itroduction to cal quality control

8/3/2019 Itroduction to cal Quality Control

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Introduction to Statistical

Quality Control


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Chapter 1

Quality Improvement in the

Modern Business Environment


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1-1. The Meaning of Quality and

Quality Improvement

1-1.1 Dimensions of Quality

1-1.2 Quality Engineering Technology


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Performance

Reliability

Durability

Serviceability

Aesthetics

Features

Perceived Quality

Conformance to

standards


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Performance Will the product perform its intended

function?

Will this industrial scale measure up to 4000

pounds in 5 pound graduations?


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Reliability How often does the product fail?

How often do I have to take this Toyota Camry

to the service department?


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Durability How long will the product last?

The product should perform satisfactorily over

a long period of life

If I buy that 1999 Toyota 4Runner when the

lease expires, will it give me good service for

10 more years?


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Serviceability How easy is it to repair the product?

If amazon.com sends the wrong book, how hard

is it to get this error corrected?


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Aesthetics Is the product pleasing to the senses?

Do you like the box in which Timberland Shoes

are packaged?


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Features What will the product do beyond the basics?

Does the new Ford Focus come with a CD

changer, or do you have to pay extra for that?


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Perceived quality What is the reputation of the company

selling this product?

Is Delta really ready when you are?

Why do people buy Gucci handbags?


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Conformance to standards

Is the product made as designed?

Why do they have to beat on those Ford Taurus

bodies when they are being assembled in

Hapeville?


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1-1.1 Dimensions of Quality Definitions of Quality

Quality means fitness for use- quality of design

- quality of conformance

Quality is inversely proportional tovariability.


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Quality of design Automobile differences

Materials used in construction

Specifications of the components

Reliability of drive train components

Reliability of accessories


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Quality of conformance How well does the product conform to the

specifications required by the design?

Choice of manufacturing processes

Training of the workers

Supervision of the workers

Motivation of the workers

Quality-assurance procedures that were used


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Quality is inversely proportional to variability

Toyota Lexus versus Ford Taurus

That transmission noise (or lack of it) is wasted

energy caused by components that dont fit

precisely

Imprecise components lead to wear and tear

Ford Taurus/Mercury Sable transmission lastsfor 64,000 miles


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Transmission Example

N(100,10)

vsN(100,4)


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Quality Improvement

Quality improvementis the reduction of

variability in processes and products.

Alternatively, quality improvementis also

seen as waste reduction.


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1-1.2 Quality Engineering

Terminology

Quality engineeringis the set of operational,

managerial, and engineering activities that acompany uses to ensure that the quality

characteristics of a product are at the

nominal or required levels.


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Inherent variability No two products are ever identical

Slight differences in materials

Slight differences in machine settings

Slight differences in operators

Slight differences in ambient temperature

during production Papermate Pens not much different

Fins on a turbine engine quite a lot


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Terminology

Two types of data:

Attributes Data - discrete data, often in theform of counts

Variables Data - continuous measurementssuch as length, weight

Both types will be discussed in the course


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TerminologySpecifications

Quality characteristics being measured are often

compared to standards orspecifications.Desired measure for the quality characteristic

Example: Shaft and bearing

Too loose the assembly will wobble causing

wearToo tight, and the assembly can not be made,

no clearance


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Nominal or target value

Desired value for a quality characteristic


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UpperSpecification Limit (USL)

LowerSpecification Limit (LSL)

Largest and smallest allowable values


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UpperSpecification Limit (USL)

LowerSpecification Limit (LSL) One-sided

The compression strength of a Coke bottle must begreater than a given psi value

Two-sided

The weight of potato chips in the bag can bebetween 7.8 and 8.3 ounces


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Design specifications Over the wall

From design to manufacturing

Cooperatively

Between design and manufacturing


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Terminology

When a component or product does not

meet specifications, it is considered to benonconforming.

A nonconforming product is considered

defective if it has one or more

nonconformities that may seriously affect

the safe or effective use of the product.


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Terminology

A new car is purchased

A bubble in the paint on the door is noticedNonconformity yes

Defective car - no


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Terminology

Concurrent Engineering

Team approach to design. Specialists frommanufacturing, quality engineering,

management, etc. work together for product

or process improvement.


