Quality Management and Reliability

Main objectives of the assessment:To enable students to demonstrate their in-depth knowledge of the principles of advanced techniques of reliability engineering and abilities to apply them to solve practical problems.

Brief Description of the assessment:Prepare an individual report to complete the four questions. They are related to all the key topics of reliability.Learning outcomes for the assessment (refer to the appropriate module learning outcomes)

Students will be able to demonstrate the following:• To gain comprehensive understanding of advanced techniques of reliability engineering;• To organise the collection of plant data and undertake an analysis of it which will facilitate the diagnosis of reliability problems and their effective elimination;• To apply and critically evaluate the most appropriate of the currently available techniques for reliability assessment.

Assessment criteria:Q1. Initial data analysis (20%)Q2. Basic reliability and availability calculation (30%)Q3. Reliability calculation based on Reliability Block Diagram (20%)Q4. Weibull analysis of lifetime data (30%)ASSIGNMENT

A company which produces railway sleepers for rail infrastructure projects, is seeking to improve its product quality and reliability. The company has provided the following qualitative and quantitative data related to its current operation. Prepare an individual report to carry out the evaluation and answer the following four questions.

Q1. The company has kept at one of its plants 24 months records of the total number of failures occurring each month, as shown in Table Q1. Produce the 3-month moving average and the 6-month moving average plots, together with the CUSUM plot (if the target value is 15).

Table Q1

Month

Failures

1

18

2

20

3

16

4

10

5

12

6

18

7

15

8

11

9

13

10

15

11

15

12

22

13

12

14

17

15

15

16

14

17

9

18

13

19

13

20

17

21

16

22

18

23

14

24

21

Q2. A machine used in a process has an MTBF of 400 hours and an MTTR of 8 hours.

1). Calculate its availability.

2). The target availability is to be 99.9% to meet demands. If the machine’s availability is less than this value, then an option is to add identical machines as a stand-by.

How many additional machines would be needed to meet the target availability? Justify your answer.

3). The cost of the machine is £350,000 and the downtime time cost of the process is £5000 per hour. For this new stand-by arrangement, what is the payback period?

Q3. Using the system reduction procedure, calculate the reliability of the independent system as shown in the form of a Reliability Block Diagrams below (Figure Q3). Illustrate how the Reliability Block Diagrams are simplified. The reliabilities of all units are shown in the diagram.

Figure Q3

Q4. In a reliability test in the company, the time-to-failure values of ten mechanical items of the same design running under identical condition were recorded and are as given in the following table (Q4):

Table Q4

Unit No.

Time to failure (hours)

1

1800

2

1370

3

1510

4

1230

5

1050

6*

1400

7

2020

8

1630

9*

1700

10*

1300

* Units 6, 9 and 10 had not failed at the end of the test period.

Using the median rank method for estimating the failure probability and assuming that the guaranteed life before failure is 500 hours,

a). Calculate and tabulate the median ranks for the data supplied.

b). Plot the cumulative percent failure versus time to failure on the Weibull graph paper supplied.

c). Estimate the shape factor and the characteristic time to failure for the distribution. Infer from the value of whether the failure is an early failure, a random failure or a wear-out failure.

Formulae that may be used for Question 4 are given below:

New_increment = N +1−(Order_number_of _ previous_ failed_item) Divided by N +1−(Number_of _ previous_items)

Order _number = New_increment + previous_order _number

Median_rank = Order_number−0.3

N +0.4

where N is the total number of items in the sample.