CHAPTER 9 - Layout Strategy Estrategia de distribucion

Assembly Line BalancingApplied Management Science for Decision Making, 1e 2012 Pearson Prentice-Hall, Inc. Philip A. Vaccaro , PhD

Assembly Line Balancing The assignment of tasks to work stations along an assembly line in such a way as to achieve the same or close to sameworking times at each work station.THE GOAL IS TO CREATE A SMOOTH,CONTINUOUS FLOW OF PRODUCT THROUGHTHE ASSEMBLY LINE FOR MAXIMUMPRODUCTIVITY AND MINIMUM IDLE TIMEAT EACH WORK STATION

Assembly Line BalancingAPPLICATIONS Cafeteria line

Carwash line

Appliance manufacturing line

Automobile manufacturing line

Registry of Motor Vehicles office line Disassembly line

Fabrication line

Physical exams for military recruits- POULTRY SLAUGHTER- AUTOMOBILE RECYCLING- PRODUCTION OF PARTS VIA SERIES OF MACHINES

Assembly Line BalancingCafeteria LineStation 1Trays, Plates, UtensilsStation 2AppetizersStation 3EntreesStation 4DessertsStation 5Cashier

Assembly Line BalancingPoultry Dissassembly LineStation 1Station 2Station 3Station 4Station 5Station 6

Assembly Line BalancingRaw Recruit Physical Examinations14 Stations includingReceptionEye ExaminationChest X-rayWeight + Height MeasurementPsychologicalHeart Rate

Assembly Line BalancingWHEN IT IS DONEBEFORE ACTUAL PRODUCTIONIN WESTERN MANUFACTURINGSYSTEMSDURING ACTUAL PRODUCTIONIN ASIAN MANUFACTURINGSYSTEMS

Individual Task Times These are set well in advance by industrial engineers and time & motion specialists

They are called standard task times and consist of normal time to perform a particular task and extra time allowances for fatigue, personal needs, and unavoidable, but recurring delays.

The Assembly Line Balancing ConceptStation1Station2Station3The Assembly LinetowarehouseorretailerAt the end of every cycle, each station hands its work-in-process unit to the next station.A cycle is the amount of time that a work-in-process unit canstay in a work station before it must move onto the next.

The Assembly Line Balancing ConceptStation1Station2Station3The Assembly LinetowarehouseorretailerThe effective production rate for the assembly line equals one completed product every 10 minutes,even though each unit requires 30 minutes to build!If the cycle time were 10 minutes, each station would hand its work-in-processunit over to the next station at the end of 10 minutes.

The Assembly Line Balancing ConceptAssumethe cycletime is10minutesA PERFECTLY-BALANCED ASSEMBLY LINE

Station 1( 10 Minutes )Station 2( 10 Minutes )Station 3( 10 Minutes )Total Time( 30 Minutes )Task A( 10 minutes )Task B( 5 minutes )Task D( 2 minutes )Task C( 5 minutes )Task E( 3 minutes )Task F( 5 minutes )10 Minutes Productive Time 10 Minutes Productive Time 10 Minutes Productive Time30 MinutesTotal Productive Time

0 Minutes Idle Time 0 Minutes Idle Time 0 Minutes Idle Time 0 MinutesTotal Idle Time

The Assembly Line Balancing Concept Tasks are measured in seconds and vary widely.

It is impossible to assign tasks to all work stations so as to get exact work times at each station per cycle. Therefore, a perfectly balanced assembly line does not exist !

The Assembly Line Balancing ConceptAssumethe cycletime is10minutesA NOT PERFECTLY-BALANCED ASSEMBLY LINE

Station 1( 10 Minutes )Station 2( 10 Minutes )Station 3( 10 Minutes )Total Time( 30 Minutes )Task A ( 9 minutes )Task B( 4 minutes )Task D( 2 minutes )Task C( 4 minutes )Task E( 2 minutes )Task F( 5 minutes ) 9 Minutes Productive Time 8 Minutes Productive Time 9 Minutes Productive Time26 MinutesTotal Productive Time

1 Minute Idle Time 2 Minutes Idle Time 1 Minute Idle Time 4 MinutesTotal Idle Time

Assembly Line Balancing Steps Provide the tools, equipment, and work methods to be used in producing a product or service at a desired volume.