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1-2. A Brief History of Quality

Control and Improvement

(Refer to Table 1-1)

Frederick Taylor (1875) introduces theprinciples of scientific management;

dividing work into tasks with standardized

procedures

The Gilbreths developed standard times and

motions (1920s)


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WalterShewhart (1924) introduced statistical

control chart concepts and QC begins

Dodge and Romig (1928), Bell Labs, develop

acceptance sampling as an alternate to 100%

inspection

During WW II the shells didnt fit the howitzers

leading to development of MIL-STDs


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The

American

Society for Quality

Controlformed in 1946 [now known as the

American Society for Quality (ASQ)]

1950s and 1960s saw an increase in

reliability engineering, experimental design,

and statistical quality control


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Competition from foreign industries (Japan)

increases during the 1970s and 1980s.

Statistical methods for quality improvement use

increases in the United States during the 1980s

Total Quality Management (TQM) emergesduring 1970s and into the 1980s as an important

management tool to implement statistical methods.


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Malcolm Baldrige National Quality Award is

established in 1988.

ISO 9000 certification activities increase in U.S.

industry in the 1990s.

Motorolas Six-Sigma initiative begins in the1990s.


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1-3. Statistical Methods for

Quality Control and Improvement

Three major areas:

Statistical process control (SPC)

Design of experiments (DOE)

Acceptance sampling


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Statistical ProcessControl (SPC)

Control charts are

used for process

monitoring and

variability reduction.

SPC is an on-line

quality control tool.


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Design of Experiments

Experimental design is an approach tosystematically varying the controllable input

factors in the process then determining the effect

these factors have on the output responses.

Experimental designs are off-line quality tools. Crucial for variability reduction.


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Quality Control and ImprovementAcceptance Sampling

Acceptance samplingis the inspection and

classification of a sample of the product selectedat random from a larger batch or lot and theultimate decision about disposition of the lot.

Two types:

1. Outgoing inspection - follows production2.Incoming inspection - before use in

production


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Quality cannot be inspected into

the product When the organization realizes this, process

improvement efforts begin


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The objective Systematic reduction of variability

First, by using acceptance sampling

Then, by using SPCFinally, by using DOE

We dont stop when requirements are met

F

urther reductions in variability lead to betterperformance

Avoid the Taurus transmission


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1-4. Other Aspects of Quality


Total Quality Management (TQM)

TQM is a managerial framework to accomplishquality improvement.

Other names and related approaches:

Company-Wide Quality Control (CWQC) Total Quality Assurance (TQA)

Six-Sigma


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1-4. Other Aspects of Quality


1-4.1 Quality Philosophy and Management

Strategies

1-4.2 The Link Between Quality and

Productivity

1-4.3 Quality Costs

1-4.4 Legal Aspects of Quality

1-4.5 Implementing Quality Improvement


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1-4.1 Quality Philosophy and

Management StrategiesThree Important Leaders

W. Edwards Deming

- Emphasis on statistical methods in qualityimprovement

Joseph Juran

- Emphasis on managerial role in quality

implementation Armand V. Feigenbaum

- Emphasis on organizational structure


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1-4.1 Quality Philosophy and

Management Strategies

Total Quality Management (TQM)

Quality Standards and Registration

ISO 9000

Six Sigma

Just-In-Time, Lean Manufacturing,

Poka-Yoke, etc.


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TQM Began in the early 80s based on the

philosophies of Deming and Juran

Evolved into wide spectrum of ideasParticipation in quality groups

Work culture

Customer focus

Supplier quality improvement

Cross-functional teams concerned with quality


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TQM A success?

Moderately

Why not?

Not enough concern for reduction of variability

Ineffective training conducted by HRpeople

No knowledge of what is important

Success measured by % of workforce trained

Management not committed


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TQM More reasons for lack of success

Zero defects, value engineering, quality is free

Programs with no emphasis on reducing variability


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ISO 9000

Quality system oriented

Say what you do, do what you say

Much effort devoted to paperwork and

bookkeeping

Not much to reducing variability and improving

processes


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ISO 9000 paragraphs

1. Management responsibility for quality

2. Design control

3. Document and data control

4. Purchasing and contract management

5. Product identification and traceability

6. Inspection and testing, includingcontrol of measurement and inspectionequipment


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ISO 9000 paragraphs

7. Process control

8. Handling of nonconforming product

9. Handling, storage, packaging and delivery ofproduct

10. Control of quality records

11. Internal audits

12. Training

13. Statistical methodology


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ISO 9000

US$40 billion annual business worldwide

Registrars, auditors, consultants

Plus, 1000s of hours of internal costs

Effective?

Does it reduce variability?


