Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Methods and Systems for Welding Copper and Other Metals Using Blue Lasers
[0001] This application: (i) claims under 35 U.S.C. 119(e)(1) the
benefit of
the filing date of US provisional application serial number 62/786,511 filed
December
30, 2018, the entire disclosure of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
Field of the Invention
[0002] The present inventions relate to laser processing of
materials, and in
particular laser joining of copper materials using laser beams having
wavelengths from
about 350 nm to about 500 nm, and greater.
[0003] Laser welding of copper has proven to be very challenging
due to high
reflectivity, high thermal conductivity and high heat capacity. Numerous
methods have
been developed to weld copper ranging from ultrasonic welding to IR laser
welding.
These prior copper welding methods, however, have many shortcomings and
limitations.
For example, one market where these limitations are seen is in the area of
high
performance electronics for the growing electronic vehicle market. A better
weld quality
with higher speed, than can be obtained by these prior techniques, is needed
to produce
high performance batteries and electronics for the growing automotive markets.
[0004] When using an IR laser source at 1030 nm, the high reflectivity of
the
copper at this wavelength makes it difficult to couple power into the material
to heat and
weld it. One method to overcome the high reflectivity is to use a high-power
level (> lkW)
IR laser to initiate a keyhole weld which then couples the power into the
material. The
problems with this method of welding, among other things, is that the vapor in
the keyhole
can lead to a micro-explosion, spraying molten copper all over the parts being
welded or
the micro-explosion can cause a hole completely through the parts being
welded.
Consequently, researchers have had to rely on rapidly modulating the laser
power to try
to prevent these defects during welding. It has been discovered that the
defects are a
direct result of the process itself, as the laser attempts to weld the copper,
it initially heats
it up to the melting point and then it rapidly transitions into vaporizing the
copper. Once
the copper vaporizes the keyhole is formed and the laser coupling rises
rapidly from the
initial 5% to 100%, this transition occurs so rapidly that the amount of heat
coupled in
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rapidly exceeds the amount of heat needed to weld the parts, resulting in the
micro-
explosion described.
[0005] Laser welding of copper with current infrared lasers method
and systems
is challenging, and has problems, due to the high reflectivity, high thermal
conductivity,
low vaporization points and high heat capacity. Numerous methods have been
attempted
to weld copper with IR lasers ranging from combining the IR laser with a green
laser,
wobbling the spot in the weld puddle, operating in a vacuum and modulating the
laser at
a high frequency. While these approaches are currently in use for some copper
welding
applications, they tend to have narrow processing windows, uncontrolled
spatter, and
.. unpredictable variability in the welds, and have generally proved to be
less than desirable
or optimal. One of the more difficult copper welding process is the how to
weld stacks of
copper foil to each other and to thicker bus bars. Today, this cannot be done
with an IR
laser reliably or in a manner that produces the weld qualities that are needed
by
manufactures. Thus, manufacturers have relied on ultrasonic welding methods to
bond
these foils together. These ultrasonic methods are also less than optimal and
are
problematic. For example, with ultrasonic welding methods, the sonotrodes can
wear
during production resulting in process variabilities ranging from incomplete
welds to welds
with debris left behind. These deficiencies limit the manufacturing yield, the
internal
resistance of batteries, the energy density of the resulting batteries and in
many cases
the reliability of the batteries.
[0006] The term "copper based material" unless expressly provided
otherwise,
should be given it broadest possible meaning and would include copper, copper
materials, copper metal, materials electroplated with copper, metallic
materials that
contain from at least about 10% copper by weight to 100% copper, metals and
alloys
containing from at least about 10% copper by weight to 100% copper by weight,
metals
and alloys containing from at least about 20% copper by weight to 100% copper
by
weight, metals and alloys containing from at least about 10% copper by weight
to 100%
copper by weight, metals and alloys containing from at least about 50% copper
by
weight to 100% copper by weight, metals and alloys containing from at least
about 70%
copper by weight to 100% copper by weight, and metals and alloys containing
from at
least about 90% copper by weight to 100% copper by weight.
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[0007] The terms "laser processing, "laser processing of
materials," and
similar such terms, unless expressly provided otherwise, should be given there
broadest
possible meaning and would include welding, soldering, smelting, joining,
annealing,
softening, tackifying, resurfacing, peening, thermally treating, fusing,
sealing, and
stacking.
[0008] As used herein, unless expressly stated otherwise, "UV",
"ultra violet",
"UV spectrum", and "UV portion of the spectrum" and similar terms, should be
given
their broadest meaning, and would include light in the wavelengths of from
about 10 nm
to about 400 nm, and from 10 nm to 400 nm.
[0009] As used herein, unless expressly stated otherwise, the terms
"visible",
"visible spectrum", and "visible portion of the spectrum" and similar terms,
should be
given their broadest meaning, and would include light in the wavelengths of
from about
380 nm to about 750 nm, and 400 nm to 700 nm.
[0010] As used herein, unless expressly stated otherwise, the
terms "blue
laser beams", "blue lasers" and "blue" should be given their broadest meaning,
and in
general refer to systems that provide laser beams, laser beams, laser sources,
e.g.,
lasers and diodes lasers, that provide, e.g., propagate, a laser beam, or
light having a
wavelength from about 400 nm to about 500 nm. Typical blue lasers have
wavelengths
in the range of about 405-495 nm. Blue lasers include wavelengths of 450 nm,
of about
450 nm, of 460 nm, of about 470 nm. Blue lasers can have bandwidths of from
about
10 pm (picometer) to about 10 nm, about 5 nm, about 10 nm and about 20 nm, as
well
as greater and smaller values.
[0011] As used herein, unless expressly stated otherwise, the
terms "green
laser beams", "green lasers" and "green" should be given their broadest
meaning, and
in general refer to systems that provide laser beams, laser beams, laser
sources, e.g.,
lasers and diodes lasers, that provide, e.g., propagate, a laser beam, or
light having a
wavelength from about 500 nm to about 575 nm. Green lasers include wavelengths
of
515 nm, of about 515 nm, of 532 nm, about 532 nm, of 550 nm, and of about 550
nm.
Green lasers can have bandwidths of from about 10 pm to 10 nm, about 5 nm,
about 10
nm and about 20 nm, as well as greater and smaller values.
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[0012] As used herein, unless expressly stated otherwise terms
such as "at
least", "greater than", also mean "not less than" ,i.e., such terms exclude
lower values
unless expressly stated otherwise.
[0013] As used herein, unless stated otherwise, room temperature
is 25 C.
And, standard temperature and pressure is 25 C and 1 atmosphere. Unless
expressly
stated otherwise all tests, test results, physical properties, and values that
are
temperature dependent, pressure dependent, or both, are provided at standard
temperature and pressure.
[0014] Generally, the term "about" and the symbol "¨" as used
herein, unless
specified otherwise, are meant to encompass a variance or range of 10%, the
experimental or instrument error associated with obtaining the stated value,
and
preferably the larger of these.
[0015] As used herein, unless specified otherwise, the recitation
of ranges of
values, a range, from about "x" to about "y", and similar such terms and
quantifications,
serve as merely shorthand methods of referring individually to separate values
within
the range. Thus, they include each item, feature, value, amount or quantity
falling within
that range. As used herein, unless specified otherwise, each and all
individual points
within a range are incorporated into this specification, and are a part of
this
specification, as if they were individually recited herein.
[0016] This Background of the Invention section is intended to introduce
various aspects of the art, which may be associated with embodiments of the
present
inventions. Thus, the forgoing discussion in this section provides a framework
for better
understanding the present inventions, and is not to be viewed as an admission
of prior
art.
SUMMARY
[0017] There is a continuing and increasing need for better weld
quality,
higher speed welds, as well as, greater reproducibility, reliability, higher
tolerances and
more robustness in the welding of metals and, in particular, the welding of
copper
metals for electronic components and batteries. Included in these needs, there
is the
need for an improved method for welding copper to itself and other metals;
and, there is
a need to address the issues associated with welding stacks of copper foils
and these
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stacks to thicker copper or aluminum parts. The present inventions, among
other
things, solve these needs by providing the improvements, articles of
manufacture,
devices and processes taught, and disclosed herein.
[0018] Thus, there is provided a system for and a method of laser
welding a
plurality of cooper foils together, the method including the steps of:
positioning a
plurality of pieces of cooper foil in a welding stand; wherein the foil
contains at least
about 50% cooper; exerting a clamping force on the plurality of pieces of
cooper foil to
clamp the pieces of foil together in the welding stand; directing a blue laser
beam along
a laser beam path at the plurality of pieces of cooper foil, wherein the laser
beam has
the following properties: (i) at least 500 Watts of power; (ii) a beam
parameter product of
about 44 mm mrad and less; (iii) a spot size of about 400 pm and less; (iv) an
average
intensity of at least of about 400 kW/cm2; (v) a peak intensity of at least
about 800
kW/cm2; and the blue laser beam lap welding the plurality of pieces of cooper
foil
together at a welding speed; and, providing a non-oxidizing beam clearing gas
in a
space along the laser beam path where the laser beam travels in free space
from an
optical element to the plurality of pieces of cooper foil; wherein clearing
gas removes
plume material from the laser beam path and prevents oxidation of the
plurality of
pieces of cooper foil; wherein the welding speed, clamping force, and a flow
rate of the
non-oxidizing clearing glass, are predetermined to thereby provide a lap weld
having no
visible splatter and no visible porosity.
[0019] Additionally, there is provided these welds, laser systems
and welding
methods have one or more of the following features: wherein the beam is a CW
beam;
wherein the beam is a pulsed beam; wherein the beam has a wavelength of about
450
nm; wherein the optical element is selected from the group consisting of a
lens, a fiber
face, and a window; wherein the clearing gas is selected from the group
consisting of
Argon, Argon-0O2, Air, Helium and Nitrogen; wherein the laser beam is not
wobbled;
thereby providing a wobble free laser welding process; wherein the plurality
of pieces of
cooper foil has from 10 to 50 pieces of foil; wherein a cooper foil piece has
a thickness
of from about 80 pm to 500 pm; wherein each of the plurality of pieces of
cooper foil has
a thickness of from about 80 pm to 500 pm; and, wherein the welding speed is
at least
10 m/min.
