Mass finishing techniques like vibratory deburring and burnishing can improve the performance and service life of aircraft parts. These techniques produce uniform, isotropic surfaces with beneficial compressive stresses. Studies show these finished surfaces increase metal fatigue resistance compared to conventional methods. Mass finishing is also being used on larger aircraft components and is more economical than manual deburring for complex parts. The uniform stress and surfaces produced by mass finishing improve part quality, durability, and consistency over single-point finishing methods.

1. Surface Finishing Reaches New Heights
Mass media finishing techniques can improve aircraft part
performance and service fife.
By David A. Davidson, Deburring/Surface Finish Specialist, Deburring, Edge Finishing
Surface Conditioning Group
M
ass finishing processes have long been wide-
ly adopted throughout industry as a pre-
ferred method for producing advanced edge
and surface finish effects on many types of
machined and fabricated components. American
industry is at the forefront for aggressively deploy-
ing these methods to improve their edge and surface
finishing operations.
In his "Deburring and Edge Finishing Hand-book"
(1999 edition)," Laroux Gillespie developed a com-
parative table which pointed out that in some
mechanical finishing equip-
ment categories, such as
rotary barrels, vibratory
finishing, and centrifugal
barrel finishing equipment,
American industry leads
the world in terms of the
number of equipment
installations. Despite this,
all too often situations still
exist where archaic, even
primitive hand or manual
finishing methods are used
to produce edge and surface
finishing effects.
This is not to say that
some industrial part appli-
cations are not going to
require a manual deburring
approach--some do. In
many cases, however, hand
or manual methods are still
being utilized because auto-
mated or mechanized methods have not been consid-
ered or adequately investigated.
Commenting on an often observed dichotomy in
precision manufacturing operations in an essay titled
"Boeing Issues an Invitation," Rodney Grover of the
Society of Manufacturing Engineers (SME) refer-
enced a situation that is still all too common. Many
manufacturers, after spending vast sums on CNC
machining equipment to produce parts to very pre-
cise tolerances and specifications, consistently, in the
This large aluminum component was previously deburred
with hand tools. Implementing a vibratory finishing
process with a tub-shaped chamber reduced processing
time from hours to minutes and reduced direct manual
deburring labor to nil. More importantly, surface finish
and edge contour effects have been produced on all criti-
cal areas of the part, with a part and feature consistency
and uniformity not possible with manually directed or sin-
gle point-of-contact abrasive methods. Photo courtesy of
Robert M. Kramer, Kramer Industries.
end, hand off these expensive parts to a deburring
and finishing department that utilizes hand methods,
with all the inconsistency, non-uniformity, rework
and worker injury potential that implies. Even when
manual methods cannot be completely eliminated,
mass media finish techniques can and should be used
to produce an edge and surface finish continuity that
cannot be duplicated with manual or single-point-of-
contact methods.
Developing an overall edge and surface finish con-
tinuity and equilibrium can have a significant effect
on the performance and
service life of critical compo-
nents as well.
In the past, mass finishing
methods have been thought to
be limited to uniformly pro-
cessing large numbers of
small to moderately sized
components to precise edge
and surface finish specifica-
tions. Increasingly,this type of
processing is being investigat-
ed by manufacturers of large
and very large components to
drive down the high costs
associated with utilizing hand
tools or hand-held power tools
to abrasively modify part
edges and surfaces.
Machinery capable of pro-
cessing very large compo-
nents can now be built.
Equipment with chamber
capacities as large as 200 cubic feet have been designed
to accommodate individual parts.
In some cases, the parts are fixtured within the pro-
cessing chamber to amplify processing effects on
specified areas, or prevent edge damage on extreme-
ly heavy parts. In other cases or circumstances,
parts are suspended in the media mass for more
equalized surfacing and stress equilibrium effects.
Complex rotating parts, such as power generation
turbine disks as large as four feet in diameter, have
March 2005 25

2. This large aircraft engine tur-
bine disk has been processed
with the Turbo-Finish method.
