2. INTRODUCTION
Deburring and surface conditioning costs are typically about 10% of the total
manufacturing costs of most formed and machined products. Only a very few enlightened
organizations invest in an appropriate amount of management and engineering talent and
an appropriate proportion of chemical expenditure for the mechanical finishing
operations. In the plant where machining operations have been automated, yet
deburring and surface conditioning has been neglected, then the proportion of total
costs attributable to the finishing processes escalates.
Every manufacturing engineer has interest in, and understanding of, in-line
automation and flexible manufacturing systems for basic manufacturing processes.
Unfortunately, it is less likely that the manufacturing engineer appreciates the
opportunities for automating the mechanical finishing operations. It is surely
advisable that the engineer should consider the finishing operations for any product
at the same time as considering the basic forming methods, particularly when
operations are being automated.
The standard means of deburring and surface conditioning in a high proportion of
manufacturing organizations, even sophisticated ones, is still hand filing, grinding
and scraping.
scraping,
It is still normal to find within U. S. industry the ha+ filing and
and to find the "finishing department" comprised of a number of manual
operations, together with a few antiquated tumbling barrels. Perhaps the centralized
deburring area is suited to many manufacturing operations but in most of them there is
tremendous opportunity to reduce costs, improve productivity and product quality. In
many of these operations it would be better for the deburring and surface conditioning
operations to be an integral part of the production line. Modern mass finishing
methods, particularly the high energy processes, greatly facilitate both centralized
and "in-process" automation.
MASSFINISHING
An adequate definition of a mass finishing machine is:
The major
"A container'into which either a mass of components, or components
together with a mass of media is loaded. Action of the container
is created to cause media to rub against parts, or parts to rub
against one another; so removing burrs, radiusing edges and
refining surfaces."
mass finishing processes are:
Barrel Tumbling.
Vibratory Finishing.
Spindle Finishing.
Chemically and Electra Chemically accelerated mass finishing processes.
Centrifugal Disc Finishing.
Centrifugal Barrel Finishing.
Barrel tumbling was the original mass finishing process, having been in use prior
to the Iron Age. With use of modern techniques and materials, barrel tumbling is
capable of handling fragile and precision parts, achieving very fine and bright
finishes. Some automated systems have been produced, but barrel tumbling is
invariably a very slow process and is more limited and less versatile than the more
modern techniques. It is the author's opinion that barrel tumbling no longer has any
Place in a modern manufacturing operation.
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3. The most standard mechnical finishing process in use by industry today is .:.
vibratory deburring and surface conditioning. There are many, many manufacturers of :
equipment, media and compounds. There has been much excellent material published ':
describing both bowl and tub type vibratory machines. Fully automated vibratory ,I
systems are available, both for in-line and flexible manufacturing.
High energy mass finishing is, by definition, a process where the energy created
within the mass in a container is greater than standard vibratory processing. The _
initial objective for developing high energy mass finishing was to have much shorter ,
process cycles than vibratory (which, in some instances, can be a matter of many
hours). An additional reason for development of some high energy processes is for ;
more efficient use of. the energy and better process control. With some modern systems
it is easy to adjust energy level:
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maximum energy can be used for very fast deburring g
edge radiusing and metal removal, then there may be an automatic change to a more :,
gentle process to refine edges and surfaces.
Some high energy processes have finishing capabilities extending beyond those of
the lower energy techniques.
1:
A major limitation of both barrel tumbling and vibratory 2
finishing is that there is invariably some impingement action as well as a rubbing 2
motion. This clearly limits the ultimate surface finish capability and the ability to
handle high precision and fragile components. There is no impingement action with
3
some high energy processes.
THE HIGH ENERGYFINISHING PROCESSES
1. High Energy Vibratory FinishinK.
Some recent developments of vibratory equipment include standard rectangular tub :-
vibrators with high frequency and high amplitude drive systems; also the oval or :
elongated bowl machines.
Figure 1: High Energy Vibrator, Oval Type
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These latter units have higher frequency than standard machines and may have a shaped
base to build up pressure as media and parts move around the ends of the oval. High
energy vibrators may be as much as four (4) times faster than conventional vibratory
equipment. Generally, high energy vibratory machines are less versatile and less able
to produce fine finishes.
