1. COB 300 C - The Operations Dimension
Quality Control
COB 300 C - The Operations Dimension
Busing

2. Causes of Variation Random Causes difficult or expensive to control
e.g., outside humidity, line voltage
Assignable Causes
easier to correct
e.g., employee error, new materials

3. Comparing Process Variation to Tolerance Limits

4. High Process Capability After Technological Process Change

5. Control Charts
Variables - concentrates on mean for some measurable characteristic.
diameter
length
Attribute - data is based on counts or the number of times we observe a particular event.
proportion defective/non-defective
go/no go
proportion pass/fail

6. Control Limits - Variables Charts
X-Bar Chart
R Chart

9. Factors for Control Limits (Slide 1 of 2)
Sample of Size n A D D 2 3 4 2 3 4 5 6 7 8 9 10
1.880
1.023
0.729
0.577
0.483
0.419
0.373
0.337
0.308
0.076
0.136
0.184
0.223
3.268
2.574
2.282
2.114
2.004
1.924
1.864
1.816
1.777

10. x-bar Chart Example (cont’d)

12. Range Chart

14. Warning Conditions Two successive points near limit
Run of five above or below mean
Trend
Erratic behavior

15. Process Control for Attributes
Proportion defective:
Number of defects per unit: