Q6 (Process Capability/NDT) A properly controlled trial was conducted on a new p
ID: 1867902 • Letter: Q
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Q6 (Process Capability/NDT) A properly controlled trial was conducted on a new process for canning a soft drink The results of the trial are presented in Table Q6. The sub group size was 5 cans and the interval between sub-groups was 1 hour. The specification for contents is 330-336ml 0 Sub- Contents (mg) rou 331.2, 331.0,332.2, 332.5, 330.8 331.5, 332.5, 333.5, 322.5, 331.9 330.9, 331.9, 332.1, 330.9, 331.8 30.2, 332.5, 331.5, 333.0, 332.4 331.2,330.2, 331.5, 333.1, 332.5 30.2, 331.5, 332.4, 332.8, 331.0 31.0, 332.5, 331.9, 332.1,332.6 330.4, 330.8, 331.5, 332.1, 331.0 Table Q6 Draw control charts for both the average contents and range, illustrating the control limits. Is the process in a state of control? a. (15 marks) If you were working as an Engineer in a manufacturing company and were tasked with setting up SPC for a process, what factors would influence your choice of the number of samples in each sub-group and the time between sub-groups? b. (5 marks) Describe the use of dye penetrant testing. List two advantages and two limitations of the method c. (5 marks)Explanation / Answer
a.
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c.
Dye penetrant inspection (DPI), also called liquid penetrate inspection (LPI) or penetrant testing (PT), is a widely applied and low-cost inspection method used to locate surface-breaking defects in all non-porous materials (metals, plastics, or ceramics). The penetrant may be applied to all non-ferrous materials and ferrous materials, although for ferrous components magnetic-particle inspection is often used instead for its subsurface detection capability. LPI is used to detect casting, forging and welding surface defects such as hairline cracks, surface porosity, leaks in new products, and fatigue cracks on in-service components.
The main advantages of DPI are the speed of the test and the low cost. Disadvantages include the detection of only surface flaws, skin irritation, and the inspection should be on a smooth clean surface where excessive penetrant can be removed prior to being developed. Conducting the test on rough surfaces, such as "as-welded" welds, will make it difficult to remove any excessive penetrant and could result in false indications. Water-washable penetrant should be considered here if no other option is available. Also, on certain surfaces a great enough color contrast cannot be achieved or the dye will stain the workpiece.
Limited training is required for the operator — although experience is quite valuable. Proper cleaning is necessary to assure that surface contaminants have been removed and any defects present are clean and dry. Some cleaning methods have been shown to be detrimental to test sensitivity, so acid etching to remove metal smearing and re-open the defect may be necessary.
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