U.S. patent application number 11/301466 was filed with the patent office on 2007-05-24 for cryogenic fluid composition.
This patent application is currently assigned to Cool Clean Technologies, Inc.. Invention is credited to David P. Jackson.
Application Number | 20070114488 11/301466 |
Document ID | / |
Family ID | 36588478 |
Filed Date | 2007-05-24 |
United States Patent
Application |
20070114488 |
Kind Code |
A1 |
Jackson; David P. |
May 24, 2007 |
Cryogenic fluid composition
Abstract
A cryogenic fluid composition, and method of forming same,
having hyperbaric, lubricating and cooling properties includes
selectivity combining a solid phase carbon dioxide, an inert
diluent gas and additives in various proportions. The cryogenic
machining fluid can be derived by combining a solid carbon dioxide
coolant, which may contain or entrain one or more machining
lubricant additives, and a diluent phase which is an inert and
relatively non-condensing gas phase in various concentrations. The
cryogenic fluid composition can be used in cleaning, machining or
manufacturing processes to cool, lubricate or ablate a substrate.
The cryogenic fluid composition can also be used in conjunction
with laser treatment or machining processes without adversely
affecting lasing qualities of the laser.
Inventors: |
Jackson; David P.; (Saugus,
CA) |
Correspondence
Address: |
DUFAULT LAW FIRM, P.C.
920 LUMBER EXCHANGE BUILDING
TEN SOUTH FIFTH STREET
MINNEAPOLIS
MN
55402
US
|
Assignee: |
Cool Clean Technologies,
Inc.
Eagan
MN
|
Family ID: |
36588478 |
Appl. No.: |
11/301466 |
Filed: |
December 13, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60635399 |
Dec 13, 2004 |
|
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|
Current U.S.
Class: |
252/71 |
Current CPC
Class: |
B23Q 11/1053 20130101;
C09K 5/041 20130101; B23Q 11/1061 20130101 |
Class at
Publication: |
252/071 |
International
Class: |
C09K 5/00 20060101
C09K005/00 |
Claims
1. A cryogenic composite fluid for treating a substrate during a
machining process, the cryogenic composite fluid comprising: a
sublimable coolant phase comprising solid carbon dioxide particles;
and a diluent phase derived from an inert gas, whereupon combining
each phase the resultant cryogenic composite fluid can be used
during the machining process for cooling purposes, heating
purposes, lubrications purposes or any combination thereof.
Description
CROSS-REFERENCE TO RELATED APPLICATION(S)
[0001] This application claims the benefit U.S. Provisional Patent
Application No. 60/635,399 filed on 13 Dec. 2004 entitled METHOD,
PROCESS, CHEMISTRY AND APPARATUS FOR SELECTIVE THERMAL CONTROL,
LUBRICATION AND POST-CLEANING A SUBSTRATE which is incorporated
herein by reference.
BACKGROUND OF INVENTION
[0002] The present invention generally relates to machining
processes. More specifically, the present invention relates to
machining processes requiring selective thermal control and/or
lubrication during lathe machining, board cutting, wafer
singulation and active electronic component thermal cycling. The
present invention may be used as a metalworking and machining fluid
for operations such as turning, milling, facing, threading, boring
and grooving, and more particularly, to a method and apparatus for
performing such metal working operations at high speeds with
extended insert life, and more particularly as a direct replacement
for flooded coolant/lubricant systems or conventional liquid
cryogenic sprays.
[0003] Most machining operations are performed by a cutting tool
which includes a bolder and one or more cutting inserts each having
a surface terminating with one or more cutting edges. The tool
holder is formed with a socket within which the cutting inserts are
clamped in place. The cutting edge of the insert contacts the
workpiece to remove material therefrom, typically in the form of
chips. A chip comprises a plurality of thin, generally
rectangular-shaped sections of material which slide relative to one
another along shear planes as they are separated 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 amount of heat, which, when combined with the heat
produced by engagement of the cutting edge of the insert with the
workpiece, can amount to 1500 degrees F. to 2000 degrees F.
[0004] Among the causes of failure of the cutting inserts of tool
holders 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 chips 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 heat generate in the formation of the
chip material along the top portion of the insert is removed
forming "craters". If 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, upon 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 matrix material such as
epoxy.
[0005] Attempts to avoid cratering and wear of the insert due to
abrasion with the workpiece have provided only modest increases in
tool life and efficiency. One method has been to form inserts of
high strength materials such as tungsten carbide. However, while
extremely hard, tungsten carbide inserts are brittle and are
subject to chipping which results 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 cutting inserts to reduce the friction between the
cutting insert and workpiece. Additionally, attempts have been made
to increase tool life by reducing the temperature in the cutting
zone, or the area about cutting edge of the insert, the
insert-workpiece interface and the area on the workpiece where
material is sheared to form chips.
[0006] One method of cooling practiced in the prior art is flood
cooling which involves the spraying of a low pressure stream of
coolant toward the cutting zone. Typically, a nozzle disposed
several inches above the cutting tool and workpiece directs a low
pressure stream of coolant 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 the 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 the cutting zone
is so intense that a heat barrier is produced which vaporizes the
coolant well before it can flow near the cutting edge of the
insert.
[0007] Several attempts have been made in the prior art to improve
upon the flood cooling technique described above. For example, the
discharge orifice of the nozzle carrying the coolant was placed
closer to the insert and workpiece, or fabricated as an integral
portion of the tool holder, to eject the coolant more directly at
the cutting area. In addition to positioning the nozzle nearer to
the insert and workpiece, the stream of coolant was ejected at
higher pressures than typical flood cooling applications in an
effort to break through the heat barrier developed in the cutting
area.
[0008] Other tool holders for various types of cutting operations
have been designed to 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
such designs, a separate conduit or nozzle for spraying the coolant
toward the cutting area was eliminated making the cutting tool more
compact. Finally, machine tools of cutting operations have been
designed to incorporate cryogenic coolant delivery through machine
tool passageways which direct the coolant flow across the exposed
top surface of the insert toward the cutting edge in contact with
the workpiece or spray cryogenic fluid such as liquid carbon
dioxide and liquid nitrogen, and cryogenic mixtures containing
water, directly onto the workpiece to cool and remove chips.
[0009] Again, the problem with the aforementioned apparatuses is
that coolant in the form of an oil-water or synthetic mixture, at
ambient temperature, is directed across 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 boundary layer or 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, heat is not dissipated from the cutting area
which causes cratering. In addition, this failure to remove heat
from the cutting area creates a significant temperature
differential between the cutting edge of the insert which remains
hot, and the rear portion of the insert cooled by coolant, causing
thermal failure of the insert.
[0010] 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 which mount the
workpiece and tool holder. If chips are formed in continuous
lengths, they tend to wrap around the tool holder or chucks which
almost always leads to tool failure or at least requires periodic
interruption of the machining operation to clear the work area of
impacted or bundled chips. This is particularly disadvantageous in
flexible manufacturing systems in which the entire machining
operation is intended to be completely automated. Flexible
manufacturing systems are designed to operate without human
assistance and it substantially limits their efficiency if a worker
must regularly clear impacted or bundled chips.
[0011] Moreover, environmental health and work safety issues are
becoming a major concern. It has been estimated that between
700,000 and one million workers are exposed to cutting fluids in
the United States. Since cutting fluids are complex in composition,
they may be more toxic than their components and may be an irritant
or allergenic even if the raw materials are safe. Also, both
bacteria and fungi can effectively colonize the cutting fluids and
serve as source of microbial toxins. Significant negative effects,
in terms of environmental, health, and safety consequences, are
associated with use of the cutting fluids.
[0012] In an attempt to address some of these issues, the use of
oil-water microemulsions has become widespread. The purpose of the
emulsion in metal working is to provide maximum cooling with water
and at the same time have the oil impart some lubricating
properties so that friction between the moving chip and the contact
surface of any cutting tool is reduced. However, as a result, the
part being machined has a working surface that contains an
inorganic contaminant, water, and an organic contaminant, oil. This
makes the post-cleaning process much more complicated.
