Statistical Process Control Concepts

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Transcript Statistical Process Control Concepts

Statistical Process Control
Concepts
Hampton Roads Section, ASQ
June 15, 2011
Scott Rutherford
Master Black Belt, Norfolk Naval Shipyard
Learning Objectives
Understand the three general areas of
SPC
 Understand the proper use of SPC in
your Quality program
 Understand SPC’s pitfalls and success
factors

History
1920’s: “Created” by Walter Shewhart for
Bell Labs
 WWII: W. Edwards Deming applies
concepts to munitions manufacturing
 After WWII: Deming teaches SPC to
Japanese to help build back their
industrial base
 1988: SPC applied to software industry
becomes CMMI (Causal Maturity Model
Integration)

Shewhart’s original concept


Physical process data is usually NOT
normally distributed
Processes either display:
◦ Controlled variation that is natural to the
process
◦ Uncontrolled variation that is generated from
outside the “process causal system” (assignable
cause)

Attacking process variation produces a
product that consistently conforms to
specifications
Three Elements of SPC
Understanding the Process
 Understanding the Causes of Variation
 Eliminating the sources of Assignable
(Special) Cause variation

Techniques for Understanding the
Process
Process Mapping
 Determine Measure of Quality

◦ From customer’s perspective
◦ Usually an output measure

Determine Measure of Quality Predictor
◦ What In-process Measure is the most reliable
predictor of the Quality Measure?

Measure the Predictor
◦ Control Charts / Run Charts
Understanding Causes of Variation

Root Cause Analysis - Reactive
◦ Causal Mapping – 5 Whys
◦ Switch Theory
◦ Human Factors Analysis and Classification System
(HFACS) – Swiss Cheese Analysis
◦ Kepner series (Tregoe, Fourie)
◦ Fishbone
◦ Others (Ford Global 8D, DuPont, etc.)

Failure Modes & Effects Analysis (FMEA) Proactive
Eliminating Special Cause Variation

Identification
◦ Control Chart monitoring
◦ Control Chart Analysis (“rules”)

Response
◦ Immediate Action (Control or Reaction Plan)
– Getting back to the norm
◦ Short-term actions – Preventing reoccurrence
◦ Long-term actions – Eliminating cause
Preventing Reoccurrence
Immediate Knowledge capture
 Start of Work / Shift briefings
 Verbal / “Pen & Ink” Procedure changes
 Training
 Periodic self-assessments
 Proper monitoring of the process

Eliminating Reoccurrence

Lean Tools
◦ 5S
◦ Standard Work codification
◦ Mistake-proofing
FMEA Analysis
 Process Knowledge Use

◦ R&D
◦ Next generation design

Behavioral / Cultural Change
Why SPC Initiatives often Fail
“It’s All about the charts”
 “More important to train”
 “Don’t have time to figure out the source,
get back to work!”
 “The control plan should have caught that!”
 “Sort out the bad to get enough good
product to sell”
 “We have the time to do it over, but not
enough time to do it right the first time”

SPC succeeds when:
Supervisors empowering front line
workers in monitoring control charts and
executing control plans
 There is a dedicated workforce to spend
the time to analyze sources of variation
 Eliminating variation is a strategic initiative

What other comments or questions
do you have?
[email protected]
[email protected]