2. Centrifugal Disc Finishing.
First available to industry in 1970, it is only during the past five years that
efficient and reliable centrifugal disc finishing machines have been available for
general purpose deburring and surface conditioning.
equipment is shown in Figure 2.
The principle of centrifugal disc
The work container is a bowl loaded with parts and
media in fashion similar to that for vibratory equipment. The base of the bowl is a
disc, separate from the sidewalls.
high speed,
Action is obtained by the disc being driven at a
while the sidewalls of the bowl remain stationary. Rotation of the disc
forces the load within the container.outwards and accelerates the load so that parts
and media are traveling at a very high speed by the time they reach the periphery of
the disc. The sidewalls of the bowl then act as a brake; parts and media closest to
the wall decelerate fastest, as particles towards the center are pressed outwards with
considerable force, while sliding against their slower moving neighbors. The result
is an essentially smooth sliding action with little likelihood of any impingement.
Figure 2: Principle of Centrifugal Disc Finishing
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Critical to the success of CDF is control of the gap between disc and sidewalls,
which must be less than 0.010" for equipment to be capable of handling anything but the
simplest applications; and the gap must be kept controlled throughout the life of the
disc and the drum. Because of the substantial activity within the centrifugal disc
machine, disc and drum walls are subject to heavy abrasion. For this reason the
materials used for the building of vibratory equipment are not normally well suited to
CDF machines. Highly abrasion resistant alloys are to be preferred and result in life
of the disc being in excess of 5,000 hours for most applications. ..
Figure 3: Action with Centrifugal Disc Machine
to 8”
Centrifugal disc equipment is normally capable of handling part sizes from l/QV
length, and can achieve better quality of finish,
conventional vibratory methods.
holding closer tolerances than
Process cycles are generally at less than one fifth
those of vibratory finishing. The cost of equipment is typically in the order of five
times that of a vibratory machine of similar capacity, so that equipment purchase is
frequently easily justified.
inspection and control.
CDF machines have open tops which facilitate in-process
Equipment is well suited to batch automation, as convenient
as any tub vibratory system.
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6. 3* Centrifugal Barrel Finishing.
Centrifugal barrel finishing was the first high energy mass finishing process.
It is the high energy process most generally used in industry today being the fastest,
the most versatile and that capable of achieving the finest finishes on precision and
fragile components.
Centrifugal barrel equipment is comprised of a number of drums mounted on the
periphery of a turret. The turret rotates at a high speed in one direction while the
drums rotate in the opposite direction at a slower speed. Parts and media are loaded
into the drums in fashion similar to that for the other mass finishing processes.
Turret rotation creates a high centrifugal force of up to fifty times earth's gravity
compacting the load within the drums into a tight mass. Rotation of the drums causes
activity of this tightly packed mass. The media slides against the parts being
processed, removing burrs and improving surfaces. Typically, centrifugal barrel
finishing is twenty to fifty times. faster than vibratory finishing, is capable of
handling more fragile parts, parts of closer tolerance and parts requiring very fine
finishes and very precise edge and corner radii.
.
PRINCIPLE OF CENTRIFUGAL BARREL PROCESS
FIG.2
XTION WITHINA CENTRIFUGAL BARREL WHINE
Figure 4: Principle of Centrifugal Barrel Finishing
Standard small CBF machines are less convenient to operate than vibratory
units normally having closed containers without capability for integral parts and
media separation. However, equipment cost is normally easily justified in comparison
to low energy equipment where process cycles are of several hours. More normal
justification for CBF machines is for applications where other mass finishing methods
do not achieve the desired results or where very high production with sophisticated
automation is needed.
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4. Other High Energy Mass Finishing Processes.
Most of the mass finishing processes can have action accelerated by combining the
standard process with either chemical or electro chemical action. These accelerated
processes are invariably somewhat special purpose, expensive and less easy to operate
and maintain. Their basic benefits are for deburring parts that cannot be handled by
conventional mass finishing: deburring or finishing the inside of parts, very deep
holes and recesses.
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Spindle finishing may also be classified as a high energy mass finishing process.
