november 2012 f4 deburring 1 final

November 2012 | ManufacturingEngineeringMedia.com 77

Mass finishing processes have

been widely adopted throughout

industry as the optimum meth-

odology for producing controlled

edge and surface finish effects

on many types of machined and

fabricated components. American industry has long been

on the forefront of aggressively deploying these methods

to improve edge and surface finishing operations.

All too often, situations still exist where archaic and

even primitive hand or manual finishing methods are

used to produce edge and surface finishing improve-

ments. This is not to say that some industrial part

applications are not going to require a manual deburring

operation—some do. In many cases, however, hand or

manual methods are still being used because more au-

The Role ofSurface Finish in ImprovingPart PerformanceMass media finishing techniquescan be used to improve partperformance and service life

Jack ClarkOwner/ConsultantSurface Analytics;Chair: SME Deburring, Edge-Finish,Surface Conditioning Technical [email protected]

David A. DavidsonDeburring/Surface Finishing SpecialistChair: SME Machining/Material Removal Technical [email protected]

Deburring

VIDEOSPECIALS

• Toseeturbo-abrasivemachiningofaerospacecomponentsforimprovedsurfacelifeatTurbo-FinishCorp.:http://tinyurl.com/massdeburring1• TolearnmoreaboutuseofacentrifugalbarrelfordevelopingextremeedgeandsurfacefinishesatMacKayManufacturing:http://tinyurl.com/massdeburring2• TolearnmoreaboutdragandspindlefinishmethodstoimprovecuttingtoollifeatBel-AirFinishing:http://tinyurl.com/massdeburring3

Centrifugal Barrel Finishing at

MacKay Mfg. in Spokane, WA is used

to produce extremely high-quality

edge and surface finish effects on

titanium, steel, aluminum and even

plastic components for the medical,

electronic, defense, consumer and

electron microscope industries.

tomated or mechanized methods have not been considered

or adequately investigated.

An often-observed dichotomy in precision manufacturing

operations is that many manufacturers, after spending vast

sums on CNC machining equipment to produce parts to very

precise tolerances and specifications consistently, in the end

hand off these expensive parts to a deburring and finishing

department that uses hand methods, with all the inconsistency,

non-uniformity, rework and worker-injury potential that implies.

Even when manual methods can’t be completely elimi-

nated, mass-media finish techniques can and should be used

to produce an edge and surface finish uniformity that simply

cannot be duplicated with manual or single-point-of-contact

methods. Developing an overall edge and surface finish

continuity and equilibrium can have a significant effect on

performance and service life of critical components.

In recent years, mass-media finishing processes have

gained widespread acceptance in many industries, primar-

ily as a technology for reducing the costs of producing edge

and surface finishes. The economics are especially striking

when manual deburring and finishing procedures are mini-

mized or eliminated.

The first casualty of overreliance on a manual deburring

and finishing approach is the investment the manufacturer

has made, often in the millions, for precise and computer-

controlled manufacturing equipment. The idea behind this in-

vestment was to have the ability to produce parts that are uni-

formly and carefully manufactured to exacting specifications

and tolerances. At this point, in too many cases, the parts are

then sent to manual deburring and finishing procedures that

will all but guarantee that no two parts will ever be alike.

Moreover, the increased complexity and precise require-

ments of mechanical products have reinforced the need for

accurately producing and controlling the surface finish of man-

ufactured parts. Variations in the surface texture can influence

a variety of performance characteristics. The surface finish can

78ManufacturingEngineeringMedia.com | November 2012

Deburring

affect the ability of the part to resist wear and fatigue; to assist

or destroy effective lubrication; to increase or decrease friction

and/or abrasion with mating parts; and to resist corrosion. As

these characteristics become critical under certain operating

conditions, the surface finish can dictate

the performance, integrity and service

life of the component.

The role of mass-finishing processes

(barrel, vibratory, centrifugal and spindle

finishing) as a method for removal of

burrs, developing edge contour and

smoothing and polishing parts has been

well established and documented for

many years. Less well known and less

clearly understood is the role special-

ized variants of these types of processes

can play in extending the service life

and performance of critical components

or tools in demanding manufacturing or

operational applications.

Manufacturers have discovered that as mass

finishing processes have been adopted, an

unanticipated development has taken place—their

parts are better.

