This presentation is my Greenbelt Six Sigma Project

1. Dryer Timer Stripped Drive Gear System
Emerson Appliance Controls Division
Indianapolis, Indiana
Final Report
Project Start Date: Jan 28, 2001
Project Completion Date: July 1, 2001
Greenbelt Candidate: Stan E. Mitchell
1

2. Table of Contents
0.0 Table of Contents page 2
1.0 Executive Summary page 3
2.0 Key Words page 4
3.0 Problem Statement page 4
4.0 Action Items page 6
5.0 Manufacturing Implementation page 8
6.0 Conclusions and Lessons Learned page 8
7.0 Team Members page 9
8.0 Acknowledgements page 9
9.0 Appendices page 9
2

3. 1.0 Executive Summary
For the fiscal year 2000, the parts per million (PPM) level of the customer
field failure returns of the M460 dryer timer manufactured at Sparta, Tn and
Juarez, Mx was 1400. This resulted in a cost of non-value added of $100,000.
The objective is to reduce the PPM level of customer field failure returns
from 1400 to 700 by July 2001. The cost of non-value added savings for this
project is projected at $50,000.
Results from the customer dryer timer teardowns (analysis of dryer timer field
failures) shows that 50% of the timer failures was due to the pinion
dislodgment from the output gear assembly. The project was narrowed to
analyzing the output gear assembly / drive gear interface. The output gear
assembly consists of a powdered metal pinion that is pressed into a plastic
output gear causing an interference fit. The drive gear is a stamped part that
interfaces with the pinion. A motor powers this drive gear system.
(Appendix 16.0)
Capability analysis of key customer specifications dimensions of the output
gear, pinion, and drive gear concluded that the manufacturing process was
capable of consistently producing quality parts. Capability analysis of the
pinion pullout force (the force it takes to dislodge the pinion from the output
gear assembly) concluded that the pinion / output gear joint was adequate.
The one-sided customer specification for the pullout force is a minimum of 60
lbs. Since the drive gear interfaces with the pinion, this joint was analyzed.
Capability and engineering design analysis proved that the drive gear does not
apply enough force to dislodge the pinion from the output gear. The customer
specification for the rotational torque for the drive system is 250 in-oz.
Because this drive gear system problem occurred during fiscal year 2000,
EAC engineering personnel implemented some design changes to the drive
gear system for manufacturing and customer analysis in the 4th quarter of
2000. Internal Highly Accelerated Stress Testing (HALT) and external
Multiple Environment Over Stress Testing (MEOST) proved that the
engineering design changes would eliminate the stripped drive gear system
problem.
The scope of the project is to verify that the enhanced drive gear system is
more robust after the engineering design changes. Six sigma tools and
methodology were used to statistically analyze the project metrics.
3

4. 2.0 Key Words
• PPM - units defective per 1 million units produced
• CVNA - cost of non-value added
• Pinion Pullout Force – the force (lbs) it takes to dislodge the pinion from the
output gear assembly
• Output Gear Assembly – metal pinion and output gear sub-assembly
• MEOST – multiple environment over stress testing
• HALT – highly accelerated life testing
3.0 Problem Statement
For fiscal year 2000, the PPM level of customer field failures of the M460 dryer
timer drive gear system manufactured at Sparta, Tn and Juarez, Mx was 1400.
This resulted in a CNVA of $50,000 in scrap and labor.
3.1 Customer Requirements
The M460 dryer timer is used on 100% of the domestic clothed dryers. Due
to increased global competition and new technologies, it is critical that
Emerson Appliance Controls stay “quality focused” and keep all internal and
external customers happy. Since the drive gear system is an integral part of
the dryer timer, robust functionality is key. Because quality “cost”, it was
important for EAC to find the root cause of the drive system stripped gear
problem and eliminate it.
3.2 Project Objective
The objective of this project was to reduce the PPM level of customer
returns of the M460 dryer timer from 1400 to 700. This resulted in a CNVA
of $100,000 in scrap and labor. The goal of this project is to reduce the
CNVA by 50% and save $50,000.
3.3 Outline of Project Strategy / Timeline
• First level pareto of dryer timer customer returns were analyzed by the
team. Actual data shows that 42% of customer returned timers failed
because of drive system stripped gear.
4

