Mr82 264

1. 1982
@ 41 ! RIGHTS RESERVED
MR82-264
High Energy Mass Finishing
abstract
The mass finishing processes are generally the most used means for
mechanized deburring and surface condition. Compared with the other
mechanical finishing techniques they are generally of low initial investment
and low operating cost; yet are very consistent in results and versatile in
application. The standard mass finishing techniques are tumbling barrels and
vibratory machines. These are relatively slow processes, with some limitations
for precision parts, fragile parts, and parts requiring fine finishes. The high
energy mass finishing processes; spindle finishing, centrifugal disc finishing,
and centrifugal barrel finishing, have been developed in large part to
overcome the limitations of the standard methods. This paper discusses the
three high-energy mass finishing processes, it reviews capabilities and
limitations, and compares these processes as well as deburring and surface
conditioning techniques.
author
J. Bernard Hignett
Vice President
The Harper Company
East Hartford, Connecticut
conference
SME’s 1982 International Tool and
Manufacturing Engineering Conference
May 17-20, 1982
Philadelphia, Pennsylvania
index terms
Deburring
Finishing
Barrel Finishing
Abrasive Machining
Metal Finishing
Society of Manufacturing Engineers l One SME Drive l P.O. Box 930
Dearborn, Michigan 48128 l Phone (313) 271-l 500

2. INTRODUCTION
Currently U.S. industry is faced with a rising need to increase productivity and
product quality. Serious international competition is new to us, and the only way we can
compete is to utilize more advanced manufacturing methods, seeking higher levels of
productivity. Consistant quality is mandatory. Moreover, we must meet broader
responsibilities; be environmentally neutral (or better still beneficial), and be energy
efficient.
Improved edge and surface finishing techniques are some of the important means by
which these objectives can be met. The high cost of finishing is often overlooked.
Recent studies of a range of components showed that the cost of mechanical finishing
typically exceeds 20% of manufacturing cost. Many of those components have much of the
deburring and surface finishing being accomplished by manual methods so substantial
opportunities do exist reduce total cost of those products by improved finishing
methods. The benefits can be significant, not only in terms of reduced manufacturing
cost but also a consistent better looking product, one that lasts longer and operates
more efficiently.
It is for these reasons that there has been dynamic development in the field of
control and improvement of edge and surface condition. Many of the developments have
taken place with the group of processes known as mass finishing particularly the high
energy processes. These techniques not only offer a means of high speed finishing, but
also new capabilities for cost saving automation and better levels of finish.
THE MASSFINISHING PROCESSES
By definition, mass finishing involves loading of components to be finished into a
container, normally with some abrasive media, water and compound. Action is applied to
the container to cuase media to rub against components surfaces, edges and corners or
components to rub against each other. This action may deburr, generate edge and corner
radii, clean the parts, remove rust and scale, and modify surface stress and grain
structure.
The basic mass finishing processes comprise:-
Barrel Finishing
Vibratory Finishing
Spindle Finishing
Centrifugal Disc Finishing
Centrifugal Barrel Finishing
There are other, less commonmass finishing processes such as reciprocal finishing,
chemically accelerated vibratory and centrifugal barrel finishing, electro-chemical
accelerated mass finishing. Barrel finishing was the original mass finishing process,
in use long before the industrial revolution and the general mechanized deburring
technique unit1 the mid 1960's.
The vibratory finishing processes started to be used by industry during the early
1960's, and are now the most comon mechanical finishing process in use. The vibratory
finishing process has enjoyed substantial development during the past 10 years.
Machines can be highly versatile, and fully automated for both batch and continuous
production. It is reasonable to expect that vibratory finishing will remain the
standard process for some years to come.
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The high energy mass finishing processes have developed in part to overcome some of
the limitations of vibratory finishing, but most importantly to replace manual finishing
and to offer a means of meeting new and increasing sophisticated surface conditioning
requirements. For example, an aircraft will be 5% more efficient with improved finishes
on engine and airframe components. A diesel engine will run 20% longer with better
quality finishes on significant edges and surfaces. With such opportunities the dynamic
development of the improved finishing methods is easily justified!
