south carolina furniture inc

8/3/2019 South Carolina Furniture Inc

1/11

A

B

C D E

G

F

H

South Carolina Furniture Inc. produces all types of office furniture. The executive

secretary is a chair that has been designed using ergonomics to provide comfort during

long work hours. The chair sells for $ 130. There are 480 minutes available during the

day, and the average daily demand has been 50 chairs. There are eight tasks:

TaskPerformance time

(min)

Task must follow

task listed below

A 4 -

B 7 -

C 6 A,B

D 5 C

E 6 DF 7 E

G 8 E

H 6 F,G

a) Draw a precedence diagram of this operation

b) What is the cycle time for this operation

c) What is theoretical minimum number of workstationsd) Assign tasks to workstations

e) How much total idle time is present each day

f) What is the overall efficiency of the assembly line

Solution

a) Precedence diagram


2/11

b) Cycle time = Production time available per day

Unit required per day

= 480 minutes

50 chairs

= 9.6 ~ 10 min/chair

c) Total task time = 4 + 7 + 6 + 5 + 6 + 7 + 8 + 6

= 49 min

Minimum number of workstations = Total task time = 49 min

Cycle time 10 min

= 4.9 ~ 5 workstations

d) Tasks to workstation

Since the tasks time in workstation must be not exceeding the cycle time. Then,

total workstation is 7.

A

B

C

D E

F

G

Station 1

4 min 6 min Station 3

5 min

Station 4

6 min

Station 5

7 minH

Station 7

6 min

Station 2

7 min

Station 6

8 min


3/11

e) Idle time

Idle times are in workstation 2 = 3 min, workstation 3 = 5 min, workstation 4 =

4min, workstation 5 = 3min, workstation 6 = 2 min, workstation 7 = 4 min and

total idle time is 21 minutes

f) Efficiency

Efficiency = (4 + 7 + 6 + 5 + 6 + 7 + 8 + 6) min = 49

(7 workstations) x (10min) 16

= 70%


4/11

Mach 10 is a one person sailboat designed to be used in ocean. Manufactured by

Creative Leisure, Mach 10 can handle 40 mph winds seas over 10 feet. The final

assembly plant is in Cupertino, California. At this time, 200 minutes are available each

day to manufacture Mach 10. The daily demand is 60 boats. Given the following

information,

a) Draw the precedence diagram and assign tasks to the fewest workstations

possible.

b) What is the efficiency of the assembly line

c) What is the theoretical minimum number of workstations

d) What is the idle time

Solution

a) Precedence diagram and fewest workstation

Cycle time = Production time available per day

Unit required per day

= 200 minutes

60 chairs

= 3.33 ~ 4 min/chair

Task Performance TimeTask must follow Task

listed below

A 1 -

B 1 A

C 2 A

D 1 C

E 3 C

F 1 CG 1 D,E,F

H 2 B

I 1 G,H


5/11

b) Efficiency of assembly line

Efficiency = (1 + 1 + 2 + 1 + 3 + 1 + 1 + 2 + 1) min = 13

(4 workstations) x (4 min) 16

= 81.25%

c) Theoretical minimum number of workstation

No of workstation = total task time = 13

Cycle time 4

= 3.25 or 4 workstations

A

C

B

D

EF

G

I

H

Station 2

Station 1

Station 3 Station 4


6/11


7/11

Dr. Lori Baker, operation manager at Nesa Electronics, prides herself on excellent

assembly line balancing. She has been told that the firm needs to complete 96

instruments per 24 hour day. The assembly line activities are:

Task Time (min) Predecessors

A 3 -

B 6 -

C 7 A

D 5 A,B

E 2 B

F 4 C

G 5 FH 7 D,E

I 1 H

J 6 E

K 4 G,I,J

a) Draw precedence diagram

b) If the daily (24- hour) production rate is 96 units, what is the highest allowablecycle time

c) If the cycle time after allowances is given as 10 minutes, what is the daily (24

hour) production rate

d) What a 10 minute cycle time, what is the theoretical minimum number of station

with which the line can be balanced

e) What a 10 minutes cycle time and six workstations, what is the efficiency

f) What is the total idle time per cycle with a 10 minute cycle time and six

workstations

g) What is the best workstation assignment you can make without exceeding a 10

minute cycle time and what is its efficiency


8/11

Solution:

a)

b) Cycle time

Cycle time = (24 hours) (60 minutes/ hours)

96 units

= 15 minutes/unit

c) Production rates

Production rates = cycle time x production units

= (10 min/unit) (96 units)

= 960 minutes

A

D

C

B

F

H

J

G

E

KI


9/11

d) Minimum workstations

No of workstation = Total time

Cycle time

= (3 + 6 + 7 + 5 + 2 + 4 + 5 + 7 + 1 + 6 + 4) min

10 min

= 5 workstations

e) Efficiency

Efficiency = 50 min

(6 workstations) (10 min/units)

= 83.33%


10/11

f) Workstations

Idle times are in workstation1 = 1 min, workstation 2 = 3 min, workstation 3 = 1

min, workstation 4 = 1 min, workstation 5 = 3 min, workstation 6 = 1 min and total

idle time is 10 minutes

A

B

C

D

F

K

H

G

I

E J

Station 1

3 min

6 min

Station 2

7 min

Station 3

4 min

5 min

Station 4

7 min

2 min

Station 5

1 min

6 min

Station 6

5 min

4 min


11/11

g) the best workstation assignment you can make without exceeding a 10 minute

cycle time and its efficiency

Efficiency = 50 min

(6 workstations) (9 min/units)

= 92.6%

A

B

C

D

F

KH

G

I

E J

Station 1

3 min

6 min

Station 2

7 min

Station 3

4 min

5 min

Station 4

7 min 1 min

Station 5

2 min 6 min

Station 6

5 min

4 min

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