5. • Identify the critical (X’s) that the team felt would contribute to the
problem solution. Tools such as Cause and Effect Diagram (Fishbone)
and X-Y Matrix were used.
• A preliminary (Failure Mode and Effects Analysis) was performed to
prioritize variables that contribute to key characteristics of the output
gear assembly pinion pullout force. This is an active document subject to
be updated.
• A Gage Reproducibility and Repeatability study (GR&R) was performed
on the output gear assembly machine. The equipment was found to be
capable of measuring the parameters specified over the range of the “Y”
of interest.
• Capability analysis was performed on the pinion pullout force of the
current drive gear system (before engineering design changes). The
output gear / pinion interface joint is marginal at best.
• Hypothesis testing proved that the drive gear system engineering design
changes increased the robustness.
• Conclusions from the design of experiments proved that 94% of the
pinion pullout force variation was not explained by the regression
equation using the output gear sub-assembly parts. Because the drive
system piece parts are inter-connected, one input factor alone did not
cause the stripped gear field failures. Internal and external dryer timer
testing (MEOST and HALT) proved that the engineering design changes
to the drive gear system would eliminate the stripped gear problem.
3.4 Project Schedule
See Attached Project Timeline (Appendix 1.0)
3.5 Final Project Description
The object of this project was to reduce the PPM level of customer field
returns on the M460 dryer timer because of stripped gears from 1400 to 700.
This CNVA for the stripped gear problem was $50,000. The original goal
was to save $25,000 in scrap and labor. The results of this project are
projected savings of 100% with “zero” customer returns because of stripped
drive gear.
5

6. 4.0 Actions Taken
The following is an outline of the experimental data associated with this
project. It is organized by the four phases of six sigma methodology:
Measurement, Analyze, Improve, and Control
4.1 Measurement Phase
• Process Maps are outlined identifying all manufacturing process steps
(Appendix 2.0)
• Dryer Timer pareto of field failures was generated. Because of the high
rate of stripped gear failures (42%), the team agreed that the drive gear
system should be the primary metric for problem resolution.
(Appendix 3.0)
• Established a Cause and Effect Diagram (Appendix 4.0)
• XY Matrix was completed to prioritize project focus (Appendix 5.0)
• FMEA was created and used to rank the areas for the most opportunities
for improvement (Appendix 5.1)
• A Gage R&R was conducted on the output gear assembly machine. The
study concluded that this machine was acceptable. (Appendix 6.0)
• An initial capability study was completed on the pinion pullout force of
the current output gear assembly. The current manufacturing process
pinion pullout force mean was 73 lbs with a Cpk of 0.53 and a Sigma
Level of 1.6 for Celmex manufacturing process. The study concluded that
the output gear / pinion interface joint needs to be more robust.
(Appendix 7.0 ,Celmex), (Appendix 7.1, Sparta)
4.2 Analyze Phase
• After determining that the manufacturing process for the output gear sub-
assembly parts was capable of consistently producing good parts, a multi-
vari study was performed to determine if any categorical factors such as
shift, date, and machine no. caused any variation in the pinion pullout
force. Conclusions from the multi-vari study proved that the categories
did not significantly affect the mean manufacturing process value of the
pinion pullout force. The day-to-day variation of the pinion pullout force
was about 2 lbs. The manufacturing process mean value of the pinion
pullout force was 105 lbs vs. a target of 85 lbs and a lower specification
limit of 60 lbs. The “take away” was that the output gear sub-assembly
manufacturing process is in control. (Appendix 8.0)
6

