Note: Descriptions are shown in the official language in which they were submitted.
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background and Summary of the Invention
The present invention relates to a method of
forming a laser butt weld and, more particularly, to a
method of progressively forming a laser butt weld between
opposed, longitudinally extending edges to be welded, such
as the opposite side edges of a sheet of material which has
been formed into a tubular-shaped workups for making a can
body or the 'Ike.
Progressively forming a laser butt weld along
opposed edges of two members has recently been made possible
by innovations such as that suggested by Syrian et at in
U.S. Patent No. 4,152,573 wherein the abutting edges to be
welded are clamped relative to one another and then moved
relative to a laser beam, and also that disclosed by Nielsen
in U.S. Patent No. 4,354,090 wherein a Z-bar guide apparatus
is used for guiding the opposed edges to be welded into
substantially abutting edge-to-edge relationship with one
another for laser welding. With both of these known laser
welding techniques, the edges to be welded are typically
sheared edges of a material such as sheet metal, so that the
edges extend essentially perpendicular to the plane of the
material adjacent the edge. The adjacent edges are
,:
positioned in abutting relationship along essentially the
; entire thickness of the joint to form a closed butt joint
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which is welded by directing a laser beam at the weld joint
from one side thereof.
It has been discovered that in forming such a but
joint between two members lying approximately in the same
Flare, there may be problems with inconsistent or irregular
weld formation along the length of the members king welded,
especially where welding is to be accomplished at a
relatively high speed and with minimum heat input so as to
reduce heat input related metallurgical problems and/or
fluid flow problems known as stubbing. Fluctuations in the
transfer efficiency of the laser energy to the edges to be
welded along the length of the weld joint is one reason for
this problem. Gore specifically, it has been found that the
presence of burrs on one or more of the sheared edges to be
welded contributes to this inconsistency. What is, when a
material such as sheet metal, for example, is sheared,
typically a burr is formed at the sheared edge, which
extends outwardly from the plane of the sheet material in
the direction of shearing. In the case where a burr extends
; 20 outwardly from the side of a butt joint to be laser welded,
and the laser beam approaches the joint on the side of the
burr, at the instance of impingement the burr tends to
scatter the laser energy and reduce the efficiency with
which the laser energy can be transmitted to the edges for
welding. Moreover, because the burrs are not of great mass
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as compared with the edges to be welded, they are vaporized
in a short period of time after being contacted by the laser
beam. This vaporization can further obstruct the
transmission of laser energy to the edges to be welded and
contribute to the initiation of a weld plasma in the area
of the burr. The presence of the plasma may also further
reduce the effectiveness of energy transmission to the edges
for welding. Thus, the intermittent presence and often
irregular configuration of burrs along the edges to be laser
butt welded can result in incomplete weld penetration and
weld formation, especially where a minimum heat input for
welding abutting edges is employed. On the other hand, if
the laser beam energy is increased so as to be sufficient to
effect a weld even in the presence of burrs, in those areas
lo having little or no burrs, an excess of heat input will
exist for the formation of a sound weld. Iris will increase
the size of the weld and weld heat effected zone, and also
increase heat input related metallurgical problems and
possibly stubbing. Thus, the presence of burrs can result
in weld defects and also a reduction in the efficiency with
which edges can be continuously laser butt welded.
The problem of course can be avoided by grinding
sheared edges to be welded prior to welding to remove the
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burrs. however, this is undesirable because it adds an
additional manufacturing step, and the consequent time and
expense associated therewith, to the production process.
Another possible solution is to ensure that any burrs on
-S abutting edges extend outwardly from the weld joint on the
side of the weld joint away from that upon which the laser
beam is to initially impinge. Unfortunately, for many
applications, this is not a practical solution since the
burrs formed on opposite sides of a sheared piece of
material will extend in opposite directions due to the
construction and operation of the existing slitter or
shearing apparatus. Porting a sheared piece of material
into a tubular-shape for butt welding will then produce a
weld joint with a burr protruding from both sides thereof.
An object of the present invention is to provide a
method of forming a laser butt weld wherein the adverse
effect of the presence of a burr on the side of the weld
joint initially impinged by the laser beam, is avoided, so
that more efficient, uniform welding of abutting edges can
be accomplished at high speed, while minimizing heat input
and heat input related problems such as stubbing.