This dry abrasive finishing
method has been successful in
bringing mass media finish
economies to large, complex,
rotationally oriented parts. In
addition to the uniform and
consistent edge contours
developed, the method also
produces highly sophisticated
isotropic surface finishes by
radically altering the character
of the as-machined or as-
ground surface finish. Photo
courtesy of Michael L.
Massarsky, Turbo-Finish Corp.
These titanium test coupons
show a before and after exam-
ple of mass finishing process-
es being used to blend in
milling cutter paths.
Transforming the positively
skewed surface profiles of
machined parts into parts
with isotropic and negatively
skewed surface characteristics
can be an important element
in any program where surface
improvements are being
developed to improve wear
resistance and metal fatigue
resistance on critical parts.
been edge-contoured
and surface condi-
tioned with spindle-
fixtured processes
such as the Turbo-
Finish method.
Mass media finish-
ing processes have
gained widespread
acceptance in many
industries primarily
as a technology for
reducing the costs of
producing edge and
surface finishes. This
is particularly true
when manual debur-
ring and finishing pro-
cedures can be mini-
mized or eliminated.
Many manufactur-
ers have discovered
that as mass finishing
processes have been
adopted, put into serv-
ice, and the parts
involved have devel-
oped a working track
record, an unantici-
pated development
has taken place.
Their parts are bet-
ter--and not just in
the sense that they no
longer have burrs,
sharp edges, or that
they have smoother
surfaces. Depending
on the application,
they last longer in
service, are less prone
to metal fatigue fail-
ure, exhibit better tri-
bological properties (less friction and better wear
resistance), and from a quality assurance perspective
are much more predictably consistent and uniform.
The question that comes up is, "Why do commonly
used mass media finishing techniques produce this
effect?"There are several reasons. The methods typical-
ly are nonselectivein nature. Edge and surface features
ofthe part are processed identically and simultaneous-
ly. These methods also produce isotropic surfaces with
negative or neutral surface profile skews.
Additionally, they consistently develop beneficial
This shafted gear utilized in heli-
copter turbine applications has
been processed in centrifugal bar-
rel finishing equipment to pro-
duce specific isotopric finishes
with high-load-bearing ratios to
improve gear tooth life and over-
all performance efficiency.
compressive stress
equilibriums. These
alterations in surface
characteristics often
improve part perform-
ance, service life, and
functionality in ways
not clearly understood
when the processes
were adopted.
In many applica-
tions, the uniformity
and equilibrium of the
edge and surface
effects obtained have
produced quality and
performance advantages for critical parts that can
far outweigh the substantial cost-reduction benefits
that were the driving force behind the initial process
implementation. This assertion has been affirmed by
both practical production experience and validation
by experiment in laboratory settings.
David Gane and his colleagues at Boeing have been
studying the effects of using a combination of fix-
tured-part vibratory deburring and vibratory bur-
nishing (referred to by them as "vibro-peening" or
"vibro-strengthening") processes to produce sophisti-
cated edge and surface finish values and beneficial
compressive stress to enhance metal fatigue resist-
ance. In life-cycle fatigue testing on titanium test
coupons it was determined that the vibro-debur-
ring/burnishing method produced metal fatigue
resistance that was comparable to high intensity
peening that measured 17A with Almen strip meas-
urements. The striking difference between the two
methods, however, is that the vibratory burnishing
Centrifugal barrel machines such as these can produce excep-
tional edge and surface finishes in very short cycle times.
Accelerated process effects can be developed because of the
high-speed interaction between abrasive media and part sur-
faces, and because media interaction with parts is characterized
by high pressure by virtue of the high centrifugal forces devel-
oped in the processes.
26 www.metalfinishing.com

3. . . . . . . . . . . . o~:
~:~=~ ~ , ~ ~
This large power generation tur-
bine blade was made utilizing 6-
axis machining technology.