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[0020] Further, there is provided a system for and a method of
laser welding a
plurality of metal pieces together, the method including: positioning a
plurality of pieces
of a metal in a welding stand; exerting a clamping force on the plurality of
pieces of
metal to clamp the pieces of metal together in the welding stand; directing a
blue laser
beam along a laser beam path at the plurality of pieces of metal, wherein the
laser
beam has the following properties: (i) at least 500 Watts of power; (ii) a
beam parameter
product of about 44 mm mrad and less; (iii) a spot size of about 400 pm or
less; (iv) an
average intensity at least of about 400 kW/cm2; (v) a peak intensity of at
least about 800
kW/cm2; and, the blue laser beam welding the plurality of pieces of metal
together at a
-- welding speed; and, providing a non-oxidizing beam clearing gas in a space
along the
laser beam path where the laser beam travels in free space from an optical
element to
the plurality of pieces of cooper foil; wherein clearing gas removes plume
material from
the laser beam path and prevents oxidation of the plurality of pieces of
cooper foil;
wherein the welding speed, clamping force, and a flow rate of the non-
oxidizing clearing
glass, are predetermined to thereby provide a weld having no visible splatter
and no
visible porosity.
[0021] Still further there is provided these welds, laser systems
and welding
methods have one or more of the following features: wherein the welding stand
has an
air gap below the pieces of metal; wherein the metal is selected from the
group
-- consisting of aluminum, Stainless Steel, copper, aluminum based metals,
Stainless
Steel based metals, copper based metals, aluminum alloys, Stainless Steel
alloys and
cooper alloys; wherein the laser beam has a wavelength of about 450 nm;
wherein the
laser beam is not wobbled, thereby providing a wobble free laser welding
process; and,
wherein the weld is selected from the group of welds consisting of a lap weld,
a butt
weld, bead on plate weld and a conduction mode weld.
[0022] Moreover, there is provided a system for and a method of
laser
welding a plurality of cooper foils together, the method including:
positioning a plurality
of pieces of cooper foil in a welding stand; wherein the foil contains at
least about 50%
cooper; wherein the cooper foil has a thickness of from about 80 pm to 500 pm;
exerting
a clamping force on the plurality of pieces of cooper foil to clamp the pieces
of foil
together in the welding stand; directing a blue laser beam along a laser beam
path at
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the plurality of pieces of cooper foil, wherein the laser beam has the
following
properties: (i) at least 600 Watts of power; (ii) a beam parameter product of
about 44
mm mrad and less; (iii) a spot size of about 200 pm to about 400 pm; (iv) an
average
intensity at least of about 2.1 MW/cm2; (v) a peak intensity approaching at
least about
4.5 MW/cm2; the blue laser beam welding the plurality of pieces of metal
together at a
welding speed of at least 10 m/min; and, providing a non-oxidizing beam
clearing gas in
a space along the laser beam path where the laser beam travels in free space
from an
optical element to the plurality of pieces of cooper foil; wherein clearing
gas removes
plume material from the laser beam path and prevents oxidation of the
plurality of
pieces of cooper foil; wherein the welding speed, clamping force, and a flow
rate of the
non-oxidizing clearing glass, are predetermined to thereby provide a weld
having no
visible splatter and no visible porosity.
[0023] There is provided a method of forming a perfect weld in
copper based
materials, the method including: placing a work piece in a laser system;
wherein the
work piece includes placing a first piece of copper based material in contact
with a
second piece of copper material; directing a blue laser beam at the work
piece, whereby
a weld is formed between the first piece of copper based material and the
second piece
of copper based material; wherein the weld includes a HAZ and a
resolidification zone;
wherein a microstructure of the copper based material, the HAZ and the
resolidification
zone are identical.
[0024] There is further provided these welds, systems and methods
having
one or more of the following systems; wherein the identical microstructures
shows no
discernable difference in the weld that would indicate a weakness in the weld;
wherein
the identical microstructure includes crystal growth regions of similar size;
wherein the
.. weld is formed by conduction mode welding; wherein the weld is formed by
keyhole
mode welding ; wherein the first and second pieces have a thickness of from
about 10
pm to about 500 pm; wherein the first piece includes a plurality of layers of
copper foil;
wherein the first piece is copper metal; wherein the first piece is a copper
alloy, having
from about 10 to about 95 weight percent copper; wherein the laser beam is
directed to
.. the work piece as a focused spot having power density is less than 800
kW/cm2;
wherein the laser beam is directed to the work piece as a focused spot having
power
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density of is less than 500 kW/cm2; wherein the laser beam is directed to the
work piece
as a focused spot having power density from about 100 kW/cm2 to about 800
kW/cm2;
wherein the laser beam is directed to the work piece as a focused spot having
power
density is greater than 100 kW/cm2; wherein the laser beam has a power of less
than
500 W; wherein the laser beam has a power of less than 275 W; wherein the
laser
beam has a power of less than 150 W; wherein the laser beam has a power in the
range of 150 W to about 750 W; wherein the laser beam has a power in the range
of
about 200W to about 500 W; wherein the laser beam is directed to the work
piece as a
focused spot having spot size of from about 50 pm to about 250 pm; wherein the
laser
beam has a wavelength from about 405 nm to about 500 nm; wherein the weld is
formed is splatter free; and, wherein the laser does not vaporize the
workpiece.
[0025] Still further there is provided a method of forming a
perfect weld in
copper based materials, the method including: placing a work piece in a laser
system;
wherein the work piece includes placing a first piece of copper based material
in contact
with a second piece of copper material; directing a blue laser beam at the
work piece,
whereby a weld is formed between the first piece of copper based material and
the
second piece of copper based material; wherein the weld includes a HAZ and a
resolidification zone; wherein a range of hardness for the HAZ is within a
range of
hardness for the copper based material.
[0026] Yet additionally, there is provided these welds, systems and methods
having one or more of the following features: wherein the range of hardness
for the
resolidification zone is within a range of hardness for the copper based
material;
wherein a microstructure of the copper based material, the HAZ and the
resolidification
zone are identical; wherein the identical microstructures show no discernable
difference
in the weld that would indicate a weakness in the weld; wherein the identical
microstructures shows no discernable difference in the weld that would
indicate a
weakness in the weld; and wherein the identical microstructure includes
crystal growth
regions of similar size.
[0027] Further there is provided a method of forming a perfect
weld in copper
based materials, the method including: placing a work piece in a laser system;
wherein
the work piece includes placing a first piece of copper based material in
contact with a
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second piece of copper material; directing a blue laser beam at the work
piece, whereby
a weld is formed between the first piece of copper based material and the
second piece
of copper based material; wherein the weld includes a HAZ and a
resolidification zone;
wherein a range of hardness for the resolidification zone is within a range of
hardness
for the cooper based material.
[0028] Further there is provided welding copper with a blue laser
with a
wavelength range of 405 nm to 500 nm, and the welds and products that are
produced
by this welding.
[0029] Moreover there is provided these welds, methods and systems
that
include one or more of the following features: wherein welding copper in a
conduction
mode; welding copper in a conduction mode with no vaporization of the weld
puddle
during the welding process; welding copper in a conduction mode producing a
micro-
structure similar to the base metal with crystal growth regions that are
similar in size to
the base material; welding copper as in a conduction mode producing a micro-
structure
similar to the base metal in the Heat Affected Zone (HAZ); welding copper in a
conduction mode producing a micro-structure similar to the base metal in the
weld
bead; welding copper in a conduction mode producing a hardness similar to the
base
metal in the Heat Affect Zone; welding copper in a conduction mode producing a
harness similar to the base metal in the weld bead; welding copper where the
micro-
structure in the weld is different from the base metal; welding copper where
the micro-
structure in the HAZ is similar to the base metal.
[0030] Moreover there is provided these welds, methods and systems
that
include one or more of the following features: welding copper in a keyhole
mode;
welding copper in a keyhole mode where very low spatter occurs during the weld
and
little or no spatter is observed on the surface of the copper after the weld;
welding
copper with a power density of 500 kW/cm2 or greater and a weld speed that
enables
the keyhole to remain open; welding copper with a power density of 400 kW/cm2
or
greater and a weld speed that enables the keyhole to remain open; welding
copper with
a power density of 100 kW/cm2 or greater and a weld speed that is sufficiently
fast to
prevent the transition to the keyhole welding regime; welding copper with a
pre-heat to
improve the penetration depth during the weld; welding copper with an Ar-0O2
assist
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gas; welding copper with an Ar-H2 assist gas; welding copper with Ar assist
gas;
welding copper with air; welding copper with He assist gas; welding copper
with N2
assist gas; and welding copper with an assist gas.
[0031] Moreover there is provided these welds, methods and systems
that
include one or more of the following features: the laser power is modulated
from 1 Hz to
1 kHz; the laser power is modulated from 1 kHz to 50 kHz; using an elongated
blue
laser spot to keep the keyhole open; using a robot to rapidly move the spot in
a circular,
oscillatory or oblong oscillation motion; using a mirror mounted on a
galvanometer to
oscillate the spot parallel to the weld direction; using a mirror mounted on a
galvanometer to oscillate the spot perpendicular to the weld direction; and
using a pair
of mirrors mounted on a pair of galvanometers to rapidly move the spot in a
circular,
oscillatory, or oblong oscillation motion.
[0032] Still additionally there is provided a method of forming a
keyhole weld
in copper based materials, the method including: placing a work piece in a
laser system;
wherein the work piece comprises placing a first piece of copper based
material in
contact with a second piece of copper material; and, directing a blue laser
beam at the
work piece, whereby a keyhole mode weld is formed between the first piece of
copper
based material and the second piece of copper based material; wherein the weld
comprises a HAZ and a resolidification zone.
[0033] Moreover there is provided these welds, methods and systems that
include one or more of the following features: wherein the laser power is less
than 1000
kW for a keyhole weld; wherein the laser power is less than 500 kW for a
keyhole weld;
wherein the laser power is less than 300 kW for a keyhole weld; comprising
elongating
the laser beam to suppress spatter from the keyhole; comprising modulating the
laser
power to suppress spatter from the keyhole; comprising rapidly scanning the
beam to
suppress spatter during the keyhole mode of welding; comprising rapidly
decreasing the
laser power after the weld is initiated either automatically or manually;
comprising using
a low atmospheric pressure to reduce entrapped gases and spatter during the
welding
process; comprising applying a shielding gas; comprising applying a shielding
gas
selected from the group consisting of He, Ar, N2; comprising applying a
shielding gas
mixture selected from the group consisting of Ar-H2, N2, N2-H2, and,
comprising
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applying a shielding gas and adding hydrogen to the shielding gas to remove
oxide
layers and promote wetting of the weld.