[0013] Typically, a solvent cleaning operation is performed
in-between or following final processing, which necessitates
removal from the manufacturing tool for such operations. For
example, a conventional strategy is to remove a machined article
from a machining center and using an alcohol to remove the water
and an organic solvent to remove the oil. Another conventional
post-cleaning operation involves the use of newer organic solvents
such as n-propyl bromide (nPB). However, solvents such as nPB are
expensive and pose airborne toxicity issues themselves to exposed
workers. Moreover, reclamation systems and other associated costs
of using organic cleaning solvents such as nPB are prohibitively
high.
[0014] The use of water-based cleaners and water rinsing is still
another method of post-cleaning common in the metalworking
industry. Although generally cheaper and safer to use with respect
to organic solvents, these agents themselves become polluted with
heavy metals and other contaminants and must be treated prior to
disposal.
[0015] Another deficiency in the prior art is in regard to the use
of dry-cold cryogenic sprays to provide selective mechanical force
and cooling within a cutting zone of a laser machining operation.
Although conventional methods of applying cryogenic sprays to a
substrate during machining processes, such as spraying liquid
carbon dioxide directly onto the machined substrate to form a cold
gas-solid aerosol, may be similarly applied to a laser machining
surface, these methods and chemistries suffer from several
disadvantages. For example, conventional cryogenic sprays can be
used to eliminate laser machining heat and debris, however, because
the spray temperature can not be controlled by these conventional
processes, significant amounts of atmospheric water vapor is
condensed as liquid and solid water in and around the laser cutting
zone during the machining operation. Liquid and solid water present
on a cutting surface absorb or reflect strongly in ultra-violet and
infra-red spectral regions, which interferes with lasing power and
beam delivery onto the substrate surface, thus producing cut
quality problems. Another limitation is that the spray pressures
cannot be controlled effectively to balance laser cutting
efficiency with fluid force, temperature and pressure.
BRIEF SUMMARY OF INVENTION
[0016] The present invention includes a cryogenic composite fluid
for use as a coolant, lubricant, carrier agent and any combination
thereof The present invention may be used to formulate a machining
spray composition which exhibits a specific cooling capacity,
lubricity, spray pressure and temperature, density, viscosity, and
other beneficial physicochemical properties for a particular
machining requirement. The cryogenic composite fluid preferably
comprises a coolant phase, a diluent phase and an optional additive
phase. The coolant phase preferably includes sublimable carbon
dioxide snow which acts as a lubricant, carrier agent and heat
extraction agent. The diluent phase is preferably derived from a
variety of organic and inorganic liquids, solids, and gases that
serve as the physical propulsion and carrier fluid which
selectively delivers solid coolant and additive agents into a
cutting zone, a dilution agent which selectively dilutes the
effects of the other compositional ingredients and as a temperature
regulation agent. The additive phase comprises any variety or
mixture of organic liquids, organic gases and solids that
selectively modify the coolant and diluent phases and provide
coolant and lubricant enhancements such as viscosity adjustment,
changes to film consistency, corrosion inhibition and modification
of lubricity.
[0017] Numerous single component, binary or ternary
coolant-lubricant spray compositions may be derived exhibiting
varying physicochemical characteristics such as wetness, dryness,
coolness, hotness, pressure, flowrate, lubricity, surface tension,
mass, spray film consistency and density. The cryogenic fluid of
the present invention can be applied to machining or treatment
processes that require selective cleaning, cooling, lubricating or
abrasion, including laser machining or treatment operations. The
cryogenic fluid composition of the present invention is capable of
sweeping away dirt, grime, oils and chips while simultaneously
providing cooling and lubrication.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is a diagram illustrating phase components of a
cryogenic spray of the present invention.
[0019] FIG. 2 is a diagram illustrating phase components of a
selected cryogenic spray of the present invention.
[0020] FIG. 3 is a diagram illustrating phase components of a
selected cryogenic spray of the present invention.
[0021] FIG. 4 is a diagram illustrating phase components of a
selected cryogenic spray of the present invention.
[0022] FIG. 5 is a diagram illustrating phase components of a
selected cryogenic spray of the present invention.
[0023] FIG. 6 is a diagram illustrating phase components of
selected cryogenic sprays of the present invention.
[0024] FIG. 7 is a flow-diagram illustrating a system to generate
the cryogenic spray of the present invention.
[0025] FIG. 8 is a partial cross sectional view of a stepped
capillary used to generate the cryogenic spray composition of the
present invention.
[0026] FIG. 9 is a partial cross sectional view of a delivery line
of used to transport the cryogenic spray composition of the present
invention.
[0027] FIG. 10 is a diagram illustrating the effects of spray
viscosity of Cryosols and Cryogels with the addition of selected
additives.
[0028] FIG. 11 is a graph illustrating the Shear Impact Pressures
for selected particle sizes of the cryogenic spray composition of
the present invention.
[0029] FIG. 12 is a side view of the spray composition of the
present invention being applied during a machining operation.
[0030] FIG. 13 is a graph illustrating profiles of Exemplary Spray
Temperatures and Heat Capacities of selected cryogenic sprays of
the present invention.
[0031] FIG. 14 is a graph illustrating certain physical properties
of a lubricating additive used in the cryogenic spray composition
of the present invention.
[0032] FIG. 15 is a side view of the cryogenic spray composition of
the present invention being applied during a laser machining
operation.
[0033] FIG. 16 a graph illustrating physical properties of infrared
and ultraviolet lasers.
[0034] FIG. 17a is a photomicrograph of a substrate treated with a
spray of the prior art.
[0035] FIG. 17b is a photomicrograph of a substrate treated with a
selected cryogenic spray composition of the present invention.
[0036] FIG. 18a is a photomicrograph of a substrate treated with a
spray of the prior art.
[0037] FIG. 18b is a photomicrograph of a substrate treated with a
selected cryogenic spray composition of the present invention.
[0038] FIG. 19a is a photomicrograph of a substrate machined using
a spray treatment of the prior art.
[0039] FIG. 19b is a photomicrograph of a substrate machined using
a first selected cryogenic spray composition of the present
invention.
[0040] FIG. 19c is a photomicrograph of a substrate machined using
a second selected cryogenic spray composition of the present
invention.
[0041] FIG. 20a is a photomicrograph of a substrate treated with a
spray of the prior art.
[0042] FIG. 20b is a photomicrograph of a substrate treated with a
selected cryogenic spray composition of the present invention.
[0043] FIG. 21a is a photomicrograph of a substrate treated with a
spray of the prior art.
[0044] FIG. 21b is a photomicrograph of a substrate treated with a
selected cryogenic spray composition of the present invention.
[0045] FIG. 22a is a photomicrograph of a substrate treated with a
spray of the prior art.
[0046] FIG. 22b is a photomicrograph of a substrate treated with a
selected cryogenic spray composition of the present invention.
[0047] FIG. 23 is a photomicrograph of a substrate treated with a
selected cryogenic spray composition of the present invention.
DETAILED DESCRIPTION
[0048] A composite machining fluid or spray of the present
invention is formed by combining fractional concentrations of a
coolant phase Fc, a diluent phase Fd and an additive phase Fa, as
is generally indicated at 30 in FIG. 1. Each phase, Fc, Fd and Fa,
are combined such that the fractional phase components of the
composite machining fluid 30 are defined by the following equation:
.SIGMA.(Fc +Fd +Fa) =100% The resulting machining fluid 30 exhibits
selected characteristics of mass, density, wetness, dryness,
coldness, hotness, lubricity and other machining fluid
characteristics such as desired impact velocity, flowrate, pressure
and spray consistency.
