statistical quality controlie.sharif.edu/~qc/lec_1_quality_improv..pdf · •introduction to...

STATISTICAL QUALITY CONTROL

Majid Rafiee

Department of Industrial Engineering

Sharif University of Technology

rafiee@sharif.ir

Quality Improvement in Modern Business

Environment

Copyright Notice

• Parts (text & figures) of this lecture adopted from:

• Introduction to Statistical Quality Control, 5th Edition, by Douglas C.

Montgomery , Arizona State University

• https://www.wikipedia.org

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Outline

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Meaning of Quality and Quality Improvement

History of Quality Control

Statistical Methods for Quality Control

Management Aspects of Quality Control

Outline

5

Meaning of Quality and Quality Improvement

History of Quality Control

Statistical Methods for Quality Control

Management Aspects of Quality Control

Are These High Quality Shoes??

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Quality Has Different Dimensions

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Performance

Reliability

Durability

Serviceability

Aesthetics

Features

Perceived Quality

Conformance to Standards

Quality Has Different Dimensions

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Performance

Reliability

Durability

Serviceability

Aesthetics

Features

Perceived Quality

Conformance to Standards

Performance

• Refers to a product's primary operating characteristics.

• Involves measurable attributes.

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Quality Has Different Dimensions

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Performance

Reliability

Durability

Serviceability

Aesthetics

Features

Perceived Quality

Conformance to Standards

Reliability

• Is the likelihood that a product will not fail within a specific time

period.

• This is a key element for users who need the product to work

without fail.

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Reliability

• R(Product Name)Time = Probability

• R(Airbus)10h = 0.999999998

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Quality Has Different Dimensions

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Performance

Reliability

Durability

Serviceability

Aesthetics

Features

Perceived Quality

Conformance to Standards

Durability

• Measures the length of a product’s life.

• When the product can be repaired, estimating durability is more

complicated.

• The item will be used until it is no longer economical to operate it.

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Quality Has Different Dimensions

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Performance

Reliability

Durability

Serviceability

Aesthetics

Features

Perceived Quality

Conformance to Standards

Serviceability

• Is the speed with which the product can be put into service when it

breaks down.

• Consumer's ease of obtaining repair service

• Example: access to service centers

• Ease of self-service

• reliability of service

• example: whether the service is performed right the first time

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Quality Has Different Dimensions

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Performance

Reliability

Durability

Serviceability

Aesthetics

Features

Perceived Quality

Conformance to Standards

Aesthetics or Style

• The aesthetic properties of a product contribute to the identity of a

company or a brand.

• Aesthetics is the subjective dimension indicating the kind of

response a user has to a product.

• It represents the individual’s personal preference.

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Quality Has Different Dimensions

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Performance

Reliability

Durability

Serviceability

Aesthetics

Features

Perceived Quality

Conformance to Standards

Features

• Features are additional characteristics that enhance the appeal of

the product or service to the user.

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Quality Has Different Dimensions

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Performance

Reliability

Durability

Serviceability

Aesthetics

Features

Perceived Quality

Conformance to Standards

Perceived Quality

• Perceived Quality is the quality attributed to a good or service based

on indirect measures.

• Consumers do not always have complete information about a product's

or service's attributes; indirect measures may be their only basis for

comparing brands.

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Made In ChinaMade In Iran

Made In Japan…

Quality Has Different Dimensions

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Performance

Reliability

Durability

Serviceability

Aesthetics

Features

Perceived Quality

Conformance to Standards

Conformance to Standards

• Is the precision with which the product or service meets the

specified standards.

• Target

• Tolerance

• the range of permitted deviation from the target

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What is The Meaning of Quality?

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What is The Meaning of Quality?

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• Quality means fitness to use

What is The Meaning of Quality?

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Quality means fitness to use

This is a traditional definition

What is The Meaning of Quality?

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Quality is inversely proportional to variability

This is a modern definition of quality

Quality is inversely proportional to “variability”

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Quality is inversely proportional to “variability”

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• The Transmission Example

What is The Meaning of Quality Improvement ?

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• Elimination of waste

• useful in service or transactional businesses

• Reduction of variability in processes & products

What Is Quality Engineering?

