Implementing Six Sigma Quality
at Better Body Manufacturing
D M A I
Define
Measure Analyze
C
Improve Control
D M A I
Overview
Define
Measure Analyze
C
Improve Control
ABC Incorporated (ABC) is not achieving Six Sigma quality levels for all critical
Body-Side Sub-Assembly dimensions as requested by their customers.
200000
DPM
150000
DPM
0
ASM_9Y
3874
ASM_10Y
776
ASM_6Y
4
ASM_6Y
50000
19786
ASM_10Y
85824
ASM_3Y
ASM_9Y
ASM_8Y
ASM_3Y
172475
ASM_8Y
100000
ASM_7Y
ASM_7Y
Dimension
Ensure that all critical body-side subassembly dimensions are within Six Sigma
quality levels of < 3.4 DPM. Cp 2.0 and Cpk 1.67.
• Determined the correlation between body side and assembly dimensions.
• Evaluated the significance of Tonnage > 935 for ASM_7Y & ASM_8Y.
• Conducted a DOE for Clamp position for ASM_9Y & ASM_10Y.
• Change tonnage to > 935 to correct ASM_7Y and ASM_8Y
• Set clamp position to location 2 for ASM_9Y and ASM_10Y
• Re-machine A-pillar die to correct A_3Y and ASM_3Y
2
Problem Statement & The Goal
D M A I
Define
Measure Analyze
C
Improve Control
ABC Incorporated’s customer wants ABC to apply Six Sigma problem solving
methodology to insure that the body side subassembly is achieving Six Sigma quality
levels of less than 3.4 defects per million for all critical body side subassembly
dimensions.
ABC needs an improvement strategy that minimizes the rework costs while achieving the
desired quality objective. ABC’s goal is to produce module subassemblies that meet the
customer requirements and not necessarily to insure that every individual stamped
component within the assembly meets it original print specifications – sub-system
optimizations vs. local optimization.
A-Pillar
Reinforcement
B-Pillar
Reinforcement
Body Side Outer
+
+
3
D M A I
Measure Phase
Define
Measure Analyze
C
Improve Control
Key Variables:
Assembly process variables:
Weld Pattern (density), Clamp Location, and Clamp Weld Pressure
Stamping process variables (body side):
Press Tonnage, Die Cushion Pressure, Material Thickness
Body Assembly Dimensions ASM_1Y through ASM_10Y
Assembly Dimensions with Highest Defects
200000
172475
DPM
150000
100000
85824
50000
19786
3874
776
4
0
ASM_7Y
ASM_8Y
ASM_3Y
ASM_9Y
ASM_10Y
ASM_6Y
4
Analyze Phase
D M A I
Define
Measure Analyze
C
Improve Control
Resolution alternatives (based upon past experience):
1. Make adjustments to assembly process settings
2. Reduce variation of components through better control of stamping
process input variables
3. Rework stamping dies to shift component mean deviation that is off
target and causing assembly defects
Target Performance Level:
All ten critical assembly dimensions at Six Sigma quality level of  3.4 DPM.
Cp 2.0 and Cpk 1.67
Fish Bone and P-Diagrams:
Understanding potential causes of defects. From this we pick the assembly and
component dimensions that require further analysis
5
D M A I
Analyze Phase
Define
Measure Analyze
C
Improve Control
Environment
Quality
Component
Variability
Inspection
Process
Clamp Weld
Pressure
Clamp
Location
Methods
For our analysis we will do a DOE to check
for levels that contribute to better quality
product.
