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12. You have been asked to set up an assembly line to assemble a computer mouse. The
precedence network is shown in Exhibit 8.12; task times in minutes are given in
parentheses. There are 480 minutes of assembly time per shift and the company
operates one shift each day. The required output rate is forecasted to be 60 units per
shift.
Exhibit 8.12 Precedence Network for Problem 12
a. Balance the assembly line using the longest processing time rule. State the tasks
associated with each workstation, total time, and idle time.
Work Station Assigned Tasks Total Time Idle Time
(b) What is the assembly line efficiency?
(c) Is your assembly line balance solution good or bad? What criteria do you used
to make this assessment? Explain.
Equation 8.5 is Total Idle Time = N*CT – t = 5(8.0) – 32 = 8 min. The firm is
paying for 8 minutes of idle time out of every 40 minutes so this is not a good (just
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13. Balance the assembly line in Exhibit 8.13 for (a) a shift output of 60 pieces and (b)
a shift output of 40 pieces. Assume an eight-hour shift, and use the rule: choose the
assignable task with the longest processing time. Compute the line efficiency for
each case.
For an output of 60 pieces/shift, cycle time = 8(60)/60 = 8 minutes/unit. You
need to go over the cycle time calculation carefully.
Work station Tasks Total Time Idle Time
Using Equation 8.6, Efficiency = 46/[7(8)] = 82.1% The idea is to strictly
follow the ALB rule like a computer would do it. Students may also ask about
For a shift output of 40 pieces, cycle time (C) = 8(60)/40 = 12 minutes/unit
Work Station Tasks Total Time Idle Time
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Using Equation 8.6, Efficiency = 46/[4(12)] = 95.8%
14. List the ergonomic features of your automobile’s interior and discuss any
improvements that you can identify.
http://www.ccohs.ca/oshanswers/ergonomics/driving.html
Automotive designers pay much attention to ergonomics, such as placement of
controls and cup holders, ability to reach them safely and comfortably, and the
ability to see them without being distracted. The BMW interface wheel (albeit a bit
dated) caused a lot of controversy when it was introduced, and you might suggest
15. Research and write a short paper (1 page maximum) on the advantages and
disadvantages of virtual teams in today’s digital environment.
One of the major trends in business is a move toward virtual workplaces. In
In a virtual team, members are dispersed, either geographically or
Advantages of a virtual team
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Saves time and travel expenses
Eliminates moving expenses
Provides access to experts
Easier to hire and retain team members
Better accommodation to team members personal & professional lives
Disadvantages of a virtual team
Greater concern with predictability and reliability
Case Teaching Notes: BankUSA Cash Movement
Overview
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The case describes a department in the investment and trust operations area of a major
bank that processes “information-intensive transactions (wires).” Notice the ALB
problem is described for a service industry. The wires are initiated by a paper-based
process. The case analysis requires a blend of numerical analysis as well as qualitative
Case Questions and Brief Answers
1. What is the best way to group the work represented by the 16 work groups
for an average demand of 306 outgoing wires per day? What is your line balance
if peak demand is 450 wires per day? What is assembly-line efficiency for each
line balance solution?
How to group work tasks most efficiently is best done with assembly line
balancing methods. Please note that this process is best described as having
dominant line flows (i.e., a flow shop) with considerable customization per
transaction (widget). The high volumes and fair degree of customization per
The cycle time at 306 wires/day is 1.47 min/wire as shown in the case. At about
150% of average demand, the cycle time in Equation 8.2 is C = A/R or C = 1/[(306
wires/day*1.5)(1/7.5 hours/day)(1 hr./60 minutes)] = 1/1.02 = 0.98 min/wire ≈ 1
You may also want to explain to students that if demand is greater than 457
wires/day, you have to redefine the work and break the 16 steps and times into
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Work Station Tasks Total Time Idle Time
1 1 0.8 0.20
2 2 0.3 0.70
Total Time Available = (Number work stations)(Cycle Time) = N*CT = 9(1) =
9.0 min (Equation 8.4)
(8.7)
Therefore, by grouping work using assembly line balancing you need 9 people,
The resulting line balance with C = 1.47 min/wire (306 wires/day) is as
follows:
Work Station Tasks Total Time Idle Time
Total Time Available = (# work stations)(Cycle Time) = N*CT = 7(1.47) =
10.29 min (8.4)
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(8.5)
(8.7)
2. How many people are needed for outgoing wires using assembly line
balancing methods versus the current staffing level of 11 full-time equivalent
employees?
Therefore, by grouping work using assembly line balancing, you need 7
people, not 11 as currently assigned if you plan for average demand of 306
Many other “what if” scenarios are possible and left to the discretion of the
instructor. For example, you could ask what if we worked 20% faster or 20%
Eliminating the 3 rework tasks is working smarter and taking non-value added
tasks out of the process. Eliminating rework saves two or three full-time
Process Cycle No. No.
Standard Output Time Work- Direct Idle
Seven Scenarios Time/Wire Rate* (min) Stations People Time
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(6) Demand Inc. 50% 7.05 min 457 0.98 10 12
2.71
*An output rate of 450 wires per day assumes 7.5 hours/day times 60
In the spirit of continuous improvement, a 20 percent decrease in standard
3. How many staff members do you need for the outgoing wire process if
you eliminate all rework?
The next line balancing “what if” scenario assumes you eliminate the three rework
areas. If this can be done, you need only 8 people instead of the original 9 people
a) Either a 20 percent decrease in standard times or staffing to meet the average
b) A 20 percent increase in standard times has severe consequences, requiring 12
c) Eliminating rework at three steps in the process would allow the reduction of one
4. What are your final recommendations?
The student must decide on the best line balance given their assumptions. Please note
Another issue in the case is “how to handle high dollar wire customers?” The case
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a) Do an ABC analysis on dollars per wire versus customer category. Who are the
b) Do a well-designed Pareto cause and effect analysis on who causes what types of
c) Another related idea is to evaluate the advantages and disadvantages of sending
high dollar wire customers a “confirmation” that once the wire is successfully
d) High dollar wire volumes may be large enough to justify a separate dedicated high
wire process. If this topic comes up in class ask the class (a) Do we need
Other questions you may or may not want to cover include:
(1) Could you balance the assembly line using the 47 more detailed work tasks
(3) Should Cash Movement set up a separate process for high dollar wires? What
(4) How should wires be processed and sequenced? What type of information do you
(5) How would you handle the tradeoff between “control and no mistakes” versus
Teaching Plan
1. What is the best way to group the work represented by the 16 work groups for an
2. How many people are needed for outgoing wires using assembly line balancing
3. How many staff members do you need for the outgoing wire process if
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