rbc organizational overview

Ross Business Consulting

An Overview of Services Provided

Services ProvidedProduct & process problem solvingProduct & process performance improvementTraining & consulting:

Process Problem SolvingStatistical Process ControlDesign of ExperimentsGeometric Dimensioning & TolerancingFailure Mode & Effects AnalysisOthers

Resumé: Phillip J. RossBME 1970: General Motors InstituteASQ CQE retired 1993-2012ASQ Fellow 2008Product Engineer Allison Div. GM 1970-1988Manufacturing Engineer Saturn Corp 1988-1996Holder of 3 product design patentsAuthor: Taguchi Techniques for Quality Engineering

1st Ed. 19882nd Ed. 1996

Independent Consultant 1996-PresentOver 5000 hours of classroom training provided

Skills & AbilitiesAble to work very well with people of varying

positions, educations, and experiencePossess very good oral and written

communication skillsPossess very good comprehension,

investigative, and diagnostic skillsVery functional in many different software

applications (Word, Excel, Visio, Powerpoint, etc.)

Self-motivated and dedicated to project results

Training ApproachContent intended for the technical product or

process person (engineer, technician, QE, SQE, etc.)

Practical applications with minimal statistics involved

Examples worked without assistance of software to aid in understanding of concepts

Trainer’s ME background provides good relationship with attendee’s viewpoints & questions

Trainer’s product & process background provides ability to understand attendee’s products, processes, & issues

Problem Solving ApproachSeveral techniques are utilized appropriate to

the problem & situation:Shoji Shiba: WV problem solving modelKepner-Tregoe: problem solving modelShainin: multi-vary study, non-parametric testsTaguchi: design of experiments, parameter

designTraditional: SPC, ANOVA, other statistical

methodsFact and data based analysis & approachPattern recognition in strategically collected

data

Customer List Accuride ACD Tridon Allied Automotive Autoliv Bohn Aluminum Company Bosch Braking Systems Carrier Corporation Carlisle Brake & Friction Clemson University Colorado State University Cordis Corporation Del-met ECC International EDS Electrolux Federal Mogul Flexible Products, Inc. Gamesa General Motors Georgetown Steel Company Grede Foundries Henkel Technologies

Hitchiner Casting Company Honda Hughes-Parker Hyundai-Kia Instafoam Johns Manville Marconi Medical Systems,

Inc. Mascotech Medtronic Xomed, Inc Mentor H/S, Inc. Midwest Research Institute Modine Manufacturing North American Lighting North Carolina State

University Northrop Grumman Oxford Instruments Inc. Pace Industries Polymerics, Inc. Prestolite Wire Purolator QED Environmental Systems

Rappahannock Wire Company

Raymark Corporation Reynolds Aluminum Saturn Corporation Simmons Singapore Quality Institute Steel Founders Society of

America Takata Restraints Tuscarora Plastics Ucar Carbon University of Alabama University of Delaware University of Kentucky University of Miami University of North

Alabama Vectron Walker Die Casting Webasto Roofing Wix Filters Yazaki-North America

Typical Successful ProjectsLost Foam Casting – DOE/SPCPaint Process – SPC/PPSComposite Molded Rocker Cover - PPSStamped Steel Torque Converter – Engrg.Grey Iron Casting – DOE Torque Converter Stator Clutch – DOE Injection Molded Door Handle – DOE Aluminum Rolling – DOEClutch Testing – SMQE/DOETransmission Reliability – Failure DiagnosisMany others

Lost Foam CastingR&D Foundry in Detroit struggled from March 1987 to

June 1988 with very limited success in making ductile iron crankshafts to print (essentially 0% yield)

Lost foam casting is an extremely complex processInitial capability studies after joining R&D foundry

showed process completely incapable with SOP scheduled for June 1990

Implemented DOEs on major portions of processBead expansion-pattern molding-pattern agingCluster coating-cluster dryingCluster sand compactionIron pouring

Lost Foam Casting Several critical changes to overall process were deployed

as a result of the capability and DOE information:Foam bead gas content levels were adjusted for longer

useful life with natural air agingAccelerated pattern aging ovens were eliminatedMold tooling shrink ratios adjusted for two above changesCluster coating and drying parameters were establishedClusters were oriented horizontally rather than vertically

with new concept for supporting clusters during sand compaction

Sand compaction parameters changed substantially to achieve dimensionally correct parts