BRIEF DESCRIPTION OF THE DRAWINGS
[0034] FIG. 1 is a photograph of an embodiment of a spatter-free conduction
mode weld of copper in accordance wit the present inventions.
[0035] FIG. 2 is a photograph of an embodiment of a keyhole weld
on copper
in accordance with the present inventions.
[0036] FIG. 3 is a chart showing penetration depth vs speed for an
embodiment of the present inventions for 127 ilm thick copper, where the
copper is fully
penetrated up to the speed of 8 m/min.
[0037] FIG. 4 is a chart showing penetration depth vs speed for an
embodiment of the present inventions for 254 ilm thick copper, where the
copper is fully
penetrated up to the speed of 0.5 to 0.75 m/min. .
[0038] FIG. 5 is a chart showing penetration depth vs speed for an
embodiment of the present inventions.
[0039] FIG. 6 is a chart showing penetration depth at several
different speeds
for embodiments of the present inventions.
[0040] FIG. 7 is an annotated photograph showing an embodiment of
a
conduction mode weld on a 70 ilm thick copper foil in accordance with the
present
inventions.
[0041] FIG. 8 is an annotated photograph of an embodiment of a
keyhole
mode weld cross section in accordance with the present inventions.
[0042] FIG. 9 is the absorption curve for a variety of metals and
shows the
difference in the absorption between and IR laser a visible laser.
[0043] FIG. 10 is a schematic view of an embodiment of a
conduction mode
weld propagation into the material in accordance with the present inventions.
[0044] FIG. 11 is a schematic view of an embodiment of a keyhole
weld
propagation into the material in accordance with the present inventions.
[0045] FIG. 12 is a perspective view of an embodiment of a part holder for
laser welding in accordance with the present inventions.
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[0046] FIG. 12A is a cross sectional view of the part holder of
FIG. 12.
[0047] FIG. 13 is a perspective view of an embodiment of a part
holder for to
hold thin parts to make a lap weld in accordance with the present inventions.
[0048] FIG. 13A is a cross sectional view of the part holder of
FIG. 13A.
[0049] FIG. 14 is a photograph of an embodiment of a bead on plate for a
conduction mode weld in accordance with the present inventions.
[0050] FIG. 15 is a photograph of an embodiment of a stack of
foils welded
with the conduction welding mode in accordance with the present inventions.
[0051] FIG. 16 is a photograph of an embodiment of a bead on plate
for a
keyhole mode weld in accordance with the present inventions.
[0052] FIG. 17 is photograph of an embodiment of a stack of 40
copper foils
welded with the keyhole mode in accordance with the present inventions.
[0053] FIG. 18 is a graph of the penetration depth in copper for
embodiments
of various power levels and various speeds in accordance with the present
inventions.
[0054] FIG. 19 is a schematic of an embodiment of a 150 Watt blue laser
system for use in performing embodiments of the present laser welding methods
in
accordance with the present inventions.
[0055] FIG. 20 is a schematic ray trace diagram of an embodiment
of using
two 150 Watt blue laser systems to make a 300 Watt blue laser system in
accordance
with the present inventions.
[0056] FIG. 21 is a schematic ray trace diagram of an embodiment
of using
four 150 Watt blue laser systems to make an 800 Watt blue laser system in
accordance
with the present inventions.
[0057] FIG. 22 is a graph of an embodiment of the radius of the
beam caustic
(microns (pm)) vs displacement from focus (pm) using a 100 mm focal length
lens at
600 W for a circular aperture containing 95% of the encircled power in
accordance with
the present inventions.
[0058] FIG. 23 is a graph of an embodiment of Coper 110 bead on
plate
(BOP) testing, showing penetration (pm) vs. speed m/min in accordance with the
present inventions.
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[0059] FIG. 24 is a graph of an embodiment of Coper 110 butt weld
testing,
showing penetration (pm) vs. speed m/min in accordance with the present
inventions.
[0060] FIG. 25 is a graph of an embodiment of a conduction mode
weld,
showing the effect of the plate thickness on the penetration depth, in
accordance with
the present inventions.
[0061] FIG. 26 is a graph of an embodiment of aluminum 1100 BOP
testing
showing penetration (pm) vs. speed m/min in accordance with the present
inventions.
[0062] FIG. 27 is a graph of an embodiment of aluminum 110 butt
weld
testing, showing penetration (pm) vs. speed m/min in accordance with the
present
inventions.
[0063] FIG. 28 is a graph of an embodiment of Stainless Steel 304
BOP
testing showing penetration (pm) vs. speed m/min in accordance with the
present
inventions.
[0064] FIG. 29 is a photograph of an embodiment of a longitudinal
cross
section of an embodiment of a keyhole welded copper 110 plate showing the
start of the
full penetration region.
[0065] FIG. 30 is a photograph of an embodiment of a 1.016 mm
thick copper
welded at 1.1 m/min with minimal porosity and spatter in accordance with the
present
inventions.
[0066] FIG. 31 is a graph showing penetration depth (pm) vs. speed (m/min)
of an embodiment of a BOP test for copper 110 welded with 600 Watts and a 200
pm
spot size in accordance with the present inventions.
[0067] FIG. 32 is photograph of an embodiment of a keyhole lap
weld of four
sheets of Stainless Steel 304 in accordance with the present inventions.
[0068] FIG. 33 is a graph of an embodiment of lap welding tests on stacks
of
copper 110 foils in accordance with the present inventios.
[0069] FIG. 34 is a photograph of an embodiment of a stack of 40,
10 mm
thick copper 110 foils welded with a 500 Watt, 400 pm spot blue laser in
accordance
with the present inventions.
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DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0070] In general, the present inventions relate to lasers, laser
beams,
systems and methods for welding metals, and in particular aluminum, stainless
steel,
copper, aluminum based metals, Stainless Steel based metals, copper based
metals
and alloys of these. Generally, the present inventions further relate to the
method for
the application of the laser beam, the beam size, the beam power, the method
for
holding the parts and the method for introducing the shielding gas to assist
in the
welding process, including to prevent oxidation of the part and managing of
the plume to
prevent plume interference with the laser beam.
[0071] In an embodiment, the present inventions provide high
quality welds,
high welding speeds, and both for copper based materials in many areas,
including for
electronic components, and further including batteries. In an embodiment, the
present
inventions provide high quality welds, high welding speeds, and both for
copper based
materials for automotive components, including automotive electronic
components,
including batteries.
[0072] In an embodiment, the present inventions provide high
quality welds,
high welding speeds, and both for stainless steel based materials in many
areas,
including for electronic components, and further including batteries. In an
embodiment,
the present inventions provide high quality welds, high welding speeds, and
both for
stainless steel based materials for automotive components, including
automotive
electronic components, including batteries.
[0073] In an embodiment, the present inventions provide high
quality welds,
high welding speeds, and both for aluminum based materials in many areas,
including
for electronic components, and further including batteries. In an embodiment,
the
present inventions provide high quality welds, high welding speeds, and both
for
aluminum based materials for automotive components, including automotive
electronic
components, including batteries.
[0074] In an embodiment of the present inventions, a high power
blue laser
source (e.g., ¨450 nm) solves the problems with prior copper welding
techniques. The
blue laser source provides a blue laser beam, at this wavelength the
absorption of copper
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is at ¨65% enabling efficient coupling of the laser power into the material at
all power
levels. This system and method provides stable welding in many welding
techniques,
including the conduction and keyhole welding modes. This system and method
minimizes, reduces and preferably eliminates, vaporization, spatter, micro
explosions,
.. and combinations and variations of these.
[0075] In an embodiment blue laser welding of copper at power
levels ranging
from 150 Watts to 275 Watts with a spot size of ¨ 200 pm achieves stable, low
spatter
welding over all power ranges. In an embodiment of this welding system and
method the
welding is in the conduction mode with the resulting weld microstructure
resembling the
base material.
[0076] Preferably, in embodiments the laser wavelengths can be in
wavelengths from 350 nm to 500 nm, the spot size (diameter, or cross section)
can range
from 100 microns (pm) to 3 mm, and larger spot sizes are also contemplated.
The spot
can be circular, elliptical, linear, square or other patterns. Preferably, the
laser beam is
continuous. In embodiments the laser beam can be pulsed, for example from
about 1
microsecond and longer.
[0077] Turning to FIG. 6 there is shown the penetration depth vs
power at
various welding speeds. The welds were performed using a system of the type
described in Example 1. The welds were made on 500 pm Copper at 275 W power
for
the laser beam with no assist gas.
[0078] The photograph of FIG. 7 shows a conduction mode weld on a 70 um
thick copper foil showing the micro-structure through the HAZ and weld. The
weld was
made using the parameters described in Example 1. The depth of penetration of
each
sample was determined by first cross sectioning, then etching the sample to
reveal the
microstructure of the weld and HAZ areas. In addition, one of the samples was
cross
sectioned and the Vickers hardness across the base metal ranged from 133-141
HV,
the weld bead was approximately 135 HV and the HAZ ranged from 118-132 HV. The
conclusion is that hardness of the base material, HAZ and weld bead, e.g.,
resolidification zone, is close to the original material. In addition, the
micro-structure for
the conduction mode weld bead, the HAZ and the base material is very similar
with
minor differences in the microstructure. A weld with these characteristics has
never
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been observed before in copper when welded with a laser or any other means.
This
weld quality is shown in FIG. 7 where the sample has been cross sectioned
transverse
to the weld and etched to reveal the microstructure.
[0079] Thus, there are embodiments of the present inventions
include the
method of welding copper based materials to obtain the following welds, and
the
resultant welds themselves. These methods and welds would include welding two
or
more copper based materials together, so that in the area around the weld the
following
the hardness of the material (as measured by a accepted and established
hardness
test, e.g., Vickers hardness, ASTM test, etc.) where the weld bead hardness is
within
the hardness of the base material, the weld bead hardness is within 1% of the
hardness
of the base materials, the weld bead hardness (e.g., resolidification zone) is
within 5%
of the hardness of the base materials, and the weld bead hardness is within
10% of the
hardness of the base materials. These methods and welds would include welding
two
or more copper based materials together, so that in the area around the weld
the
following hardness of the material (as measured by a accepted and established
hardness test, e.g., Vickers hardness, ASTM test, etc.) where the HAZ hardness
is
within the hardness of the base material, the HAZ hardness is within 1% of the
hardness of the base materials, the HAZ hardness is within 5% of the hardness
of the
base materials and the HAZ hardness is within 10% of the hardness of the base
materials. These methods and welds would include welding two or more copper
based
materials together, so that in the area around the weld the microstructure of
the base
material, the bead (e.g., the resolidification zone), and the HAZ are
identical, i.e., there
are no discernable difference in the microstructure that would suggest or
shown a
weakness in the welded structure in the area of the weld or a weakness in the
area of
the weld).
