Six Sigma For Process & Quality Improvement

Chapter 4: Six Sigma for Process and Quality Improvement

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Chapter 4

Six Sigma For Process & Quality Improvement


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Quality Management and Six Sigma in Perspective

Two primary sets of costs are involved in quality: control costs failure costs

Costs broken into four categories: Prevention costs Appraisal costs Internal costs of defects External costs of defects


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Japanese Approaches to Quality

In 1950 the Japanese government invited W. Edwards Deming (then a professor at New York University) to give a series of lectures on quality control to help Japanese engineers reindustrialize the country.


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W. Edwards Deming

Major source of poor quality is variation

Quality improvement the responsibility of top management

All employees should be trained in use of problem solving tools and especially statistical techniques


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Deming’s 14 Points

1. Create constancy of purpose

2. Adopt the new philosophy

3. Cease dependence on mass inspection

4. End practice of awarding business on basis of price tags

5. Improve constantly and forever

6. Institute modern methods of training


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Deming’s 14 Points continued

7. Institute modern method of supervision

8. Drive out fear

9. Breakdown organizational barriers

10.Eliminate arbitrary numerical goals

11. Eliminate work standards and quotas

12.Remove barriers that reduce pride of workmanship


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Deming’s 14 Points continued

13. Institute a vigorous program of education and training

14. Push the 13 points everyday


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Total Quality Management (TQM)

Better to produce item right the first time than to try to inspect quality in

Quality at the source - responsibility shifted from quality control department to workers


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History of TQM

Dr. Shewart began using statistical control at the Bell Institute in 1930s

Military standards developed in 1950s After World War II, Japanese Union of

Scientist and Engineers began consulting with Deming

Deming Prize introduced in Japan in 1951


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History of TQM continued

Quality assurance concept proposed in 1952 Juran makes first trip to Japan in 1954 Quality becomes Japan’s national slogan in

1956 First quality circles created in 1957 10,000 quality circles by 1966 100,000 quality circles by 1977 First U.S. quality circle 1974


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Five Steps in TQM

Determine what customers want Develop products and services Develop production system Monitor the system Include customers and suppliers


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Joseph Juran

Quality Control Handbook (1951) Employees speak in different languages Quality Trilogy

Quality Planning Quality Control Quality Improvement

Need to place more emphasis on planning and improvement


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Joseph Juran continued

Organizations progress through four phases Minimize prevention and appraisal costs Appraisal costs increased Process control introduced increasing

appraisal costs but lowering internal and external failure costs

Prevention costs increased in effort to lower total quality costs


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A Brief History of Six Sigma

The Six Sigma concept was developed by Bill Smith, a senior engineer at Motorola, in 1986 as a way to standardize the way defects were tallied.

Sigma is the Greek symbol used in statistics to refer to standard deviation which is a measure of variation.

Adding “six” to “sigma” combines a measure of process performance (sigma) with the goal of nearly perfect quality (six).


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A Brief History of Six Sigma continued

In the popular book The Six Sigma Way, Six Sigma is defined as: a comprehensive and flexible system for

achieving, sustaining and maximizing business success. Six Sigma is uniquely driven by close understanding of customer needs, disciplined use of facts, data, and statistical analysis, and diligent attention to managing, improving, and reinventing business processes. (p. xi)


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The DMAIC Improvement Process

Six Sigma projects generally follow a well defined process consisting of five phases. define measure analyze improve control pronounced dey-MAY-ihk


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The DMAIC Improvement Process


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The Define Phase The define phase of a DMAIC project focuses

on clearly specifying the problem or opportunity, what the goals are for the process improvement project, and what the scope of the project is. Identifying who the customer is and their requirements is also critical given that the overarching goal for all Six Sigma projects is improving the organization’s ability to meet the needs of its customers.


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Defining and Measuring Quality

Conformance to specifications Performance Quick response Quick-change expertise Features Reliability Durability Serviceability Aesthetics Perceived quality Humanity Value


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Benchmarking

Benchmarking involves comparing an organization's processes with the best practices to be found. Benchmarking is used for a variety of purposes, including: Comparing an organization's processes

with the best organization's processes. Comparing an organization's products and

services with those of other organizations.


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Benchmarking continued

Identifying the best practices to implement.

Projecting trends in order to be able to respond proactively to future challenges and opportunities.


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Quality Function Deployment (QFD)

Two key drivers of an organization’s long-term competitive success are the extent to which its new products or services meet customers’ needs, and having the organizational capabilities to develop and deliver such new products and services.

Tools for helping translate customer desires directly into product service attributes.


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Four Houses of Quality

Customer requirements Technical requirements Component requirements Process deployment requirements


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House of Quality Details


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The Measure Phase

The measure phase begins with the identification of the key process performance metrics.

Once the key process performance metrics have been specified, related process and customer data is collected.

Two commonly used process performance measures, namely, Defects per Million Opportunities (DPMO) and Process Sigma.


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Defects Per Million Opportunities

Earlier it was noted that a literal interpretation of Six Sigma is 3.4 defects per million opportunities (DPMO). This may have caused some confusion for more statistically inclined readers, which we shall now attempt to reconcile.


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Defects Per Million Opportunities


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Process Sigma

How sigma itself can be used to measure the performance of a process. One way to measure the performance of

a process is to calculate the number of standard deviations the customer requirements are from the process mean or target value.


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DPMO for Alternative Process Sigma Levels


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Motorola’s Assumption the Process Mean Can Shift by as Much as 1.5 Standard Deviations


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Comparison of 3 Sigma Process and 6 Sigma Process


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The Analyze Phase

In this phase our objective is to utilize the data that has been collected to develop and test theories related to the root causes of existing gaps between the process’ current performance and its desired performance.

