1. Line
Balancing
Operations Management

2. Introduction
 While looking at product layout there are
many aspects to focus on.
 Production Lines, Product design, Market
demand, number of workers, technology
or machines.
 This info is provided by line balancing.

4. Line Balancing
 Line Balancing is levelling the workload across
all processes in a cell or value stream to
remove bottlenecks and excess capacity.
 A constraint slows the process down and
results if waiting for downstream operations
and excess capacity results in waiting and
absorption of fixed costs.
 Emphasis on Workstation and Work Center.

5. Important Terms
 Tasks
 Task Precedence
 Task Times
 Cycle Time
 Productive Time Per Hour
 Number of work stations working
 Minimum number of workstations = sum of all
tasks * demand per hr / productive time per
hour
 Actual number of workstations
 Utilization = min no of workstations / actual no
of stations

6. Line Balancing Heuristics
 Methods used to develop solutions for
product layout problems.
1. Incremental Utilization Heuristic – adds
task to a workstation one at a time until
100% is utilized
2. Longest Task Time Heuristic – where the
task that takes the longest time is added
in the precedence diagram.

7. The Process
1. Determine the tasks to be performed
2. Determine the order
3. Formulate a precedence diagram
4. Estimate the time
5. Calculate Cycle Time
6. Calculate Minimum Workstations
7. Use the heuristics to assign tasks

8. Example. Problem 1
Incremental Heuristic
 Textech a large electronic manufacturer
assembles a model AT75 handheld calculator
at its Midland , Texas Plant.
 The assembly tasks that must be performed on
each calculator are given below;
 The parts used in this assembly line are supplied
by materials handling personnel to part bins
used in each task. The assemblies are moved
along by belt conveyors between workstations.
 Textech wants this assembly line to produce
540 calculators per hour.

9. A. Compute the cycle time per calculator in
minutes.
B. Compute the minimum number of workstations
C. How would you combine the tasks into
workstations to minimize idle time.? Evaluate
your proposal.
Here we need to note that an average of 6 mins
per hour In this example is not productive due
to lunch, personal time, machine break
down, and start up and shut down time.

10. Tasks Task details Tasks that must Time to perform
be immediately task (in minutes)
proceed
A Place circuit frame on Jig 0.18
B Place Circuit No 1 into A 0.12
frame
C Place Circuit No 2 into A 0.32
frame
D Place circuit No 3 A 0.45
E Attach circuits to frame B,C,D 0.51
F Solder circuit connections E 0.55
to central circuit control
G Place circuit assembly in F 0.38
calculator inner frame
H Attach circuit assembly to G 0.42
calculator inner frame

11. I Place and attach display H 0.30
J Place and attach keyboard I 0.18
K Place and Attach top body J 0.36
L Place and attach power K 0.42
assly
M Place and attach bottom K,L 0.48
body
N Test circuit integrity M 0.30
O Place calculator and N 0.39
printed matter in box
Total 5.36

12. a.)Compute the cycle time per calculator:
Cycle Time = Productive time per Hr / Demand Per Hr
=54 minutes per Hr / 540
= 0.100 min per hr
b.) Compute the minimum number of workstations:
Minimum no of workstations = sum of task times *Demand per /
Productive time per Hr
= 5.36 minutes per calculator x 540 cal per
hr / 54 minutes per hr
= 53.60 workstations .

13. Precedence Diagram

14. Work tasks Min/calc No of work Actual no. Utilisation
centre (2) (3) stations = of work (%)
(1) (3)/ cycle stations Col 4/col
time 5*100
1 A .18 1.8 2 90
A,B .18 +.12= .3 3 3 100
2 C .32 3.2 4 80
C,D .32+.45=.77 7.7 8 96.3
C,D,E 1.28 12.8 13 98.5
C,D,E,F 1.83 18.3 19 96.3
3 F .55 5.5 6 91.7
F,G .55+.38=.93 9.3 10 93
F,G,H,I 1.65 16.5 17 97.0
F,G,H,I,J 1.83 18.3 19 96.3
4 J,K,L,M,N,O 2.13 21.3 22 96.8
Total 55

15. Explanation of Task allotment
 If we look at work center 1 and note that we first
consider task A alone = (1.8/2.00) x 100 = 90%;
next we consider A and B together (3.0/3.0) x 100
= 100 %. Because this combination has a 100%
utilization tasks A and B are together combined to
work center 1 and we move on work center 2.
 In work center 2 as tasks C , D and E are
combined one task at a time the work utilization
increases from 80 % to 96.3% and to 98.5 % , but
when task F is added to C,D, and E , utilization
comes down to 96.3%. Work center therefore
includes tasks C,D and E and we go on to work
center 3.

16. Summary of tasks in work
stations
Tasks in work A,B C,D,E F,G,H,J J,K,L,M,N,O
centers
1 2 3 4
WORK
CENTERS
3 13 17 22
Actual no of ( 55 total)
work stations

17. Efficiency of the proposal
 Utilization
= minimum no of work stations /
actual no of work stations
= 53.6 / 55
= 97.5%

18. Example. Problem 2
Long time task heuristic
Task Immediate predecessor Task time (minutes)
A - 0.9
B A 0.4
C B 0.6
D C 0.2
E C 0.3
F D,e 0.4
G F 0.7
H G 1.1
Total 4.6

19.  Using the above information ;
 Draw a precedence diagram
 Assuming that 55 minutes per hour are
productive, compute the cycle time needed to
obtain 50 units per hour.
 Determine the minimum number of workstations.
 Assign tasks to workstations using the longest task
time heuristic.
 Calculate the utilization of the solution in part d

20. Precedence diagram
D
A B C F G H
E

21.  Assumingthat 55 minutes per hr are
productive, compute the cycle time
needed to obtain 50 units per hour.
cycle time = productive time per hr /
demand per hr
= 55 min per hr / 50 Products per hour
=1.1 minute per product

22.  c. Determine the min.no of workstations;
Min.no.of workstations = sum of all task times x
demand per hour / productive time per hour
= 4.6 mins per product x 50 products per hour / 55
mins per hour
= 4.2 workstations

23. Assign tasks to workstations using the LTT
heuristic;
Workstation Candida Task Task time Sum of (6)
te list task times Unassigned task
time at
(1) (2) (3) (4) (5) workstations
(1.1-(5)
1 A A 0.9 0.9 0.2
2 B B 0.4 0.4 0.7
2 C C 0.6 1.0 0.1
3 D,e E 0.3 0.3 0.8
3 D D 0.2 0.5 0.6
3 F F 0.4 0.9 0.2
4 G G 0.7 0.7 0.4
5 H H 1.1 1.1 0

24.  Task „e‟ is chosen ahead of „d‟ because its
task time is longer
 To Summarize the assignment of tasks to
work stations on the production line
 Tasks in workstations workstations
A 1
B, C 2
E, D, F 3
G 4
H 5

25.  Calculate the utilization of the solution
 Utilization = Minimum No .of workstations /
actual no of workstations x 100
= 4.2 / 5 x 100
= 84 %

26. Limitations of Line Balancing
 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

27. Conclusions
 The classic example is Henry Ford‟s auto
chassis line.
• Before the “assembly line Balancing”
was introduced in 1913, each chassis
was assembled by one worker and
required 12.5 hours.
• Once the new technology was
installed, this time was reduced to 93
minutes.