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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

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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

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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.

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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.

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• 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.

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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)

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• 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

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♦ 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.

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• 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

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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

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Appendix 2.0 Process Map (Overall)

START

STOCKROOMOUTPUT GEAR

STOCKROOMPINION

SECURE PINIONAND OUTPUT

GEAR INFIXTURE

INSPECTION

SHIP TOCUSTOMER/DOMESTICMARKET

ASSEMBLEOUTPUT GEAR

AND PINIONSUB-ASSEMBLY

(S) OPERATOR STANDARDS

(S) OPERATOR STANDARDS

(S) OPERATOR STANDARDS(C) PRESS FORCE(C) PRESS SPEED(C) ALIGNMENT FIXTURING(C) PINION / OUTPUT GEAR INTERFACE DIMENSIONS

(X) INPUT

(Y) OUTPUTPINION PULLOUT FORCE

SCRAP

GOOD

NVA

NVA

NVA

NVA

BAD

FAILED DRYERTIMERS RETURNEDTO SUPPLIER FOR

ROOT CAUSEANALYSIS

(Y) OUTPUTFIELD RETURNS PINION POP OFFS

STOP

NVA

output gear inside diameter (C) 0.393 - 0.0015 inoutput gear inside diameter depth (C) 0.202 +/- 0.005 inoutput gear assy working height (C) 0.442 +/- 0.008 in

pinion base diameter (C) 0.311 +/- 0.002 inpinion height (C) 0.371 +/- 0.003 in

pinion diametral pitch (C) 57drive gear thickness (C) 0.036 in

drive gear diametral pitch (C) 57housing gear centers distance (C) 0.468 +/- 0.002 in

test procedures (SOP) N/A

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Appendix 3.0 Pareto of Field Failures

STRIPPED PINION /GEAR

NO APPARENT DEFECT

IMPROPER ASSY

DAMAGED / BROKEN

OPEN COIL

Others

47 39 10 8 3 342.7 35.5 9.1 7.3 2.7 2.7

42.7 78.2 87.3 94.5 97.3 100.0

0

50

100

0

20

40

60

80

100

DefectCount

PercentCum %

Perc

ent

Cou

nt

DRYER TIMER FIELD FAILURES 2000

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Appendix (4.0) Cause and Effect Diagram

DISLODGED PINIONS

documented

up to date

documented

scheduled

knowledgeable

trained

documented

understood

per customer specs

dimensonally correct

robust

set-up

calibration

MACHINES

PARTS

CUSTOMER SPECIFICATIONS

PERSONNEL

MAINTENANCE

WORK INSTRUCTIONS

cycle time

handlingoperator

designenvironment

accessible

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Appendix (5.0) XY Matrix

CHARACTERISTIC SELECTION MATRIX RESULTS

0%2%4%6%8%

10%12%14%

outsi

de ge

ar be

aring

inside

diam

eter h

eight

outpu

t gea

r ass

ebly

beari

ng ou

tside

diam

eter

outpu

t gea

r bea

ring

outsi

de di

amete

r

pinion

base

diam

eter

pinion

heigh

t

INPUT CHARACTERISTICS

CH

AR

AC

TER

ISTI

CS

IMPO

RTA

NC

E %

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

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Appendix (5.1) FMEA

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Appendix 6.0 (Gage R&R)

GOOD GAGE

GOOD GAGE

GOOD GAGE

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Appendix 7.0 Initial Short-Term Capability Analysis

Celmex

30 40 50 60 70 80 90

L S LL S L

P R O C E S S C A P A B IL ITY A N A L Y S IS F O RP IN IO N P U L L O U T F O R C E F O R C E L M E XB E F O R E D R IV E S Y S TE M D E S IG N C H A N G EC a lc ula tio ns B a s e d o n W e ibull D is tr ibutio n M o de l

Mean: 73.8 Std. Dev.: 9.5 Cpk: 0.53 PPM: 55,000 Sigma Level: 1.6

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Appendix 7.1 Initial Short-Term Capability Analysis

Sparta

40 50 6 0 70 80 90 100

L S LL S L

P R O C E S S C A P A B IL ITY A N A L Y S IS F O RP IN IO N P U L L O U T F O R C E F O R S P A R TAB E F O R E D R IV E S Y S TE M D E S IG N C H A N G E

