Note: Descriptions are shown in the official language in which they were submitted.
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MULTIPLE BEAM LASER WELDING APPARATUS
SCOPE OF THE INVENTION
The present invention relates to a method and an
apparatus for laser welding together two or more sheet
blanks along a seamline, and more particularly, to an
apparatus which adjusts the focal intensity of the laser
beam energy on the seamline and/or weld time to compensate
for variations in the spacing between the edges of the
blanks to be joined.
BACKGROUND OF THE INVENTION
Present day manufacturing requirements often
necessitate the formation of various workpiece components
by welding together two or more sheet metal blanks. More
frequently, lasers have been used to weld abutting edge
portions of the sheet blanks along seamlines in the
formation of workpiece components.
Conventional laser welding apparatus have
suffered the disadvantage in that heretofore, the use of
lasers to weld the blanks together has necessitated that
the edges of the sheet blanks be pre-f finished and have a
mirror-smooth ffinish, The requirements of blank edge
preparations have to a large extent been responsible for
the reluctance by industries to adapt the use of laser
welding apparatus in continuous seam welding processes used
to form sheet blanks.
Conventional laser apparatus have suffered the
further disadvantage in that to ensure the formation of a
complete weld and prevent butt-weld seams having concavity,
it is necessary to ensure precise abutting contact between
the proximal edges of the sheet metal blanks along the
entire- length of the weld seam. The necessity of
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maintaining the sheet blanks in precise contact during
welding disadvantageously results in an increase in
workpiece production time as a result of the necessity of
ensuring the blanks are in an exact abutting position prior
to welding.
SUMMARY OF THE INVENTION
The inventor has appreciated an improved
apparatus for butt welding together sheet metal blanks
which incorporates a yttrium aluminum garnet (YAG) laser,
and has disclosed the operation of such an apparatus in
pending Canadian patent application serial No. 2,167,111,
which was filed 15 January 1996. The use of a YAG laser to
butt weld together sheet blanks advantageously has been
found to produce weld seams without a concave weld profile,
where gaps of up to 0.1 mm exist between the sheet blanks.
The applicant has, however, appreciated that
providing an apparatus which may effectively butt weld
sheet blanks which are separated by larger gaps, would
facilitate workpiece production by requiring less stringent
positioning and edge finishing of the sheet blanks prior to
welding. This, in turn, would increase production time and
reduce sheet blank manufacturing cost.
To at least partially overcome the disadvantages
of the prior art, the present invention provides a welding
apparatus for use in industrial processing, which is
operable to emit an energy beam or ion beam (hereinafter
collectively referred to as an energy beam), to weld blanks
and the like together along a seamline. The energy beam
used to weld the blanks preferably consists of a multiple
beam of two or more coherent light sources. The apparatus
includes a mechanism to selectively reposition the
orientation of the multiple beam relative to the seamline.
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Another object of the invention is to provide an
apparatus for butt welding together proximal edge portions
of two or more sheet blanks which are separated by a gap of
up to 0.25 mm or more.
Another object of the invention is to provide an
apparatus for laser welding together two or more sheet
blanks, without requiring the edge portions of the blanks
to be pre-finished.
A further object of the invention is to provide
an apparatus for joining together workpiece blanks to form
a composite workpiece, and which does not require precise
alignment and positioning of the blanks prior to joining.
Another abject of the invention is to provide an
apparatus for welding together proximal edge portions of
sheet blanks having different relative thicknesses.
A further object of the invention is to provide
an apparatus for laser butt welding together two or more
sheet blanks along a seamline, and which automatically
senses the spacing between proximal edge portions of the
sheet blanks and compensates either the speed and/or
positioning and/or power of the laser energy to ensure the
formation of an effective weld seam across the proximal
portions.
Another object of the invention is to provide a
laser welding apparatus adapted to weld proximal edge
portions of sheet metal blanks along either straight, non-
linear or curved weld seams.