THE HIGH ENERGYPROCESS
Fig. 1) Spindle Finishing Machine
-
i
TWO SPINDLE FINISHING CONCEPT
Spindle finishing is the oldest high energy process, but the least versatile. It
requires components to be mounted on fixtures for deburring and finishing.
The spindle machine comprises a circular tub holding abrasive media, water and
compound which rotates at a high speed in a horizontal plane. The fixtured part on the
end of a spindle is immersed into the rapidly moving abrasive slurry, and then either
rotated or oscillated. This causes abrasive to flow swiftly over rough edges and over
the surfaces of components.
Generally small aluminum oxide nugget media are used although all forms of mass
finishing media may have application. There are some occasions when the machine can be
utilized with a dry mixture of fine abrasives and corn cobs or walnut shells for super
finishing.
Process cycles in spindle equipment rarely exceed 5 minutes, and are frequently
less than 30 seconds. The equipment is ideal for uniform shaped parts such as gears,
sprockets and bearing cages where fixturing is simple and action of abrasive will be
uniform over all significant edges and surfaces. Equipment can deburr, edge radius and
produce very fine finishes. There is no possibility of part-on-part impingement during
the process nor at reload time. The limitations result primarily from the time and cost
expense of fixturing the work pieces and where parts can be effectively handled in other
mass finishing equipment without fixturing, then those machines will be normally more
economial, convenient and versatile.
..
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Fig. 2) Centrifugal Disc Finishing
The centrifugal disc process is the newest form of high energy mass finishing. The
basic design comprises a tub, or vertical cylinder, the side walls of which are
stationary. The top of the tub is opened, the bottom of tub is formed by a disc which is
driven at high speed.
Media, compound and parts are contained in the tub. As the disc rotated with
peripheral speeds of up to 2,000 feet per minute, the mass within the container is
accelerated outwards and then upwards against the stationary side walls of the
container. The walls act as a brake, so that media and parts rise to the top of the
load, and then flow inwards towards the center of the tub, and from there back down to
the disc to be accelerated once more.
The action achieved in the centrifugal disc machine is substantially faster then in
vibratory equipment. Centrifugal forces of as much as 10 times gravity, press the
abrasive media against the components. Process cycles are up to one twentieth of those
of vibratory processing. The short process cycles result in reduced floor space
requirements in the finishing department, increased versatility and less work in
progress. Like vibratory equipment, parts can be readily inspected during the process
cycle, and variable speed can, on occasions, combine deburring with a final more gentle
surface refinement operation.
Centrifugal disc equipment is available with capacities ranging from 1.5 to 20
cubic' foot with the probability that larger equipment will become available as the
process becomes more widely used. As in vibratory equipment, automation is readily
achieved. The total load from the container can be fed out through a door in the
container wall, from there into material handling system, and media storage and return.
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/

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been
While centrifugal disc machines were developed more than 10 years ago, and have
in operation in Europe during this period, it is only during the past three years
that reliable, versatile and readily automated equipment has been available in the U.S.
Major development has centered around the seal area between the spinner and the
container walls or ring upon which the spinner sits. In modern eqUipIWnt the spinner and
ring are made of extremely hard and wear resistant ferrous materials for long life. The
gap between spinner and ring can be maintained to 0.005"; with properly designed
compound inlets in the gap to maintain lubrication there is possibility of fine media
resting in the gap to abrade either ring or spinner.
thousands of hours.
These parts now have life of many ,-
Variable speed, in centrifugal disc machines is as important for any mass finishing
process. There are certainly special purpose applications for the equipment where one
speed or two speed machines are satisfactory but with variable speed it is possible to
modify the forces applied to generate optimum cutting and optimum surface conditioning
with the chosen media and compounds. Automatic changing of speed, and changing of
compound can frequently result in two operations being combined into a single process
cycle.
Fully automated centrifugal disc machines are available for batch processing (not
continuous flow through), material handling can be for one or more machines, or the
central material handling system of a complete finishing department may be used. CNC
systems are in operation offering precise control monitoring centrifugal disc systems
for a multiplicity of operations.
Centrifugal disc equipment has the versatility and convenience of tub vibratory
equipment with process cycles reduced by 80%.