Lost Foam Casting By December 1988 yield from same equipment,

however substantially revised and reprocessed, was up to 75%

By February 1989 yield was up to 90%Factory equipment and process was designed &

fabricated based on knowledge from R&D foundryEquipment in was qualified in factory during late

1989 and early 1990 for SOP July of 1990Crankshaft production was able to successfully

ramp-up to match vehicle production without any powertrain or vehicle assembly interruptions

Paint ProcessAfter one summer shutdown, a substantial number of

craters (fish-eyes 1.0-1.5 mm dia. Through the clear coat down to base coat) were occurring in both main paint booths at a vehicle assembly plant

There were a considerable number of accusations and denials among the primer supplier, base & clear coat supplier, and the plant as to the cause of the paint defects

The craters were causing a substantial amount of scrap and rework of exterior panels to meet production requirements

The cause of the craters was thought to be due to contamination of some type, although a silicon based contaminant was considered most likely

Paint ProcessA huge task force was formed to address the issue

Primer supplier representativesBase & clear coat supplier representativesSaturn paint process representativesProblem solving internal consultant (my role)

Many facts and opinions were put forth by the group as to what was behind the incident but with much acrimony

In order to bring clarity and effectiveness to the group, four tools were deployed:Kepner-Tregoe “Is-Is Not” matrix for information management &

root cause diagnosisPictographs of crater occurrence locationsSPC attribute charts of crater occurrencesTimeline chart

Paint ProcessThe K-T “Is-Is Not” matrix organizes only factual

information concerning the problem into a 16 cell table :What: Is – Is Not – Distinctions – ChangesWhere: Is – Is Not – Distinctions – ChangesWhen: Is – Is Not – Distinctions – ChangesExtent: Is – Is Not – Distinctions – Changes

The K-T matrix is:Modeled after the thought processes of several successful

problem solving individuals interviewed by Kepner & Tregoe

Applicable to situations where a problem suddenly occurs

Paint ProcessThe K-T matrix allowed the group to agree on several

conclusions because of the facts displayed in the chart:The plant was exonerated as the cause due to other

paint facilities having the same issue starting at the same time (over summer shutdown)

The primer supplier was exonerated as the cause due to other primer suppliers being used at other paint facilities which also had the problem

The base & clear coat supplier was suspected to be involved in some manner due to other paint facilities having the same issue at the same time with the same paint supplier

Paint ProcessThe pictographs of crater occurrences were organized

by:Type of vehicle: sedan or coupe (roughly same paint

area)Base coat color: 3 high demand colors were originally

involved, but other colors later joined the problem groupPictographs indicated that craters were occurring

randomly over the vehicle surface regardless of type or color of vehicle

Pictographs allowed the group to agree that some contaminant must be mixed in the base or clear coat because of the random location of craters

Paint ProcessSPC attribute c charts were created according

to base coat color (vehicle style did not matter)Conclusions from the c charts were:

Crater rates were in control (stable rate) by colorCrater rates were different by colorCrater rates were different by tote of same color

When a “bad” tote (275 gallon container) was replaced by a new tote of same color the crater rate would change (could be higher or lower or zero)

Base coat was thought to be primarily involved in the incident

Paint ProcessThe base coat supplier’s “triangular “ process

was:Make a batch of paint and load several cleaned

totes from that batchShip loaded totes to a paint facility which used the

totes on a FIFO basisTotes were emptied as a result of painting vehicles

and were shipped to the tote cleaning supplierCleaned totes were returned to the base coat

supplier for reuse (may or may not be the same color)

Paint ProcessTo determine the cause of craters a timeline chart was

established that generated a window of time where something had to have changed (latest good batch loading date to earliest bad batch loading date)

Based on the chart below, the only change that occurred in the window of time between good and bad batches of several colors was the tote cleaning supplier

