1. Besterfield: Quality Control, 8 th ed..© 2009 Pearson Education, Upper Saddle River, NJ 07458. All rights reserved Quality Control PowerPoint presentation to accompany Besterfield Quality Control, 8e PowerPoint presentation to accompany Besterfield Quality Control, 8e Chapter 5- Control Charts for Variables

2. Besterfield: Quality Control, 8 th ed..© 2009 Pearson Education, Upper Saddle River, NJ 07458. All rights reserved The variation concept is : A law of nature in that no two natural items in any category are the same. Variation

3. Besterfield: Quality Control, 8 th ed..© 2009 Pearson Education, Upper Saddle River, NJ 07458. All rights reserved  The variation may be quite large and easily noticeable  The variation may be very small. It may appear that items are identical; however, precision instruments will show difference  The ability to measure variation is necessary before it can be controlled Variation

4. Besterfield: Quality Control, 8 th ed..© 2009 Pearson Education, Upper Saddle River, NJ 07458. All rights reserved There are three categories of variation in piece part production: 1. Within-piece variation: Surface 2. Piece-to-piece variation: Among pieces produced at the same time 3. Time-to-time variation: Difference in product produced at different times of the day Variation

5. Besterfield: Quality Control, 8 th ed..© 2009 Pearson Education, Upper Saddle River, NJ 07458. All rights reserved Materials Tools OperatorsMethods Measurement Instruments Instruments HumanInspectionPerformance EnvironmentMachines INPUTS PROCESS OUTPUTS Variation (Perbezaan) Sources of Variation in production processes:

6. Besterfield: Quality Control, 8 th ed..© 2009 Pearson Education, Upper Saddle River, NJ 07458. All rights reserved Sources of variation are: 1. Equipment: 1. Toolwear 2. Machine vibration 3. Electrical fluctuations etc. 2. Material 1. Tensile strength 2. Ductility 3. Thickness 4. Porosity etc. Variation

7. Besterfield: Quality Control, 8 th ed..© 2009 Pearson Education, Upper Saddle River, NJ 07458. All rights reserved Sources of variation are: 3. Environment 1. Temperature 2. Light 3. Radiation 4. Humidity etc. 4. Operator 1. Personal problem 2. Physical problem etc. Variation

8. Besterfield: Quality Control, 8 th ed..© 2009 Pearson Education, Upper Saddle River, NJ 07458. All rights reserved There is also a reported variation which is due to the inspection activity. Variation due to inspection should account for one tenth of the four other sources of variation. Variation

9. Besterfield: Quality Control, 8 th ed..© 2009 Pearson Education, Upper Saddle River, NJ 07458. All rights reserved Variation may be due to chance causes (random causes) or assignable causes. When only chance causes are present, then the process is said to be in a state of statistical control. The process is stable and predictable. Variation

10. Besterfield: Quality Control, 8 th ed..© 2009 Pearson Education, Upper Saddle River, NJ 07458. All rights reserved  Variable data  x-bar and R-charts  x-bar and s-charts  Charts for individuals (x-charts)  Attribute data  For “defectives” (p-chart, np-chart)  For “defects” (c-chart, u-chart) Control Charts

11. Besterfield: Quality Control, 8 th ed..© 2009 Pearson Education, Upper Saddle River, NJ 07458. All rights reserved What is Control Chart?  Control charts are used to determine whether your process is operating in statistical control.  Basically a control chart is a run chart (described earlier) that includes statistically generated upper and lower control limits.  The purpose of a control chart is to detect any unwanted changes in your process.

12. Besterfield: Quality Control, 8 th ed..© 2009 Pearson Education, Upper Saddle River, NJ 07458. All rights reserved Control Charts R Chart Variables Charts Attributes Charts X Chart P C Continuous Numerical Data Categorical or Discrete Numerical Data Control Charts

13. Besterfield: Quality Control, 8 th ed..© 2009 Pearson Education, Upper Saddle River, NJ 07458. All rights reserved The control chart for variables is a means of visualizing the variations that occur in the central tendency and the mean of a set of observations. It shows whether or not a process is in a stable state. Control Charts for Variables

14. Besterfield: Quality Control, 8 th ed..© 2009 Pearson Education, Upper Saddle River, NJ 07458. All rights reserved Control Charts Figure 5-1 Example of a control chart

15. Besterfield: Quality Control, 8 th ed..© 2009 Pearson Education, Upper Saddle River, NJ 07458. All rights reserved Control Charts Figure 5-1 Example of a method of reporting inspection results

16. Besterfield: Quality Control, 8 th ed..© 2009 Pearson Education, Upper Saddle River, NJ 07458. All rights reserved The objectives of the variable control charts are: 1. For quality improvement 2. To determine the process capability 3. For decisions regarding product specifications 4. For current decisions on the production process 5. For current decisions on recently produced items Variable Control Charts

17. Besterfield: Quality Control, 8 th ed..© 2009 Pearson Education, Upper Saddle River, NJ 07458. All rights reserved Procedure for establishing a pair of control charts for the average Xbar and the range R: 1. Select the quality characteristic 2. Choose the rational subgroup 3. Collect the data 4. Determine the trial center line and control limits 5. Establish the revised central line and control limits 6. Achieve the objective Control Chart Techniques

18. Besterfield: Quality Control, 8 th ed..© 2009 Pearson Education, Upper Saddle River, NJ 07458. All rights reserved The Quality characteristic must be measurable. It can expressed in terms of the seven basic units: 1. Length 2. Mass 3. Time 4. Electrical current 5. Temperature 6. Substance 7. Luminosity as appropriate. Quality Characteristic

19. Besterfield: Quality Control, 8 th ed..© 2009 Pearson Education, Upper Saddle River, NJ 07458. All rights reserved How’s to construct? 1. Select the quality characteristic. 2. Choose the rational subgroup. 3. Collect the data.

20. Besterfield: Quality Control, 8 th ed..© 2009 Pearson Education, Upper Saddle River, NJ 07458. All rights reserved 4. Determine the trial center line. (CL) Central Lines are obtained using:

21. Besterfield: Quality Control, 8 th ed..© 2009 Pearson Education, Upper Saddle River, NJ 07458. All rights reserved 5. Determine the control limits for Xbar and R chart After get the value, then you draw both chart and determine the assignable causes.

22. Besterfield: Quality Control, 8 th ed..© 2009 Pearson Education, Upper Saddle River, NJ 07458. All rights reserved 6. Establish the revised central line and control limits for both chart.

23. Besterfield: Quality Control, 8 th ed..© 2009 Pearson Education, Upper Saddle River, NJ 07458. All rights reserved 7. Construct the new chart after get the new value

24. Besterfield: Quality Control, 8 th ed..© 2009 Pearson Education, Upper Saddle River, NJ 07458. All rights reserved Achieve the Objective Figure 5-7 Continuing use of control charts, showing improved quality

25. Besterfield: Quality Control, 8 th ed..© 2009 Pearson Education, Upper Saddle River, NJ 07458. All rights reserved When a point (subgroup value) falls outside its control limits, the process is out of control. Out of control means a change in the process due to a special cause. A process can also be considered out of control even when the points fall inside the 3ơ limits State of Control

26. Besterfield: Quality Control, 8 th ed..© 2009 Pearson Education, Upper Saddle River, NJ 07458. All rights reserved Lets do exercise!