During the next 5 years centrifugal disc finishing will be a standard Process
technique for a broad range of applicat-ions.
Fig. 3) Centrifugal barrel finishing
FIG.1 FG2
PRINCIPLE OF CENTRIFUGAL BARREL PROCESS
MR82 - 264
KTKM WITHIN A CENTRIFUGAL BARREL MpIcH*E

6. L
-5-
Centrifugal barrel equipment, better known as HARPERIZING, comprises a number of
containers mounted on the periphery of a turret. The turret rotates at a high speed in
one direction while the drums rotate at a slower speed in the opposite direction. The
drums are generally loaded in a manner similar to that for normal tumbling or vibratory
operations, that is with parts, media, water and some form of compound. Turret rotation
creates a high centrifugal force, up to as much as a hundred times gravity. This force
compacts the load within the drums into a tight mass. Rotation of the drums causes the
media to slide against the work load removing burrs, and refining surfaces.
The abrading action under high centrifugal force results in short process cycles,
generally less than one fiftieth of the time taken in vibratory equipment. Of more
importance, as a result of the counter rotation of drums to turret, a completely smooth
sliding action of media against components is generated with no possibility of one part
falling or impinging against another. Because of this completely smooth sliding action,
consistent and reproducible results are achieved. Very high tolerances can be
maintained even with fragile parts,and very high surface finishes are achievable.
Process variables are similar to those of other mass finishing process, but an
additional advantage of centrifugal barrel finishing is the ability to control the force
with which media are pressed against components. This gives greater latitude in choice
of media. For example hard and low abrasion media may be used to deburr by running at a
high speed, and then the same media will refine surface when the machine is
automatically switched to low speed, hence two operations are combined into a single
cycle. Partical size of media can be selected to meet requirements of uniformity and
ease of separation without increasing the time of the process cycle.
An additional advantage of centrifugal barrel equipment involves the ability of the
process to impart a high compressive stress to the surface layer of components, so
increasing resistance to fatigue failure of the finished part. The capability of
imparting such improved fatigue strength is utilized in bearings, aircraft engine parts,
compressor and pump components. The improved fatigue strength is generally
$Ll:!:)than that which can be achieved by any of the other finishing processes combined
with shot peening, and almost always at significantly lower cost.
Economic considerations will frequently dictate the choice between centrifugal
barrel equipment and other mass finishing processes. In general, if satisfactory
results can be achieved with process cycle, of less than one hour vibratory equipment
will be a more economical method. If the process cycle is longer, if there is a wide
variety of components to be handled, or if there are special finishing requirements or
if fragile or precision parts are involved, then centrifugal barrel machines are likely
to prove better suited.
Equipment is available in sizes ranging from less than a quarter of a cubic foot
capacity to 50 cubic feet capacity. The process can be fully batch automated with
enormous versatility to handle the requirements of the most sophisticated industries.
COMPARISONOF PROCESSES
Conventional tumbling and vibratory equipment are still the standard means of
deburring and surface conditioning in the metal working, plastics and rubber industries.
Modern vibratory equipment can be fully automated and simple low cost semi-automatic
equipment is readily available. Most vibratory machines are open-top enabling in-
PrOCeSS inspection, they are well established machines, easily set up and operated,
require low maintenance and are reliable. Equipment is available in sizes from l-cubic
foot to Over 200 cubic foot, for parts of up to 40-foot long and parts weighing several
hundred pounds.
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The initial cost of equipment for the high energy deburring and surface finishing
processes is likely to be higher than for standard mass finishing although capital cost
for a given through put may not be as high, due to shorter process cycles. Some
comparisons of different process is outlined on the enclosed table.
