Six Sigma Example

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Implementing Six Sigma Quality at Better Body
Manufacturing
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Overview
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Problem Statement The Goal
PROBLEM STATEMENT
ABC Incorporateds 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. ABCs 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.
GOAL
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Measure Phase
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
KEY PROCESS INPUT VARIABLES
KEY PROCESS OUTPUT VARIABLES
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Analyze Phase
A
Analyze
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 ³ 2.0 and Cpk ³ 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
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Analyze Phase
A
Analyze
FISHBONE DIAGRAM
P-DIAGRAM
For our analysis we will do a DOE to check for
levels that contribute to better quality product.
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Analyze Phase
A
Analyze
Analysis of ASM_7Y and ASM_8Y
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).
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Analyze Phase
A
Analyze
Capability of B_7Y
Capability of BS_7Y
698416 DPM
0 DPM
Conclusion B_7Y has 0 ppm compared to 700K DPM
in BS_7Y. Furthermore, BS_7Y shows strong
correlation on dimension ASM_7Y. (Pearson
correlation, R of 0.786).
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Analyze Phase
A
Analyze
XY Plot of Tonnage vs. BS_7Y
Conclusion Tonnage values above 935 greatly
improves BS_7Y and brings it closer to the mean.
Lets see what impact this has on ASM dimensions
7Y, 8Y, 9Y, and 10Y by creating a subset of the
data looking only at Tonnage gt 935.
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Analyze Phase
A
Analyze
Impact this has on ASM dimensions 7Y, 8Y, 9Y
10Y on Tonnage
Conclusion Setting Tonnage to greater than 935
resulted in ASM_7Y and ASM_8Y meeting the goal of
lt3.4 DPM. ASM_9Y and ASM_10Y require further
analysis.
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Analyze Phase
A
Analyze

• DOE for Response Variable ASM_9Y
• DOE factorial analysis shows Clamp Position is
  the only significant factor in determining
  ASM_9Y dimension
•  
• DOE Response Optimization for ASM_9Y
• Set Clamp Position to Location 2 (level 1)
• 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.

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Analyze Phase
A
Analyze

• 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.

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Analyze Phase
A
Analyze

• 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 lt 920 may improve BS_3Y
• Die Pressure appears to have no clear
  correlation to BS_3Y

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Analyze Phase
A
Analyze

• Process Capability of BS_ 3Y and ASM_3Y at
  Tonnage lt 920
• Created subset of body data looking only at
  dimensions with Tonnage lt 935
• Tonnage lt 920 appears to improve the mean of
  BS_3Y slightly, but has no impact on improving
  the mean of ASM_3Y.

• 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 capability shows 0 defects for A_3Y and
  ASM_3Y with this mean offset

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Analyze Phase
A
Analyze

• Conclusions
• From the analysis of ASM_7Y and ASM_8Y we can
  conclude that
• Setting tonnage gt 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

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Analyze Phase
A
Analyze
With the recommended changes the process
performance will improve significantly
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Improve Phase

• 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.

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Control Phase

• 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.

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Summary