Because parts must be fixtured, spindle finishing is less versatile than the other
techniques. For deburring regular shaped parts which are easily fixtured, spindle
equipment has been proven to be of substantial benefit and equipment has been
available for as long as vibratory machines. Because the process is well established
and much good information is already available, it will not be discussed further in
this paper.
AUTOMATION
In-line automated vibratory finishing systems have been available for some years.
Figure 5 shows an automated tub vibratory system where parts and media are loaded into
one end of the tub vibrator and exit at the other. Parts to go on for further
processing while the media is reclassified and then returned to storage, or returned
directly to the load end of the machine. Some modern systems of this type are using
high amplitude and high frequency vibration, but energy level is substantially below
that which can be achieved by CDF and CBF.
Figure 5: Automated Tub Vibrator
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Continuous in-line vibratory systems offer excellent automation for deburring a
single product for a very limited range, where parts can be satisfactorily finished
with process cycles of less than 30 minutes. Automated batch vibratory equipment is
used where greater versatility is needed and where process cycle exceed 30 minutes -
even with the higher energy vibratory systems.
Flexible automation is much newer for the mechanical finishing processes, as with
other manufacturing operations. Figure 6 shows what was probably the first flexible
mass finishing system ever installed. This system was built to deburr and finish a
multiplicity of missile components in a number of tub vibratory units. The unit has a
programmable controller which selects the appropriate machine, media, compound and
process cycle for components coming into the system. At the end of process cycle,
parts and media are unloaded, the media reclassified and returned to the appropriate
storage unit while parts are rinsed, passivated and dried. The complete system
typically handles 100 different part numbers in any single shift, parts range from
l/4" maximum dimension to over 2 feet; some require fine finishes, others very heavy
deburring. There are eight different types of media and four compounds which may be
used in any of the eight machines. Control of media size, process cycles, mix of parts
and media, machine vibration, etc., are all held plus or minus 2% of standard.
Figure 6: Flexible Automated Vibrator System
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Automation of Centrifugal Disk and ?entr Lfugal Barrel Prccesses.
Neither the centrifugal barrel nor the centrifugal (disc have been adapted for in-
line automation. There are two reasons for this; the first is that cost of building
equipment with ccntinuing process capability is very high; the second is that the
basic benefit of both processes is versatility. Each can handle a wide range of
components to achieve a wide range of edge and surface conditions. The processes are
therefore intrinsically well suited for fLexibLe autcmation but not in-line. Due to
its greater flexibility, higher speed and ability to achieve finer finishes,
developments of automated CBF have been greater than centrifugal disc, but centrifugal
disc processes can be semi-automated at lower cost, and therefore fulfills a very
important function within industry.
Automated Centrifugal Disc Processes.
Figure 7 shows centrifugal disc finishing equipment with semi-automated
handling. Equipment is available in sizes ranging from 1 to 20 cubic foot capacity
(parts and media load). Some machines are designed for the complete bowl to tip,
unloading parts and media, others with a door in the side of the bowl which opens to
allow parts and media to flow out. The machine has an open top bowl so that semi-
automated material handling is simple in either case. More sophisticated material
handling and controls are used where systems incorporating a number of machines are to
be installed.
Figure 7: Semi Automatic Centrifugal Disc Machine
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The CDF machine in Figure 7 is loaded by feeding the correct proportion of parts
and media through the open top above the bowl. Most modern CDF machines have
infinitely variable speed disc drive so that the process cycle is programmed to run
first at high speed for maximum deburring and abrading, then switching automatically
to a slower speed in order to refine surfaces. Automated compound addition is simple -
as for vibratory equipment. Compound may be automatically switched: a cutting
compound initially, followed by a "coloring" compound while the machine is running at
its slower speed.
At the end of the process cycle the door in the side of the bowl opens while the
machine is running at slow speed, feeding parts and media out into the material
handling system. In the case of the machinery shown this is a hoist pan which then
lifts parts and media to feed the total load into a separator where parts exit from the
system and media feeds back into the centrifugal disc bowl.
satisfactory if there is
Such a system is entirely
no need for frequent change of media nor for media
reclassificsation, and if operator addition of fresh media is acceptable. For more
versatile automated systems it is normal to have single material handling system
servicing a number of machines; incorporating media classification after parts-media
separation; media storage and selection, and parts drying.
programmable controller is normally easily justifiable.
