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

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