dchobany article ep04-2008!10!18

8/14/2019 DChobany Article EP04-2008!10!18

1/910 APR-JUN 2008 engine professional

This article will describetypical plateau honingprocesses used by largeoriginal equipment (OE)manufacturers of dieselengines. Included will be themachine methodologies aswell as the hone tooling,abrasives, gauging andcoolant considerations andtheir effect on bore size,surface finish, and cylindricity.The transfer of this OEtechnology to the engineremanufacturing shops will bediscussed with the emphasis

on selecting the proper tooldesign, abrasive selection andmetrology to assure a bestbore condition to theircustomer.

OE Diesel Block

Honing OperationMachine ToolHigh volume machining ofdiesel engine blocks istypically accomplished usingvarious milling, drilling,reaming and boringoperations as part of adedicated transfer stylemachining line. The finalcritical operation performedon these blocks would be thehoning of the cylinder bores.

This operation is done on astand alone and dedicatedmachine utilizing multiplespindles to accomplish therequired stock removal as wellas the finish bore size andsurface finish structuringrequired from the OE. Thesemachines are constructed withheavy duty bases andprecision slides toaccommodate the accuracyrequired to precision hone

thousands of bores daily formultiple years of service life.

The engine blocks are fixturedand have the ability to berotated and transferred withinthe machine to allow for eachbore to be rough and plateauhoned in the various stationsand passed on to a post gagestation to complete thecylinder bore honing process.

The machine toolreferenced throughout thisarticle will be a typicalMicromatic machine designedto hone the cylinder bores ofan eight cylinder diesel engine.Bore sizes in this example willbe approximately 4.00 inches(101.6mm) in diameter and5.000 inches (127mm) deep.

Speeds and FeedsIntegral to the machine tool isa sophisticated programmablelogic controller (PLC) with theability to precisely maintain,control, and adjust thevarious spindle speeds, tool

reciprocation rates, toolreversal points (length of

stroke), feed and expansionrates, as well as the in-processair gaging of the bores withinthe hone process. This isneeded to assure that properand consistent pressures areapplied to the stones duringthe hone process. This alongwith precise stroke length andreversal point accuracy is builtin to assure that the stockremoval rates and boregeometry shape is met. Dieselblock line tooling is designedto run in the rotational rangeof 140 to 200 surface feet perminute. Care is taken early onin the hone processdevelopment to determine theappropriate feeds and speedsrequired to achieve the desiredstock removal rates and cycletimes.

CrosshatchA critical feature of thecylinder bore that is directly

Perfection of diesel

engine cylinder boresA review of OEM honing considerations as they relateto the engine remanufacturing industry

BY DAVID CHOBANY PHOTOS PROVIDED BY BATES TECHNOLOGIES, INC.


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engine professional APR-JUN 2008 11

FEATURE

Fig. 1: Micromatic OEhone machine shownwith Bates toolingdesigned to hone cylinderbores of engine blocks.


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12 APR-JUN 2008 engine professional

affected by changes tofeeds/speeds is the crosshatchangle as designated by theOE. A defined crosshatchpattern is a required cylinderbore feature that the strokehone is responsible forachieving. The main purposeof this angle is to retain (hold)the appropriate amount of oilwithin a given crevice valleywhich has been generated inthe rough hone operation.Most OEs will specify theangles to intersect at or near45 to each other or at 22 to32 to the horizontal decksurface.

Machine Cycle TimesThe number of hone spindleson these machines is usuallydependant upon cycle timerequirements with many

applications requiring onespindle to hone multiple boresof a six or eight cylinderblock.

First Pass OperationSingle stroke Microsize (fixeddiameter tool with mounteddiamond abrasives) techniquedesigned to improve upon thebored geometry and toprovide a repeatable surfacefinish to the stroke honingstations.

Second and Third PassOperationStroke honing stationsconsisting of four spindles toRough hone (second pass) andfour spindles to Plateau Hone(third pass). Each spindle istooled to hone two of theeight bores in each block.