With such systems a simple
Automated Centrifugal Barrel Processes
The simplest centrifugal barrel equipment with any degree of automation is that
shown in Figure 8(a).
media and water.
This equipment has two work containers to be loaded with parts,
Turret and drums rotate in a horizontal plane and there is an opening
at the center of each drum.
speed for maximum action,
During the process cycle the machine can be run at a high
then automatically switched to a slower speed for fine
finishing. Water and compounds are added through the center of the turret to
distribute equally to each of the drums. Abrasive compound may be rinsed out and then,
when the machine is running at slow speed, burnishing or finishing compound is added.
Hence, a deburring cycle followed by super finishing can be automatically combined
into a single process.
Figure 8(a): Small CBF Equipment
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11. CBF is the fastest high energy process; that is, it has greatest capability for
heavy burr removal, edge and corner radiusing, and stock removal. It also has
capability to obtain the finest finishes, and it can handle the highest precision and
most fragile components. The capability to switch from maximum abrasion to very fine
finishing frequently permits semi-automatic CBF Machines to combine in a single
process cycle that which would take three or even more processes in other mass
finishing equipment.
Figure 8(b): Inside View of Small CBF Machine
With the small CBF machine described above, drums are removed from the machine
and replaced with preloaded drums for maximum machine utilization. Material handling
systems for reloading the drums are built to suit individual company needs, dependent
upon the selection of parts to be processed, and the variety of media and compounds to
be used. This particular machine handles a total load of one cubic foot parts and
media mix so that it is normally not economical to utilize sophisticated material
handling nor automated drum removal and replacement.
For high production deburring and finishing, complete automation of CBF
equipment becomes more easily justified and there are a number of machines and systems
available:
The machine shown in Figure 9 is a machine which is easily totally automated.
This machine has two drums, capacity of up to 350 lbs. in each. The machine is
programmed to start running at a slow speed, feeding parts, media, compound and water
into the machine through the tube at the center top of the turret. This load gets
equally distributed to each of the drums. The machine is then switched to the
appropriate high speed for the deburring or heavy stock removal cycle; then, as with
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the machine prt?Viously described it will normally be switched to slower speeds and
have compound change for fine finishing. At the end of the process cycle, dump plugs
in the base of each of the two drums automatically open to feed the total load into the
conical base of the machine. The load is then metered out of this cone into separating
equipment, usually media reclassification, parts, dryers, media storage, etc. The
machine is ready to accept its next load.
Figure 9: Automatic CBF Machine
Larger systems than that described above are available. Figure 10 shows a
machine with total capacity of up to 1500 lbs. of parts and media with somewhat
simpler, but more versatile material handling. With this type of equipment it is
possible to run different parts in each of the two drums. While one load of parts is
being processed the next load is preloaded into storage conveyors mounted on the top
of the machine. Immediately one load is finished and unloaded, the second is metered
into the machine and the equipment starts up. Typically reloading cycle is less than 2
minutes, process cycles normally range from 10 to 30 minutes.
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13. Figure 10: Automatic CBF Machine
Still larger CBF equipment is available with capacity of 3,000 lbs. parts and
media per load. Of similar configuration to the two machines just described equipment
has capability of handling many thousand pounds of finished parts per hour, so that
sophisticated material handling and automation can be easily justifiable.
A completely automated system built to handle production from two large CBF
machines is shown in Figure 11 and 11(a). This system is designed to handle a range of
different parts requiring deburring and finishing at a number of different stages
during the manufacturing cycle. Parts and fresh media enter the system from the
"smart carts" - the material handling system for the complete plant. Parts are fed
direct into the storage unit, media are fed via the separator into their storage
units. In operation, loads are made up by weighing the correct proportion of parts and
media out of the storage units, controlling the load plus or minus 2 lbs. Total load
is conveyed to a bi-directional conveyor to feed into one of the holding hoppers (one
for each machine). A second drum load is fed onto the bi-directional hopper. This
preloading takes place while the machines are in operation with a previous load.