To achieve at least some of the foregoing
objects, the present invention includes a welding apparatus
for welding together proximal edge portions of two or more
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sheet blanks. The welding apparatus is configured to emit
a multiple or composite energy beam which consists of two,
three or more energy beams. Preferably, the energy beams
are laser beams or coherent light sources used to weld the
sheet blanks together along a seamline, however, the use of _.
the invention with other energy beams such as ion or
electron beams and the like is also possible and will
operate in a like manner.
The coherent light sources or laser beams which
make up the composite beam are focused towards a portion of
the blanks to be welded together at respective focal area
or focal spot. The focal areas of each of the laser beams
have an optic centre, wherein the optic centres of at least
two of the laser beams (i.e. a first laser beam and a
second laser beam) which make up the composite beam are
spaced or offset from each other.
The spaced optic centres of the first and second
laser beams provide the composite beam with a beam energy
or intensity profile which is elongated in the orientation
of the optic centres. The optic centres of the laser beam
may thus be said to each define one end of a focal line of
elongation of the composite beam.
The composite beam of laser energy is emitted
from a laser head which is movable over the workpiece
blanks. The apparatus further includes mechanisms to vary
the intensity per unit area of the composite beam. For
example, the laser head is preferably rotatably mounted to
move the focal line of the composite beam relative to the
proximal edge portions of the blanks to be welded. The
beam may be moved between a position wherein the focal line
is positioned substantially normal to the proximal edge
portions of the blanks and a position wherein the focal
line is oriented in a position substantially aligned with
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the proximal edge portions of the workpieces which are to
be welded.
Other suitable mechanisms to alter the beam
intensity per unit area also would include a drive _.
mechanism used to vary the speed at which the laser head
moves over the seamline, or a power regulator used to vary
the output power of the laser beams.
The coherent light sources making up the
composite beam may, for example, comprise almost any type
of laser beam, including COz lasers. More preferably,
however, high energy lasers, such as yttrium aluminum
garnet (YAG) lasers are used to weld the blanks.
The laser head is preferably movably provided in
the apparatus to move the composite beam relative to the
sheet blanks along a predetermined or sensed linear and/or
curved path. The laser may thus be activated and the laser
head moved along its sensed/predetermined path to weld
proximal edges of the sheet blanks together along a
seamline.
More preferably, the apparatus includes a sensing
mechanism for sensing the spacing between abutting edge
portions of the blanks to be welded. A microprocessor
control is provided to rotate the laser head or fiber optic
connectors relative to the seamline in response to the
sensed spacing. In this manner, the composite beam may be
selectively rotated to move the focal line. The focal line
may be rotated to a preset orientation relative to the
portion of the seamline which is to be formed, as for
example, in an orientation at or between a position normal
to the abutting edge portions of the blanks and a position
substantially aligned thereover.
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Where a gap exists between the abutting edge
portions of the blanks which are to be joined, the
composite beam is positioned so that the optic centres of
the first and second laser beams are each located on a
respective edge portion of each blank, with the focal line _.
of the composite beam straddling the gap. This position
provides a maximum spread of laser energy across the gap
producing the maximum infill of molten metal into the gap
from the edge portions of the blanks.
Where no gap exists between the abutting edge
portions of the blanks, the laser head may be rotated so
that the composite beam is positioned with its focal line
moved towards or into alignment with the seamline. In this
position, the laser energy is focused along the seamline
which is to be formed. This advantageously concentrates
the intensity of the laser energy along the seamline and
decreases the time required to form a complete weld seam,
enabling a finished blank to be produced with higher weld
speeds.
More preferably, the speed of movement of the
laser head above the blank is controlled having regard to
the degree of spacing between the proximate portions of the
blanks and/or the orientation of the focal line of the
composite beam relative to the seamline which is to be
formed. As indicated, if desired, the power output of the
energy beam could also be varied with any sensed spacing
between the abutting edge portions of the blanks. In this
manner, higher energy outputs may be provided when the
focal line of the beam energy straddles any gap and lower
beam energy used when the focal line is aligned with the
weld seam.