[0049] The coolant phase Fc used in the present invention has
several roles including performing as a de facto lubricant, carrier
agent and heat extraction agent. Upon formation, the coolant phase
Fc generally has a greater mass and density, at approximately 1.6
grams/ml, as compared to conventional liquid and aerosol sprays.
Having a greater density, and when combined with a propulsion
agent, the carbon dioxide snow of the coolant phase is able to
penetrate a high speed cutting zone and deliver both its coolant
packet (sublimation heat) and additive packet deep into the
boundary layer. Also, with the heat of vaporization, the
sublimating coolant phase (Heat of Sublimation (.DELTA.H.sub.s)-250
BTU/lb) produces greater heat extraction and delivery control as
compared to using a boiling liquid carbon dioxide coolant-lubricant
(Heat of Vaporization (.DELTA.H.sub.v)-62 BTU/lb). Moreover, as
used in the present invention and under diluent pressures of just
550 kPa (80 psi), solid carbon dioxide impacts a surface at a
velocity sufficient to liquefy part of the solid phase to fill
voids, cracks and other surface irregularities with liquid phase
carbon dioxide and additive. Much higher pressures, up to 6.9 MPa
(1000 psi), are required to accomplish this when spraying liquid
phase carbon dioxide into a cutting zone.
[0050] The coolant phase, Fc, suitable for use in the present
invention, preferably comprising in part solid phase carbon
dioxide, is used at concentrations of between 0% and 100% at a
flow-rate of between 0 and 45 grams per second (0.1 pounds per
second). Carbon dioxide gas, liquid carbon dioxide or super
critical carbon dioxide, preferably at pressures between 2.1 MPa
(300 psi) and 13.8 MPa (2000 psi) and temperatures between 273 K
and 373 K is used to derive the solid phase carbon dioxide,
preferably using any of the following three condensation methods:
gas phase carbon dioxide, which may contain or entrain one or more
machining lubricant gas additives, is condensed by reducing
temperature and/or increasing pressure to form first a liquid phase
and condensed further by reducing temperature and/or pressure using
a stepped capillary apparatus to form a solid or
semi-solid/gas/liquid coolant composition; liquid phase carbon
dioxide, which may contain or entrain one or more machining
lubricant additives, is condensed by reducing temperature and/or
pressure using a stepped capillary apparatus to form a solid or
semi-solid/gas/liquid coolant composition; or supercritical phase
carbon dioxide, which may contain or entrain one or more machining
lubricant additives, is condensed by reducing temperature and/or
pressure using a stepped capillary apparatus to form a solid or
semi-solid/gas/liquid coolant composition, or may be applied
directly to a machining tool interface.
[0051] The diluent phase Fd used in the present invention performs
several distinct roles, including serving as a physical propulsion
agent and carrier fluid which selectively delivers solid coolant
and additive agents into a cutting zone, a dilution agent which
selectively dilutes the cooling capacity and additive effects of
the other composition ingredients, and a temperature regulation
agent. The diluent phase Fd also has the ability to selectively
control the concentrations of the coolant phase and additive phases
which provides variable physicochemistry in the composite spray 30.
The diluent phase Fd is preferably derived from an inert gas,
including carbon dioxide gas, which beneficially modifies the
surface tension and viscosity of various additive phases used
within the cryogenic fluid composition 30. Also, employing carbon
dioxide gas as the diluent phase in the present invention provides
inherent lubrication properties. Carbon dioxide gas may be used
with a suitable additive in select machining applications
benefiting from both high temperature and high lubricity
characteristics. The diluent phase, Fd, suitable for use in the
present invention generally comprises any variety of inert gases
including, but not limited to, nitrogen, argon, clean dry air,
compressed air and carbon dioxide, used at concentrations between 0
and 100%, at pressures between 34 kPa (5 psi) and 34 MPa (5000 psi)
at temperatures between 294 K (70 degrees F.) and 477 K (400
degrees F.), and a flow-rate of between 14.6 liters per minute (0.5
cubic feet per minute (cfm)) and 1400 liters per minute (50
cfm).
[0052] The additive phase Fa used in the present invention also
plays several roles. The additive phase Fa is used to modify either
(or both) the diluent or coolant phases to selectively form
gas-liquid-solid sprays termed aerosols, cryogenic aerosols termed
"Cryosols" herein, cryogenic solid-gas sprays termed "Cryogels"
herein, and hybrid composite cryogenic or heated carbon dioxide
sprays. Additives used in the present invention provide
coolant-lubricant enhancements such as viscosity adjustment,
changes to film consistency, corrosion inhibition, and modification
of lubricity, among other beneficial effects. The additive phases
are derived from a variety of organic and inorganic liquids,
solids, and gases. The additive phase, Fa, suitable for use in the
present invention is used at concentrations of between 0% and 100%
and comprises any variety or mixture of organic liquids, organic
gases and solids. Non-exhaustive examples of organic liquids
include: bio-based oils, alcohols and esters such as rapeseed,
ThetraHydrooFurfurylAlcohol (THFA) and ethyl lactate; soy methyl
esters; petroleum oils; alcohols such as isopropanol (IPA) and
ethanol; ketones such as acetone and MEK; polyglycols; phosphate
esters; phosphate ethers; synthetic hydrocarbons;
DiethyleneGlycolMonobutylEther (DGME); and silicones.
Non-exhaustive examples of organic gases include carbon dioxide and
condenseable hydrocarbon additives such as HydroFluoroCarbon 134a,
a refrigerant gas and butane. Non-exhaustive examples of solids
include: oxidation, corrosion and rust inhibitors; extreme pressure
agents such as chlorinated paraffinic oils; PolyTeteraFluroEthylene
(PTFE); boron nitride; pour point additives; detergents;
dispersants; foam inhibitors; hydrogen peroxide; percarbonic acid;
water; and nanoscopic solid particles such as nanolubricants. Each
of the aforementioned exemplary compounds for the additive phase
include emulsions and carbonated mixtures. The additive phase Fa
may be added indirectly to the coolant phase Fc by first entraining
and carrying the additives as an aerosol intermediate composition
within the diluent phase Fd and entraining or condensing a portion
of the aerosol into the solid carbon dioxide phase Fc, to form a
Cryosol or Cryogel fraction. Alternatively, the additive phase Fa
may be added directly by injection into the carbon dioxide gas
phase Fc, liquid phase Fc or supercritical phase Fc and condensed
to form the solid phase carbon dioxide coolant Fc.
[0053] A unique aspect of the present invention is that a transient
liquid phase Fc is selectively re-formed from the solid phase
coolant Fc due to impact stress within the cutting zone. For
example, using diluent phase Fd pressures of just 550 kPa (80 psi),
solid carbon dioxide particles, which may contain dissolved or
entrained additives, contact a machined surface with adequate
impact stress, as much as 50 MPa (7,200 psi) or more, to liquefy a
portion of the solid coolant phase to fill voids, cracks and other
surface irregularities with both liquid phase carbon dioxide,
behaving now as a lubricant, and optional additives.
[0054] When employing the machining fluid composition of the
present invention, as much as 80% of the of the solid phase coolant
Fc impacts the cutting zone before completely sublimating,
absorbing significantly more heat per volume and depositing its
additive component if present. Also, incorporated additive(s)
intimated with the machining surface flow freely into and fill
voids, cracks and other surface irregularities with the solid and
re-formed liquid phase carbon dioxide.
