Note: Descriptions are shown in the official language in which they were submitted.
WO92/04151 ' ' PCT/US91/06114
METHOD AND APPARATUS OF
MACHINI~G WITH IMPROVED CHIP CONTROL
Field of the Invention
This invention relates to metal working
operations such as turning, milling, facing, thread-
ing, boring and grooving, and, more particularly, to a
method and apparatus for performing such metal working
operations at high speeds with improved chip control.
Backqround of the Invention
Most machining operations are performed by a
cutting tool which includes a tool holder and one or
more cutting inserts each having a top surface termi-
nating with one or more cutting edges. Thei tool
holder is formed with a socket within which a cutting
insert is clamped in place. The leading or cutting
edge of an insert makes contact with the workpiece to
remove material therefrom in the form of chips. A
chip comprises a plurality of thin, generally rectan-
gular-shaped sections of material which slide relative
to one another along shear planes as they are sepa-
rated by the insert from the workpiece. This shearing
movement of the thin sections of material relative to
one another in forming a chip generates a substantial
wo g2,04l51 2 ~ 8 9 0 ~ ~ PCT/US91/06114
. 2
amount of héat, which, when combined with the heat
.~, j .
produced by engagement of the cutting edge of the
insert with the workpiece, can amount to 1500-2000F,
or higher.
5Among the causes of failure of the cutting
inserts employed in prior art machining operations are
abrasion between the cutting insert and workpiece, and
a problem known as cratering. Cratering results from
the intense heat developed in the formation of the
lOchips and the frictional engagement of the chips with
the cutting insert. As the material forming the chip
is sheared from the workpiece, it moves along at least
a portion of the exposed top surface of the insert.
Due to such frictional engagement, and the intense
15heat generate in the formation of the chip, material
along the top portion of the insert is removed forming
"craters". I~ these craters become deep enough, the
entire insert is subject to cracking and failure along
its cutting edge, and along the sides of the insert,
20upon contact with the workpiece. Cratering has become
a particular problem in recent years due to the
development and extensive use of hard alloy steels,
high strength plastics and composite materials formed
of high tensile strength fibers coated with a rigid
25matrix material such as epoxy.
Prior attempts to avoid cratering and wear
of the insert due to abrasion with the workpiece have
WO92/04151
--3--
provided only modest incr~ases in tool life and
machining efficiency. One approach has been to form
inserts of high strength materials such as tun~sten
carbide. Although extremely hard, tungsten carbide
5 inserts are brittle and are subject to chipping which
can result in premature failure. To improve the
lubricity of inserts, such materials as hardened or
alloyed ceramics have been employed in the fabrication
of cutting inserts. Additionally, a variety of low
friction coatings have been developed for cutt1ng
inserts to reduce the friction between the cutting
insert and workpiece.
In addition to the improved materials and
coatings used in the manufacture of cutting inserts,
attempts have been made to increase tool life by
reducing the temperature in the "cutting area", i.e.,
the cutting edge of the insert, the insert-workpiece
interface and the area on the workpiece immediately
upstream from the insert where material is being
sheared to form chips.
One method commonly employed to cool the
cutting area is known as flood cooling which involves
the spraying of a low pressure stream of coolant
toward the insert and workpiece. Typically, a nozzle
disposed several inches above the cutting tool and
workpiece directs a low pressure stream of coolant
WO(12/04151 ~ ~8~ t~ PCT/US9t/06114
toward the workpiece, tool holder, cutting insert and
on top of the chips being produced.
The primary problem with flood cooling is
that it is ineffective in actually reaching the
cutting area. The underside of the chip which makes
contact with the exposed top surface of the cutting
insert, the cutting edge of the insert and the area
where material is sheared from the workpiece, are not
cooled by a low pressure stream of coolant directed
from above the tool holder and onto the top surface of
the chips. This is because the heat in such cutting
area is so intense, i.e., on the order 2000-F or
higher, that a heat barrier is produced which vapor-
izes the coolant well before it can flow near the
cutting edge of the insert.
Several attempts have been made to improve
upon the flood cooling technique described above. For
example, the discharge orifice of the nozzle carrying
the coolant has been placed closer to the insert and
workpiece, and/or fabricated as an integral portion of
the tool holder, to eject the coolant more directly at
the cutting area. See, for example, U.S. Patent Nos.
1,695,955; 3,323,195; and, 3,364,800. In addition to
positioning the nozzle nearer to the insert and
workpiece, the stream of coolant has been ejected at
higher pressures than typical flood cooling applica-
tions in an effort to break through the heat barrier
W092/0~15l 2 0 8 9 0 6 5 ~ jPCr/US9l/06l14
5--
developed in the cutting area. See U~S. Patent No.
2,653,517.