Accordingly, in one aspect, the present invention
resides in an apparatus for joining together proximal edge
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portions of two workpiece blanks along a seamline
comprising,
' laser means for emitting a composite beam to weld
said blanks together along said seamline,
said composite beam including a first laser beam
and a second laser beam, each of said first and second
laser beams being focused towards a portion of said blanks
to be welded at respective focal areas having an optic
centre, wherein the optic centres of said first and second
laser beams are offset from each other and each define one
end of a focal line of said composite beam,
rotation means for selectively rotating said
laser means to move said focal line relative to said
portion of said blanks between a position wherein said
focal line is oriented substantially normal to said portion
of said seamline, and a position wherein said focal line is
oriented substantially aligned with said portion of said
seamline.
In another aspect, the present invention resides
in a laser apparatus for welding together abutting edge
portions of two sheet blanks along a seamline, the
apparatus comprising:
a laser head operable to emit laser energy to
weld said blanks together along the seamline,
rotation means for rotating the laser head and
change the orientation of said laser energy relative said
seamline,
wherein said laser energy comprises a multiple
beam of at least two offset laser beams.
In a further aspect, the present invention
resides in a method as claimed in claim 15, wherein said
apparatus further includes sensing means for sensing
spacing between the abutting portions of the blanks, and
wherein said method includes the further step of
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sensing the spacing between the adjacent portions of the
blanks at said portion of said blanks to be welded prior to
moving said focal line therealong, and
wherein said preset position of said focal line
is determined by the sensed spacing between the adjacent _.
portions of the blanks.
In another aspect, the present invention resides
in an apparatus for joining together proximal edge portions
of two workpiece blanks along a seamline comprising,
means for emitting a composite energy beam to
weld said blanks together along said seamline,
said composite energy beam including a first
energy beam and a second energy beam, each of said first
and second energy beams being focused towards a portion of
said blanks to be welded at respective focal areas having
a centre, wherein the centres of said first and second
laser beams are offset from each other and each define one
end of a focal line of said composite energy beam,
sensor means for sensing any spacing between the
proximal edge portions of the blanks, and means for
changing the beam intensity per unit area selected from the
group consisting of,
rotation means for selectively rotating said
means for emitting said composite energy beam to move said
focal line relative to said portion of said blanks between
a position wherein said focal line is oriented
substantially normal to said portion of said seamline, and
a position wherein said focal line is oriented
substantially aligned with said portion of said seamline,
drive means for moving said means for
emitting said composite energy beam along said seamline,
said drive means activatable to vary the speed of movement
of said laser beam depending on the sensed spacing between
the proximal edge portions of the blanks, and
power regulating means to vary the composite
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energy beam energy output depending on the sensed spacing
between the proximal edge portions of the blanks.
