Assembly Line Balancing

The process of equalizing the amount of work at each work station on an assembly line.

How to Balance a Line Specify the task relationships and their order

of precedence. Draw and label a precedence diagram. Calculate the desired cycle time (Cd). Calculate the theoretical minimum number of

workstations (N). Group elements into workstations recognizing

cycle time & precedence. Evaluate the efficiency of the line (E). Repeat until desired line efficiency is reached.

Order of Precedence

Joe’s Sub ShopTask Work Element Precedence Time (min)

A Receive Order — 2

B Cut Bread A 1

C Prepare Toppings A 2

D Assemble Sandwich B,C 3

E Wrap Sandwich D 1

F Deliver Sandwich E 3

Specify the task relationships and their order of precedence.

The Precedence Diagram

Draw and label a precedence diagram.

A2 min

B1 min

The Precedence Diagram

Draw and label a precedence diagram.

A2 min

B1 min

C2 min

D3 min

E1 min

F3 min

Cycle Time

Calculate the desired cycle time (Cd). If Joe’s Sub Shop has a demand of 100

sandwiches per day. The day shift lasts 8 hours.

Cd =production time available

desired units of output

Cd =8 hours x 60 minutes/hour

100 sandwiches

Cd = 4.8 minutes

Minimum Work Stations

Calculate the theoretical minimum number of workstations (N). If Cd = 4.8 minutes

N = ti

Cd

j

i =1

ti = completion time for

task i

j = number of tasks

Cd = desired cycle time

Minimum Work Stations

Calculate the theoretical minimum number of workstations (N). If Cd = 4.8 minutes

N = ti

Cd

j

i =1 N =2 + 1 + 2 + 3 + 1 + 3

4.8

N = 2.5 workstations 3 workstations

Order Work Stations Group elements into workstations

recognizing cycle time & precedence.

Joe’s Sub Shop

Workstation TaskElement

Time (min)Workstation Time (min)

1 A 2 3

B 1

2 C 2 2

3 D 3 4

E 1

4 F 3 3

Line Efficiency

Evaluate the efficiency of the line (E). If Ca = 4 minutes and n = 4 work stations.

E = ti

nCa

j

i =1

ti = completion time for

task i

j = number of tasks

Ca = actual cycle time

n = actual number of workstations

Line Efficiency

Evaluate the efficiency of the line (E). If Ca = 4 minutes and n = 4 work stations.

E = ti

nCa

j

i =1 E =2 + 1 + 2 + 3 + 1 + 3

4 * 4

E = 75.0% effective

Trial and Error Repeat until desired line efficiency is reached.

Joe’s Sub Shop

Workstation TaskElement Time

(min)Workstation Time (min)

1 A 2 4

C 2

2 B 1 4

D 3

3 E 1 4

F 3

E = 100.0% effective

Class Exercise

Task Precedence Time (min)

A — 3

B A 5

C — 2

D B,C 4

E D 2

A sample precedence chart

Class Exercise

Draw and label a precedence diagram.

A3 min

B5 min

Class Exercise

Draw and label a precedence diagram.

A3 min

B5 min

C2 min

D4 min

E2 min

Calculate the desired cycle time (Cd). If, there is a demand for 100 units to be

produced every 12 hours.

Class Exercise

Cd =production time available

desired units of output

Cd =12 hours x 60 minutes/hour

100 units

Cd = 7.2 minutes

Class Exercise

Calculate the theoretical minimum number of workstations (N). If Cd = 7.2 minutes

N = ti

Cd

j

i =1

ti = completion time for

task i

j = number of tasks

Cd = desired cycle time

Class Exercise

Calculate the theoretical minimum number of workstations (N). If Cd = 7.2 minutes

N = ti

Cd

j

i =1N =

2 + 5 + 2 + 4 + 2

7.2

N = 2.08 workstations 3 workstations

Class Exercise Group elements into workstations

recognizing cycle time & precedence.

Workstation TaskElement

Time (min)Workstation Time (min)

? A 3 ?

? B 5 ?

? C 2 ?

? D 4 ?

? E 2 ?

Class Exercise

Evaluate the efficiency of the line (E).

E = ti

nCa

j

i =1

ti = completion time for

task i

j = number of tasks

Ca = actual cycle time

n = actual number of workstations

Class Exercise The most efficient set up of the line

Workstation TaskElement

Time (min)Workstation Time (min)

1 A 3 5

C 2

2 B 5 5

3 D 4 6

E 2

E = 83.3% effective