysis. or the data a"ove, there is nochange in further iteration.

- 0tep > (0'%): compute similarity coefficients for all possi"le pairs of machines.0everal similarity measures have "een used, and one of them is the single4lin6agecluster analysis (0'%). ccording to 0'%, the similarity coefficient "etweentwo machines is defined as the ratio of the num"er of parts visiting "oth machinesand the num"er of parts visiting one of the two machines as follows:

( )

=

=

+

=N

k

ijkjkik

N

k

ijk

ij

XZY

X

S

1

1

where,Xijk@ operation on part 6 performed "oth on machines iandjHYik@ operation on part 6 performed on machine iHZjk@ operation on part 6 performed on machinej.

or the data a"ove, the similarity coefficient "etween machines 1 and iscalculated "elow:

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&um"er of operations performed "oth on machines 1 and : >&um"er of operations performed on machine 1: N&um"er of operations performed on machine : >S1@ (>) G (N B > Q >) @ A.>>?

he calculation results are summari!ed in the following ta"le:

a"le ?: he similarity measure of different cell formation

#1 #1 #1 #1 # # # #2 #2 ##achines # #2 # #> #2 # #> # #> #>

0imilarity A.>> A.2A A.?7 A.7A A.AA A.2 A.2A A.AA A.>A A.A

A1 &ote that there are other similarity measures, for e5ample:

( )

=

=

+

=N

k

ijkjkikk

N

k

ijkk

ij

XZYn

Xn

SV

1

1

he result should "e similar ("ut no the same).

- 0tep ? (0'%): select the machine pair that has the largest similarity and usethem to form the first cell. or the data a"ove, it is # Q #.

- 0tep 7 (0'%): select the machine pair that the second largest similarity and usethem to form the second cell. &ote that if one of the machines has "een used for acell, form the cell "y using the machine and the cell. or the data a"ove, it is #1 Q#>.

- 0tep (0'%): repeat 0tep 7. or the data a"ove, in the first iteration the cellformation is # Q # and #> Q #1. In the second iteration, the cell formation is

made of #> Q (# Q #) and #> Q #1. he result is a dendrogram as shown inigure 7.1A. he final cell formation is shown in the ta"le as well.

ig.7.1A:he

dendrogram for the data a"ove.

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1.AA

A.2A.7AA.?7

A.>A

A.2A

A.AA

# # #> #1 #2


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he actual cell formation depends on the threshold value. or e5ample, if thethreshold is set at A., only # and # will form a cell. Pn the other hand, if thethreshold is set at A.>, all the machines will form a cell. he following ta"lesummari!es all the possi"le cell configurations.

a"le 7: summary of different cell configurations0imilaritycoefficient

&um"er of cellsformed

%ell configuration

1.AA > (#1), (#), (#2), (#), (#>)A.2 (#, #), (#>), (#1), (#2)A.7A 2 (#, #), (#1, #>), (#2)A.?7 ((#1, #, #, #>), #2A.> 1 (#1, #, #2, #, #>)

(7) /valuation of cell design.- In the previous section, the remaining pro"lem is to determine which cell design is

the "est.- he goal of cell design is to minimi!e the part motion cost during the manufacturing.

&ote that there are two types of moves:- Inter4cellular moves: parts move within a cell- Intra4cellular moves: parts move among the cellshey "ear different cost of motions.

- he following factors influence the part motion cost:- he layout of machines in a group- he layout of machine groups- he sequences of parts through machines and machine groups

- In general, the e5pected distance a part moves "etween two machines:

D@ dk

where, k@ num"er of moves "etween two machines, d@ e5pected distance moved"etween two machines, In particular, for a straight line layout, the e5pected distancemoved is:

2

1+=N

d

where, & is num"er of machines in the group. or rectangle layout, the e5pecteddistance moved is:

2

Ld

+=

where,is num"er of rows andLis num"er of machines in each row. or squarelayout, the e5pected distance moved is:

2 N

d=

- he total distance moved injth cell for the ith configuration:

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=m

j

ijiji kdTD

- he total cost of inter4 and intra4cellular movements (%) for the ith configuration:

+=m

j

ijijii kdCNCTC 1

where, C1@ cost of an inter4cell movement, % @ cost per unit distance of an intra4cellmovement, andNi@ num"er of inter4cell movements for ith configuration.