To understand how edge condition

and surface topography improvement

can impact part performance, some

understanding of how part surfaces

developed from common machining,

grinding, honing, and other methods can

negatively influence part function over

time. A number of factors are involved:

1) Positive vs. Negative Surface

Skewness: The skew of surface profile

symmetry can be an important surface

attribute. Surfaces are typically char-

acterized as being either negatively or

positively skewed. This surface charac-

teristic is referred to as Rsk (Rsk—skewness—the measure of

surface symmetry about the mean line of a profilometer trace).

Conventionally machined parts usually display a concentration

of surface peaks above this mean line, a positive skew (Fig 1.).


Thus it is axiomatic that almost all surfaces produced by

common machining and fabrication methods are positively

skewed. These positively skewed surfaces have an undesir-

able effect on the bearing load of surfaces, negatively impact-

ing the performance of parts involved in applications where

there is substantial surface-to-surface contact. Specialized

high-energy finishing procedures can truncate these surface

profile peaks and achieve negatively skewed surfaces (Fig 2.)

that are plateaued, presenting a much

higher surface bearing contact area.

Application: The transition from

Gaussian (Fig. 1) honed surfaces to

carefully specified plateaued surfaces

(Fig 2.) in diesel fuel injector bore and

mating timing plungers resulted in

eliminating a multi-million dollar war-

rantee problem for an over-the-road

diesel engine manufacturer. One in six

injectors would “stick” and usually allow

raw fuel to flow, misfire, and some-

times cause that cylinder to seize. The

plateaued surface has a high “bearing

ratio” to distribute the high fuel pres-

sure loads and a uniform valley lay that

effectively distributes fuel (the fuel oil

is the system’s lubricant). Today, these

are “standard” two or three proces-

honing techniques and mass finishing

processes used by all high-performance

fuel injector manufacturers that elimi-

nate failures due to part-to-part contact

through the lubricant film.

2) Directional vs. Random (Iso-

tropic) Surface Texture Patterns:

Somewhat related to surface texture


Deburring

Figure 1 Figure 2

skewness in importance is the directional nature of surface

textures developed by typical machining and grinding meth-

ods. These machined surfaces are characterized by tool

marks or grinding patterns that are aligned and directional in

nature (Fig. 3).

It has been established that tool or part life and perfor-

mance can be substantially enhanced if these types of surface

textures can be altered into one that is more random in nature.

Post-machining processes that utilize free or loose abrasive

materials in a high-energy context can alter the machined sur-

face texture substantially, not only reducing surface peaks, but

generating a surface in which the positioning of the peaks has

been altered appreciably. These “isotropic” surface effects (Fig

4.) have been demonstrated to improve part wear and fracture

resistance, bearing ratio and improve fatigue resistance.

Application: Figures 3 and 4 are automotive camshaft roll-

ers that connect the rotating action of the cam to the recip-

rocating valve. The loads on this surface are high and must

be transmitted through a consistent layer of oil to maintain a

rolling action between the moving elements. The directionally

ground roller (Fig 3.) was contacting the cam lobe and failing

both the roller and the camshaft to result in an engine manu-

facture liability in the many millions of dollars.

Each failure would force the manufacturer to, in the field,

replace the camshaft, rollers and, many times, other normally

non-related components because of wear debris moved

throughout the engine via the lubrication system. The random,

high load bearing surface shown in Fig 4. maintains a predict-

able oil film and keeps the rollers from contacting the cam

and, therefore, resisting wear.

3) Residual Tensile Stress vs. Residual Compressive

Stress: Many machining and grinding processes tend to devel-


Deburring

Figure 3 Figure 4

op residual tensile stresses in the surface area of parts. These

residual tensile stresses make parts susceptible to premature

fracture and failure when repeatedly stressed. High-energy

mass finishing processes can be implemented to modify this

surface stress condition and replace it with uniform residual

compressive stresses.

Many manufacturers have discovered that as mass finish-

ing processes have been adopted, put into service, and the

parts involved have developed a working track record, an

unanticipated development has taken place—their parts are

better. In the case of automotive valve springs (Fig 5.): they

last longer in service, are less prone to metal fatigue failure

and, from a quality assurance perspective, are much more

predictably consistent and uniform.

Application: Springs of any type have a predictable life

based on the material, shape, movement range, load and

interference/resonance with a mating spring in multiple spring

applications. High-performance automotive valve springs are

some of the most stressed movement

control applications. The spring is con-

trolling the vertical movement of a mass

(the valve) over a distance (over 0.5"

or 12.7 mm) at very high frequencies

(5000–10,000 openings a minute). The

valve spring is typically a drawn wire

wound into the coil shape and “shot

peened” for “stress relief”.

