Note: Descriptions are shown in the official language in which they were submitted.
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The presen~ invention pertains generally to the cutting
of glass by means of an abrasive fluid ~et and more particularly
eo the cutting of glass along any desired line of cut, including
intricate patterns, at relatively high speed wlth resultant high
quality cut surfaces by means of an abrasive fluid ~et dlrected
against the glass.
Because of its extreme hardness and frangible nature,
unique problems are presented in the cutting or severing of
glass. Conventional glass cutting actually lnvolves a controlled
breaking or fracturing of the glass. Thus, the surface of the
glass is scored by a relatively harder instrument along the
desired path of fracture, and the glass is then flexed along the
score line to cause it to fracture and separate along this line.
While such a procedure is satisfactory for certain purposes, it
also has many limitations. A glass sheet is very rigid and it
must be flexed along the score line to cause the f~nal fracture.
As wlll be apparent, wh le the sheet can be readily flexed along
a straight score line, extending substantially across the sheet,
flexing is much more difficult along score lines of an interior
cutout and be~omes nearly impossible for such openings of small
dimensions. Flexing along a curved score line may be
troublesome, and it becomes increasingly difficult as the degree
of curvature increases. Flexing along lines with short radii of
curvature iB virtually impossible so that intricate patterns can
be cut only with great difficulty, if at all. Likewise,
formation of small mountlng openings as commonly required in
present day automobile sidelites is not feasible by this method,
so that such open~ngs must generally be formed by means of a
diamond drill.
The procedure is effective in cuttlng relatively thin
glass wherein, because of the depth of the score mark relative to
the total glass thickness, the fracture will follow the score
line. ~owever, in cutting thicker glass by this method the line
of fracture may not follow the score line so that a ragged edge
is formed, or the glass may actually fracture along a random
line, destroying the glass sheet. The d~fficulty of cuttlng
increases as the thickness increases, so that cuttlng very heavy
glass is time consuming and expensive, and the yield of useable
glass is relatively lo~. The method also tends to leave a sharp
edge at the surface opposite the score line, which is
objectionable in additional fabricating steps.
Other systems such as so-called hot line cutting,
wherein the glass is heated along a line and then chilled to
cause fracturing along the line, and cutting with a diamond saw,
have been suggested for cutting glass and particularly thick
glass. However, neither has proven entirely satisfactory in a
commercial operation, and particularly for production of other
than straight line cuts. Such methods tend to be slow and
expensive and may create undesirable stresses in the glass. They
also are not readily adapted to cutting complex shapes in glass.
The concept of liquid ~et cutting of various materials
is known in the prior art, as is the use of abrasive particles in
conjunction with the liquid jet. While it is suggested, for
example, by U.S. patent No. 3,888,054, that hard or brittle
materlals such as glass may be cut by a stream of abrasive
particles carried in a fluid, it is also disclosed that the
workpiece should be immersed in a liquid to avoid abrading away
of the surface adjacent the cut. U.S. patent No. 4,380,138
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discloses abraslve liquid ~et cutting wherein abrasive particles
are positioned ad~cent the surface of the material to be cut and
then driven into the workpiece by the liquid jet, and suggests
that it was previously unknown to add abrasive particles directly
to high velocity liquid cutting ~ets. In any event, the prior
art is not believed to appreciate the cutting of glass with an
abrasive fluid ~et in the manner and at the pressure contemplated
by the present invention.
Thus, it has been found that when flat glass sheets of
thicknesses in general commercial use are initially impacted
interiorly of their periphery by an abrasive fluid ~et
pressurized to a level materially exceeding 10,000 psi, as in
forming holes or interior cut-outs in the glass, chipping, severe
venting or shattering of the glass at the point of impact is
likely to occur. The vents and chipped edges may extend into the
ad~acent glass part, rendering it unuseable for its intended
purpose. Consequently, it has heretofore generally been
considered necessary for such cutting on a large scale to be done
with a fluid under a pressure on the order of 10,000 psi or less
in order to prevent damage to or destruction of the glass. The
line or cutting speed is a function of the degree of
pressurization of the abrasive fluid, and at this pressure the
cutting speed is so limited as to make the procedure marginally
useful for commercial purposPs.
