SCMT Exam 2 - FLASHCARDS - Chapter 13
What is variation that is inherent in the process itself?
Common variation
The range of values in a measure associated with a process that is allowable given the intended use of the product is known as which of the following?
Specification limits
According to Genichi Taguchi,as customers get more demanding, there is pressure to reduce
Variability
The _____ is used to measure how well our process is able to produce relative to the design specifications
Capability index
Common variation is often referred to as ______
Random variation
True or false: It is generally accepted that as variation is reduced, quality is improved
TRUE
If the design specifications are 10.00 inches ± 0.2 inch, then 10.20 is the _____ specification limit.
Upper
What does Taguchi say about about specifications?
Being within specification is a continuous function
Being within specification is not a yes/no decision
When the mean and standard deviation of the process are operating such that the upper and lower control limits are acceptable relative to the upper and lower specification limits, we say the process is
Capable
To generate a Cpk value of 1.00, the design limits must be _____ standard deviation(s) away from the process mean.
3
A traditional way of interpreting such a specification is that any part that falls within the allowed range is equally
______, whereas any part falling outside the range is totally ______
Good; bad
Because the process mean can shift in either direction, the direction of shift and its distance from the design specification set the limit on the process capability. The direction of shift is toward the ______ number.
Smaller
Which distribution is used to calculate the probability of producing a defect?
Normal
According to Genichi Taguchi, from the customer’s view, there is often practically no difference between a product just ______ specifications and a product just ______
Inside; outside
With a process control chart, what does it indicate when one point is below the LCL?
The process is out of control
The ______ shows how well the parts being produced fit into the range specified by the design specification limits.
Capability index
Which of the following is the control chart that measures the fraction defective of each individual sample tested?
P chart
Which of the following are typical objectives of process control plans?
Detect shifts in the process
Provide information about whether items are meeting design specifications
Identify new design specifications
Develop new processes
Detect shifts in the process
Provide information about whether items are meeting design specifications
What is used to measure how well our process is capable of producing relative to the design specifications?
Capability index
A rule of thumb when setting up a p-chart is to make the sample large enough to expect to count the attribute ______ in each sample?
Twice
To generate a Cpk value of 2.00, the design limits must be _____ standard deviation(s) away from the process mean
6
With a process control chart, what does it indicate when there is a run of five points below the center line?
The process is out of control
The underlying distribution for the c-chart is which of the following?
Normal
Poisson
Gamma
Exponential
Poisson
What formula is used to calculate the LCL?
p
- z sp or 0 if less than 0
Measuring the torque and horsepower of a motor is known as sampling by
Variables
Which of the following charts is used when the measure for the sample is weight, volume, number of inches or other variable measurements?
C chart
Range chart
Mean chart
P chart
Range chart and mean chart
Which of the following control charts must make the sample large enough to allow counting of the attribute?
P chart
Sample sizes of _____ or _____ units seem to be the preferred numbers for sample sizes of x-bar charts.
four or five
What is the minimum number of samples suggested for control charts with variable measurement?
25
Usually, it is best to start off with _____ sampling of a process and taper off as _____ in the process builds.
Frequent; confidence
The standard practice in statistical process control for variables is to set control limits how many standard deviations from the mean?
Three
When the product or service can have more than one defect per unit, which of the following is the most appropriate chart?
C chart
Which of the following indicates the process is out-of-control?
A point is below the lower control limit
A point is above the upper control limit
A point is near the center line of the chart
A point is below the lower control limit
A point is above the upper control limit
If the lower control limit for the c-chart is negative, then which of the following values should be used?
0
What is Statistical Quality Control (SQC)?
uses statistics & control charts to tell when to adjust a process?
What is Statistical Quality Control (SQC) used for?
Used to:
– Control the process as products/services are produced
– Inspect samples of finished products/services
What is the objective of SQC?
Provide statistical signal when assignable causes of variation are present
What does statistical quality control involve?
- Creating standards (upper & lower limits)
- Measuring sample output (e.g. mean wgt.)
