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Q:
Q:
Which of the following is true regarding the process capability index Cpk?A) A Cpk index value of 1 is ideal, meaning all units meet specifications.B) The larger the Cpk, the more units meet specifications.C) The Cpk index can only be used when the process centerline is also the specification centerline.D) Positive values of the Cpk index are good; negative values are bad.E) None of the above is true.
Q:
A Cp of 1.33 indicates how many sigma limitsA) 1B) 1.33C) 2D) 3E) 4
Q:
The process capability measures Cp and Cpk differ becauseA) only one ensures the process mean is centered within the limitsB) Cp values above 1 indicate a capable process, Cpk values above 2 indicate a capable processC) both are identicalD) Cp values for a given process will always be greater than or equal to Cpk valuesE) both A and D
Q:
A run test is usedA) to examine variability in acceptance sampling plansB) in acceptance sampling to establish controlC) to examine points in a control chart to check for natural variabilityD) to examine points in a control chart to check for nonrandom variabilityE) none of the above
Q:
Q:
Q:
Q:
The c-chart signals whether there has been aA) gain or loss in uniformityB) change in the number of defects per unitC) change in the central tendency of the process outputD) change in the percent defective in a sampleE) change in the AOQ
Q:
Q:
The normal application of a p-chart is inA) process sampling by variablesB) acceptance sampling by variablesC) process sampling by attributesD) acceptance sampling by attributesE) none of the above
Q:
Which of the following is true of a p-chart?A) The lower control limit is found by subtracting a fraction from the average number of defects.B) The lower control limit indicates the minimum acceptable number of defects.C) The lower control limit equals D3 times p-bar.D) The lower control limit may be at zero.E) The lower control limit is the same as the lot tolerance percent defective.
Q:
According to the text, the most common choice of limits for control charts is usuallyA) 1 standard deviationB) 2 standard deviationsC) 3 standard deviationsD) 3 standard deviations for means and 2 standard deviations for rangesE) none of the above
Q:
Q:
Plots of sample ranges indicate that the most recent value is below the lower control limit. What course of action would you recommend?A) Since there is no obvious pattern in the measurements, variability is in control.B) One value outside the control limits is insufficient to warrant any action.C) Lower than expected dispersion is a desirable condition; there is no reason to investigate.D) The process is out of control; reject the last units produced.E) Variation is not in control; investigate what created this condition.
Q:
A manager wishes to build a 3-sigma range chart for a process. The sample size is five, the mean of sample means is 16.01, and the average range is 5.3. From Table S6.1, the appropriate value of D3 is 0, and D4 is 2.115. The UCL and LCL for this range chart areA) 33.9 and 11.2B) 33.9 and 0C) 11.2 and 0D) 6.3 and 0E) 31.91 and 0.11
Q:
The usual purpose of an R-chart is to signal whether there has been aA) gain or loss in dispersionB) change in the percent defective in a sampleC) change in the central tendency of the process outputD) change in the number of defects in a sampleE) none of the above
Q:
Q:
The mean and standard deviation for a process for which we have a substantial history are= 120 and u03c3 = 2. For the x-bar chart, a sample size of 16 will be used. What is the mean of the sampling distribution?A) 1/8 (0.125)B) 7.5C) 2D) 40E) 120
Q:
The p-chart tells us whether there has been aA) gain or loss in dispersionB) change in the percent defective in a sampleC) change in the central tendency of the process outputD) change in the number of defects in a sampleE) none of the above
Q:
The type of inspection that classifies items as being either good or defective isA) variable inspectionB) attribute inspectionC) fixed inspectionD) all of the aboveE) none of the above
Q:
A manager wants to build 3-sigma control limits for a process. The target value for the mean of the process is 10 units, and the standard deviation of the process is 6. If samples of size 9 are to be taken, the UCL and LCL will beA) -8 and 28B) 16 and 4C) 12 and 8D) 4 and 16E) 8 and 12
Q:
Up to three standard deviations above or below the centerline is the amount of variation that statistical process control allows forA) Type I errorsB) about 95.5% variationC) natural variationD) all types of variationE) assignable variation
Q:
Q:
A high school senior is seeking admission into her state's flagship university. The admission requirements are as follows. The student must meet at least ONE of the criteria A, B, C. The student must meet criterion D. These criteria are detailed below. And the student must file a complete application, file a medical form, and pay an application fee by a stated date.
A: score a composite 28 on the ACT exam
B: have a high school GPA of 3.0 or greater
C: place in the top ten percent of the high school class
D: complete all courses in the state-mandated "core college preparatory" curriculum (CCPC); OR complete all but one course in CCPC with a 3.5 GPA on all CCPC courses taken.
Using the tools of reliability analysis with redundancy, translate these conditions into the appropriate reliability schematic.
Q:
Consider a product that is "settled in." Its MTBF distribution has been found to be normal with a mean of 1,000 hours and a standard deviation of 250 hours. What is the probability of a breakdown before 750 hours? Before 500 hours? Would you prefer a policy of preventive maintenance, or a policy of breakdown maintenance, on this product? Explain your choice.