[0080] Turning to FIG. 8 is the microstructure observed for a
sample of the
500 pm thick copper sheet when operating in the keyhole welding mode. During
the
keyhole welding process, a vapor plume was clearly visible and molten copper
was
slowly ejected along the length of the weld. There were no indications during
the weld,
or after the weld of spatter from the welding process as is usually observed
when
welding with an IR laser. This indicates a stable, well controlled keyhole
process which
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is suitable for creating high quality welds on electrical components. The
keyhole mode
weld cross section, of very high quality and uniformity, of the type shown in
FIG. 8, is
obtainable for a power density, as low as 800 kW/cm2 and lower. The
resolidification
area [1] ¨ [2] was from 442 pm to 301 pm and the HAZ [2] was 1314 pm.
[0081] An embodiments of the present invention relates to methods, devices,
and systems for the welding of copper to copper or other materials using a
visible laser
system to achieve benefits including an efficient heat transfer rate to the
copper
material; a stable weld puddle; and having these benefits in particular in
either the
conduction mode or keyhole mode of welding. Copper is highly absorbent in the
blue
wavelength range as shown in FIG. 9. The presently preferred blue laser beams
and
laser beam systems and methods couple the laser power into the copper in a
very
efficient manner. The present laser beam systems and methods heat the base
material
(the material to be welded, e.g., copper) faster than the heat can be
conducted away
from the laser spot. This provides for highly efficient, and excelled weld
properties for
.. conduction mode laser welding, i.e., the material in the laser beam is
rapidly heated to
the melting point and maintained at the melting point by the continuous laser
beam
resulting in a stable weld bead being formed. In the present conduction mode
welding,
the metal is melted rapidly, but the penetration depth of the weld is dictated
by the
thermal diffusion into the material and progresses with a spherical shape into
the
material. This is shown in FIG. 10, which shows a schematic of an embodiment
of a
conductive mode welding 1000, showing the direction of the weld with arrow
1004. The
laser beam 1001, e.g., blue wavelength, is focused on to, and maintains a weld
pool
1002. Behind the weld pool 1002 is a solid weld material 1003. The base
material, e.g.,
copper metal or alloy, is below the weld. A shielding gas stream 1005 is also
used.
[0082] An embodiment of the present inventions relates to keyhole welding
of
copper with a blue laser system. These methods and systems open new
possibilities
for welding thick copper materials as well as stacks, including thick stacks,
of copper
foils. This keyhole mode of welding occurs when the laser energy is absorbed
so
rapidly that it melts and vaporizes the material being welded. The vaporized
metal
creates a high pressure in the metal being welded, opening a hole or capillary
where the
laser beam can propagate and be absorbed. Once the keyhole mode is initiated,
deep
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penetration welding can be achieved. The absorption of the laser beam changes
from
the initial absorption of 65% for a blue laser in copper to 100% absorption in
the
keyhole. The high absorption can be attributed to multiple reflections off the
walls of the
keyhole, where the laser beam undergoes continuous absorption. When combined
with
the high absorptivity of the copper at the blue wavelength, the power required
to initiate
the keyhole and maintain it is substantially lower than when using an IR
laser. Turning
to FIG. 11, which shows a schematic of an embodiment of a keyhole mode weld
2000,
showing the direction of the weld with arrow 2007. There is a metal/vapor
plasma in the
keyhole 2006. The blue laser beam 2002, creates a plasma cloud 2002, a weld
pool
2003, and a solid weld metal 2004. A shielding gas stream 2005 is also used.
[0083] Comparing the keyhole weld of FIG. 11 with the conduction
mode weld
of FIG. 10, the walls of the final weld resolidification zone in the keyhole
weld are more
vertical through the part or base material than the conduction mode weld.
[0084] Preferably, the high power laser beams, (e.g., visible,
green and blue
laser beams), for the embodiments of the present systems and methods are
focused, or
have the ability to be focused through the optics in the system, to a spot
size of about
50 pm or more and have a power of at least 10 W or more. The powers for the
laser
beams, including the blue laser beams may be 10 W, 20 W, 50 W, 100 W, 10 ¨50
W,
100 ¨ 250 W, 200 ¨ 500 W, and 1,000 W, higher and lower powers are
contemplated,
.. and all wavelengths within these ranges. The spot sizes (longest cross
sectional
distance, which for a circle is the diameter) for these powers and laser beams
may be
from about 20 pm to about 4 mm, less than about 3 mm, less than about 2 mm,
from
about 20 pm to about 1 mm, about 30 pm to about 50 pm, about 50 pm to about
250
pm, about 50 pm to about 500 pm, about 100 pm to about 4000 pm, large and
smaller
.. spots are contemplated, and all sized within these ranges. The power
density of the
laser beam spots may be from about 50 kW/cm2 to 5 MW/cm2, about 100 kW/cm2 to
4.5
MW/cm2, about 100 kW/cm2 to 1000 kW/cm2, about 500 kW/cm2 to 2 MW/cm2, greater
than about 50 kW/cm2, greater than about 100 kW/cm2, greater than about 500
kW/cm2,
greater than about 1000 kW/cm2, greater than about 2000 kW/cm2, and higher and
lower power densities, and all power densities within these ranges. Welding
speeds of
from about 0.1 mm/sec to about 10 mm/sec for copper, and slower and faster
speeds
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depending upon various conditions, and all speeds within these ranges. The
speed
depends upon the thickness of the material being welded, thus speed per
thickness
mm/sec/thickness in mm can be, for example, from 0.1/sec to 1000/sec for 10 pm
to 1
mm thickness copper.
[0085] Embodiments of the present methods and systems can use one, two,
three or more laser beams to form the welds. The laser beams can be focused on
the
same general area to initiate the weld. The laser beam spots can be
overlapping, and
can be coincident. The plurality of laser beams can be used simultaneously;
and
coincident and simultaneous. A single laser beam can be used to initiate the
weld
followed by addition of the second laser beam. A plurality of laser beams can
be used
to initiate the weld followed by using less beams, e.g., a single beam, to
continue the
weld. The laser beams in this plurality of laser beams can be different powers
or the
same powers, the power densities can be different or the same, the wavelengths
can be
different or the same, and combinations and variations of these. The use of
additional
laser beams can be a simultaneous, or sequentially. Combinations and
variations of
these embodiments of using multiple laser beams may also be used. The use of
multiple laser beams can suppress spatter from the weld, and can do so in deep
penetration welding methods.
[0086] In embodiments hydrogen gas, H2, can be mixed with an inert
gas to
remove oxide layers from the base material during the welding process. The
hydrogen
gas is flowed over the weld area. The hydrogen gas also promotes wetting of
the weld.
The hydrogen gas can be added to, or form a mixture with, the shielding gas
and be
applied to the weld as a part of the shielding gas. These mixtures would
include for
example, Ar-H2, He-H2, N2-H2,
[0087] FIG. 18 provides examples of the penetration depth, laser beam power
and welding speed on copper for various embodiments of laser system
configurations
and material thicknesses ranging from 127 ilm to 500 ilm
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Methods for conduction mode welding of copper, copper alloys and other
metals with a blue laser system
[0088] The present systems overcome the problems and difficulties
associated with IR welding, when applied to copper based materials. The high
absorptivity (65%) of copper at blue wavelengths of the present laser beam and
beam
spots overcomes the thermal diffusivity of the material, and can do so at
relatively low
power levels ¨ 150 Watts. The present blue laser beam's interaction with
copper allows
the copper to readily reach its melt point and allow a wide processing window.
[0089] In an embodiment a steady conduction mode weld, is
performed and
high-quality welds are obtained at a steady and rapid rate, through the use of
a part
holding devices or fixture.
[0090] A welding fixture is used to hold the material to be welded
in place
during the thermal transient induced in the parts by the laser beam. The
fixture in
FIGS. 12 and 12A, which are a prospective and cross-sectional view
respectively, of an
embodiment of a linear section of a welding clamp that can be used for lap,
butt and
even edge welds. The welding fixture 4000 has a base plate or support
structure 4002.
Attached to the baseplate 4002 are two clamp members, or hold downs, 4001. The
hold downs 4001 have a tab that rests on the surface of the baseplate 4002,
and a free
end that contacts and holds the work piece(s) to be welded. There is a slot
4003, e.g.,
2 mm wide x 2 mm deep, in the baseplate 4002 in the area between the free ends
for
the hold downs 4001. Four bolts, e.g., 4004, (other types of adjusting
tightening
devices may also be used) adjust, tighten and hold the clamps against the work
piece,
thus holding or fixing the work piece.
[0091] The preferred material for this fixture is a low thermal
conductivity
material such as stainless steel because it is sufficiently stiff to apply the
clamping
pressure required to hold the parts in place during the weld. In embodiments
the
clamps, the baseplate and both can have insulating qualities or effects on the
work
piece during the welding process. The use of a material having low thermal
conductivity
for the fixture prevents, minimizes and reduces the heat that is deposited
into the part
-- form being rapidly conducted away by the fixture itself. This provides
added benefits
when welding high thermal conductivity materials such as copper. Therefore,
the
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material selected for the clamp, the width of the clamp and the gap under the
parts are
all parameters which determines the depth of penetration of the weld, the
width of the
weld bead and the overall quality of the weld bead. Turning to FIG. 14, there
is shown a
cross section (after etching) where the conduction mode weld can be identified
by the
circular shape 6001 of the weld bead in the base material, e.g., the work
piece. The
weld takes this shape because of the isotropic nature of the heat transfer
process in
copper or any other material when the heat is applied at the top surface of
the part.
[0092] In a preferred embodiment, the baseplate 4002 of the
fixture 4000 is
constructed of stainless steel, a 2 mm wide gap 4003 is cut into the baseplate
to be
positioned just below the weld zone and flooded with an inert gas such as
Argon,
Helium, or Nitrogen (as a covering or shielding gas) to minimize oxidization
of the back
surface of the weld. The covering gas can be a mixture of hydrogen and an
inert gas.
