OM5 C8
Test Bank
19. Cycle time should be smaller than the largest operation time.
20. Cycle time is related to the output rate and the available time to produce output.
21. Because of precedence relationships in a network, assembly-line efficiencies will generally
be very high.
22. Assembly-line balancing problems involving many distinct products (mixed-model line
balancing) are generally easier to solve than single-model balancing problems because there are
more alternatives available to assign tasks to workstations.
23. An assembly-line balancing minimizes the number of workstations for a given production
rate or maximizes the production rate for a given number of workstations.
24. In a process layout technique, improvement is done on a current solution by exchanging two
or three departments at a time to determine if total materials handling costs have been reduced.
25. In designing process layouts, arrangement of departments or work centers relative to each
other is a primary concern.
26. A Gallup study showed that workers who are allowed to personalize their workplaces were
no more productive than those who are not allowed.
27. Ergonomics is the science that is concerned with determining specific job tasks and
responsibilities.
28. Job enlargement approaches give workers more variety of work, but not necessarily more
responsibility.
29. Teams are a way of accomplishing job enrichment.
30. Virtual teams are empowered work teams that assume many traditional management
responsibilities.
31. Self-managed teams perform entire jobs, rather than specialized, assembly-line work.
Case Study Questions (To reward students who attend class, listen and learn, and take
good class notes on the case discussion and/or student team presentation.)
1. Which one of the following statements is TRUE regarding the BankUSA: Cash Movement
case study?
a. The cycle time for the outgoing wire process was less than 2.0 minutes per wire.
b. Commercial (business) outgoing wires used a separate process different from the one for
individual customer tractions.
c. Outgoing wire error rate data was not available in the case study.
d. The current assembly line for outgoing wires was understaffed based on assembly-line
balancing (ALB) analysis.
Problems for Manual Grading, Take-Home Exams and Partial Credit (Also, review the
OM Instructor’s Manual for end-of-chapter questions/problems)
1. Discuss four reasons for conducting a facility layout study.
1.
a new facility is constructed;
2.
there is a significant change in demand or throughput volume;
3.
a new good or service is introduced to the customer benefit package;
4.
different processes, equipment, and/or technology are installed.
2. Differentiate between product layout, process layout, cellular layout, and fixed-position
layout. State the advantages and disadvantages of each.
3. Differentiate between a flow-blocking delay and lack-of-work delay. How can each be
reduced?
4. Explain assembly-line balancing. Discuss the three types of information needed to balance an
assembly line.
OM5 C8
Test Bank
1.
The set of tasks to be performed and the time required to perform each task;
2.
The precedence relationships among the tasks—that is, the sequence in which the tasks
must be performed;
3.
The desired output rate or forecast of demand for the assembly line.
5. Describe approaches used for process layout design.
6. A product requires the following tasks to make it on an assembly line. Assume 7.6 hours per
workday and 5 workdays per week.
Task
Time (in seconds)
Predecessors
A
10
none
B
14
A
C
12
none
D
8
none
E
11
C
F
17
C, D
G
20
B
H
9
E
I
13
D
J
15
G, H
K
17
H, I
L
8
J
M
10
I
N
15
K, L, M
a.
Using only the information given, what would be the maximum output per day that can be
achieved?
b.
Assume that the activities have been assigned to five workstations. What is the line
efficiency for a cycle time of 40 seconds?
The minimum cycle time is the maximum task time, 20 seconds.
Output = (7.6 hours/day)(60 min/hour)(60 sec/min)/20 sec/unit = 1368 units per day
Assembly-line efficiency = t/(N x CT) = 179/(5 x 40) = 89.5%
7. For the following assembly-line data, balance the line for an output of 30 units in a 7.5 hour
shift. Use the “longest-task-time-first” rule.
Task
Time (in minutes)
Predecessors
A
8
none
B
1
none
C
2
none
D
3
A, B
E
3
B, C
F
2
D
G
9
E
H
6
E
I
7
F, G
J
1
H
K
3
I, J
Total
45
Station 1:
Station 2:
Station 3:
Station 4:
8. A small electronics company assembles microchips for use in computers, printers and fax
machines. They want to set up an assembly line to make their operation more efficient and plan
to use line balancing with the longest-task-time heuristic. The demand for microchips is 70 per
hour, and the productive time per hour is 52 minutes. The following table provides details on
their operation.
Task
Time (in minutes)
Predecessors
A
0.54
none
B
0.34
A
C
0.11
A
D
0.09
A
E
0.43
B, C
F
0.22
D
G
0.62
E
H
0.35
F, G
I
0.21
H
J
0.57
H
K
0.33
I, J
a.
What is the cycle time?
b.
What is the theoretical minimum number of workstations?
c.
What tasks go into the first workstation?
d.
How many workstations are needed for the entire line?
e.
What is the assembly-line efficiency?
a.
Cycle time = 54 min per hour/40 units per hour= 1.35 minutes/unit
b.
Sum of task times = 6.45 minutes
Theoretical minimum number of workstations
c.
9. A company is setting up an assembly line to produce cellular phones. They intend to use line
balancing with the longest-task-time heuristic. They know the demand per hour is 40 phones and
the productive time per hour is 54 minutes. Displayed below is the data they have collected
regarding task precedence and times.