Other tool holders for various types of
cutting operations incorporate coolant delivery
passageways which direct the coolant flow across the
exposed top surface of the insert toward the cutting
edge in contact with the workpiece. In these designs,
a separate conduit or nozzle for spraying the coolant
toward the cutting area is eliminated making the
cutting tool more compact. Examples of this type of
design are shown in U.S. Patent Nos. 4j302,135;
4,072,438; 3,176,330; 3,002,140; 2,360,385; and, West
German Patent ~o. 3,004,166.
A common problem with apparatus of the type
disclosed in the patents mentioned above is that
coolant in the form of an oil-water or synthetic
mixture, at ambient temperature, is directed onto the
top surface of the insert toward the cutting area
without sufficient velocity to pierce the heat barrier
surrounding the cutting area. As a result, the
coolant fails to reach the interface between the
cutting insert and workpiece, and/or the area on the
workpiece where the chips are being formed, before
becoming vaporized. Under these circumstances, no
heat is dissipated from the cutting area to prevent
cratering. In addition, failure to remove heat from
the cutting area creates a significant temperature
:'
W092/041~ 0 8 ~ O ~ ~ ~ PCT/~S91/06114
differential between the cutting edge of the insert
which remains hot, and the rear portion of the insert
which is cooled by coolant, thus causing thermal
failure of the insert.
A failure to effectively reduce temperature
in the cutting area resuits in a number of disadvan-
tages and limitations in machining operations. As
discussed above, high temperatures cause insert
failure. This directly affects production speed in
several ways. In order to reduce temperatures, the
machine tools must be run at lower speeds, reduced
depths of cut and reduced feed rates, each of which
lowers productivity. If speeds are increased, the
downtime of the machine tool increases because the
inserts must be replaced more frequently. The less
tlme the insert is in the cut, the lower the produc-
tivity of a given machine tool. Overall productivity
is therefore limited by the useful life and perfor-
mance of the cutting inserts which have historically
lagged far behind the operating speeds of machine
tools.
Another serious problem in present day
machining operations involves the breakage and removal
of chips from the area of the cutting insert, tool
holder and the chucks associated with the machine tool
which mount the workpiece and tool holder in place.
If chips are formed in continuous lengths, ~hey tend
WO9~/04151 2 ~ 8 9 ~ ~ ~ PCT/US91/06114
to wrap around the tool holder or chucks which can
lead to tool failure or at least require a periodic
interruption of the machining operation to clear the
area of impacted or bundled chips. This is particu-
larly disadvantageous in flexible manufacturingsystems in which the entire machining operation is
intended to be completely automated. If a worker must
regularly clear impacted or bundled chips from the
tool holders and/or chucks of such systems, their
efficiency is drastically reduced.
one attempt to solve the problem of removal
and breakage of chips involves the formation of chip
breaker grooves in cutting inserts. Chip breaker
grooves extend inwardly from the exposed top surface
of t~le insert, and are spaced from the cutting edge.
The chip breaker groove engages chips as they are
sheared by the cutting edge from the workpiece, and
then turn or bend them upwardly from the exposed
surface of the insert so that the chips tend to
fracture.
While acceptable performance has been
achieved with some chip breaker groove designs in some
applications, variables in machining operations such
as differing materials, types of machines, depths of
cut, feed rates, speeds and other factors make it
virtually impossible for one chip breaker groove
design to be effective in all applications. This is
W2~ rj 5 - PCT/US91/0611~
-8-
evidenced by the multitude of chip breakers now
available. ~el~cti~n of a suitable cutting insert for
a particular machining application, if one exists at
all, is a difficult and continuing problem.
S In an effort to improve upon the chip
control obtained with cutting inserts having chip
breaker grooves, apparatus have been designed to
control and break chips hydraulically, i.e., with a
stream of coolant which is delivered to the cutting
area at high speeds compared to flood cooling devices
and other prior art systems. For example, my prior
Patent No. 4,621,547 discloses a tool holder in which
the clamp or cap which secures the insert to the tool
holder is formed with a coolant delivery passageway
for directing coolant at high speed toward the cutting
edge of the insert. Coolant is accelerated within the
clamp or cap and is preferably discharged at a speed
of greater than about 250 feet per second in an effort
to pierce the heat barrier developed in the cutting
area and flow beneath the chips being formed from the
workpiece.
It has been found that the apparatus dis-
closed in Patent No. 4,621,547 effectively breaks
chips into relatively small lengths, but only under
specific operating parameters and for certain types of
materials. Specifically, where the discharge outlet
of the coolant delivery passageway is maintained at a
WO92/04151 2 ~ 8 9 0 6 5 ` ` PCT/US91/06114
_9_
distance of about .040 inches to .440 inches from the
cutting edge of the insert, and the feed rate is set
in the range of about .004 to .025 inches, a coolant
jet having a velocity of at least about 250 feet per
second is effective to break chips into small lengths
for some materials. A potential problem with this
apparatus, however, is that the parameters within
which the apparatus is effective cannot always be
maintained for different types of machining opera-
tions. In addition, the apparatus is relatively
ineffective in machining harder materials at higher
spe~ds and feed rates because of the elevated tempera-
tures associated with such machining operations.
