Deck 16: Quality Control and Spc

Question 1

"Quality at the source" focuses on supplier quality at the beginning of a value chain.

Answer 1

False

Question 2

Poor quality that might result from a broken tool or an employee who is ill would be an example of special cause variation.

Answer 2

True

Question 3

Quality control of front-office operations in services can effectively use many of the same techniques that are applied in manufacturing.

Answer 3

False

Question 4

Special cause variation tends to be easily detectable using statistical methods.

Question 5

As long as no points are outside of the control limits in a control chart, the process would be considered to be in control.

Question 6

A process is considered to be in control when all common and special causes have been eliminated.

Question 7

If the mean in the range chart shifts down significantly, it indicates that the variation in the process has decreased.

Question 8

It generally costs more to correct an error or defect at the design stage than after it has reached the customer.

Question 9

The goal of statistical process control (SPC) is to help identify and eliminate unwanted causes of variation.

Question 10

In developing process control charts, if special causes are present, they are not representative of the true state of statistical control, and the calculations of the center line and control limits will be biased.

Question 11

In-process quality control is typically performed by the employees who run the processes.

Question 12

A key element of a control system is the ability to measure performance and compare it to a performance standard.

Question 13

Over-adjusting a process that is in control will usually increase the variation in the output.

Question 14

An -chart is always analyzed first because the control limits in the R-chart depend on the mean ( ) of the data.

Question 15

Collecting continuous data is usually easier than collecting discrete data.

Question 16

Common cause variation generally accounts for about 10 to 15% of all variation within a process.

Question 17

In manufacturing, quality control is generally applied at the receiving stage from suppliers, during various production processes, and at the finished goods stage.

Question 18

Quality control focuses on the design of a good or service to ensure meeting customer expectations.

Question 19

With good management, all variability of output from any goods- or service-producing process can be eliminated.

Question 20

A system governed only by common causes is called a stable system.

Question 21

Common cause variation

A)Cannot be explained except in an aggregate sense
B)Is easily detectable with statistical methods and control charts
C)Cannot be reduced through better technology, process design, or training
D)Is the responsibility of the workers who run the processes

Question 22

In the 1:10:100 Rule, which of the following would be correct?

A)If a defect or service error is identified and corrected at the design stage, it might cost $100 to fix.
B)If a defect or service error is identified and corrected at the production process stage, it might cost $100 to fix.
C)If a defect or service error is identified and corrected after it reaches the customer, it might cost $100 to fix.
D)If a defect or service error is identified and corrected at the design stage, it might cost $1 * $10 * $100 = $1,000 to fix.

Question 23

The lower the rate of defects, the higher the sample size should be in p-charts.

Question 24

Larger sample sizes allow smaller changes in process characteristics to be detected with higher probability.

Question 25

Evaluating the trade-offs between the costs of detecting and replacing a defective part or allowing it to continue on through the production process is related to

A)Supplier certification and management
B)In-process control
C)Finished goods control
D)Statistical process control

Question 26

Testing whether a computer boots up the first time is an example of

A)Supplier certification and management
B)In-process control
C)Finished goods control
D)Statistical process control

Question 27

Which of the following is most closely related to Statistical Process Control (SPC)?

A)Removing common causes of variation
B)Removing special causes of variation
C)Removing all causes of variation
D)Computing process capability

Question 28

When the range of process variation is larger than the design specifications, the process capability index will be less than 1.

Question 29

If process quality approaches six sigma levels, then standard types of control charts are not useful.

Question 30

Quality at the source means that quality is controlled by

A)People responsible for the work
B)Quality control managers
C)Front line supervisors
D)Top management

Question 31

Common cause variation is

A)Controllable at the sources
B)Called assignable cause
C)Can be reduced by statistical process control methods
D)The responsibility of management

Question 32

It is not necessary to have a process in control when establishing control limits.

Question 33

If no special causes affect the output of a process, we say that the process is ____; when special causes are present, the process is said to be ____.

A)Qualified; not qualified
B)In control; out of control
C)Capable; not capable
D)Certified; not certified

Question 34

Which of the following is not a component of a control system?

A)Statistical sampling
B)Measures of actual performance
C)Goals or standards
D)Comparison of actual performance with standards or goals for corrective action if necessary

Question 35

To account for the process centering, a two-sided capability index is often used.