7. • A One Sample T test was performed on the pinion pullout force vs. the
customer specifications. The “take away” is the current manufacturing
process mean of the pinion pullout force in “better” than the customer
specifications. Manufacturing process mean of 105 lbs vs. customer
specification of 85 lbs. (Appendix 8.1)
• A Multi-Vari study and One Sample T test was performed on the critical
output gear assembly / drive gear interface height. This dimension is
critical for form/fit/function in achieving an adequate drive gear / pinion
contact ratio. Conclusions from the multi-vari study and one sample t test
prove that the manufacturing process of the output gear sub-assembly is
in control. (Appendix 9.0 and 9.1)
• A capability study was performed on the rotational torque of the pinion
/drive gear interface. If was inferred that due to design tolerance stack-up,
the force from the drive gear at worst case dimensionals would cause the
pinion to dislodge from the output gear assembly. Although a possibility,
design engineering calculations prove that the drive gear/ pinion interface
joint is not a major factor since the actual design rotational torque of 5.32
in-oz in much less than the customer specification of 250 in-oz.
(Appendix10.0)
4.3 Improvement Phase
• Design of Experiments results proved that the output gear sub-assembly
piece parts (individually) do not have a major impact on my project
metric
• Drive gear system engineering design changes (Appendix 11.0)
Drive gear / pinion contact ratio changed from 1.3 to 1.6
Drive gear and output gear diametral pitch changed from 64 to 57
Drive gear thickness changed from 0.032 in to 0.036 in
Contact area between metal pinion and plastic gear lengthened by
0.050 in.
• HALT and MEOST test were performed on the drive gear system with
the engineering design enhancements. The conclusions of the test are
listed below:
♦ Highly Accelerated Life Test
Shipping and Storage, Environmental Thermal Shock, and
Durability test were conducted
Timer motor was accelerated to 180hz (3 times normal speed)
Timers were tested to 4300 resets (simulates 11 years of timer life)
The drive gear system had “zero” failures
7

8. ♦ Multiple Environment Over Stress Test
Old drive gear system vs. New drive gear system testing
Test levels ranged from 1 to 11 (11 being the highest “input” stress
level)
Test parameters: vibration, temperature cycling, humidity and
durability
Two timers with the old drive gear system failed at level 2
Two timers with new drive gear system did not have any failures at
level 11.
4.4 Control Phase
• An engineering change order was initiated with the output gear design
changes. Suppliers have been notified of these engineering drive gear
design changes.
5.0 Manufacturing Implementation
• The customers are very happy with the results of the HALT and MEOST
testing. EAC was given customer approval to implement the new drive
gear system into full production by Mar 2001.
6.0 Conclusion and Lessons Learned
This project is projected to cause a 100% PPM level reduction of the dryer
timer customer returns because of the drive system gear “stripping” failures.
The original goal was to reduce the PPM by 50% from 1400 to 700. It was
concluded statistically using six sigma tool and empirically that the new drive
gear system is more robust. The savings for this project were targeted at
$50,000 The projected savings is 100% or $100,000.
This project was very important to Emerson and the customer base. Many
customers are requiring much more “up front” analysis of solutions to dryer
timer mechanical and electrical problems. Dryer timer customers want root
cause analysis to problems with timely production implementation. The
success of this effort is directly proportional to the committment of the EAC
management team. EAC management recognizes the importance of Six Sigma
Tools and Methodology.
8

9. • Further improvements to the output gear sub-assembly manufacturing
process
Punch added to enhance the alignment of the output gear and
pinion during assembly
Lessons learned from this project include the importance of understanding
the goal of the project. It is very important that the project scope is written to
focus on a desired metric. This metric should be easily measured and
analyzed. Secondly, it is vital that the Six Sigma Tools and Methodology are
understood and applied correctly for accurate statistical analysis.
7.0 Team Members – Thank You !
Stan E. Mitchell Green Belt Candidate / EAC Project Manager
Andre White Master Black Belt
Howard Andrews Sparta Quality Engineer
Jack Holtz Celmex Resident Engineer
Cesar Gutierrez Celmex Quality Manager
Hector Mendez Celmex Quality Engineer
Ted Maynard Sparta Quality Engineer
8.0 Acknowledgements
Rick Burns Master Black Belt / Six Sigma Qualtec
Chris Reynolds Black Belt / White Rodgers Harrison
Fidel Gutierrez Black Belt / MMM
Pardeep Sood EAC President
Russ Epplett EAC Vice President of Engineering
George Adams EAC Director of Product Engineering
Ben Chestnut EAC Engineering Manager
John Bonnema EAC Vice President of Quality
9.0 Appendices
1.0 Project Timeline
2.0 Process Map
9