Cycle times for this stylemachine to hone and transfera V8 diesel block throughthese operations is less than50 seconds.

Hone ProcessProduction tools are designedto expand the abrasive stonesoutward to bore contact and

then to hone the wall with apreset amount of work loador pressure which isdetermined by the type ofmaterial being honed alongwith the desired end results.The machine tool abrasiveexpansion system isaccomplished through either astepper motor or hydraulic/airtorque limit feed systems.Both are proven methods andcan be used independently or

jointly depending upon whichmethod produces the bestresults within any givenprocess application. In theeight cylinder example notedabove, the honing processeswould utilize both forms ofexpansion as follows:

Rough (Base) Hone Process

Stepper feed system.

Tool enters the bore,stepper feed system expandsthe abrasives to borecontact as the spindlerotation begins.

Tool continues to expand tomeet an initial size offset,followed by a second feedvelocity programmed tomeet the final preset size forthis operation.

Fig. 2: Integral to the machine tool is a sophisticatedprogrammable logic controller (PLC) with the ability toprecisely maintain, control, and adjust the variousspindle speeds, tool reciprocation rates, tool reversalpoints (length of stroke), feed and expansion rates, aswell as the in-process air gaging of the bores within thehone process.

Fig. 3: Hone crosshatch angle definition.

Fig. 4: Single stroke Microsize (fixed diameter tool withmounted diamond abrasives) technique designed toimprove upon the bored geometry and to provide arepeatable surface finish to the stroke honing stations.

PERFECTION OF DIESEL ENGINE CYLINDER BORESBY DAVID CHOBANY

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The tool stokes to a setlower position (lowerreversal point) then reversesand moves to a set upperposition (upper reversalpoint). These set points areprecisely controlled andmonitored by the machinesuse of finite linear positionindicators.

The reversal set points aredesigned to stroke the honestones so that 25 to 33% ofthe stone length exits thebore on both ends. Theexact percentage of stoneexiting the bore is based onpre-production honeprocess studies to determinebest bore geometry that canbe achieved with respect toany stoke or wall supportlimitations that may be

inherent in the blockdesign.

An in-tool air gage systemmonitors the bore size at alltimes and signals themotion control andexpansion unit when thefinal preset bore size isdetected.

A stroke run-out cycleoccurs followed up bycollapsing the abrasives andtool withdrawal from thepart.

Plateau Hone Process

Pressure feed system.

Hone tool enters the boresimultaneously as thetorque limit feed pressureexpands the abrasives to

bore contact and spindlerotation begins.

A predetermined strokecount is initiated

Abrasives remain expandedat a predetermined loaduntil the stroke count isdone.

End of cycle command is

initiated which collapses theabrasives and retracts tool.

Tooling and AbrasivesHone tooling design alongwith abrasive selection isconsidered to be one of themost critical elements neededto assure a hone process thatis highly capable of providingpredictable and repeatablebore geometry while also

achieving critical surface

finish and structuring

requirements.

The conventional

approach to honing in thepast produced a finish honed

bore surface consisting of a

high peak to valley ratio

(referred to as Peak Honing)

which relied on the engine

piston ring package to shear

the top of the peaks during a

break in period in order to

produce a smoother sliding

and bearing surface. The

advancing technology of

honing cylinder bores has

progressed to Plateau Honing

which produces a finish honed

surface that is relatively

smooth and overlays oil

retention valleys and

crosshatch patterns which

have been produced by the

depth of cut from the previous

rough hone operation.

Hone tools used at the OE

level are designed and built to

function as high precision,

close tolerance and durable

tools. The tool itself consists

of a hone head (referred to as

a pineapple) which is fitted

with wear guides, a feed cone

assembly and a universal joint

designed to allow a slight

float of the tool to the piece

part. These tools are designed

to allow for a maximum

number of stones in the hone

head (per specific bore size) to

assure best bore geometry

possible.

Fig. 5: Stoke honingstations consisting ofRough and Plateau passes.

