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Semester II Examinations 2009/
Exam Code(s) 4BI1, 1AP1, 1AP
Exam(s)^4 th^ Industrial Engineering M.Applied Science (Enterprise Systems)
Module Code(s) IE Module(s) Quality Engineering
Paper No. 1 Repeat Paper
External Examiner(s) Prof. J. Antony
Internal Examiner(s) Dr P. Donnellan Prof P. McHugh
Instructions: Answer Q1 and any two from Q2, Q3, Q4, Q5.
Duration (^) 2 Hours
No. of Pages Cover + 4 pages College/Discipline Engineering & Informatics/Industrial Engineering Course Co-ordinator(s) Prof P. McHugh
Requirements : Cambridge Elementary Statistical Tables Graph Paper
Control Chart Factors attached.
Q1. ( 40 marks - 10 x 4 marks )
(i) Define/explain the terms: in statistical control, assignable cause.
(ii) The standard deviation of a machined dimension is 0.1 mm. Determine values for the centreline and 3-sigma control limits of an R-chart , to monitor variability in this machined dimension; the subgroup size is 4.
(iii)A process is controlled by plotting the proportion of nonconforming units in samples of size n= 64 on a p-chart with centreline = 0.04, UCL= 0.12 and LCL= 0. What are the centreline, UCL and LCL, of the equivalent np-chart?
(iv) In your own words, viz. without using any formulae, explain what is represented by the OC-curve of a control chart.
(v) In reporting a machine capability study, a quality engineer notes that Cp = 1.2, Cpk = 0.8. Interpret this finding.
(vi) In the context of acceptance sampling, explain the concepts of producer’s risk and consumer’s risk.
(vii) Why are lower control limits sometimes omitted from control charts? Now name/list three chart types, where this applies.
(viii) Briefly explain the approaches to inspection and decision-making which are characteristic of multiple sampling plans, sequential sampling plans and continuous sampling plans.
(ix) A process is monitored using a c-chart with an upper limit only. What should this limit be, so that the ARL is 8 when the defect rate is
(x) A Critical dimension of a machined part caries the specification 15 ± 0.1. In a Gage R & R study on the instrument used to measure this dimension, repeatability and reproducibility were found to be 0.02 and 0.008 respectively. Compute the P/T ratio for this case, and comment accordingly.
Q2. (30 marks)
a) Describe four patterns that you might see on a control chart and the appropriate corrective action required in each case. (8 marks)
b) The data below are X-bar and R values for 24 samples of size n=5 taken from a process producing bearings. The measurements are made on the inside diameter of the bearing and are in millimetres.
Q4. (cont.)
A company monitors one of its processes by analysing samples of output at regular intervals. Sample means for the last 16 such samples are listed below: 8.00 8.01 8.02 8.01 8.00 8.01 8.06 8. 8.05 8.04 8.03 8.05 8.06 8.04 8.05 8. Construct a CUSUM plot from this data and provide detailed comment/opinion on process performance over the period concerned. (14 marks)
Q5. ( 30marks )
a) Why are Process Capability Studies undertaken? (4 marks) Establish a role for (i) Control Charts, (ii) Histograms, and (iii) Probability paper in conducting capability analyses. (6 marks)
b) What are natural tolerance limits? (4 marks) What does the term statistical tolerancing signify (4 marks)
A potential customer for the five-part assembly shown below has specified 23 ± 0.03 cm for the overall length. From past experience it is known that the components have natural tolerances on their lengths, as follows: Component Tolerance Limits A 2 ± 0.005 cm B 5 ± 0.010 cm C 6 ± 0.010 cm D 7 ± 0.015 cm E 3 ± 0.008 cm
B D
A C
E
Can the customer’s requirement be met? Justify your answer and state your assumptions. (12 marks)