It has now been determined that cutting may
advantageously be accomplished with the abrasive fluid ~et
pressurized to a much higher level, with a consequent increase in
line or cutting speed, while still achieving cut edges of
acceptable quality e~uivalent to those previously achieved at the
lower pressures. More particularly, abrading away of the glass
along the line of cut by the advancing ~et ideally occurs with
the abrasive fluid ~et pressurized to a level on the order of
20,000 psi to 35,000 psi, and preferably about 30,000 psi,
wbereby cut edges of acce~table quality can be produced at
greatly increased line speeds for all thicknesses of glass.
Pressures materially above 35,000 psi, however, may result in cut
edges of reduced quality regardless of line speed.
Thus, in accordance with the present invention,
annealed glass of various thicknesses may be cut along any
desired path, irom straight lines to intricate shapes, relatively
quickly and inexpensively with a resul~ing edge finish of high
quality. To that end, the glass i5 firmly supported along the
path which the cut is to follow, and a high velocity fluld ~et,
into whlch a fine abraslve material is aspirated in carefully
controlled amounts, is directed against the glass surface in a
highly collimated stream. Where the cut is to begin at an edge
of a glass sheet that is, initial contact with the glass begins
at an exposed edge, the abrasive fluid ~et is discharged under
the normal high operating pressure and moved toward and into
engagement with the glass to begin cutting at the free edge with
a line speed at which cut edges of acceptable quality are
produced. On the other hand, where initlal penetration is to be
in the interior of the sheet, the fluid is discharged under a
reduced entry level pressure during initial penetration of the
glass so as to begin the cut without undue spalling or complete
shattering of the glass at the point of entry, and the pressure
i8 then increased to the substantially hlgher level as the cut
proceeds in order to achieve maximum cutting or line speed, with
the resulting cut edges having the desired high quality. It will
be understood, of course, that while the invention has been
illustrated and described herein as creating relative movement
between the fluid ~et and glass by moving a no~zle assembly
relative to a stationary glass sheet, it is fully contemplated
the relative movement may likewise be created by moving the glass
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relative to a fixed nozzle assembly or by combined movements
of the two.
In summary, therefore, the present invention may
be seen as providing a method of maximizing the speed of
cutting glass of various thicknesses along a desired path by
means of an abrasive fluid jet so as to produce cut edges
having at least a predetermined level of quality, the level
of quality being a function of the rate of movement of the
abrasive jet along the path, comprising discharging a highly
collimated fluid jet from a pressurized source maintained at
an ultra-high pressure level, entraining abrasive particles
into the fluid jet, engaging the glass with the abrasive
particle-containing fluid jet, moving the abrasive jet and
glass relative to one another whereby the abrasive jet
advances along the path and cuts through and severs the
glass, observing the quality of the cut glass edge, and
controlling the rate of movement of the abrasive jet
relative to the glass in response to the observed quality to
maintain the rate of movement at the maximum at which the
cut glass edge has at least the predetermined level of
quality.
Also, in accordance with this invention, there is
provided a method of maximizing the speed of cutting glass
of various thicknesses along a desired path by means of an
abrasive fluid jet so as to produce cut edges having at
least a predetermined level of quality, the level of quality
i~ being a function of the rate of movement of the abrasive jet
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along the path, comprising directing a highly collimated
fluid jet against the surface of the glass from a
pressurized source maintained at the first pressure level,
aspirating abrasive particles into the fluid iet as it is
directed toward the glass, initially penetrating the glass
with the abrasive jet while the pressurized source is
maintained at the first pressure level whereby the glass
does not fracture, vent or chip in the area of initial
severing, increasing the pressure in the p~essurized ~ourc~
to a second level significantly greater than the first
pressure level while continuing to direct the abrasive jet
against the glass, advancing the abrasive jet along the path
st the second pressure level whereby the abrasive jet cuts
through and severs said glass along the path, observing the
quality of the cut glass edge, and advancing the abrasive
jet in response to the observed quality to maintain the rate
of movement at the maximum at which the cut glass edge has
at least the predetermined level of quality.
In the accompanying drawings:
Fig. 1 is a schematic perspective view of a system
for practicing the invention;
Fig. 2 is an enlarged side elevational view,
partly in section, of a jet nozzle assembly employed in
cutting glass by means of an abrasive fluid jet;
Fig. 3 is a graph illustrating the relationship
between cutting or line speed and the grit size of the
abrasive particles for a particular glass thickness; and
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Fig. 4 is a graph illustrating the relationship
between cutting or line speed and glass thickness for a
particular grit size of the abrasive particles.