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Rough (Base) Hone Tooling

12 stone tool body.

Responsible for themajority of the bore stockremoval (~ .0025 /.0635mm).

Designed to correct andimprove upon incomingbore geometry conditionssuch as out of round, taper,

barrel, hourglass, etc.

The abrasive stonedimensions along with themachine tool accuracy onstroke reversal allow formaximum cutting actionthroughout the full lengthof the bore, even withrestricted through boreconditions.

Proprietary abrasive gritand grade selection sinteredin a medium/hard metal

bond matrix to allow for afree cutting action and adefinable depth of cut toproduce the base Rk, Rvkand Vo specifications (oilretention valley depth andwidth requirements). Arelative crevice valley depthand width is created toassure the appropriateamount of oil is retained inany one area of the bore atall times.

Inherent in-process airgaging allows for automaticsize control of the bores asthey are being machined inthe block.

Plateau Hone Tooling

12 stone tool body with2.000 (50.8mm) long x.093 (2.3622mm) wideabrasives.

Designed specifically forremoval of the peak surfaceleft from the roughoperation and to producethe required finish boresize, surface finish andstructuring.

Minimal stock removalrates (~ .0002 /.00508mm).

Produces the final surfaceplateau level of 70 to 90%of a total surface area as

defined by the ratio of thebearing surface length to asurface length measured ata depth below the 5%plateau level asmeasured from the highestsurface point as reflected inthe Abbott Curve (BAC)calculation andcorresponding chart.

Abrasive grit (D35) andgrade selection in a specialblended metal bond matrix.

A predetermined strokecount and feed pressureallow abrasives to hone thewall to meet final finish sizealong with surface finishand structuringrequirements.

Coolants andFiltration

Most modern block line honemachines use water basedhoning coolants with alubrication package designedto work within a specific

block or liner material and iscompatible with the makeupof the metal bond honingstones. The proper selection ofhoning fluids used inconjunction with a highquality metal bond abrasiveselection has led to higherpart quality improvements inboth size control andgeometry. Coolant suppliersuch as Castrol, Nalco,Houghton and others haveexperience in the honingenvironment and should beconsulted along with yourabrasive supplier to determine


Fig. 6: Plateau Hone Tooling produces the final surfaceplateau level of 70 to 90% of a total surface area asdefined by the ratio of the bearing surface length to a surfacelength measured at a depth below the 5% plateau level as measured from the highest surface point as reflected inthe Abbott Curve (BAC) calculation and corresponding chart.(Photo used with permission from the Society ofManufacturing Engineers.)

Fig. 7: Post air gage heads monitor pre set attributes andalerts are activated if a deviation occurs outside of the sizetolerance range so that a correction can be made to theprocess.

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the appropriate choice of the

correct coolant or lubricant to

use in your application.

A critical feature of any

honing application is the

proper selection of a filtration

methodology. Large block line

hones typically use special

filter media integral to a large

dedicated gravity filtration or

vacuum filter systems. In

addition many of these media

filter applications are assisted

by magnetic separators,

canisters, or tubular backwash

filters. A hone filtration

system should be capable to

filter the chips (swarf)

generated by the finest grit

abrasive stone used in theprocess which is reflected in

final surface finish of the OE.

Typical systems of today will

filter out to


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determined in the pre-production stage through adevelopmental and statisticalhoning process. This processleads to the most efficient tooldesign, abrasive selection and

machine working pressures toassure a capable and reliableproduction hone process.

Particular attention isgiven to the ability of thehone to perfect boregeometries passed on from theprevious boring operation andalso to produce honed boresthat meet cylindricityrequirements in the range of


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Ability to precisely controltool stroke speed and stonefeed expansion.

Accuracy and repeatabilityto maintain stroke reversalpoints.

Ability to accurately gageor monitor bore size in-process.

Ability to measure surfacefinish accurately with aprofileometer.

Tooling and AbrasivesOnce the proper machine isselected it is most critical thatyou begin to look early on atdetermining and choosing themost efficient hone toolingand abrasive systems based ona design to maximizeefficiencies in your honingprocess.

