Assembly Line Balancing

ASSEMBLY LINE BALANCING

KOUSHIK S V-11P624

MANIVANNAN V -11P629

SIBI VISHVAK-11P643

VIGNESH D-11P648



The assignment of tasks to work stations along an assembly line in such a way as to achieve the same or close to same working times at each work station.

The goal is to create a smooth,continuous flow of products through the assembly line for maximum productivity and minimum idle time at each work station.


Assigning each task to a workstation within an assembly line in order to meet the required production rate and to achieve a minimum amount of idle time.

Line balancing is the procedure in which tasks along the assembly line are assigned to work station so each has approximately same amount of work.

In production line,workstations and work centers are arranged in a sequence of task to be done along a straight or curved line.

CAFETERIA LINEStation 1

Trays, Plates, Utensils

Station 2Appetizers

Station 3Entrees

Station 4Desserts

Station 5Cashier

ASSEMBLY LINE BALANCINGGOALS

Number of workstations needed.Type of task to be assigned to each

workstation.To know the minimum number of

workers,tools and machines that can be used to provide the required amount of capacity.

ASSEMBLY LINE BALANCINGOBJECTIVES

Assigning a task to each workstation in such a way that there is only a little idle time.

Increased efficiency. Increased productivityLow cost manufacturing.Potential increase in costs.

TERMINOLOGIES RELATED TO PRODUCTION LINE ANALYSIS

TASKS:All the elements of the work. TASK PRECEDENCE:The sequence in which

tasks are performed. TASK TIMES: Time required by a well-trained

worker or unattended machine to perform a task.This is usually expressed inn minutes.

CYCLE TIME: The time expressed in minutes between two simultaneous products coming off the end of a production line.

CONTINUED… PRODUCTIVE TIME PER HOUR: The average

number of minutes a workstation in an hour. WORKSTATION:A physical area where a worker

performs a particular set of task in a production line.

WORKCENTRE: A small group of identical workstations,where each workstation performs the same set of task.

NUMBER OF WORKSTATIONS WORKING:The amount of workdone at a work centre expressed in number of work stations.

CONTINUED… MINIMUM NUMBER OF WORKSTATIONS:The

least number of workstations that provides the required production.

ACTUAL NUMBER OF WORKSTATIONS:This is the total number of workstations required on the entire production line.It is calculated as the next higher integer of the number of workstation working.

UTILISATION:The percentage of time a production line is working.

LINE BALANCING PROCEDURE1. Determination of tasks that must be performed

to complete one unit of a product.

2. Determining the order or sequence of performing the whole set of tasks.

3. Drawing precedence diagram. In this flowchart circles represents task and joining arrows represents precedence.

4. Estimation of task time.

5. Calculation of cycle time.

6. Determination of minimum number of workstation required.

7. Use of heuristics to assign a task.

COMPUTERISED LINE BALANCING

Line balancing by hand becomes unwieldy as the problems grow in size.

There are software packages that will balance

large lines quickly. IBM's COMSOAL (Computer

Method for Sequencing Operations for Assembly

Lines) and GE's ASYBL (Assembly Line

Configuration Program) can assign hundreds of

work elements to workstations on an assembly

line.

CONTINUED…

They use various heuristics, to balance the line at an acceptable level of efficiency.

The POM for Windows software lets the user select from five different heuristics: ranked positional weight, longest operation time, shortest operation time, most number of following tasks, and least number of following tasks. These heuristics specify the order in which work elements are considered for allocation to workstations.

UNBALANCED LINE

High work load in some stages (Overburden) Maximizes wastes (over-processing, inventory, waiting, rework,

transportation, motion) High variation Restrict one piece flow Maximizes Idle time Poor efficiency

Work Station 1

Work Station 4

Work Station 3

Work Station 2

!? Zzz Zzz

Overproduction!

40 sec 15 sec 15 sec

10 sec

BALANCED LINE

Work Station 1

Work Station 4

Work Station 3

Work Station 2

25 sec 25 sec 20 sec 15 sec

Promotes one piece flowAvoids excessive work load in some stages (overburden)Minimizes wastes (over-processing, inventory, waiting, rework…)Reduces variationIncreased EfficiencyMinimizes Idle time

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.