Task
Time (in minutes)
Predecessor(s)
A
0.40
none
B
1.20
A
C
0.90
A
D
0.70
B
E
0.60
B
F
0.35
C
G
1.00
D, E
H
0.80
F, G
I
0.50
H
a.
What is the cycle time?
b.
What is the theoretical minimum number of workstations?
c.
What tasks are assigned to the first workstation?
d.
How many workstations are needed for the entire line?
e.
What is the assembly-line efficiency?
Theoretical minimum number of workstations
= [(3.81 min/unit)[(70 units/hour)/(52 min/hour)]] = 5.134 = 6 workstations
c.
Tasks A ,C, and D
d.
7 workstations
Station 1
A, C
0.65
Station 2
0.65
Station 3
E
Station 4
G
0.62
Station 5
Station 6
J
Station 7
K
0.33
Total
3.81
Efficiency = t/(N CT) = 3.81/(7 0.742) = 3.81/5.18 = 0.735 = 73.552%
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10. The nine tasks necessary to assemble a vacuum cleaner are listed below. The time to perform
each task and the tasks that must immediately precede are also listed. 300 vacuums are needed
per hour and 50 minutes per hour are productive.
Task
Time (in minutes)
Predecessors
A
0.15
none
B
0.06
A
C
0.05
B
D
0.12
B
E
0.09
B
F
0.16
B
G
0.08
C, D, E
H
0.06
G, F
I
0.05
H
a.
Compute the cycle time per unit in minutes.
b.
Compute the minimum number of workstations required.
c.
Use the longest-task-time heuristic to balance the production line.
d.
Compute the efficiency of the assembly line.
a.
Cycle time = 50/300 = 0.167 minutes per unit
Minimum number of workstations = t/CT =0.82/0.167 = 4.91 = 5 workstations
c.
Using the longest-task-time heuristic:
Efficiency = t/(N CT) = 0.82/(6 0.167) = 0.818332 = 81.83 %
11. The twelve tasks necessary to assemble a food blender are listed below. The time to perform
each task and the tasks that must immediately precede are also listed. 200 blenders are needed
per hour and 50 minutes per hour are productive:
d.
Five workstations
Efficiency = t/(N CT) = 6.45/(5 1.35) = 6.45/6.75 = 0.9556 = 95.56%
OM5 C8
Test Bank
Task
Time (in minutes)
Predecessors
Task
Time (in minutes)
Predecessors
A
0.20
none
G
0.08
E, F
B
0.05
none
H
0.12
none
C
0.15
none
I
0.05
none
D
0.06
none
J
0.12
H, I, G
E
0.03
A, B
K
0.15
J
F
0.16
C, D
L
0.08
K
a.
Compute the cycle time per unit in minutes.
b.
Compute the minimum number of workstations required.
c.
Use the longest-task-time heuristic to balance the assembly line.
d.
Compute the efficiency of your assembly line.
a.
Cycle time = 50/200 = 0.25 minutes per unit
Minimum number of workstations = t/CT = (1.25)(200)/50 = 5.0
c.
Workstation
Tasks in workstation
A, B
F, G
K, L
12. The Florida Appliance Company is installing an assembly line to produce vacuum cleaners,
and you, as an operations manager, are responsible for balancing the line. The tasks to be
performed are listed, along with their times and immediate predecessors.
Task
Time (in seconds)
Immediate Predecessor(s)
A
60
none
B
40
A
C
30
B
D
20
B
E
40
B
F
60
C
G
70
D
H
50
F, G
I
20
E
J
60
H, I
The company is planning to operate 2 shifts per day, 8 hours per shift. The desired output rate of
the line is 480 units per day.
a.
Compute the cycle time per unit in minutes.
b.
Compute the minimum number of workstations required.
c.
Use the longest-task-time heuristic to balance the assembly line.
d.
Compute the efficiency of your assembly line.
a.
Cycle time: CT = A/R = 960/480 = 2 minutes = 120 seconds per unit
Cycle time = 480/60 = 8 minutes per unit
Minimum number of workstations = t/CT = 32/8 = 4 stations
c.
Balanced line:
C
5
6
2
Efficiency = t/(N CT) = 32/(5 8) = 32/40 = 0.80 = 80%
13. John, an operations manager at Clan Corp. must set up an assembly line to assemble a
computer mouse. The precedence diagram below is defined with task times in parentheses and
stated in minutes. There are 480 minutes of assembly time per shift and there is one shift. The
forecast (output rate) is 60 units per shift.
a.
Compute the cycle time per unit in minutes.
b.
Compute the minimum number of workstations required.
c.
Use the longest-task-time heuristic to balance the assembly line.
d.
Compute the efficiency of your assembly line.
Minimum number of workstations = t/CT = 450/120 = 3.75 = 4
Workstation
workstation
Efficiency = t/(N CT) = 450/(5 120) = 450/480 = 0.75 = 75%
14. List the many questions that must be addressed while designing a workstation.
15. Explain the role of ergonomics in job design.
16. Explain the sociotechnical approach to job design and some ways to implement it.
17. Explain the three types of teams effective for job enrichment.
OM5 C8
Test Bank
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