Identify the standard time for each assembly or service task involved in the creation of the product or service.


Identify the standard time for each assembly or service task involved in the creation of the product or service.

Identify the precedence relationships.THE ORDER IN WHICH THE TASKS MUST BE PERFORMED

Practical Problem StatementDevelop the Assembly Line !A firm wants to produce160 units of a producteach 8-hour day on anassembly line.

Nine ( 9 ) separatetasks are neededto complete eachunit of product.

Assume no break timeand no paid lunch time

Task Predecessor Standard Time

Anone60BA80Cnone30DC40EB,D40Fnone50GF100HD,G70IE,H30 = 500 seconds

The Precedence Diagram A network showing the sequential relationships among all tasks to be performed on the assembly line, together with their respective standard times.

An optional, useful tool for avoiding precedence relationship violations when assigning tasks to work stations, without benefit of the computer.

The Precedence DiagramTHE ORDER IN WHICH TASKS MUST BE PERFORMEDA60C30F50B80D40G100E40H70I30

The Cycle TimeSHOWN IN SECONDSThe maximum period of time that a work-in-processunit can stay in any givenwork station before it mustmove on to the next workstation.

The Cycle Time FormulaTotal Available Daily Production TimeDaily Production Quota28,800 Seconds160 Units( FROM THE PROBLEM )= 180 Seconds

The Minimum Number of Work Stations The minimum number of work stations that the new assembly line, when balanced, will contain.


The actual number of work stations may well exceed the minimum number by one or more.


The actual number of work stations may well exceed the minimum number by one or more.

Also known as the theoretical minimum number of work stations.

The FormulaTotal Task Time Per Unit of ProductThe Cycle Time500 Seconds180 Seconds= 2.77 3.00FRACTIONS ARE ALWAYS ROUNDED UP( i.e. 2.01 becomes 3.00 )MINIMUM NUMBER OF WORK STATIONS

The Line-Balancing Spreadsheet To assign individual tasks to each work station. The theoretical minimum number of work stations. The cycle time for each work station. The cycle time for the entire assembly line. The productive time per cycle at each work station. The idle time per cycle at each work station.SHOWS

The Line Balancing Spreadsheet

Cycle Time180seconds180seconds180seconds540secondsStation1Station2Station3ProductiveTimePer CycleIdle TimePer Cycle

Task Assignment Heuristic From the Greek ( heuriskein ) meaning to discover or to guide.


A rule of thumb or guideline for finding a solution in general.


A rule of thumb or guideline for finding a solution in general.

Here, a particular rationale for assigning tasks to work stations in line balancing.

Heuristic SelectionThe LOT rule longest operating time

The SOT rule shortest operating time

The MFT rule the most follower tasks

The LFT rule the least follower tasks

The Ranked Positional Weight or Highest Sum ruleFIVE POPULAR HEURISTICS FOR LINE BALANCING

The LOT Assignment Heuristic Also known as the longest operating time rule.

Assigns the longest tasks to the work stations first.SUBJECT TO MAINTAINING THE PRECEDENCE RELATIONSHIPS AMONG THE WORK TASKSTask AbeforeBB and Dbefore E

Precedence Diagram LegendXYZNON-CANDIDATE TASKS( SHOWN IN BLUE )ADAN ASSIGNED TASK( SHOWN WITH X ACROSS )XCANDIDATES FOR THE NEXTTASK ASSIGNMENT( SHOWN IN RED )

BCDXDX

The Precedence DiagramA60C30F50B80D40G100E40H70I30

The Precedence DiagramA60C30F50B80D40G100E40H70I301st TASK ASSIGNMENTCANDIDATES FOR STATION 1

The Line Balancing Spreadsheet TASK A( 60 sec )

Cycle Time180seconds180seconds180seconds540secondsStation1Station2Station3ProductiveTimePer Cycle

Idle TimePer Cycle

The Precedence DiagramA60C30F50B80D40G100E40H70I302nd TASK ASSIGNMENTCANDIDATES FOR STATION 1X

The Line Balancing Spreadsheet TASK A( 60 sec ) TASK B( 80 sec )