ASSEMBLY LINE BALANCING CONCEPTS

The Assembly Line

Station1

Station2

Station3

TO WAREHOUS

E

If the cycle time were 10 minutes,each station would hand its WIP to the next at the end of 10 minutes.

PERFECTLY BALANCED ASSEMBLY LINE

NOT PERFECTLY BALANCED ASSEMBLY LINE

PROBLEM STATEMENT A firm wants to

produce 160 units for each 8-hour day production on an assembly line.

Nine separate tasks are needed to complete the product.

Assume no break time.

Develop the assembly line!!

TASK PREDECESSOR STANDARD TIME

A none 60

B A 80

C none 30

D C 40

E B,D 40

F none 50

G F 100

H D,G 70

I E,H 30

Σ = 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 CYCLE TIME FORMULA

Total Available Daily Production Time

Daily Production Quota

28,800 Seconds

160 Units( FROM THE PROBLEM )

= 180 Seconds

MINIMUM NUMBER OF WORK STATIONS

Total Task Time Per Unit of Product

The Cycle Time

500 Seconds

180 Seconds= 2.77 ≈ 3.00

FRACTIONS ARE ALWAYS ROUNDED UP( i.e. “2.01” becomes “3.00” )

THE LINE BALANCING SPREADSHEET

Cycle Time

180seconds

180seconds

180seconds

540seconds

Station1

Station2

Station3

ProductiveTime

Per Cycle

Idle Time

Per Cycle

LINE BALANCING HEURISTICS

There are two types of heuristics used for line balancing:

Incremental utilisation heuristic Longest task time heuristic

INCREMENTAL UTILISATION HEURISTIC

Tasks are added to each workstation in order of task precedence one at a time until utilization is 100 percent or is observed to fall.

Used when one or more task time is equal to or greater than the cycle time.

LONGEST TASK TIME HEURISTIC

Add tasks to a workstation one at a time in the order of task precedence.

If a choice must be made between two or more tasks, the one with the longest task time is added.

This has the effect of assigning as quickly as possible the tasks that are the most difficult to fit into a station.

Tasks with shorter times are then saved for fine-tuning the solution.

CONDITIONS1. It can be used only when each and every

task time is less than or equal to the cycle time.

2. There can be no duplicate work stations.

If each and every task time is less than or equal to the cycle time, and if the primary focus of the analysis of production lines is minimizing the number of workstations and the amount of tools and equipment required, then this heuristic would be appropriate.

STEPS IN LONGEST TASK TIME HEURISTIC

1. Lei i = I. where i is the number of the workstation being formed.

2. Make a list of all the tasks that are to be assigned to a workstation. Have to satisfy the following conditions

a. It cannot have been previously assigned to this or any previous workstation.

b. Its immediate predecessors must have been assigned to this or a previous workstation.

c. The sum of its task time and all other times of tasks are already assigned to work station must be less than or equal to the cycle time . If no such tasks are found. Go to step 4.

3. Assign the from the list with the longest task time to the workstation. Go back to the step 2.

4. Close the assignment of tasks to Workstation i. This can occur in two ways. If there are no tasks on the list for the work station but there are still tasks to be assigned, set i=i+1 and go back to step 2. If there are no more tasks, the procedure is completed.

PRECEDENCE DIAGRAM LEGEND

X

Y

Z

NON-CANDIDATE TASKS

( SHOWN IN BLUE )

A

D

AN ASSIGNED TASK( SHOWN WITH “X”)

X

CANDIDATES FOR THE NEXTTASK ASSIGNMENT( SHOWN IN RED )

B

C DX

DX


A60

C30

F50

B80

D40

G100

E40

H70

I30

1st TASK ASSIGNMENTCANDIDATES FOR

STATION 1


Cycle Time

180seconds

180seconds

180seconds

540seconds

Station1

Station2

Station3

ProductiveTime

Per Cycle

Idle Time

Per Cycle

TASK A( 60 sec )


