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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.)
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