Idle TimePer Cycle

The Precedence DiagramA60C30F50B80D40G100E40H70I303rd TASK ASSIGNMENTCANDIDATES FOR STATION 1XX

The Line Balancing SpreadsheetTASK A ( 60 sec )TASK B ( 80 sec )TASK C ( 30 sec )10seconds


Idle TimePer Cycle

The Precedence DiagramA60C30F50B80D40G100E40H70I301st TASK ASSIGNMENTCANDIDATES FOR STATION 2XXX

The Line Balancing SpreadsheetTASK A ( 60 sec )TASK B ( 80 sec )TASK C ( 30 sec )10secondsTASK F( 50 sec )


Idle TimePer Cycle

The Precedence DiagramA60C30F50B80D40G100E40H70I302nd TASK ASSIGNMENTCANDIDATES FOR STATION 2XXXX

The Line Balancing SpreadsheetTASK A ( 60 sec )TASK B ( 80 sec )TASK C ( 30 sec )10seconds TASK F ( 50 sec) TASK G (100 sec)30seconds


Idle TimePer Cycle

The Precedence DiagramA60C30F50B80D40G100E40H70I301st TASK ASSIGNMENTCANDIDATES FOR STATION 3XXXXX

The Line Balancing SpreadsheetTASK A ( 60 sec )TASK B ( 80 sec )TASK C ( 30 sec )10seconds TASK F (50 sec) TASK G (100 sec)30seconds TASK D( 40 sec )


Idle TimePer Cycle

The Precedence DiagramA60C30F50B80D40G100E40H70I302nd TASK ASSIGNMENTCANDIDATES FOR STATION 3XXXXXX

The Line Balancing SpreadsheetTASK A ( 60 sec )TASK B ( 80 sec )TASK C ( 30 sec )10seconds TASK F (50 sec) TASK G (100 sec)30secondsTASK D( 40 sec )TASK H( 70 sec )


Idle TimePer Cycle

The Precedence DiagramA60C30F50B80D40G100E40H70I303rd TASK ASSIGNMENTCANDIDATES FOR STATION 3XXXXXXX

The Line Balancing SpreadsheetTASK A ( 60 sec )TASK B ( 80 sec )TASK C ( 30 sec )10seconds TASK F (50 sec) TASK G (100 sec)30secondsTASK D (40 sec)TASK H (70 sec)TASK E (40 sec)


Idle TimePer Cycle

The Precedence DiagramA60C30F50B80D40G100E40H70I304th TASK ASSIGNMENTCANDIDATES FOR STATION 3XXXXXXXX

The Line Balancing SpreadsheetTASK A ( 60 sec )TASK B ( 80 sec )TASK C ( 30 sec )10seconds TASK F (50 sec) TASK G (100 sec)30secondsTASK D (40 sec)TASK H (70 sec)TASK E (40 sec)TASK I (30 sec)0seconds


Idle TimePer Cycle

The Line Balancing SpreadsheetTASK A ( 60 sec )TASK B ( 80 sec )TASK C ( 30 sec )10seconds TASK F (50 sec) TASK G (100 sec)30secondsTASK D (40 sec)TASK H (70 sec)TASK E (40 sec)TASK I (30 sec)0seconds500seconds40secondsTOTAL


Idle TimePer Cycle

Evaluating The Balanced LineEfficiency = total productive time on the assemblyline per cycletotal available time on the assemblyline per cycle500 seconds540 seconds= 92.6%EFFICIENCY => 90% IS CONSIDERED ACCEPTABLE

Evaluating The Balanced LineBalance Delay Factor ( % IDLE TIME )line idle time per cycleline total time per cycle=40 seconds540 seconds== 7.4%A BALANCE DELAY FACTOR=< 10% IS CONSIDERED TO BE ACCEPTABLE

Evaluating The Balanced Line Effectiveness is achieved if theassembly line meets managements daily production quotaTHE EMPLOYMENT OF THEMAXIMUM ALLOWABLE CYCLETIME GUARANTEED DAILY QUOTA COMPLIANCE !101010

Line Balancing under QM for Windows

We Select The Assembly Line BalancingProgram

We Desire ToSolve A NewProblem

The Dialog BoxAppears

Nine ( 9 ) TasksNeed To BeAssignedTo Work StationsTask Times AreNormally StatedIn SecondsWe Label Tasksas A,B,C,D, etc.