This system has been improved in my U.S.
Patent No. 4,829,859 which discloses a method of
machining in which a high velocity, mixed phase
coolant stream is directed toward the cutting edge of
the insert and workpiece to lower the temperature of
the cutting area and to break the material sheared
from the workpiece into very small chips or particles.
The "mixed phase" coolant stream comprises a combina-
tion of a water-oil coolant, carbon dioxide gas and
ice particles which is formed by intermixing a coolant
stream with liquified carbon dioxide or similar fluid
within an insert clamp prior to discharge into the
cutting area. The heat produced by shearing material
from the workpiece is transferred from the workpiece
W092/04ts1 2 0 8 9 0 6 ~ ~ PCT/~S91/06114
--10--
to the mixed phase coolant stream, thus converting the
ice particles within the stream from solid to vapor
phase. In the o~urse of vaporization, the ice parti-
cles underg'o an explosive, volumetric expansion which
produces a force capable of assisting in the shearing
the material from the workpiece, and of breaking such
sheared material into minute particles.
It has been found that the method and
apparatus disclosed in U.S. Patent No. 4,829,859
enables machining operztions to proceed at much higher
feed rates and speeds, and at greater depths of cut,
while obtaining excellent chip control. But one
potential limitation of this system is that liquified
carbon dioxide or similar liquified gas is required to
lS form the mixed phase coolant stream. Liquified gases
are available commercially in tanks which must be
stored on the premises of the machining facility
before use, replaced at regular intervals during
production and then stored for shipment back to the
supplier after they are emptied. These handling and
storage requirements can create problems, particularly
for smaller machining facilities. In addition, a
relatively large quantity of liquified gas is needed
to perform the machining operation, especially on
harder materials, and this can increase the expense of
the machining operations.
W092/04l51 2 089b6~ PCT~US9~/06114
Summary of the Invention
It is therefore among the objectives of this
invention to provide^ a method ~nd apparatus for
machining which provides for excellent chip control,
which permits machining operations to be run at high
speed, which is easily adapted for machine tools of
different configuration and which is relatively
inexpensive to operate and maintain.
These objectives are accomplished in a
nozzle apparatus adapted for use with machine tools of
different configuration, which perform different
machining operations, comprising a nozzle body having
a nozzle insert which is mounted within an outlet
passageway formed in the nozzle body at its intersec-
tion with a coaxial, larger diameter inlet passagewayconnected to a source of coolant, e.g., a water-oil
mixture. The nozzle insert is constructed to acceler-
ate the stream of coolant received from the inlet
passageway, and to induce the formation of shock waves
in the course of passage of the coolant stream through
the interior of a nozzle body. These shock waves
increase the energy and velocity of the coolant stream
so that it is effective to pierce the heat barrier
developed in the cutting area to reduce the tempera-
ture thereat and to assist in the breakage of chipsfrom the workpiece.
:
w~ 92/04151 2 Q 8 9 06 S PCT/US91tO6114
-12-
In the presently preferred embodiment, a
portion of the nozzle body of this invention is
constructed in ~ccordance with the teachings of my
Patent No. 4,830,280, the disclosure of which is
incorporated by reference ,in its entirety herein. The
inlet passageway formedj i~ the nozzle body is adapted
to connect to a so ~ ce of conventional water-oil
coolant through a supply line and pump. The outlet
passageway is formed with a smaller diameter than the
inlet passageway, and is coaxial with and intersects
the inlet passageway forming a shoulder at such
intersection. A donut-shaped recess is formed in such
shoulder, and this recess is concentrically disposed
about the nozzle insert carried within the outlet
passageway in the nozzle body. Preferably, the nozzle
insert is ~ormed with a throughbore having a radially
inwardly tapering throat portion beginning at an
angled inlet end of the throughbore, and a minimum
diameter portion at approximately the midpoint of the
throughbore. The throat portlon and minimum diameter
portion collectively form an the inlet section of the
nozzle insert and are disclosed in Patent No.
4,830,280. As described below, the nozzle insert of
this invention is modified to include a radially
outwardly tapering outlet portion which extends from
the midpoint of the throughbore to its outlet end.
WO~2/(14151 2 0 8 g ~ ~ 5 PCT/US9t/06114
-13-
As described in detail in U.S. Patent No.
4,830,280, the inlet section of the nozzle insert is
effective to accelerate the coolant from the inlet
passageway in the nozzle body through the reduced
diameter portion o~ the insert with minimal losses due
to drag or turbulence. A portion of the coolant
stream which flows into the inlet passageway of the
nozzle body is made to enter the donut-shaped recess.
