1DSC 335, Fall 2009

Quality and Capability

DSC 335

Zhibin Yang, Assistant Professor

Decision Sciences

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DSC 335 Roadmap

Operations Strategy

Process Management

Process strategy/analysis

Capacity analysis/planning

Quality management

Lean systems

Supply Chain Mgmt.

Supply chain dynamics

Inventory management

Case: Kristen’s Cookie

Case: Blanchard

Littlefield Game 1

Littlefield Game 2

Case: A Pain in Chain

Beer game

Decision Making Tools

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Quality and Capability – Outline

Quality management

6-Sigma

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What is Quality (quoted)

Quality is hard to define and measure

“…If no one knows what it is, then for all practical purposes it doesn’t exist at all. But for all practical purposes it really does exist. What else are the grades based on? Why else would people pay for some things and throw others in the trash pile? Obviously some things are better than others – but what’s the ‘betterness’…?”

--- From Zen and the Art of Motorcycle Maintenance, by Robert Pirsig

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What is Quality?

Design quality: Inherent value of the product in the marketplace Dimensions include: …

Good quality does not mean luxury.

Conformance quality: Degree to which the product or service design specifications are met

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Total Quality Management (TQM)

TQM – managing the entire organization so that it excels on all dimensions of products and services that are important as perceived by the customer

Three principles of TQM

Two fundamental operational goals of TQM

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Quality and Capability – Outline

Quality management

6-Sigma Philosophy Methodology (DMAIC) Statistics & Process Capability Index

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What is Six Sigma (6)?

A philosophy and set of methods to eliminate defects in products and processes

Developed by Motorola for manufacturing Extended by General Electric to non-manufacturing sectors

Practiced by many industrial leaders

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What is Six Sigma (6)?

Seeks to reduce variation in the processes that lead to product defects - standard deviation of probability

distribution

For normal distribution: (Mean 3) contains about _____

of the data values (Mean 6) contains about

______ of the data values A sample falling out of interval is

considered a _____

With 6 process, __ defects per billion products (literally zero defects)

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Magnitude of Difference for Sigma Levels

Sigma Spelling Time

1-Sigma 170 misspelled words per page 31.75 years per century

2-Sigma 25 misspelled words per page 0.45 years per century

3-Sigma 1.5 misspelled words per page 3.5 months per century

4-Sigma 1 misspelled word per 30 pages 2.5 days per century

5-Sigma1 misspelled word in a set of

encyclopedias30 minutes per century

6-Sigma 1 misspelled words in a library 6 seconds per century

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Six Sigma Roles in Organizational Implementation Executive Leaders

Setting up a vision Empowering other roles with freedom and resources

Champions (Quality Leaders, in GE) Integrating implementation across the organization Mentoring (Master) Black Belts

Master Black Belts (MBB) Acting as in-house coaches Integrating at the function and department level

Black Belts Focusing on project execution under MBBs

Green Belts (Trained employees) Implementing six-sigma on their jobs

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Quality and Capability – Outline

Quality management

6-Sigma Philosophy Methodology (DMAIC) Statistics & Process Capability Index

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1. Define (D)

2. Measure (M)3. Analyze (A)

4. Improve (I)

5. Control (C)

Customers and their priorities

Process and its performance

Causes of defects

Remove causes of defects

Maintain quality

Six Sigma Methodology: DMAIC Cycle

Developed by General Electric as a means of focusing effort on quality using a methodological approach

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Step 1. Define

Identify customers and their priorities

Identify key characteristics of the process’s output that are critical to quality (CTQ) and customer satisfaction

Identify gaps between these characteristics and process capabilities

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Step 2. Measure

Identify the key aspects of the current process that influence Critical To Quality (CTQs) characteristics

Collect relevant data of the current process

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Tracks process behavior

“Eyeball” trends

Tracks process behavior

“Eyeball” trends

0.44

0.46

0.480.5

0.52

0.54

0.56

0.58

1 2 3 4 5 6 7 8 9 10 11 12Time (Hours)

Dia

met

er o

f a

dri

ll p

roce

ssMeasure: Run Chart – Precision Drift over Time in a Drilling Process

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Measure: Pareto Charts

Assy.Instruc.

Fre

qu

ency

Design Purch. Training Others

80%

Focus on most important problems using the 80/20 rule

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EffectEffect

Possible categories of causesSymptoms /

effectsEquipmentEquipment

EnvironmentEnvironment

MaterialsMaterialsMethodsMethods

People People

Step 3. Analyze – Diagnose Root Cause

Fishbone Diagram

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Analysis: 5 Whys

A question-asking method used to explore the cause/effect relationships

Example: My car will not start. (the problem)1. Why? - The battery is dead. (first why)

2. Why? - The alternator is not functioning. (second why)

3. Why? - The alternator belt has broken. (third why)

4. Why? - The alternator belt was well beyond its useful service life and has never been replaced. (fourth why)

5. Why? - I have not been maintaining my car according to the recommended service schedule. (fifth why, a root cause)

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Step 5. Control

Use tools such as statistical process control chart to maintain the level of quality

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Quality and Capability – Outline

Quality management

6-Sigma Philosophy Methodology (DMAIC) Statistics & Process Capability Index

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Six Sigma Statistics

Control charts and control limits

Tolerance Limits and process capabilities

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Control Charts and Control Limits

Set Upper Control Limits (UCL) and Lower Control Limits (LCL)

Example: Not too much or too little raisin in cereal On average a box of cereal contains 80 grams of raisin. The quality is considered good if the amount of raisin is more

than 75 grams and less than 85 grams. Your control limits are LCL= ___ and UCL= ___ grams.

