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1. Assembly line
balancing
INTRODUCTION

2. Definition of assembly lines
 Assembly line is a sequence of work stations performing a specified
repeated tasks on a product units moving along the line at constant speed.
 Each unit of the product spends the same amount of time in every station,
this time is called cycle time.
 The sequence, in which operations must be performed, follow certain
constraints called precedence relations.

3. Assembly line balancing (ALB)
 It is the procedure concerning the assignment of tasks to work stations so
that:
• Precedence relations are respected.
• Workstation time do not exceed the cycl time.
• Minimize the total idle time.

4. Important relations
 Cycle time (C) =
𝐴𝑣𝑎𝑖𝑙𝑎𝑏𝑙𝑒 𝑤𝑜𝑟𝑘𝑖𝑛𝑔 𝑡𝑖𝑚𝑒
𝐶𝑢𝑠𝑡𝑜𝑚𝑒𝑟 𝑑𝑒𝑚𝑎𝑛𝑑 𝑜𝑟 𝑡ℎ𝑒 𝑑𝑒𝑠𝑖𝑟𝑒𝑑 𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑖𝑜𝑛
 Theoretical number of work stations (N)=
𝑆𝑢𝑚𝑚𝑎𝑡𝑖𝑜𝑛 𝑜𝑓 𝑡𝑎𝑠𝑘 𝑡𝑖𝑚𝑒𝑠
𝑐𝑦𝑐𝑙𝑒 𝑡𝑖𝑚𝑒
 Theoretical line efficiency =
𝑆𝑢𝑚𝑚𝑎𝑡𝑖𝑜𝑛 𝑜𝑓 𝑡𝑎𝑠𝑘 𝑡𝑖𝑚𝑒𝑠
𝑁∗𝐶
%
 Balance delay (BD) =1-Efficiency.
 Smoothing index (SI)= (𝑀𝑎𝑥𝑖𝑚𝑢𝑚 𝑠𝑡𝑎𝑡𝑖𝑜𝑛 𝑡𝑖𝑚𝑒 − 𝑠𝑡𝑎𝑡𝑖𝑜𝑛 𝑡𝑖𝑚𝑒)
2
 SI is preferred to be small and near zero. This indicates a perfect workload
balance.

5. Goals of ALB
 The ALB problem can be classified to different types according to the
objective as the following:
• Type-1: minimizing the total number of stations.
• Type-2: minimize the number of work stations.
• Type-3: maximize the work load balance.
• Type-E: this type is concerned with maximizing the efficiency of assembly
line by minimizing cycle time and number of stations.

6. Example
 The example below shows the tasks required for assembly of electric fan
and the time of each task and the precedence relations between tasks.
Code task time
A Assemble frame 3
B Mount switch 1
C Assemble motor housing 3.25
D Mount motor housing in frame 1.2
E Attach blade 0.5
F Assemble and attach safety grill 1
G Attach cord 1
H Test 1.4
A
C
B
D E F
G
H
2
3.25
1
1.2 .5
1
1.4
1

7.  Daily demand 100 units per day and the available working time is 420
minutes daily.
 Required cycle time (C) =
420
100
= 4.2 minutes/ unit
 Theoretical number of work stations =
𝑆𝑢𝑚𝑚𝑎𝑡𝑖𝑜𝑛 𝑜𝑓 𝑡𝑎𝑠𝑘 𝑡𝑖𝑚𝑒𝑠
𝑐𝑦𝑐𝑙𝑒 𝑡𝑖𝑚𝑒
=
11.35
4.2
=
2.702. (round up to nearest integer number = 3).

8. Station no. Task Description Predecessors Assigned
time (min)
Remaining
time
1 A
B
G
Assemble Frame
Mount Switch
Attach Cord
-
A
B
2
1
1
2.2
1.2
0.2
2 C Assemble Motor Housing - 3.25 0.95
3 D
E
F
H
Mount motor housing in
frame
Attach Blade
Assemble and attach safety
grill
Test
A,C
D
E
F,G
1.2
0.5
1
1.4
3
2.5
1.5
0.1

9. Performance criteria of the line
 Actual cycle time (realized cycle time) =4.1
 Line efficiency =
11.35
4.1∗3
= 92.27 %
 SI= 0.98

10. Thank you