10. 3.0 Pareto of Field Failures
4.0 Cause and Effect Diagram
5.0 XY Matrix
5.1 FMEA
6.0 Gage R&R
7.0 (Celmex) Initial Short-Term Process Capability
7.1 (Sparta) Initial Short-Term Process Capability
8.0 Multi-Vari Study (pinion pullout force lbs)
8.1 One-Sample T-test (pinion pullout force lbs)
9.0 Multi-Vari Study “Y” sub-assembly dimension
9.1 One-Sample T-test “Y” sub-assembly dimension
10.0 Capability Analysis of Rotational Torque in-oz
11.0 Drive System Engineering Design Changes
12.0 Celmex Capability Analysis of Pinion Pullout Force lbs
(after drive system engineering design changes)
12.1 Sparta Capability Analysis of Pinion Pullout Force lbs
(after drive system engineering design changes)
13.0 Celmex Two Sample T-test (pinion pullout force lbs)
14.0 Sparta Two Sample T-test (pinion pullout force lbs)
15.0 Design of Experiments Results
16.0 Project Primary Matrix
17.0 Project Secondary Matrix
18.0 Drive System Components
19.0 Dryer Timer X-Section
20.0 Output Gear Assembly Machine
21.0 Pinion Location and Alignment
22.0 Staking Punch, Output Gear Assembly
10

11. 11

12. Appendix 2.0
Process Map (Overall)
START
output gear inside diameter (C) 0.393 - 0.0015 in
output gear inside diameter depth (C) 0.202 +/- 0.005 in
A
output gear assy working height (C) 0.442 +/- 0.008 in NV
pinion base diameter (C) 0.311 +/- 0.002 in A
NV
pinion height (C) 0.371 +/- 0.003 in STOCKROOM STOCKROOM
pinion diametral pitch (C) 57 OUTPUT GEAR PINION
drive gear thickness (C) 0.036 in
drive gear diametral pitch (C) 57
housing gear centers distance (C) 0.468 +/- 0.002 in
test procedures (SOP) N/A
(X) INPUT SECURE PINION
AND OUTPUT
(S) OPERATOR STANDARDS GEAR IN
FIXTURE
ASSEMBLE
OUTPUT GEAR
(S) OPERATOR STANDARDS AND PINION
SUB-ASSEMBLY
(S) OPERATOR STANDARDS (Y) OUTPUT
(C) PRESS FORCE A
PINION PULLOUT FORCE NV
(C) PRESS SPEED SCRAP
A INSPECTION
(C) ALIGNMENT FIXTURING NV
(C) PINION / OUTPUT GEAR BAD
INTERFACE DIMENSIONS
GOOD
SHIP TO
CUSTOMER/
DOMESTIC
MARKET
A
NV
FAILED DRYER
TIMERS RETURNED (Y) OUTPUT
TO SUPPLIER FOR FIELD RETURNS PINION POP OFFS
ROOT CAUSE
ANALYSIS
STOP
12

13. Appendix 3.0
Pareto of Field Failures
DRYER TIMER FIELD FAILURES 2000
100
100
80
Percent
Count
60
50
40
20
0 0
EA
R CT SY KE
N
/G FE AS IL
DE RO CO er s
ION NT ER
D/
B
EN
PIN E OP OP Oth
Defect E D P AR
IM
PR
MA
GE
IP P AP DA
STR NO
Count 47 39 10 8 3 3
Percent 42.7 35.5 9.1 7.3 2.7 2.7
Cum % 42.7 78.2 87.3 94.5 97.3 100.0
13

14. Appendix (4.0)
Cause and Effect Diagram
MAINTENANCE CUSTOMER SPECIFICATIONS MACHINES
scheduled understood calibration
documented documented cycle time
set-up
environment design
DISLODGED PINIONS
accessible per customer specs
knowledgeable
dimensonally correct
documented operator
handling
up to date trained
robust
WORK INSTRUCTIONS PERSONNEL PARTS
14

