Assembly Line Balancing
Introduction to Industrial
Engineering
The Line Balancing Problem
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The problem is to arrange the individual
processing and assembly tasks at the
workstations so that the total time
required at each workstation is
approximately the same.
Nearly impossible to reach perfect
balance
Things to consider
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Sequence of tasks is restricted, there is
a required order
Called precedence constraints
There is a production rate needed, i.e.
how many products needed per time
period
Design the line to meet demand and
within constraints
Terminology and Definitions
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Minimum Work Element
Total Work Content
Workstation Process time
Cycle Time
Precedence Constraints
Balance Delay
Minimum Work Element
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Dividing the job into tasks of a
rational and smallest size
Example: Drill a hole, can’t be
divided
Symbol – Time for element j: Tej
is a constant
Tej
Total Work Content
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Aggregate of work
elements
n
Twc   Tej
j 1
Workstation Process time
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The amount of time for an individual
workstation, after individual tasks have
been combined into stations
Sum of task times = sum of workstation
times
Cycle time
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Time between parts coming off the line
Ideally, the production rate, but may
need to be adjusted for efficiency and
down time
Established by the bottleneck station,
that is station with largest time
Precedence Constraints
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Generally given, determined by the
required order of operations
Draw in a network style for
understanding
Cannot violate these, an element must
be complete before the next one is
started
Balance Delay
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Measure of line
inefficiency due to
imbalances in
station times
nTc  Twc
d
nTc
Method – Largest Candidate Rule
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List elements in descending order of T
Assign elements to first station, from top
to bottom of list, minding constraints, and
not causing sum to exceed cycle time
Continue assigning elements to stations
where each station < cycle time, largest
assigned first, until all assigned
EXAMPLE