lean 6 sigma - 7 qc tools

8/6/2019 Lean 6 Sigma - 7 QC Tools

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Process Variability Concepts 1

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7 QC Tools:The Lean Six Sigma Pocket

Toolbook

Flowchart [p. 33-41]

Check Sheet [p. 78-81]

Histogram [p. 111-113]

Pareto [p. 142-144]Cause-and-Effect [p. 146-147]

Scatter [p. 154-155]

Control Chart [p. 122-135]

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Pareto Diagram


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Step 1: Decide on problem, type ofdata, and causes or categories.

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Step 2: Collect the data.


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Step 3: Order the causes or categories.

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Step 4: Calculate the cumulative totals.


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Step 5: Draw and label the horizontal

axis.

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Step 6: Draw, scale, and

label the vertical axis.


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Step 7: Draw bars for each cause orcategory.

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Step 8: Draw cumulative total lines.


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Interpret the Pareto Chart.

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Pareto Diagram

Error Category Jan Feb Mar Apr May Jun Total

Improper credit check 2 1 1 4

Unsigned signature card 4 3 2 3 4 2 18Starter checks not provided 4 1 1 6

Disclosures not provided 1 1 1 3

Checks not ordered 2 4 3 2 5 16

Paperwork lost at DP center 1 1 2

Incorrect data entry at DP 2 2 4

source: Brightman, Data Analysis

1. Create a table listing the sources of defects in the first column

and in the second column calculate the total number of defects per

source.

(Using EXCEL)


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2. Sort the table by the total number of defects in descending order.

In the third column, calculate the cumulative percentage for each row

in the table.

Error Category Total

Unsigned signature card 18

Checks not ordered 16

St art er chec ks not provided 6

Improper credit check 4

Incorrect data entry at DP 4

Disclosures not provided 3

Paperwork los t at DP center 2

Error Category Total Cum %

Unsigned signature card 18 33.96%

Checks not ordered 16 64.15%

Starter checks not provided 6 75.47%

Improper credit check 4 83.02%

Incorrect data entry at DP 4 90.57%

Disclosures not provided 3 96.23%

Paperwork lost at DP center 2 100.00%

3. Create a chart with the ChartWizard (custom --- line-column

on two axes).

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Opening checking account errors

0

5

10

15

20

Unsig

nedsig

natu

recard

Checks

not

ordered

Starte

rche

cksnotp

rovid

ed

Improp

ercredit

che

ck

Incorrect

dataentry

atD

P

Disclos

ures

not

provid

ed

Pape

rworkl

osta

tDP

center

0.00%

20.00%

40.00%

60.00%

80.00%

100.00%


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Cause and Effect Diagram

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Step 1: Develop problem statement.


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Step 2: Brainstorm causes.

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Step 2: Brainstorm causes.


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Step 3: Determine the major cause categories.

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Step 4: Determine the category for

Each listed cause.


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Step 4: Determine the category for

Each listed cause.

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Step 5: Put categories and causes

On cause & effect diagram.


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Step 6: Identify the most likely causes.

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Failure to understand variation isthe central problem of

management.


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Stable vs. Unstable process

Stable process: a process in which variation in

outcomes arises only from common causes.

Unstable process: a process in which variation is a

result of both common and special causes.

source: Moen, Nolan and Provost, Improving Quality Through Planned Experimentation

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Red Bead experiment


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Red Bead Experiment

What are the lessons learned?

1.

2.

3.

4.

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Time

Process

Parameter

Upper Control Limit (UCL)

Lower Control Limit (LCL)

Center Line

Track process parameter over time

- mean

- percentage defects

Distinguish between

- common cause variation

(within control limits)

- assignable cause variation

(outside control limits)

Measure process performance:

how much common cause variation

is in the process while the process

is in control?

Statistical Process Control:

Control Charts


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Conceptual

view

of SPC

source: Donald Wheeler, Understanding Statistical Process Control

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Process

Stability

vs.

Process

Capability

Wheeler, Understanding Statistical Process Control


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Advantages of Statistical Control

1. Can predict its behavior.

2. Process has an identity.

3. Operates with less variability.

4. A process having special causes is unstable.

5. Tells workers when adjustments should not be made.

6. Provides direction for reducing variation.

7. Plotting of data allows identifying trends over time.

8. Identifies process conditions that can result in an

acceptable product.

source: Juran and Gryna, Quality Planning and Analysis, p. 380-381.

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Identifying Special Causes of Variation

source: Brian Joiner, Fourth Generation Management, pp. 260.

See also Lean Six Sigma

Pocket Toolbook, p. 133-135.


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Strategies for Reducing Special Causes of Variation

Get timely data so special causes are signaled

quickly.

Put in place an immediate remedy to contain any

damage.

Search for the cause -- see what was different.

Develop a longer term remedy.

source: Brian Joiner, Fourth Generation Management, pp. 138-139.

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In a common cause

situation, there is no such

thing as THE cause.

Brian Joiner


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Improving a Stable Process

Stratify -- sort into groups or categories; look for

patterns. (e.g., type of job, day of week, time, weather,

region, employee, product, etc.)

Experiment -- make planned changes and learn from

the effects. (e.g., need to be able to assess and learn

from the results -- use PDCA .) Disaggregate -- divide the process into component

pieces and manage the pieces. (e.g., making the

elements of a process visible through measurements

and data.)

source: Brian Joiner, Fourth Generation Management, pp. 140-146.

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Take this example: In finance we set a budget. The actual expenditure, month by

month, varies - we bought enough stationery for three months, and thats going to be

a miniblip in the figures. Now, the statistician goes a step further and says, How do

you know whether its a miniblip or theres a real change here? The statistician says,

Ill draw you a pair of lines here. These lines are such that 95% of the time, youre

going to get variation between them.

Now suppose something happens thats clearly outside the lines. The odds are

somethings amok. Ordinarily this is the result of something local, because the

system is such that it operates in control. So supervision converges on the scene to

restore the status quo.

Notice the distinction between whats chronic [common cause] and whats sporadic

[special cause]. Sporadic events we handle by the control mechanism. Ordinarily

sporadic problems are delegable because the origin and remedy are local. Changing

something chronic requires creativity, because the purpose is to get rid of the status

quo - to get rid of waste. Dealing with chronic requires structured change, which has

to originate pretty much at the top.

A Conversation with Joseph Juran

Source: A Conversation with Joseph Juran, Thomas Stewart, Fortune, January 11, 1999, p. 168-170.

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