BRIEF DESCRIPTION OF THE DRAWINGS
Further objects and advantages of the invention
will appear from the following description, taken together
with the accompanying drawings in which:
Figure 1 shows a schematic top view of a
production assembly line for forming composite workpieces
in accordance with the present invention;
Figure 2 shows a schematic side view of a laser
welding head used in the production assembly line of Figure
1;
Figure 3 shows the laser welding apparatus shown
in the production assembly line of Figure-1, taken along
lines 3-3' showing the use of a laser to weld sheet blanks;
Figure 4 shows graphically an intensity profile
of a composite laser beam in accordance with a first
embodiment of the invention;
Figure 5 shows schematically a plan view of the
laser beam focal areas of the composite laser beam profile
shown in Figure 4;
Figure 6 shows a plan view of the laser beam
focal areas of the composite laser beam shown in Figure 4,
wherein the composite beam is oriented with its focal line
positioned normal to the abutting portions of the blanks to
be welded;
Figure 7 shows a plan view of the laser beam
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focal areas of the composite laser beam shown in Figure 4,
wherein the composite beam is oriented with its focal line
positioned in alignment with the abutting portions of the
blanks to be welded; and
Figures 8 and 9 show schematically the laser beam
focal areas of a coherent light source bundle for use with
the laser of Figure 1, in accordance with a further
embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION
Reference is made to Figure 1 which shows a
production assembly line l0 used in the simultaneous
manufacture of two composite workpieces 12a,12b. With the
assembly line 10 shown, robot vacuum lifts 18a,18b are used
to move pairs of sheet metal blanks 14a,16a, 14b,16b from
respective supply stacks. Each robot 18a,18b is adapted to
move the paired blanks 14a,16a, 14b,16b, respectively onto
a conveyor array 20 used to convey the blanks 14a,16a,
14b,16b and finished workpieces 12a,12b along the assembly
line 10. The conveyor array 20 consists of three sets of
elongated magnet stepping conveyors 22,24,26 which are
operable to move the pairs of blanks 14a,16a and 14b,16b
and workpieces 12a,12b in the longitudinal direction of
arrow 28. The magnetic stepping conveyors which comprise
each conveyor set 22,24,26 are shown in Figure 1 arranged
in a parallel orientation to both each other and the
conveyors in the remaining sets. It is to be appreciated
that other conveyor configurations are also possible.
As will be described hereafter, the first set of
conveyors 22 are used in the initial positioning of the
blanks 14a,16a and 14b,16b in the production line 10, and
the conveyance of the positioned blanks 14a,16a and 14b,16b
on to the second set of conveyors 24.
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The conveyors 24 are provided as part of a laser
welding station 32 in which the proximal edge portions of
the blanks 14a,16a and 14b,16b are welded together along a
seamline by a yttrium aluminum garnet (YAG) laser 36. The
conveyors 24 thus are used to move the unwelded blanks ..
14a,16a and 14b,16b to a welding position, and then convey
the completed workpiece 12a,12b onto the third set of
conveyors 26.
The third set of conveyors 26 are used to convey
the completed composite workpieces 12a,12b to robotic
vacuum lifts 38a,38b which lift the workpieces 12a,12b
therefrom and onto output stacks.
The production line 10 shown in Figure 1 is
configured for the concurrent manufacture of two completed
workpieces 12a,12b by a single laser 36. As shown best in
Figures 1 to 3, the YAG laser 36 includes a coherent light
source generator 40 used to generate two-coherent light
sources or laser beams, a movable laser head assembly 42
(Figure 2) and a fibre optic coupling 44 (Figures 1 and 3)
optically connecting the generator 40 and laser head
assembly 42. The fibre optic coupling 44 consists of a
bundle of two fibre optic cables (not shown). The energy
of the two coherent light sources generated in the
generator 40 thus travels via a respective fibre optic
cable to the laser head assembly.
Figure 2 shows best the laser head assembly 42
includes a light emitting laser head 46 from which laser
energy is emitted. As disclosed, the laser energy
comprises the composite beam which consists of the two
coherent light sources. The assembly 42 further includes
a support 48 which rotatably mounts the laser head 46, and
a drive motor 52 used to rotate the laser head 46 on the
support 48. The laser head assembly 42 may be
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preprogrammed in movement, but is preferably provided with
a microprocessor controlled seam-tracking sensor 49 (Figure
2). The sensor 49 senses the spacing between the proximal
edge portions of each pair of sheet blanks 14a,16a, 14b,16b
to be joined. The sensor 49 may, for example, include a _.
separate coherent light source which directs a beam of
coherent light downwardly onto the proximal portions of the
sheet blanks and a vision or optic sensor for sensing light
reflected therefrom. By the absence of reflected light,
the vision or optic sensor 49 may thus be used to provide
data indicative of the spacing between the abutting edge
portions of the sheet blanks. More preferably, the sensor
49 is used to track the seamline 34 and provides control
signals to the drive motors 52 and 64 and the gantry robot
54 to automatically position the laser head 42 so that the
composite beam 30 is directed at the weld seam.