239952389223451 24110 24222 24313

Batch Nos. with no cratersBatch Nos. with craters

Color #1

2342 02331823292 23505 23582 23631Color #2

233402322123100 23402 23619 23840Color #3

Paint ProcessIt was found that the new tote cleaning supplier was

using a silicon based lubricant in the motors which spun an agitator for the cleaning solvents in the totes

The lubricant (silicon) was leaking from some of the motors which:Was not rinsed away by the solventsVaried in amount of lubricant in individual totes

Previous supplier was aware not to use silicon based lubricants in the cleaning process; new supplier was not

Elimination of the silicon based lubricant eliminated the crater issue

Composite Molded Rocker CoverAt one model year changeover, Product Engrg. had

decided to change to a composite molded rocker cover as a replacement for the more expensive die cast aluminum version

Other vehicle lines had already converted to this material with success

Supplier of component:Did not deliver PPAP samples on timeProcrastinated with promises of good parts to comeFinally advised Saturn purchasing that they were unable to

make good parts 1 week prior to SOP for new model year

Composite Molded Rocker Cover3 person team went to supplier to:

Understand issues with rocker cover production process

Make 2 weeks production of parts so that original aluminum die cast cover could be returned to production within that two week time span

Upon arrival, my role, was to get the process to function as quickly as possible

The main issue holding back production was that the parts could not pass a 100% leak test just after molding

Composite Molded Rocker CoverThe process was:

Manually load a slab of composite material into the dieClose the die (no in-gates or out-gates) under

temperature and pressure for a given amount of time (composite material was a thermoset type)

Open the die and eject the rocker coverTrim the rocker cover of any flash at die parting lineLeak test the cover by:

Clamp down at the designated bolt location using the production o-ring gasket

Plug the spark plug holes and other openings Introduce water under pressure within the cover Monitor for minor leaks (automatic and visual)

Composite Molded Rocker CoverSince this was a closed die molding process,

ideally, the composite material (CM) should fill the die to exactly 100%No “short shots” where there were unfilled

portionsNo flash at the die parting lineMaterial “packed” tightly enough to eliminate

porosityTo accomplish this as an end result a specific

amount of CM must be placed in the die for each cycle

Composite Molded Rocker CoverOne thing that the supplier had not done was

to weigh each slab of composite prior to molding (the supplier had depended on their supplier to cut each slab to a certain length (it was extruded to a certain width & thickness)

By gradually increasing the weighed amount of CM a successful process weight was determined

Composite Molded Rocker CoverThe main issue that limited production was

“short shots” where the die was not completely filled

With CM there was a conflict with one key process parameter, die temperature:Higher temperature made the material flow

easier to fill the dieHigher temperature made the material cure

more quickly which made it harder to fill the die

Another aspect was material distribution within the die which the supplier had not considered at all

Composite Molded Rocker CoverPreviously successful rocker covers for GM were of

the design for a V8 engine; the covers were a “single bubble” configuration

A slab of material could be laid in the bottom of the die and easily flow up the four walls as the die closed

100% fill was relatively easily achieved

The new dual overhead cam rocker cover had 3 bubbles (refer to earlier picture) which significantly changed material distribution within the part

Composite Molded Rocker CoverBy adding more material to one end of the Saturn

die and pre-forming the slab to wrap around the timing chain bubble, complete fill was obtained

Again material weight was gradually increased to achieve complete fill with minimal flash which guaranteed the CM was fully compressed as it cured

At this point a wooden form was fabricated to allow the operator , after training, to repeatedly produce fully formed and compressed parts

These parts would fit the dowel locators on the leak test pad and would pass the leak test

Composite Molded Rocker CoverThese parts were also dimensionally checked

for other features with success (fortunately the die was made correctly for dimensional specifications)

Two weeks worth of parts were generated within a few production days at supplier and the project was closed down

The new model year started without delay and the aluminum rocker cover came on stream to minimize the risk of releasing the CM version without any validation testing

Stamped Steel Torque ConverterIn 1977 a technology transfer agreement was reached

between two transmission companies to:Design a stamped steel torque converter (TC) to replace

a die cast aluminum version (company A)Develop a more effective way to design the blades & slots

for stamped steel TC pumps and turbines (Company B)As part of that tech transfer, I was assigned to be on

site at Company B to:Develop software to shorten the blade design timeLead a group of drafting people to design a TC for

