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?
scott.rutherford@navy.mil
srlean6@gmail.com