Referring now to the drawings, there is
illustrated schematically at 10 in Fig. 1 a system which may
be employed in
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cutting gl~ss shee~s in accordance with the invention. More
particularly, the system is adapted for cutting glass sheets or
blanks along prescribed lines of any preferred configuration and
includes an optical tracer apparatus 11 and an abrasive fluid jet
cuttlng apparatus, generally designated 12. The cutting
apparatus 12 includes a support stand 13 adapted to firmly
support a glass sheet S, as on a sacrificial support plate, for
cutting as will be hereinafter more fully described. While the
illustrated system represents a preferred embodiment for
practicing the invention, as wlll be readily appreciated the
invention is not limited to use with such a system but also has
utility with other and different equipment.
In the illustrated embodiment the fluid ~et cutting
apparatus 12 includes a discharge or nozzle assembly 14, as will
be hereinafter more fully described, mechanically connected to
the optical tracer 11 by meanæ of a tie bar 15. The tracer is
provided for guiding the movement of the nozzle assembly 14 in
accordance with a template or pattern 16 on a plate member 17
mounted on a table 18. The optical tracer 11 is affixed to a
carriage 19 slidably mounted on an elongated transverse track 20
which is provided at its opposite ends with a pair of carriages
21 and 22. The carriages 21 and 22 are slidably mounted on
parallel tracks 23 and 24, respectively, supported by stanchion
members 25 on a floor 26. The nozzle assembly 14 is affixed as
by a plate 27, to a carriage 28 also slidably mounted on the
transverse track 20. The carriage 28 is rigidly connected in
spaced relationship to the carriage l9 by the tie bar 15, with
the spacing between the carriages 19 and 28 being such that the
optical tracer 11 and the nozzle assembly 14 overlie the plate 17
and the support stand 13, respectively.
Thus, as will be readily appreciated, with the above
described carriage system the tracer 11 is capable of movement in
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any direction longitudinally, laterally or diagonally, with the
carriage 28 and nozzle assembly 14 followlng the same motion due
to the union of the carriages 19 and 28 by the tie bar 15 and the
track 20. In operation, as the tracer 11 follows the outline or
pattern 16, the fluid jet cutting nozzle 14, via the carriage 28,
is caused to move correspondingly over the support stand 13 and
the glass sheet S thereon. For purposes of illustration the path
of the cut along the sheet S has been illustrated as beginning at
an edge and running diagonally across the sheet. It will be
understood, of course that inasmuch as the path is dLctated by
the template or pattern 15, it may as well prescribe a closed
interior cut-out or circular opening if so dictated by the
template. Control of the tracer functions such as power on/off,
speed, automatic and manual operation, level of pressurization of
the fluid ~et, etc., may be effected as from a conveniently
located control panel 29.
The fluid ~et cutting apparatus itself as shown
schematically in Fig. 1, includes an electric motor 30 driving a
hydraulic pump 31, which in turn supplies working fluid through a
conduit 32 to a high pressure intensifier unit 33. The function
of the intensifier unit 33 is to draw in fluid (for example,
deionized water) from a suitable source, such as a reservoir 34,
and place it under a very high pressure which may be variably
controlled, preferably on the order of 10,000 to 30,000 psi. 9 for
discharge through a conduit 35. Mounted at the discharge end of
the conduit 35 ls nozzle assembly 14 for directing a very high
velocity, small dia0eter fluid jet toward the glass sheet S upon
the support stand 13.
As best shown in Fig. 2, the nozzle assembly 14
comprises a generally rectangular housing 36 having a threaded
bore 37 at its upper end, axially aligned with a flow passageway
38 extending through the housing. An externally threaded
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connector 39, having a flow passageway 40 extending therethrough,
is suitably attached to the discharge end of the conduit 35 for
connecting the conduit to the houslng. A recess 41 is provided
in a boss 42 at the threaded end of the connector 39, within
which is mounted a fluid jet orifice 43 having a discharge
opening 44 of very small, for example, on the order o~ 0.004 to
0.018 inch (.10 to .46 mm) and preferably about 0.014 inch (.35
mm), diameter. '~he~ s~curely threaded in the bore 37, the
connector 39 properly seats the orifice 43 in the upper, reduced
diameter portion 45 of the flow passageway 38. The lower end of
the passageway 38 includes an enlarged diameter portion 46 for
receiving a nozzle or mixing tube 47. The nozzle tube includes a
relatively small diameter, for example on the order of .040 to
.062 inch (1.0 to 1.57 mm) and preferably about .062 inch (1.57
mm) longitudinal passageway 48 with an outwardly flared entrance
opening 49 for more readily receiving the ~et stream from the
orifice 43.