See next slide Table 4.3 Common tools and methodologies in the Six Sigma toolset.


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Brainstorming

The brainstorming approach: Do not criticize ideas during the

brainstorming session. Express all ideas no matter how radical,

bizarre, unconventional, ridiculous, or impractical they may seem.

Generate as many ideas as possible. Combine, extend, and/or improve on one

another’s ideas.


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Brainstorming: Actions to Enhance Team Creativity

Create diversified teams. Use analogical reasoning. Use brain writing. Use the Nominal Group Technique. Record team ideas. Use trained facilitators to run the brainstorming

session. Set high standards. Change the composition of the team. Use electronic brainstorming. Make the workplace a playground.


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Cause and Effect Diagrams


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Process Capability Analysis


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Process Capability Analysis continued


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The Improve Phase: Design of Experiments (DOE)

OFAT and 1FAT - one factor at a time. Shortcomings

Not typically possible to test one factor at a time and hold all the other factors constant.

Not possible to account for interactions or joint variation between variables (Figure 4.16).


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Design of Experiments (DOE)


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DOE: continued


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DOE: continued


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DOE continued

Some of the major considerations associated with DOE include: Determining which factors to include in

the experiment. Specifying the levels for each factor. Determining how much data to collect. Determining the type of experimental

design.


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Taguchi Methods

Design for Manufacturability (DFM) Procedure for statistical testing to

determine best combination of product and transformation system design that will make output relatively independent of normal fluctuations in the production system


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Statistical Quality Control


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Chance Versus Assignable Variation

Chance variation is variability built into the system.

Assignable variation occurs because some element of the system or some operating condition is out of control.

Quality control seeks to identify when assignable variation is present so that corrective action can be taken.


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Control Based on Attributes and Variables

Inspection for Variables: measuring a variable that can be scaled such as weight, length, temperature, and diameter.

Inspection of Attributes: determining the existence of a characteristic such as acceptable-defective, timely-late, and right-wrong.


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Control Charts


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Control Charts

Developed in 1920s to distinguish between chance variation in a system and variation caused by the system’s being out of control - assignable variation.


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Control Charts continued

Repetitive operation will not produce exactly the same outputs.

Pattern of variability often described by normal distribution.

Random samples that fully represent the population being checked are taken.

Sample data plotted on control charts to determine if the process is still under control.


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Control Chart with Limits Set at Three Standard Deviations


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Control Charts for Variables


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Two Control Charts

Sample Means Chart Range Chart


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Sample Data of Weights of Tacos (Ounces)

Sample Scenario 1 Scenario 2

1 4, 5, 6 4, 5, 6

2 6, 7, 8 3, 5, 7

3 7, 8, 9 2, 5, 8


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Analysis of Scenario 1

Sample Mean Range

1 5 2

2 7 2

3 8 2Sample means show problem having increased from 5 ounces to 8 ounces. Sample ranges have not changed from sample to sample.


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Analysis of Scenario 2

Sample Mean Range

1 5 2

2 5 4

3 5 6Sample ranges show problem having increased from 2 ounces to 6 ounces. Sample means have not changed from sample to sample.


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Patterns of Change in Process Distributions


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Control Limits

Sample Means Chart:

RAXLCL

RAXUCL

2X

2X

Range Chart:

RDLCL

RDUCL

3R

4R


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Calculating the Grand Mean and the Average Range

N

RR

N

XX


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Mean Age of Ice Cream


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Range in Ice Cream Age


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Control Charts for Attributes


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Fraction-Defective (p) Charts

pp

pp

p

zp

zp

n

pp

p

LCL

UCL

)1(

sampled units ofnumber total

defects ofnumber total


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Number-of-Defects (c) Charts

cc

cc

c

zc

zc

c

c

LCL

UCL

sampled units ofnumber

observed incidents ofnumber


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Six Sigma in Practice

Six Sigma Roles: Master Black Belts. Black Belts. Green Belts. Yellow Belts.

Supporting Roles: Champions/Sponsors. Process owners.


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Quality in Services

Measuring is difficult Training in standard procedures often

used to improve quality One way to measure quality of services

is to use customer satisfaction surveys J.D. Power and Associates uses

surveys to rate domestic airlines, hotel chains, and rental car companies.


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Rating the Performance of Domestic Airlines

On-time performance (25%) Airport check-in (11%) Courtesy of flight attendants (11%) Seating comfort (11%)


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Service Defections

Organizations should monitor customer defections feedback from defecting customers can

be used to identify problem areas can determine what is needed to win

them back changes in defection rate can be used as

early warning signal


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Quality Awards/Certifications


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The Malcolm Baldrige National Quality Award


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ISO 9000

Guidelines for designing, manufacturing, selling, and servicing products.

Selecting an ISO 9000 certified supplier provides some assurance that supplier follows accepted business practices in areas covered by the standard


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Elements of ISO 9000

Management Responsibility Quality System Contract Review Design Control Document and Data Control Purchasing Control of Customer Supplied

Product Product Identification and Traceability Process Control Inspection and Testing

Control of Inspection, Measuring, and Test Equipment

Inspection and Test Status Control of Nonconforming

Product Corrective and Preventive

Action Handling, Storage,

Packaging, Preservation, and Delivery

Internal Quality Audits Training Servicing Statistical Techniques


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ISO 14000 Series of standards covering environmental

management systems, environmental auditing, evaluation of environmental performance, environmental labeling, and life-cycle assessment.

Intent is to help organizations improve their environmental performance through documentation control, operational control, control of records, training, statistical techniques, and corrective and preventive actions.


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