Operations Management : Line Balancing

 Line balancing is the procedure in which tasks along task the assembly line are assigned to work
station so each has approximately same amount of work.
 A workstation within an assembly line in order to meet the required production rate and to achieve
a minimum amount of idle time.

BALANCED LINE
 Promotes one piece flow
 Avoids excessive work load in some stages
(overburden)
 Minimizes wastes (over-processing, inventory,
waiting, rework, transportation, motion)
 Reduces variation
 Increased Efficiency
 Minimizes Idle time
UNBALANCED LINE
 High work load in some stages (Overburden)
 Maximizes wastes (over-processing, inventory,
waiting, rework, transportation, motion)
 High variation in output
 Restrict one piece flow
 Maximizes Idle time
 Poor efficiency

 TASK PRECEDENCE:The sequence in which tasks are performed.
 CYCLETIME:The time expressed in minutes between two simultaneous products coming off
the end of a production line.
 PRODUCTIVETIME PER HOUR:The average number of minutes a workstation is working in
an hour.
 WORKSTATION:A physical area where a worker with tools/ one or more machines, or an
unattended machines like a robot performs a particular set of task in a production line.
 WORK CENTER:A small group of identical workstations, where each workstation performs the
same set of task.
 NUMBER OF WORKSTATIONSWORKING:The amount of work done at a work centre
expressed in number of workstations.
 MINIMUM NUMBER OF WORKSTATIONS:The least number of workstation 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
workstations working.
 UTILIZATION:The percentage of time a production line is working.

Example of Assembly-Line Balancing
Problem: An Assembly consists of the following elements as given in table below.
The production rate required is one assembly every 15 minute. Determine the
minimum no of workstations required so as to minimize the Balance- Delay. Find
Balance Delay Station-wise.
STEP 1. List the sequential relationships among tasks and then draw a precedence diagram
Task A B C D E F G H I J K L
Immediate
Predecessor
Nil A B B B B C,D G E I,F H,J K
Task Time 12 6 6 2 2 12 7 5 1 4 6 7
7 min.
12 min.
12 min
F
6 min
C
6 min
B
2 min
D
6 min

Incremental Utilisation (IU) Heuristic
A heuristic method is a procedure that can find a good feasible solution
for a given class of problems, but which is not necessarily an optimal
solution.
❖ It add tasks to a workstation in a precedence task order.
❖ To each task added to the station, operators are added when necessary, and the station
utilization is calculated by equation.
❖ Tasks are added at the used station until its utilization is 100%, or until a reduction
occurs, considering the new task and another operator when necessary.
❖ Then, a new station is considered, and the procedure is repeated on the next
workstation for the remaining tasks.

The incremental utilization heuristic is appropriate when one or
more task times is equal to or greater than the cycle time. An
important advantage of this heuristic is that it is capable of
solving line-balancing problems regardless of the length of task
times relative to the cycle time.

Example
The back room operations of a fast food restaurant have these tasks:

If 100 burgers per hour must be prepared by the crew and 50 minutes per
hour must be prepared by the crew and 50 minutes per hour are
productive:
a.Draw a diagram of the precedence relationships.
b. Compute the cycle time per burger in minutes.
c. Compute the minimum number of workstations required.
d. How would you combine tasks into workstations to minimize idle time?
Use the incremental utilization heuristic. Evaluate your proposal.

Solution
a) Compute the cycle time per burger:
Cycle time = Productive time/ hour
Demand/ hour
= 50 minutes/hour
100 burgers/ hour
= 0.50 minute/burger
b) Compute the minimum number of workstations:
Minimum no. = Sum of task times x Demand/hour
of workstations Productive time/hour
= 5.07 minutes/burger x 100 burgers/hour
50 minutes/hour
= 0.14 workstations

d) Evaluation of the proposal:
Utilization= Minimum number of workstations
Actual number of workstations
= 10.14
43
= 0.2358 or 23.58 %

STEP 2. . Calculate the required workstation cycle time
CYCLE TIME = (PRODUCTION TIME PER DAY) /(OUTPUT PER DAY) = 15 minutes
STEP 3. Calculate the theoretical minimum number of workstations.
NUMBER OF WORK STATIONS = ( SUM OF TOTAL TASK TIMES) / (CYCLE TIME)
= 70 min’s / 15 min’s
= 4.67 ≈ 5 (rounded)
STEP 4. Choose a primary rule that will determine how
tasks are to be assigned to workstations
 For this example, our primary rule is to prioritize
tasks based on the largest number of following tasks.
 If there is a tie, our secondary rule is to prioritize
tasks in the order of the longest task time.
 In general, select rules that prioritize tasks
according to the largest number of followers or based on
length of time.
STEP 5. Beginning with the first workstation, assign each task, one at a time, until the sum of
the task times is equal to the workstation cycle time or until no other tasks can be assigned
due to sequence or time restrictions.
Task
Number of
Following Tasks
A 11
B 10
C or D or E 4
I,F or G 3
H or J 2
K 1
L 0

Stations Task TaskTime
(in minutes)
Number of
Following
Tasks
Remaining
Unassigned
Time
(Balance-Delay)
Feasible
Remaining
Tasks
Task with
Most
Followers
Task with
Longest
Operating
Time
Station 1 A 12 11 3 IDLE None
Station 2 B
C
D
6
6
2
10
4
4
9
3
1 IDLE
C,D,E
D,E
None
C,D,E
D,E
C
D ,E
Station 3 E
F
I
2
12
1
4
3
3
13
1
0 IDLE
F,I, G
I
None
F,I,G F
Station 4 G
H
7
5
3
2
8
3 IDLE
H, J
None
H, J H
Station 5 J
K
4
6
2
1
11
5 IDLE
K
None
Station 6 L 7 0 8 IDLE None

STEP 7. Evaluate the efficiency of the line balance.
EFFICIENCY = (SUM OF ALL TASK TIMES)/(ACTUAL NO OF
WORKSTATIONS)X(CYCLE TIME)
= (70) / (6) X (15)
= 0.778 OR 77. 78 %

 Cars for the masses
 Cost $850
 Built new plant at Highland Park, Michigan
 Ford consulted FrederickTaylor, Creator of Scientific Management
 Installation of Gravity Slides
 December 1, 1913, the first large scale assembly line was officially launched
Assembly Line- The Ford Way

 Cars 84 Steps in the assembly line
 Interchangeable parts
 Less waste and higher quality product
 Production time dropped from over 12 hours to just 93 mins
 Produced 3,08,612 cars in 1914
 Cost of ModelT dropped to $260 in 1924
 Work time was reduced from 9 to 8 hours and wages doubled to $5 a day
Assembly Line- The Ford Way

Apparel Industry
With proper implementation of line balancing it was seen that the efficiency was further
increased.

•Technical Benefits
•Economic Benefits

 Production lines were designed so that conveyor belts paced the
speed of the employees work.This arrangement wasn't
appreciated by the employees.
 Inevitable changes lead to production lines being out of balance.
 Rebalancing causes disruptions to production

Operations Management : Line Balancing

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