Q:
A product design team is preparing to build a new doohickey. A doohickey consists of one A module, one B module, and one C module. There are different versions of these modules available in the company's design library. For example, there are two choices for A: A1 is .99 reliable, while A2 is .975 reliable. The table below details the choices available, along with the cost of each choice. Module variation
Reliability
Cost, each A1
.99
$17 A2
.975
$10 B1
.995
$4 B2
.992
$3 C1
.98
$2 C2
.90
$0.50 C3
.60
$0.25 Help the design team by selecting the least costly version of a doohickey that has system reliability of at least .96. Draw a schematic of your finished design.
Q:
A manufacturing firm wants to apply 6-sigma standards to its automated tolerance-check process. Suppose that each scanner makes the correct decision only 50% of the time, however only 1 correct decision by any scanner makes the entire process a success. How many scanners are needed to ensure 6-sigma quality?
Q:
Suppose that a three stage process in a nuclear reactor had reliability ratings of .98 at each station and that only one stage needed to be successful for the process to work. If the plant wants to establish 6-sigma standards, what % reliable redundant controls need to be added to each station.
Q:
Suppose that a three stage process had reliability ratings of .7, .8, and .9 at each station and that a failure at any station represented a failure for the entire process. If each station is given a redundant check with .9 reliability, what is the increase in system reliability?
Q:
Suppose that a manufacturing plant is considering contracting out some preventative maintenance work. For $2000 each year a firm would cover all breakdowns free of charge and provide preventative maintenance. Two other options exist that entail the use of regular employees however. The first is to skip preventative measures and simply fix breakdowns, which occur at a rate of 2/year. Each breakdown costs about $750 to fix. The final option is to divert excess labor capacity to preventative measures, which reduces the chance of a breakdown per year by Y% given X hours of preventative maintenance subject to Y=10X-X^2. If each preventative maintenance hour costs $50, which option should the firm choose?
Q:
Suppose that a car mechanic offers you a deal that for the next 3 years any breakdowns will be covered, so long as you bring your car in for $50 preventative maintenance sessions each month. If you predict the likelihood of a breakdown being 25% without the maintenance, how much must a breakdown cost for you to prefer the preventative maintenance?
Q:
Consider a product that is "settled in." Its MTBF distribution has been found to be normal with a mean of 10,000 hours and a standard deviation of 100 hours. What is the probability of a breakdown before 8,000 hours? Before 9,000 hours? Would you prefer a policy of preventive maintenance, or a policy of breakdown maintenance, on this product? Explain your choice.
Q:
Which product design below has the higher system reliability?
Q:
Which product design below has the higher system reliability?
Q:
General Grant must send orders to General Butler. Carrier pigeons are the medium of choice. A single pigeon has a .7 probability of arriving at the proper destination in a timely fashion. How many pigeons, each carrying an identical set of orders, must Grant send in order for him to have 98% confidence that the orders reached General Butler?
Q:
A component must have reliability of .9925. Two technologies are available for this component: one produces a component with .999 reliability at a cost of $2000. Another produces a component with .73 reliability at a cost of $450. Which is cheaper: one high quality component or a parallel set of inferior components?
Q:
A product has three components X, Y, and Z. X has reliability of 0.991; Y has reliability of 0.993. If Z has reliability of 0.991, what is the reliability of the entire product? Can Z be redesigned to be reliable enough for the entire product to have reliability of 0.99? Explain.
Q:
A product has four components A, B, C, and D. The finished product must have a reliability of .95. The first three components come from a supplier, and have reliabilities of .99, .98, and .995. The fourth component is being designed now. What must the reliability of component D be in order to meet the product reliability condition?
Q:
A simple electrical motor has three components: windings, armature, and housing. These three components have reliabilities of .97, .992, and .999. There is no possibility of redundant parts. The motor must have an overall reliability of 0.980, according to the product line manager who will use the motor as an input. What would you do to redesign the motor to meet this specification? Discuss, including a recalculation to meet the standard.
Q:
A simple electrical motor has three components: windings, armature, and housing. These three components have reliabilities of .9998, .9992, and .9999. There is no possibility of redundant parts. What is the reliability of the motor? Round your answer to four decimal places.
Q:
The academic service commonly referred to as "registration" consists of several smaller components: advising, registration for courses, fee assessment, financial aid calculations, and fee payment. Each of these modules operates independently and has some probability of failure for each student. If the five probabilities which accompany these services are 95%, 90%, 99%, 98%, and 99%, what is the "reliability" of the entire product from the student's perspectivethe probability that all five will work according to plan?
Q:
The Everstart is a battery with an intended design life of 72 months. Stephanie Bradley recently put five of these batteries through accelerated testing (the company couldn't wait six years) to simulate failure patterns. The test results had one failure at 26 months, one failure at 32 months, one failure at 50 months, and one failure at 62 months. Calculate FR(%), FR(N), and MTBF.