Company B

The turbine blades, shown above, are highly complex three-dimensional shapes (pump blades are not as complex)

Pumps and turbines typically have 35 to 50 blades eachCartesian coordinates (3D data) were generated for the inner

and outer curves by computer modelingPump blades have tabs & mating slots to facilitate assembly:

2 inner shell through slots (tall tab to be bent over at assy.)3 outer shell indented slots (short tabs)

Turbine blades have tabs & mating slots also:2 inner shell through slots (tall tabs)3 outer shell through slots (tall tabs)

Stamped Steel Torque Converter

Stamped Steel Torque ConverterDrawings were manually created at the time

in this manner:Carefully lay out the math data for each bladeConstruct true views of the designated

positions for the tabs (5 true views required per blade)

Construct the tab configuration in the true view

Transfer the tab design back to the original coordinate system

A blade drawing took approximately 6 man-weeks to complete; 12 man-weeks for one TC

Stamped Steel Torque ConverterA 3000 line PL1 program was developed to design TC pump &

turbine blades, as well as, the adjacent slots in the inner and outer shells

The software:Utilized the same blade 3D data as a starting point Generated true view data for each tabGenerated tab and slot dataGenerated tab and slot data in the original coordinate system

The software reduced drafting time from 12 man-weeks to 1 man-week for both pump & turbine blades

The software is still in use today in a different format, was a precursor to now available CAD systems, and has saved a considerable amount of design time and money since creation

34

Grey Iron CastingA problem suddenly occurred in a center support casting

that had been in production for many years at the same foundry without this issue

A machinist at the manufacturing/assembly plant actually discovered the issue while processing the casting

Approximately 10-15% of castings were found to be cracked at the end of the casting process

An internal casting engineer was assigned to determine how to eliminate the cause of cracks

Magnaflux inspection was temporarily deployed to detect cracks and sort out the good products

35

Grey Iron CastingThe cracking problem had been addressed by

the foundry and customer experts to no availBased on the experience of the casting

engineer, pouring temperature and cooling time were thought to be causing the cracks

Pouring temperature was reduced to the lowest level possible and cooling time in the mold was increased significantly over past production times

The cracking rate continued at the current levels

No other solution was considered at the time

Grey Iron CastingA problem solving team was formed with members:

Foundry representativeManufacturer

Product engineer Purchasing representative Casting engineer Problem solving internal consultant (my role)

At the initial meeting discussion was about what had been done at the foundry and what to do next

A designed experiment was suggested by the consultant

Grey Iron CastingA designed experiment was planned which addressed

more factors in various combinations rather than the one shot previously attempted

The simplest DOE uses two levels (conditions) for the factors being evaluated as a contrast

Because the pouring temperature had been reduced to the lowest possible level, a higher temp. would be tested

Because mold time had been increased substantially, a lower mold time would be tested

Two other possible factors were discussed and includedThe list of factors and levels follows

38

Grey Iron CastingFactors Level 1 Level 2

Pouring Temperature Production Higher

Mold Time Production Lower

Cooling Rate(cooling tunnel)

Production (fan on)

Fan Off

Shot Blast(cleaning method)

Production(1 cycle)

3 Cycles

Grey Iron CastingAn 8 trial orthogonal array was selected to

evaluate the four 2-level factorsFactors were strategically assigned to certain

columns to achieve a medium resolution, fractional factorial experiment

Eight unique groups of 24 castings were made at the foundry according to the combinations dictated by the array

The number of cracked castings per trial was determined by magnafluxing each part; the results follow

Gray Iron Casting DOE (observation & column effects method)

Factors and Column Numbers

A B C D # Temp. Time Temp.

x Time

Cool. Temp.x Cool

Temp.x Shot

Shot Blast

Cracked

Trial # 1 2 3 4 5 6 7 (LB) 1 1 1 1 1 1 1 1 4 2 1 1 1 2 2 2 2 1 3 1 2 2 1 1 2 2 1 4 1 2 2 2 2 1 1 2 5 2 1 2 1 2 1 2 4 6 2 1 2 2 1 2 1 4 7 2 2 1 1 2 2 1 0 8 2 2 1 2 1 1 2 0