C a lc u la tio ns B a s e d o n W e ibu ll D is tr ibu tio n M o de l

Mean: 82.4 Std. Dev.: 9.2 Cpk: 0.80 PPM: 8155 Sigma Level: 2.4

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Appendix 8.0 Multi-vari study

4/19/014/18/014/17/014/16/01

SP1SP1

SP1SP1

110

105

100

DATE

PIN

ION

PU

LLO

UT

FOR

CE

(LBS

)

A

B

Multi-Vari Chart for PINION PULLOUT FORCE by MACHINE POSITION - DATE

MOLD TOOL NO

MACHINE POSITION

TAKEAWAY: OUTPUT GEAR SUB - ASSY MACHINE “IN” PROCESS

F

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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

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Appendix 9.0

Multi-Vari Study

4/16/01 4/17/01 4/18/01 4/19/01

A B A B A B A B

0.439

0.440

0.441

0.442

0.443

0.444

0.445

DATE

Y D

IMEN

SIO

N (I

N)

1

2

Multi-Vari Chart for Y DIMENSION by SHIFT - DATE

MACHINE POSITIONSHIFT

TARGET

TAKEAWAY: OUTPUT GEAR SUB - ASSY MACHINE IN” CONTROL

Y SUB-ASSEMBLY DIMENSION

0.442 +/- 0.008 IN

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Appendix 9.1 One Sample T-test

TAKEAWAY: MANUFACTURING PROCESS MEAN EQUAL TO TARGET MEAN

MANUFACTURINGPROCESS MEAN

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Appendix 10.0 Capability Analysis of Rotational Torque

220 240 260 280 300 320 340

LSLLSL

Process Capability Analysis for ROTATIONAL TORQUE (IN OZ)

USLTargetLSLMeanSample NStDev (Within)StDev (Overall)

CpCPUCPLCp

Cpm

PpPPUPPLCPk

PPM < LSLPPM > USLPPM Total

PPM < LSLPPM > USLPPM Total

PPM < LSLPPM > USLPPM Total

* *

250.000284.438

1622.044420.7086

* *

0.520.52

*

* *

0.550.55

125000.00 *

125000.00

59121.85 *

59121.85

48160.33 *

48160.33

Process Data

Potential (Within) Capability

Overall Capability Observed Performance Exp. "Within" Performance Exp. "Overall" Performance

Within

Overall

TAKEAWAY: DRIVE GEAR INTERFACE WITH PINION NOT A FACTOR (ACTUAL DESIGN TORQUE OF 5.32 IN OZ <<< 250 IN OZ)

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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

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Appendix 12.0

Capability Analysis

14013012011010090807060

LSLLSLAFTER DRIVE SYSTEM DESIGN CHANGEPINION PULLOUT FORCE FOR CELMEXPROCESS CAPABILIITY ANALYSIS FOR

Mean: 110.4 Std. Dev: 10.7 Cpk: 1.57 PPM: 213 Sigma Level: 4.7

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Appendix 12.1

Capability Analysis

60 70 80 90 100 110 120

L S LL S L

P R O C E S S C A P A B IL ITY A N A L Y S IS F O RP IN IO N P U L L O U T F O R C E F O R S P A R TAA F TE R D R IV E S Y S TE 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

Mean: 105.3 Std. Dev.: 4.83 Cpk: 1.59 PPM: 0.90 Sigma Level: 4.8

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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

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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

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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

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Appendix 16.0 Primary Metrix

STRIPPED GEAR BASELINE

0 0 00200400600800

1,0001,2001,4001,600

TargetActual

Drive system design changes implemented into production

Projected Field Failure returns

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Appendix 17.0 Secondary Metrix

INTERNAL MANUFACTURING DEFECTS

200

250 250

200 200 200

0

50

100

150

200

250

300

350

TARGETACTUAL

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Appendix 18.0

Drive System Components

PINION

OUTPUT GEAR

SHAFT

DRIVE GEAR

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Appendix 19.0 Dryer Timer X-Section

TIMER HOUSING

PINION

OUTPUT GEAR

SHAFT

DRIVE GEAR

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Appendix 20.0 Output Gear Assembly Machine

OUTPUT GEAR SUB - ASSEMBLY

PINION INSERT LOCATION

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Appendix 21.0

Pinion Location and Alignment

PINION FIXTURING

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Appendix 22.0 Staking Punch, Output Gear Assembly Machine