South Carolina Furniture Inc

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: Performance time

Task must follow

(min)

task listed below

A

4

-

B

7

-

C

6

A,B

D

5

C

E

6

D

F

7

E

G

8

E

H

6

F,G

Task

a) Draw a precedence diagram of this operation b) What is the cycle time for this operation c) What is theoretical minimum number of workstations d) 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 A

F C

B

D

H

E G

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

Station 1 A 4 min

C 6 min

Station 3 D 5 min

Station 2

Station 4 E 6 min

Station 5 F Station 7 7 min Station 6

H 6 min

G 8 min

B 7 min

Since the tasks time in workstation must be not exceeding the cycle time. Then, total workstation is 7.

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)

= 70%

16

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 Task must follow Task

Task

Performance Time

A

1

-

B

1

A

C

2

A

D

1

C

E

3

C

F

1

C

G

1

D,E,F

H

2

B

I

1

G,H

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

listed below

Station 2

Station 3

C

Station 4

D

G

Station 1 A

E

F

I

H

B

b) Efficiency of assembly line

Efficiency = (1 + 1 + 2 + 1 + 3 + 1 + 1 + 2 + 1) min = 13 (4 workstations) x (4 min)

= 81.25%

c) Theoretical minimum number of workstation

No of workstation = total task time = 13 Cycle time

4

=3.25 or 4 workstations

16

d) Idle time Station 2

Station 4 D

Station 1

G Station 3 1 min

1 min

C

E A

2 min

I

3 min F

1 min

1 min

1 min B 1 min

H 2 min

Idle times are in workstation 1 = 1 min, workstation 2 = 1 min, workstation 3 = 1min and total idle time is 3 minutes

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

F

H

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 allowable cycle 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

Solution:

a)

A

B

C

F

G

D

H

I

E

J

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

K

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%

f) Workstations

Station 1

Station 2

A

C

3 min

Station 3

Station 6

F

7 min

G

4 min D

5 min Station 4

Station 5

H

5 min

I

7 min B 6 min

E 2 min

K 4 min

1 min J 6 min

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

g) the best workstation assignment you can make without exceeding a 10 – minute cycle time and its efficiency Station 1

Station 2

A

C

F

7 min

4 min

3 min

Station 3

Station 6 G 5 min Station 4

D

H

5 min

7 min

B

E

6 min

2 min

Efficiency =

50 min (6 workstations) (9 min/units)

= 92.6%

I

Station 5

1 min J 6 min

K 4 min