1. Business Processes Sales Order Management Aggregate Planning Master Scheduling Production Activity Control Quality Control Distribution Mngt. © 2001 Victor E. Sower, Ph.D., C.Q.E.

2. © 2000 by Prentice-Hall Inc Russell/Taylor Oper Mgt 3/e Chapter 4 Statistical Quality Control

3. Ch 4 - 2 © 2000 by Prentice-Hall Inc Russell/Taylor Oper Mgt 3/e Quality Control Approaches Statistical process control (SPC) – Monitors production process to prevent poor quality Acceptance sampling –Inspects random sample of product to determine if a lot is acceptable

4. Ch 4 - 3 © 2000 by Prentice-Hall Inc Russell/Taylor Oper Mgt 3/e Statistical Process Control Take periodic samples from process Plot sample points on control chart Determine if process is within limits Prevent quality problems

5. Ch 4 - 4 © 2000 by Prentice-Hall Inc Russell/Taylor Oper Mgt 3/e Variation Common Causes –Variation inherent in a process –Can be eliminated only through improvements in the system Special Causes –Variation due to identifiable factors –Can be modified through operator or management action

6. Ch 4 - 5 © 2000 by Prentice-Hall Inc Russell/Taylor Oper Mgt 3/e Types Of Data Attribute data Product characteristic evaluated with a discrete choice –Good/bad, yes/no Variable data Product characteristic that can be measured –Length, size, weight, height, time, velocity

7. Ch 4 - 6 © 2000 by Prentice-Hall Inc Russell/Taylor Oper Mgt 3/e SPC Applied To Services Nature of defect is different in services Service defect is a failure to meet customer requirements Monitor times, customer satisfaction

8. Ch 4 - 7 © 2000 by Prentice-Hall Inc Russell/Taylor Oper Mgt 3/e Service Quality Examples Hospitals –timeliness, responsiveness, accuracy Grocery Stores –Check-out time, stocking, cleanliness Airlines –luggage handling, waiting times, courtesy Fast food restaurants –waiting times, food quality, cleanliness

9. Ch 4 - 8 © 2000 by Prentice-Hall Inc Russell/Taylor Oper Mgt 3/e Control Charts Graph establishing process control limits Charts for variables –Mean (X-bar), Range (R) Charts for attributes –p and c

10. Ch 4 - 9 © 2000 by Prentice-Hall Inc Russell/Taylor Oper Mgt 3/e Process Control Chart 12345678 9 10 Sample number Upper control limit Process average Lower control limit

11. Ch 4 - 10 © 2000 by Prentice-Hall Inc Russell/Taylor Oper Mgt 3/e A Process Is In Control If No sample points outside limits Most points near process average About equal number of points above & below centerline Points appear randomly distributed

12. Ch 4 - 11 © 2000 by Prentice-Hall Inc Russell/Taylor Oper Mgt 3/e Development Of Control Chart Based on in-control data If non-random causes present discard data Correct control chart limits

13. Ch 4 - 12 © 2000 by Prentice-Hall Inc Russell/Taylor Oper Mgt 3/e Control Charts For Attributes p Charts –Calculate percent defectives in sample c Charts –Count number of defects in item

14. Ch 4 - 13 © 2000 by Prentice-Hall Inc Russell/Taylor Oper Mgt 3/e p-Chart

15. Ch 4 - 14 © 2000 by Prentice-Hall Inc Russell/Taylor Oper Mgt 3/e The Normal Distribution  =011 22 33 95% 99.74% -1  -2  -3 

16. Ch 4 - 15 © 2000 by Prentice-Hall Inc Russell/Taylor Oper Mgt 3/e Control Chart Z Values Smaller Z values make more sensitive charts Z = 3.00 is standard Compromise between sensitivity and errors

17. Ch 4 - 16 © 2000 by Prentice-Hall Inc Russell/Taylor Oper Mgt 3/e p-Chart Example 20 samples of 100 pairs of jeans Sample ## Defects Proportion Defective 16.06 20.00 34.04 ……… 2018.18 200

18. Ch 4 - 17 © 2000 by Prentice-Hall Inc Russell/Taylor Oper Mgt 3/e p-Chart Calculations

19. Ch 4 - 18 © 2000 by Prentice-Hall Inc Russell/Taylor Oper Mgt 3/e Example p-Chart.. 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 02468 101214161820 Proportion defective Sample number

20. Ch 4 - 19 © 2000 by Prentice-Hall Inc Russell/Taylor Oper Mgt 3/e c-Chart

21. Ch 4 - 20 © 2000 by Prentice-Hall Inc Russell/Taylor Oper Mgt 3/e c-Chart Example Count # of defects in 15 rolls of denim fabric Sample ## Defects 112 28 316…15 190

22. Ch 4 - 21 © 2000 by Prentice-Hall Inc Russell/Taylor Oper Mgt 3/e c-Chart Calculations

23. Ch 4 - 22 © 2000 by Prentice-Hall Inc Russell/Taylor Oper Mgt 3/e Example c-Chart

24. Ch 4 - 23 © 2000 by Prentice-Hall Inc Russell/Taylor Oper Mgt 3/e Control Charts For Variables Mean chart (X-Bar Chart) –Uses average of a sample Range chart (R-Chart) –Uses amount of dispersion in a sample

25. Ch 4 - 24 © 2000 by Prentice-Hall Inc Russell/Taylor Oper Mgt 3/e Range (R) Chart

26. Ch 4 - 25 © 2000 by Prentice-Hall Inc Russell/Taylor Oper Mgt 3/e R-Chart Example Slip-ring diameter (cm) Sample 12345xR 15.025.014.944.994.964.980.08 25.015.035.074.954.965.000.12 34.995.004.934.924.994.970.08 …………………… 105.014.985.085.074.995.030.10 50.091.15

27. Ch 4 - 26 © 2000 by Prentice-Hall Inc Russell/Taylor Oper Mgt 3/e 3  Control Chart Factors Sample sizex-chartR-chart nA 2 D 3 D 4 21.8803.27 31.0202.57 40.7302.28 50.5802.11 60.4802.00 70.420.081.92 80.370.141.86

28. Ch 4 - 27 © 2000 by Prentice-Hall Inc Russell/Taylor Oper Mgt 3/e R-Chart Calculations