Figure 1 shows best the laser 36 as being
entirely housed within an enclosure 50. The enclosure 50
is provided with mailbox type entry and exit doors 51,53.
The entry and exit doors 51,53 are opened to permit
movement of the blanks 14a,16a, 14b,16b and workpieces
12a, 12b into and out of the enclosure 50. The entry and
exit doors 51,53 are closed during welding operations to
optically isolate the laser 36 and contain any potentially
eye damaging YAG laser energy.
Clamping units 60 are provided within the
enclosure 50 for maintaining the sheet blanks 14a,16a and
14b,16b in fixed abutting position during welding
operations. While numerous types of clamping arrangements
are possible, the clamping units 60 preferably each consist
of a magnetic clamping unit of the type disclosed in the
applicant's Canadian patent application serial No.
2,167,111, laid open 12 July 1997.
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The entire laser head assembly 42 is configured
for two axis movement horizontally. The assembly 42 is
movable in a first horizontal direction over the conveyors
24 and blanks 14a,16a, 14,16b via a gantry robot 54, along
a paired overhead support and slave support 56a,56b. The _.
laser head assembly 42 moves in the first direction via the
gantry robot 54, along a track 58 (Figure 3 ) provided on
the overhead support 56a. Each of the pairs of supports
56a,56b are further slidable in a second horizontal
direction which is perpendicular to the first on parallel
spaced end supports 62a,62b.
Each of the end supports 62a,62b in turn movably
support the ends of the parallel supports 56a,56b. A servo
drive motor 64 (Figure 1) is provided at the end of support
56a and engages a track 66 which extends along one end of
support 62a. The movement of the laser head assembly 42
along the supports 56a,56b, and the movement of the
supports 56a,56b on the end supports 62a,62b permits the
laser head 46 to move over the blanks 14a,16a, 14b,16b in
any horizontal direction. In addition, it is preferable
that the laser head 42 be vertically movable, as for
example, by a rack and pinion lift drive mechanism or
pneumatic slide 68 (Figure 2), thereby permitting movement
of the laser head 42 along a11 three axis to provide
increased adaptability to the assembly line 10. It is to
be appreciated that with this construction, the laser 36
may be used to not only join together workpieces 14a,16a,
14b,16b along preprogrammed linear weld seams, but also
along curved weld seams for a variety of different
workpieces, without extensive pre-setup and pre-positioning
of the sheet blanks.
During welding operations, two coherent light
sources are produced in the coherent light source generator
40. The coherent light sources travel via a respective
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fibre optic cable in the coupling 44 to the laser head 42
and are emitted therefrom towards the portion of the
seamline 34 to be laser welded. Two laser beams are thus
emitted from the laser head 42 to weld proximal edges of
the blanks 14a, 16a and 14b, 16b as a composite laser beam __
30.
Figure 4 shows graphically the energy profile of
the composite beam 30 made up of the two substantially non-
overlapping laser beams B~,BZ. Figure 5 shows best the
divergence or focal area FAQ , FA2 of the two laser beams B~ , Bz
at the surface of the workpieces 14,16 to be joined. Each
of the laser beams has an optic centre Cj and CZ,
respectively, and a divergence radius at the workpieces
selected at between about 0.2 mm and 1 mm, and more
preferably, about 0.6 mm. The optic centres C~,C2 are
offset from each other by a distance D~ (Figure 4) of
between about 0.1 mm to 3.0 mm, and more preferably about
1.2 mm. The optic centres C~,CZ each define one end of a
focal line L~ (Figure 5) of the composite laser beam 30
which extends in the direction along which the energy
spread of the laser beam 30 is elongated.
In operation of the assembly line 10, pairs of
component sheets 14a,16a and 14b,16b are moved sequentially
via the robotic vacuum lifts 18a, 18b from respective supply
stacks. The pairs of blanks 14a,16a and 14b,16b are
positioned on the parallel magnetic feed conveyors 22. The
robotic vacuum lifts 18a,18b are used to move each
component sheets 14a,16a, l4b,l6b, respectively, through an
initial qualifying procedure. The qualifying procedure
ensures correct positioning of the sheets on the feed
conveyors 22, and involves sliding the sheet blanks 14,16
against sets of retractable locating pins 72 (Figure 1) to
ensure the sheet blanks are in the desired initial
position.