The clamps 4001 are designed to put pressure on the parts to be welded at 2 mm
from
the edges of the gap 4003 in the baseplate 4002. Thus, in this embodiment a 6
mm
wide area of the parts to be welded is open to the laser beam (recognizing
that the laser
beam will be a slight distance away from the clamp). This positioning of the
clamps
allows the laser beam easy access to the surface as well as a tight clamping
of the
parts. This type of clamp is the preferred method for butt welding two foils
or sheets of
copper together varying in thickness from 50 pm to multiple mm. This fixture
is also
suited to lap welding two thicker copper plates together ranging from 200 pm
to multiple
mm. The amount of clamping pressure is very important, and depending on the
amount
of laser power, the speed of the weld, the thickness of the parts and the type
of weld
being performed the clamping bolts may be torqued to 0.05 Newton-m (Nm), up to
3
Nm, or more for thicker materials. This torque value is highly dependent on
the bolt size,
the thread engagement and the distance from the bolt center to the clamping
point.
[0093] In an embodiment high quality and excellent welds are
obtained by
providing sufficient clamping force to prevent movement of the parts during
the weld
while minimizing the parasitic heat loss to the fixture itself. It should be
understood that
the embodiment of the fixture in FIGS. 12 and 12A, represents a cross section
of a
straight portion of a weld fixture and may be designed into any arbitrary 2-D
path (e.g., -
S -, -C -. ¨V1/ ¨ etc.) for welding any types of shapes together. In another
embodiment,
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the fixture may be preheated, or heated during the welding process to increase
the
speed or depth of penetration of the weld while reducing the parasitic heat
losses to the
fixture. The fixture when heated to a few 100 C can improve the weld speed,
or depth
of penetration and quality by a factor or two or more. The shielding gas for
the top side
of the weld is delivered longitudinally from the front of the weld travel
direction to the
back of the weld travel direction as shown in FIG. 10. A bead on plate
conduction mode
weld is shown in FIG. 14 that was performed with this fixture 4000 on a sheet
of 254 pm
thick copper. The freeze pattern of the weld bead shows the spherical melt
pattern
typical of this type of weld.
[0094] Lap welding two parts using the conduction mode welding process
requires the parts to be placed and held in intimate contact. The two parts
(collectively
the work piece) can be placed in a fixing device, preferably of the type shown
in FIGS.
13 and 13A, which are perspective and cross-sectional view respectively of
fixture 5000.
The fixture 5000 has a baseplate 5003 and two clamps 5002. The clamps have
four
slots, e.g., 5010 that correspond to hold down bolts, e.g., 5001. In this
manner the
position of the clamps relative to the work piece, relative to each other can
be adjusted
and fixed, as well as the amount of clamping force or pressure. The clamps can
have
magnets to assist in their positioning, and fixation. The clamps 5002 have
internal
channels, e.g., 5004 for transporting shielding gas. The channels 5004 are in
fluid
communication with shielding gas outlets, e.g., 5005. The shielding gas
outlets and the
shielding gas channels from a shielding gas delivery system within the clamps.
Thus,
the gas delivery system is, and is through, a row of holes along the length of
the clamp
that deliver an inert gas such as Argon, Helium, or Nitrogen. Argon is the
preferred gas
because it is heavier than air and will settle on the part, displacing the
oxygen and
preventing oxidation of the upper surface. A small amount of Hydrogen can be
added
to the inert gas to promote scavenging of the oxide layer on the part and
promote the
wetting of the parts during the melting process.
[0095] There is also an insert 5006, which is used to force the
individual foils
in a stack of foils to keep and maintain contact with each other in the stack.
The insert
5006 can stretch and force the foils into tight, and uniform contact with each
other. In
the embodiment of FIGS. 13 and 13A, the insert 5006 is an inverted V shape. It
can be
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curved, humped or other shaped depending upon the stack of foils, and their
individual
thicknesses. Additionally, in the embodiment of FIGS. 13 and 13A the insert
5006 is
adjacent to, but not covered by the clamps 5002. The insert can be removed
from the
ends of the clamps, or one or both of the clamps may partially cover the
insert.
[0096] In the preferred embodiment, the baseplate 5000 is made from
stainless steel, as are the clamps 5002. The fixation device can be made from
a
ceramic or thermally insulating material. The hump 5006 provides pressure from
the
bottom of the weld to keep the overlapping plates (two, three, tens, etc.) in
intimate
contact. In this embodiment, a provision for shielding gas is built into the
clamps (2) in
the form of a row of holes along the length of the clamp that deliver an inert
gas such as
Argon, Helium, or Nitrogen. Argon is the preferred gas because it is heavier
than air
and will settle on the part, displacing the oxygen and preventing oxidation of
the upper
surface. The insert hump 5006 in the baseplate 5003 may also have a series of
channels, holes or slots, to deliver a cover or shielding gas to the backside
of the weld
to prevent oxidation. The fixture 5000, as shown in the figures, represents a
cross
section of a straight portion of a weld and may be designed into any arbitrary
2-D path
for welding arbitrary shapes together. In this application, the torque values
for the bolts
can be important, depending upon the nature of the work piece, too low of a
torque
value, e.g., 0.1 Nm, and the parts may not remain in contact, too high of a
torque value
>1 Nm and the parasitic heat transfer reduces the efficiency of the welding
process,
reducing penetration and weld bead width.
Method for keyhole mode welding copper, copper alloys and other metals
with a blue laser system
[0097] The blue laser light has a much higher level of absorption
than the IR
laser (65%) and can initiate a keyhole weld at a relatively low power level of
275 Watts
(in contrast to 2,000 to 3,000 W required for an IR system to initiate the
keyhole welding
process. Upon initiation the IR system will further face the problem of
runaway, among
other problems.) As the keyhole mode is initiated with the blue laser system,
the
absorption increases, now it is not a runaway process because it increases
from 65% to
about 90% and to 100%. Thus, the present keyhole welding process has a very
different absorption time profile from IR. The present blue keyhole welding
process has
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an absorption time profile form initiation to advancing the weld that is 35%
or less. The
startup of the blue laser welding process and the transition to a continuous
weld, using
the present laser welding systems, is accomplished without having to rapidly
changing
the power level of the laser or the weld speed, as required when using an IR
laser to
prevent spatter. A high-speed video of the start of the keyhole weld when
using a blue
laser shows a stable process, capable of welding multiple layers of copper
foils and
plates with minimal to no spatter ejected from the keyhole. Cross sections of
two
keyhole welded sample are shown in FIG. 16 and 17, where the material freeze
pattern
is clearly different from the shape of the conduction mode welded sample shown
in FIG.
14. The formation of material freeze patterns perpendicular to the surface of
the
material, as seen in FIG. 16 and 17, is different from a conduction mode weld
because
the heat transfer occurs along the entire length of the keyhole which
penetrates the
surface of the part and extends to the final weld depth. This contrasts to the
conduction
mode weld, where all the laser energy is deposited on the surface of the
material.
[0098] The keyhole welding process like the conduction mode welding
process requires the parts to be held in a fixture to prevent any movement
during the
weld. The keyhole mode is typically used in a lap weld configuration, where
the keyhole
penetrates through the parts, welding a stack of two or more parts together
(e.g., as see
in FIG. 17).
[0099] The laser system of FIG. 20, can produce a 275 W blue laser beam,
with a power density at the spot of 800 kW/cm2. The laser system of FIG. 20
has a first
laser module 1201, and a second laser module 1202, laser beams leave the laser
module and follow laser beam paths as shown by ray trace 1200. The laser beams
go
through turning mirrors 1203, 1205 and through a focusing lens configuration
1205,
having a 100 mm focusing lens and 100 mm protective window. The focusing lens
in
the configuration 1205 creates spot 1250.
[00100] The laser system shown in FIG. 21, can be used to create a 400 pm
spot or a 200 pm spot. The laser system of FIG. 21 consists of 4 laser modules
1301,
1302, 1303, 1304. The laser modules can each be of the type disclosed and
taught in
US Patent Publ. No. 2016/0322777, the entire disclosure of which is
incorporated herein
by reference. For example, the modules can be of the type shown in FIG. 19,
where
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composite beam from each of the laser diode subassemblies, 210, 210a, 201b,
210c,
propagates to a patterned mirror, e.g., 225, which is used to redirect and
combine the
beams from the four laser diode subassemblies into single beams. A
polarization beam
folding assembly 227 folds the beam in half in the slow axis to double the
brightness of
the composite laser diode beam. The telescope assembly 228 either expands the
combined laser beams in the slow axis or compresses the fast axis to enable
the use of
a smaller lens. The telescope 228 shown in this example expands the beam by a
factor
of 2,6x, increasing its size from 11 mm to 28.6 mm while reducing the
divergence of the
slow axis by the same factor of 2.6x. if the telescope assembly compresses the
fast
axis then it would be a 2x telescope to reduce the fast axis from 22 mm height
(total
composite beam) to 11 mm height giving a composite beam that is 11 mmxl 1 mm.
This
is the preferred embodiment, because of the lower cost. An aspheric lens 229
focuses
the composite beam.
[00101] It should be understood that at 500 Watts and a 200 pm spot, the
power density is >1.6 MW/cm2, which is substantially above the keyhole welding
threshold at this wavelength. At this power density, even the blue laser has
the
potential to create spatter and porosity in the weld. However, since the
absorption is
well controlled, the ability to suppress, control or eliminate, the spatter is
possible. The
first method for suppressing the spatter is to reduce the power level once the
spatter
process begins, while holding the welding speed constant. The second method
for
suppressing the spatter is to elongate the weld puddle to allow the shielding
gases and
vaporized metal to exhaust from the keyhole, producing a spatter free, defect
free weld.
The third method for suppressing the spatter is to wobble the blue laser beam
using
either a set of mirrors mounted on a set of galvanometer motors or a robot.
The fourth
method for suppressing the spatter is to reduce the pressure of the welding
environment
including the use of a vacuum. Finally, the fifth method for suppressing the
spatter is to
modulate the laser beam power over a range of 1 Hz to 1 kHz, or as high as 50
kHz.
Preferably, the welding parameters are optimized to minimize the spatter
during the
process.
[00102] In general, embodiments of the present inventions relate to laser
processing of materials, laser processing by matching preselected laser beam
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wavelengths to the material to be processed to have high or increased levels
of
absorptivity by the materials, and in particular laser welding of materials
with laser
beams having high absorptivity by the materials.
[00103] An embodiment of the present invention relates to using laser beams
having visible laser beams, wavelengths from 350 nm to 700 nm, to weld or
otherwise
join through laser processing, materials that have higher absorptivity for
these
wavelengths. In particular laser beam wavelengths are predetermined based upon
the
materials to be laser processed to have absorption of at least about 30%, at
least about
40%, at least about 50% and at least about 60%, or more and from about 30% to
about
65%, from about 35% to 85%, about 80%, about 65%, about 50, and about 40%.
