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## INT 4843 Statistical Quality Control

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### INT 4843 Statistical Quality Control Bruce Barnard Terry Parish Mark Tegeler Quality Quality is inversely proportional to variability . Montgomery(2001) Steps to ... – PowerPoint PPT presentation

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Title: INT 4843 Statistical Quality Control

1
INT 4843Statistical Quality Control
• Bruce Barnard
• Terry Parish
• Mark Tegeler

2
Quality
• Quality is inversely proportional to
variability. Montgomery(2001)

3
Steps to Statistical Quality Control
• Identify the process to be monitored.
• Identify the variable to be monitored.
• Measure historical data.
• Construct an R chart and an Xbar chart.
• Plot the data.

4
Steps to Statistical Quality Control
• Evaluate the data looking for signals, trends and
outliers.
• Construct a revised control chart without the
outliers.
• Use revised control limits to predict process
control.
• Monitor the process.

5
Tomato Can Process
6
Tomato Can Process (Histogram)
• Data indicates a unimodal distribution
• Central tendency is close to 22 oz.
• The variability is relatively high

7
Tomato Can Process (Scatterplot)
8
Tomato Can Process (R Chart)
9
Tomato Can Process (Xbar Chart)
10
Decisions
• The R chart has a point plotting outside the
range.
• The outlier was removed from the data.
• The control limits were revised replotted.

11
Revised ChartsR Chart
12
Revised Charts Xbar Chart
13
Evaluation of Control ChartsAction Signals
• One or more points outside of the control limits
• Two of three consecutive points outside of the
two-sigma warning limits but still inside the
control limits.
• Four of five consecutive points beyond the
one-sigma limits
• A run of eight consecutive points one side of the
center line
• Six points in a row steadily increasing or
decreasing.

14
Evaluation of Control ChartsAction Signals
• Fifteen points in a row zone C (both above and
below the center line).
• Fourteen points in a row alternating up and down
• Eight points in a row on both sides of the
centerline with none in zone C.
• An unusual or nonrandom pattern in the data.
• One or more points near a warning or control
limit

15
Evaluation
16
Process Capability (Cp Cpk)
• Cp .4105
• Cpk .626

17
Recommendations
• Revise sampling techniques, insuring samples are
collected at regular intervals
• ( 1 per hour)
• Devise and implement a capability study
• Consider use of scatterplot to study potential
relationships (operator, source of inputs, etc.)