• Variability is described in statistical terms

• Statistical methods play central role in quality improvement

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Applying statistical methods to quality

engineering.

What Is Quality Engineering?

Quality engineering is the combination of engineering, statistics, and

management to reduce variability while maintaining the average.

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Quality Characteristics

• Also called Critical-To-Quality ( CTQ )

• What the user or consumer thinks of as quality

• Types of Quality Characteristics

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Physical Time Orientation

Sensory

Types of Quality Characteristics

• Physical

• Length, weight, voltage, viscosity

• Sensory

• Taste, appearance, color

• Time orientation

• Reliability, durability, serviceability

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[from: https://www.latestquality.com/ctq-tree-example/, last seen on January 2019]

Classifying Data On Quality Characteristics

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Data

Variables Attributes

Classifying Data On Quality Characteristics

• Variables

• Often continuous measurements

• Length, voltage, viscosity

• Following continuous distribution

• Attributes

• Usually discrete data

• Often taking the form of counts

• Following discrete distribution

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Outline

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Meaning of Quality and Quality Improvement

History of Quality Control

Statistical Methods for Quality Control

Management Aspects of Quality Control

History

• Walter A. Shewhart

• 1920’s

• Control chart

• More on Wiki

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Outline

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Meaning of Quality and Quality Improvement

History of Quality Control

Statistical Methods for Quality Control

Management Aspects of Quality Control

Statistical Methods for Quality Control

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Statistical Methods for Quality Control

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Statistical Methods

Acceptance Sampling

(AS)

Designed experiments

(DOX)

Statistical process control (SPC)

Statistical Methods for Quality Control

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Statistical Methods

Acceptance Sampling

(AS)

Designed experiments

(DOX)

Statistical process control (SPC)

Acceptance Sampling (AS)

• Uses statistical sampling to determine whether to accept or reject a production lot of material

• Off-line technique (after production)

• Pros

• Simplest quality control technique

• Economy of time and money in comparison to 100% inspection

• Cons

• Not corrective & preventive

• likelihood or risk

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Variations Of Acceptance Sampling

• outgoing inspection

• Receiving/ incoming inspection

• Disposition of lots

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Variations Of Acceptance Sampling

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Statistical Methods for Quality Control

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Statistical Methods

Acceptance Sampling

(AS)

Designed experiments

(DOX)

Statistical process control (SPC)

Designed experiments (DOX)

• Discovering the key factors that influence process performance for

Process optimization

• Off-line technique (before production)

• Pros

• The most desirable quality control technique

• corrective & preventive

• Cons

• Cost & time needed

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Designed experiments (DOX)

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A factorial experiment with three factors

Statistical Methods for Quality Control

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Statistical Methods

Acceptance Sampling

(AS)

Designed experiments

(DOX)

Statistical process control (SPC)

Statistical process control (SPC)

• Using Control charts, plus other problem-solving tools. Useful in

monitoring processes, reducing variability through elimination of

assignable causes

• On-line technique (during production)

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Control chart & Specifications

• a statistical process control tool used to determine if a

manufacturing or business process is in a state of control.

• Specifications

• Lower specification limit

• Upper specification limit

• Target or nominal values

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Control chart & Specifications

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Outline

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Meaning of Quality and Quality Improvement

History of Quality Control

Statistical Methods for Quality Control

Management Aspects of Quality Control

Management Aspects of Quality Control

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Management Aspects of Quality Control

Quality Planning

Quality Assurance

Quality Control and

Improvement

Management Aspects of Quality Control

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Management Aspects of Quality Control

Quality Planning

Quality Assurance

Quality Control and

Improvement

Quality Planning

• Strategic activity

• As important as financial plan, marketing plan, …

• Involves identifying customers & their needs

• Listening to voice of the customer

• Developing products or services meet or exceed customer

expectations

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Management Aspects of Quality Control

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Management Aspects of Quality Control

Quality Planning

Quality Assurance

Quality Control and

Improvement

Quality Assurance

• Is the set of activities that ensures the quality level

• Documentation of quality system

• Involves for: policy, procedures, work instructions and specifications

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Management Aspects of Quality Control

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Management Aspects of Quality Control