- %ontinuing the a"ove e5ample, let us consider the cell formation S(#, #), (#1,#>), (#2)T, assuming:- ll the machines are lined in a straight line- he num"er of moves "etween (#, #) is > (as seen from the ta"le)- he num"er of moves "etween (#1, #>) is 7 (also seen from the ta"le)- C1@ M.AA and C@ M1.AALence, the total distance of moves, D, is as follows:

D2

@ (>)( B 1)G2 B (7)( B 1)G2 B A @ 1

lso, it can "e seen that there are 1A intra4cell moves. Lence, the total cost is:TC2@ (M)(1A) B (M1)(1) @ M2

- he following ta"le summari!es the total cost of moves under different cellformations. rom the ta"le, it is seen that "est formation is 2. In other words, we shalluse the 24cell design, which will minimi!e the material handling cost.

a"le 7: he operating cots of different cell configuration

0imilaritycoefficient

&um"er ofcells formed

%ell configuration otal cost

1.AA > (#1), (#), (#2), (#), (#>) ()()B(1)(A) @ A.2 (#, #), (#>), (#1), (#2) ()(1)B(1)(>) @ 1A.7A 2 (#, #), (#1, #>), (#2) ()(1A)B(1)(1) @ 2A.?7 ((#1, #, #, #>), #2 ()()B(1)(2A) @ 2A.> 1 (#1, #, #2, #, #>) ()(A)B(1)() @

() 0olving the "ottlenec6 pro"lem- In cellular manufacturing, some parts must "e processed using more than one cell.

or instance, in the e5ample a"out, art , 2 and must "e processed "y two cells.his may cause over"urden for the machine and the transportation. his pro"lem iscalled the "ottlenec6 pro"lem.

- =ottlenec6 pro"lem can "e solved "y

- enerating alternative process plans- Duplication of machines- 0u"contracting operations.

7.>. le5i"le #anufacturing 0ystems(1) Introduction

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- le5i"le #anufacturing 0ystems (#0) is a strategic approach to answer thecompetitive glo"al manufacturing challenge

- #0 is made possi"le "y advanced technologies such as %D, %#, %, %I#, and etc.

- In this section, we will "riefly descri"e the "asics of #0 including-

le5i"ility- *olume4variety- 'ayout- art G tool management

() le5i"ility- le5i"ility can "e defined as a collection of properties of a manufacturing system that

support changes in production activities or capa"ilities- num"er of types of fle5i"ility have "een discussed including

- #achine fle5i"ility: use multi4purpose %&% machines- $outing fle5i"ility: use %-

rocess fle5i"ility: use multi4purpose %&% machines- roduct fle5i"ility- roduction fle5i"ility- /5pansion fle5i"ility

(2) *olume4*ariety- here are five types of manufacturing systems:

- ransfer line- 0tand4alone %&% machine- #anufacturing cell- 0pecial manufacturing system- le5i"le manufacturing system.

- Different systems have different characteristics and hence, suit for different productsand production types.

-


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ig.7.7he

characteristics of different types of manufacturing methods

- he 6ey characteristics of various manufacturing systems

() 8hat is #0- n #0 is an automated, mid4volume, mid4variety, central computer4controlled

manufacturing system.- he essential physical components of the #0 are:

- Independent %&% machines capa"le of performing multiple functions and havingautomated tool changer

- utomated material4handling system to move parts "etween machines andfi5tures

- ll components are computer4controlled- /quipment such as coordinate measurement machines and part4washing devices

-n #0 consists of two su"systems:- hysical su"system- %ontrol su"system

- 0ome e5amples are shown in the te5t"oo6

(>) Pperation pro"lems in #0- he operation pro"lems in #0 include

- art selection and tool management- i5ture and pallet selection- #achine grouping and loading (part and tool assignment)

- art selection and tool management methods

-here are several methods availa"le.

- he mathematical programming approach (Lwang-s model). 'et:i@ 1, , ;,N@ part typesc@ 1, , ;, C@ tool types!@ tool maga!ine capacity

=otherwiseA

toolrequrespart typeif1 cibic

dc@ num"er of slots required to hold tools in the tool maga!ine of each machine

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productivity ransferline

#0

%&% machines

fle5i"ility


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=otherwiseA

"atchin theselectedispart typeif1 i"i

=otherwiseA

machineaonloadedistoolif1 cyc

&ote that"iandycare decision varia"les. he goal is:

i

i"#a5imi!e

su"Cect to: 1c

ccyd

bic"iyc, for all i, c

"i@ A or 1, for all i, cyc@ A or 1, for all i, c

- fter the parts and tools are selected, one must determine the tool allocation pro"lem.here are several different policies for tool allocation- =ul6 e5change policy: change all the tools according to a preset schedule

-ool migration policy: change the tools once the parts are processed

- $esident tooling policy: allocate the tools according to the similarity and changethe tools only when they worn out. he tool allocation algorithm is the same asthe machine allocation algorithm discussed in the previous section.