15. Appendix (5.0)
XY Matrix
Input Variables Rank %
outside gear bearing
271 12.34
inside diameter height
output gear assembly
185 8.42
bearing outside diameter
output gear bearing
290 13.20
outside diameter
pinion base diameter 252 11.47
pinion height 241 10.97
pinion base surface finish 165 7.51
output gear sub-assembly
290 13.20
machine alignment
output gear sub-assembly
271 12.34
machine press force
output gear sub-assembly
232 10.56
machine press speed
14% CHARACTERISTIC SELECTION MATRIX RESULTS
CHARACTERISTICS
12%
IMPORTANCE %
10%
8%
6%
4%
2%
0%
ba iam g
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di ter
te ing
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on ter
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INPUT CHARACTERISTICS
be
15

16. Appendix (5.1)
FMEA
16

17. Appendix 6.0
(Gage R&R)
GOOD
GAGE
GOOD
GAGE
GOOD
GAGE
17

18. Appendix 7.0
Initial Short-Term Capability Analysis
Celmex
P R O C E S S C A P A B IL IT Y A N A L Y S IS F O R
P IN IO N P U L L O U T F O R C E F O R C E L M E X
B E F O R E D R IV E S Y S T E M D E S IG N C H A N G E
C a lc ula tio ns B a s e d o n W e ib ull D is tr ibutio n M o de l
LSL
30 40 50 60 70 80 90
Mean: 73.8
Std. Dev.: 9.5
Cpk: 0.53
PPM: 55,000
Sigma Level: 1.6
18

19. Appendix 7.1
Initial Short-Term Capability Analysis
Sparta
P R O C E S S C A P A B IL IT Y A N A L Y S IS F O R
P IN IO N P U L L O U T F O R C E F O R S P A R T A
B E F O R E D R IV E S Y S T E M D E S IG N C H A N G E
C a lc u la tio n s B a s e d o n W e ib u ll D is tr ib u tio n M o d e l
LSL
40 50
60 70 80 90 100
Mean: 82.4
Std. Dev.: 9.2
Cpk: 0.80
PPM: 8155
Sigma Level: 2.4
19

20. Appendix 8.0
Multi-vari study
Multi-Vari Chart for PINION PULLOUT FORCE by MACHINE POSITION - DATE
MOLD TOOL NO
1 1 1 1
SP SP SP SP MACHINE POSITION
A
B
110
PINION PULLOUT FORCE (LBS)
105
100
4/16/01 4/17/01 4/18/01 4/19/01
DATE
TAKEAWAY: OUTPUT GEAR SUB - ASSY MACHINE “IN” PROCESS
F
20

21. Appendix 8.1
One Sample T-test
One-Sample T: PINION PULLOUT FORCE (LBS)
Test of mu = 85 vs mu > 85
Variable N Mean StDe SE Mean
PINION PULLOUT 30 105.56 4.80 1.20
Variable 95.0% CI T P
PINION PULLOUT( 103.00, 108.12) 17.1 0.000
Current
Manufacturing
Process
TAKEAWAY: CURRENT PROCESS MEAN IS DIFFERENT / BETTER THAN THE STANDARD
21

22. Appendix 9.0
Multi-Vari Study
Multi-Vari Chart for Y DIMENSION by SHIFT - DATE
MACHINE POSITION
A B A B A B A B
SHIFT
0.445 1
2
0.444 TARGET
0.443
Y DIMENSION (IN)
0.442
0.441
0.440
0.439
4/16/01 4/17/01 4/18/01 4/19/01
DATE
TAKEAWAY: OUTPUT GEAR SUB - ASSY MACHINE IN” CONTROL
Y SUB-ASSEMBLY DIMENSION
0.442 +/- 0.008 IN
22

23. Appendix 9.1
One Sample T-test
MANUFACTURING
PROCESS
MEAN
TAKEAWAY: MANUFACTURING PROCESS MEAN EQUAL TO TARGET MEAN
23

24. Appendix 10.0
Capability Analysis of Rotational Torque
Process Capability Analysis for ROTATIONAL TORQUE (IN OZ)
LSL
Process Data
USL *
Within
Target *
LSL 250.000 Overall
Mean 284.438
Sample N 16
StDev (Within) 22.0444
StDev (Overall) 20.7086
Potential (Within) Capability
Cp *
CPU *
CPL 0.52
Cp 0.52
Cpm *
220 240 260 280 300 320 340
Overall Capability Observed Performance Exp. quot;Withinquot; Performance Exp. quot;Overallquot; Performance
Pp * PPM < LSL 125000.00 PPM < LSL 59121.85 PPM < LSL 48160.33
PPU * PPM > USL * PPM > USL * PPM > USL *
PPL 0.55 PPM Total 125000.00 PPM Total 59121.85 PPM Total 48160.33
CPk 0.55
TAKEAWAY: DRIVE GEAR INTERFACE WITH PINION NOT A FACTOR
(ACTUAL DESIGN TORQUE OF 5.32 IN OZ <<< 250 IN OZ)
24

