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Statistical Process Control (SPC) Techniques and Gauge Capability

## Types of Variation in Atypical Production Processes

Name and describe the two types of variation that may be observed in atypical production process, also discuss how Statistical Process Control (SPC) techniques can be used to identify them. Who is responsible for eliminating each type of variation?
[9 marks]
(b) Magazines are printed onto continuous paper. The final process on the printing press is to cut and fold the continuous paper into finished copies of  the magazine. Every 30 minutes, 10 copies are selected at random andinspected for process control purposes. The number of defects in each sample of 10 copies is noted.Briefly describe the four main types of attribute control charts.
[4 marks]
(ii) Which type of attribute control chart would you use in this case, and
why?
[2 marks]
(iii) Calculate the upper and lower control limits of a suitable attribute control chart for the data. ( Statistical Process Control Chart design guidelines are given in Appendix 1) and plot the chart, thus conclude whether the process is in or out of statistical controlWhat can happen when variation is incorrectly identified? Include in your
answer a description of an experiment that can be used to demonstrate this phenomenonWhy is Gauge Capability important? Describe a type of study that may be used
to determine Gauge Capability and explain the methodology used for such a study.
[6 marks]
(b) What is meant by “Process Capability”? Explain the terms Cp and Cpk, hence describe why both are needed in order to give a meaningful measure of processcapability.
[6 marks]
(c) As part of a process for the manufacture of a control valve, the dimension for a particular feature is given as 51.84mm to 52.00mm. In an effort to establish process capability, sixty (60) samples are taken from the process and measured.
The mean and standard deviation of the process are determined as 51.90 mm and 0.025 mm respectively. The customer insists that a process capability giving a value of Cpk = 1.33 is required. Demonstrate whether the process is capable of manufacturing parts to these specifications and determine how the process would need to be improved to achieve the required Cpk value. Distinguish between operator and management actions and state any assumptions.
[12 marks]
(d) On further examination, the data above is found to be non-normal. Explain how this may affect the validity of the calculations and briefly describe an approach which alleviates the normality requirements. What are thelimitations of this approach?

Q3. A quality characteristic of a component is dependent on 3 settings of amanufacturing process. A study is performed to determine how the three settings
affect the quality characteristic. An experiment consisting of varying each of the
three factors about two levels is conducted.
(a) Draw the geometrical representation of this experiment and label each
corner of the cube with the corresponding test conditions
(eg +, -,).
[11 marks]
(b) Figure Q3(b) shows the Interaction Plots from a full factorial (23)
experimental design applied to the manufacturing process.
(i) Explain why a factorial design is considered to be better than changing one factor at a time.
[4 marks]
(ii) Explain the concept of the Interaction Plot and by examining the plots presented in Figure Q3(b) determine which factors indicate an interaction.
[6 marks]
(iii) Explain why it is necessary to use Response Surface Methodology to find the optimum settings of the manufacturing process.
[2 marks]
(iv) Outline the procedure for generating the Response Surface