THE DATA INPUT TABLEPROVIDES COLUMNS FOR LISTING EACHTASKS PREDECESSOR(S)THE SOFTWAREDETERMINES HOW MANY COLUMNSSHOULD BE PROVIDEDFOR LISTING PREDECESSOR TASKS

The Predecessor TasksMust Be Shown InIndividual Cells,AlphabeticallyHere, We Entered TheCycle Time ForThe Software ToWork WithWe Selected TheLOT AssignmentHeuristicFor Balancing This Assembly Line

Line Efficiency = 92.59%

Balance Delay Factor = 7.41%Idle Time Per Cycle,Per Work StationTask CandidatesTasks A,B,C assignedTo Work Station # 1

This Is The Programs Way of Asking UsIf This Is The CorrectPrecedence RelationshipAmong The Nine Tasks

The Amount of ProductiveTime Per Cycle In Each Work StationThe Cycle Timeis 180 seconds

If task I had a standard time offorty seconds..

What changes must be made to the line-balancing spreadsheet?

How would the efficiency of the line be affected?NEW SCENARIO??

The New Precedence DiagramA60C30F50B80D40G100E40H70I40TASK I BECOMESFORTYSECONDS

The Line-Balancing SpreadsheetMODIFIED FOR TASK I NEW STANDARD TIMEsecondsProductiveTime Per CycleIdle TimePer Cycle10 seconds30 seconds30 seconds140seconds

Cycle time180seconds180seconds180seconds180seconds 720

station1station 2station 3station 4TASK ATASK BTASK C170 secondsTASK FTASK G

150 secondsTASK DTASK HTASK E150 secondsTASK I40 seconds = 510seconds = 210seconds

Spreadsheet Modifications A 4th work station would need to be opened exclusively for task I.

Total assembly line available time per cycle would jump to 720 seconds ( 180 secs x 4 stations )

Total assembly line idle time per cycle would jump to 210 seconds ( under any assignment heuristic )

The balanced line would no longer be efficient ( 71% )

Evaluating The Balanced LineFOURTH STATION ADDED FOR TASK I Efficiency = = 71%Balance Delay Factor 210 seconds720 seconds== 29%THE LINE FAILS IN EFFICIENCY510 seconds720 seconds

Minimum Allowable Cycle Time THE OTHER CYCLE TIME Cycle time based on the bottleneck task*

No guarantee that the daily production quota will be met

Line efficiency will most likely change under this cycle time

* THE LONGEST TASK TIME

Minimum Allowable Cycle Time From the text example, the longest task is G which takes 100 seconds to perform.

The minimum allowable cycle time therefore is 100 seconds.

The theoretical minimum number of work stations: EXAMPLE500 seconds

100 seconds= 5ASSUME TASK I = 30 SECONDS

Minimum Allowable Cycle TimeLINE-BALANCING SPREADSHEET

CycleTime10seconds20seconds10seconds0seconds30seconds30secondsASSUME TASK I = 30 SECONDSWE ENDED UP WITH SIX WORK STATIONS IN ORDER TO ASSIGN ALL 9 TASKS

100seconds100seconds100seconds100seconds100seconds100seconds 600secondsStation1Station2Station3Station4Station5Station6ProductiveTime Per CycleTASK ATASK C90 secondsTASK B

80 secondsTASK FTASK D90 secondsTASK G

100 secondsTASK H

70 secondsTASK ETASK I70 seconds 500seconds

Idle TimePer Cycle 100seconds

Evaluating The Balanced Line MINIMUM ALLOWABLE CYCLE TIME Efficiency = 500 seconds = .833 = 83.3%

600 secondsBalance DelayFactor= 100 seconds = .167 = 16.7%600 secondsTHE LINE FAILS TOMEET ACCEPTABLEEFFICIENCY000ASSUME TASK I = 30 SECONDS