[0055] Referring again to FIG. 1, machining fluid 30 are derived
and used in the present invention by combining fractional
concentrations of coolant phase Fc, diluent phase Fd and additive
phase Fa. As such, the composition 30 of the present invention may
comprise a single phase composition, a binary phase composition or
a ternary phase composition. The vertices of the exemplary fluid or
spray composition graph represent the extreme single component
elements which may generally be used in selected machining
applications including dry cryogenic machining 32 (Fc=100%), dry
gas machining 34 (Fd=100%) and wet machining 36 (Fa=100%). Any two
sides of the fluid or spray composition 30 graph of FIG. 1 comprise
binary mixtures of either coolant-additive spray compositions
(Fc+Fa), coolant-diluent spray compositions (Fc+Fd) or
diluent-additive spray compositions (Fd+Fa). Within the interior of
the spray composition graph exist ternary mixtures of
coolant-diluent-additive (Fc+Fd+Fa), and which are combinations of
fluid or spray compositions having the widest range of
physicochemical properties. For example, small amounts of coolant
phase Fc and additive phase Fa are combined with a larger amount of
diluent phase Fd to form cool, dry or damp sprays 38; small amounts
of diluent phase Fd and additive phase Fa are combined with a
larger amount of coolant phase Fc to form cryogenic, dry or damp
sprays 40; small amounts of coolant phase Fc and diluent phase Fd
are combined with a larger amount of additive phase Fa to form
warmer wet sprays 42; and measured amounts of diluent phase Fd,
additive phase Fa and coolant phase Fc are combined to form
cryogenic wet sprays 44 or cold wet sprays 46. As depicted in FIG.
1, any number of fluid or spray compositions including aerosols,
cryosols and cryogels may be formulated to meet the desired needs
of a particular machining application.
[0056] FIG. 2 depicts an exemplary ternary fluid or spray
composition 48 combining solid carbon dioxide coolant phase Fc,
clean dry air diluent phase Fd and a soy methyl ester additive
phase Fa at a Fc:Fd:Fa ratio of 60:30:10 to form a fluid or spray
composition for machining Inconel, a nickel-based alloy with
chromium and iron. The diluent pressure is 550 kPa (80 psi) and the
composition spray temperature is approximately 227 K (-50 degrees
F.). The fluid or spray mixture forms a gel-like or semi-solid
consistency because the spray temperature is below the melting
point for the soy methyl ester additive. The composite fluid or
spray 48 tends to stick to surfaces applied as compared to liquid
additive sprays where the melting point temperature has not been
reached.
[0057] FIG. 3 depicts an exemplary binary fluid or spray
composition 50 for machining plastic by combining solid carbon
dioxide coolant phase Fc and compressed air diluent phase Fd at a
Fc:Fd;Fa ratio of 30:70:0. The diluent phase Fd pressure is 550 kPa
(80 psi) and the composition spray temperature is approximately 239
K (-30 degrees F.). The spray mixture forms a gel-like or
semi-solid consistency because the spray temperature is below the
melting point for the soy methyl ester additive. The composite
spray 50 tends to stick to surfaces applied as compared to liquid
additive sprays where the melting point temperature has not been
reached.
[0058] FIG. 4 depicts an exemplary ternary fluid or spray
composition 52 formed for machining glass by combining a solid
carbon dioxide coolant phase Fc, a nitrogen gas diluent phase Fd
and liquid isopropyl alcohol (IPA) additive at a Fc:Fd:Fa ratio of
18:80:2. The diluent pressure is 550 kPa (80 psi) and the
composition spray temperature is approximately 244 K (-20 degrees
F.). The composite spray tends to evaporate quickly from surfaces
being machined.
[0059] FIG. 5 depicts an exemplary ternary fluid or spray
composition 54 formed for treating titanium by combining solid
carbon dioxide coolant phase Fc, compressed air diluent phase Fd
and liquid DGME additive Fa, which itself contains a suspension of
5% V:V of PTFE and boron nitride particles, at a Fc:Fd:Fa ratio of
80:10:10. The diluent pressure is 550 kPa (80 psi) and the
composition spray temperature is approximately 222 K (-60 degrees
F.). The composite spray 54 tends to evaporate quickly from
surfaces being machined.
[0060] FIG. 6 depicts an exemplary binary fluid or spray
composition 56 formed for machining magnesium by combining carbon
dioxide gas diluent phase Fd and liquid soy methyl ester additive
phase Fa at a Fc:Fd:Fa ratio of 95:5. The resulting carbonated soy
methyl ester spray has a diluent phase pressure is 1 MPa (150 psi)
and the composition spray temperature is approximately 294 K (70
degrees F.). The higher gas spray mixture forms a wet carbonated
liquid with lower viscosity and better wetting power than
non-carbonated soy methyl ester under these conditions. It is
believed by the present inventor, and which is supported in the
scientific literature, that improved performance of organic
additives used in the present invention is due to the cohesive
energy and plasticizing effect of carbon dioxide upon organic
liquid additives such as soy methyl ester, which significantly
reduces viscosity and surface tension of the resulting composite
machining fluid. This effect is described more fully under FIG. 14
herein.
[0061] Also depicted in FIG. 6 is a single phase fluid or spray 58
comprising a heated diluent phase Fd of carbon dioxide at a
pressure of 690 kPa (100 psi) and temperature of 373 K (212 degrees
F.). Such a fluid or spray may be used to provide dry lubrication
and chip removal during a ceramic machining process.
[0062] Referring to FIG. 7, a composite fluid or spray generation
system 60 for generating the cryogenic machining fluid and
composite spray 30 generally includes a diluent phase generator
subsystem 62, coolant phase generator subsystem 64, a coaxial
machining tool 66 and a fluid or spray applicator 68. Additionally,
the diluent phase generator subsystem 62 and coolant phase
generator subsystem 64 are individually integrated with an additive
phase supply 70. A common supply of high pressure carbon dioxide
gas 72 having a preferred pressure range of between 2.1 MPa (300
psi) and 6.2 MPa (900 psi).
[0063] With respect to the coolant phase generation subsystem 64,
carbon dioxide gas contained in a supply cylinder 72 is fed through
a connection pipe 74 to a tube-in-tube heat exchanger 76. The
common supply of high pressure carbon dioxide gas 72 preferably has
a pressure range of between 2.1 MPa (300 psi) and 6.2 MPa (900
psi). Upon the carbon dioxide gas entering the heat exchanger 76, a
compressor-refrigeration unit 78 re-circulates cooled refrigerant
80 countercurrent with the carbon dioxide gas contained in heat
exchanger 76, condensing the carbon dioxide gas into a liquid
carbon dioxide coolant stock. The liquid carbon dioxide coolant
stock flows from the heat exchanger through a micrometering valve
82, through one or more base stock supply pulse valves 84, 86 and
into one or more stepped capillary condenser units 88, 90.
Referring to FIG. 8, the one or more capillary condenser units 88,
90 are preferably constructed using first a segment 92 of smaller
diameter polyetheretherketone (PEEK) tubing, for example a 60 cm
(24 inch) segment of 0.8/1.6 mm (0.030/0.0625 inch) inside/outside
diameter tubing, coupled to a second segment 94 of larger diameter
PEEK tubing, for example a 91 cm (36 inch) segment of 1.52/3.18 cm
(0.060/0.125 inch) inside/outside diameter tubing, providing a
stepped capillary apparatus for condensing, or crystallizing,
liquid carbon dioxide into solid carbon dioxide particles having
various sizes. Alternatively, the stepped capillary condenser 88,
90 is that as taught by the present inventor and fully disclosed in
U.S. application Ser. No. ______ entitled CARBON DIOXIDE SNOW
APPARATUS, filed concurrently with the present application and
claiming priority from U.S. Provisional Application No. 60/635,230,
both of which are hereby incorporated herein by reference. The
stepped capillary condenser 88, 90 efficiently boils liquid carbon
dioxide base stock under a pressure gradient to produce a mass of
predominantly solid phase carbon dioxide coolant phase Fc.
Preferably, the stepped capillary condenser 88, 90 is wrapped with
self-adhering polyurethane insulation foam tape 96 as supplied by
Armstrong World Industries, Inc. of Lancaster, Pa.
[0064] The coolant stock supply valves 84, 86 may be pulsed first
opened and then closed at a pulse rate of greater than 1 pulses per
second (>1 Hertz) using one or more electronic pulse timers 98.