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The vacuum lifts 18a,18b operate with suction
cups which have variable suction pressures. Initially, the
robotic lifts 18 are operated under a high vacuum pressure
to initially pick up the sheet blanks 14a,16a, 14b,16b so
as to fixably retain each sheet blank as it is raised from
its supply stack. As the sheet is moved in the qualifying
procedure, the suction pressure is reduced. The reduced
suction pressure is chosen so that the sheet blanks 14a,16a
and 14b,16b continue to be retained by the vacuum force of
the respective lift l8a,l8b, while permitting the blanks to
slide laterally relative to the suction cups. The edges of
the sheet blanks 14a,16a, 14b,16b are moved against the
locating pins 72 to position the sheets 14,16 on the
conveyors 22 in a desired initial position. Following the
initial qualifying positioning of the sheets 14a,16a,
14b,16b, the vacuum lifts 18a,18b are deactivated to fully
release the sheets, and the locating pins 72 are retracted
beneath the surface of the conveyors 22 permitting the
sheets 22 to be conveyed into the enclosure-50 unhindered.
Following the initial qualifying, the pairs of
sheet blanks 14a,16a, 14b,16b are moved into the enclosure
50 for laser welding. The blanks 14a,16a and 14b,16b move
from conveyors 22 onto conveyors 24 via the enclosure mail
box or sliding door 51. The enclosure 50 functions as a
laser operations room and provides an added safety feature,
whereby workers are shielded by the room from laser energy
which is emitted during laser welding of the blanks.
The conveyors 24 in turn move the blanks 14a,16a,
14b,16b into the magnetic clamping assemblies 60 which are
activated magnetically to clamp the pairs of sheet blanks
14a,16a and 14b,16b. The pairs of blanks 14a,16a and
14b,16b are positioned in respective clamping units 60 so
that their proximal edge portions which are to be welded
together are in a substantially abutting relationship.
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While it is preferred that the workpiece blanks 14a,16a,
14b,16b be positioned so that their proximal edge portions
to be joined precisely abut along the entire length of the
seamline 34, the laser 36 advantageously may be used to
perform welding operations where gaps of up to 0.3 mm exist
between the proximal edge portions, without producing a
finished weld seam which has a concave profile.
Following clamping, the laser 36 is activated to
emit the composite laser beam 30 from the laser head 42.
The laser head 42 is positioned so that each of the laser
beams Bi,B2 or contiguous light sources are focused at a
respective focal spot or focal area FAi,FA2 on the surfaces
of one of the pairs of blanks 14a,16a, 14b,16b. The focus
of the contiguous light sources is such that the divergence
or focal area FAQ , FA2 of the beam B~ , BZ will have an
approximate average diameter of 1.2 mm. The laser beams
Bi, B2 are further oriented so that the optic centre C~, CZ of
each beam B~ , BZ is spaced from the other by a distance of
1.2 mm.
To weld the blanks, the coherent light source
generator 40 is activated to emit the composite beam 30
from the laser head 46 while it is moved first along the
seamline 34 of the blanks 14a,16b and then along the
seamline 34 of blanks 14b,16b. The laser head 46 is moved
by the movement of the laser head assembly 42 on the
supports 56a,56b and 62a,62b by the gantry robot 54 and
servo drive motor 64; as well as through its rotation on
the support 48 by drive motor 52.
The operation of the laser 36 to weld the
individual pairs of blanks 14,16 along the seamline 34 is
shown best with reference to Figures 6 and 7 which
illustrate an enlarged view of the proximal edge portion of
the blanks 14,16 which is to be welded. As the laser head
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46 moves along each seamline 34 in the direction of arrow
79, the sensor 49 continuously senses the spacing between
the abutting edge portions of the sheet blanks 14a,16a,
14b,16b and provides signals to the microprocessor control.