A further object of the invention is to provide a
method of progressively forming a laser butt weld between
opposed abutting edges of two members, which method permits
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an increased welding speed with a given heat input and
thereby a more efficient transfer of laser energy to the
work pieces, so that a very narrow, uniform weld can be
formed with a relatively small heat affected zone.
An additional object of the invention is to
provide a method of the aforementioned type which permits
keyhole welding of abutting edges to be accomplished at high
speed and high efficiency to produce a weld having a
relatively uniform cross section through the entire
thickness of the members being joined.
These and other objects of the invention are
attained by the method of the invention which comprises the
steps of providing two members to be butt welded,
positioning respective edges of said members in abutting
lo contact with the two members being canted slightly with
respect to one another so that the butt joint formed by said
edges is open toward a first side of said members with said
edges contacting one another toward a second side of said
members opposite said first side, and directing at least one
high energy density laser beam at said but'. joint from said
first side of said members so that at least a portion of
said laser beam extends into the open side of said butt
joint to said edges while urging said edges of the two
members in the direction of said butt joint for butt welding
said members.
According to a preferred embodiment, the butt
weld between the two members is continuously formed along
the length of the edges of the members by moving at least
one of the laser beam and the members relative to the other
in a direction along the butt joint to progressively weld
the edges. In this embodiment, the two members are the
opposite sides of a single piece of sheet material, and the
step of providing the two members to be butt welded includes
I; forming the piece of sheet material into a tubular-shaped
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workups having opposed longitudinally extending edges to
be butt welded. The step of positioning the edges includes
moving the tubular-shaped workups relative to a guide
apparatus which may be a Z-bar, with the edges being guided
by the guide apparatus into the abutting contact as
described above. Further in this preferred embodiment the
method may include the step of supporting the tubular-shaped
workups by support means as it is moved relative to the
guide apparatus, the location of the support means being
adjusted with respect to the guide apparatus to effect the
slight canting of the opposed sides of the workups with
respect to one another.
Preferably, the tubular-shaped workups disclosed
is generally cylindrical in cross section. It is supported
by the support means relative to the guide apparatus, which
may be a Z-bar as above indicated, such that it has a
slightly pear-shaped cross section with the edges to be
welded located at the top thereof to thereby cant the
opposed sides of the workups with respect to one another
and open the joint on the outer side. This causes any burrs
on that side of the joint to be pulled outwardly from the
center of the joint so as to offer reduced or no
interference to the incoming laser beam as compared to the
conventional methods. Also, at least a portion of the
approaching laser beam is free to pass directly into the
open side of the butt joint to the edges for heating and
melting the material thereof.
Preferably, the edges of the members to be welded
are essentially straight sheared edges extending
approximately perpendicular to the plane of the adjacent
member. Burrs are present on the edges from the shearing
operation. Thus, when the edges are positioned according to
the invention, they make, as seen in a sectional view taken
transverse to the edges, essentially point contact with one
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another at the second side of the members with the edges
tapering away from each other in the direction toward the
first side of the members.
Further, according to the invention, the high
energy density laser beam preferably penetrates completely
through the butt joint to effect keyhole welding of the
edges. When this occurs, an additional step of the method
may include, providing a laser beam dump on the second
side of the members to absorb the laser beam passing through
the butt joint during the keyhole welding. This prevents
damage to the inside of a tubular workups such as a can
body or the like, for example, as well as collecting any
debris expelled from the weld keyhole. The safety of the
welding operators is also enhanced with the use of such a
beam dump which prevents unwanted reflectance of the laser
energy. Alternatively, the method may include providing a
means to accurately reflect the laser beam which has passed
through the butt joint back toward the joint to slow the
cooling rate thereof.
A second preferred embodiment of the invention may
comprise clamping the members to be welded in a welding jig
with clamping means to position the respective edges in the
described abutting contact.
According to the present invention there is also
provided a method of forming a laser butt weld comprising
the steps of providing two members to be butt welded,
positioning respective edges of said members in abutting
contact with the two members being canted slightly with
respect to one another so that the butt joint formed by said
edges is open toward a first side of said members with said
edges contacting one another toward a second side of said
members opposite said-first side, directing at least one
high energy density laser beam at said butt joint while
moving at least one of said laser beam and said members
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relative to the other in a direction along said butt joint
for progressively butt welding said members, said laser beam
being directed at said joint from said first side of said
members so that at least a portion of said laser beam
extends into the open side of said butt joint and penetrates
completely through said butt joint to form a keyhole
there through with molten material of said members
surrounding said keyhole, and urging said two members in the
direction of said butt joint during said welding so that the
molten edges of said members are mashed together immediately
behind the keyhole as said keyhole and laser beam are moved
relative to said members in a direction along said butt
joint.
