Statistical Quality control
- 1. Statistical Quality Control Production and operation management Unit 5 1 B.V. Patel Institute of BMC & IT Prepared by Divya Paulose
- 2. What is SQC ? Statistical quality control (SQC) is the term used to describe the set of statistical tools used by quality professionals. 2 Prepared by Divya Paulose
- 3. History SQC was pioneered by Walter A. Shewhart at Bell Laboratories in the early 1920s. Shewhart developed the control chart in 1924 and the concept of a state of statistical control. Shewhart consulted with Colonel Leslie E. Simon in the application of control charts to munitions manufacture at the Army's Picatinney Arsenal in 1934. 3 Prepared by Divya Paulose
- 4. History W. Edwards Deming invited Shewhart to speak at the Graduate School of the U.S. Department of Agriculture, and served as the editor of Shewhart's book Statistical Method from the Viewpoint of Quality Control (1939) which was the result of that lecture. Deming was an important architect of the quality control short courses that trained American industry in the new techniques during WWII. 4 Prepared by Divya Paulose
- 5. Deming traveled to Japan during the Allied Occupation and met with the Union of Japanese Scientists and Engineers(JUSE)in an effort to introduce SQC methods to Japanese industry 5 Prepared by Divya Paulose
- 6. SQC Categories6 Descriptive statistics Statistical process control (SPC) Acceptance sampling Prepared by Divya Paulose
- 7. Descriptive Statistics Descriptive statistics are used to describe quality characteristics and relationships. 7 Prepared by Divya Paulose
- 8. Descriptive Statistics The Mean- measure of central tendency. The Range- difference between largest/smallest observations in a set of data. Standard Deviation measures the amount of data dispersion around mean. 8 Prepared by Divya Paulose
- 9. The Mean To compute the mean we simply sum all the observations and divide by the total no. of observations. 9 Prepared by Divya Paulose
- 10. The Range Range, which is the difference between the largest and smallest observations. 10 Prepared by Divya Paulose
- 11. Standard Deviation Standard deviation is a measure of dispersion of a curve. It measures the extent to which these values are scattered around the central mean. 11 Prepared by Divya Paulose
- 12. • Extend the use of descriptive statistics to monitor the quality of the product and process. • Statistical process control help to determine the amount of variation. • To make sure the process is in a state of control. 12 Statistical process control Prepared by Divya Paulose
- 13. STATISTICAL QUALITY CONTROL: Application of statistical techniques to accept or reject products already produced or to control the process while it is being carried out. STATISTICAL PROCESS CONTROL: Statistical evaluation of the output of a process during production. 13 Prepared by Divya Paulose
- 14. Variation in Quality No two items are exactly alike. Some sort of variations in the two items is bound to be there. In fact it is an integral part of any manufacturing process. This difference in characteristics known as variation. This variation may be due to substandard quality of raw material, carelessness on the part of operator, fault in machinery system etc.. 14 Prepared by Divya Paulose
- 15. Types Of Variations15 Prepared by Divya Paulose
- 16. Variation due to chance causes/common causes Variation occurred due to chance. This variation is NOT due to defect in machine, Raw material or any other factors. Behave in “random manner”. Negligible but Inevitable The process is said to be under the state of statistical control. 16 Prepared by Divya Paulose
- 17. Variation due to assignable causes Non – random causes like: Difference in quality of raw material Difference in machines Difference in operators Difference of time 17 Prepared by Divya Paulose
- 18. 18 Prepared by Divya Paulose
- 19. Specification and control limits No item in the world can be a true copy of another item. It is not expressed in absolute values but in terms of a range. For Eg: The diameter of a pen is expected by its manufacturer not as 7mm but as 7mm ± 0.05. Thus, the diameter of a pen produced by the manufacturer can vary from 6.95 mm to 7.05 mm. 19 Prepared by Divya Paulose
- 20. Setting Control Limits20 Prepared by Divya Paulose
- 21. HOW CONTROL LIMITS ARE USEFUL…..? 21 Prepared by Divya Paulose
- 22. SPC Methods-Control Charts Control Charts show sample data plotted on a graph with CL, UCL, and LCL Control chart for variables are used to monitor characteristics that can be measured, e.g. length, weight, diameter, time Control charts for attributes are used to monitor characteristics that have discrete values and can be counted, e.g. % defective, number of flaws in a shirt, number of broken eggs in a box 22 Prepared by Divya Paulose
- 23. Control Charts for Variables x-bar charts (Average Quality) It is used to monitor the changes in the mean of a process (central tendencies). R-bar charts (Variation) It is used to monitor the dispersion or variability of the process 23 Prepared by Divya Paulose
- 24. Thank You 24 Prepared by Divya Paulose