25. Appendix 11.0
Drive System Design Change
• Gear mesh contact ratio changed from 1.3 to 1.6
• Drive gear / output gear diametral pitch changed from 64 to 57
• Drive gear thickness changed from 0.032 in to 0.036 in
• Contact area between metal pinion and plastic gear inside
diameter lengthened by 0.050 in.
- DESIGN CHANGES IMPLEMENTED DURING PROJECT PHASE
- ANALYSIS VARIFIED THAT DESIGN CHANGES ELIMINATED
STRIPPED GEAR FIELD PROBLEM
25

26. Appendix 12.0
Capability Analysis
PROCESS CAPABILIITY ANALYSIS FOR
PINION PULLOUT FORCE FOR CELMEX
AFTER DRIVE SYSTEM DESIGN CHANGE
LSL
60 70 80 90 100 110 120 130 140
Mean: 110.4
Std. Dev: 10.7
Cpk: 1.57
PPM: 213
Sigma Level: 4.7
26

27. Appendix 12.1
Capability Analysis
P R O C E S S C A P A B IL IT Y A N A L Y S IS F O R
P IN IO N P U L L O U T F O R C E F O R S P A R T A
A F T E R D R IV E S Y S T E M D E S IG N C H A N G E
C a lc ula tio ns B a s e d o n W e ibull D is tr ibutio n M o de l
LSL
60 70 80 90 100 110 120
Mean: 105.3
Std. Dev.: 4.83
Cpk: 1.59
PPM: 0.90
Sigma Level: 4.8
27

28. Appendix 13.0
Two Sample T-test
CELMEX MANUFACTURING
SINCE P< 0.05, THE PINION PULLOUT FORCE MEDIANS ARE
SIGNIFICANTLY DIFFERENT BEFORE AND AFTER DRIVE
GEAR DESIGN CHANGE
28

29. Appendix 14.1
Two Sample T-test
SPARTA MANUFACTURING
SINCE P< 0.05, THE PINION PULLOUT FORCE MEDIANS ARE
SIGNIFICANTLY DIFFERENT BEFORE AND AFTER DRIVE
GEAR DESIGN CHANGE
29

30. Appendix 15.0
Design of Experiments Results
SINCE ALL P VALUES
ARE > 0.05, NON ARE
SIGNIFICANT TO MY
OUTPUT VARIATION
94.4% OF THE VARIATION IS NOT EXPLAINED BY THE
REGRESSION EQUATION USING THESE FACTORS
CONFIRMING THAT THESE DO NOT HAVE A MAJOR
IMPACT ON MY PROJECT
30

31. Appendix 16.0
Primary Metrix
STRIPPED GEAR BASELINE Target
Actual
1,600
1,400
1,200
1,000
800
600 Projected
Field
400 Drive system design changes Failure
implemented into production returns
200
0 0 0 0
31

32. Appendix 17.0
Secondary Metrix
INTERNAL MANUFACTURING DEFECTS TARGET
ACTUAL
350
300
250 250 250
200 200 200 200 200
150
100
50
0
32

33. Appendix 18.0
Drive System Components
PINION
SHAFT
OUTPUT GEAR DRIVE GEAR
33

34. Appendix 19.0
Dryer Timer X-Section
TIMER HOUSING SHAFT
PINION DRIVE GEAR
OUTPUT GEAR
34

35. Appendix 20.0
Output Gear Assembly Machine
OUTPUT GEAR PINION
SUB - ASSEMBLY INSERT
LOCATION
35

36. Appendix 21.0
Pinion Location and Alignment
PINION FIXTURING
36

37. Appendix 22.0
Staking Punch, Output Gear Assembly Machine
37