According to the present invention there is also
provided a method of forming a butt weld comprising the
steps of providing two members to be butt welded,
positioning respective edges of said members in abutting
contact with the edges being canted slightly with respect to
one another so that the butt joint formed by said edges is
open toward a first side of said members with said edges
contacting one another toward a second side of said members
opposite said first side, and directing at least one high
energy density beam at said butt joint, said beam being
directed at said butt joint from said first side of said
members so that at least a portion of said beam extends into
the open side of said butt joint to said edges for butt
welding said members.
These and other objects, features and advantages
of the present invention will become more apparent from the
following description when taken in connection with the
accompanying drawings, which show, for purposes of
illustration only, two embodiments in accordance with the
present invention.
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BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is an enlarged side elevation Al view of
the edges of two members arranged in a conventional butt
joint for laser welding according to the prior art method;
S Figure 2 is a cross-sectional view, 100X
magnification, taken transverse to the welding direction, of
a laser butt weld produced in members according to the prior
art method;
Figure 3 is an enlarged side elevation Al view of
the ends ox two members whose edges are to be laser butt
welded according to the method of the present invention, and
wherein the two members are canted slightly with respect to
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one another so that the butt joint formed by the edges to be/J
welded is open toward a first side of the members, with the
edges contacting one another toward a second side of the
members opposite the first side
Figure 4 is an enlarged cross-sectional view, lox
magnification, of a laser butt joint welded according to the
invention, the view of the weldment taken transverse to the
welding direction;
Figure 5 is a side elevation Al view, partially in
cross-section, of an apparatus for laser butt welding
opposed abutting edges of a longitudinally extending weld
joint on the side of a tubular member such as a can body or
the like according to the present invention;
Figure PA is a cross-sectional view taken along
15 the line I-I of the apparatus of Figure 5 when used
according to the prior art method
Figure Boyce an enlarged cross-sectional view
taken along the line II-II of the apparatus of Figure 5, and
illustrating the prior art method of bringing the edges into
abutting contact for laser welding;
; Figure PA is a cross-sectional view similar to
Figure PA, but illustrating the apparatus in Figure 5 in a
modified condition for effecting a continuous laser butt
welding according to the method of the present invention;
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Figure 7B is an enlarged, cross-sectional view
similar to Figure 6B, but illustrating the opposed abutting
edges to be welded according to the method of the present
invention, the edges being so arranged by the modified
apparatus of Figure PA,
Figure 8 is a side elevation Al view, partially in
cross-section, of the Z-bar guide apparatus of Figure 5,
wherein a mandrel is secured to the lower surface of the
Z-bar guide apparatus and carries a laser beam dump to
absorb laser energy passing through the edges to be welded
during keyhole welding;
Figure 9 is a cross-sectional view of the
apparatus of Figure 8, taken along the line III-III;
Figure 10 is a schematic illustration of the
forces on the tubular-shaped workups whose edges are being
laser welded according to the method of the invention, the
forces effectively urging the opposed abutting edges to be
welded in the direction of the butt joint;
Figure if is a view similar to Figure 3, and
schematically illustrating clamping means for clamping the
respective edges in a welding jig with the two members being
canted slightly with respect to one another for a laser
welding according to the method of the invention and
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Figure 12 is an enlarged metallurgical section
taken transverse to a weld made according to the method of
the invention.
Description of the Disclosed embodiments
_ _ _ . ............................ .
Referring now to the drawings, Figure 1
illustrates the opposed abutting edges of two members 1 and
2 to be laser butt welded according to the known method as
disclosed in U.S. Patent Nos. 4,152,573 and 4,354,090. The
edges 3 and 4 of the members to be laser welded are
essentially straight sheared edges which extend
perpendicularly to the Flare 5 of the respective members,
and have burrs 6 and 7 remaining thereon from the shearing
operation. The burr 6 on one of the members is on the top
side of the joint as shown in Figure 1, while the burr 7 on
the other member extends downwardly from the joint. Of
course, both burrs could be on the same side of the joint.
During laser welding of the joint in Figure 1
according to the prior art method, a laser beam is directed
to the butt joint in the direction of the arrow A, so as to
impinge on the edges of the members on one side, in this
case the to, of the joint. when the laser beam first
strikes the burr 6 on the top side of the joint, the light
of the laser beam is scattered somewhat due to the
configuration of the burr, and, after a very short time, the
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burr will be heated and vaporized due to its small mass.
