variability reduction
TRANSCRIPT
Variability Reduction Program Business Excellence1
Variability Reduction Variability Reduction ProgramProgramolol
Variability Reduction Program Business Excellence2
OutlineOutline
Section 1: Understanding the Impact Section 1: Understanding the Impact of Variationof Variation
Section 2: Process Control SystemsSection 2: Process Control Systems
Section 3: Measurement Capability Section 3: Measurement Capability AnalysisAnalysis
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What is Variation?What is Variation?
Loss FunctionLoss Function
What is the target for a given process?What is the target for a given process?
How far away from the target is still OK?How far away from the target is still OK?
Target
??
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A curve representing loss in quality as A curve representing loss in quality as a function of a measured valuea function of a measured value
What is Variation?What is Variation?
Lossin
Quality
Measurement
Loss FunctionLoss Function
target
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What is Variation?What is Variation?Traditional “Loss Function”Traditional “Loss Function”
Spec limits define Spec limits define acceptableacceptable and and unacceptableunacceptable quality quality
Lossin
Quality
LowerSpecLimit
UpperSpecLimit
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Modern “Loss Function”Modern “Loss Function”
Target: Desired Value or OutcomeTarget: Desired Value or Outcome
What is Variation?What is Variation?
Lossin
Quality
Target
Loss in QualityIncreases as
Variation fromTarget Increases
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What is Variation?What is Variation?How the Loss Function Affects ProductHow the Loss Function Affects Product
Both are within specBoth are within specWhich is more desirable?Which is more desirable?
LSLLSL USL USL
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TargetNumber of Defects
Lossin
Quality
What is Variation?What is Variation?Loss Function for DefectsLoss Function for Defects
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What is Variation?What is Variation?
Less Variation Less Variation
==
Higher QualityHigher Quality
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Examining VariationExamining VariationDefinitionDefinition
A A Stable ProcessStable Process has the has the same normal distribution at same normal distribution at
all times.all times.
A stable process is A stable process is In ControlIn Control
A stable process still has variationA stable process still has variation
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Examining VariationExamining VariationStable ProcessStable Process
Normal distribution at all timesNormal distribution at all times
Prediction
Time
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Examining VariationExamining Variation
Common CausesCommon Causes
The cause of variations in a The cause of variations in a stable process is called a stable process is called a
Common CauseCommon Cause..
A common cause is a natural cause of A common cause is a natural cause of variation in the system.variation in the system.
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Examining VariationExamining Variation
Machine vibrationMachine vibration Temperature fluctuationsTemperature fluctuations Slight variation in raw materialsSlight variation in raw materials Human variation in setting control Human variation in setting control
dialsdials
Common Cause ExamplesCommon Cause Examples
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Examining VariationExamining VariationTools for Examining StabilityTools for Examining Stability
Trend ChartTrend Chart: A plot showing the : A plot showing the behavior of a process over time.behavior of a process over time.
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Time
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Examining VariationExamining VariationTools for Examining StabilityTools for Examining Stability
HistogramHistogram: A barchart showing the : A barchart showing the distribution of the process.distribution of the process.
Perc
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700 80
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Thickness
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Examining VariationExamining Variation
Thic
kness
Activity: Comparing stable processesActivity: Comparing stable processes
Which process has better quality?Which process has better quality?
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Thic
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Sequence0 5 10 15 20 25
Sequence0 5 10 15 20 25
AA BB
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Examining VariationExamining VariationActivity: Comparing stable processes Activity: Comparing stable processes
(cont’d)(cont’d)
Which process has better quality?Which process has better quality?
Thic
kness
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kness
Sequence0 5 10 15 20 25
Sequence0 5 10 15 20 25
AA BB
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Examining VariationExamining VariationUnstable ProcessUnstable Process
Any process that is not stable is called an Any process that is not stable is called an unstableunstable or or out-of-controlout-of-control process. process.
Prediction
Time
??
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Examining VariationExamining VariationKinds of Instability: Kinds of Instability: ExcursionsExcursions
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Examining VariationExamining Variation
Kinds of Instability: Kinds of Instability: ShiftsShifts
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Examining VariationExamining Variation
Kinds of Instability: Kinds of Instability: DriftsDrifts
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Examining VariationExamining Variation
Kinds of Instability: Kinds of Instability: CyclesCycles
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Examining VariationExamining Variation
Kinds of Instability: Kinds of Instability: ChaosChaos
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Examining VariationExamining Variation
Special CausesSpecial Causes
Anything that causes variations that Anything that causes variations that are not part of the stable process are not part of the stable process
is called a is called a special causespecial cause, , assignable causeassignable cause, or , or unnatural unnatural
causecause..