This portion of the coslant stream is rotated within
the recess in the same direction as the flow of
coolant through the nozzle body. As the main body of
the coolant stream moves through a transition area
between the larger diameter inlet passageway and the
smaller diameter outlet passageway, the rotating
portion of the coolant within the recess impacts the
outer boundary of the main body of coolant and func-
tions to both guide and accelerate it into the inlet
portion of the throughbore in the nozzle insert.
The combined effect of the rotating coolant
within the recess, and the radially inwardly tapering
inlet portion of the throughbore, is to eliminate much
of the turbulence and drag which can occur as the
coolant stream moves from the larger diameter inlet
passageway into the smaller diameter outlet passage-
way. As a result, the coolant stream is efficientlyaccelerated from the inlet passageway to the outlet
passageway, and its actual velocity at the reduced
W092/041~1 2 0 8 9 ~ 6 ~ PCT/US~1/06tl4
-14-
diameter portion of the throughbore in the nozzle
insert more nearly approaches the theoretical velocity
which would b~`i?o~tained absent any losses due to drag
~,
or turbule~ce.
Depending upon the flow rate and pump
pressure at which the coolant stream is introduced
into the nozzle body, it is believed that the coolant
stream is accelerated to a velocity in the range of
about lO00 to 1200 feet per second (fps) in the area
of the reduced diameter portion or midpoint of the
throughbore in the nozzle insert. It is theorized
that such acceleration of the coolant stream produces
a condition wherein a shock wave can be produced in
the coolant stream in which at least some portion of
the dissolved gases therein, i.e., nitrogen, oxygen,
carbon dioxide, etc., are caused to evolve or escape
from the stream and form bubbles.
An important aspect of this invention is
that the formation of the shock wave within the
coolant stream is induced and enhanced by the pro-
vision of an expansion chamber defined by the radially
outwardly tapering outlet portion of the throughbore
in the nozzle insert, and a larger diameter discharge
tube which is inserted within the outlet passageway of
the nozzle body immediately downstream from the nozzle
insert. This expansion chamber provides for volu-
metric expansion of the coolant stream as the
WO~2/04151 2 ~ 8 9 ~ ~ ' P~T/US9t/06114
-15~
dissolved gases evolve or escape from solution, and
thus allows the shock wave formed within the
throughbore of the nozzle insert to propagate
downstream. It has been found through experimenta~
tion, that the wall in the nozzle insert formed by the
radially outwardly tapering portion of the throughbore
therein is preferably oriented at an included angle of
about 8- with respect to the longitudinal axis of the
throughbore to permit the coolant stream to expand
l~ radially outwardly to a sufficient extent to avoid
undue damping or choking of the shock wave developed
within the nozzle insert.
The coolant stream including bubbles is
transmitted from the expansion chamber downstream
through the discharge tube of the nozzle body.
Preferably, the discharge tube has a constant diameter
~rom the nozzle insert to its discharge outlet where
the outlet passageway in the nozzle body terminates.
It is theorized that while gaseous bubbles are allowed
to form immediately downstream from the reduced
diameter section of the nozzle insert, i.e., within
the expansion chamber, these bubbles will tend to
dissolve back into the coolant stream in the course of
movement through the remainder of the discharge tube.
It is believed that this occurs because the discharge
tube functions to confine further expansion of the
bubbles soon after they are allowed to form, causing
Wo92/~4151 2 0 8 9 0 6 ~ PCT/US91/06114
-16-
the ~ubbles to burst or collapse and re-enter the
coolant stream.
It is presently believed that a second shock
wave is then formed in the coolant stream in the
course of its passage through the outlet of the
discharge tube into atmosphere.~As the coolant stream
is emitted from the discharg ~ ube to atmosphere, the
dissolved gases within th~coolant stream are again
allowed to escape and form bubbles. It is theorized
that this produces a second shock wave within the
coolant stream which accelerates it outwardly from the
discharge outlet, and toward the cutting insert and
workpiece being machined, at an increased velocity
which may be in excess of 1200 fps. The energy and
velocity of the coolant stream created by the second
shock wave is utilized to assist in the machining
operation, i.e., the coolant stream is directed onto
the top surface of the insert toward its cutting edge
and functions to both cool the cutting edge and
workpiece, and to assist in the Dreakage of chips into
relatively small lengths or par~icles as material is
removed from the workpiece. Preferably, the coolant
stream or jet emitted from the discharge outlet of the
nozzle body is directed at an angle of about 20 upon
the top surface of the insert and is oriented to cover
the entire width of the chip being sheared from the
workpiece.
WO92/04151 2 0 8~9 0 6 ~ PCT/US9t/06114
-17-
In some applications, particularly in
connection with the machining of harder materials, it
is desirable to provide at least some initial cooling
o~ the workpiece in the area immediately above the
cutting insert where material is about to be sheared
from the workpiece. In one presently preferred
embodimént, an air jet passageway is formed in the
nozzle body having a discharge outlet which is
oriented to direct pressurized air to this area on the
workpiece. A source of pressurized air, i.e., shop
air, is preferably directed into a manifold and then
through !a line connected to the air passageway within
the nozzle body. In some instances, a small quantity
of liquified gas, such as liquified nitrogen, is
introduced into the mani~old with the pressurized air
to reduce the temperature of the pressurized air prior
to introduction into the air passageway of the nozzle
body. The operation of the manifold and the addition
of liquified gas therein is controlled by a controller
such as any commercially available personal computer
or the like, which also controls the supply of coolant
into the inlet passageway of the nozzle body.