Question 36

Regarding special cause variability, all are true except

A)Disrupt the random patterns of common cause variation
B)Arises from external sources that are not inherent in the process
C)Appear sporadically
D)Hard to detect using statistical methods

Question 37

A c-chart is used to monitor the fraction nonconforming, whereas a p-chart monitors the number of nonconformances per unit.

Question 38

Process capability quantifies the variation that results from common causes.

Question 39

Both the p-chart and the c-chart use variable data.

Question 40

The value of C_pk is the average of the lower and upper capability indexes; that is, C_pk = (C_pl + C_pu)/2.

Question 41

Indications in a control chart of an out-of-control situation include all of the following except

A)Six or seven consecutive points that increase or decrease in value
B)About the same number of points above and below the center line
C)There are points outside control limits
D)There are no more points near the center line than there are close to the control limits

Question 42

The upper and lower specification limits for a component are 4.20 and 4.30 ounces, respectively. The process standard deviation is .02, and the process average is 4.24 ounces. Which one of the following statements is true?

A)The C_p index indicates the process is centered.
B)The C_p index indicates the process is not centered.
C)The C_pk index indicates the process is centered.
D)The C_pk index indicates the process is not centered.

Question 43

c-charts

A)Are used for the fraction of non-conforming items
B)Count the number of nonconformances per unit
C)Use continuous metrics
D)Can have negative lower limits

Question 44

The center line (p-bar) for a p-chart is 0.50 with an UCL = 0.70 and a LCL = 0.35. The results of the next eight sample means are 0.45, 0.60, 0.39, 0.44, 0.48, 0.53, 0.54, and 0.61. What would you do?

A)Nothing; the process is in control.
B)increase the sample size to get a better measure.
C)investigate assignable causes because four observations are above the center line.
D)investigate assignable causes because there is a bad trend (run).

Question 45

Define "quality at the source."

Question 46

To monitor the fraction of printed circuit boards that do not pass a functional test, a(n) ____ is used.

A) -chart
B)p-chart
C)c-chart
D)R-chart

Question 47

Statistical calculations will show that if p = .01, then the sample size needed to have at least a 95% chance of finding at least one nonconformance is

A)30
B)100
C)300
D)1,000

Question 48

Which one of the following statements is true?

A)Common cause variation arises from external sources that are not inherent in the process and is where statistical quality control methods are most useful.
B)If the metric is discrete, a p- or c-chart is normally used.
C)Statistical process control is not used in hospitals due to the high liability costs.
D)Statistical process control charts are used when trying to monitor and control 5- and 6-sigma quality levels.

Question 49

A supplier is producing a machined part for the transmission of your vehicle. The upper specification limit is 0.125 cm and the lower specification limit is 0.085. The process standard deviation for the process that makes this part is 0.008 and the process average is 0.105. What conclusion can be drawn from these process capability data?

A)The process is centered and capable.
B)The process is not centered and capable.
C)The process is centered and not capable.
D)The process is not centered and not capable.

Question 50

p-charts

A)Are used for the fraction of non-conforming items
B)Count the number of nonconformances per unit
C)Use continuous metrics
D)Can have negative lower limits

Question 51

A bottling process sometimes results in overfills or underfills. Overfills are especially damaging to the equipment. Which process capability index would this company most want to monitor?

A)C_p
B)C_pl
C)C_pu
D)C_pk

Question 52

Which of the following is not related to a continuous metric?

A)Measured as the degree of conformance to a specification
B)x-bar and R-charts
C)p-chart
D)Time

Question 53

Honda wants to monitor the number of blemishes (scratches, blisters, etc.) on the fenders of its cars using a statistical process control chart. The most appropriate type of SPC chart is

A)x-bar.
B)R-bar chart.
C)C_pk chart
D)c-chart

Question 54

Ritz-Carlton Hotel Company uses which one of the following methods to control quality?

A)R-bar and x-bar control charts to monitor customer complaints.
B)The 1:10:100 rule for goods quality only
C)Self-control of the individual employee based on their spontaneous behavior.
D)The process capability index for all goods and services provided by the hotel.

Question 55

Explain and give the significance of the 1:10:100 Rule.

Question 56

Which of the following suggests a process that is not in control?

A)Points follow a smooth pattern from the lower control limit to the upper control limit
B)The number of points above and below the center line is about the same
C)Points fall randomly above and below the center line
D)No points are outside the control limits

Question 57

If one was monitoring the average time to load a web page, the chart to use would be the

A) -chart
B)R-chart
C)p-chart
D)c-chart

Question 58

Define and give an example of the three components of any control system.