- ool sharing policy: com"ine "ul6 e5change and resident tooling policies.- i5ture and pallet selection

- i5ture is the interface "etween the machine and the material4handling system.- he use of palleti!ed parts is very important in the integration of machines,

material4handling equipment and storage facilities.- he fi5ture and pallet selection pro"lem can "e considered as a su"set of the part

selection pro"lem. he appro5imate num"er of pallets required is:

NPPTCTP#

=palletsof&um"er

where,P#@ parts required per shiftCT@ average pallet cycle timePT@ planned production time per shiftNP@ num"er of parts per pallet

- #achine grouping and loading- he machine grouping and loading pro"lem refers to grouping of machines and

allocation of operations and tools required for the selected part types.- num"er of criteria have to "e considered:

-=alance the assigned machine processing times

- #inimi!e the num"er of movements from machine to machine- =alance the wor6load per machine in the system- ill the tool maga!ines as densely as possi"le- #a5imi!e the num"er of weighted operations.

7.? %omputer Integrated #anufacturing and /nterprise Integration(1) n introduction to %omputer Integrated #anufacturing (%I#)

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- ccording to 0#/, %I# is the integration of the total manufacturing enterprisethrough the use of integrated systems and data communications coupled with newmanagerial philosophies that improve organi!ational and personal efficiency.

- %I# is made possi"le "y the computer technology today and has many advantagesover the traditional manufacturing systems.

-

step forward is enterprise integration.

() he idea in enterprise4wide integration is to integrate people, technology, "usinessprocesses, customers and suppliers located at dispersed geographic locations.

- here are three essential tools for enterprise integration:- &etwor6 communication- Data"ase management systems- roup4ware.

- In this section, we will "riefly introduce these tools, following "y a discussion on theframewor6 of %I#.

(2) &etwor6 communication- erminology used in networ6 communication

- Lert! (L!): num"er of cycles per second- =aud: num"er of signals per second- Data rate: num"er of "its sent per second ("ps)- %hannel: a logic communication path- =andwidth: the "and of frequency used "y a communication path- %hannel capacity: num"er of "its that can "e transmitted per second- Interopera"ility: two systems wor6 with each other through interface- 'ocal area networ6: '& is used to interconnect local computers at 1AA #"ps- 8ide area networ6: 8& is used to connect remote computers at 1.> #"ps- #etropolitan area networ6: #& is large '&s that connects '&s

- he communication networ6 is the "ac6"one of enterprise integration- In general, there are three levels of communication in a company, and each require a

different type of networ6:- Device level at the shop floor Q su"4networ6 connects individual devices such as

machine tools and ro"ots- lant level Q local area networ6 ('&) connects manufacturing cells and

departments- /nterprise level Q wide area networ6 (8&) or #etropolitan area networ6

(#&) lin6s various plants G sites and interconnect corporations through datae5change protocols.

- &etwor6 topology: the general physical layout of the networ6 is called networ6topology. s shown in igure 7.N, there are four types of networ6 topology:- 0tar- $ing- =us- ree

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ig. 7.N: Illustration of networ6 topology

- he networ6 access control: there are several commonly used method for networ6access control- %arrier 0ense #ultiple ccess with %ollision Detection (%0#G%D) or /thernet

(I/// A.2 standard). hysically, two ethernet coa5ial ca"les are connectedtogether using a repeater (an amplifier). hrough the ca"les, the ethernet cards cansend and receive pac6ets. igure 7.1A shows the format of %0#G%D. It is a

series communication lin6. 8hile one computer sends a message the other onewaits. 8hile two computers sends message together, it may crash. %0#G%D iswidely used in manufacturing "ecause of its simplicity.

ig.7.1A:

%0#G%D frame format

- o6en ring (I/// A.> standard) and o6en "us (I/// A. standard) aredesigned to resolve the communication crash pro"lem. hey use multiple coa5ialca"les to connect the computers into a ring. 0o when a communication path is"usy the other one can ta6e over.

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pream"le Destinationaddress

0ourceaddress

data pad %hec6 4sum

0tart of frame

delimiter

'ength of data

field

=ytes7 1 or ? or ? A41>AA A4?


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- he networ6 protocol- he interpretation of the transmitted data among a networ6 is done "ased on

networ6 protocol.- protocol is a set of rules of information e5change "etween two devices- ccording to I0PGP0I (open system interconnection), protocols can "e divided

into seven layers:- he physical layer: specifies the hardware- he data lin6 layer: handles the data transformation such as synchroni!ation,

error control and flow control- he networ6 layer: decides the paths of the information in the networ6- he transport layer: esta"lishes the connection, initiate the data transfer and

manage the data transfer- he session layer: controls communication- he presentation layer: coding and decoding- he application layer: user interface

- =ased on I0PGP0I, several different protocols have "een developed. or e5ample,

the #anufacturing utomation rotocol (#) is developed "y eneral #otors%o. he most commonly used protocol is however, the ransmission %ontrolrotocol G Internet rotocol (%GI) developed "y 0 Dept. of Defense. %GIsuit now consists of several protocols including elnet, , &etwor6 file systems(&0), and simple mail transfer protocol (0#).