Sum L1

8 13 5 9 9 10 10 16

Sum L2

8 3 11 7 7 6 6 Total

Differ. 0 10 6 2 2 4 4

Grey Iron CastingThe OA with accompanying data allowed

these conclusions:Trials 7 & 8 had no defective castings out of 48

total, so higher pouring temperature and a shorter mold time actually prevented cracked castings in this case

Column effects indicated that: Pouring temperature by itself had no effect overall Mold time was the strongest effect overall There was a temperature-time interaction in this

processThe interaction plot follows

42

Grey Iron Casting

Lower Time

Lower Time

Prod. Time

Prod. Time

0

1

2

3

4

5

Prod. Temp. Higher Temp.

# of

Cra

ck C

astin

gs p

er T

rial

0%6.3%

10.4%16.7%

Grey Iron CastingThe only combination that was successful at completely

eliminating cracks was the high temp. & low timeEvidently someone at the foundry knew how to pour good

castings in the past (it had been done for several years)However, that knowledge was lost or ignored when an

incident occurred at the foundry and pouring ladle temperature had dropped or mold time had increased due to some delay in the process and bad parts were shipped

When conjecture as to the cause of the problem took over, the process never recovered until the DOE was completed

The DOE was completed in a very short time (within a week) and the validity of the results proven as production resumed without any further cracked castings

Torque Converter Stator ClutchA certain transmission was successfully in

production for several years and represented a significant cash flow for the manufacturer

An upgraded version was requested by the customer

Development and validation tests for the upgrade were successfully completed

The customer gave approval for SOPFinal functionality test

All transmissions were run through a final testSome transmissions were disassembled for inspection

after final test to detect any distress to components

Torque Converter Stator ClutchOctober 1st of SOPFirst transmission disassembled post test

which had a converter one-way, stator clutch failure

The second and third units also had the same failure

Production was suspended by customer until cause rectified

Torque Converter Stator Clutch

Inner Race(Grounded)

Roller

Cam (Stator; one-way rotation)

SpringThe stator may

only rotate in one direction (orange arrow)

The opposite direction is prevented when the rollers lock between the ramp & inner race

Torque Converter Stator ClutchRollers in one-way clutch were severely

distressedScuffed, flattened, heat discoloration, etc.Always had to be replaced for further tests

Inner race sometimes lightly distressed and sometimes replaced for further tests

Outer cam never distressed and never had to be replaced for further tests

Product Engineering had made many changes in component design and processing to accommodate the increased horsepower

PE investigated several changes 1 factor at a time during Oct. but no answer found and no shipments were made

Only thing learned: it was -an infant failure modeSome transmissions would pass first test and then pass

subsequent testsWhen a rebuilt transmission would pass a test it would pass

all subsequent testsCustomer approved multiple testing to resume shipments

As an internal problem solving consultant, I recommended a DOE approach but was rejected due to the fact that “we don’t have time”


November and December passed with many 1FAT tests, still no answer found

Continued with multiple tests to ship some transmissions

Recommended DOE approach on more than one occasion and finally accepted at the end of Dec.


At least 20 engineers called into meeting including management and a problem solving consultant (my role)

2 DOEs were eventually used:A 16 trial orthogonal array: to test the high

priority factorsAn 8 trial orthogonal array: test remaining low

priority factorsFinal 8 trial array disclosed that the roller

finish was single contributing factorIt only took 6 weeks to determine the cause


Difference between validation units & production versionValidation units had centerless ground roller finishProduction units had tumbled roller finish (too smooth)

Learning points:Focus on the physics of failure (in this case problem has

something to do with rollers and inner race relationship) More accurate , shorter factor list Test all the factors on your list in one DOE to shorten total

screening test time (could have been done in 1 8 trial DOE within 2 weeks)

When time is your enemy, use a DOE


Injection Molded Door HandleThe Quality Manager requested assistance

concerning defects in injection molded inner door handlesFlow lines or “creases” directly opposite the ingateHad to be sanded prior to paintingOnly first two cavities in die had defect; last two did notVery consistent shot after shot