Some applications where high energy mass finishing has become established, offering
improved product quality and productivity are:
Aircraft Compressor blade
Aircraft Turbine blades and vanes
Airframe components
Automotive (stressed and precision parts)
Bearings
C.R.T. components
Carbide tooling
Ceramic capacitors
Compressor valves
Computer parts
Dental and Orthodontal components
Diesel Engine, moving parts
Electrical switch gear
Fuel pump components
Gears (Particularly precision)
Hand tools
Hydraulic valves
Instrument components
Investment castings
Jewelry
Machine tool parts
Molds and Dies
Office machinery
Ordnance and missile parts
Orthopedic implants
Photographic and optical equipment
Pneumatic valves
Precision stampings
Precision forgings
Pumps
Screw machine parts
Sintered metal parts
Springs
Surgical instruments
Textile machinery
Transmission and timing chain
Watch and clock parts
SOMECONCLUSIONS
High energy finishing equipment is now available to handle all but the largest
components that can be processed in vibratory equipment. In terms of quality of surface
condition and the handling of fragile and high precision parts the high energy processes
have much greater capability.
Where conventional mass finishing processes can achieve entirely satisfactory
results with short process cycles, then high energy equipment will remain unnecessary
and expensive. However, for many other applications the high energy processes will
become increasingly used and of ever increasing importance for the following reasons:
1. Cost of inventory and work in progress will become increasingly expensive so that
equipment with short process cycles will become more readily justified.
In the factory of the future for automation will be essential, complete consistency
of result, absolute controlability of quality and production. For precision and
semi-precision metal parts in particular, the high energy processes will offer
greater benefits.
2. Improved edge and surface condition result in improved performance of many stressed
components. High energy processes have capabilities to achieve finer finishes,
some of them also to generate high compressive stresses which still further improve
performance of many stressed components.
?
3. Cost of floor space will be increasing, high energy deburring processes are means
of reducing floor space within the finishing department.
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4. The high energy processes offer greater opportunity to combine fairly heavy metal
removal operations with very fine finishing, not only increasing the scope for mass
finishing but also combining what may currently be multiple processes into a single
production cycle.
For the reasons outlined it behooves any manufacturer to investigate the high
energy mass finishing processes offering greater capability and versatility for the
finishing department. It is necessary that these techniques are compared not only with
conventional mass finishing but also other methods, such as buff, brush and polish,
chemical, electrochemical, thermal and abrasive flow. Development of the high energy
mass finishing methods is at a high level and fresh opportunities exist for most
manufacturing organizaitons.
Fig. 4) Table
VIBRATORY FINISHING SPINDLE FINISHING I
Industry Standard Process High -
Low initial cost
Process cycles, hours or
substantial proportions of
one hour
Can handle part sizes
Open for in-process inspec-
tion
Full batch automation
practicle
Continuous in-line automatio
possible for some applica-
tions
Integral and internal separa
tion practicle with some
applications
Well established, normally
simple and reliable
Very fast processing
No part-on-part impingement
Limited application for Size
and shape of part
Parts must be fixtured
Comparatively high labor cost
F
0
A
P
S
P
0
(
t
f
1
I
CENTRIFUGAL DISC FINISHING CENTRIFUGAL BARREL FINISHING
Energy Processes
ast process
pen for in-process inspection
utomated batch process
article
mall floor space
'art sizes only up to about
ne foot dimension
:ost approximately three times
:hat of vibratory per cubic foot
'recess cycles typically less
than l/4 that of vibratory
t i
t
I
c
,
I
,
,
!
NO in-process inspection
High inltla; 1nvest~nent
Cost 8 to I5 t.met tld: o! Y'
ratory per cubic Foot
Process cycles l/5 to i/Z{; 1'
of vibratory
lery fast processing'
iandles fragile parts
ktomated batch process posr-'
)nly with expensive equipwr.
lery flexible
'ossible to automatically
:hange from heavy metal re-
roval to super finish in single
cycle
Finest quality finisnes
Improves fatigue strength
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BIBLIOGRAPHY
1. M. Punamia and P. T. Blotter, "Workpiece Kinetics in Centrifugal Barrel Finishing"
Utah State University Report August 1981.
2. J. B. Hignett, "The Centrifugal Barrel Process-Precision Deburring and Surface
Finishing" SMETechnical Paper MR81-231.
3. J. B. Hignett, "Mass Finishing-A Look To The Future", Metal Finishing Magazine,
March 1981.
4. SME Book, "Cost Guide For Automatic Finishing Processes" edited L. J. Rhoades,
1981.
5. J. Coffield, "Advances In High Energy Finishing", SMETechnical Paper MR81-398.
.
MR82 - 264