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Variation is the change or deviation, in form, condition, appearance or extent from a usual state, or from an assumed standard.
Explain how statistical quality control (SQC)
can assist in manufacturing systems.
- The goal of statistical quality control (SQC) is to find out which variations are due to normal random fluctuations and which variations have an abnormal cause that can be detected and
List the four input factors in processes that contribute to random fluctuations and Inconsistencies.
- ●Methods (procedures)
Explain the difference between common cause and special cause variation
Common cause variation is inherited in a process over time while a special cause variation arises because of unusual circumstances. Also a common cause variation requires redesigning the process while special cause requires locating and removing the cause.
List two known facts about a process that is in
- ●The process is doing what it was designed to do. It is doing the best it can.
- ●Operators are not able to improve the process
An operator is working on a unit that stays in statistical control; however, some off-specification product is occasionally produced. The operator can help improve the process.
Explain the necessity of control charts for
They are used to identify two factors that adversely effect their process. They identify the effects of entropy and the presence of assignable causes. No other tool provides such consistent and reliable information
How is an operator “driving blindfolded” if his work process relies on inspection to determine quality?
- The operator should be able to evaluate the
- products as they build them. Inspection after the product is built is inefficient and is the same as “driving blindfolded”.
List the information contained in a histogram.
- A histogram is a statistical method that makes
- bar charts of the values from a data set grouped into classes. Histograms are important diagnostic tools because they give a clear picture of data distributions that might otherwise be difficult to visualize.
Define standard deviation
- The standard deviation is the measure of the
- dispersion of observed values from the mean (how far away values are from the centerline).
State the percentage of area under a normal distribution curve for 1, 2, and 3.
- (1) would be 68 percent
- 2 would be 27 percent
- 3 would be 4.7 percent
State the percentage of chance that a data point will fall within 3.
99.7 will fall between 3
State the percentage of chance that a data point will fall outside of 3.
.30 percent will fall out of 3
Explain the usefulness of SPC charts.
SPC charts and associated problem-solving techniques provide a picture of the performance of a process. This picture can be analyzed to detect an incipient problem and make a correction before a process produces off-specification product.
List five advantages of SPC charts
- ●Improved product quality
- ●Increased quality consciousness
- ●Cost reduction
- ●Data-based decisions
- ●Predictable processes
Explain what information an X— chart reveals
that an R chart does not
X chart provides information of how average the system is.
Explain what information an R chart reveals that an X— chart does not.
R chart provides information about the variability of the system
If the R chart is out of control, then
There is no use in checking the X-bar chart
When a data point falls outside of the UCL or
LCL, this means that
Special cause has changed the process population
Explain what process capability reveals about a
- Process capability or capability index (Cp) reveals whether a process (people, materials,
- machines, and methods) can meet product specifications and how effectively it can meet those specifications
Explain what the values 0.8, 1.0, and 2.0 reveal
about a process capability.
If the value is 0.8 this means that process specifications are not being met. At 1.0 the process is doing exactly what it should be doing. 2.0 means the capability of the process is great
You would never do a process capability study of a unit that has assignable causes interfering with the finished product quality
Explain why process capability studies are conducted
Because these studies provide a method for analyzing and changing distributions. They show the many different forms in which basically similar problems may present themselves
List some problems solved by process capability
- ●Too many defects by operations
- ●Product unstable or drifting
- ●Wrong distribution
- ●Bad material entering the process
- ●Too many adjustments
List four advantages to a company that has a
- ●Quality is a collection of powerful tools and concepts that work and are applicable in every aspect of a business.
- ●Quality is achieved with people, not things.
- ●Quality is defined by external customer satisfaction.
- ●Quality includes continuous improvement and
- breakthrough events
Explain what is meant by the sentence “Quality
is a function of the process.”
If the process is flawed, the work will be flawed no matter how hardan employee works to prevent the flaw. An employee is just a worker in a process
A company with good statistical tools will have a good quality system.
A company with good statistical tools and empowered employees does not need a performance system
- Explain your answer to question number four.
- Because without a performance system employees will not be encouraged to improve.
Explain why empowered workers are so important for continuous improvement.
Because an organization cannot improve unless its people improve. Quality doesnot depend on equipment; it depends on the workers who run the equipment (process)