It is recommended that acomparison be made of the

available tooling and abrasivepackages in the marketplaceto the styles used by the OEindustry. One should seek adurable hone head designed touse the maximum amount ofstones in a given bore size to

provide for a longer life andmore repeatable boregeometry. There are readilyavailable hone heads (withdrive-shafts) whose designoriginated within the OE honeenvironment but have beenadapted to fit and function onany hone machines found inuse today in theremanufacturing industry.

Stone suppliers that have aknown history in the OEindustry should be sought outto provide guidance anddirection in the properselection of the honingabrasive that will provideconsistent and repeatablestock removal rates bore

geometry and surface finishesper your specific enginecylinder bore specifications.Proper diamond abrasiveselection will allow for thebest available crystal shapesand friability as they may

relate to the material beinghoned.

The hone stones should bedesigned with free cuttingabrasives to allow the primarystock removal that is requiredto meet the cycle timeobjectives while assuring thatthat the desired bore geometryand oil retention parametersare established. Properselection of bond matrix,crystal size and characteristicof the finish or plateau stonesshould allow for a definedsurface that meets many ofthe current plateauspecifications of today.

Preventative maintenanceof the hone tooling is critical

to assure their ability toequally and easily expand theabrasives within the tighttolerances of the tool body.Too tight or too loose a fitmay restrict the ability of thestone to effectively accomplish

their work.Additionally critical tool

wear items such as feed coneand expander wear, stonepocket tolerances, andcleanliness should be checkedfrequently. A PM watch listshould also be established toinspect and monitor any honemachine wear issues such abelt or gear wear, alignment,etc.

Coolant selection shouldbe made based on the type ofmaterial being honed. It isadvisable that you coordinatethe coolant selection withyour hone stone abrasivesupplier to assurecompatibility with the

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composition of the abrasive/bond matrix.

Filtration should be sizedto remove the smallest chip(swarf) that is removed in youhone operation.

Honing on CNCMachining CentersAn opportunity now exists forthose in the remanufacturingindustry to potentially utilizeexisting or new CNCequipment to complete thehone process. A flexiblehoning system has beendeveloped by a leading OEtooling and abrasive supplierthat brings the same design oftooling, abrasive and in-process air gaging that is usedwithin many of the OE enginemanufacturers of today.

This patented toolingpackage is designed tofunction within many styles of

CNC machine tools including

machining centers, lathes, and

vertical chuckers. The hone

tools are built to fit into the

various style of machine tool

holders such as CAT, HSK,

etc., and utilize the coolant

pressure (thru spindle) to

expand and control the

cutting pressure required of

the abrasives.

The addition of the in-tool

air gage system allows for

continuous monitoring of part

diameter during the honing

operation. This also allows

for the potential to close the

loop with prior operations

such as finish boring. This

would allow for a morecompliant size control to the

hone which in turn would

provide more consistent and

repeatable surface structuring

that the industry requires.

Recap

Technology exists today toallow the remanufacture ofengine blocks to utilize honetooling and abrasive systems

that are representative ofthose used in the OE industry.Factors such as bore geometryand finish requirements maybe impacted by the inability ofsome lighter duty hones tomeet the accuracies providedby the OE production honemachine tools. Additionallythe reduction of wall supportcreated by re-boring thecylinder bores prior to honingwill influence the final shapeand size characteristics ascompared to the OE.

It is recommended that acomparison be made of all thecurrently available technologyto discern which combinationof hone machine and tooling

and abrasive system best suitsthe individual type ofremanufacturing process thata business may be involvedwith.I

David Chobany is a Senior Member of

the Society of Manufacturing Engineers(SME). Over the past years he has

presented technical honing andtraining seminars to internationalSME audiences, corporate process

engineers and independentmetalworking businesses. He has over

15 years of technical expertise in themetalworking industry and is currently

employed as Vice President of BatesTechnologies.


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dchobany article ep04-2008!10!18

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