Additionally, the coolant stock supply valves 84, 86 may be
oscillated on and off to feed coolant stock selectively and
alternately into each capillary condenser 88, 90 at different times
and rates using an electronic oscillator 98. Alternatively, high
frequency pulsation may be preferred to introduce significant
velocity gradients (energy waves) within the solid particle stream
without discontinuing the generation and flow of solid particles.
Oscillation may be preferred to selectively introduce coolant flow
through additional fluid or spray applicators 68 or to produce
alternations within the machine tool applicator 66. Alternating the
spray within a cutting zone is beneficial for selectively directing
a fluid or spray composition 30 onto a select portion of the cut to
optimize cooling and lubrication as well as assist with chip
evacuation.
[0065] An additive injection pump 100 may be incorporated for
injecting an optional additive phase derived from the additive
supply 70 and injected and mixed directly into liquid carbon
dioxide coolant stock using an in-line static mixer 102 and prior
to condensing into a coolant-additive binary composition using the
capillary condenser(s) 88, 90.
[0066] With respect to the diluent phase subsystem 62, the supply
of carbon dioxide gas 72 is fed via a connection pipe 104 and into
a pressure reducing regulator 106 regulating the carbon dioxide gas
pressure between 70 kPa and 1030 kPa (10 and 150 psi), or more. The
regulated carbon dioxide gas is fed into an electrical resistance
heater 108 controlled by a thermocouple 110 and temperature
controller 112 at a temperature of between 293 K and 473 K, or
more. Following this, temperature-regulated carbon dioxide
propellant gas may be fed via an aerosol generator inlet valve 114
into an aerosol generator 116. The aerosol generator 116 is
connected to the additive supply 70 which mixes a selected amount
of the aforementioned additives Fa into the temperature-regulated
carbon dioxide propellant gas at a rate of between 0 and 0.02
liters per minute or more, thus forming the temperature-regulated
carbon dioxide diluent phase Fd (aerosol) which is fed into a
diluent phase feed tube 118. Alternatively, temperature-regulated
carbon dioxide propellant gas may be fed via an aerosol generator
bypass valve 120, by-passing the aerosol generator 116, and
connecting directly into the diluent phase feed tube 118. It should
be noted that pressure-regulated compressed air or nitrogen gas, or
other inert gas, may be used in place of the pressure-regulated
carbon dioxide gas described above to produce the diluent phase
supply for the particular machining applications.
[0067] Having formed a coolant phase Fc, containing option additive
phase component if desired, and a diluent phase Fd, containing
optional additive phase component if desired, as described above,
both components Fc and Fd are integrated and delivered to the
machine tool 66 and/or the spray applicator 68 using a coaxial
spray delivery line 122. The coaxial delivery line 122, as
illustrated in FIG. 9, comprises an outer diluent phase delivery
tube 124 for containing and delivering the diluent phase and
additive phase, and an inner PEEK tube 126 for containing and
delivering the coolant phase and optional additives. The delivery
line 122 preferably has an overall length necessary to deliver the
coolant/additive phase and diluent/additive phases to the machining
tool 66 and spray applicator 68. Preferably, the coaxial machining
tool 66 is that as taught by the present inventor and fully
disclosed in U.S. application Ser. No. ______ entitled DEVICE FOR
APPLYING CRYOGENIC COMPOSITION, filed concurrently with the present
application, which is hereby incorporated herein by reference.
Preferably, the fluid or spray applicator is a co-axial dense fluid
spray applicator as taught by the present inventor and fully
disclosed in U.S. Pat. No. 5,725,154 which is hereby incorporated
herein by reference. More preferably, the fluid or spray applicator
is a tri-axial type delivering device as taught by the present
inventor and fully disclosed in U.S. Provisional Application No.
60/726,466, which is hereby incorporated herein by reference. It
should be noted, however, that any type of machining tool 66 or
spray applicator 68 capable of applying the composite fluid or
spray is well within the scope of the present invention.
[0068] Additionally, the coolant phase composition, with optional
additive, may be derived from a supply of supercritical phase
carbon dioxide. In certain instances, additive components may be
more easily solubilized in a supercritical phase carbon dioxide as
compared to liquid carbon dioxide due to cohesion energy
differences. Referring back to FIG. 7, a pressure reactor 128
having a band heater 130 is fed liquid carbon dioxide coolant stock
from the carbon dioxide generation subsystem 64. The liquid carbon
dioxide stock may be blended with selected additive(s) from
additive supply line 132 using the metering pump 100. The pressure
and temperature within the mixed reactor 128 are raised above the
critical point for the mixture to form a supercritical fluid
coolant base stock. Experimentation may be required to determine
the exact critical parameters for any given coolant mixture. Once
formed, the homogenized supercritical fluid coolant stock may be
metered directly into the selected capillary condenser 88, 90 using
a metering valve 134 and pulse valve assembly 102 to form the
coolant phase Fc as described herein. Alternatively, the
supercritical fluid-based coolant-additive phase may be applied
directly to a machining surface through a ball valve 136 and into
either the machine tool 66, the spray applicator 68 or both. It
should be noted, however, that FIG. 7 is for illustrative purposes
only, and does not include all possible valve configurations.
[0069] Coolant-lubricant spray consistency (mist-like, liquid-like,
gel-like) may be a highly desirable attribute for a particular
machining application. Using the present invention, spray
consistency can be variably controlled from heated gas or gases
that cool and discharge light machining chips, heated or unheated
liquid-gas sprays (aerosols/cryosols) that immediately film and
evaporate from an applied surface, gel-like viscous cold solid-gas
sprays (Cryogels) that tend to stick to an applied surface, and any
hybrid form within this range. This is accomplished by controlling
additive phase concentration, additive injection/mixing point,
coolant particle size and concentration, and diluent phase flow,
pressure and temperature. Referring to FIG. 10, adding a additive
phase 138 to a diluent phase 140 to form an Aerosol (intermediate
composition) and selectively mixing said Aerosol into a coolant
phase 142 will produce a variety of Cryosol sprays 144 having
gas-liquid, gas-solid or gas-solid-liquid consistencies. By
contrast, selectively adding an additive phase 146 such as soy
methyl ester into a coolant phase 148 forms a Cryogel intermediate
compound. Selectively forming and mixing said Cryogel into a
diluent phase 150 produces a variety of Cryogel spray compositions
152 having cold gas-liquid to gas-solid consistency. Using these
different mixing and delivery techniques described above, the
viscosity 154 of the spray mixture can be altered from very low to
very high viscosity, which is very useful when optimizing a
particular machining fluid application.
[0070] The coolant phase Fc of the present invention, which
provides selective machining heat extraction elements as well as
lubrication, comprising solid carbon dioxide may be used at a mass
injection range of 0 to 45 grams per second (0.1 lbs/sec), or more.
In addition the particle composition may be altered to provide
large or small solid particles, which is beneficial for adjusting
impact stress and penetration into a machining interface, as will
be discussed. Moreover, pulsing or oscillating coolant sprays used
in the present invention may be employed to provide beneficial
physical energies such as increased outflow velocities and a more
turbulent boundary layer. Also, pressure spikes or thermoacoustic
waves created through rapid velocity changes produce and sustain
much higher peak velocities as compared to continuous flow fluid
velocities, which can be as high as 500 meters/sec. Oscillatory
flow prevents boundary layer thickening by increasing the surface
outflow velocities which results in increased snow particle-surface
impacts and more efficient solid-liquid transitions. This allows
for the delivery of the impacting fluid or spray particles to a
greater surface area with shorter contact duration. Thus Hertzian
sprays more efficiently unload with the complex topography of a
substrate surface which decreases boundary layer thickness and
viscosity, increases surface penetration and improves energy
exchange.
