November 2012 F4 Deburring 1 Final
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Transcript of 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.).
November 2012 | ManufacturingEngineeringMedia.com 79
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
80ManufacturingEngineeringMedia.com | November 2012
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-
82ManufacturingEngineeringMedia.com | November 2012
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-
November 2012 | ManufacturingEngineeringMedia.com 83
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
84ManufacturingEngineeringMedia.com | November 2012
Deburring
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
November 2012 | ManufacturingEngineeringMedia.com 85
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
Further Reading