As a result, the efficiency of transfer of the laser energy
to the edges 3 and 4 of the members to be welded is
adversely effected. That is, the burr initially scatters
the incident laser energy, thereby making it unavailable for
welding purposes, and the subsequent vaporization of the
burr contributes to the formation of a weld plasma above the
edges to be joined. The plasma and metal vapor at least
partially obstruct the transmission of laser energy to the
edges to be welded. The effect of the burr on the welding
process is particularly pronounced where the laser energy
and consequent heat input to the work during welding are to
be minimized to reduce heat input related metallurgical
problems, such as stubbing, which may occur during welding
as in the high speed welding of thin materials for making
can bodies and the like. Because of the varying size and
configuration of the burrs on the edges to be joined, with a
given laser beam energy focused at edges to be progressively
welded, a satisfactory weld may be made at a first location
along a weld joint, while incomplete penetration and other
weld defects can occur at other locations along the joint.
Thus, to ensure the formation of a full penetration weld
along the entire length of a joint, the minimum laser beam
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energy that must be applied is that necessary for welding ,'
where the least efficient transfer of laser energy to the
edges occurs. The locations along a weld joint where
energy transmission is more efficient will then necessarily
have an additional, undesired heat input during welding.
A metallurgical cross section of a laser welded
butt joint made according to the prior art method, with the
edges arranged as shown in Figure l, and with minimal heat
input for accomplishing keyhole welding, is shown in Figure
2. The weld 8 between the adjacent edges has a wine-glass
configuration with the widest section thereof occurring at
the top of the joint, and the narrowest at the bottom. This
occurs because of the relatively longer time for heat
conduction on the side of the joint initially impinged by
the laser beam. A non-uniform weld configuration of this
type may be problematical in some instances because of the
different metallurgical properties of the weld metal and the
heat affected zone which can occur across the thickness of
the welded members. This is the case in the fabrication of
metal can bodies and the like, for example, where uniform
properties are desired because the ends of the can bodies
may have to be curled, necked-in, outwardly flanged, etc.
In order to reduce or avoid the adverse effects of
burrs on the sheared edges to be welded, and also the
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non-uniform weld characteristics which occur when heat input
for welding is minimized, according to the method of the
invention and as depicted in Figure 3, the opposed edges 9
and 10 of the members 11 and 12 to be butt welded are
positioned in abutting contact with the two members 11 and
12 being canted slightly with respect to one another through
a total angle so that the butt joint formed by the edges
is open toward a first, top side of the members with the
edges contacting one another at 13 toward a second, bottom
side of the members opposite the first side. A laser butt
weld is then effected at the joint by directing a high
energy density laser beam at the butt joint, while urging
the edges of the two members in the direction of the butt
joint. The laser beam is directed at tune butt joint from
the first, top side of the members, as shown by arrow B in
Figure 3, so that at least a portion of the laser beam
extends into the open side of the butt joint to the edges 9
and 10. In this way, the burr on the top side of the joint
is actually pulled back away from the center line of the
: 20 joint to avoid or reduce its scattering effect and to reduce
the effect of vaporization of the burr by the laser energy.
Since at least a portion of the laser beam extends into the
Jo open side of the butt joint, heating takes place along all
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of the exposed edges to be welded from the instance of
impingement, rather than only at the top side as in the
prior art method as discussed above with respect to Figures
1 and 2. In this way, the method of the invention permits
keyhole laser butt welding with minimum heat input, and, at
the same time, with the attainment of relatively uniform
weld characteristics across the thickness of the members
being joined. A cross section of a weld made according to
the present invention is illustrated in Figure 4, wherein it
is seen that the width of the weld 14 is relatively uniform
across the entire thickness of the material.