Obliquely oriented to the passageway 38 is a bore 50
for delivering abrasive material, as will be hereinafter more
fully described, into the path of the 1uid ~et stream. A
regulated supply of the abrasive is carried from a storage
container 51 and regulator 52 to the bore 50 by means of a
flexible conduit or carrier tube 53. The abrasive material is
aspirated into the fluld ~et stream as the stream passes through
the passageway 38, wherein it ls mixed and accelerated into the
high pressure stream prior to enterlng the passageway 48 in the
nozzle tube 47. In operation, the exit end of the tube 47 is
generally positioned relatively close to the surface of the
workpieces, as will be more fully described, in order to minimize
dispersion of the ~et stream and thus provide a minimum kerf or
impingement area width. It will be appreciated that the
aforedescribed nozæle assembly is only intended to be
_ 9 _
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representative of those which may be employed in practicing the
invention.
In order to produce a cut edge of acceptable quality at
a rapid rate by means of an abrasive fluid ~et, it is imperative
that a number of parameters in the process be properly correlated
and controlled. Thus, it has been found that factors such as the
type and particle or grit size of abrasive material, type of
fluid medium and degree to which it is pressurized, feed rate of
the abrasive materi~l, diameter of the orifice discharge opening
44, length and diameter of the passageway 48 in the nozzle tube
47, distance of the nozzle from the glass surface, thickness of
the glass, and rate of progression of the cuttlng ~et along the
glass, all interact and must be properly correlated in order to
produce a cut of high quality at a suitable line speed.
A number of products are commercially available for use
as the abrasive medium, including those sold under the names
Biasil, AMA Zircon, ~ircon M, Florida Zircon, Zircon 'T', Idaho
Garnet, Barton Garnet, 0-I Sand and Rock Quartz. The products
are available in a range of nominal sizes extending from 60 grit
or coarser to 220 grit or finer. It has been found that while
glass can be successfully cut in accordance with the inventio-n
using abrasive particles having any of the aforementioned sizes
by approprlately varying interrelated parameters such as line
speed and fluid pressure, use of abrasive particles within a
particular qize range will produce a cut edge of hig~ ~uality at
faster line speeds than other grit sizes in glass of most
commercially available thicknesses. Thus, in the graph of Fig. 3
there is plotted the experimentally determined relationship
betwen abrasive particle grit size and line or cutting speed in
cutting glass of .235 inch (6.0 mm) thickness at a fluld pressure
of 30,000 psi in accordance with the invention. The upper,
broken-line curve represents the maximum speed oE the cutting
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head, i.e., line speed, at which the advancing abrasive ~et will
sustain a cut enti~ely through the glass. At such a speed th~
cut glass edges tend to chip and develop undesirable strlations
and vents running into the adjacent glass, so that the cut may
not be of acceptable quality. The lower, solid-line curve
represents the attainable spced at which the cut glass edges will
be of a smooth, uniformly high quality. As will be apparent,
maximum speed is attained whlle achieving both complete severance
and quality edge condition with an abrasive particle grit size in
10 the 130 to 150 range. The family of curves representing cutting
speed vs. grit size for commercially manufactured glass
thicknesses below 0.235 inch (6.0 mm) is generally similar to
that illustrated in Fig. 3, while the curves for thicker glass,
particularly of 0.500 inch (12.7 mm) and 0.750 inch (19.1 mm)
thicknesses, tend to be more flat and horizontal. Thus, abrasive
particles in the intermediate grit size range are well suited to
cutting glass of varing commercially ava~lable thicknesses. As
indicated above abrasive particles of differing grit sizes may be
employed in practising the invention by varying other parameters
such as the line speed. However, as a matter of convenience it
is preferable that material of a single grit si~e be employed in
cutting the various thicknesses, and a grit size in the
above-noted range is well suited for this purpose. Abrasive
material is readily available in a 150 grit size and thus such a
material, for example, that i8 available under the name Barton
garnet, may advantageously be employed in cutting glass in
accordance with the invention.
