set4 qc

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STRUCTURED/ESSAY (100 marks)

Instruction: This section consists of 6 structured/essay questions.

Answer 4 questions only.

QUESTION 1

(a) Define the following terms:

i. Quality control.

(2 marks)

ii. Continuous Improvement.

(2 marks)

iii. Total Quality Management.

(2 marks)

(b) The following data shows the length of products obtained from a sample of a

population.

26 47 40 34 43 30 53 22 38 32

35 32 40 23 44 37 27 40 52 61

20 34 60 44 38

Based on the data:

i. Build a frequency distribution table consisting of the class data,

frequency, class boundary and class midpoint.

(8 marks)

ii. Find the range of the grouped data

(2 marks)

iii. Find the mean of the grouped data

(4 marks)

iv. Find the standard deviation of the grouped data

(5 marks)

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QUESTION 2

(a) Define:

i. In control process.

(2 marks)

ii. Out of control process.

(2 marks)

(b) A quality inspector intends to construct a mean ( ) and Range(R) Chart to

monitor the quality of service in a bank. 20 samples of the length of time to

process loan application were taken. Each sample has four observations and

all values are in minutes as shown in Table 1.

TABLE 1

Sample Number

Observation X1 X2 X3

1 12 10 11 2 9 10 8 3 10 10 10 4 8 9 12 5 13 14 15 6 7 8 10 7 15 10 10 8 14 13 8 9 10 9 10

10 9 10 10 11 14 8 9 12 8 9 9 13 7 10 9 14 10 10 8 15 10 9 15 16 10 14 14 17 14 8 10 18 16 16 17 19 17 15 14 20 8 7 8

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i. Calculate the mean and range for each sample

(4 marks)

ii. Refer to the Table of Constant for Variables Control, determine the

value of Center Line, Upper Control Limit and Lower Control Limit

for a Mean ( ) and Range (R) control chart.

(8 marks)

iii. Construct the Mean( ) and Range (R) Chart on a graph paper

(8 marks)

iv. State whether the process of loan applications is in control or out of

control based on the chart

(1 mark)

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QUESTION 3

(a) Explain THREE (3) advantages of using attributes control chart

(6 marks)

(b) A production line supervisor decides to count the number of non conforming

units from a process. The supervisor then makes an inspection on 23 samples

and records the data as shown in Table 2. Each sample contains 250 units of

products.

TABLE 2 Number of Sample Number of Non-

Conforming 1 30 2 24 3 26 4 34 5 40 6 33 7 32 8 22 9 26

10 21 11 20 12 45 13 32 14 56 15 43 16 44 17 43 18 43 19 44 20 33 21 32 22 23 23 30

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i. Calculate the fraction of non conformity for each sample

(2 marks)

ii. Determine the value of Center Line, Upper Control Limit and Lower

Control Limit for a p-chart

(7 marks)

iii. Construct the p-chart of the process

(7 marks)

iv. Based on the graph in question (b) iii, state whether the process is in

control or out of control. Explain your answer.

(3 marks)

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QUESTION 4

(a) Define:

i. Random variation.

(2 marks)

ii. Assignable variation.

(2 marks)

(b) Explain THREE (3) purposes of using control chart.

(6 marks)

(c) Table 3 indicates number of defects carried out on 20 samples of rectangular

steel plate surface.

TABLE 3

Plate Number Number of Defects 1 0 2 2 3 4 4 1 5 2 6 3 7 0 8 0 9 1 10 2 11 2 12 2 13 3 14 0 15 2 16 3 17 4 18 0 19 1 20 1

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i. Calculate the value of Central Line (CL), Upper Control Limit (UCL)

and Lower Control Limit (LCL) for c-chart.

(7 marks)

ii. Construct a c-chart on a graph paper

(7 marks)

iii. Interpret the process control based on the chart

(1 mark)

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QUESTION 5

(a) Define:

i. Producer’s risk

(2 marks)

ii. Consumer’s risk

(2 marks)

(b) Explain the following sampling plan:

i. Single sampling plan

(3 marks)

ii. Double sampling plan

(3 marks)

iii. Multiple sampling plan

(3 marks)

(c) Given the following sampling plan:

Lot size, N=5000, Sample size, n=80 Acceptance number, c=2

Use the Cumulative Poisson Distribution Table in Appendix 3, construct an

Operational Characteristics (OC) Curve with the value of fraction defective

from 0.01 to 0.08.

(12 marks)

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QUESTION 6

(a) Define the cost of quality below. Give two examples for each cost.

i. Appraisal cost.

(3 marks)

ii. Internal failure cost.

(3 marks)

iii. External failure cost.

(3 marks)

(b) Construct a cause and effect diagram based on the following Table 4.

TABLE 4

Method Material Staff Machine

- Speed of printer

-Techniques of

printing

-Paper

-Carbon density

-Carbon types

-Less supervision

-Less of training

-Type

-Age

-Maintenance

frequency

-Maintenance for

tension adjustment

(6 marks)

(c) State the application of the following ISO series:

i. ISO 9000

(2 marks)

ii. ISO 9001

(2 marks)

iii. ISO 9002

(2 marks)

iv. ISO 9003

(2 marks)

v. ISO 9004

(2 marks)

set4 qc

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