Developing an overall edge and surface finish continuity

and equilibrium can have a significant effect on

performance and service life of critical components.

The peening process consists of

steel balls pounded into the spring’s

surface during an aggressive tumbling

or wheel blast action. This does impart

some compressive stress but in a macro

form. Even with this level of compres-

sive residual stress the spring will

fracture unpredictably in many high-


Figure 5

performance applications requiring the users (race teams)

to change the springs for at least every event during a racing

season. The same spring subjected to a high-energy mass

finishing process will result in the spring lasting easily 5–10

times longer before eventual failure. Even more important is

that the pressure the spring exerts on the system is consis-

tent, allowing for predictable engine performance over the

entire life of the spring. The fact that the spring will last this

extended time compared to a “stan-

dard” spring results in reduced cylinder

head maintenance, no premature fail-

ures that catastrophically can ruin the

engine, and higher frequency operation

(higher RPM equals more horsepower).

Even when manual methods can’t be completely

eliminated, mass-media finish techniques can and should be used to produce an edge and surface finish

uniformity that simply cannot be duplicated with manual or single-point-of-contact

methods.

4) Mixed Bag—Compatible Surfaces

but Different Function: The “draw and

iron” process used to make aluminum

beverage cans is complicated, uses very

fast production rates and requires tight

punch and die tolerances. The punch

drives a sheet of aluminum through a

progressively smaller and smaller pack

of dies to thin the material and form the

can in one (1) stroke of the punch at the

rate of 400 cans per minute. If the sur-

face finish of the punch does not retain

lubricant, the newly formed can cannot

be “stripped” off the punch, damaging

the can. If the finish on the dies is not

such that they produce a bright can and

do not allow aluminum “pickup,” the

cans OD will be unacceptable.

Also, due to surface specification,

the tolerance between the punch and


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dies can be reduced and maintained, the wall thickness of the can be controlled

and reduced. All these functions are dependent on the directionality and control

of the surface finish on both components.

The punch must have the random isotropic surface discussed in #2 above and

the dies must have a negatively skewed surface, discussed in #1 above, that is in

the direction of the drawn material (perpendicular to the diameter of the die). When

all these criteria are met, one can expect bright OD finished cans that strip eas-

ily (reducing scrap) and have a minimally thick wall. Wall thickness is not a trivial

matter—savings of up to $10M per year per 0.001" (0.0254-mm) wall thickness

reduction in a given can plant have been reported.

To summarize: Mass media finishing techniques (barrel, vibratory, centrifugal

and spindle finish) can be used to improve part performance and service life, and

these processes can be tailored or modified to amplify this effect. Although the

ability of these processes to drive down deburring and surface finishing costs when

compared to manual procedures is well known and documented, their ability to

dramatically affect part performance and service life is not widely recognized, nor

well understood.

Abundant opportunities exist for part performance and part life improvement

with substantial economic advantages. All that is required is a more thoughtful and

purposeful approach to the selection and implementation of the mass finishing

processes available to manufacturers. ME


1. Massarsky,Dr.M.L.,Davidson,D.A.“Turbo-ChargedAbrasiveMachiningOffersConsistency,Uniformity,”ProductsFinishing,June2012Vol.76,No.9,pp.24-27,Cincinatti,OH:GardnerPublications

2. Clark,Jack,Massarsky,Dr.M.L.,Davidson,D.A.“It’stheFinishThatCounts”,MetalFinishing,July2005,pp24-29,WhitePlains,NY:ElsevierScience

3. Davidson,D.A.,“PrecisionFinishingProcessesinCentrifugalBarrelEquipment,”MetalFinishing,July/August2005,pp65-67.WhitePlains,NY:ElsevierScience

4. Massarsky,Dr.M.L.,Davidson,D.A.,“Turbo-AbrasiveMachiningandTurbo-PolishingintheContinuousFlowManufacturingEnvironment”,SMETechnicalPaperMR99-264,[ConferenceProceedings:3rdInternationalMachiningandGrindingConference,Cincinnati,OH,Oct4–7,1999]Dearborn,MI:SocietyofManufacturingEngineers,1999.

5. Davidson,D.A.,“SurfaceConditionImpactsPartPerformance,”MetalFinishing,February2007,WhitePlains,NY:ElsevierScience

6. Gillespie,LaRoux,MassFinishingHandbook,pp68-69,NewYork,NY:IndustrialPress,2007

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november 2012 f4 deburring 1 final

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