Material Thickness
Humidity
Gage R&R
Weld Pattern
(density)
Inputs
Temperature
Operator
Training
Body
Assembly
Yield
Strength
Material
Thickness
Die Cushion
Pressure
Elastic
Limit
Materials
Press
Tonnage
Machine
Control Variables
Clamp Location Press Tonnage
Weld Density
Die Pressure
Clamp Pressure
Body Side Sub-Assembly
Stamping Process
Yield Strength
Outputs
Body Side Sub-Assemblies at
Six Sigma quality levels
Noise Variables
Environment
Inherent Variation
Error
States
Dimensional
defects
6
D M A I
Analyze Phase
Define
Measure Analyze
C
Improve Control
Analysis of ASM_7Y and ASM_8Y
Run Chart for ASM_7Y
Run Chart for ASM_8Y
1.0
ASM_8Y
ASM_7Y
1.0
0.5
0.5
0.0
0.0
2
7
2
12
4.00000
7.00000
5.00000
0.03464
0.96536
Number of runs up or down:
Expected number of runs:
Longest run up or down:
Approx P-Value for Trends:
Approx P-Value for Oscillation:
12
Subgroup Number
Subgroup Number
Number of runs about median:
Expected number of runs:
Longest run about median:
Approx P-Value for Clustering:
Approx P-Value for Mixtures:
7
6.00000
7.66667
3.00000
0.10778
0.89222
Number of runs about median:
Expected number of runs:
Longest run about median:
Approx P-Value for Clustering:
Approx P-Value for Mixtures:
4.00000
7.00000
5.00000
0.03464
0.96536
Number of runs up or down:
Expected number of runs:
Longest run up or down:
Approx P-Value for Trends:
Approx P-Value for Oscillation:
8.00000
7.66667
2.00000
0.59781
0.40219
XY Plot of ASM_8Y and ASM_7Y
1.0
ASM_7Y
Conclusion: BS_7Y and ASM_7Y are following a similar trend.
A correlation chart to study this further shows high correlation.
(Pearson correlation, R of 0.701).
0.5
0.0
0.0
0.5
1.0
ASM_8Y
7
D M A I
Analyze Phase
Define
Capability Analysis of B_7Y
Capability of B_7Y
USL
0 DPM
Within
Overall
Potential (Within) Capability
Cp
2.96
CPU
2.50
CPL
3.43
Cpk
2.50
Cpm
*
Overall Capability
Pp
PPU
PPL
Ppk
2.95
2.49
3.41
2.49
Improve Control
Capability Analysis of BS_7Y
Capability of BS_7Y
LSL
Process Data
USL
0.70
Target
*
LSL
-0.70
Mean
0.11
Sample N
36
StDev (Within) 0.0788122
StDev (Overall) 0.0791215
Measure Analyze
C
LSL
Process Data
USL
0.700000
Target
*
LSL
-0.700000
Mean
0.899444
Sample N
36
StDev (Within) 0.149640
StDev (Overall) 0.383691
USL
698416 DPM
Within
Overall
Potential (Within) Capability
Cp
1.56
CPU
-0.44
CPL
3.56
Cpk
-0.44
-0.8
-0.6
-0.4
Observed Performance
PPM < LSL
0.00
PPM > USL
0.00
PPM Total
0.00
-0.2
0.0
0.2
0.4
Exp. "Within" Performance
PPM < LSL
0.00
PPM > USL
0.00
PPM Total
0.00
0.6
0.8
Exp. "Overall" Performance
PPM < LSL
0.00
PPM > USL
0.00
PPM Total
0.00
Cpm
*
Overall Capability
Pp
PPU
PPL
Ppk
0.61
-0.17
1.39
-0.17
-1.0
-0.5
0.0
Observed Performance
PPM < LSL
0.00
PPM > USL
666666.67
PPM Total
666666.67
0.5
1.0
Exp. "Within" Performance
PPM < LSL
0.00
PPM > USL
908706.09
PPM Total
908706.09
1.5
2.0
Exp. "Overall" Performance
PPM < LSL
15.33
PPM > USL
698400.06
PPM Total
698415.39
XY Plot of ASM_7Y and BS_7Y
1.3
Furthermore, BS_7Y shows strong correlation on
dimension ASM_7Y. (Pearson correlation, R of
0.786).
1.2
1.1
1.0
BS_7Y
Conclusion: B_7Y has 0 ppm compared to ~700K
DPM in BS_7Y.
