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Design for Quality and Product Excellence 32
26. Bestronics has a three-step process for processing customer sales. First, the cashier must
look up the customer’s loyalty card on the company’s information system. Second, the
cashier enters the transaction on the point-of-sale register. Third, the cashier processes
the credit card through a verification system.
a. If the reliability of the information system is 0.998, the reliability of the point-of-sale
register is 0.992 and the reliability of the credit card verification system is 0.978, what is
the overall system reliability?
b. If the store manager wants to ensure at least a 98 percent system reliability, make a
recommendation of how to do this.
Answer
26. a) RaRbRc = (0.998)(0.992)(0.978) = 0.968
27. Manuplex, Inc. has a complex manufacturing process, with three operations that are
performed in series. Because of the nature of the process, machines frequently fall out of
adjustment and must be repaired. To keep the system going, two identical machines are
used at each stage; thus, if one fails, the other can be used while the first is repaired (see
accompanying figure).
Design for Quality and Product Excellence 33
The reliabilities of the machines are as follows:
Machine Reliability
A 0.85
B 0.92
C 0.90
a. Analyze the system reliability, assuming only one machine at each stage (all the
backup machines are out of operation).
b. How much is the reliability improved by having two machines at each stage?
Answer
28. An automated production system at Autoprod, Inc. consists of three operations: turning,
milling, and grinding. Individual parts are transferred from the prior work center to this
production system by a robot. Hence, if the robot fails or one machine goes down, the
process stops.
a. If the reliabilities of the robot, turning center, milling machine, and grinder are 0.994,
0.980, 0.95, and 0.88, respectively, what is the reliability of the system?
b. Suppose that two grinders are available and the system does not stop if one fails. What
is the reliability of the system?
Answer
29. CajaGigante, a large department store, has a very successful and profitable package
wrapping department. The department uses two very complex bow-making machines that
work inline to make the bows for the packages. There is one skilled operator who knows
how to operate the machines. She had been very reliable, but recently has had increasing
health problems which caused her to miss work about 10 percent of the time. Bow-
making Machine #1 has a reliability of 97%. Machine #2 has a reliability of 90 percent.
a. What is the current reliability of the system, including the operator?
b. Management is considering either scrapping Machine #2 and replacing it with a new
#2 machine which is 97 percent reliable, at a cost of $5,000, or training another operator
to fill in when the first operator is absent, at a cost of $5,100. The prospective trainee has
an excellent attendance record and has only been absent 4 days out of 250 work days for
the department, last year. Management estimates that profits from the department would
increase by$6,000 per year, if the bow-making line operated at 100 percent of capacity. If
Design for Quality and Product Excellence 34
management wants to pay off its investment in the first year, determine the expected net
profit for each alternative, and recommend which one will be the most profitable to
management.
Answer
b) Alternatives
30. National Partamiento installs and maintains thousands of refrigerators and other
appliances in rental apartments across the country. They have conducted a short study of
failure rates based on following the performance of 25,440 refrigerators that were
installed during one month a year ago. The table found in the worksheet tab Prob.7-30 in
the Excel file C07Data on the Student Companion Site contains the data. The data show
the number of failures of these 25,440 refrigerators each month over the past year.
a. Compute the average failure rate, . Is the failure rate relatively constant each month?
b. Use regression analysis to predict future failures. What is the predicted number of
failures each month for the next two years (that is, through month 36)?
c. If the refrigerators are typically under a 36-month warranty, how many cumulative
failures would be predicted in 36 months? What percentage of the total does this
represent?
d. What are the strengths and limitations of using regression analysis for such reliability
predictions in this setting?
Answer
a. The average failure rate is λ = 199 failures / (1708 + [24241 X 12]) unit operating
months) = 0.000680109 average failures per month
Design for Quality and Product Excellence 35
The total unit operating months are
Design for Quality and Product Excellence 36
The predicted number of failures each month for the next two years (that is, through month 36),
based on the regression formula of: Y = -2.257575 + 2.898601 * (months in service) is as
follows:
Months in
Service
Number
Installed
Number
Failed
Number Not
Failed
Cumulative
Failures
13
24241
35
24206
234
14
24206
38
24168
272
22
23818
62
23756
684
23
23756
64
23692
748
24
23692
67
23625
815
25
23625
70
23555
885
26
23555
73
23482
958
27
23482
76
23406
28
23406
79
23327
29
23327
82
23245
30
23245
85
23160
31
23160
88
23072
32
23072
90
22982
33
22982
93
22889
34
22889
96
22793
35
22793
99
22694
36
22694
22592
15
24168
41
24127
313
16
24127
44
24083
357
17
24083
47
24036
404
18
24036
50
23986
454
19
23986
53
23933
507
20
23933
56
23877
563
21
23877
59
23818
622
Design for Quality and Product Excellence 37
c. The trend that is evident from the data is the increasing number of units which failed.