Thus,
for example, laser beams having wavelengths from about 400 nm to about 500 nm
are
used to weld gold, copper, brass, silver, aluminum, nickel, alloys of these
metals,
stainless steel, and other metals, materials, and alloys.
[00104] The use of a blue laser, e.g., about 405 to about 495 nm wavelength,
to weld materials such as gold, copper, brass, silver, aluminum, nickel,
nickel plated
copper, stainless steel, and other, materials, plated materials and alloys, is
preferred
because of the high absorptivity of the materials at room temperature, e.g.,
absorptivities of greater than about 50%. One of several advantages of the
present
inventions is the ability of a preselected wavelength laser beam, such as the
blue laser
beam, that is better able to better couple the laser energy into the material
during the
laser operation, e.g., the welding process. By better coupling the laser
energy to the
material being welded, the chance of a run away process is greatly reduced and
preferably eliminated. Better coupling of the laser energy also allows for a
lower power
laser to be used, which provides cost savings. Better coupling also provides
for greater
control, higher tolerances and thus greater reproducibility of welds. These
features,
which are not found in with IR lasers and IR laser welding operations, are
important, to
among other products, products in the electronics and power storage fields.
[00105] In an embodiment a blue laser that operates in a CW mode is used.
CW operation can be preferred over pulsed lasers, in many applications,
because of the
ability to rapidly and fully modulate the laser output and control the welding
process in a
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feedback loop, resulting in a highly repeatable process with optimum
mechanical and
electrical characteristics.
[00106] In an embodiment of the present inventions involve the laser
processing of one, two or more components. The components may be made from any
type of material that absorbs the laser beam, e.g., the laser beams energy,
plastics,
metals, composites, amorphous materials, and other types of materials. In an
embodiment the laser processing involves the soldering together of two metal
components. In an embodiment the laser processing involves the welding
together of
two metal components.
[00107] In an embodiment there is provided the tools, systems and methods
wherein the laser welding operation is selected from the group consisting
autogenous
welding, laser-hybrid welding, keyhole welding, lap welding, filet welding,
butt welding
and non-autogenous welding.
[00108] Laser welding techniques may be useful in many varied situations, and
in particular where welding is needed for forming electrical connections, and
in
particular power storage devices, such as batteries. Generally, embodiments of
the
present laser welding operations and systems include visible wavelength, and
preferably blue wavelength, lasers that can be autogenous which means only the
base
material is used and is common in keyhole welding, conduction welding, lap
welding,
filet welding and butt welding. Laser welding can be non-autogenous where a
filler
material is added to the melt puddle to "fill" the gap or to create a raised
bead for
strength in the weld. Laser welding techniques would also include laser
material
deposition ("LMD").
[00109] Embodiments of the present laser welding operations and systems
include visible wavelength, and preferably blue wavelength, lasers that can be
hybrid
welding where electrical current is used in conjunction with a laser beam to
provide
more rapid feed of filler material. Laser Hybrid welding is by definition non-
autogenous.
[00110] Preferably, in some embodiments active weld monitors, e.g., cameras,
can be used to check the quality of the weld on the fly. These monitors can
include for
example x-ray inspection and ultrasonic inspection systems. Furthermore, on
stream
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beam analysis and power monitoring can be utilized to have full understanding
of
system characteristics and the operations characterizations.
[00111] Embodiments of the present laser systems can be a hybrid system that
combine the novel laser systems and methods with conventional milling and
machining
equipment. In this manner material can be added and removed during the
manufacturing, building, refinishing or other process. Examples of such hybrid
systems,
using other embodiments of laser systems, which have been invented by one or
more of
the present inventors, is disclosed and taught in US Patent Application Serial
No.
14/837,782, the entire disclosure of which is incorporated herein by
reference.
[00112] Typically, in embodiments, laser welding uses a very low flow of gas
to
keep the optics clean, an air knife to keep the optics clean or an inert
environment to
keep the optics clean. Laser welding can be performed in air, an inert
environment, or
other controlled environment, e.g., N2.
[00113] Embodiments of the present invention can find great advantage in
welding copper materials, which would include copper, pure copper, alloys of
copper
and all materials having sufficient amounts of copper to have at about a 40%
to 75%
absorption in the blue laser wavelengths, and preferably about 400 nm to about
500 nm.
[00114] There are two preferred autogenous welding modes, and autogenous
welds that they produce, that are performed with embodiments of the present
laser
systems and processes, a conduction weld and a keyhole weld. The conduction
weld is
when a laser beam with a low intensity (< 100 kW/cm2) is used to weld two
pieces of
metal together. Here the two pieces of metal may be butted up to each other,
overlapping to one side and completely overlapping. The conduction weld tends
not to
penetrate as deeply as a keyhole weld and it generally produces a
characteristic
"spherical" shape weld joint for a butt weld, which is very strong. However, a
keyhole
weld occurs with a relatively high laser beam intensity (> 500 kW/cm2) and
this weld can
penetrate deep into the material and often through multiple layers of
materials when
they are overlapped. The exact threshold for the transition from conduction
mode to
key-hole mode has not yet been determined for a blue laser source, but the key-
hole
weld has a characteristic "v" shape at the top of the material with a near
parallel channel
of refrozen material penetrating deep into the material. The key-hole process
relies on
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the reflection of the laser beam from the sides of the molten pool of metal to
transmit the
laser energy deep into the material. While these types of welds can be
performed with
any laser, it is expected that the blue laser will have a substantially lower
threshold for
initiating both of these types of welds than an infrared laser.
[00115] The welding of electroplated material using blue laser operations to
weld these materials is contemplated, including the blue laser welding of
electroplated
materials, such as materials electroplated with copper, electroplated with
platinum, and
electroplated with other conductive material.
[00116] A welding process for copper requires that the power be coupled
efficiently into the parts, and for the welding process to be stable and
capable of
producing a low porosity, low spatter weld. The present inventions accomplish
these,
and other objectives. The blue laser accomplishes the first part of these
requirements
by being at a wavelength that is highly absorbed by the copper (65%) compared
to an
IR laser (<5%). The second requirement is a function of not only the laser
absorption,
but also the processing ramp or time profile, fixturing, beam profile and
quality and the
clamping pressure used on the parts. The present embodiments provide that both
a
keyhole mode and a conduction mode weld are possible with the blue laser as a
heat
source. Conduction mode welding does not produce any spatter during the
process or
porosity in the part. The keyhole mode of welding, will allow for greater
penetration.
.. The embodiments of the present high-power blue CW laser source is ideal for
welding
copper parts with very low porosity in the part and very low spatter during
the process.
[00117] Full penetration, bead on plate tests of a 1 mm thick copper plate
with a
600-Watt blue laser with nominal spatter remaining on the surface. The 600-
Watt, CW
laser is focused to a spot size of approximately 200 pm , resulting in an
average intensity at
the surface of the part of 2.1 MW/cm2. This intensity is well above the power
density required
to initiate and sustain the keyhole in the part. During the welding process,
the keyhole forms
rapidly and once full penetration is achieved, the molten puddle exhibits a
very stable surface
indicating low turbulence in the weld puddle as the weld progresses. The
stable welding
process is observed over a wide range of welding speeds and with an Ar-0O2
cover gas
for, among other things, suppressing the surface oxidation during the welding
process. This
ability to create a stable keyhole weld can be attributed to, among other
things, the high
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absorptivity of the copper in the blue. The blue laser light is uniformly
absorbed by the walls of
the keyhole during the welding process, however, when instabilities in the
keyhole arise
due to turbulence in the melt puddle, the heat input is maintained, and the
keyhole
remains stable.
[00118] The following examples are provided to illustrate various embodiments
of the present laser systems and operations and in particular a blue laser
system for
welding components, including components in electronic storage devices. These
examples are for illustrative purposes, may be prophetic, and should not be
viewed as,
and do not otherwise limit the scope of the present inventions.
[00119] EXAMPLE 1
[00120] The laser source is a high power blue direct diode laser capable of 0-
275 Watts. The beam is delivered through a 1.25X beam expander and focused by
a
100mm aspheric lens. The spot diameter on the workpiece is 200pm x 150pm which
produces a power density at maximum power of 1.2MW/cm2. A stainless steel
fixture is
used to hold the samples in place and tests were performed with He, Ar, Ar-0O2
and
Nitrogen, all were beneficial, with the best results achieved with Ar-0O2.
[00121] EXAMPLE 1A
[00122] Using the system of Example 1, initial test results produced high
quality
conduction mode welds at power levels of 150 Watts on the copper surface. A
series of
Bead on Plate (BOP) tests were conducted to characterize the welds produced by
the
high power blue laser source. FIG. 1 shows the chevron pattern for a
conduction mode
weld, the unique characteristics of this weld include; no spatter during the
welding
process, a microstructure that resembles the base material and hardness of the
weld is
like the base material. FIG. 1 shows the BOP formed when welding with a blue
laser at
150 Watts on a 70,um thick copper foil.
[00123] EXAMPLE 1B
[00124] Using the system of Example 1 and scaling the power output of the
laser
to 275 Watts increased the power density to 1.2 MW/cm2which is sufficient
power density
to initial keyhole welding in copper. FIG. 2 shows an example of a keyhole
weld on a 500
pm thick copper sample. During the keyhole process, the vapor pressure
developed in
the keyhole forces molten copper out of the weld bead. This can be seen in
FIG. 2 where
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the ejected copper lines the edges of the weld bead. This ejection process is
stable and
does not result in micro-explosions in the material and consequently it does
not produce
the spatter patterns observed when welding copper with an IR laser source.
[00125] EXAMPLE 1C
Using the system of Example 1, welding experiments were performed for copper
thicknesses ranging from 127-500 pm. FIGS. 3 ¨ 5 summarize the results of
these BOP
tests. FIG. 3 shows full penetration up to 9 m/min at 275W followed by a
falloff of the
penetration depth with speed as expected. FIG. 4 shows BOP results with full
penetration up to 0.6m/min with no-assist gas and 0.4m/min when using Ar-0O2
cover
gas. FIG. 5 shows depth of penetration vs. Speed for 500pm Copper at 275W.