- &etwor6 hardware. In addition to the computers, various hardware devices are neededin networ6 connections. hese include:- $eapeater: circuit used to connect the devices with same protocols- =ridge: circuit used to connect two similar or dissimilar '&s- $outers: a com"ination of "oth repeater and "ridge- ateway: a special purpose computer that does the protocol conversions.

- &etwor6 performances. he networ6 performances can "e measured "y the followingcriteria: networ6 availa"ility and response time.- &etwor6 availa"ility can "e determined "ased on the relia"ility theory. If there are

ncomponents connected in series and the their pro"a"ility of "eing availa"le is ai,i@ 1, ;, n, then the system availa"ility is:

=

=n

i

iaA

1

Pn the other hand, suppose the ncomponents are connected in parallel, thesystem availa"ility is:

=

=n

i

iaA1

1

-the response time is determined "y the summation of service time and waiting.

() Data"ase management- =asic terminology

- Date item: the smallest unit of data- Data record: a collection of data items- ile: a collection of similar date records

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- Data "ase: a collection of files as an organi!ed assem"ly of information that userscan access for various purposes.

- Data model: a logic representation of a collection of data elements. It is the"uilding "loc6 for data"ases.

- In modern engineering, a great deal amount of information is required for any tas6 to

"e accomplished. Imaging that a manufacturing company producing simple gears.he following data must "e availa"le:- 8or6 material- Dimensions, surface finish and tolerance- #achines to "e used in manufacturing- ools- ;.herefore, it is very important to have a proper data"ase management system.

- Data model. here are two types data models:- $ecord "ased models, which can further decomposed as networ6 model,

hierarchical model, and relational model.-

P"Cect4oriented models- In recent years, o"Cect4oriented models "ecome dominant. he o"Cect4oriented model

is "ased on following important concept.- P"Cect: any physical or imagery entities may "e referred to as an o"Cect- ttri"ute and methods: o"Cects are characteri!ed "y attri"utes, which may include

its intrinsic properties or its relationship with other o"Cects. method is anoperation applied to the o"Cects.

- #essage: a method is invo6ed "y a client "y sending a message to the o"Cect.- %lass: o"Cects can "e categori!ed into classes, which descri"es the common

"ehavior of the o"Cect with respect to its family.- or those who have learnt the o"Cect4oriented programming (%BB), the a"ove

concepts should "e easy to follow. ollowing is an e5ample

- P"Cect: ro"ot- %lass:

%lass name: ro"otttri"ute: ro"otUid

$o"otUtype#ethod: move

ic6upDrop off

- particular instance is:%lass name: #1ttri"ute: 1A2

rticulate#ethod: ic6up(8or61)

&ote that J8or611K is another o"Cect (a wor6piece), the interactions "etween thetwo o"Cects are defined "y the operation (association) Jic6upK.

- he procedure of designing an o"Cect4oriented data"ase system is as follows:(a) develop a conceptual model of the system "y identifying 6ey o"Cects

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(") associate attri"utes and methods with each o"Cect identified in step 1(c) arrange o"Cects into a class inheritance hierarchy(d) refine the hierarchy "y emphasi!ing, speciali!ation, and generali!ing(e) identify client4server relationships and message e5changes among o"Cects to

capture system dynamics

(f) develop a prototype implementation to validate requirements(g) refine the system design iteratively "y modifying or adding o"Cects, attri"utes,operations, or associations.

(>) roupware- roupware is the networ6ed hardware and software that allow people to support each

other in their effort to achieve wor6 goals regardless of where and when they want todo this.

- roupware shall have consider the following issues- $e4eneineer, re4tool, re4si!e, re4invent, re4manufacture, ;- eamwor6, virtual teaming-

ocus on customer needs- ocus on core competencies- he networ6 enterprise- latter, leaner organi!ations- Drive for efficiency and productive gain.

- ow of the most important groupware handware tools are email and networ6ing.- lso, now there are several software systems that can "e used as groupwares, such as

I4D/0, nigrphics, and ro/ngineering.

=y now we have pretty much descri"ed all the important technologies used in modernmanufacturing systems. hese technologies will help you to understand and hence, tosolve the practical pro"lems in manufacturing systems. If you have any pro"lems, pleasedo not hesitate to contact me at the following address.

$u5u DuDept. of Industrial /ngineeringniversity of #iami%oral a"les, ' 221A. 0. .

Documents

Ch 7 Manufacturing Systems