The graph of Fig. 4 plots the relationship between line
speed in inches per minute and glass thickness in cutting the
various thicknesses of glass in accordance with the invention,
employing a 150 grit garnet as the abrasive medium in a fluid
pressurized to about 30,000 psi. Again, the upper, broken line
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represents ehe ~aximum line speed at which the advancing abrasive
~et will penetrate completely through the glass, while the solid
line represents the line speed at which the cut glass edges ~ill
be of a smooth, uniformly high quality. In prepar-ng the test
data it was found that the maximum line speed for completely
severing very thin glass, that ls havlng a thlckness less than
about 0.150 inch (3.8 mm), exceeded the maximum line speed
capabillty of the rnachine of Figs. 1 and 2 employed for cutting
the glass. In other words, glass of less than about 0.150 inch
(3.8 mm) could be cut at speeds in excess of 100 inches per
minute. The apparatus employed in ~ut~ing the glass in
accordance with Figs. 3 and 4, as best shown in Fig~ 2, included
a jewelled orifice 43 having a discharge opening 44 of 0.014 inch
(.35 mm) diameter, with a nozzle tube 47 having a length of 3
inches (7.62 cm) and a passageway 48 therethrough of 0.052 inch
(1.57 mm) dlameter. The end of the nozzle tube was located 0.050
inch (1.27 mm) from the surface of the glass. Deionized water
was utilized as the ~et fluid, and garnet abrasive particles were
aspirated into the fluid stream at a feed rate of about one pound
(0.454 kg) per minute.
In practicing the invention the fluid medium, generally
deionized water, iæ pressurized in the h1gh pressure intensifier
for discharge through the nozzle assembly. Abrasive particles,
for example 150 grit garnet, are aspirated into the jet stream at
a rate of about one pound (.454 kg) per minute. Where the
advancing abrasive ~et is to initially engage the glass at an
exposed edge thereof, the fluid medium is pressurized in the high
pressure intensifier to an ultra-high pressure on the order of
20,000 psi to 357000 psi, and preferably about 30,000 psi, and
the cutting apparatus 12 and nozzle assembly 14 are advanced so
that the abrasive ~et begins the cut at the edge and follows the
path prescribed by the template 16. In those situations where
_12
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the abrasive ~et initially engages the glass at an interior
location, the fluid medium is pressurized to a level on the order
of 10,000 psi until the abrasive ~et has made the initial cut
through the glass, and the pressure in the high pressure
intensifier is then significantly increased, for example to a
level on the order of 20,000 psi to 35,000 psi and preferably
about 30,000 psi. The cutting apparatus 12 and nozzle assembly
14 are then advanced along the path prescribed by the template 16
to cut the prescribed opening in the glass sheet S. After the
initial penetration has been made, the glass does not shatter or
vent when impacted by the abrasive ~et stream pressurized to the
aforementioned ultra-high pressure, apparently due to the
progressive abrasive removal of glass fragments. Due to the
speed at which the ultra-high pressure abrasive stream cuts
through the glass, the line speed or movement of the nozzle
assembly 14 relative to the glass can be signficantly increased
while still producing cut edges of uniformly high quality.
As hereinabove described, abrasive particles of 150
grit size are particularly suitable for cutting the range of
glass thicknesses most often employed in commercial practice at
high line speeds in accordance with the invention. It will be
understood, however, that cut edges of high qualiey can be
achieved using abrasive particles of different grit size by
suitably varying other parameters. Thus, it is noted that
smaller abrasive particles, for example of 180 or 220 grit size,
will produce very smooth cut edges but the line or cutting speed
will be slower than with 150 grit Material. Conversely, it is
possible to cut through glass at faster overall line speeds with
coarser 60 or 100 grit material but, due to edge chipping and
30 hazlng at the high speeds, the cut edge will be of reduced
quality. In order to achieve edge quality equivalent to that
produced with 150 grit material, it will be necessary to reduce
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the line speed. The angle of taper of the cut edges is dependent
upon both grit size of the abrasive particles and line speed of
the cutting device. Thus, the angle of taper of the cut edge
increases as the abrasive particles are made finer and as the
line speed increases.
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