Centrifugal barrel finishing tech-
nology was used to clear and
blend in the milling cutter paths
and then develop very refined
and burnished isotropic surfaces
in the foil area.
method produced the
effect while retaining
an overall surface
roughness average of 1
pm (Ra), while surface
finish values on the
test coupon that had
been processed with
the 17A high-intensity
peening had climbed to
values between 5 to 7
~m (Ra). The conclu-
sion the authors
reached in the study
was that the practical-
ity and economic feasi-
bility of the vibro-deburring and burnishing method
increased with part size and complexity.
Michael Massarsky of the Turbo-Finish Corp. was
able to supply comparative measurements on parts
processed by his method for edge and surface finish
improvement. Utilizing this spindle oriented deburr
and finish method, it is possible to produce compres-
sive stresses in the MPa = 300 to 600 range that
formed to a surface layer of metal to a depth of 20 to
40 ~m.
Spin pit tests on turbine disk components
processed with the method showed an improved
The mass finishing method is usually thought of in terms of facil-
itating the surface finishing of large numbers of smaller parts. As
can be seen from this photo, very large structural components
such as this titanium airframe bulkhead can also be processed.
When coupled with both fixtured and sequential finish tech-
niques, these kinds of processes can not only be used to replace
costly manual deburr operations, but also produce significant
compressive stress and work-hardening effects that can dramati-
cally increase metal fatigure resistance properties. Studies have
shown that as part size grows, the more economical and practical
vibratory deburring and vibratory peening/burnishing processes
become as potential replacements for hard deburring and con-
ventional shot peening process combinations. Photo courtesy of
Giant Finishing Inc.
cycle life of 13,090 +450 cycles when compared to
the test results for conventionally hand- deburred
disks of 5,685 _+335 cycles, a potential service life
increase of 2 to 2.25 times, while reducing the dis-
persion range of cycles at which actual failure
occurred. Vibratory tests on steel test coupons were
also performed to determine improvements in metal
fatigue resistance. The plate specimens were tested
with vibratory amplitude of 0.52 mm and load stress
of 90 MPa. The destruction of specimens that had
surface finishes developed by the Turbo-Finish
method took place after (3-3.75)'104 cycles, a signif-
icant improvement over tests performed on conven-
tional ground plates that started to fail after
(1.1-1.5)'104 cycles (see Figure 2).
In his handbook, Gillespie makes a very astute
observation. "Typical burrs are not the result of poor
planning or poor engineering. They are a natural
result of machining and blanking processes. Large
burrs, however, may be the result of poor planning."
A similar axiom could be said to exist regarding sur-
face finishes. "Rough, non-isotropic surface finishes
with undesirable stress conditions are not the result
ofpoor planning or poor engineering. They are a nat-
ural result of almost all common machining, grind-
ing, fabrication and abrasive methods. These results
can be exacerbated by abusive machining and grind-
ing, and improved or reversed with mass media fin-
ishing techniques."
Mass media finishing techniques improve part
performance and service life, and these processes
can be tailored or modified to amplify this effect (see
Figure 3). 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 are not. This facet
of edge and surface finishing deserves closer scruti-
ny. This is also true with larger and more complex
parts--only more so.
REFERENCES
1.Gane, DavidH., et al.,"Evaluation ofVibro strengthen-
ing for FatigueEnhancement of Titanium
StructuralComponents on Commercial Aircraft," Ti-
2003 Science and Technology;Proceedings of the lOth
World Conference on Titanium, Hamburg, Germany,
edited by G. Lutejering and J Albrecht.Wiley-Vch,
Vol 2., pp 1053-1058;July 13-18,2003.
2.Massarsky,M.L.,and D.A.Davidson,"Turbo-Abrasive
Machining," CODEF Proceedings, 7th International
Deburring Conference, Berkeley, Calif.: CODEF
[Consortium on Deburring and Edge Finishing],
University ofCalifornia at Berkeley;June 2004.
March 2005 27

4. This graph was developed from the results of spin pit testing
performed on turbine disks to determine the effects of
edge/surface finishing methods on metal fatigue resistance.