This invention therefore provides a number
of advantages over prior methods of machining intended
to increase speeds and feeds, and control the forma-
tion of chips. No liquified gas or other cooling
means are combined with the coolant stream as in
wo 92/04151 2 0 8 9 0 6 ~ PCT/US9t/06114
-18-
Patent No. 4,82~7859. This reduces costs, and the
,, ~, ~
problems assoclated with storage of a large number of
containers of liquified gas. The substantial energy
and velocity produced in the coolant stream is
obtained by promoting the formation of shock waves
which result, in part, from the efficient transfer of
the coolant stream from a larger diameter inlet
passageway to a smaller diameter outlet passageway in
the nozzle body with minimal turbulence and drag
losses. High coolant stream velocity is therefore
achieved by the efficiencies obtained with the struc-
ture herein, which permits the use of a relatively
small pump operating at relatively low flow rates.
More expensive, higher pressure pumps are not required
for many machining operations.
Description of the Drawinqs
The structure, operation and advantages of
the presently preferred embodiment of this invention
will become further apparent upon consideration of the
following description taken in conjunction with the
accompanying drawings, wherein:
Fig. 1 is a partial isometric view, exag-
gerated for purposes of illustration, showing a tool
holder and cutting insert for performing a turning
operation, including the apparatus of this invention;
Fig. 2 is a cross sectional view taken
generally along line 2-2 of Fig. 1; and
WO92/04t5l 2 ~ 8 ~ 0 6 ~ PCT/~S91/06114
~19--
Fig. 3 is an enlarged cross sectional view
of a portion of the nozzle body illustrated in Eig. 2.
Detailed Descri~tion of the Invention
Referring now to Figs. 1 and 2, one present-
1~ preferred embodiment of the nozzle apparatus 10 ofthis invention is illustrated for use with a turning
holder 12 performing a turning operation on a work-
piece 14. The workpiece 14 is mounted in a chuck of a
machine tool (not shown) which is adapted to rotate
the wor~piece 14 in the direction indicated in Fig. 1.
While a turning holder 12 is illustrated in Fig. 1, it
should be understood that the method and apparatus of
this invention is applicable for use in other machin-
ing operations such as milling, boring, cutting,
grooving, threading, drilling and others, and the
turning operation illustrated is shown solely for
purposes of describing the present invention.
The turning holder 12 comprises a support
bar 16 formed with a seat adapted to receive a cutting
insert 18 having an upper sur'ace 20 terminating with
a cutting edge 22. The cutti.ng insert 18 is secured
within the seat of the support bar 16 by a clamp 24 of
conventional design. The nozzle apparatus 10 is
mounted with respect to the upper surface 20 of insert
18 to direct a high energy, high velocity coolant
stream toward the cutting edge 22 of insert 18 and the
workpiece 14, as described in detail below. The
~ V ~ ~U J
W092/041s1 PCT/US91/06114
-20-
nozzle apparatus lO is pre~era~ly carried on the
turret ~f~t~hè`machine tool (not shown) by mounting
structure which is designed specifically for a partic-
ular machine. Such mounting structure forms no part
of this invention per se and i5 therefore not
described herein.
In the presently preferred embodiment, the
nozzle apparatus lO comprises a nozzle ~ody 26 formed
with an inlet passageway 28 connected by a line 30 to
a pump 32 which communicates with a supply of coolant
34. The pump 32 is connected to a controller 35 such
as a personal computer, microprocessor or other closed
loop controller, which, as described below, is opera-
tive to control the flow of coolant into inlet pas-
sageway 28. The term "coolant" as used herein is
meant to refer to any one o~ a variety of commercially
available liquid coolants employed in the machine tool
industry which generally comprise a mixture of oil,
water and other additives. The nozzle body 26 is also
formed with an outlet passageway 36 which is coaxial
with the inlet passageway 28. In the presently
preferred embodiment, the outlet passageway 36 has a
smaller diameter than the inlet passageway 28 forming
a shoulder 38 where such passaseways 28, 36 intersect.
As shown in Figs. 2 and 3, the nozzle body
26 is formed with an annular, donut-shaped recess 40
at the shoulder 38 formed by the intersection of the
WOg~/Q4151 P~T/US91/~6114
208901~
-21-
inlet and outlet passageways 28, 36. Preferably, the
recess 40 is formed with a generally U-shaped cross
section, although it is contemplated that other cross
sections could be employed for the purposes described
5 below.