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Six Sigma

Developed by Motorola in the late 80s

Consider that + 3Wprovides 0.00135 in

each tail, or 0.00270 in the two tales

So, in 1 million parts, 2700 would be

defective


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Six Sigma

Consider an assembly of 100 parts that must

all function for the assembly to function

.9973 x .9973 x ..9973 = (.9973)100 = .7631

Thus, about 23.7% of the products under 3W

will fail

Not usually an acceptable situation


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Six Sigma

But, + 6W results in 0.999999998 inside

specs

(0.999999998)100 = .9999998

Or, 2 parts/billion defective

i.e., 0.2 ppm

Much better than + 3W


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Six Sigma

Has moved beyond Motorola

Has come to encompass much more

Has become a method for improving

corporate business performance

Companies involved in Six Sigma use

teams that work on projects involving

quality and costs


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Six Sigma

More successful than TQM

More managerial commitment

Involves costs

But, its still another slogan and program

Better to train everyone in quality tools and

make efforts to reduce variability


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JIT, Lean Manufacturing, etc.

Programs that devote too little attention to

variance reduction

For example, JIT

The variability in demand results in a need for

inventory

Reduce the variability and reduce the inventory


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1-4.2 The Link Between Quality

and Productivity

Effective quality improvement can be

instrumental in increasing productivity andreducing cost.

The cost of achieving quality improvements

and increased productivity is often

negligible.


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An example

Data

100 parts/day are manufactured

75% are conforming

60% of the nonconforming can be reworked for

a cost of$4

Remainder are scrapped Direct manufacturing cost is $20/part


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An example

Cost/conforming part

[$20 (100) + $4 (15)]/90 = $22.89

Note that the yield is 90 conforming/day


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An example

New process us introduced

Fallout is 5%

60% can be reworked

Cost/conforming part

[$20 (100) + $4 (3)]/98 = $20.53

Note that the yield is 98 conforming/day

Up from 90/day

And, costs are reduced by 10.3%


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1-4.3 Quality Costs

Quality Costs are those categories of costs that are

associated with producing, identifying, avoiding,

or repairing products that do not meetrequirements. These costs are:

Prevention Costs

Appraisal Costs

Internal Failure Costs

External Failure Costs


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Quality costs

Prevention costs

Quality planning and engineering

New products review

Product/process design

Burn-in

Training Quality data acquisition and analysis


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Appraisal costs

Inspection and test of incoming material

Product inspection and test

Materials and services consumed

Maintaining accuracy of test equipment


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Internal failure costs

Scrap

Rework

Retest

Failure analysis

Downtime

Yield losses

Downgrading (off-specing)


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External failure costs

Complaint adjustment

Returned product/material

Warranty charges

Liability costs

Indirect costs


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Pareto analysis

Cost reduction through identifying

improvement opportunities

Identifying quality costs by category, or by

product, or by type of defect or

nonconformity


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Monthly quality costs forPCB assembly

Type of defect % of total defects Scrap & rework costs

Insufficient solder 42 $37,500

Misaligned components 21 $12,000

Defective components 15 $8,000

Missing components 10 $5,100

Cold solder joints 7 $5,000

All other causes 5 $4,600

Total 100 $72,200


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Pareto analysis

Insufficient solder

42% of defects and 52% of scrap and rework

costs Work on that defect first

Most of the cost reductions will come fromattacking the few problems that are

responsible for the majority of the qualitycosts


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Appraisal or prevention

Many firms spend far too much of their

quality management budget on appraisal

and not enough on prevention Money spent on prevention has a much better

payoff than money spent on appraisal


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1-4.4 Legal Aspects of Quality

The re-emergence of quality assurance as

an important business strategy is in

part a result of

1. Consumerism

2. Product Liability


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Consumerism

Virtually every product line of today issuperior to that of yesterday

But, many consumers see it otherwise Consumer tolerance for minor defects &

aesthetic problems has decreasedconsiderably

Blemishes, surface-finish defects, noises,appearance problems


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Consumerism

Many manufacturers introduce new designs

before they are fully evaluated and tested

To remain competitive

Unproved designs


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Product liability

Manufacturers and sellers are likely to incur

a liability when they have been

unreasonably careless or negligent in whatthey have designed, or produced, or how

they have produced it


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More stringent: Strict liability

1. There is a strong responsibility for both

manufacturer and merchandiser requiring

immediate responsiveness to unsatisfactoryquality through product service, repair, or

replacement of defective product

Extends into the period of use by the consumer By producing the product, manufacturer and

seller must accept responsibility for use


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More stringent: Strict liability

2. All advertising statements must be

supportable by valid company quality or

certification data


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Introduction to Statistical Quality Control,

1-4.5 Implementing Quality

Improvement Strategic management of quality

Almost all successful efforts have been

management-driven. Too much emphasis on registration and

certification programs (ISO, QS)

Insufficient focus on quality planning and design,

quality improvement, overemphasis on qualityassurance

Poor use of available resources

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