Q:
Century Digital Phone advertises phone battery life (on standby) of up to three days. The standard deviation is thought to be five hours. Tina Talbot, an employee at CDP, tested 10 of these batteries for 72 hours. One failed at 40 hours; one failed at 62 hours; one failed at 70 hours. All others completed the test. Calculate FR(%), FR(N), and MTBF.
Q:
The diagram below identifies the elements of service as provided by a soft drink vending machine. Each element has an estimate of its own reliability, independent of the others. What is the reliability of the "system"?
Q:
Tiger Island Fabricators, which builds offshore oil platforms, has been experiencing problems with its profiling machine, a computer-driven device that cuts the ends of pipe so that it can be welded to another pipe, as shown in the data below. Number of breakdowns
0
1
2
3
4
5 Breakdown frequency
2
2
2
6
7
1 Each time a machine breaks down, the company loses about $3,000. If the company implements preventive maintenance, it will be able to reduce the number of breakdowns to one per month. Preventive maintenance costs would be $500 a month. Is preventive maintenance a cost-effective option?
Q:
A system has six components in series. Each component has a reliability of 0.99. What is the reliability of the system?
Q:
A system consists of four components in series. The reliability of each component is 0.96. What is the reliability of the system?
Q:
A system has four components in a series. What is the reliability of the system? Component
1
2
3
4 Reliability
.90
.95
.90
.99
Q:
Great Southern Consultants Group's computer system has been down several times over the past few months, as shown below. Number of breakdowns
0
1
2
3
4 Monthly frequency
9
2
4
4
1 Each time the system is down, the firm loses an average of $400 in time and service expenses. They are considering signing a contract for preventive maintenance. With preventive maintenance, the system would be down on average only 0.5 per month. The monthly cost of preventive maintenance would be $200 a month. Which is cheaper, breakdown or preventive maintenance?
Q:
Given the following data, find the expected breakdown cost. The cost per breakdown is $100. Number of breakdowns
0
1
2
3 Monthly frequency
5
20
23
2
Q:
Given the following data, find the expected breakdown cost. The cost per breakdown is $200. Number of breakdowns per week
0
1
2
3
4 Weekly frequency
5
12
10
18
5
Q:
A product is composed of a series connection of four components with the following reliabilities. What is the reliability of the system? Component
1
2
3
4 Reliability
.90
.95
.97
.88
Q:
Ten high-intensity bulbs are tested for 100 hours each. One failed at 40 hours; another failed at 70 hours; all others completed the test. Calculate FR(%), FR(N), and MTBF.
Q:
Ten high-intensity bulbs are tested for 100 hours each. One failed at 10 hours; all others completed the test. Calculate FR(%), FR(N) and MTBF.
Q:
Ten high-intensity bulbs are tested for 100 hours each. One failed at 40 hours; all others completed the test. Calculate FR(%) and FR(N).
Q:
How do expert systems improve maintenance systems?
Q:
What is the primary concept of total productive maintenance (TPM)? List the other elements of total productive maintenance.
Q:
Under what conditions is preventive maintenance likely to be appropriate?
Q:
How do many electronic firms deal with infant mortality in their products?
Q:
Is there an optimal amount of preventive maintenance? What caution should be exercised before calculating this optimal amount?
Q:
Why is it that many cost curves associated with maintenance rarely consider the full cost of a breakdown?
Q:
Explain why a small standard deviation of the MTBF distribution makes a product, machine, or process a good candidate for preventive maintenance while a large standard deviation does not.
Q:
What is breakdown maintenance?
Q:
What is FR(N)? How is it calculated? How are FR(N) and MTBF related?
Q:
"High reliability can be achieved in a product without having high reliability in the component parts. In fact, any reliability target, no matter how high, can be achieved with only mediocre parts, so long as enough of them are present." Discuss; an example may help.
Q:
Why is it that many cases of infant mortality of products are not due to product failure?
Q:
Explain carefully how redundancy improves product reliability.
Q:
Increasing the number of parts or components in a product tends to reduce its reliability. Why is this true only when adding components in series?
Q:
What is the impact on system reliability of adding parts or components in parallel?
Q:
Define maintenance.
Q:
Define reliability.
Q:
Identify the two reliability tactics and the two maintenance tactics.
Q:
What is the role of people, especially empowered employees, in an effective maintenance strategy?
Q:
Describe how Orlando Utilities Commission obtains competitive advantage through its maintenance practices.
Q:
__________ combines total quality management with a strategic view of maintenance from process equipment design to preventive maintenance.
Q:
The __________ takes into account such costs as deteriorated customer relations and lost sales.
Q:
__________ is the failure rate early in the life of a product or process.
Q:
__________ is a plan that involves routine inspections, servicing, and keeping facilities in good repair to prevent failure.
Q:
__________ is the use of a component in parallel to raise reliabilities.