Question

1. As part of a major plant renovation project, the industrial engineering department has been asked to balance a revised assembly operation to achieve an output of 240 units per eight-hour day. Task times and precedence relationships are as follows:

Task	Duration (minutes)	Immediate Predecessor
A	0.3	-
B	0.5	A
C	0.4	B
D	0.5	-
E	1.9	D
F	0.8	C
G	1.2	E, F

1. Draw the precedence diagram.
2. Determine the minimum cycle time, the maximum cycle time, and the calculated cycle time.
3. Determine the minimum number of stations needed.
4. Assign tasks to workstations on the basis of most following tasks. Use longest processing time as a tiebreaker. If ties still exist, assume indifference in choice.
5. Compute the percentage of idle time for the assignment in part d.

Answer 1

A) The precedence diagram as follows :

A	D
B
C
F	E
G

a) Minimum cycle time =0.3 minutes

Maximum cycle time = Sum of all activities = 5.6 minutes

Calculated cycle time = 8 hour of 480minutes/240 units = 2 minutes per item

b) Minimum number of stations needed

= Sum of duration of all tasks /calculated cycle time

= 5.6 /2

= 2.8 ( 3 stations rounded to nearest whole number )

c) Assignment of tasks against workstations will be done in such a way so that sum of tasks allocated to a workstation does not exceed calculated cycle time of 2 minutes

Workstation	Tasks	Total time	Idle time = calculated cycle time of 2 minutes – total time
1	A,B,C,D	03+0.5 +0.4+0.5 = 1.7	0.3
2	E	1.9	0.1
3	F,G	0.8 + 1.2 = 2	0

Percentage of idle time

= Total idle time in all workstations / ( actual number of workstations x calculated cycle time) x 100

= 0.4 /( 3 x 2) x 100

= ( 0.4/6) x 100

= 6.67%