[0071] The diluent phase Fd, an inert gas, may be used at pressures
of between 0 and 34.5 MPa (5000 psi), flows of between 0 and 1.4
meters cubed per minute (50 cfm) and temperatures of between 294 K
and 478K (70 and 400 degrees F.). The diluent phase Fd used in the
present invention provides physical control of the fluid or spray;
providing a coolant-additive dilution, temperature control and
fluid or spray propulsion.
[0072] The additive phase Fa, which can be a solid, liquid or gas,
is used to modify either the coolant or diluent phases to impart
physicochemical characteristics such as viscosity, enhanced
lubricity, and wetness. It may be added to the coolant and diluent
phases in concentrations of between 0 and 100% by volume. The
additive phase may include gaseous constituents, such as phase
change constituents, that are condensed as a liquid phase into the
coolant phase to form a wet liquid-solid coolant phase. Compared to
conventional flooded liquid coolants and lubricants, as well as
high pressure liquid carbon dioxide sprays described in prior art,
the cryogenic machining sprays of the present invention provide
several functional advantages such as variable and higher density,
as much as 60% greater bulk fluid density (solid carbon dioxide
-1.6 g/ml versus liquid coolant -1.0 g/ml), variable viscosity, low
surface tension of 5 dynes/cm, variable heat capacity from 4.7 Kw
(16,000 BTU/hour) of heat extraction to 2.5 Kw (8,500 BTU/hour),
and high penetration velocities of up to 500 m/sec.
[0073] Referring to FIG. 11, the present invention can produce
solid carbon dioxide particles having diameters ranging 0.5 to 500
microns (fine to coarse) which are able to produce variable impact
stresses. A fine particle spray 156 can produce a range of impact
stresses from <0.1 MPa to approximately 15 MPa at diluent phase
pressures of between 0 and 1 MPa (150 psi). A coarse particle spray
158 can produce a range of impact stresses from <0.1 MPa to
approximately 50 MPa at diluent phase pressures of between 0 and 1
MPa (150 psi). Higher impact stresses can be imparted at higher
diluent phase pressures and lower impact stresses are able to be
imparted at lower diluent phase pressures. Diluent spray pressure
and temperature can be used selectively to alter both the impact
stress and impact particle density by selectively sublimating a
portion of the solid phase carbon dioxide Fc particles entrained in
the diluent phase in transit to the substrate surface through heat
transfer from the diluent phase Fd to the solid carbon dioxide
phase Fd. Moreover, spray impact stress experiments performed using
Prescale Series contact pressure measuring films, manufactured by
FujiFilm USA, reveal that spray impact pressures may be selectively
controlled by controlling the composition of the various coolant,
additive and diluent phases described in the present invention.
Particle size and consistency control is accomplished using various
lengths and diameters of capillary condensers to produce a mass of
sublimable particles and coupling said particle stream with a
diluent phase, as disclosed in U.S. Patent Application entitled
CARBON DIOXIDE SNOW APPARATUS, already referenced herein.
[0074] Referring to FIG. 12, the delivery line terminates with a
mating coaxial adaptor (not shown) whereupon the fluid or spray
composition is fed either into coaxial ports 160 within the
machining tool 66 or the fluid or spray applicator 68. The
composite sprays produced and delivered either through the coaxial
machining tool 66 and/or the spray applicator are selectively
directed into a cutting zone 162 and/or workpiece substrate 164 to
provide boundary layer cooling and lubrication, selective build-up
edge (BUE) removal 166. During machining, composite fluid or spray
particles penetrate the cutting zone 162, tool-workpiece and
tool-chip interfaces, wetting or wicking into said interfaces,
sublimating, supercooling and liquefying under the impact stresses
generated. Simultaneously with the penetration into the cutting
zone 162, solid carbon dioxide particles change phase to form gas
and liquid carbon dioxide films, providing a thin carbonated
lubricating (additive) and cooling film 168 at the interface.
Liquid carbon dioxide and carbonated films 168 have extremely low
viscosities of between 1.times.10.sup.-4 Pascal seconds (0.1 cP)
and 0.01 Pascal seconds (10 cP) and surface tensions of between
5.times.10.sup.-6 J/cm.sup.2 (5 dynes/cm) and 1.times.10.sup.-5
J/cm.sup.2 (10 dynes/cm), which enable fluid or spray constituents,
such as entrained additives, to penetrate into microscopic surface
voids and cracks (not shown) and deposit thin films of additive
phase when present. Diluent phase pressure is adjusted as necessary
to enable composition particles and additives to overcome
centrifugal forces generated by high rotational speeds 170 and
penetrate the machine tool-workpiece interface 172. Several types
of fluid or spray configurations are possible using the present
invention, including continuous, pulsed fluid or spray, and
oscillating sprays, with a lubricating fluid or spray or dry spray
characteristics, and heating or cooling spray characteristics.
[0075] Referring to FIG. 13, the aforementioned fluid or spray
configurations can be composed and selectively delivered to produce
a range of thermal capacities; a single coaxial composite fluid or
spray can provide from 4.7 Kw (16,000 BTU/hour) of heat extraction
to 2.5 Kw (8,500 BTU/hour) of heat input 174 and a variety of
temperatures from 197 K (-105 degrees F.) to 422 K (300 degrees F.)
176, or more during a machining operation. Heating sprays 178,
which have temperatures above the temperature of the cutting zone,
add heat to a substrate surface. Cooling sprays 180, which have
temperatures below the temperature of the cutting zone, extract
heat from a substrate surface. The heating and cooling sprays may
be applied in combination to produce any variety of machined
substrate thermal cycles. For example one exemplary thermal cycle
demonstrates first applying a heating fluid or spray 178 having a
temperature above 358 K (185 degrees F.) followed by a cooling
fluid or spray 182 having a temperature below 244 K (-20 degrees
F.). Another exemplary thermal profile, demonstrates first applying
a cooling fluid or spray 180 to reach a substrate temperature below
244 K (-20 degrees F.) followed by a heating fluid or spray 184 to
return the substrate back to ambient temperature. Another example
profile shows applying a cooling fluid or spray 186 which produces
a substrate having a temperature approaching 197 K (-105 degrees
F.) 188, the sublimation temperature for solid carbon dioxide.
Moreover, Hertzian pulsation 190, multiple coax oscillation 192 or
continuous flow 194 of the coolant phase may be applied. These
various physical fluid or spray energy augmentations can enhance
heat transfer between the spray particles and substrate surface as
well as improve machining swarf ejection during a machining
operation.
[0076] Carbon dioxide, unlike other diluent phase fluids such as
compressed air, nitrogen or argon, can chemically enhance additive
chemistries because of its much large molecular cohesion energy. To
demonstrate this chemical enhancement effect, and referring to FIG.
14, the viscosity 196 and surface tension 198 of a typical
lubricating additive phase (soy methyl ester) under atmospheric
pressure and saturated with carbon dioxide exhibits a 30% to 40%
decrease 200 in both viscosity and surface tension. Carbon dioxide
swells or plasticizes organic additives, which reduces internal
friction. This chemical enhancement effect combined with the
physical energy aspects of the present invention, including
propellant thrust and momentum transfer, translates into extremely
effective penetration into boundary regions such as those present
in high speed, high force machining. This carbon dioxide chemical
enhancement can be introduced and controlled by adding an additive
phase into a carbon dioxide gas used in the diluent phase and/or
mixing an additive phase into the coolant phase.
[0077] Another aspect of the present invention is the use of the
composite machining fluid or spray in laser machining operations.
Referring to FIG. 15, a laser 202 is directed at a substrate 204
wherein the laser cuts or ablates the substrate. In order to
contain a heat affected zone 206 when lasing polymeric or metallic
materials, a spray applicator 208 directs a composite machining
fluid or spray 210 of the present invention towards the ablation
area. The composite machining fluid or spray 210 passes through a
beam 212 emitted by the laser 202 and extinguishes excess burning
which minimizes or eliminates plasma formation, fumes and soot
generation (polymers) within the ablation area. This results in
little or no attenuation of the laser power reaching the substrate
surface to perform more precise and pyrolytic laser ablation
processes, further resulting in the elimination of laser optical
surface build-up and light obscuration. Additionally, upon applying
the composite fluid or spray of the present invention, lased
substrate surfaces remain cool and dry during ablation operation,
with the substrate requiring no cleaning operation upon completion.