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.5
1.0
1.5
ASM_7Y
8
D M A I
Analyze Phase
Define
Measure Analyze
C
Improve Control
XY Plot of Tonnage vs. BS_7Y
XY Plot of Tonnage vs. BS_7Y
BS_7Y
1.5
1.0
0.5
905
915
925
935
945
Tonnage
Conclusion: Tonnage values above 935 greatly improves BS_7Y and brings it closer
to the mean. Let’s see what impact this has on ASM dimensions 7Y, 8Y, 9Y, and
10Y by creating a subset of the data looking only at Tonnage > 935.
9
D M A I
Analyze Phase
Define
Measure Analyze
C
Improve Control
Impact this has on ASM dimensions 7Y, 8Y, 9Y & 10Y on Tonnage
Capability Analysis of ASM_8Y at Tonnage > 935
Capability Analysis of ASM_7Y at Tonnage > 935
Process Data
USL
1.00
Target
*
LSL
-1.00
Mean
0.09
Sample N
12
StDev (Within)
0.163174
StDev (Overall)
0.147855
LSL
USL
Within
Overall
*
Overall Capability
Pp
PPU
PPL
Ppk
2.25
2.05
2.46
2.05
LSL
Within
Overall
-1.0
-0.5
Observed Performance
PPM < LSL
0.00
PPM > USL
0.00
PPM Total
0.00
0.0
0.5
Exp. "Within" Performance
PPM < LSL
0.00
PPM > USL
0.01
PPM Total
0.01
1.0
Cpm
Exp. "Overall" Performance
PPM < LSL
0.00
PPM > USL
0.00
PPM Total
0.00
*
Overall Capability
Pp
PPU
PPL
Ppk
3.74
4.22
3.26
3.26
-1.0
LSL
*
Overall Capability
Pp
PPU
PPL
Ppk
1.88
0.90
2.86
0.90
0.0
0.5
Exp. "Within" Performance
PPM < LSL
0.00
PPM > USL
0.00
PPM Total
0.00
1.0
Exp. "Overall" Performance
PPM < LSL
0.00
PPM > USL
0.00
PPM Total
0.00
Capability Analysis of ASM_10Y at Tonnage > 935
USL
Within
Overall
Potential (Within) Capability
Cp
1.62
CPU
0.78
CPL
2.46
Cpk
0.78
Cpm
-0.5
Observed Performance
PPM < LSL
0.00
PPM > USL
0.00
PPM Total
0.00
Capability Analysis of ASM_9Y at Tonnage > 935
Process Data
USL
1.00000
Target
*
LSL
-1.00000
Mean
0.52083
Sample N
12
StDev (Within)
0.206010
StDev (Overall)
0.177098
USL
Potential (Within) Capability
Cp
3.27
CPU
3.69
CPL
2.85
Cpk
2.85
Potential (Within) Capability
Cp
2.04
CPU
1.86
CPL
2.23
Cpk
1.86
Cpm
Process Data
USL
1.00000
Target
*
LSL
-1.00000
Mean
-0.12833
Sample N
12
StDev (Within)
0.101825
StDev (Overall)
0.089161
Process Data
USL
1.00
Target
*
LSL
-1.00
Mean
0.39
Sample N
12
StDev (Within)
0.215541
StDev (Overall)
0.187663
LSL
USL
Within
Overall
Potential (Within) Capability
Cp
1.55
CPU
0.94
CPL
2.15
Cpk
0.94
-1.0
-0.5
Observed Performance
PPM < LSL
0.00
PPM > USL
0.00
PPM Total
0.00
0.0
0.5
Exp. "Within" Performance
PPM < LSL
0.00
PPM > USL
10010.77
PPM Total
10010.77
1.0
Exp. "Overall" Performance
PPM < LSL
0.00
PPM > USL
3408.51
PPM Total
3408.51
Cpm
*
Overall Capability
Pp
PPU
PPL
Ppk
1.78
1.08
2.47
1.08
-1.0
-0.5
Observed Performance
PPM < LSL
0.00
PPM > USL
0.00
PPM Total
0.00
0.0
0.5
Exp. "Within" Performance
PPM < LSL
0.00
PPM > USL
2326.72
PPM Total
2326.72
1.0
Exp. "Overall" Performance
PPM < LSL
0.00
PPM > USL
576.00
PPM Total
576.00
Conclusion: Setting Tonnage to greater than 935 resulted in ASM_7Y and ASM_8Y
meeting the goal of <3.4 DPM. ASM_9Y and ASM_10Y require further analysis.
