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LINE BALANCINGByArun Mishra

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Line Balancing

Definition: the apportionment of sequential

work activities into work stations in order to gain

a high uti l ization of labour and equipment and

therefore minimize idle time.

Arranging a production line so that there is an

even flow of production from one work station to

the next, so that there are no delays at any work

station that will leave the next work station withidle time.

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Introduction : What is line balancing?

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Introduction : What is line balancing?

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Objectives of Line Balancing

Capacity Minimization of total idle time (maximization of the use of the

line).

Minimization of product flow-time.

Balance the levels of capacity used at the workstations. Cost

Minimization of the machinery costs, tools or idle equipment.

Minimization of the costs of materials or reworks.

Minimization of the costs by adjustment and change.

Organizational-social

Job Enrichment

Modifications at the Line balancing

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Line Balance : Simple

Example

1 2 3 4

25 mins5 mins 15 mins 10 mins

Constraint

Overburden

This operator

must WAIT for

operator 2

Overproduction which

causes the other 6wastes

Waiting

Over-processing

Inventory

Rework

Transportation Motion

This operator

must WAIT for

operator 3

5

10

15

20

25

1 2 3 4

mins

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Line Balance : Simple

Example

5

10

15

20

25

Redistribute the work

1 2 3 4

15 mins15 mins 15 mins 10 mins

Promotes one-piece FLOW

Avoidsoverburden

Minimises the 7wastes

ReducesVariation

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Line Balancing Procedure in Assembly

Layouts

i. Step 1 : Determine what tasks must be performed tocomplete one unit of a finished product and thesequence in which the tasks must be performed. Drawthe precedence diagram.

ii. Step 2 : Estimate the task time (amount of time it takesa worker to perform each task).

iii. Step 3 : Determine the cycle time (the amount of timethat would elapse between products coming off the endof the assembly line if the desired hourly production

were being produced.)iv. Step 4 : Assign each task to a worker and balance the

assembly line. This process results in determining thescope of each workers job or which tasks that he or shewill perform.

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Terminologies used in Line Balancing

Tasks: element of work or activity.

Task Precedence: Indicated the sequence in which tasksmust be performed. Except the beginning task, all other

tasks have preceding tasks.

Task times: The amount of time required for an

automated machine or a well-trained work to perform a

task.

Work station: Physical location where a particular set of

tasks is performed. It could be either machine or

equipment operated by a worker or robot.

Work Centre: A physical location where two or moreidentical workstations are located in order to provide the

need production capacity.

Productive time per hour: The duration a work station

or machine is working in each hour. It is always lesserthan actual available time.

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Tool used in line balancing to display elemental

tasks and sequence requirements

A Simple Precedence

Diagrama b

c d e

0.1 min.

0.7 min.

1.0 min.

0.5 min. 0.2 min.

Precedence Diagram

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Cycle Time (CT) is the time interval at whichcompleted products leave the production line.

Determination of cycle time (CT)

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Determination of the Ideal or Theoretical

Minimum Number of Workers Required in the

Line

workperperiodpertimeAvailable

periodperrequired

unitsOutput

task timeor

operationTotal

.productionline/

assy.theinrequired

workersof.nominimumltheoreticaorIdeal

CT

t

CT

1XtN

The least number of work stations that can provide the

required production. The formulae is;

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Balancing Efficiency

An efficient line balancing will minimize the amount ofidle time.

The balance efficiency can be calculated as:

NCT

t

timesnworkstatiobyInput

timetaskofOutput

FFBE(i)

workersofnumberActual

workersofnumberminimumlTheoreticaFFBE(ii)

Where, t = sum of the actual worker times or task times to complete one unit.

CT= cyclic time; N= No. of workers or work stations.

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Line Balancing Procedure (Steps)

Calculate the cyclic time and determine the theoretical

minimum number of workstations.

Compute the total actual number of workstation (N)

required by rounding up the theoretical number of

workstations to the next higher integer value.

Assign the tasks to the workstations beginning with

station1. Tasks are assigned to work stations moving fromleft to right through the precedence diagram.

Before assigning each task to a workstation, use the

following criteria to determine which tasks are eligible to

be assigned to a workstation. All preceding tasks in the sequence have been assigned

already.

The task time does not exceed the time remaining at the

workstation.

If no task are eligible to be assigned to a particular

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Line Balancing Procedure (Steps) Conti

After each task assignment, determine the time

remaining at the current work station by subtractingthe sum of times for tasks already assigned to the

work station from the cycle time.

When there is a tie between two tasks (parallel tasks)

to be assigned, use one of these rules:

Assign the task with the longest task time.

Assign the task with greatest number of followers.

If there is still a tie, choose one task arbitrarily.

Continue assignment of tasks until all tasks havebeen assigned to workstations.

Calculate the idle time (or balance delay), percent

idle time and efficiency of balancing the line.

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Line Balancing Methods

The various line balancing methods or

techniques used are:

1. Heuristic methods

2. Linear Programming3. Dynamic Programming

4. Computerized line-balancing

Heuristic and Computer based technique are most widelyused for solving large scale line balancing problems.

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Heuristic Method

Thumb rule method which gives asatisfactory rather than optional

solution to the line balancing problem.

Acceptable when optimizing solutionsare not feasible or are too costly to

obtain.

In this work elements are groupedsuch that the cyclic time is not violated

& the preceding diagram is used to

group the activities as per the

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Types of Heuristic Methods

Incremental Utilization Heuristic:

Assigns tasks to a workstation in the order of task

precedence one at a time until the utilization of

workstation in 100% or as near to 100% as

possible.

This method is appropriate when one or moretask times is equal to or greater than the cyclic

time.

Longest-task time-Heuristic:

Adds tasks to workstations one at a time in the

order of task precedence.

Tasks with shorter times are kept pending for

assignment later to fine tune the balancing

solution.

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Computerized Line Balancing

Use of software packages that will balance

large line quickly.

Examples are; COMSOAL (Computer

Method for Sequencing Operations for

Assembly Lines), GEs ASYBL (AssemblyLine Configuration Program)

They use various heuristics or rules are;

Ranked positional weight

Longest operational time

Shortest operational time

Most number of followings

Least number of following tasks.

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Problem The precedence diagram for assembly activities A to

G is shown below. The element time required for the

activities are shown in the diagram in minutes. Theline operates for 7 hrs. Per day and an output of 550

units per day is desired.

Calculate Cycle time & theoretical min. number of workers.

Group the tasks into an appropriate no. of work stations. Calculate the balance efficiency.

A B C

D

E

F G

0.65 Min. 0.40 Min. 0.30 Min.

0.20 Min.

0.45 Min.

0.40 Min. 0.30 Min.

S l i

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Solution

CT =

Available time per period

Output units required per period =

7x60

550 = 0.76 mts

N = t

CT=

0.76

0.65+0.4+0.3+0.2+0.45+0.4+0.3=

0.76

2.7= 3.552

Ideal Time = CT Work station time

Balance Efficiency:

NCT

t

timesnworkstatiobyInput

timetaskofOutputFFBE(i)

=

0.76x4

2.7x 100 = 88.81%

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