Informed the QM that a DOE was applicable in this case and should provide guidance within 2 days

Injection Molded Door HandleMet with QM, process engineer, and operating tech.They were convinced that the problem was created

in the last four stages of the die filling process:Stage 1 & 2 filled the runnersStages 3-6 filled the remainder of the part which had

the defectAn 8 trial DOE was planned for the factors used in

the last four stages (Wed. afternoon)The DOE was executed on Thurs., but no answer

was forth coming; all trials still had the defect in multiple shots

Injection Molded Door HandleA 4 trial DOE was then planned & executed on the

factors for the first two stages (Fri. morning)2 of the trials had a greatly reduced defectConclusions

Problem was not in stages 3-6Problem was in stages 1 or 2Faster injection speed was betterHigher temps were better

Subsequently injection speeds and temperatures were optimized for stages 1 & 2 to eliminate the defect and the need for sanding and painting

Aluminum RollingAfter a class for several of the metallurgists at one

metal rolling facility, a DOE was planned concerning an “earing” problem for their customers

Rolls of very thin (≈ 0.010 inches, 0.25 mm) aluminum are sent to their customers to deep draw beverage containers

The deep drawn cylinders had ears on the top edge which had to be trimmed for successful sealing of caps after fluid was placed in container

Aluminum RollingAluminum billets (very large) are run through a rolling

mill in alternate directions to reduce thicknessEventually the thickness is reduced to approximately

0.010 inches on a roll that is several thousand feet longRolling parameters were thought to play a part in how

much earing would be produced during a deep drawAn 8 trial DOE was planned and executed over the next

several monthsEach of the 8 rolls had to be produced in a specific mannterEach of the 8 rolls had to be used at the customer where

standard samples were taken to quantify the amount of earing

Aluminum RollingConclusion:

Gradual reduction in thickness significantly reduced the amount of earing as compared to large amounts of reduction in thickness

The rolling mill had the option of reducing thickness in 5 small steps in each pass or 2 large steps in each pass

The mill had previously used on 2 steps because it was easier to set up and run

Now they knew the value of using the complete capability of the mill to make a better product

Clutch Testing

Assigned to lead the “Components Development” group in 1980 (one component was clutch plates)

Commonly asked by friction material suppliers to evaluate new materialsCheaperNon-asbestosAlternative

It was determined that the company needed to deploy a more effective clutch friction material testing and qualification method

Clutch TestingThe company had based approvals of friction

material on an industry standard testFriction material test parameters:

Given amount of energy per engagement (given inertia and rpm brought to a stop)

Given engagement & cycle times (given power per cycle & average power)

Given lubrication type, flow rate, & temperature

Must survive 3000 cycles (∼)

Clutch TestingCurrent production material

Performed well in customer’s application & environment

Successfully passed the 3000∼ testSupplier’s new material:

Also passed the 3000∼ test Was cheaper than current production materialSought approval to release to production

The concern was that based on this test one could not discern the difference in capability of the two materials

Clutch TestingTest changes:

Clutch plates were tested to failureEnvironment was made more severe to

reduce test timeFive items made up the test sampleCurrent test took approximately two

days for 1 item to pass 3000∼

Clutch Testing

0 500 1000 1500 2000 2500 3000 35000

102030405060

Current Clutch Plate Test

Cycles

Ener

gy

Operating Envelope

Clutch TestingA new approach promoted by Dorian Shainin

as one form of accelerated testingUsed current envelope as basis for first

portion of testConverted a success test into a failure testIncreased energy & cycles in 10% steps until

failure was reached

Clutch Testing

0 1000 2000 3000 4000 5000 60000

20406080

100

Accelerated Clutch Plate Test

Cycles

Ener

gy

Clutch Testing

2000 2500 3000 3500 4000 4500 5000 5500 6000405060708090

100

Accelerated Clutch Plate Test

Cycles

Ener

gy

xxxxx

X = current production material failures O = new material failures

o ooo o 7th

4th & 5th

Clutch TestingConclusions:

New material not as strong as current production materialCurrent material = 7th step failuresNew material = 4th & 5th step failures