Where larger gaps between the proximal edges of the
workpiece blanks 14,16 are sensed, as for example is shown
in Figure 6, the microprocessor control activates the motor
52 to rotate the laser head 46 so that the focal line L~ of
the composite beam 30 extends generally transverse to the
direction of the seamline 34 and head movement, and normal
to the portion of the proximal edge portions of the sheet
blanks 14,16 which are being welded. Simultaneously, the
microprocessor control signals the gantry robot 54 and
servo drive motor 64 to slow the horizontal movement of the
laser head 46 over the portion of the seamline 34. The
slower movement of the laser head 46 thereby increasing the
residence time of the laser energy on the corresponding
portions of the sheet blanks 14,16 to ensure a complete
weld seam is formed.
If desired, simultaneously with the movement of
the laser head 46, the power output from the generator 40
may be varied to increase the composite beam 30 output
power when the focal line L~ is positioned transverse to the
seamline 34. The increased power of the beam 30 would thus
compensate for the fact that the focal area of only one
laser beam B~,Bz impinged upon each workpiece 16,14,
respectively.
The energy of each laser beam B~,B2 on each sheet
metal blanks 16,l4, respectively, penetrates the edge
portions of the sheet metal blanks 16,14. The vapour
pressure created by vaporized metal from the blanks 14,16
holds the liquid metal in suspension at the edges of the
beam until the laser head 46 moves along the joint. The
liquified metal from the edge portions of each blank flows
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into the gap separating the blanks 14,16 and solidifies to
form an autogenous, full penetration butt weld.
As the laser head 46 moves along the seamline 34,
and the sensor 49 senses that a smaller or no gaps exist __
between the abutting edge portions of the blanks 14,l6, as
shown in Figure 7, the microprocessor control activates the
motor 52 to rotate the laser head 46, so that the focal
line L~ of the composite beam 3o is aligned over and in the
direction of the seamline 34, in the position shown in
Figure 7. In this orientation, the energy of the two laser
beams B~,BZ is focused along the seamline 34. Less
residence time is needed to achieve the composite beam 30
vaporization of the metal. As such, the microprocessor
control preferably activates the gantry robot 54 and servo
drive motor 64 to increase the speed at which the laser
head 46 moves horizontally over the seamline 34, speeding
workpiece production, and/or decrease the power intensity
of the output composite beam 30.
It is to be appreciated that where gaps of a size
between the maximum tolerable gap and no gap exist, the
microprocessor control activates the motor (or another
actuator such as an air cylinder) 52 to rotate the laser
head 46 and move the focal line L~ of the composite beam 30
to a position extending obliquely relative to the proximal
edge portions of the blanks 14,16.
Following the welding of the pairs blanks 14a,16a
and 14b,16b to form the workpieces 12a,12b, the workpieces
are moved on conveyors 24, through the exit door 53 and
onto the conveyors 26. The conveyors 26 move the completed
workpieces 12a,12b to an offload station where the offload
robots 38a,38b place the workpieces 12a,12b in offload
containers 74a,74b (Figure 1).
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While the preferred embodiment of the invention
discloses the use of a rotating laser head 46 to reposition
the focal line L~of the composite beam 30, the invention is
not so limited. If desired, the laser head 46 could be
provided with 2 , 3 , 4 or more selectively activatable fibre __
optic cables in a bundle, each providing a contiguous
energy source. In this manner, by selectively emitting two
or more contiguous light sources from the fibre optic
bundle, the orientation of the focal line L~ of the
composite beam 30 could be varied almost instantaneously.
Similarly, although Figures 4 to 7 describe a
composite laser beam 30 consisting of two non-overlapping
contiguous light sources, the invention is not so limited.
The composite beam could, for example, consist of two,
three or more laser beams provided having energy profiles
with an overlapping or non-overlapping configuration.
