Recent advances in spindle finishing technology have expanded its production capabilities. High pressure spindle finishing and continuous spindle finishing allow for faster cycle times. High pressure spindle finishing uses baffles and domes to increase media velocity and confinement, generating higher finishing forces for faster removal rates up to 5-10 times faster. Continuous spindle finishing uses multiple spindles on a rotating head to keep parts immersed continuously, increasing output by up to 100% compared to standard spindle machines where spindles pivot in and out of the media.

1. w. u
1981
@ ALL RIGHTS RESERVED
MR81-391
New Developments In
High Pressure Spindle Finishing
abstract
Recent equipment design advances in spindle finishing has expanded
and enhanced the production capabilities in the finishing of a wide
variety of parts. High pressure spindle finishing and continuous
spindle finishing are recent advancements and are discussed in detail.
author
Kent R. Olsen
Director, Research & Development
Almco Division/King-Seeley Thermos Co.
Albert Lea, Minnesota
conference
Deburring & Surface Conditioning ‘81
September 30-October 2, 1981
New Orleans, Louisiana
index terms
Abrasives
Deburring
Finishing
Grinding
Society of Manufacturing Engineers l One SME Drive l P.O. Box 930
Dearborn, Michigan 48128 l Phone (313) 271-l 500

2. ABSTRACT
Recent equipment design advances in spindle finishing has expanded and enhanced
the production capabilities in the finishing of a wide variety of parts. High
pressure spindle finishing together with continuous spindle finishing are recent
advancements and are discussed in detail.
INTRODUCTION
The basic spindle finishing concept is not a new concept, however, its use has
become more commonly accepted over the past decade due to the distinct precision
finishing capabilities of this process. The use of the spindle machine had a
relatively slow start, however, the momentum has substantially increased in recent
years as processing techniques, materials and tooling have constantly been expanded
upon and refined to offer greater process capabilities. These increased processing
capabilities have broadened the scope of potential applications. This has allowed
for industries recognition and acceptance of the spindle finishing concept as a
primary consideration in the finishing and deburring processes. Recent additional
advances in equipment design offer greatly increased process and production
capabilities which will further enhance spindle finishing applications.
PROCESSING PRINCIPLES
The basic spindle finishing concept basically consists of a circular rotating
tub which contains a loose abrasive media, the work piece is fixtured on a rotating
spindle which is lowered into the rapidly moving abrasive slurry. The resulting
effect is like a "form fitting grinding wheel" which flows over and around the part
to remove burrs and improve surface finish.
This is the basic principle of the spindle finishing concept of which there
are many variations in equipment designs and processing techniques. These variations
can offer a wide variety of finishing solutions for many parts.
CAPABILITIES AND ADVANTAGES
Spindle finishing capabilities and advantages are numerous, however, the basic
points are as follows:
1. Precision - Precision finishing of your workpiece in an easily operated
machine --- not a high degree of skill required as may be
in hand finishing.
2. Repeatability - Process repeatability is easily maintained through very
elementary adjustments and process procedures.
3. Short Time Cycles - Short time cycles due to aggressive centrifugal action
of form fitting grinding wheel type action.
4. No Impingement - Individual fixturing and holding of part assures no part
damage from contact.
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5. Low Materials Cost - Low media cost, as media basically only wears when
in contact with workpiece.
6. Discriminatory - Fixturing allows to position workpiece so as to direct
finishing media flow into areas needing the most work.
Also, it-is possible to mask areas where no work is
desired.
LIMITATIONS
As in every process, there are some limitations to the use of the spindle
finishing concept which should be recognized in order to have a good understanding
of the process. Some of the limitations are as follows:
1. Production - Production output is generally less when compared to other
means of mass finishing (such as vibratory finishing) due to
parts individually fixtured for process. However, time
cycles are generally short.
2. Labor - It is generally necessary for an operator to be in attendance to
operate machine at all times. The speed at which an operator
replaces the finished part with an unfinished part and returns
the part to the finishing mass is critical to production.
3, Fixturing - Each individual part needs to be fixtured or held for
processing.
4. Size - The size of the part to be processed is limited by the size of
equipment that has been selected. Very large parts are not
generally considered as practical for spindle finishing.
New advances in equipment design have reduced some of the major limitations
of spindle finishing concept. These new advances specifically are "High Pressure
Spindle Finishing" and "Continuous Spindle Finishing" to which the rest of this
paper will be devoted.
HIGH PEESSHEE SPINDLE FINISHING
High pressure spindle finishing is a new concept in spindle finishing which can
generate reduced finishing time cycles on a variety of parts.