When process cycle of one of the machines is complete it stops and automatically
indexes for one of the drums to be located directly over the separator. Parts and
media are fed out onto the separator, parts exiting through a washing and drying unit
back into the plant automation system. Media are reclassified and appropriate sizes
returned to storage.
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14. Figure 11: Automation for large CBF Machine
Control of this system is by programmable controller which is coupled to the
plant automation control computer.
Systems such as this are capable of handling a range of different components in
very large quantities. Equipment such as this is normally justified by the direct
cost savings; saving of floor space and labor; with further benefits of reduced work
in progress and improved inventory control. In practice the major benefits of these
systems once installed are improved consistency of quality, and improved customer
service. The totally automatic finishing system is new to industry, and the real
15. costs of edge and surface condition inspection; rework and faiiilres in service
resulting from poor finish are not normally appreciated until after lut~2mated system
is installed and the benefits become apparent. Similarily the delays that occur in
the traditional finishing shop are not always noticed by management :Intil the old
mechanical finishing department ceases to exist and the automatic system is installed.
Figure 11(a): Automation for large CBF Machine
Figures 12 and 13 show a highly sophisticated flexible CBF system capable of
finishing a very wide variety of parts with total control of all process parameters.
This type of system comprises a series of 4 drum CBF machines. Drums are approximately
18" x 18" , and each has capacity of about 2 cu. ft. of parts and media. Drums are
removable from the machines for reloading purposes. With this system a robot removes
the barrels from the CBF machine and transports them to the material handling system.
Machines can be completely reloaded in 5 minutes, process cycles normally range from
15 to 30 minutes.
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The CBF robot transports the drum to a lid remover unit and then to the central
material handling system. This system is designed for maximum flexibility and to
handle the most delicate and fragile parts with no possibility of their being damaged.
Drums are emptied by rotating them about the center lip of the opening onto the
separating conveyor so that there is no falling or impingement action. The separator
is multiple tier so able to handle wide variety of parts and media and also very
closely reclassify the media. Media are returned to storage; this particular system
having capability to handle eight different types. Loading of drums is very precise,
typically plus or minus 1 part, typically plus or minus l/2 lb. of media, exact water
level and compound addition.
The system is totally automated operating from a programmable controller. There
may be as many as 16 different components being processed simultaneously with 4
different types of media in use; different compounds, different process times and
speeds. The most advanced flexible mechanical finishing system in industry today.
Figure 12: Flexible CBF System
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17. Modern mechanical finishing processes do exist to replace most manual operations;
to reduce cost and improve product quality compared with the older techniques that are
still so much in evidence in U. S. industry. Opportunities to automate the deburring
operations are almost as good as for the machining operations, and there is no excuse
for industry to consider automating machining without giving similar consideration to
mechanical finishing.
Mass finishing is the standard mechanized deburring and surface conditioning
process. High energy mass finishing is a group of processes which should be in far
more general use. Automated high energy mass finishing is proving of substantial
benefit in several industries with substantially greater return that that originally
anticipated. Most of the metal working industry can benefit from the recent develop-
ments of these processes.
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CONCLUSIONS
Figure 13: Another Flexible CBF System
The metal working industry typically spends between 5% and 10% of total
manufacturing cost on mechanical finishing operations. Development of machining and
forming operations for improved technology and greater automation has been considered
an essential task of the manufacturing engineer for more than a decade. Although the
finishing operations may frequently be as costly as those of machining and forming,
the efforts to develop better and more automatic finishing processes are much more
recent and much less general.
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BIBLIOGRAPHY
Hignett, J. B. "Mechanical Finishing - The Future of this New Technologyll, SME
Technical Paper MR81-383.
Hignett, J. B. "High Energy Mass Finishing', SME Technical Paper MR82-264.
Obrzut, John J. 'Processes Polish Up on Mechanical Finishing", Iron Age Magazine,
6/6/83.
Rhoades, L. J. "Cost Guide for Automatic Finishing Processes', SME Book (edited by L.
J. Rhoades), 1981.
"Flexible Mechanical Finishing System", Products Finishing Magazine, i/i/83.
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