om lecture 17
TRANSCRIPT
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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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