Significantly improved results in terms of service life were
obtained by theTAM finish method.TAM produced a feature-to-
feature stress equilibrium that could not be matched by meth-
ods that involved manual methods. Similar effects have also
been noted when other mass media finish methods replace
manual deburring.
3.Massarsky, M.L., and D.A.Davidson, "Turbo-Abrasive
Machining--A New Technology for Metal and Non-
Metal Part Finishing," The Finishing Line, Vol.18. No.
4, Dearborn Mich.:Association ofFinishing Processes,
Society ofManufacturing Engineers; Oct. 30, 2002.
Shown here is an automotive engine blockready for mass media
finishing. High performance automotive engine applications are
one of the most rapidly expanding areas for mass media finish-
ing technology, Many involved in competitive automotive racing
have adopted mass media finishing techniques as a way of
reducing friction, improving wear resistance and increasing
horsepower. The techniques used to produce these effects take
mass finishing methods to the next level, in terms of producing
specialized surfaces that will materially affect the performance of
the component. Much of the information available about these
effects is highly anecdotal in nature. However, the fact that these
surface finish methods are being so widely adopted in such a
competitive and results-oriented environment may encourage
other manufacturers to explore what surface finish improvement
can do for their critical part performance.
4. Massarsky, M.L., and D.A.Davidson, "Turbo-Abrasive
Machining and Turbo-Polishing in the Continuous
Flow Manufacturing Environment," SME Technical
Paper MR99-264, Conference Proceedings: 3rd
International Machining and Grinding Conference,
Cincinnati, Oct 4-7, 1999, Dearborn, Mich.: Society of
Manufacturing Engineers; 1999.
5. Gillespie, LaRoux, Deburring and Edge Finishing
Handbook, Dearborn, Mich., Society ofManufacturing
Engineers, 1999.
6. Davidson, D.A., "Mass Finishing Processes," Metal
Finishing GuidebookDirectory, 100(1A):104-117;2002.
7. Davidson, D.A., "Micro-Finishing and Surface
Textures," Metal Finishing, 100(7):10-12; July, 2002.
8. Massarsky, M.L. and D. A. Davidson, "Turbo-Abrasive
Machining and Turbo-Polishing in the Continuous
Flow Manufacturing Environment," SME Technical
Paper MR99-264, Conference Proceedings: 3rd
International Machining and Grinding" Conference,
Cincinnati; Oct 4-7, 1999, Dearborn, Mich.: Society of
Manufacturing Engineers; 1999.
9. Rossman,Edward F., [Boeing],"CollectedThoughts On
High Speed Machining of Titanium," SME Technical
Paper, Dearborn, Mich.: Society of Manufacturing
Engineers; 2004.
10. Grover, Rodney, "Boeing Issues an Invitation,"
Dearborn, Mich.: Society ofManufacturing Engineers;
2004; http://www.sme.org.
ACKNOWLEDGEMENTS
The author wishes to acknowledge the technical
assistance of the following members of the newly
formed Society of Manufacturing Engineers DESC
Technical Group [Deburring, Edge-Finish, Surface
Conditioning]: Michael Massarsky, Turbo-Finish
Corp.; David H. Gane, Boeing; Edward F. Rossman,
Ph. D., Boeing; Jack Clark, ZYGO Corp.; LaRoux
Gillespie, PE, CmfgE, Honeywell; and Rodney
Grover, Society of Manufacturing Engineers. Many
of these colleagues will be present at a technical
session concerning deburring and surface finishing
methods for aircraft frame components sponsored
by the Society of Manufacturing Engineers at
WESTEC on April 6 in Los Angeles.
Dave Davidson is a deburring and surface finishing
specialist, consultant, and the 2005 chair for the
Deburring, Edge Finishing Surface Conditioning
(DESC) Group. He can be reached (e-mail) ddavid-
son@deburringsolutions.com FITf
28 www, metalfinishing.com