10
D M A I
Analyze Phase
Define
Measure Analyze
C
Improve Control
DOE for Response Variable ASM_9Y
• DOE factorial analysis shows Clamp Position is the only significant factor in
determining ASM_9Y dimension
Input Variable
Proposed ASM_9Y Setting
Proposed ASM_10Y Setting
DOE Response Optimization for ASM_9Y
Clamp Location
Location 2
Location 2
Weld Density (welds per X inches)
1.33
1.33
• Set Clamp Position to Location 2Clamp
(level
Pressure1)
2100 psi
2100 psi
• Optimizer recommends setting Weld Density to 1.33 weld per inch (level 1),
but this appears to be a robust parameter, which could be changed for the benefit
of process without reducing quality if processing time or cost shows a benefit.
• Optimizer recommends setting Clamp Pressure to 2100 psi (level 1), but this
appears to be a robust parameter, which could be changed for the benefit of process
without reducing quality if processing time or cost shows a benefit.
• Run additional tests at recommended settings to confirm results
• Weld Density and Clamp Pressure are robust parameters and can be set to optimize
the process capability to maximum level and lowest cost.
11
Analyze Phase
D M A I
Define
Measure Analyze
C
Improve Control
DOE for Response Variable ASM_10Y
• DOE factorial analysis shows Clamp Position is also the only significant
factor in determining ASM_10Y dimension
DOE Response Optimization for ASM_10Y
• Setting clamp to location 2 also improves ASM_10Y
• Recommend same settings used to improve ASM_9Y to improve process
capability which also allows for no changes to machine setup and helps reduce
possible process concerns
• Run additional tests at recommended settings to confirm results
• Weld Density and Clamp Pressure are robust parameters and can be set to optimize
the process capability to maximum level and lowest cost.
12
Analyze Phase
D M A I
Define
Measure Analyze
C
Improve Control
DOE for Response Variable ASM_3Y
• DOE factorial analysis shows that no factors are significant
• Response Optimization shows no solution for response optimizer
Observe Process Capability of A_3Y and BS_3Y
• ASM_3Y and A_3Y have a similar mean shift in the -Y direction
Correlation of Output Variables
• No dimensional correlations appear to exist between ASM_3Y and
A_3Y or BS_3Y
Stepwise Regression Analysis of BS_3Y
• Tonnage and Die Pressure appear to be significant in determining
dimension BS_3Y
• Tonnage values < 920 may improve BS_3Y
• Die Pressure appears to have no clear correlation to BS_3Y
13
D M A I
Analyze Phase
Define
Measure Analyze
C
Improve Control
Process Capability of BS_ 3Y and ASM_3Y at Tonnage < 920
• Created subset of body data looking only at dimensions with Tonnage < 935
• Tonnage < 920 appears to improve the mean of BS_3Y slightly, but has no
impact on improving the mean of ASM_3Y.