In order to explain this concept we need to first examine the standard type
spindle machine tub together with the variables that control finishing time cycles.
The typical cross section of a standard type spindle finishing tub is sho&n in
Figure #l. Basically, the standard tub offers a great deal of versatility in
finishing a large variety of sizes of parts.
The rate of finishing in this type of machine (Figure 81) largely depends on
the following factors:
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1. Media - The size and aggressiveness of the abrasive media has a direct
effect on the finishing rate. Media selection is very important
in establishing the optimum finishing cycle for the desired results.
Media selection is comprised of two major criteria, which are size
and aggressiveness.
Selection of the proper size of the media, several factors need to
be considered and are as follows: (a) the proper size is required
to probe into the areas that require finishing, (b) size selection
is required so that the media will not lodge in a part requiring
hand removal, (c) also size selection is important, as the larger
the particle size the greater the momentum the particle has when
it comes in contact with the workpiece, resulting in more work
being accomplished.
Selection of the proper aggressiveness of the media is important
so as to accomplish the desired work and also achieve the desired
resultant finish. Media is available in many forms and proper
selection is critical.
2. Velocity - The velocity of the media has a direct effect on the finishing
rates. Greater velocity is obtained by controlling the speed
of rotation of the spindle finishing tub. The greater the
velocity the greater the momentum of the media allowing more
work to be accomplished as the media comes in contact with the
work piece. There are definite limitations as to the maximum
RPM and resultant velocity that can be used in any process.
The controlling factors generally are as follows: (a) a physical
limitation generated as the media (Ref. Figure #l) can tend to
climb out of tub due to centrifugal force, (b) too high of speed
can throw media depending on part configuration, (c) part
damage could result on more delicate parts due to forces
generated from too high of speed.
Optimal tub rotational speed can be established by careful
laboratory tests.
3. Confinement - The confinement of the media has a direct effect on the
amount of work done on the workpiece. The positioning
of the workpiece close to the outer periphery of the tub
and close to the tub bottom increase the finishing rate.
The confinement of the media between the workpiece and the
tub reacts by not allowing the media to readily flow away
from the workpiece,which then applies more force from other
mass particles resulting in higher finishing forces and
consequently, more work is done.
There are limitations as to how close a part can be
positioned in relation to the tub and still maintain a
proper flow of media between part and tub. This distance
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is dependent on the size of the media used and part size
and configuration. Also, the amount of media in the tub
contributes to the amount of confinement offered, the
more the media in the tub the greater the resistance for
the media to flow around the part which increases pressure
and amount of work done on workpiece.
The optimum finishing process can only be determined by actually processing
the parts in a laboratory condition to establish the best possible combination of
these major variables to achieve the desired results. Proper selection of each of
these variables is critical and should be done in conjunction with an expert in
this field.
"High Pressure Spindle Finishing" principle is based upon the concept of
higher velocity and confinement of the media to generate greater finishing forces.
Figure f2 shows a standard type tub with a baffle installed, which basically allows
the spindle tub to be operated at a higher RPM as the baffle tends to force the
media back down into the workpiece pocket due to centrifugal force, The baffle
will allow substantial increases in the amount of work that is accomplished.
Figure 83 shows the same configuration of tub with additional dome added in
center of tub creating a pocket type effect, which does not allow the media to
readily flow into the center area of the tub. For small parts this would have
effectiveness mainly by holding the media into the pocket area,allowing the media
to recover in a shorter period of time, and creating a dense solid mass. For
larger parts which approach the cross section of the tub it would provide a high
degree of confinement and would generate high finishing forces resulting in short
time cycles.
Examination of the data shown in Figure #4 reveals that on a small part
(l-1/2" dia. ball in a 8" wide pocket) that the addition of the baffle increased
the metal removal rate 2.62 times and that the further addition of the center
baffle increased the finishing rates up to 3.04 times at 900 surface feet per
minute. Other tests have shown results of 5 to 10 times faster on larger parts,
The faster finishing rates that are afforded by the high pressure spindle
finishing concept, also allow the use of smaller finishing media to penetrate
small areas and provide better finishes without lengthening the time cycle beyond
practicality.
The high pressure spindle finishing machine is not without limitations, as
it does limit the size of the pact that can be processed. The machine is more
of a speciality machine than a standard machine. An example would be as follows:
FEATURES
Tub Diameter
Tub Depth
Maximum Part Diameter
Maximum Part Length
STANDARD
2SF-48A
48"
18"
18"
14"
HIGH PRESSURE
2SF-48HP
48"
18"
6"
8"
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Despite some limitations of the high pressure design fur parts that fall
within the size limitations, the benefits can be tremendous and well worth your
time to explore this concept.
