Block 25 Control Charts 13
33
Construction QC/QA Control Charts 1 Quality control/quality assurance Control Charts Senior/Graduate HMA Course
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Transcript of Block 25 Control Charts 13
Construction QC/QA Control Charts 1
Quality control/quality assurance
Control Charts
Senior/GraduateHMA Course
Construction QC/QA Control Charts 2
Control
Charts
Construction QC/QA Control Charts 3
Variation
- Chance Causes- Assignable Causes
Construction QC/QA Control Charts 4
Chance Causes
1. Everything varies2. Individuals are unpredictable3. Groups from a constant system tend to be predictable
8-31
Construction QC/QA Control Charts 5
Example: Chance Causes
1. People live to different ages
2. No one knows how long he or she will live
3. Insurance companies can predict the percentage of people who will live to certain ages
Construction QC/QA Control Charts 6
Assignable Causes
If identified -
It can be eliminated
Construction QC/QA Control Charts 7
Benefits of Control Charts
- Early Detection of Trouble- Decrease Variability- Establish Process Capability- Reduce Price Adjustment Costs- Decrease Inspection Frequency
Construction QC/QA Control Charts 8
Benefits of Control Charts
• Basis for Altering Specification Limits
• Permanent Record of Quality
• Provide a Basis for Acceptance
• Instill Quality Awareness
Construction QC/QA Control Charts 9
Control Chart Analysis
AASHTO
“To Develop a Quality Control/Quality
Assurance Plan for Hot Mix Asphalt”
Construction QC/QA Control Charts 10
1 2 3 4 5 6 7Lot Number
Upper control limit
Lower control limit
Construction QC/QA Control Charts 11
Data Points
Statistical Control Chart
Upper Control Limit
Lower Control Limit
Target
Value
Construction QC/QA Control Charts 12
Five lines on a statistical process control chart
• Target value• Warning upper control limit• Warning lower control limit• Action upper control limit• Action lower control limit
Construction QC/QA Control Charts 13
Upper Control Limit
Lower Control Limit
Mean
1 2 3 4 5 6 7Lot Number
Construction QC/QA Control Charts 14
Statistical Control Charts
Upper and Lower Warning Control Limits
UWCL = X + { 2 (s) / (n)1/2 }
LWCL = X + { 2 (s) / (n)1/2 }
Construction QC/QA Control Charts 15
Statistical Control Charts
Upper and Lower Action Control Limits
UWCL = X + { 3 (s) / (n)1/2 }
LWCL = X + { 3 (s) / (n)1/2 }
Construction QC/QA Control Charts 16
Example Problem
• Given:– Target asphalt binder content: 5.7 %– Standard deviation – 0.25 %– The rolling average is based on five data
points
Construction QC/QA Control Charts 17
Example Problemwarning limits
UWCL = X + { 2 (s) / (n)1/2 }
UWCL = 5.7 + { 2 (.25) / (5)1/2 }
UWCL = 5.9
Construction QC/QA Control Charts 18
Example Problemwarning limits
LWCL = X - { 2 (s) / (n)1/2 }
LWCL = 5.7 - { 2 (.25) / (5)1/2 }
LWCL = 5.5
Construction QC/QA Control Charts 19
Example Problemwarning limits
UACL = X + { 3(s) / (n)1/2 }
UACL = 5.7 + { 3 (.25) / (5)1/2 }
UACL = 6.0
Construction QC/QA Control Charts 20
Example Problemwarning limits
LACL = X - { 3 (s) / (n)1/2 }
LACL = 5.7 - { 3 (.25) / (5)1/2 }
UWAL = 5.4
Construction QC/QA Control Charts 21
Look for Assignable Cause If:
• One point is outside of control limits
• Eight consecutive points are on one side of the target value
Interpreting
X & R
Charts
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5
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0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50
Sample Number
% A
ir V
oid
s
Action Limit (UCL)
Warning Limit
Action Limit (LCL)
Chart
0
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5
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0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50
Sample Number
% A
ir V
oid
s
(UCL)
(LCL)
Range (R) Chart
Control ChartsRules of Thumb
Lack of Control Occurs When:
Change in , R Constant
Change in R, Constant
Change in Both & R
X
X
X
Sustained Shift in
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0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50
Sample Number
% A
ir V
oid
s
Action Limit
Warning Limit
Mean Increases
Trend in
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Sample Number
% A
ir V
oid
s
Production "Upward Drift"
Action Limit
Warning Limit
Irregular Shift in
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0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50
Sample Number
% A
ir V
oid
s
Action Limit (UCL)
Warning Limit
Action Limit (LCL)
Sudden Change in R
0
1
2
3
4
5
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8
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0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50
Sample Number
% A
ir V
oid
s
(UCL)
(LCL)
Gradual Change in R
0
1
2
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5
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8
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0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50
Sample Number
% A
ir V
oid
s
(UCL)
(LCL)
Irregular Shift in & R
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3
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5
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0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50
Sample Number
% A
ir V
oid
s
Action Limit (UCL)
Warning Limit
Action Limit (LCL)
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3
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5
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0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50
Sample Number
% A
ir V
oid
s
Eight Points Below Target
Single Point AboveAction LimitAction Limit
Warning Limit
Lack of Control?
Construction QC/QA Control Charts 33
Questions?