With the joint open toward the upper side of the
members 11 and 12 as shown in Figure 3 and the opposed edges
9 and 10 making only essentially point contact at 13 with
one another at the lower side of the members, a high energy
density laser beam extending into the open side of the butt
joint in the direction of arrow B can readily melt the
opposed edges in the area of contact 13 and continue out the
lower side of the joint, thereby establishing a keyhole for
welding. Because of the spacing of the edges at the joint
created by the slight canting of the members and the absence
of additional filler material it is necessary to urge the
edges of the two members being welded in the direction of
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the butt joint, while the laser beam is being directed at
the joint. The application of forces in the direction of
the joint is schematically illustrated by the arrows C and D
in Figure 3. This force should be sufficient to effectively
mash the opposed molten edges of the members together
subsequent to the laser killing through the joint
In continuous butt welding along the length of two
members to be joined according to the invention, the weld is
progressively formed by positioning the respective edges of
the members in the manner described, directing a high energy
density laser beam at the butt joint to keyhole through the
joint and moving at least one of the laser beam and the
members relative to the other in a direction along the joint
to progressively weld the edges while urging the two members
together in the direction of the butt joint. The magnitude
of the force urging the members toward the butt joint should
be sufficient to mash the molten edges together without
causing significant amounts of upset at the joint. The
required force will vary depending upon the thickness of the
members being joined, as will be readily understood by the
skilled artisan.
According to a preferred embodiment of the method
of the invention, the two members to be butt welded are the
opposite sides of a single piece of sheet material, which is
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formed into a tubular-shaped workups having opposed
longitudinally extending edges to be butt welded. The edges
are positioned by moving the tubular-shaped workups
relative to a Z-bar guide apparatus with the edges being
guided by the Z-bar guide apparatus into the desired
abutting contact. A known Z-bar guide apparatus and method
of butt welding are disclosed in U.S. Patent No. 4,354,090,
referred to above. Figure 5 of the drawings illustrates a
portion of such an apparatus, wherein the Z-bar 15 extends
along a can forming and welding machine 16, and generally
terminates adjacent a laser welder 17. As shown in Figure
S, the upper portions of the central guide member and the
upper guide bar of the Z-bar have cantilevered nose portions
18 which extend outwardly beyond the discharge end of the Z-
lo bar and beyond the welding point W. A conical opening 19 is provided through the nose portions 18. The opening is
aligned with the welding head WHY to permit an energy beam B
to be focused on the edges of the sheet material passing
there below. The nose portions 18 provide a vertical barrier
which will further restrain the edges of the sheet material
from relative vertical displacement, as discussed more fully
hereinafter.
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The material used to make cans with the a~Faratus
of Figure 5 ordinarily has a thickness within the range of
0.005 inch ( 0.127 mm) to 0.02 inch mm), and,
preferably, may be a 75 lb. tin plate which has a thickness
of aFFroximately 0.008 inch (0.203 mm), for example. The
sheets of material used to make the can bodies are sheared
by a conventional slitter arrangement and, therefore, are
formed with burrs extending outwardly along their edges in
the direction of shearing, as shown in Figures 1 and 3. The
sheared material is Fussed through a roll former to the feed
bar of the can forming machine and is urged into a
cylindrical configuration by a plurality of spaced rollers,
some of which are shown at 20 in Figure S, PA and PA.
Guides 44 are also employed in combination with the rollers
as shown therein. Inhere may be several sets of such rollers
and guides disposed along the length of the machine, which
cause a substantially flat sheet of material to be formed
into a generally cylindrical configuration with the side
edges being slide ably received within the grooves of the
feed bar of the forming machine.
in addition to the means for forming the sheet
material, there is also some means provided for advancing
the sheet material along the grooves of the forming machine,
the Z-bar and through the welding station. In this regard,
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conventional chain-type conveyors, drive rollers,
reciprocating pistons or push rods, or the like, Jay be
used. However, for high speed welding, the apparatus
disclosed in U.S. Patent 4,497,995 issued on February Thea,
1985 and having as inventor Carl J. Nielsen is preferred.
The Z-bar guide apparatus of Figure 5 is operated
according to the prior art method to advance and form the
individual sheets of material 21 into a generally
cylindrical configuration as shown in Figure PA, with the
edges to be welded being in contact across the entire
thickness of the material as shown in Figure 6B, as
previously discussed with reference to Figures 1 and 2. In
order to perform the method of the invention, the apparatus
of Figure 5 is modified by lowering the support rollers 20
of the apparatus slightly and moving the upper support
rollers and guides inwardly slightly, so that the
configuration of the tubular workups 22 is somewhat pear-
shaped, as illustrated in Figure PA. As a result of this,
the edges to be welded are canted slightly with respect to
one another, as shown in Figures 3 and 7B, so that the butt
joint formed by the edges is open toward the outer side of
the tubular workups with the edges contacting one another
toward the inner side thereof.