[00126] EXAMPLE 2
[00127] The fixture 5000 of FIGS. 13 and 13A is used to successfully lap weld
a stack of 2 copper foils, 178 pm thick with a conduction mode weld. The
fixture when
heated to a few 100 C results in an improvement in the weld speed and quality
by a
factor or two or more because the energy lost to heating the part during the
weld is now
provided by the pre-heat. The shielding gas for the top side of the weld is
delivered at
the front of the weld travel direction to the back of the weld travel
direction as shown in
FIG. 10.
[00128] EXAMPLE 3
[00129] Two 125 pm thick copper plates were lap welded together using the
fixture 5000, with a conduction mode weld. This weld is shown in the cross-
section
photograph of FIG. 15.
[00130] EXAMPLE 4
[00131] Using the fixture 5000 shown in FIGS. 13 and 13A, a stack of 40
copper foils, 10 pm thick are welded with no porosity and no defects. A cross
section of
this weld is shown in FIG. 17. Welding this stack depends on how the foils are
prepared, how the foils are clamped and how much torque is applied to the
clamps.
The foils are sheared and flattened, then they are cleaned with alcohol to
remove any
manufacturing or handling oils and finally stacked in the fixture. The
clamping bolts
5001 are torqued to 1 Nm to insure the parts are held firmly in place during
the welding
process. The laser used to weld these parts consist of four of the 150-Watt
lasers
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shown in FIG. 19 optically combined as shown in FIG. 21 to create a 500-Watt
laser
system. This laser produces a 400 pm spot with an average power density of 400
kW/cm2, and a peak power density sufficient to initiate the keyhole welding
process.
[00132] EXAMPLES
[00133] Embodiment of the present laser beam welding techniques are
evaluated using the first full penetration, bead on plate (BOP) welds of a 1
mm thick
copper plate with a 600-Watt blue laser with nominal spatter remaining on the
surface.
The 600-Watt, CW laser is focused to a spot size of approximately 200 um,
resulting in
an average intensity at the surface of the part of 2.1 MW/cm2. This intensity
is well above
the power density required to initiate and sustain the keyhole in the part.
During the
welding process, the keyhole is observed to form rapidly and once full
penetration is
achieved, the molten puddle exhibits a very stable surface indicating low
turbulence in
the weld puddle as the weld progresses. The stable welding process is observed
over a
wide range of welding speeds and with an AJ-0O2 cover gas for suppressing the
surface
oxidation during the welding process. This ability to create a stable keyhole
weld can be
attributed to the high absorptivity of the copper in the blue and the
uniformity and high
quality of the laser beam. The blue laser light is uniformly absorbed by the
walls of the
keyhole during the welding process, however, when instabilities in the keyhole
arise due
to turbulence in the melt puddle, the heat input is maintained, and the
keyhole remains
stable.
[00134] EXAMPLE 6
[00135] Embodiments of the present inventions use the present high power
visible lasers, and in particular blue lasers, blue green lasers and green
lasers, for in
industrial applications, such as welding. In embodiments of these processes
power
levels of 500-600 Watts and spot sizes of 200 -400 um are used. The wavelength
for
these embodiments is in the blue range. Stable conduction mode welding of
copper is
observed over a wide range of speeds for both the 400 and 200 um spot sizes on
Oxygen Free Copper (OFC). This welding mode is spatter free and fully dense
with no
signs of porosity throughout the welded parts. The stable keyhole mode welding
is
observed in copper with only the 200 um spot size, however with lower
conductivity
materials such as Inconel and stainless steel, even the 400 um spot size can
achieve a
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keyhole weld. Modelling of the welding process reveals a significant
difference in the
shape and size of the weld puddle when welding copper compared to stainless
steel.
The stainless steel with the lower thermal conductivity exhibits a classic
teardrop shape
weld puddle, however, the copper with its high thermal conductivity exhibits a
circular
weld puddle much smaller in size for the same power level as used in the
welding of the
stainless samples.
[00136] EXAMPLE 7
[00137] Laser welds of metals using blue, blue green or green laser beams are
conducted without wobbling the beam. These welds have deep penetration. Thus,
there is provided wobble free welding of metals, including copper foils, and
copper
plates, using these laser beams. There is provided wobble free welding on
aluminum,
stainless steel, copper, aluminum based metals, stainless steel based metals,
copper
based metals and alloys of these.
[00138] In an embodiment of this wobble free laser welding, blue laser welding
is conducted on copper having a thickness of less than 1 mm and with a blue
laser
beam having a wavelength of 450 nm.
[00139] In an embodiment of this wobble free laser welding, blue laser welding
is conducted on aluminum having a thickness of less than 1 mm and with a blue
laser
beam having a wavelength of 450 nm.
[00140] In an embodiment of this wobble free laser welding, blue laser welding
is conducted on stainless steel having a thickness of less than 1 mm and with
a blue
laser beam having a wavelength of 450 nm.
[00141] EXAMPLE 8
[00142] An embodiment a 600-Watt laser having four 200-Watt blue laser
modules providing a laser beam having a wavelength of 450 nm. The lasers
diodes are
individually collimated, and the beam divergence is circularized as shown in
FIG. 19
resulting in a beam parameter product of 22 mm mrad for each module. The laser
beams from the four blue laser modules are optically sheared in both the
horizontal, as
well as the vertical direction, to fill out the aperture of the 100 mm
diameter focusing
optic as shown in FIG. 21. This composite beam (450 nm) has a beam parameter
product of 44 mm mrad and is suitable for launching into a 400 pm fiber. For
Examples
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8A to 8K and 9, an optical fiber was not used and this blue laser beam is
delivered via
free space to the work piece.
[00143] For these Examples an optical breadboard is used having a 4' x 6'
optical bench which allows the integration of real time beam diagnostics into
the setup.
The composite output beam is sampled with a 1% beam sampler and a portion of
the
beam is sent to a far-field profile camera and a power meter. The far-field is
generated
with the same focal length lens as the welding lens, either a 100 mm F/1 lens
or a 200
mm F/2 lens. Both lenses are BK7 aspheres from ThorLabs. The lenses are
underfilled
to about 80 mm, and the spot at the workpiece is approximately 200 pm for the
100 mm
.. FL lens, and approximately 400 pm for the 200 mm FL lens.
[00144] The beam caustic is measured by translating the Ophir beam profiler
through the focus of the 100 mm FL lens in the beam sampling arm of the setup
and
measuring the diameter of the beam at the 95% encircled power point. The graph
of
the beam caustic is shown in FIG. 22. This measurement demonstrates the
relatively
short depth of focus for the 100 mm FL lens.
[00145] A Fanuc 6 -axis robot (FANUC M-16iB) is used to move the sample
through the free space beam focus with the cover gas being provided by a 3/8"
diameter
sparger tube mounted on the robot adapter and directed along the direction of
the weld.
For Examples 8A to 8K and 9, an embodiment of a welding fixture of the type
shown in FIGS 12 and 12A is used. The welding fixture is a part of the welding
process
and when welding high thermal conductivity materials, it can affect the
penetration
depth, weld speeds, and both, that can be achieved. FIGS. 12 and 12A are
drawings of
the embodiment of the welding fixture. In one embodiment aluminum (6061
series) is
used. In another embodiment stainless steel (316) is used. The aluminum
welding
fixture tends to take the heat out of the part rapidly, while the stainless-
steel fixture
allows most of the heat to stay within the part. Both materials are evaluated
along with
different methods for clamping the samples (e.g., work piece, part). An inert
gas such
as Argon - CO2 is flowed over the top of the part placed in the fixture to
suppress any
oxidation of the parts during the welding process. A small gap 4003 is located
under
the center of the sample to minimize the heat sinking at the point of the bead
on plate
Examples and allow an assist gas to be added to the back side of the weld.
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[00146] In the keyhole mode of welding can produce a strong plume when
welding. Since the atoms and ions in the plume readily absorb the 450 pm
light, this
plume should be managed and preferably suppressed. A 3/8" diameter tube
sparger is
used to suppress the plume by delivering 50 scfh of Argon or Argon-0O2 across
the top
of the part. Welds can be conducted or made with various gasses to manage the
plume
and avoid oxidation of the parts, including Argon, Argon-0O2, Air, Helium and
Nitrogen.
The goals of optimizing welding processes, among others, is to achieve the
greatest
penetration at the highest possible speed. The data presented in Examples 8A
to 8K
use Argon as the cover gas. In other laser welding and processing
applications, such
as butt welding, plume management is desirable, and preferred.
[00147] For the 500 Watts welding tests of Examples 8A to 8F, a 200 mm focal
length lens is used to focus the beam to a 400 pm spot size resulting in an
average
intensity of ¨400 kW/cm2 and a peak intensity approaching 800 kW/cm2.
[00148] For the 600 Watts welding tests of Examples 8G to 8K, a 100 mm focal
length lens is used to focus the beam to a 200 pm spot size resulting in an
average
intensity of approximately 2.1 MW/cm2 and the peak intensity approaches 4.5
MW/cm2.
[00149] EXAMPLE 8A
[00150] Using the laser, processes, and set up of Example 8, bead on plate
welding is conducted and evaluated with copper (OFC), Stainless Steel (304)
and
aluminum (1100 series) using 500 Watts, a spot size of 400 pm and an average
power
density of 400 kW/cm2. The samples are all cut to 10 mm x 45 mm in size with a
shear
and cleaned with acetone prior to processing. The surface finish is as
supplied from
McMaster Carr, which looks like a rolled finish for the thinner samples and a
milled
finish for the thicker samples. These evaluations characterize the full
penetration
capability of the welding process of Example 8 for a given sheet thickness.
[00151] Using the laser, processes, and set up of Example 8, Bead on plate
evaluations are performed with Oxygen Free Copper (99.99% - 110) samples that
ranged in thickness from 80 pm to 500 pm. FIG. 23 shows the weld speed at
which a
full penetration bead is observed on the backside of the welded sample.
[00152] The samples were wiped down with acetone prior to the evaluation and
clamped in the fixture with the bolts torqued to 1 Newton-meter. The fixture
and sample
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were held at a 20-degree angle to the beam normal to prevent back reflections
into the
laser, causing an elongation of the spot to 400 pm x 540 pm for the 200 mm FL
lens.
The beam angle is from the beam normal to the trailing side of the part to be
welded.
This tilt of the sample most likely reduces the maximum welding speeds that
can be
achieved due to the lower intensity on the part. The sequence of the weld is
the robot is
commanded to translate the part, with enough distance between the part and the
laser
beam to insure the robot has reached the programmed speed, the laser is
initiated just
as the weld fixture crosses the position of the laser beam. The part is
translated
through the beam at a constant velocity, once the end of the weld fixture is
reached, the
laser beam is turned off and the robot is commanded to return to its home
position. The
samples are cross sectioned, polished and etched to reveal the microstructure.