Quality Planning

Quality Assurance

Quality Control and

Improvement

Quality Control and Improvement

• Involve the set of activities used to ensure that the products &

services meet requirements and are improved on a continuous basis

• Using statistical techniques

• SPC, DOX, …

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Quality Philosophies and Management Strategies

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Feigenbaum

Total Quality Control

quality leadership, quality technology, organizational

commitment

Deming

PDCA

Plan, do, control, act

Juran Trilogy

Planning, Control,

Improvement

Common Concepts of Quality Philosophies

• Importance of leadership & management in quality improvement

• Emphasis on using statistical methods

• Quality as a competitive advantage

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International Organization for Standardization (ISO)

• Wiki

• is an international standard-setting body composed of representatives

from various national standards organizations.

• ISO 9000, ISO 14000, ISO/TS 16949, …

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Quality Awards

• EFQM, MBNQA, Deming Prize, …

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Six Sigma

• Focus of Six Sigma is on Process Improvement with an Emphasis on

Achieving Significant Business Impact

• Involves a five-step process (DMAIC)

• Define, Measure, Analyze, Improve, Control

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[from: http:// xlncacademy.com/blog/top-5-unique-benefits-of-six-sigma , last seen on January 2019]

Six Sigma

• LSL & USL are fixed

• It is the process which changes

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Six Sigma

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Six Sigma

• A visit to a fast-food store: Hamburger (bun, meat, special

sauce, cheese, pickle, onion, lettuce, tomato), fries, and

drink. This product has 10 components.

• Q1) Probability of customer satisfaction for a single meal in

Six Sigma & Three Sigma?

• Q2) Family of four, once a month; Probability of customer

satisfaction for all meals in a month & in a year ?

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The Process Improvement Triad:DFSS, Lean, and DMAIC

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Design for Six Sigma (DFSS)

• Only so much improvement can be wrung out of an

existing system

• New process design

• New product design (engineering)

• DFSS Matches Customer Needs with Capability &

enhances product design methods

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Lean

• A set of methods and tools used to eliminate waste in

a process

• identify anything not absolutely required to deliver a

quality product on time

• reduce inventory, lead time, and cost

• increase productivity, quality, on time delivery,

capacity, and sales

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DMAIC

• Solves problems by using Six Sigma tools

• Define problems in processes

• Measure performance

• Analyze causes of problems

• Improve processes/ remove variations and nonvalue-

added activities

• Control processes so problems do not recur

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[from: http:// xlncacademy.com/blog/top-5-unique-benefits-of-six-sigma , last seen on January 2019]

Six Sigma

• Pros

• A limit of 3.4 defects per one million products or services

• addresses the entire process, rather than just the final outcome

• It is proactive rather than reactive

• determines how improvements can be made even before defects are found

• Useful for product with several components

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Six Sigma

• Cons

• rigidity that can create delays & stifle creativity

• an inexpensive measure that carries a risk of a higher defect rate is

rejected in favor of a more expensive measure that helps to achieve Six

Sigma, but adversely affects profitability

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Quality Costs

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Quality Costs

Prevention Costs

Appraisal Costs

Internal Failure Costs

External Failure Costs

Quality Costs

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Quality Costs

Prevention Costs

Appraisal Costs

Internal Failure Costs

External Failure Costs

Prevention Costs

• Quality planning & engineering

• New products review

• Product/ process design

• Process control

• Burn-in

• Training

• Quality data acquisition & analysis

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Quality Costs

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Quality Costs

Prevention Costs

Appraisal Costs

Internal Failure Costs

External Failure Costs

Appraisal Costs

• Inspection & test of incoming materials

• Product inspection & test

• Materials & services consumed

• Maintaining accuracy of test equipment

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Quality Costs

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Quality Costs

Prevention Costs

Appraisal Costs

Internal Failure Costs

External Failure Costs

Internal Failure Costs

• Scrap

• Rework

• Retest

• Failure analysis

• downtime

• Yield losses

• Down grading

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Quality Costs

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Quality Costs

Prevention Costs

Appraisal Costs

Internal Failure Costs

External Failure Costs

External Failure Costs

• Complaint adjustment

• Returned product/ material

• Warranty charges

• Liability costs

• Indirect costs

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Backup

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