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Control Charts and Control Limits

x (central line): ______________________________

UCL and LCL define __________________________

970980990

100010101020

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

LCL

UCL

x

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Use Control Charts & Control Limits

Plot your samples / observations of a process

When observation falls outside control limits You must take action – ____________________________

A process is called “________”, if samples are reliably within the control limits

970980990

100010101020

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

LCL

UCL

x

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xLCL =x – 3 UCL =x + 3

99.73%

Typical Control Limits

UCL =x + 3; UCL =x – 3 x – Average of past sample means – standard deviation of a process

distribution 3 is taken to be “natural variation”

Covering 99.73% occurrences Only 3 in 1,000 are out of control

limits Out of control observations do

occur, but infrequently

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Normal BehaviorNormal Behavior

Possible problem, investigate

Possible problem, investigate

UCL

LCL

1 2 3 4 5 6 Time

UCL

LCL 1 2 3 4 5 6 Time

Statistical Process Control (SPC) Charts

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Normal BehaviorNormal Behavior

UCL

LCL

1 2 3 4 5 6 Time

Possible problem, investigate

Possible problem, investigate

UCL

LCL

1 2 3 4 5 6 Time

Statistical Process Control (SPC) Charts

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Tolerance Limits (a.k.a. specification in text)

Example: Not too much or too little raisin (con’t) A customer might complain if there is more than 90

grams or less than 70 grams of raisin So, you obtain the tolerance limits:

LTL = ___ g

UTL = ___ g

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Tolerance limits set performance target of a process

Control limits characterize the current process

Tolerance Limits Control Limits

Who determines?

What type of quality does it pertain to?

What happens beyond limits?

Tolerance Limits vs Control Limits

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Tolerance Limits vs Control Limits

Ideally, 3σ control limits fall within tolerance limits. This makes the process easy to monitor and avoid defects.

970

980

9901000

1010

1020

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

LCL=X – 3σ

UCL=X + 3σ

LTL

UTL

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(cont’d)

But, we’re not always so lucky… Depends on the spread of the distribution

We need to measure how well the process is satisfying customers (or the designer)

970

980

9901000

1010

1020

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

LCL=X – 3σ

UCL=X + 3σ

LTL

UTL

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Process Capability Index, Cpk

Process Capability Index measures how well the process is centered as well as whether the variability is acceptable

Based on closest tolerance limit.

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Cases of Process Capability Index

Cpk >1, the process is _______ ___________

Cpk = 1

Cpk < 1, the process is _______ ____________

LCL UCLx

LTL UTL

LCL UCLx

LTL UTL

LCL UCLx

LTL UTL

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Not too many or too few raisins in cereal (con’t) LTL = 70g, UTL = 90g, x = 80, = 3

Process capability index Cpk =

What isx shift to 84? Cpk =

Example

min3 3pk

x LTL UTL xC ,

ó ó

⎛ ⎞− −= ⎜ ⎟

⎝ ⎠

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LTL UTL

σ = 10

LTL UTL

σ = 5

σ = 10

LTL UTL LTL UTL

σ = 5

99.73 %

Improving Process Capability by Variance Reduction

LCL UCL

99.73 %

LCL UCL

99.73 % 99.73 %

Even if the process distribution is not centered

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A metal fabricator produces connecting rods with an outer diameter that has a 1plus/minus 0.01 inch specification. A machine operator takes several sample measurements over time and determines the sample mean outer diameter to be 1.002 inches with a standard deviation of 0.003 inch.

1. Calculate the process capability index for this example

2. What does the index tell you about the process This process is not capable at present due to the process mean off the

center. The process center should be adjusted.

Exercise: Process Capability

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(cont’d)

Suppose the production manager can improve the process by reducing the standard deviation, , of the process

At what value of , the process would be capable of process?

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Effect of # of Parts / steps in a Process

Quality drops as # processing steps increases

6 process remains high quality than a 6 process

0.0%

0.05%

0.1%

1.0%

10.0%

100.0%

1 10 100 1000 10K 100K 1M

# parts / steps

6 - sigma5 - sigma

4 - sigma3 - sigma

Pro

babi

lity

that

pr

oces

s m

eets

spe

cs

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6 Example: Mumbai’s “Dabbawallahs”

Mumbai’s network for delivering lunch boxes from family kitchens to workplaces Dabba – lunch box Wallah – delivery guy

Youtube Video: Follow that bicycle

Employs 5000 people. Using bicycles, carts, and city rail network.

Delivery Cost: $4 / month.

400,000 lunches delivered / day,

Quality: 1 error in 8 million deliveries

Process is > 5-sigma.