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Examining VariationExamining Variation
Batch of defective raw materialBatch of defective raw material Faulty set-upFaulty set-up Human errorHuman error Incorrect recipeIncorrect recipe Blown gasketBlown gasket EarthquakeEarthquake
Examples of Special CausesExamples of Special Causes
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Reducing VariationReducing Variation
Centering at TargetCentering at Target
Reducing Common Cause VariationReducing Common Cause Variation
Improving a Stable ProcessImproving a Stable Process
Two strategies for improving a stable processTwo strategies for improving a stable process
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Reducing VariationReducing VariationCentering at TargetCentering at Target
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Reducing VariationReducing VariationReducing Common Cause VariationReducing Common Cause Variation
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Reducing VariationReducing Variation
Structured problem solvingStructured problem solving Planned experimentsPlanned experiments
Reducing Variation in a Stable Reducing Variation in a Stable ProcessProcess
Make Permanent ChangesMake Permanent Changes
Changes are based on the scientific Changes are based on the scientific approachapproach
Examples: new equipment, equipment upgrade, new procedure, new machine
settings, better raw material
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Reducing VariationReducing Variation
Do not Do not ignore special causes.ignore special causes. DoDo quickly detect special cause quickly detect special cause
variations.variations. DoDo stop production until the process stop production until the process
is fixed. (Reactive)is fixed. (Reactive) DoDo identify and permanently identify and permanently
eliminate special causes. (Preventive)eliminate special causes. (Preventive)
Reducing Variation in an Reducing Variation in an Unstable ProcessUnstable Process
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Reducing VariationReducing Variation
DetectDetect the special cause variation. the special cause variation. IdentifyIdentify the special cause. the special cause. FixFix the process the process
• Remove the special cause, orRemove the special cause, or• Compensate for the special cause.Compensate for the special cause.
PreventPrevent the special cause from the special cause from occurring againoccurring again
Improving an Unstable ProcessImproving an Unstable Process
Four Step ProcessFour Step Process
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Reducing VariationReducing VariationImproving an Unstable ProcessImproving an Unstable Process
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Detect HereNot Here
Detect Here
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Reducing VariationReducing VariationImproving an Unstable ProcessImproving an Unstable Process
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Unstable Stable
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Detecting VariationDetecting Variation
How can we decide if How can we decide if variation is the result of variation is the result of
common or special cause?common or special cause?
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Detecting VariationDetecting VariationTool: Control ChartTool: Control Chart
Benefit: Prevents tampering or ignoringBenefit: Prevents tampering or ignoring
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Detecting VariationDetecting VariationControl Chart for Detecting VariationControl Chart for Detecting Variation
ObserveVariation
CommonCause
DetectSpecial Cause
Identify
Fix
Prevent
Don’tTamper
Reduce OverallVariation
ControlControlChartChart
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Detecting VariationDetecting VariationControl Chart for Detecting VariationControl Chart for Detecting Variation
Control ChartControl Chart
Trend ChartTrend Chart Center LineCenter Line Control LimitsControl Limits++ ++
Upper Control Limit
Lower Control Limit
Center Line
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Detecting VariationDetecting VariationControl LimitsControl Limits
Control limits tell us where the Control limits tell us where the measurements in a stable process measurements in a stable process
should fallshould fallLowerControlLimit
UpperControlLimit
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Detecting VariationDetecting VariationControl LimitsControl Limits
Calculated statistically, based on:Calculated statistically, based on:– Historical DataHistorical Data– Characteristics of the stable processCharacteristics of the stable process
Also called Also called 6 sigma6 sigma limits limits
HighlyUnlikely
1.5 out of1000
HighlyUnlikely
1.5 out of1000
+3-3
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Detecting VariationDetecting VariationCreating a Control ChartCreating a Control Chart
Turn the distribution on its sideTurn the distribution on its side
Upper Control Limit
Lower Control Limit
Center Line
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Detecting VariationDetecting Variation
Can we use spec limits as Can we use spec limits as control limits?control limits?
Can we compute control limits Can we compute control limits for an unstable process?for an unstable process?
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Detecting VariationDetecting Variation
What is the Center Line?What is the Center Line?
Process mean, based on historical Process mean, based on historical datadata
oror
Process TargetProcess Target
Creating a Control ChartCreating a Control Chart
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Detecting VariationDetecting Variation
Creating a Control ChartCreating a Control Chart
Selecting the Center LineSelecting the Center Line
The center line should be the The center line should be the target, unless we are target, unless we are unableunable or or unwilling to control the process unwilling to control the process to target.to target.
Since the target is zero defects, Since the target is zero defects, the center line is the process the center line is the process mean.mean.
Measurements:Measurements:
Defects:Defects:
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Detecting VariationDetecting Variation
Control LimitsControl Limits Based on Based on
performance of performance of the the processprocess..
Tell us when to Tell us when to take action on take action on the the processprocess..
Spec LimitsSpec Limits Based on Based on
performance of performance of the the productproduct..
Tell us when to Tell us when to disposition the disposition the productproduct..
Control Limits vs. Spec LimitsControl Limits vs. Spec Limits
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Detecting VariationDetecting Variation
Focus OnFocus On
Control LimitsControl Limits
Improve Process Improve Process QualityQuality
Spec LimitsSpec Limits
Improve Product Improve Product QualityQuality
Control Limits vs. Spec Limits
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Detecting VariationDetecting Variation
On-LineOn-Line: Assess the present : Assess the present stability of a process, as part of a stability of a process, as part of a process control system process control system (PCS)(PCS)
Off-LineOff-Line: Assess the historical : Assess the historical stability of a processstability of a process
Uses of a Control ChartUses of a Control Chart
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What is a PCS?What is a PCS?A PCS is a subset of the A PCS is a subset of the
Reduction in Variation flowReduction in Variation flow
ObserveVariation
CommonCause
Don’tTamper
Reduce OverallVariation
ControlControlChartChart
DetectSpecial Cause
Identify
Fix
Prevent