- Collecting, organizing, and interpreting data
- Taking corrective action (if necessary)
What is statistical process control (SPC)?
Statistical technique for testing a random sample of output to
ensure process is making product (or service) to standard
What is the variation of SPC?
Random and inherent in the process itself (Natural
Causes)
What are specification design limits?
Limits imposed by enginerring in the product’s design (someone outside your company)
What are control (process) limits?
Limits within which the process operates for a specified (very high) percentage of the time (typically x ± 3* sigma).
What is the upper specification?
The maximum acceptable value for a characteristic
What is the lower specification?
The minimum acceptable value for a characteristic
How do we know if a process is capable?
A process is capable if its upper and lower control limits are within the upper and lower specification limits
What is the range of values allowed divided by the range of values produced?
Process capability index (Cpk)
Is Cpk a relative measure?
No
What are characteristics of a variable chart?
• Quantities that you measure, e.g., weight, length
• May be in whole or in fractional numbers
• Continuous numerical data. Examples are X bar or R charts
What are characteristics of an attribute chart?
• Characteristics for which you focus on defects
• Products are either ‘good’ or ‘bad’, or count number of defects
• Categorical or discrete numerical data. Examples are P or C charts
What type of chart is used when an item or service is either good or bad (a yes‐no decision, or attribute characteristic)?
P chart
What type of chart is used to monitor the number (or count) of defects per unit?
– When an item (or service) may have multiple defects
C chart
What type of chart shows sample means over time?
X bar chart
What type of chart monitors process average?
X bar chart
What type of chart shows sample ranges over time?
R chart
What type of chart monitors variability in a process?
R chart
How should samples be for X bar and R charts?
Preferable to keep small (usually 4 or 5 units)
What are solutions for losing control?
- Redesign the process so that it can achieve the desired output
- Use an alternate process that can achieve the desired output
- Retain the current process but attempt to eliminate unacceptable output using 100 percent inspection
- Examine the specifications to see whether they are necessary or could be relaxed without adversely affecting customer satisfaction.
What is acceptance sampling?
Performed on goods that already exist to determine what percentage of the products conform to specifications
– Determine quality level
– Ensure quality is within predetermined level
What are disadvantages of acceptance sampling?
• Risks of accepting “bad” lots and rejecting “good” lots
• Added planning and documentation
• Sample provides less information than 100 percent inspection
What are advantages of acceptance sampling?
• Economy
• Less handling damage
• Fewer inspectors
• Upgrading of the inspection job
• Applicability to destructive testing
• Entire lot rejection (motivation for improvement)
True or false: Acceptance sampling is performed on goods that already exist to determine what percentage of items conforms to specifications?
TRUE
True or false: It is impossible to have zero variability in production processes?
TRUE. As noted in class, it is impossible to have zero variability
For which of the following should we use an R-chart to monitor process quality?
A. Weighing trucks at a highway inspection station to determine if they are overloaded
B. Deciding whether an airliner has sufficient fuel for its trip
C. Student grades measured from 1 to 100
D. Determining whether vehicles from a motor pool will run
E. Determining the accuracy of a forecast of “snow”
Student grades measured from 1 to 100. We are looking at things that have continuous types of numbers. In attribute sampling, we determine whether something is good or bad, fits or doesn’t fit—it is a go/no-go situation. In variables sampling we measure the actual weight, volume, number of inches, or other variable measurements, and we develop control charts to determine the acceptability or rejection of the process based on those measurements. X-bar and R-charts are used with variable measurements
You are developing an X-bar chart based on sample means. You know the standard deviation of the sample means is 100, the desired confidence level is 99.7 percent, and the average of the sample means is 400. Which of the following is your UCL?
A. 500
B. 300
C. 600
D. 200
E. None of these
None of the above. From the notes (and book), we know the rule of thumb z = 3 (which is the 99.7% level). Using Equation 13.12 from the book, X-bar = 400, standard deviation = 100 and z = 3. UCL = 400 + (3 x 100) = 700