Minimum Allowable Cycle TimeLINE-BALANCING SPREADSHEET

CycleTime10seconds20seconds10seconds0seconds30seconds20secondsASSUME TASK I = 40 SECONDS

100seconds100seconds100seconds100seconds100seconds100seconds 600secondsStation1Station2Station3Station4Station5Station6ProductiveTime Per CycleTASK ATASK C90 secondsTASK B

80 secondsTASK FTASK D90 secondsTASK G

100 secondsTASK H

70 secondsTASK ETASK I80 seconds 510seconds

Idle TimePer Cycle 90seconds

Evaluating The Balanced Line MINIMUM ALLOWABLE CYCLE TIME Efficiency = 510 seconds = .850 = 85.0%

600 secondsBalance DelayFactor= 90 seconds = .150 = 15.0%600 secondsTHE LINE FAILS TOMEET ACCEPTABLEEFFICIENCY000ASSUME TASK I = 40 SECONDS

Evaluating The Balanced LineEffectiveness UnderMaximum AllowableCycle Time

28,800 seconds180 seconds

= 160 units produced daily

EffectivenessUnderMinimum AllowableCycle Time

28,800 seconds100 seconds

= 288 units produced daily

___________________________________________________

ScoreboardACCEPTABLE EFFICIENCY

Type CycleCycle TimeTask I EfficiencyBalanceDelay MAXIMUMAllowable180 seconds30 seconds92.59%7.41%MAXIMUMAllowable180 seconds40 seconds70.83%29.17%MINIMINAllowable100 seconds30 seconds83.33%16.67%MINIMINAllowable100 seconds40 seconds85.00%15.00%

Line Balancing under QM for WindowsADDITIONAL SCENARIOS

The MaximumAllowableCycle TimeAssume Task I Equals 40 SecondsTheLOT AssignmentHeuristic

Rebalanced Assembly Line

Maximum Allowable Cycle Time

Task I = 40 Seconds

LOT Assignment Heuristic

The Minimum AllowableCycle TimeTask I Equals30 SecondsTheLOT Assignment HeuristicIs Employed


Minimum Allowable Cycle Time

Task I = 30 Seconds


LOT Assignment HeuristicTask I Equals 40 SecondsTheMinimum AllowableCycle Time



Minimum Allowable Cycle Time

Task I = 40 Seconds

ScoreboardACCEPTABLE EFFICIENCY

Type CycleCycle TimeTask I EfficiencyBalanceDelay MAXIMUMAllowable180 seconds30 seconds92.59%7.41%MAXIMUMAllowable180 seconds40 seconds70.83%29.17%MINIMINAllowable100 seconds30 seconds83.33%16.67%MINIMINAllowable100 seconds40 seconds85.00%15.00%

Decision ProcessLine Efficiency < 90%Try Minimum Allowable Cycle TimeLine Efficiency Still < 90%Product RedesignWorker Training Faster Equipmentetc.Rebalance LineOUTSIDETHEREALM OFLINEBALANCINGMAY TAKE MONTHSTO ACCOMPLISH

Why Labor Idleness Is Costly Average worker wage rate is $25.00 per hour

Ten (10) seconds of idle time per cycle in one particular work station.

One hundred sixty (160) cycles per work day.ASSUME THE FOLLOWING

IDLE TIME COSTS1 Station$11.20Daily1 Station$2,800.00Annually20 Stations$56,000.00Annually5 Plants$250,000.00Annually

Assembly Line Efficiency The overall efficiency of the assembly line cannot be changed by employing a different task assignment heuristic. This would merely reshuffle the tasks among the work stations.MFTSOTLFTA FINAL WORD

Fairness in Line Balancing Experimenting with different task assignment heuristics may prove useful if management is seeking a more equitable distribution of work among all of its work station employees.

Per CycleSTATION 1STATION 2STATION 3PRODUCTIVE TIME167 seconds167 seconds167 secondsIDLE TIME13 seconds13 seconds13 secondsAVAILABLE TIME180 seconds180 seconds180 seconds

Assembly Line BalancingTHE ENDApplied Management Science for Decision Making, 1e 2011 Pearson Prentice-Hall, Inc. Philip A. Vaccaro, PhD

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CHAPTER 9 - Layout Strategy Estrategia de distribucion