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The method of the invention also preferably
includes the additional stew of providing a laser beam dump
on the inside of the tubular workups to absorb the laser
beam energy passing through the butt joint during welding.
This Prevents the inner side of the tubular workups from
being damaged by laser energy during welding as well as
collecting any debris expelled from the weld keyhole.
Operator safety is also enhanced by using the beam dump.
As shown in Figures 8 and 9, a mandrel 23 includes a laser
beam dump 24 positioned adjacent the welding area for
absorbing light from the laser beam B Produced by the laser
welder 17. The mandrel 23 is supported from the Z-bar lo by
means of connecting bolts 25, US illustrated in Figure 8.
The trailing portion of the mandrel extends beyond the end
of the Z-bar guide in cantilever fashion. In this Position,
the mandrel 23 extends internally and in the direction of
movement of the work pieces as they are advanced through the
Z-bar guide and Fast the laser welder.
The laser beam dump 24 and mandrel 23 are
Positioned immediately below the laser welder 17 for
absorbing light from a laser beam B Produced by the laser
welder, a 2 OW C02 gas laser, for expel. The laser beam
dump 24 includes a receptacle 26 in the form of a cup for
receiving the light. The cut is provided with an opening
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through which the light can enter. The inside of the cup is
colored a dark color, preferably black, for absorbing the
light. isle most of the laser energy is absorbed by the, Jo
beam dump, the beam dump is not Luke efficient in
absorption. According to a preferred form of the invention,
the cup is furrowed of an aluminum alloy with the inside of
the cup being anodized black. The cut could also be formed
of other materials such as copper, for example.
the receptacle is cylindrical in shape and is
removably positioned by means of a slide fit within a
central opening in a cooling jacket 27 in the form of a
spool positioned within the mandrel. The receptacle is
sorted within the spool on a snap ring 28, which is
received within a groove in the wall of the cylindrical
central opening of the spool The spool closely surrounds
; the receptacle for good heat conductivity. Preferably, a
I' thermal grease is provided between the receptacle and the
cooling jacket to increase the efficiency of the heat
transfer. the 6~001 is preferably formed of copper for good
heat conductivity and corrosion resistance, and is
cylindrical in shave for positioning within a cylindrical
hole formed in the mandrel. An annular coolant Passage 29
is formed around the outer circumference of the stool. A
coolant such as water is continuously supplied to the
Passage by means of inlet and outlet passages 30 extending
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through the mandrel to the passage, as illustrated in
Figures 8 and 9. O-ring sealing members 31 on opposite
sides of the passage effectively seal the spool in the
cylindrical hole to contain the coolant. According to
another form of the invention, the cooling jacket can be
brazed in the hole. Further details of the laser beam dump
and mandrel are set forth in U.S. Patent 4,436,979 issued on
March 13, 1984 and having as inventor Carl J. Nielsen.
Alternatively, according to another embodiment of
the invention, the method includes the additional step of
providing a means to reflect the laser beam which has
penetrated the joint back toward the joint to perform pro-
and post heating thereby slowing the cooling rate thereof. A
reflecting means 32 for this purpose is schematically
illustrated beneath the joint in Figure 11. A highly
reflective surface formed on a water-cooled copper member
could be used as the reflecting means, for example. Figure
11 also further illustrates a variation of the method of the
invention wherein the respective edges 33 and 34 of the
members 35 and 36 are positioned in abutting contact by
clamping the members in a welding jig 37 with clamping means
38-41. Relative movement is then effected between the laser
beam and the work pieces in the welding jig for
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Progressively welding the edges along the longitudinal
extent of the butt joint. Tangential forces indicated by
arrows E and F are applied to the members during welding to
urge the edges of the two members in the direction of the
butt joint in the manner described above. Clamping forces
applied by the clamping means 38-41 are shown by arrows G,
- I, I and J.
