ET ZC432-18

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BITSPilaniPilani Campus

Quality Control Assuranceand Reliability

Nitin KotkundeLecturer

Department of Mechanical EngineeringBITS Pilani Hyderabad Campus

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BITSPilaniPilani Campus

Lecture 18: REVIEW SESSION

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BITS Pilani, Pilani Campus

OC Curve

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Three SQC Categories

Statistical quality control (SQC): the term used to describe the set of

statistical tools used by quality professionals; SQC encompasses

three broad categories of:

1. Statistical process control(SPC)

2. Descriptive statistics include the mean, standard deviation, andrange

Involve inspecting the output from a process

Quality characteristics are measured and charted

Helps identify in-process variations

3. Acceptance samplingused to randomly inspect a batch of goods to

determine acceptance/rejection

Does not help to catch in-process problems

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Control chart for variables:

x bar-R, x bar-s charts, non-random patterns, process capability estimation

Control chart for Attributes: P chart, C Chart

Control Charts

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Control chart for variables

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Sampling and population

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a) (i).Calculate probability for each possible gradeoutcome (using the relative frequency approach)

(ii).Calculate the expected grade value E(x)

b) Compare and contrast the philosophies of Deming,Crosby, and Juran.

c) What are the advantages of using quality functiondeployment (QFD)? Explain the steps of QFDprocess

Grade letteroutcome

Score variable Number of studentsresponding

A 5 10

B 4 20

C 3 30

D 2 30

F 1 10

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(i)

(ii)

Solution1(a)

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Solution1(b)

CROSBY DEMING JURAN

Definition of

Quality

-It is conformance to

requirements , not as

goodness

-It is managements job to

set the requirements and

communicate to employees.

Meeting and

exceeding the

customers need

and expectations

and then

continuing to

improve.

-Quality mission of the

company is fitness for use

as perceived by customers.

-The mission of individual

departments are to workaccording to specifications

designed to achieve fitness for

use.

Degree of

Seniormanagement

involvement

-Quality improvement starts

from the top.

-Senior management is 100percent responsible for the

problems with Quality and

their continuance.

-Quality is madein the board room.

Majority of Quality problems

are the fault of poormanagement rather than poor

workmanship.

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CROSBY DEMING JURAN

Improve

ment

basis

-Quality improvement is

built on getting everyone

to do it right the first

time (DIRFT)

-Quality improvement isa process ,not a program

, and it takes a long time

for it to become a

normal part of the scene.

-Put everyone in the company to

work to accomplish the

transformation. The

transformation is every bodysjob.

- Repeated use of PDSA cycle.

-Quality improvement is not

fire fighting ,or removing a

sporadic spike. More than that

quality improvement raises

quality performance to

imprecedented or break

through levels.

-All quality improvement takes

place project by project.

Team

work

Management must break down

barriers between departments.

Each department must see other

department as internal customer ,

when this is practiced the

barriers begin to fall.

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CROSBY DEMING JURANSingle sourcing of

supplyThere should be a

single supplier for

any one item , on a

long term relationship

of loyalty and trust

Cost of quality

- Measurement of

quality is the price of

non-conformance, not

indexes.

- Price of non-

conformance is by

counting every thing

that is spent if

everything was not

done right the first

time.

- Companies should

look at the total cost

of product or service

provided by others,

and not just thepurchase price.

Accepting the lowest

bid does not

guarantee the lowest

total cost.

- Cost Of Poor Quality

(COPQ) is the sum of all

costs that would disappear

if there were no qualityproblems.

- Quality improvement

does not come free.

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CROSBY DEMING JURAN

Training

-Orientation to the concepts and

procedures of quality

-Direct skill improvement

-Continual quality data

communications.

-Training should be given on the

job.

-Everyone should be trained in

basic statistical methods.

- Training boosts morale

because it provides workers with

a greater sense of security and

value and a lower stress level.

Quality

awareness

Share with employees the

measurement of what

nonconformity is costing to the

company.

Management must eliminate

slogans , exhortations and

targets asking for zero defectsand new levels of productivity

from the work force.

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CROSBY DEMING JURAN

Recognition

Individual recognition for

those who meet their goals

or perform outstanding acts.

Abolish the annual merit or rating

system. Instead leader should

learn who is in need of individual

help , whose work processes show

extra good performance. Improve

the system and shrink the

difference between the people

that belong to the system.

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Quality Function Deployment (QFD) was developed to bringthis personal interface to modern manufacturing and business. Intoday's industrial society, where the growing distance betweenproducers and users is a concern, QFD links the needs of the customer(end user) with design, development, engineering, manufacturing, and

service functions.