Number
installed
Cumulative
No. of
failures
Number
not failed
% failures
d. The danger in using regression to forecast both number installed and the number of
units failed is primarily in assuming that these two trends are linear (straight line). Since
many failure rate curves have the “bathtub” shape, it follows that the percentage of
failures might increase at an increasing rate in the months following the first or second
year.
25
30
35
0 2 4 6 8 10 12 14
Months in Service
Months in Service Line Fit Plot
Design for Quality and Product Excellence 38
SUGGESTIONS FOR PROJECTS, ETC.
1. Customer attributes and technical requirements might be:
Attributes Technical Requirements
a. Book purchase:
Hours Schedule of open hours
Organization By dept./course/professor
Pre–processing availability Reservations on Internet
Ease of payment Cash, check, credit card
personnel to solve problems
b. Registration:
Convenience Time, dates, Internet, phone
Speed Process standards
personnel to solve problems
c. Hotel room – business:
Convenience Business location , dates, methods
Speed – check in/out Process standards, system knowledge
Technology FAX, Internet connection
d. Hotel room – family:
Convenience Location near recreation, moderate
dining facilities, dates, methods
Speed – check–in Process standards, system knowledge
2. Customer requirements would likely include freshness, taste, consistency, appearance of the
product; knowledge, attentiveness, friendliness of customer service personnel; speed and
accuracy of the cooks and order fillers; accuracy and friendliness of the counter personnel.
Technical requirements might be explored to determine what would be required to deliver
the product to in-house versus delivery customers. The former would require wait staff
training in customer service techniques, while the latter would require knowledgeable
drivers substituting (in some ways) for wait staff. Technology for deliver orders would
Design for Quality and Product Excellence 39
involve equipment to receive orders via FAX machines or over the Internet. Regarding
cooks and order fillers (common to both in-house and external product delivery), how much
of the assembly of the pizza should be done by hand (versus machine-made or machine
assisted)? This is merely suggestive of the types of questions concerning customer and
technical requirements that students should consider. Construction of the House of Quality
is left to the student.
3. For a glider the following customer attributes and technical requirements might be:
Attributes Technical Requirements
Ease of assembly “Design for assembly”; Simple instructions
4. The best way to prioritize the voice of the customer would be to have a focus group of
typical customers, such as craftspeople, “do-it–yourselfer’s”, hobbyists to provide input on
HOUSE OF QUALITY MATRIX
FOR A SIMPLE SCREWDRIVER
Price
Interchg
Bits
Steel
Shaft
Rubber
Grip
Ratchet
Capabil.
Plastic
Handle
Easy to use
Does not rust
Durable
Comfortable
Versatile
Inexpensive
Priority
3
1
6
5
2
4
• = Very strong relationship
= Strong relationship
= Weak relationship
Design for Quality and Product Excellence 40
5. Answers will vary, depending on the service processes chosen by the students. The case on
ANSWERS TO CASE QUESTIONS
Case – The Elevator Dilemma
The wall of bookcases and file cabinets approach is not a feasible solution for the long term!
The engineers need to be taught the basics of concurrent engineering and design for
manufacturability. Concurrent engineering involves multifunctional teams, usually consisting
of 4 to 20 members and including every specialty in the company. The functions of such
teams are to perform and coordinate the activities in the product development process
simultaneously, rather than sequentially. Designers must pay particular attention to cost,
Case – Applying Quality Function Deployment to a University Support Service
1. The answer to the question of whether students agree or disagree with the relative
importance rankings obtained from the study of the RRC at Tennessee Tech ultimately
depends on students’ opinions. However, a strong case might be made that the relative
importance score would depend on the situation. For small, rush, duplicating jobs, prompt
2. Concentrating on the top four characteristics, the following weighted scores can be
calculated:
Design for Quality and Product Excellence 41
Resources (personnel) 135
Customer handling 68
3. Given the high ranking of resources (personnel), it appears that more attention should be
paid to selection and retention issues. Information handling, in second place, also has a
Case – Black Elk Medical Center
1. The next steps would include gathering data using the checklist form that the committee
2. The data from the checklist should be put into a format, perhaps in a spreadsheet, where it
3. Improved processes and systems should be developed based on analysis of the checklist
Instructor Reserve Materials
