Operations Management 303 chp10 – Flashcards

The more effective and all-encompassing a firm's quality control and continuous improvement efforts, the less that company will need to rely on: A. insourcing. B. inspection. C. acceptance sampling. D. capability assessment. E. outsourcing.

Low-cost, high-volume items often require more intensive inspection than other types of items. A. True B. False

_______ variation is a variation whose cause can be identified. A. Controllable B. Theoretical C. Random D. Assignable E. Statistical

Quality control, in contrast to quality assurance, is implemented: A. before inspection. B. after production. C. during production. D. by top management. E. by self-directed teams.

Quality control tools are not really used to fix quality so much as they are used to: A. point out when random variation is present. B. alert when corrective action is needed. C. monitor the quality of incoming shipments or outgoing finished goods. D. highlight when processes are not capable. E. initiate team-building exercises.

A run test checks a sequence of observations for randomness. A. True B. False

Quality control is making sure that processes are performing in an acceptable manner. A. True B. False

An R value of zero (on a range chart) means that the process must be in control since all sample values are equal. A. True B. False

If a process is performing as it should, it is still possible to obtain observations which are outside of which limits? (I) tolerances (II) control limits (III) process variability A. I B. I and II C. II and III D. I, II, and III E. II

The greater the volume of the process being targeted for inspection, the more attractive __________ inspection is. A. monitored B. automated C. periodic D. controlled E. variable

A p-chart is used to monitor the fraction of defectives in the output of a process. A. True B. False

The assurance that processes are performing in an acceptable manner is the focus of: A. acceptance sampling. B. capability assessment. C. quality assurance. D. quality control. E. variability analysis.

Range charts are used mainly with attribute data. A. True B. False

A control chart used to monitor the process mean is the: A. x-bar chart. B. R-chart. C. p-chart. D. Gantt chart. E. c-chart.

The optimum level of inspection minimizes the sum of inspection costs and the cost of passing defectives. A. True B. False

The output of a process may not conform to specifications even though the process may be statistically "in control." A. True B. False

The number of defective parts in a sample is an example of variable data because it will "vary" from one sample to another. A. True B. False

Statistical process control is the measurement of rejects in the final product. A. True B. False

The amount of inspection needed depends on __________ and __________. A. the quality of the supplier; the target market of the process B. where in the process the inspection occurs; the volume of the process C. the amount of automation; the reliability of inspectors D. the cost of the item being inspected; the use of the item being inspected E. the costs of inspection; the costs of passing on defective items

Problem 10-7 The postmaster of a small western town receives a certain number of complaints each day about mail delivery. DAY 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Number of complaints 4 10 16 8 9 6 5 14 13 7 6 4 2 10 a. Determine three-sigma control limits using the above data. (Round your intermediate calculations to 4 decimal places and final answers to 3 decimal places. Leave no cells blank - be certain to enter "0" wherever required. Round up any negative control limit value to zero.) UCL LCL b. Is the process in control? Yes No

Suppose your manager presents you with the following information about machines that could be used for a job, and wants your recommendation on which one to choose. The specification width is .48 mm. In this instance, you can narrow the set of choices, but you probably wouldn't make a recommendation without an additional piece of information. (Round your answers to 3 decimal places.) Machine Cost per Unit ($) Standard Deviation (mm) A 20 .059 B 12 .060 C 13 .061 D 10 .062 We can narrow the choices to processes:

As part of an insurance company's training program, participants learn how to conduct an analysis of clients' insurability. The goal is to have participants achieve a time in the range of 30 to 47 minutes. Test results for three participants were: Armand, a mean of 38.0 minutes and a standard deviation of 3.0 minutes; Jerry, a mean of 36.0 minutes and a standard deviation of 3.0 minutes; and Melissa, a mean of 38.5 minutes and a standard deviation of 1.6 minutes. a.Which of the participants would you judge to be capable? (Do not round intermediate calculations. Round your answers to 2 decimal places.) Participants Cpk Cp Capable ? Armand Jerry Melissa b.Can the value of the Cpk exceed the value of Cp for a given participant? Yes No

Problem 10-3 The time to replace vehicle wiper blades at a service center was monitored using a mean and a range chart. Six samples of n = 20 observations have been obtained and the sample means and ranges computed: Sample Mean Range Sample Mean Range 1 3.06 .42 4 3.13 .46 2 3.15 .50 5 3.06 .46 3 3.11 .41 6 3.09 .45 Factors for three-sigma control limits for formula X and R charts n A2 D3 D4 2 1.88 0 3.27 3 1.02 0 2.57 4 0.73 0 2.28 5 0.58 0 2.11 6 0.48 0 2.00 7 0.42 0.08 1.92 8 0.37 0.14 1.86 9 0.34 0.18 1.82 10 0.31 0.22 1.78 11 0.29 0.26 1.74 12 0.27 0.28 1.72 13 0.25 0.31 1.69 14 0.24 0.33 1.67 15 0.22 0.35 1.65 16 0.21 0.36 1.64 17 0.20 0.38 1.62 18 0.19 0.39 1.61 19 0.19 0.40 1.60 20 0.18 0.41 1.59 a.Using the factors in the above table, determine upper and lower limits for mean and range charts. (Do not round intermediate calculations. Round your mean value to 3 decimal places and range value to 4 decimal places.) Upper limit for mean Lower limit for mean Upper limit for range Lower limit for range b.Is the process in control? Yes No

If this new product is a low volume item with a large cost of passing along defective products, what inspection plan would you recommend?

Why should Jim Peterson collect the mean and range data for each sample rather than just the mean measurements?

What might a higher frequency of sampling detect that a lower frequency of sampling might miss? For example, what might sampling every 30 minutes detect that might be missed if samples are taken every 4 hours?

The oven process is charted, no points fall outside the control limits, and run tests do not indicate anything special, so:

Michelle would also like to monitor the percentage of items coming out of the oven that display unacceptable surface cracking. Which chart should she use?

The oven is a costly, irreversible process. In which place would you recommend inspection be done?

Which of the following sample sizes has the most narrow sampling distribution?

In which step of the control process are the characteristics defined?

When plotting sample statistics on a control chart, 99.7% of the sample statistic values are expected to fall within plus/minus how many sigma?

We measure the following values: 100, 90, 110. What is the range?

A customer has specified that a tolerance of 10 to 20 mm is acceptable. Our process has a standard deviation of 2 mm. What is the Cp?

p-bar is 0.1, n = 20. What is sigma?