Creating Factory Layout
Dr. Deepu Philip
1 10/19/2023
Designing Product Layouts
Goal is to balance the assembly line
Precedence requirements are physical restrictions in the
order in which operations are performed
Specify which operations must precede others, which can be
done concurrently, and which must wait until later
Another objective is to attain the required output rate as
efficiently as possible
For this, first, each job is to be broken down into the smallest
indivisible proportions called as work elements
The work elements are then grouped to work stations so that
product flow is smooth through the assembly line
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Workstation
Is any area along the assembly line that requires at least
one worker or one machine
If each work station on the assembly line takes the same
amount of time to perform the work elements that are
assigned
Then products will move successively from workstation to
workstation without waiting
Also no need for worker to be idle
This process of equalizing the amount of work at each
workstation is called line balancing
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Line Balancing
Assembly line balancing has two constraints
Precedence
Cycle time
Precedence requirements are usually expressed as
precedence diagram
Precedence diagram is a network that describes any
restrictions on the order in which work elements must be
performed
Work elements represented by nodes and precedence
relationships represented by directed line segments (arcs)
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Example 1
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Cycle Time
It is the maximum amount of time a product is allowed to
spend at each workstation
Mathematically: max{ individual time at workstations}
Calculated by dividing the time available for production by
the number of units to be produced
Cycle time can also be viewed as the time between
completed items rolling off the assembly line
Time required to complete an item is known as flow time
or lead time
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Line Efficiency
For small layout problems, method of trial and error will
work, but not for large problems some guideline is a must
Line efficiency along with theoretical minimum number of
workstations can be used as a guideline to create
workstations j
∑t
j
∑t i
i
Efficiency = i =1 # WS = i =1
nC C
Where ti is the completion time of element i, j is the
number of work elements, n is the actual number of work
stations, and C is the cycle time
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Example 2
8 10/19/2023
Balance Delay
Total idle time of the line is called as balance delay
Balance delay is calculated as (1 – efficiency) in
percentage
Actual cycle time is the maximum workstation time on
the line
Actual efficiency is obtained by dividing with the actual
cycle time
It is very difficult to attain 100% efficiency or theoretical
number of workstations
9 10/19/2023
Computerized Line Balancing
COMSOAL – Computer Method for Sequencing
Operations for Assembly Line by IBM
ASYBL – Assembly Line Configuration Program by GE
Both can assign hundreds of work elements to
workstations on assembly line
They do not guarantee optimal solutions, instead they use
various heuristics to balance line at an acceptable
efficiency
Most common is ranked positional weight technique
10 10/19/2023
Ranked Positional Weight Technique
Compute the cycle time.
Construct the precedence network.
Compute the positional weight for each element, which is the
element’s operation time plus the operation time of all
elements following that element in the network.
Sort the positional weights in the descending order and create
the ranking.
Start assigning elements to workstations in the rank order.
Keep on adding elements to the workstation until time on
workstation is less than or equal to the cycle time.
If no more elements can be added, create the workstation
Repeat until all elements are assigned.
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Example 3
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