the forces applied to the generally cylindrical
tubular workups 22 being welded according to the method of
the invention with the apparatus of Figures 5, PA and 7B
are schematically illustrated in Figure 10. The supporting
rollers I urging the workups 22 into the generally
cylindrical, albeit slightly peâr-shaped, configuration are
each biased by means of compression springs 42 in the
direction of the workups, so that the forces Fly F2, F6,
En and F8 are directed radially inwardly upon the tubular
workFiece. The guides 44 also interact with the workhouse
with forces F9 and F10. The stationary nose portions 18
extending from the Z-bar on both sides of the weld area are
in continuous contact with the upper surface of the ends of
the members before and after welding to provide a vertical
barrier restraining the edges of the sheet material from
relative vertical displacement. The radially directed force
F3 schematically shown in Figure 10 depicts the function of
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the nose portions in this regard. Absent the nose Portions
; 18 and guides 44, the free ends of the members to be welded
would tend to rise upwardly because of the resilient nature
of the workhouse material. the radial forces upon the
tubular workFiece induce tangential forces F4 and F5 urging
the edges of the two members in the direction of the butt
joint 43. Thus, when killing of the laser beam through
the joint takes Flare with the melting and displacement of
the lower contacting Portions of the edges, the offside
molten edges are moved closer to one another and actually
mashed together in response to the forces F4 and F5. Gore
Particularly, the molten edges are mashed together behind
the keyhole as the laser beam is moved along the butt joint
to Progressively weld the tubular body.
In an actual application of the method of the
invention, generally cylindrical can bodies were laser butt
welded using the apparatus of Figures 5, PA and foe. A steel
- sheet material having a thickness of 0.008 inch was used to
form the can bodies. The sheared edges of the opposite
sides of a tubular-shaFed workhouse were Positioned in
I; abutting contact using the Z-bar guide aFFaratus 15. The
two ends of the workFiece were canted slightly with respect
to one another at an angle of 17 so that the butt joint
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lZ3519Z
formed by the sheared edges was oxen towered the outer side
of the tubular workhouse a distance d=0.002 inch with the ,
edges contacting one another toward the inner side of the
tubular workFiece. A laser beam, from a 2 I C02 was laser,
I I.
having an energy density of at least love wits and a
beau width of 0.003-0.004 inch at the workFiece was directed
at the butt joint to accomplish Frogressive,,keyhole welding
along the length of the joint as the can body was moved at a
steed of 30 m/min. beneath the laser welder 17. The
resulting weld was well formed throughout the length of the
weld joint and, in addition, had a relatively uniform
cross-sectional configuration on top and bottom,
notwithstanding the presence of burrs on the sheared edges.
A metallurgical cross-sectional view of the weld 44 is shown
in Figure 12. As will be readily affront to the skilled
artisan, other thicknesses of material and other shaves of
workhouses could be butt welded with the method of the
invention. The angle at which the offside edges are
canted could be varied, and Preferably is no more than would
allow the maximum team diameter to Fuss through the oxen
joint regardless of the thickness of the material being
welted. l-his fulls any burrs from. the centerline of the
joint and allows sufficient laser energy to enter the oxen
joint and i~,F,nge directly on the offside edges.
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1~3519Z
Thus, the method of the invention is particularly
advantageous in avoiding the aforementioned problems which
occur as a result of the presence of burrs on the edges of
sheared workFieces, and, in addition, offers the additional
advantage of enhanced efficiency of welding because the weld
plasma is not solely formed on the to of the work pieces
being welded during the initial impingement of the laser
beam, but rather can form toward the opposing side of the
members as well to attain a more efficient, uniform heat
lo distribution. This results in a reduction in heat input
related metallurgical problems such as stubbing and damage
to the base material in the heat affected zones adjacent the
weld material. Ike method is also advantageous in that it
aids the killing of the laser beam through the weld joint
and results in welds having more uniform characteristics or
shape. Strongly reflecting surfaces of the material also
need not be removed or masked for laser welding, since
reflected laser energy will tend to be trapped within the
open joint. The method of the invention is therefore an aid
to high steed laser butt welding, wherein the abutting edges
may be welded at speeds of 15 to 75 meters per minute, for
example .
Chile I have shown and described only two
embodiments in accordance with the present invention, it is
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lZ3S192
understood that the same it not limited thereto, but is
susceptible to numerous changes and modifications as known
to those skilled in the art. For example, it is envisioned
that the method of the invention is applicable to other
high energy density welding processes wherein a beam of
energy is employed to effect fusion of the work pieces.
Thus, the method of the invention would have utility with an
electron beam as the high energy density welding beam, for
example. the material welded in the disclosed example is a
thin sheet Natalie, but the method of the invention is also
a~Flicable to welding thicker material and also non-metallic
materials, such as plastic members, for example. Several
laser beams could also be employed from the same or opposite
sides of the weld joint for welding the members. Therefore,
I do not wish to be limited to the details shown and
described herein, but intend to cover all such changes and
modifications as are encompassed by the scope of the
aEEended claims.
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