In the presently preferred embodiment, the
outlet passageway 36 of nozzle body 26 is formed with
internal threads to mount a nozzle insert 42 and a
discharge tube 44. The nozzle insert 42 has a cylin-
drical-shaped, threaded outer surface 46 and an
hourglass-shaped throughbore 48. The shape of the
inlet portion of throughbore 48 is determined experi-
mentally, and.in accordance with the teachings of my
U.S. Patent No. 4,830,280, the disclosure of which is
incorporated by reference in its entirety herein.
Preferably, the inlet portion of throughbore 48
includes a rounded inlet end 52 which extends at least
partially into the outlet passageway 28, and a throat
portion 54 which tapers radially inwardly from the
inlet end 52 to a minimum diameter designated Do
located at about the midpoint 56 of the throughbore
48. As explained in U.S. Patent No. 4,830,280, the
exact configuration of this radially inwardly tapering
throat portion 54 is determined empirically by experi-
mentation, but it can generally be characterized as a
smoothly tapering polynomial curve extending between
: the inlet end 52 of throughbore 48 and the diameter Do
WO92/04151 2 0 ~ ~ 0 6 S PCT/~S91/06114
-22-
at the midpoint 56 of throughbore 48. This inlet
portion of the ~throughbore 48 in the nozzle insert 42
thus forms ~' vènturi, for purposes described below.
It is estimated that the axial distance between the
inlet 52 and midpoint 56 of throughbore 48 is approxi-
mately three times the diameter Do of the throughkore
48 at midpoint 56. See Fig. 3.
The discharge portion of the hourglass-
shaped throughbore 48 of the nozzle insert 42, i.e.,
downstream from the midpoint 56, is characterized by a
radially outwardly tapering discharge portion 58
extending from the midpoint 56 to the outlet end 60 of
the nozzle insert 42. It has been determined experi-
mentally that the wall of the throughbore 48 formed by
this discharge portion 58 should be tapered at
included angle ~ o~ about 8' measured between a line
62 extending parallel to the longitudinal axis of the
throughbore 48, and a line 63 which extends from the
midpoint 56 and is substantially coincident with such
wall of throughbore 48 formed along the discharge
portion 58. See Fig. 3. The axial distance of the
discharge portion 58 measured between the midpoint 56
and the outlet end 60 of nozzle insert 42 is pref-
erably on the order of about three times the minimum
diameter Do of the throughbore 48.
The discharge tube 44 is threaded into the
outlet passageway 36 of nozzle body 26 downstream from
W092/n4151 2 0 8 9 0 6 ~ PCT/US91/06114
-23-
the nozzle insert 42 and has an end 47 which abuts the
outlet end 60 of nozzle insert 42. Preferably, the
discharge tube 44 is cylindrical in shape and has a
constant diameter DE. The diameter DE of discharge
S tube 44 can be obtained with the following formula:
E Do + 2(tan. 8~
As shown in Figs. 2 and 3, and the discharge tube 44
has a discharge end 64 located flush with the terminal
end of the outlet passageway 36 which defines a
discharge outlet 65. In the embodiment illustrated in
the Figs., the axial length of the discharge tube 44
is on the order of about twelve times the smallest
diameter Do of the throughbore 48 of nozzle insert 42.
For some applications, as described below,
lS it is advantageous to employ chilled air in connection
with the machining operation performed with the nozzle
apparatus lO of this invention. For this purpose, the
nozzle body 26 is formed with an air passageway 66
connected by a line 68 to a cooling manifold 70. See
Figs. l and 2. This cooling manifold 70, in turn, is
connected to ~ source of pressurized air 72, e.g.,
shop air, and a tank 74 of liquified gas such as
liquified nitrogen. The controller 35 is operatively
connected to the liquified gas tank 74 and manifold 70
to control their operation as described below.
wo ~/o~1Sl 2 0 8 9 0 6~ ; PCT/US91/06114
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System O~eration
An initial objective in the operation of the
nozzle apparatus lO is to reduce turbulence and drag
in the flow of the coolant stream to and through the
inlet portion of the nozzle insert 42 in nozzle body
26 in order to assist in obt,alning maximum energy and
velocity of the coolant st ~ m 78 which is ultimately
ejected from the discharge'outlet 65 of tube 44 toward
the cutting insert 18 and workpiece 14. In this
respect, the nozzle apparatus lO of this invention
employs the teachings of my U.S. Patent No. 4,830,280
to transmit coolant from the supply 34 through pump 32
and line 30 into the inlet passageway 28, and then
through inlet portion of nozzle insert 42 within the
nozzle body 26.