Thus, the cryogenic composite fluid or spray of the present
invention uniquely enables laser machining without the coolant
itself attenuating the laser light contacting the substrate surface
for wavelengths generated by most common machining lasers.
[0078] Tables 1 and 2 list non-exhaustive examples of infrared (IR)
and ultraviolet (UV) lasers for use with the present invention.
TABLE-US-00001 TABLE 1 Exemplary Infrared Lasers Lasing Medium
Laser Type Wavelength Er:Glass Solid State 1540 nm Cr:Forsterite
Solid State 1150-1350 nm HeNe Gas 1152 nm Argon Gas-Ion 1090 nm
Nd:YAP Solid State 1080 nm Nd:YAG Solid State 1064 nm Nd:Glass
Solid State 1060 nm Nd:YLF Solid State 1053 nm Nd:YLF Solid State
1047 nm InGaAs Semiconductor 980 nm Krypton Gas-Ion 799.3 nm
Cr:LiSAF Solid State 780-1060 nm GaAs/GaAlAs Semiconductor 780-905
nm Krypton Gas-Ion 752.5 nm Ti:Sapphire Solid State 700-1000 nm
[0079] TABLE-US-00002 TABLE 2 Exemplary UV Lasers Lasing Medium
Laser Type Wavelength Argon Gas-Ion 364 nm (UV-A) XeF Gas (excimer)
351 nm (UV-A) N2 Gas 337 nm (UV-A) XeCl Gas (excimer) 308 nm (UV-B)
Krypton SHG Gas-Ion/BBO crystal 284 nm (UV-B) Argon SHG Gas-Ion/BBO
crystal 264 nm (UV-C) Argon SHG Gas-Ion/BBO crystal 257 nm (UV-C)
Argon SHG Gas-Ion/BBO crystal 250 nm (UV-C) Argon SHG Gas-Ion/BBO
crystal 248 nm (UV-C) KrF Gas (excimer) 248 nm (UV-C) Argon SHG
Gas-Ion/BBO crystal 244 nm (UV-C) Argon SHG Gas-Ion/BBO crystal 238
nm (UV-C) Argon SHG Gas-Ion/BBO crystal 229 nm (UV-C) KrCl Gas
(excimer) 222 nm (UV-C) ArF Gas (excimer) 193 nm (UV-C)
[0080] FIG. 16 graphically illustrates contrasting generalized
light absorption profiles for substrates, composite sprays of the
present invention, and the commonly used lasers listed in Tables 1
and 2. FIG. 16 also overlays a generalized absorption profile for
water, which is typically considered a laser machining process
impediment. It can also be seen from FIG. 16 that polymeric and
metallic substrates 214 generally fall along a path from increased
absorption within the highly energetic UV regions 216 to a lower
absorption within the less energetic IR light regions 218. The
exemplary IR lasers listed in Table 1 fall within discrete bands
ranging from 700 nm to 1540 nm, while the exemplary UV lasers
listed in Table 2 fall within discrete bands ranging from 284 nm to
364 nm. Overlaying these exemplary substrate and laser spectrums is
the carbon dioxide absorption spectrum 220 which exhibits very
little or no absorption within the common IR and UV laser machining
bands. This is beneficial because the composite coolant sprays of
the present invention do not themselves become light-attenuating
impediments to the laser machining process. Also, it can also be
seen that water 222 exhibits a generalized light absorption profile
that tends to increase in both the UV and IR laser bands which
attenuates and reflects laser light at the substrate surface-laser
contact point. Composite machining fluids and sprays of the present
invention therefore produce dry-cold composite sprays which, during
laser ablation or machining, minimize or eliminate condensed
solidified or liquefied water from entering the laser cutting
zone.
EXAMPLES
[0081] Several experiments were designed and performed to compare
and contrast the relative performance of the present invention
against exemplary conventional cooling and lubrication techniques.
In the experiments that follow, it should be noted to those skilled
in the art that optimum fluid or spray composition parameters such
as spray distance, fluid or spray composition, spray angle, spray
delivery means, and optimum number of spray delivery devices for a
given machining operation were not optimized. The purpose of the
experiments was to gage the performance of the composite sprays
herein under approximately similar application conditions and
replicated machining operations.
High Speed Precision Grinding
[0082] A machining test was performed to examine the machined
surface quality and compare this to conventional flooded coolants.
The machining process performed was a rough and finish grinding of
a stainless steel-steatite-epoxy article having a steatite portion
224, an epoxy portion 226 and an Iron/Nickel alloy (Alloy 52)
portion 228. The machining process was accomplished using a diamond
grinding tool operating at 20,000 rpm in a Tsugami Model MA3 HMC.
The cryogenic machining fluid derived from the present invention
was a composite spray composition comprising solid carbon dioxide
as the coolant Fc, compressed air as the diluent Fd and isopropyl
alcohol as the additive Fa at a Fc:Fd:Fa ratio of 18:80:2 was used
at a diluent pressure of 620 kpa (90 psi), producing a composite
spray temperature of approximately 240 K (-30 degrees F.). The
composite spray was directed into the cutting zone at the contact
point between a diamond grinding tool and the inside surface of the
machined article using a 45 degree angled coaxial spray nozzle,
shown below.
[0083] Results from the machining experiment show that a better
quality finish is obtained using a composite spray of the present
invention as compared to a conventional flooded coolant system, as
depicted in FIGS. 17a, 17b and 18a, 18b. Referring to the FIGS. 17a
and 18a, the conventional approach causes smearing of the soft
alloy and deep grooves from the grinding bit, suspected to be
caused by insufficient chip removal, cooling and/or lubrication
within the high speed grinding zone. In contrast, the present
invention produces a very clean and bright finish with excellent
separation of steatite, epoxy and metal bands, as depicted in FIGS.
17b and 18b.
Low-Speed Drilling of Stainless Steel
[0084] A machining test was performed to examine the surface
quality of a stainless steel sheet drilled with a carbide drill
bit. A 0.64 cm (0.25 inch) substrate of stainless steel was drilled
using a Ryobi Drill Press, Model No. DP100, at a drilling speed of
3,600 rpm. Three spray compositions were derived. The first spray
composition consisted only of cooled compressed air as the diluent,
representing the prior art, with no coolant or additive phases for
a Fc:Fd:Fa ratio of 0:0:100, and applied at a diluent pressure of
550 kPa (80 psi) and 57 liters per minute (2 cfm), producing a
composite spray temperature of approximately 283 K (50 degrees F.).
The second spray composition comprised solid carbon dioxide as the
coolant, compressed air as the diluent and no additional additive
phase for a Fc:Fd:Fa ratio of approximately 30:70:0, and applied at
a diluent pressure of 550 kPa (80 psi) and temperature of 373 K
(212 degrees F.), producing a composite spray temperature of
approximately 240 K (-30 degrees F.). The third spray composition
comprised solid carbon dioxide coolant, compressed air as the
diluent and soy methyl ester as the additive for a Fc:Fd:Fa ratio
of approximately 29:70:1, and was applied at a diluent pressure of
550 kPa (80 psi) and temperature of 373 K (212 degrees F.),
producing a composite spray temperature of approximately 240 K (-30
degrees F.).
[0085] Each test spray was directed into the cutting zone at the
contact point between a drilling tool and contacting surface of the
machined article using an approximate 45 degree spray angle. FIG.
19a depicts a machined hole treated with the first spray, while
FIG. 19b depicts a machined hole treated with the second spray and
the FIG. 19c depicts a machined hole treated with the third spray.