Capability Analysis of ASM_3Y
Die remachined to move mean +0.80
Capability of A_3Y and ASM_3Y with +0.80
mm mean offset
• Manipulate data for A_3Y and ASM_3Y
by +0.80 mm to simulate re-machining
Process Data
USL
1
Target
*
LSL
-1
Mean
0
Sample N
36
StDev (Within) 0.0851436
StDev (Overall) 0.0971725
USL
Within
Overall
Potential (Within) Capability
Cp
3.91
CPU
3.91
CPL
3.91
Cpk
3.91
Cpm
• Process capability shows 0 defects for
A_3Y and ASM_3Y with this mean offset
LSL
*
Overall Capability
Pp
PPU
PPL
Ppk
3.43
3.43
3.43
3.43
-1.0
-0.5
Observed Performance
PPM < LSL
0.00
PPM > USL
0.00
PPM Total
0.00
0.0
Exp. "Within" Performance
PPM < LSL
0.00
PPM > USL
0.00
PPM Total
0.00
0.5
1.0
Exp. "Overall" Performance
PPM < LSL
0.00
PPM > USL
0.00
PPM Total
0.00
14
Analyze Phase
D M A I
Define
Measure Analyze
C
Improve Control
Conclusions
• From the analysis of ASM_7Y and ASM_8Y we can conclude that:
•
Setting tonnage > 935 results in ASM_7Y and ASM_8Y meeting the goal
• Analyzing ASM_9Y and ASM_10Y helps determine that:
•
Setting clamp position to location 2, weld density to 1 weld every 1.33”
and clamp pressure to 2000 psi helps with dimensions ASM_9Y and
ASM_10Y
• Analyzing ASM_3Y helps us conclude that:
•
Re-machine A-Pillar die to move A_3Y to nominal – which could cause
BS_3Y to shift towards nominal – effectively shifting ASM_3Y to nominal
15
D M A I
Analyze Phase
Define
Measure Analyze
C
Improve Control
With the recommended changes the process performance will improve significantly
Dimension Mean
StDev
Overall
DPM_Obsv DPM_Within DPM_Exp
Pp
Ppk
Cp
Cpk
ASM_1Y
-0.035
0.165
0
0
0
2.01
1.94
2.47
2.39
ASM_2Y
0.259
0.152
0
0
1
2.20
1.63
2.31
1.71
ASM_3Y
0.000
0.097
0
0
0
ASM_4Y
0.009
0.115
0
0
0
2.90
2.87
3.53
3.50
ASM_5Y
-0.330
0.145
0
0
2
2.30
1.54
3.72
2.50
ASM_6Y
-0.284
0.160
0
1
4
2.08
1.49
2.24
1.60
ASM_7Y
0.090
0.148
0
0
0
2.25
2.05
2.04
1.86
ASM_8Y
-0.128
0.089
0
0
0
3.74
3.26
3.27
2.85
ASM_9Y
0.521
0.180
0
0
0
ASM_10Y
0.395
0.191
0
0
0
16
Improve Phase
D M A I
Define
Measure Analyze
C
Improve Control
Recommendations for improving the process:
• Set Tonnage to above 935 to improve ASM_7Y & ASM_8Y
• Set Clamp to Location 2 to improve ASM_9Y & ASM_10Y
• Re-machine the A-Pillar die to move the mean of A_3Y to nominal which in turn
will move ASM_3Y to nominal
Implement the above recommendations and run additional samples to verify results.
17
Control Phase
D M A I
Define
Measure Analyze
C
Improve Control
Recommended controls :
• Implement a gauge on the body side component press to monitor tonnage
• Implement an alarm and shut-off feature on the body side press if tonnage
falls below 935 tons
• Implement poke-yoke clamping fixture that ensures clamp is always in
Position 2
• Establish an affordable control plan for ongoing monitoring of the 10
critical assembly dimensions.
18
Summary
D M A I
Define
Measure Analyze
C
Improve Control
ABC Incorporated is not achieving Six Sigma quality levels for all critical BodySide Sub-Assembly dimensions as requested by their customers. BBM needs to
apply Six Sigma problem solving methodology to establish an improvement strategy
that minimizes rework costs, yet achieves the desired quality objective.
Bring the key process output variables within Six Sigma quality level of < 3.4 DPM.
Cp 2.0 and Cpk 1.67
Set Tonnage to above 935 to improve ASM_7Y & ASM_8Y
• Set Clamp to Location 2 to improve ASM_9Y & ASM_10Y
• Re-machine the A-Pillar die to move the mean of A_3Y to nominal
•
Implement a gauge on the body side component press to monitor tonnage
• Implement an alarm & shut-off feature on body side press if tonnage falls below 935
• Implement poke-yoke clamping fixture that ensures clamp is always in Position 2
• Establish control plan for ongoing monitoring of the 10 critical assembly dimensions.
•
19