QFD is:

Understanding Customer Requirements

Quality Systems Thinking + Psychology + Knowledge/EpistemologyMaximizing Positive Quality That Adds Value

Comprehensive Quality System for Customer Satisfaction

Strategy to Stay Ahead of The Game

Solution1(c)

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As a quality system that implements elements ofSystems Thinking with elements of Psychology andEpistemology (knowledge), QFD provides a system ofcomprehensive development process for:

Understanding 'true' customer needs from thecustomer's perspective

What 'value' means to the customer, from the customer'sperspective

Understanding how customers or end users becomeinterested, choose, and are satisfied

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Analyzing how do we know the needs of the customer

Deciding what features to include

Determining what level of performance to deliver

Intelligently linking the needs of the customer withdesign, development, engineering, manufacturing, andservice functions

Intelligently linking Design for Six Sigma (DFSS) with the

front end Voice of Customer analysis and the entiredesign system

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QFD is a comprehensive quality system thatsystematically links the needs of the customer with variousbusiness functions and organizational processes, such asmarketing, design, quality, production, manufacturing, sales,

etc., aligning the entire company toward achieving a commongoal.

It does so by seeking both spoken and unspokenneeds, identifying positive quality and business opportunities,

and translating these into actions and designs by usingtransparent analytic and prioritization methods, empoweringorganizations to exceed normal expectations and provide alevel of unanticipated excitement that generates value.

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The QFD methodology can be used for both tangibleproducts and non-tangible services, includingmanufactured goods, service industry, software products,IT projects, business process development, government,

healthcare, environmental initiatives, and many otherapplications.

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(a) Holden Construction Co. builds primarily three-and four-unit apartment buildings (called triplexes andquadraplexes) for investors and it is believed that the totalconstruction time in days follows a normal distribution. The

mean time to construct a triplex is 100 days, and thestandard deviation is 20 days. If the firm finishes this triplexin 75 days or less, it will be awarded a bonus payment of$5,000. What is the probability that Holden will receive the

bonus?

Question - 2

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(b) In 12 samples of size n = 7, the average value of thesample means is x double bar = 6.860 cm for thedimension of interest, and the mean of the ranges of thesamples is R bar= 0.027 cm. Determine (a) lower and

upper control limits for the x bar chart and (b) lower andupper control limits for the R chart. (c) What is your bestestimate of the standard deviation of the process?

(c) The upper and lower control limits for a p chart are: LCL= 0 and UCL = 0.20. Determine the minimum possiblesample size n that is compatible with this control chart.

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Solution - 2(a)

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(a) x chart:x = 6.860 cm = CL

LCL =x - A2R = 6.860 - 0.419(0.027) = 6.8487 cm

UCL =x + A2R = 6.860 + 0.419(0.027) = 6.8713 cm

(b) R chart:R = 0.027 = CLLCL =D3R = 0.076(0.027) = 0.0205 cm

UCL =D4R = 1.924(0.027) = 0.0519 cm

(c) Thex chart is based on 3 x/ n

Therefore,A2R = 3 x/ n

x=A2R n /3 = 0.419(0.027) 7 /3 = 0.00998 cm

Solution - 2 (b)

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p = 0.5(UCL + LCL) = 0.5(.20 + 0) = 0.10

LCL =p - 3p(1p) / n = 0

Therefore,p = 3p(1p) / n

0.10 = 3 0.10( 0.90) / n(0.10)2= 0.01 = 32(0.10)(0.90)/n = 0.81/n

n = 0.81/0.01 = 81

Solution - 2 (c)

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a) Demonstrate an understanding of the relationshipbetween the time to failure distribution, the reliabilityfunction, and the hazard rate. Describe the reliabilityevaluation of series and parallel system.

b) Four components A,B, C and D are placed in parallel tomake a subassembly in a circuit board. The reliabilities of

A, B, C and D are 0.93, 0.88, 0.95, and 0.92, mean time tofailure of 3000h. Find the reliability of the subassembly for

2500h of operation. What is the mean time to failure of thesubassembly? If it is desired that the subassembly has amean time to failure of 6600h, what would have tobe the mean time to failure of the components?

Question - 3

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c) A standby system has a basic unit with four standby

components. The time to failure of each component

has an exponential distribution with a failure rate of 0.008 per

hour. For a 400h operation period, find the reliability of the

standby system. What is mean time to failure? Suppose allfive components are operating simultaneously in parallel.

What would be the system reliability be in that situation?

What would be the mean time to failure?

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Explanation about failure rate function, r(t) =f(t)R(t),

Reliability of Series system

A series system is a configuration such that, if any one of

the system components fails, the entire system fails.Conceptually, a series system is one that is as weak as its

weakest link. A graphical description of a series system is shown

in Figure.

RS= R1R2... Rn(if the component reliabilities differ,

or)

RS= [R

i]n (if all i = 1, ... , n components are identical)

Solution3(a)

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Reliability of parallel system

parallel system is a configuration such that, as long as not

all of the system components fail, the entire system works.

Conceptually, in a parallel configuration the total system

reliability is higher than the reliability of any single system

component. A graphical description of a parallel system of "n"

components is shown in Figure.

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Solution3(b)

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Solution3(c)

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GOOD LUCK

ET ZC432-18

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