New material has more variation in strengthCurrent material = only 7th step failuresNew material = mix of 4th & 5th step failures

Clutch TestingSupplier was not too happy initially (previous

production releases had been based on simply passing the test)

Engineering management liked the approach:Baseline test was part of new protocolDifferences in performance now apparentBetter able to make release/no release

decision with confidence (non-parametric test: 99% confident new material not as good as current material)

Transmission ReliabilityNot too many years after start of production, 3 models of

transmissions had developed a poor track record of reliability One engineer was assigned to each of the three models; my

role was the lowest capacity model in terms of application weight & HP

Concurrently, Product Engrg. had made several changes to the transmission without thoroughly investigating the failures

The transmission was used in school buses, beverage delivery trucks, and other utility vehicles and had a two year warranty in those applications

The goal was to find ways to improve reliability/durability of the transmission

Transmission ReliabilityThe project began by investigating warranty claims

against the transmission and making Pareto charts of the items with high claim frequency; mainly prior to any PE changes

There was enough failure data available to make Weibull plots of the overall transmission and the highest failure rate components

Using this information:Warranty rebuild/repair centers were visited and personnel

interviewed about frequent failure itemsactual field failure components were inspected to

determine the failure modes or causes; what actually failed first

Transmission ReliabilityBased on this information several things were

determined concerning the high frequency failures:Forward clutch partial failures always started at the end of

the clutch pack away from the hub lubrication holesUsed. but not failed, original rear thrust bearing show

considerable radial fretting on the races and pitted rollers)The uprated rear thrust bearing failed in a new way

(chipped outer lip as opposed to fretted races & rollers)Sun gear shafts were sometimes fractured longitudinally

along the forward spline root (high stress portion of shaft)Sun gear shaft forward bushings were spun even when the

sun gear shaft was not fractured (PE had just added a cross-drilled hole to prevent the bushing from spinning)

Transmission ReliabilityForward clutch hub

(top)

Rear thrust bearing & output shaft (middle)

Sun gear shaft (bottom)

Transmission ReliabilityThings of interest on field failure

components:The forward clutch hub lubrication holes were

misaligned with the wear pattern of the clutch plate spline teeth; thought to allow one end of the clutch to run “hot” when the clutch was applied

The outer lip of the uprated rear thrust bearing was sometimes chipped and its mating output shaft showed damage (a bump) on the thrust face

The short spline (forward end) was sometimes fractured along the root of the spline (the bushing was always spun in those cases)

Transmission ReliabilityBased on the problems with field failure

items these changes were made:Forward hub lubrication holes relocated and

temperature profile improvement documented in test department

Output shaft was instrumented to measure load and torque converter turbine induced thrust was verified in the test department This was why the low capacity thrust bearing failed

after about two years of use in school buses High capacity thrust bearing should perform well

Transmission ReliabilityBased on the problems with field failure items these

changes were made:An output shaft was found among production items

that had handling damage on the thrust face (two parts a banged against one another to create a bump on the thrust face)

This particular output shaft was tested in a transmission assembly and found to have created a chipped lip on the thrust bearing within a minimal number of hours on test

A chamfer was added on the forward end of the output shaft to prevent the formation of a bump should handling damage occur

Transmission ReliabilityBased on the problems with field failure items these

changes were made:The cross-drilled hole on the sun gear shaft increased

stress in that portion of the shaftDetermined that one transmission out of six “improved”

designs had failed due to fractures in the spline of the sun gear shaft and a subsequent spun bushing

With great resistance from PE, I convinced management to withdraw that change from production and find the root cause for spun bushings

The hole was removed and it was later determined that there was approximately a 10% failure rate for that item alone within the warranty period

Transmission ReliabilitySingle-handedly examined transmission field failure units and

reviewed warranty claims to identify key components to redesign to improve product reliability

Tools: Pareto charts of high frequency failure itemsWeibull plots of overall reliability & some component reliability

Key changes:Forward clutch hub lubrication path modifiedRemoval of temporary “fix” for spun bushing failuresVerification of increased capacity thrust bearing (TC induced high

thrust loads)Identification of new failure mode in thrust bearing

With these changes transmission reliability was greatly improved

rbc organizational overview

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