The results shown below demonstrate the progressive improvement in
machined surface quality from cool air machining to cryogenic
composite sprays of the present invention.
IR Laser Milling of Butyl Rubber
[0086] A machining test was performed to examine the surface
quality of a butyl rubber milled using an IR Diode Laser with a 60
Watt power source and operating at a wavelength of approximately
940 nm as compared to using gas-assist cooling. A 0.64 cm (0.25
inch) substrate of butyl rubber was milled using an Opto Power
Laser System, Model No. H01 D060 MMM FCMS, equipped with a IR Laser
power control unit and fiber optically delivered Laser beam module
Model Number OPC-OPC-02. An automated rectangular scan pattern was
performed using a Janome Cartesian Robot, Model No. JR2203. Robot
scan speed was set to 10 mm/sec with the Laser focuses at a
distance of approximately 2.54 cm with a plunge depth (Laser
Focusing Distance) of approximately 0.5 mm. Laser power was
adjusted to 25 watts with approximately a 1 mm beam diameter. A
rectangular pattern of approximately 1.0 cm.times.0.5 cm was milled
into each sample surface for each type of spray tested.
[0087] Two spray compositions were derived. The first spray
composition, representing the prior art, consisted only of carbon
dioxide with no additive or coolant phases for a Fc:Fd:Fa ratio of
0:100:0, and applied at a diluent pressure of 550 kPa (80 psi) and
temperature of 294 K (70 degrees F.), producing a composite spray
temperature of approximately 294 K (70 degrees F.). The second
spray composition comprised solid carbon dioxide as the coolant,
compressed air as the diluent and no additive phase for a Fc:Fd:Fa
ratio of approximately 20:80:0, and was applied at a diluent
pressure of 550 kPa (80 psi) and temperature of 373 K (212 degrees
F.), producing a composite spray temperature of approximately 244 K
(-20 degrees F.).
[0088] FIG. 20a depicts the substrate treated with the first spray
of the prior art, while FIG. 20b depicts the substrate treated with
the second spray of the present invention. The results demonstrate
that Laser milling with a spray composition of the present
invention as compared to gas-assist Laser milling produces a
cleaner channel and minimal sidewall melting. A closer look at the
machined surfaces reveals the improvements in sidewall definition,
deeper trench depth, and cleaner channel cut using a composite
spray of the present invention with IR Laser machining.
[0089] An interesting observation during Laser machining was that
the composite spray of the present invention produced much less
black char and residues following machining. The gas assist test
produced an extremely dirty surface and significant airborne soot
following processing.
IR Laser Milling of Fluorosilicone Rubber
[0090] A machining test was performed to examine the surface
quality of a fluorosilicone rubber milled using an IR Diode Laser
with a 60 Watt power source and operating at a wavelength of
approximately 940 nm. A 0.64 cm (0.24 inch) substrate of
fluorosilicone rubber was milled using an Opto Power Laser System,
Model No. H01 D060 MMM FCMS, equipped with a IR Laser power control
unit and fiber optically delivered Laser beam module Model Number
OPC-OPC-02. An automated rectangular scan pattern was performed
using a Janome Cartesian Robot, Model No. JR2203. Robot scan speed
was set to 10 mm/sec with the Laser focuses at a distance of
approximately 2.54 cm with a plunge depth (Laser Focusing Distance)
of approximately 0.5 mm. Laser power was adjusted to 25 watts with
approximately a 1 mm beam diameter. A rectangular pattern of
approximately 1.0 cm.times.0.5 cm was milled into each sample
surface for each type of spray tested.
[0091] Two spray compositions were derived. The first spray
composition, representing the prior art, consisted only of carbon
dioxide gas as the diluent with no additive or coolant phases for a
Fc:Fd:Fa ratio of 0:100:0, and was applied at a diluent pressure of
550 kPa (80 psi) and temperature of 294 K (70 degrees F.),
producing a composite spray temperature of approximately 294 K (70
degrees F.). The second spray composition, representing the present
invention, comprised of solid carbon dioxide as the coolant,
compressed air as the diluent and no additive phase for a Fc:Fd:Fa
ratio of approximately 20:80:0, and applied at a diluent pressure
of 550 kPa (80 psi) and temperature of 373 K (212 degrees F.),
producing a composite spray temperature of approximately 244 K (-20
degrees F.).
[0092] FIG. 21a depicts the substrate treated with the first spray
of the prior art, while the FIG. 21b depicts the substrate treated
with the second spray of the present invention. The results
demonstrate that Laser milling with a spray composition of the
present invention as compared to gas-assist Laser milling produces
a cleaner channel and minimal sidewall melting, shown below. Also,
the profile of the gas-assist experiment in FIG. 21a depicts
minimal penetration and a plume which indicates overheating and
non-uniform melting of the surface. By contrast, the Laser plunge
profile of the composite spray test gives excellent circular
uniformity, approximately equal to the Laser beam diameter, and
much greater penetration depth. Referring to FIGS. 22a and 22b,
magnification reveals significant differences in kerf width,
channel depth, and relative smoothness. A closer examination under
magnification reveals significant differences in kerf width,
channel depth, and relative smoothness.
[0093] It was observed during the Laser machining of the
fluorosilicone substrate that the gas assist spray was unable to
extinguish a visible burning at the cutting zone during the Laser
milling operation. The surface of the substrate was visibly charred
following milling and required spray cleaning prior to taking the
photomicrographs to reveal the machined surfaces. By contrast, the
composite spray test resulted in a very clean and invisible IR
Lasing operation, which suggests a much improved pyrolytic
ablation.
[0094] An inherent advantage of the present invention was
discovered to be the absence of significant soot generation and
build-up on the Laser optics, which is detrimental to the Laser
operation and attenuates Laser light energy reaching surface.
High Speed Spindle Milling of Acrylic Plastic
[0095] A machining test was performed to examine the surface
quality of an acrylic plastic milled using a high speed robotic
spindle operating at 40,000 rpm. A 0.64 cm (0.25 inch) substrate of
acrylic plastic was milled using an Air Turbine Spindle Model 600.
An automated rectangular scan pattern was performed using a Janome
Cartesian Robot, Model No. JR2203. Robot scan speed was set to 10
mm/sec with a plunge depth of less than 0.5 mm using a 1/8 inch
router bit. The spindle speed was not adjustable and was operated
at 40,000 rpm. A rectangular pattern of approximately 1 cm.times.1
cm was milled into each sample surface for each type of spray
tested.
[0096] A spray composition was derived comprising solid carbon
dioxide as the coolant, compressed air as the diluent and no
additive phase at a Fc:Fd:Fa ratio of approximately 20:80:0, and
applied at a diluent pressure of 550 kPa (80 psi) and temperature
of 373 K (212 degrees F.), producing a composite spray temperature
of approximately 244 K (-20 degrees F.).
[0097] The results demonstrate that spindle milling with a spray
composition of the present invention produces a clean channel and
minimal surface chipping, as depicted in FIG. 23.
[0098] The present invention has been developed to address the
cooling and lubricating challenges of high technology manufacturing
operations such as high and low speed metalworking, micro-device
machining, copper wafer dicing, and LASER drilling. However, the
present invention is not limited in use or application to a
specific market or application. For example the present invention
can be used to selectively solidify freeze biological tissues such
as tumors or warts, a means for relieving pain due to burns, and a
method for removing skin blemishes through a cryokinetic removal
processes, and a means for directional solidification. The present
invention provides a unique and very useful hybrid technology,
providing cooling, lubricating and cleaner processing for
integration into original equipment manufacturer (OEM) tools as
well as serving as a stand-alone tool for manufacturing companies
requiring this combination of dry and semi-dry thermal control,
cooling and/or lubrication.
[0099] Although the present invention has been described with
reference to preferred embodiments, workers skilled in the art will
recognize that changes may be made in form and detail without
departing from the spirit and scope of the invention.
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