quality book lecture

Chapter 1 1Introduction to Statistical Quality Control, 7th Edition by Douglas C. Montgomery. Copyright (c) 2012 John Wiley & Sons, Inc.

IE 4653/6653 Industrial Quality Control I

Lecture 1

Quality Improvement in the Modern Business Environment

Chapter 1


Definitions - Meaning of Quality and Quality Improvement

The Eight Dimensions of Quality1. Performance - Will the product do the intended job?

2. Reliability - How often does the product fail?

3. Durability - How long does the product last?

4. Serviceability - How easy is it to repair the product?

5. Aesthetics - What does the product look like?

6. Features - What does the product do?

7. Perceived Quality - What is the reputation of the company or its product?

8. Conformance to Standards - Is the product made exactly as the designer intended?


Definitions• Quality means fitness for use

– This is a traditional definition

– Quality of design

– Quality of conformance

• Quality is inversely proportional to variability– This is a modern definition of quality


Water Faucet Example• Target: best performance when internal diameter =

1.25cm• 100 faucets from supplier A, 100 from supplier B,

100 from supplier C• Supplier A: mean diameter 1.25cm, every faucet close

to target• Supplier B: mean diameter 2cm• Supplier C: mean diameter 1.25cm, faucets more

variable• Conclusion: A has the best quality


Quality Improvement• Quality improvement is the reduction of variability in

processes and products

• The water faucet example illustrates the utility of this definition

• An equivalent definition is that quality improvement is the elimination of waste. This is useful in service or transactional businesses.


Terminology• Quality (critical-to-quality) characteristics

– Physical: length. weight, voltage, viscosity– Sensory: taste, appearance, color– Time orientation: reliability, durability, serviceability

• Statistical methods: describe the variability– Variables data: continuous measurements

• Length• Voltage• Viscosity

– Attributes data: discrete data• # of emergency room arrivals


Terminology cont’d• Specifications

– Lower specification limit– Upper specification limit– Target or nominal values

• Defective or nonconforming product• Defect or nonconformity

– A specific type of failure

• Not all products containing a defect are necessarily defective


Statistical Methods for Quality Control and Improvement


Statistical Methods• Statistical process control (SPC)

– Control charts, plus other problem-solving tools– Useful in monitoring processes, reducing variability

through elimination of assignable causes– On-line technique

• Design of experiments (DOE)– Discovering the key factors that influence process

performance– Process optimization– Off-line technique

• Acceptance Sampling


Typing Example• Consider improvement of typing quality, which is measured by

typing accuracy and clearness. • Statistical process control (SPC) - Every hour one page is selected

and its quality is measured. Plot the measurements from each hour on a control chart. If a shift of quality is detected, the root cause of this shift (e.g., typist tiredness, lack of ink) is identified and fixed.

• Design of experiment (DOE) - Conduct experiments with combinations of different typists, typewriters, papers, working schedules. The best combination of these factors are selected to achieve optimal typing quality.

• Acceptance sampling - Several sample pages are inspected from every “lot” (e.g., every 100 typed pages). If the selected sample pages have satisfactory quality, the whole “lot” is accepted. Otherwise, the whole lot is rejected and rework should be done.


Walter A. Shewart (1891-1967)• Trained in engineering and physics

• Long career at Bell Labs

• Developed the first control chart about 1924

Statistical Process Control


Design of Experiments


Acceptance Sampling

• Outgoing inspection− Inspection before the

product is shipped to the customer

• Incoming inspection− Inspection after the

product is received from the supplier

• Disposition of lots


Variation Reduction Approaches


Effective management of quality requires the execution of three activities• Quality Planning

– Strategic activity

• Quality Assurance– Ensure the quality levels of products and services are properly

maintained

• Quality Control and Improvement– Ensure the products and services meet requirements and are

improved on a continuous basis

Management Aspects of Quality Improvement


Shewhart Cycle


Statistical Quality Control Procedures

Process

DecisionFormulate action Data analysis

EvaluationFaulty discovery

Diagnosis

Take actionImplementation

Data collectionObservation


Six Sigma• A disciplined and analytical approach to process and

product improvement• First developed by Motorola in the late 1980s• Specialized roles for people; Master Black belts, Black

Belts, Green Belts• BBs and MBBs have responsibility (project definition,

leadership, training/mentoring, team facilitation)• Involves a five-step process (DMAIC)

– Define – Measure– Analyze– Improve– Control


• Three sigma quality− 2700 ppm defective− (0.9973)100=0.7631

• Six sigma quality− 0.002 ppm defective− (0.999999998)100=0.9999998

• Three sigma quality− 66810 ppm defective

• Six sigma quality− 3.4 ppm defective


Why “Quality Improvement” is Important: A Simple Example

• 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 - is 99% good okay?

10

4

12

{Single meal good} (0.99) 0.9044

Family of four, once a month: {All meals good} (0.9044) 0.6690

{All visits during the year good} (0.6690) 0.0080

P

P

P

10 4

12

{single meal good} (0.999) 0.9900, {Monthly visit good} (0.99) 0.9607

{All visits in the year good} (0.9607) 0.6186

P P

P


Three Generations of Six Sigma Implementations

• Generation I– Defect elimination and basic variability reduction

• Generation II– Emphasis on variability and defect reduction remained– Strong effort to business performance improvement

through cost reduction

• Generation III– Additional focus of creating value throughout the

organization and for its stakeholders


Lean Systems• Focuses on elimination of waste

– Long cycle times– Long queues – in-process inventory– Inadequate throughput– Rework– Non-value-added work activities

• Makes use of many of the tools of operations research and industrial engineering– Discrete-event simulation


Lean Focuses on Waste Elimination• Definition

– A set of methods and tools used to eliminate waste in a process

– Lean helps identify anything not absolutely required to deliver a quality product on time.

• Benefits of using Lean– Lean methods help reduce inventory, lead time,

and cost– Lean methods increase productivity, quality, on

time delivery, capacity, and sales

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