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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 of data, 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 or category.

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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 TotalImproper credit check 2 1 1 4Unsigned signature card 4 3 2 3 4 2 18Starter checks not provided 4 1 1 6Disclosures not provided 1 1 1 3Checks not ordered 2 4 3 2 5 16Paperwork lost at DP center 1 1 2Incorrect data entry at DP 2 2 4

source: Brightman, Data Analysis

1. Create a table listing the sources of defects in the first columnand 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 rowin the table.Error Category TotalUnsigned signature card 18Checks not ordered 16Starter checks not provided 6Improper credit check 4Incorrect data entry at DP 4Disclosures not provided 3Paperwork lost 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

Unsign

ed si

gnatu

re ca

rd

Check

s not

ordere

d

Starter

chec

ks no

t prov

ided

Imprope

r cred

it che

ck

Incorr

ect d

ata en

try at

DP

Disclos

ures n

ot pro

vided

Pape

rwork

lost

at DP c

enter

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 forEach listed cause.

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Step 4: Determine the category forEach listed cause.

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Step 5: Put categories and causesOn cause & effect diagram.

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Step 6: Identify the most likely causes.

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“Failure to understand variation is the 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

ProcessParameter

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 variationis in the process while the processis “in control”?

Statistical Process Control: Control Charts

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Conceptualview

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 that’s going to be a miniblip in the figures. Now, the statistician goes a step further and says, ‘How do you know whether it’s a miniblip or there’s a real change here?’ The statistician says, ‘I’ll draw you a pair of lines here. These lines are such that 95% of the time, you’re going to get variation between them.’

Now suppose something happens that’s clearly outside the lines. The odds are something’s 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 what’s chronic [common cause] and what’s 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.