All the
welds exhibited a spherical melt-freeze pattern indicative of a conduction
mode weld.
[00153] EXAMPLE 8B
Using the laser, processes, and set up of Examples 8 and 8A, butt welding of
samples was also evaluated. The parts were prepared the same as in the Example
8A
and clamped with the same clamping force. The edge of the samples produced by
the
shear is the basis for the butt-welded parts. Some of the results of these
tests are
shown in FIG. 24. The weld speed is the speed at which the two parts can be
joined
with a full penetration weld showing on the backside of the welded parts.
There is no
observation of spatter during the weld or on the parts that were welded,
indicating a
conduction mode weld process.
[00154] EXAMPLE 8C
[00155] During the evaluation of the Copper 110 series samples of Example
8A, a dependence on the penetration depth of the weld as a function of the
sample
thickness was observed. FIG. 25 shows how the penetration depth can decrease
as
the copper sample thickness increases. This dependence is due to the greater
thermal
mass of the part and the high thermal conductivity of copper which allows the
heat to be
dissipated rapidly away from the weld bead. This is in part because of the
high thermal
conductivity and the ability of the copper to effectively heat sink the laser
energy during
the welding process. As can be seen from FIG. 25, at a given speed the
penetration
depth can decrease by over a factor of four as the material thickness is
increased by a
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factor of two. The penetration depth for the top case does not decrease as
dramatically
as the other two cases because it is at a much lower speed and it is
saturating the
copper's ability to heatsink the laser energy. Consequently, when designing a
welding
process for copper using the conduction mode process, the finite thickness of
the parts
to be welded should be taken into consideration.
[00156] EXAMPLE 8D
Using the laser, processes, and set up of Examples 8, and 8A, aluminum 1100
series samples are welded and evaluated. Aluminum 1100 series samples were
prepared and mounted in the weld fixture the same as the copper parts in
Example 8A.
The weld process is similar to the cooper welding process, of Example 8A, with
only the
robot speed being changed. The weld speed shown in FIG. 26 is for the case
where a
full penetration bead is observed on the backside of the part of that
thickness. There is
no spatter from the melt puddle observed during the welding process.
[00157] EXAMPLE 8E
[00158] Using the laser, processes, and set up of Examples 8 and 8A, butt
welds and welding tests are performed for two Aluminum 1100 samples placed
side by
side in the welding fixture. The samples are prepared with a shear, and the
two edges
had no special preparation prior to the weld being performed. The samples are
wiped
down with acetone prior to the weld. The welding process is the same as
described for
the copper parts, in Exhibit 8A, except for the weld speed. The final weld
speed plotted,
is the speed at which a full penetration bead is obtained over the entire
length of the
samples being welded. A summary of this data is shown in FIG. 27.
[00159] EXAMPLE 8F
[00160] Using the laser, processes, and set up of Examples 8 and 8A, BOP
welds and weld tests are conducted on 304 Stainless Steel samples. The samples
are
cut to the 10 mm x 45 mm size that fits in the fixtures, wiped down with
acetone and the
robot speed was adjusted until a full penetration weld is obtained on the test
sample.
Again, there is no spatter or porosity noted in the welded samples. The
results of this
test are shown in FIG. 28.
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[00161] EXAMPLE 8G
[00162] Welds and evaluations of the 600 Watt system and process of
Example 8 are conducted. A 100 mm focal length lens is used to focus the beam
to a
200 pm spot size resulting in an average intensity of approximately 2.1 MW/cm2
and
the peak intensity approaches 4.5 MW/cm2. A series of welds are made and tests
are
conducted at this higher power level and with a shorter focal length lens (100
mm) to
further evaluate and illustrate the penetration capabilities of this laser at
various speeds.
In these tests the average intensity is 2.1 MW/cm2, a power density that is
well within
the requirements to vaporize either the copper and create a keyhole. The part
is tilted
at 20 degrees, decreasing the effective power density to 1.4 MW/cm2 which is
sufficient
intensity to initiate the keyhole welding mode in copper, aluminum and
Stainless Steel.
[00163] The first indication of a keyhole process in copper at was a
significant
increase in spatter during the welding process. This spatter is observed with
an on-axis
camera while monitoring the weld puddle. The weld samples are cross sectioned,
polished and etched revealing a micro structure freeze pattern typical of a
keyhole weld.
The cross section also reveals a significant amount or porosity where ever the
beam did
not fully penetrate the part. However, the sections where the beam fully
penetrated
showed nominal porosity.
[00164] EXAMPLE 8H
[00165] Using the laser, processes, and set up of Examples 8 and 8G, a
longitudinal cross section of a keyhole mode weld on a 500 pm thick copper 110
plate is
performed to determine the porosity along the entire length of the weld as
shown in the
photograph of FIG. 29. The first cm of the weld on the right hand side of the
picture
exhibited a substantial amount of porosity as well as a lack of penetration
through the
sample. As the heat builds up in the part during the weld, the keyhole process
fully
penetrates the copper plate. This result indicated that if the keyhole process
is allowed
to stabilize, then it is possible to produce welds with nominal spatter and
porosity.
[00166] EXAMPLE 81
[00167] Using the laser, processes, and set up of Examples 8 and 8G, and
based on the results from Example 8H, welds and tests where the keyhole is
allowed to
stabilize first before moving the part are conducted. The welding process is
modified by
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allowing the laser beam to dwell on the part for a short time period, then the
robot is
accelerated, dragging the keyhole through the part. After a series of tests
varying the
dwell time from 0.6 seconds to 1.5 seconds, the preferred results are achieved
with the
0.6 second dwell time. FIG. 30 is a photograph of a cross section for a bead
on plate
weld of copper 110 performed with the 0.6 second dwell on the sample followed
by
translating the sample at a speed of 1.1 m/min. A series of welds are
performed at this
speed to verify that the process is stable and well controlled. All samples
exhibited
similar results, very low porosity, and a very stable keyhole weld.
[00168] EXAMPLE 8J
[00169] Using the laser, processes, and set up of Examples 8 and 8G, welds
are made and evaluated on a range of different copper 110 material
thicknesses. A plot
of the maximum weld speed achieved for full penetration of each sample is
plotted in
FIG. 31. Keyhole mode welding, translation mode welding, and conduction mode
welds
are all observed across these welding speeds. The result is a substantial
increase in
the welding speeds and penetration depths compared to the 500 Watt, 400 pm
system.
[00170] EXAMPLE 8K
[00171] Using the laser, processes, and set up of Examples 8 and 8G, a
Stainless Steel sample is welded and evaluated. The result is the lap welding
of four
sheets of 304 Stainless Steel at a speed of 1.2 m/min. The cross section shown
in FIG.
32, shows a classical profile of a keyhole welded sample. The porosity at the
bottom of
the keyhole may have been caused by the gap between the third and fourth sheet
in the
stack. This porosity can be eliminated by optimization of this welding
process.
[00172] EXAMPLE 9
[00173] Using the laser, processes, and set up of Examples 8 and 8A, a series
of tests are conducted with stacks of Oxygen Free Copper foils to determine
how many
sheets of foil can be lap welded in a single pass. The experimental setup is
the same
as Example 8, but now the fixture is changed and a small steel insert is used
in the gap
under the center of the parts. The foils are clamped in place and the sample,
tilted at a
20-degree angle to the beam normal is passed through the beam with an Ar-0O2
cover
gas. The results of these tests are summarized in FIG. 33 for up to 40 foils
in a stack.
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The two different lens configurations are used with very good results over a
wide range
of foil thickness and stacks.
[00174] FIG. 34 is a photo of an example of a successful weld of 40 cooper
foils with no porosity and no spatter on the top surface. This stack of foils
was welded
with 500 Watts and the 200 mm FL lens which corresponds to the 400 pm spot
size.
The weld speed was 0.5 m/min. The manner of clamping of the sheets can effect
the
weld quality, and good and consistent clamping of the sheets provide
consistently high-
quality welds.
HEADINGS AND EMBODIMENTS
[00175] It should be understood that the use of headings in this specification
is
for the purpose of clarity, and is not limiting in any way. Thus, the
processes and
disclosures described under a heading should be read in context with the
entirely of this
specification, including the various examples. The use of headings in this
specification
should not limit the scope of protection afford the present inventions.
[00176] It is noted that there is no requirement to provide or address the
theory
underlying the novel and groundbreaking processes, materials, performance or
other
beneficial features and properties that are the subject of, or associated
with,
embodiments of the present inventions. Nevertheless, various theories are
provided in
this specification to further advance the art in this area. The theories put
forth in this
specification, and unless expressly stated otherwise, in no way limit,
restrict or narrow
the scope of protection to be afforded the claimed inventions. These theories
many not
be required or practiced to utilize the present inventions. It is further
understood that
the present inventions may lead to new, and heretofore unknown theories to
explain the
function-features of embodiments of the methods, articles, materials, devices
and
system of the present inventions; and such later developed theories shall not
limit the
scope of protection afforded the present inventions.
[00177] The various embodiments of systems, equipment, techniques,
methods, activities and operations set forth in this specification may be used
for various
other activities and in other fields in addition to those set forth herein.
Among others,
embodiments of the present inventions can be used with the methods, devices
and
system of Patent Application Publication Nos. WO 2014/179345, US 2016/0067780,
US
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2016/0067827, US 2016/0322777, US 2017/0343729, US 2017/0341180, and US
2017/0341144 the entire disclosure of each of which are incorporated herein by
reference. Additionally, these embodiments, for example, may be used with:
other
equipment or activities that may be developed in the future; and with existing
equipment
or activities which may be modified, in-part, based on the teachings of this
specification.
Further, the various embodiments set forth in this specification may be used
with each
other in different and various combinations. Thus, for example, the
configurations
provided in the various embodiments of this specification may be used with
each other.
For example, the components of an embodiment having A, A' and B and the
components of an embodiment having A", C and D can be used with each other in
various combination, e.g., A, C, D, and A. A" C and D, etc., in accordance
with the
teaching of this Specification. The scope of protection afforded the present
inventions
should not be limited to a particular embodiment, configuration or arrangement
that is
set forth in a particular embodiment, example, or in an embodiment in a
particular
.. Figure.
[00178] The invention may be embodied in other forms than those specifically
disclosed herein without departing from its spirit or essential
characteristics. The
described embodiments are to be considered in all respects only as
illustrative and not
restrictive.
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