Question

An assembly line is to operate eight hours per day with a desired output of 240 units per day. The following precedence diagram contains information on this product’s task times and precedence relationships.

What is the efficiency of your line balance, assuming it is running at the cycle time from part (a)?

Determine the theoretical minimum number of workstations required (the actual number may be greater).

60 60

Answer 1

CYCLE TIME = OPERATING TIME / DESIRED OUTPUT

TOTAL OPERATING TIME = 8 * 60 * 60 = 28800

CYCLE TIME = 28800 / 240 = 120

THEORETICAL NUMBER OF WORKSTATIONS REQUIRED = SIGMA(TASK TIMES) / CYCLE TIME

N = (60 + 80 + 20 + 50 + 90 + 30 + 30 + 60) / 120 = 4

ASSIGNED USING PRECEDENCE RELATIONSHIP

WORKSTATION	ASSIGN TASK	TASK TIME	TIME REMAINING	IDLE TIME
1	A	60	60
	D	50	10	10
2	B	80	40
	C	20	20	20
3	E	90	30
	F	30	0	0
4	G	30	90
	H	60	30	30

TOTAL IDLE TIME = 60

EFFICIENCY = (1 - (SIGMA(IDLE TIME) / (NUMBER OF WORKSTATIONS * CYCLE TIME))) * 100

EFFICIENCY = (1 - (60 / (4 * 120))) * 100 = 87.5