A60

C30

F50

B80

D40

G100

E40

H70

I30

2nd TASK ASSIGNMENTCANDIDATES FOR

STATION 1X


Cycle Time

180seconds

180seconds

180seconds

540seconds

Station1

Station2

Station3

ProductiveTime

Per Cycle

Idle Time

Per Cycle

TASK A( 60 sec ) TASK B( 80 sec )


A60

C30

F50

B80

D40

G100

E40

H70

I30

3rd TASK ASSIGNMENTCANDIDATES FOR

STATION 1X X


Cycle Time

180seconds

180seconds

180seconds

540seconds

Station1

Station2

Station3

ProductiveTime

Per Cycle

Idle Time

Per Cycle

TASK A ( 60 sec )TASK B ( 80 sec )TASK C ( 30 sec )

10seconds


A60

C30

F50

B80

D40

G100

E40

H70

I30


STATION 2X X

X


Cycle Time

180seconds

180seconds

180seconds

540seconds

Station1

Station2

Station3

ProductiveTime

Per Cycle

Idle Time

Per Cycle


10seconds

TASK F( 50 sec )


A60

C30

F50

B80

D40

G100

E40

H70

I30


STATION 2X X

X

X


Cycle Time

180seconds

180seconds

180seconds

540seconds

Station1

Station2

Station3

ProductiveTime

Per Cycle

Idle Time

Per Cycle


10seconds

TASK F ( 50 sec) TASK G (100 sec)

30seconds


A60

C30

F50

B80

D40

G100

E40

H70

I30


STATION 3X X

X

X X


Cycle Time180

seconds180

seconds180

seconds540

seconds

Station1

Station2

Station3

ProductiveTime

Per Cycle

Idle Time

Per Cycle


10seconds

TASK F (50 sec) TASK G (100 sec)

30seconds

TASK D( 40 sec )


A60

C30

F50

B80

D40

G100

E40

H70

I30


STATION 3X X

X

X X

X


Cycle Time180

seconds180

seconds180

seconds540

seconds

Station1

Station2

Station3

ProductiveTime

Per Cycle

Idle Time

Per Cycle


10seconds


30seconds

TASK D (40 sec)TASK H (70 sec)


A60

C30

F50

B80

D40

G100

E40

H70

I30

3rd TASK ASSIGNMENTCANDIDATES FOR

STATION 3X X

X

X X

X

X


Cycle Time180

seconds180

seconds180

seconds540seconds

Station1

Station2

Station3

ProductiveTime

Per Cycle

Idle Time

Per Cycle


10seconds


30seconds

TASK D (40 sec)TASK H (70 sec)TASK E (40 sec)


A60

C30

F50

B80

D40

G100

E40

H70

I30

4th TASK ASSIGNMENTCANDIDATES FOR

STATION 3X X

X

X X

X

X

X


Cycle Time180

seconds180

seconds180

seconds540

seconds

Station1

Station2

Station3

ProductiveTime

Per Cycle

Idle Time

Per Cycle


10seconds


30seconds

TASK D (40 sec)TASK H (70 sec)TASK E (40 sec)TASK I (30 sec)

0seconds

500seconds

40seconds

TOTAL

EVALUATING THE BALANCED LINE

Efficiency =

total productive time on the assemblyline per cycle

total available time on the assemblyline per cycle

500 seconds

540 seconds= 92.6%

EFFICIENCY => 90% IS CONSIDERED ACCEPTABLE

EVALUATING THE BALANCED LINE

Balance Delay Factor ( % IDLE TIME )

line idle time per cycle

line total time per cycle=

40 seconds

540 seconds= = 7.4%

A BALANCE DELAY FACTOR=< 10% IS CONSIDERED TO

BE ACCEPTABLE

CONCLUSION Effectiveness is achieved when the assembly line

meets the daily production quota. As the efficiency is more than 90% the assembly

line is expected to meet the daily production quota.


APPLICATIONS

CARWASH LINE

CAFETERIA LINE

APPLIANCE MANUFACTURING LINE

AUTOMOBILE MANUFACTURING LINE

FABRICATION LINE

DISSASSEMBLY LINE

Assembly Line Balancing

Documents

curved line

production line analysistasks

entire production line

cafeteria line station

estimation of task time

number of workstations

task precedence

sequence of task