Figures 8 an 9 show a further embodiment wherein
like reference numerals are used to identify like
components. In the embodiment shown, up to seven
contiguous light sources B~ , B2, B3, B4, Bs , B6, B7 may be
selectively emitted from a fibre optic bundle of seven
fiber optic cables (not shown) to form the composite beam
30. Switching between the fibre optic cables in the bundle
may be performed, as for example, by the selective
activation and deactivation of independent laser energy
sources in the generator 40, or by the selective
positioning of lenses or other focusing apparatus.
In use, where larger gaps exist between proximal
edge portions of blanks 14,16, as shown in Figure 8, light
sources B~ , B3, B4, Bs and B~ are simultaneously activated. This
effectively provides a composite laser beam 30 which is
elongated in two directions along focal lines Li and L2. As
shown in Figure 8, the focal lines L~,LZ of the composite
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beam 30 thus extend obliquely to the direction of seamline
34 and the direction of the movement of laser head 42. The
transverse orientation of the beam energy thereby is
focused further onto the edge portions of the sheet blanks
14,16. Again, the microprocessor control may be used to
signal the gantry robot 54 and servo drive motor 64 to slaw
the movement of the laser head 46 over the seamline 34,
and/or increase the output power of the output laser beams.
Where the proximal edge portions of the blanks
14,16 are in close abutting contact as shown in Figure 9,
light sources BZ,B4,B6 are emitted as the composite beam 30.
The composite beam 30, shown in Figure 9, therefore has a
single focal line L~ which is aligned with the seamline 34.
As with the composite beam shown in Figure 7, the laser
energy is thereby focused along the seamline 34 and a
shorter residence time is required for the laser beam to
form the butt weld. The microprocessor control, therefore
may be used to increase the speed by which_the laser head
42 moves over the seamline 34 in the direction of arrow 79
in the manner previously described.
In addition, if desired, the fibre optics may be
selectively activated so that one or more of the laser
beams is provided either aligned with, or off centre from
the focal line L~ of the composite beam 30. In this regard,
the laser beam B2, shown in Figure 8, may be used to
partially pre-vaporize edge portions of spaced sheet blanks
14,16 to be welded.
The preferred embodiment of the invention
discloses the use of a YAG laser for use in butt welding
operations, the invention is not so limited. If desired,
other lasers may also be used, including C02 lasers. While
the present invention is suitable for use in butt welding
together sheet blanks, other welding applications are also
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possible and will now become apparent.
Figure 1 shows the simultaneous production of two
work pieces 12a,12b, each having a linear seamline 34. If
desired, however, the present invention may equally be used ..
to weld one, two or more workpieces along straight, curved
or angled seamlines.
Although Figures 1 to 3 show a production
assembly line 10 which incorporates a single laser 36 used
to weld pairs of blanks 14a,16a 14b,16b together, the
invention is not so limited. If desired, two or more
lasers could be used, each with its own movable laser head
for simultaneously welding a respective pair of blanks
14,16 along a seamline.
Although the preferred embodiment of the
invention discloses the apparatus as including a sensor 49
for continuously sensing the spacing between the sheet
blanks 14, the invention is not so limited. In a more cost
effective embodiment, the sensor 46 may be omitted. With
such a configuration, the positioning of the laser head 42
may be continuously manually adjusted by an operator
concurrently as welding operations are performed.
Alternately, the laser head 42 may be moved to a fixed
initial position which is maintained constant during
welding, as for example, when blanks 14 of different
thicknesses are to be joined.
While the preferred embodiment of the invention
discloses the coherent light source generator 40 as
generating separate laser beams, if desired, the energy
source could be used to generate a single coherent light
source which is separated into two or more laser beams in
or en route to the laser head 42.
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Although the detailed description describes and
illustrates preferred embodiments of the invention, the
invention is not so limited. Many modifications and
variations will now occur to persons skilled in the art.
For a definition of the invention reference may be had to-
the appended claims.