In accordance with the teachings of Patent
No. 4,830,280, a relatively low velocity stream of
coolant 78, e.g., on the order of about 20 to 40 feet
per second, is directed from pump 32 through line 30
into the inlet passageway 28 of the nozzle body 26. A
portion 80 of this coolant stream 78 flows into the
annular, U-shaped recess 40 which is concentric to the
nozzle insert 42. It is believed that the coolant 80
entering the recess 40 is made to rotate in the
direction of the arrow shown in Fig. 3, i.e., in the
same direction as the flow of the mai.n body of the
coolant stream 78 through nozzle body 26. The portion
W~92/041~1 2 0 8 9;0~ 5; PCT/US91/06114
-25-
80 of the stream within recess 40 impacts the outer
surface 82 of the coolant stream 78 and functions to
guide and accelerate the main body of the coolant
stream 78 into the smoothly angled, rounded inlet end
52 of the hourglass-shaped throughbore 48 in nozzle
insert 42. The shape of the angled inlet end 52, and
the radially inwardly tapering, throat portion 54 of
throughbore 48, cooperate to smoothly receive the main
body of the -oolant stream 78 which lessens the
turbulence in the transition area between the larger
diameter inlet passageway 28 and the smaller diameter
outlet passageway 36 in nozzle body 26. This produces
minimal losses due to drag or turbulence and results
in improved efficiency.
Because the throat portion 54 of throughbore
48 tapers radially inwardly from the inlet 52 thereof,
this inlet portion of the nozzle insert 42 functions
as a venturi to substantially accelerate the velocity
of the coolant stream 78 in the course of passage from
the inlet passageway 28 of nozzle body 26 into the
nozzle insert 42. For example, ~hen employing a pump
32 rated at about 3000 psi operating pressure, at a
flow rate of about one gallon per minute, it is
believed that the velocity of the coolant stream 78
increases from about 20 to 40 feet per second within
the inlet passageway 28 to a velocity on the order of
about 1000 to 1200 feet per second at or about the
wo 92/G4151 2 0 8 9 0 6 S PCT/US91/06114
-26-
midpoint 56 o~ throughbore 48 having the minimum
diameter Do. This substantial increase in velocity is
achieved because of the rotating coolant 80 within the
recess 40, and the configuration of the input portion
of throughbore 48. Reference should be made to my
U.S. Patent No. 4,830,820 for a;~more detailed discus-
sion of same, and to obtain ~;eàchings on the design
considerations for this str~cture based on desired
pump pressure, flow rate and coolant velocity.
It is believed that such an acceleration of
the coolant stream 78 from the inlet passageway 28
into the nozzle insert 42 creates a condition wherein
a shock wave can develop within the coolant stream 78
in which the dissolved gases within the water portion
of the coolant stream, e.g., nitrogen, carbon dioxide,
oxygen, etc., leave or e~cape from solution and form
bubbles 84. The formation of this shock wave, and the
production of bubbles 84, is induced and enhanced by
the configuration of the discharge portion 58 of
throughbore 48 immediately downstream from the mid-
point 56 of nozzle insert 42 having the minimum
diameter Do. That is, it is believed that the
radially outwardly tapering configuration of the
discharge portion 58 of throughbore 48, in combination
with the larger diameter discharge tube 44 immediately
downstream therefrom, provides an expansion section or
chamber 86 which allows for volumetric expansion of
.
WO92/04151 2 0 8 9 g 6 5 . PcT/us9l/o61l4
the coolant stream as the bubbles 84 are formed. It
has been determined experimentally that where the dis-
charge section 58 tapers radially outwardly from the
midpoint 56 at an included angle ~ of about 8, the
air bubbles 84 are allowed to freely form within the
coolant stream 78 which undergoes at least a limited
volumetric éxpansion. As shown in Fig. 3, the coolant
stream 78 inciuding bubbles 84 contact the inner wall
of tube 44 at a distance of about three times the
diameter Do from the outlet end 60 of nozzle insert
42.
Having induced the formation of bubbles 84
within the coolant stream 78 in the expansion chamber
86, it is believed that at least a portion of these
bubbles 84 are forced back into solution as the
coolant stream 78 continues moving through the dis-
charge tube 44. While the diameter DE of discharge
tube 44 is sufficient to permit the initial formation
of bubbles 84 as the coolant stream 78 moves from the
midpoint 56 of throughbore 48 to the expansion area
86, further volumetric expansion of the coolant stream
?8 is prevented as it continues toward the discharge
outlet 65 of discharge tube 44. It is theorized that
as the bubbles 84 try to expand further radially
outwardly downstream from the expansion area 86, they
are confined by the wall of discharge tube 44 which
causes such bubbles 84 to burst or collapse and return
wo 92,04l51 2 0 8 9 0 ~ ~ PCT/US91/06114
-28-
into solution within the coolant stream 78. As a
result, the coolant stream 78 has a lesser quantity of
bubbles 84 by t~'.time it reaches the discharge outlet
65 of disch ~ ge tube 44, than within the expansion
area 86. See center portion of tube 44 in Fig. 3.