The tub shown in Figure 1'15illustrates where the part is fixtured
horizontally and immersed into a rotating tub. This type of a tub can be very
aggressive, but does limit the size of part which can be processed. Due to the
shape of the tub very high RPM's can be achieved without loss of media because
of centrifugal force. Consequently, with the high velocity of the media a very
high finishing rate can be achieved. The length of the part is limited to
relatively short parts with respect to diameter,as the amount of work done away
from the wall towards the center rapidly diminishes due to both the confinement
and centrifugal force generated.
CONTINUOUS SPINDLE FINISHING
In the standard spindle machine such as shown in Figure #l or #5, the spindle
head pivots in and out of the mass for removal of the finished part and replacement
with a new unfinished part. The time that the spindle is out of the mass is
unproductive time for that spindle plus you are dependent on the operator as to
how fast he unloads and loads the spindle. The importance of the unload and load
time is dependent on the length of the time cycle.
Another new spindle machine concept is that of the "continuous spindle
finishing" machine which has multiple spindles mounted on a rotating head
(see Figure #6 and 117). The obvious advantage of this arrangement is that there
is always parts in the finishing media all of the time. As the wheel rotates
around into the center area the operator unloads the finished part and loads an
unfinished part into the fixture. This not only allows for continuous finishing
of parts, but in addition allows the operator a more leisurely pace to remove and
replace the workpiece parts. This has resulted in much higher production
situations than formerly existed with the standard type spindle machines.
TOTAL
TIME
CYCLE
STANDARD
MACHINE ONLY
UNLOADTIME
STANDARD (2)
SPINDLE MACHINE
MAXIMUM
PRODUCTION
OUTPUT PC/HR
CONTINUOUS (2)
SPINDLE MACHINE
OUTPUT PC/HR
%
INCREASE
5 Sec. 5 720 1440 100%
10 5 480 720 50%
15 5 360 480 33%
20 5 288 360 25%
30 5 205 240 17%
45 5 144 160 11%
60 5 55 60 9%
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As illustrated in the chart is a comparison of production between the standard
two spindle finishing machine versus the continuous two spindle machine. The
production listed for the standard spindle machine is providing the operator always
meets the schedule of changing the part in 5 seconds whenever the spindle is
retracted. In actual production situations the productivity of the continuous
versus standard has proven to be much more significant than is shown on the chart
due to operator efficiency. As noted, the maximum effectiveness realized in the
shorter time cycles with the advantage diminishing as time cycles become longer.
However, the average time cycle in this type of a machine is generally in the 10
to 20 second range so substantial production increases can be realized.
In the continuous spindle finishing machine, such as shown in Figure 116, the
majority of the work is being performed as the part rotates to a position in the
finishing mass where it is closest to the tub bottom and side wall which would be
in line with the tub centerline.
Another approach is to index the spindle head rapidly into the work area for
work exposure. After a preset time cycle, the spindle head again indexes to bring
another part into the maximum work area and rotating the finished prices out of the
slurry. The advantage to this method is that the part is not moving while the
operator unloads the part and makes the unload and load operation easier for the
operator.
AUTOMATION
The continuous spindle finishing machine with the indexing mechanism is an
ideal machine to automate providing there is a large number of similar parts which
can be readily handled by a robot. By replacing the operator by a robot, the
operation now becomes highly desirable for today's high production society.
CONCLUSION
The spindle finishing concept has become a highly desirable finishing process
for precision type components. Recent advancements in equipment design, in the
areas of (1) high pressure spindle finishing and (2) continuous spindle finishing,
together with recent advancements in materials, offer an expanded finishing concept
with a lot of versatility to meet your finishing needs. Automation of a continuous
spindle finishing machine is now a very distinct possiblity for high production
situations.
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TAL REMOVAL ; SPINDLE FINISHING
TEST CONDITIONS:
16A Aluminum Oxide Media
23 RPM Spindle rotation
1 -l/2 diameter low carbon steel balls
2 minute time cycle
TEST RESULTS: COMPARISON OF METAL REMOVAL
1 FIG. 1 11 FIG. 2 II FIG. 3 I
. 1000
metal
removal
Iwl
Tub Speed IS.F.M.1
FIGURE 4.
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HIGH
FIGURE 5.
SPEED SPINDLE MACHINE
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