Question 59

Historically, the average proportion of defective bars has been 0.015. Samples of 100 bars each are taken. Construct a p-chart using z = 3. Suppose a sample had 0.044 defectives. What would you do?

A)Nothing; it appears to be random variation.
B)Look for assignable causes.
C)Delete the sample with 0.044 defects and take another sample that is better.
D)None of these choices

Question 60

Which is not related to a discrete metric?

A)Counting
B)Visual inspection
C)Good or bad
D)Time

Question 61

The time to check out guests at a hotel was measured over the course of several weeks. Management believes that the target time for checking out guests should be between 2 and 4 minutes with a target of 3 minutes. The data gathered had a mean time of 2.75 minutes with a standard deviation of 0.4 minutes. Find and interpret C_p, C_pl, C_pu, and C_pk in the context of this situation.

Question 62

Fifteen samples of size 5 have been taken from a production process. The sum of the sample averages was found to be 92.54 cm while the sum of the ranges was 115.36. Find the values of the center lines for the x-bar and R-charts.

Question 63

In general, discuss how to interpret control charts.

Question 64

An airline found that on average, 0.62% of the luggage they received from passengers at LAX (Los Angeles Airport) is lost or damaged. On a typical day, 1000 pieces of luggage pass through this airport. What are the control limits for a p-chart for monitoring the daily fraction nonconforming?

Question 65

A manufacturing company has a production process that has a target percent nonconforming of 4% which was developed based on numerous samples of 200 observations each. They want to develop control charts using 3 standard deviation limits.
a.What is the center line for the p-chart?
b.What is the upper control limit for a p-chart?
c.What is the lower control limit for a p-chart?

Question 66

Explain the issues associated with selecting the appropriate sample size and sampling frequency for control charts.

Question 67

Discuss the three basic quality control practices used in manufacturing.

Question 68

Define Statistical Process Control (SPC) and differentiate between common cause and special (or assignable) cause variation.

Question 69

Find the control limits for a c-chart with = 7.

Question 70

A company is measuring the time it takes to complete an order. Twenty-five samples of size 6 resulted in an average time of 80 minutes with an average range of 20 minutes. Find control limits for the appropriate control chart(s) that would be used to monitor this process.

Question 71

A manufacturer inspected 40 circuit boards and found a total of 640 defects. If the company wants to use SPC to control the manufacturing process by monitoring the number of defects per circuit board, what type of chart should they use and what should the control limits be?

Question 72

Flaws are counted on a standard steel plate (sheet). Each sheet has the exact same dimensions. Ten sheets are selected at random and the number of flaws per sheet is as follows:
Determine the lower and upper control limits for a c-chart.

Question 73

Discuss the difference between a continuous metric and a discrete metric, give examples of each, and list the common control charts associated with each.

Question 74

A Procter and Gamble factory process fills boxes with detergent. Construct an appropriate set of control charts to monitor the process. Historical data for fill weight (in ounces) of eight samples is presented below. A sample size of six was used.
a.Compute the limits for both an R-chart and x-bar chart. Compare the sample results to the limits of the charts.
b.Briefly explain what the quality control charts tell you. What actions, if any, would you take?

Question 75

Over several days, 25 samples of 100 items each were tested for electrical resistance. A total of 60 items failed. Determine and the control limits for a p-chart.

Question 76

A high-paced discount store in Los Angeles has noticed that checking errors have increased recently. They plan to use control charts with three standard deviation control limits to monitor the process. They decided to take a sample of 100 transactions over each of 10 days. The number of transactions in error for each day was 5, 7, 6, 5, 6, 4, 6, 3, 10, and 8.
a.What is the center line for the p-chart?
b.What is the upper control limit for the p-chart?
c.What is the lower control limit for the p-chart?

Question 77

A bottling machine fills soft drink bottles with an average of 12.000 ounces with a standard deviation of 0.002 ounces. Determine the process capability index, C_p, if the design specification for the fill weight of the bottles is 12.000 ounces plus or minus 0.015 ounces.

Question 78

What is the purpose of a process-capability study and what is a process capability index?

Question 79

An operator has determined what her percent defectives is for the machine which she operates. Based on several samples of 75 observations, she found p-bar to be 10%. She wants to set up a control chart using 3 standard deviation control limits.
a.What is the upper control limit for a p-chart?
b.What is the lower control limit for a p-chart?

Question 80

A production process is sampled 24 times with a sample size of 6 yields an overall mean of 25.2 and an average range of 0.8. Determine the control limits for the x-bar and R-charts.