It is theorized that the process of first
allowing bubbles 84 to form in the coolant stream 78,
and then forcing the bubbles 84 back into solution
within the discharge tube 44, contributes to the
formation of a second shock wave within the coolant
stream 78 as it is emitted from the discharge outlet
65 of discharge tube 44 to atmosphere. As viewed in
Figs. 2 and 3, when the coolant stream is exposed to
atmosphere upon discharge from the tube 44, air
bubbles 84 again are formed within the coolant stream
78 as at least some of the dissolved gases therein
leave solution. This has the effect of greatly
accelerating the velocity of the coolant stream l78,
e.g., in excess of lO00 to 1200 fps, and increasing
its energy, so that the coolant stream 78 can effec-
tively break the chips 87 being sheared from workpiece
14 by the insert 18, and reduce the temperature in the
cutting area, i.e., at the insert-workpiece interface
and in the area 88 on the workpiece 14 where the chips
2; 86 are being sheared.
As shown in Fig. 3, the high velocity
coolant stream including air bubbles 84 is directed at
W092/041~1 2 0 8 9 ~6 5 : PCT/US91/06114
-29
an angle ~ of about 20- with respect to the upper
surfac~ 20 of cutting insert l8, and is oriented such
that the top portion 89 of the coolant stream 7Z is
aimed at the cutting edge 22 of insert 18 while the
remaining portion of the coolant stream 78 flows along
the upper surface 20 of insert 18. This has the
effect of directing the coolant stream beneath the
chips 87 being sheared from the workpiece 14 to help
break them into relatively small lengths or particles.
Preferably, the distance at which the discharge outlet
65 is spaced from the insert 18 is sufficient so that
the width of the coolant stream 78 covers the entire
width of the chips 87 being formed. ! Such spacing can
be obtained during operation of apparatus lO by visual
observation, but is typically on the order of about
one inch or more.
In some machining operations, particularly
those performed on harder materials, a jet 92 of
pressurized air is discharged from the air passageway
66 in nozzle body 26 onto the area 88 of the workpiece
14 immediately above the chips 87 being formed. As
mentioned above, the temperature of the air jet 92 may
be reduced by combining a liquified gas such as
nitrogen gas with the pressurized air in the cooling
2S manifold 7~. This reduced temperature air jet 92 is
then directed through the air passageway 66 onto the
area 88. Such reduction in the temperature o~ ~he
~092/04151 2 0 8 9 ~ ~ ~ PCT/US91/06114
-30-
wor~piece 14 at area 88 assists in the breakage of
chips 87 therefrom, which is particularly usefu' for
harder materials. ~
The introduction of liquified gas into the
coollng manifold 70 is controlled by the controller 35
as desired. It is contemplate~d;that for many types of
materials, no liquified ga~would be required. For
harder materials, the liquified gas can be combined
with the pressurized air as needed, e.g., in pulsed
intervals, to reduce the temperature of the pressur-
ized air jet 92 and thus reduce the temperature in the
area 88 of the workpiece 14 to the extent desired.
Additionally, the controller 35 is operative to
control the flow of coolant entering the nozzle body
26 in accordance with the requirements of a particular
application. For example, in the machining of harder
materials, it may be necessary to increase the flow
rate of coolant entering the nozzle body 26 and/or the
operating pressure of pump 32, in order to obtain the
optimum velocity of the coolant stream 78 ejected from
the nozzle body 26.
While the invention has been described with
reference to a preferred embodiment, it will be
understood by those skilled in the art that various
changes may be made and equivalents may be substituted
for elements thereof without departing from the scope
of the invention. In addition, many modifications may
., ~ .
,
W092/04151 2 0 8 9 ~:6 5 : "i PCT/US91/06114
-31-
be made to adapt a particular situation or material to
the teachings of the invention without departing from
the scope thereof.
For example, thé nozzle body 26 is illus-
trated in the Figs. as including a separate nozzle
insert 42 and discharge tube 44. These items are
provided in the preferred embodiment because they may
be removed from the outlet passageway 36 in nozzle
body 26, and replaced with other nozzle inserts 42
and/or discharge tubes 44 having different dimensions
to accommodate varying operating parameters such as
different pump sizes and different coolant flow rates
which may be required for different types of materials
or machining operations. It is contemplated, however,
lS that the nozzle body 26 could be integrally formed
with the structure provided by the separate nozzle
insert 42 and discharge tube 44. Specifically, the
discharge tube 44 could be eliminated and replaced by
a constant diameter bore in nozzle body 26, and the
hourglass-shaped throughbore 48 in the nozzle insert
42 could be machined directly into the nozzle body 26
using conventional machining techniques. A nozzle
body 26 of this construction, therefore, is considered
to be within the scope of this invention.
Therefore, it is intended that the invention
not be limited to the particular embodiment disclosed
as the best mode contemplated for carrying out this
WO92/04151 2 0 8 9 Q 6 S PCT/US91/06114
-32-
invention, but that the invention will include all
embodiments falling within the scope of the appended
claims.
;~
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