Laser welding system

A laser welding system for welding sheets of material, such as automobile body parts, together includes a plurality of clamps. The system includes a fiber optic cable for each clamp having a first end coupled to a laser beam source and a second end coupled to the clamp for transmitting a laser beam from the laser beam source to the clamp. The system further includes a focusing head secured to each clamp and the second end of the cable for focusing the laser beam onto the material to be welded.

FIELD OF THE INVENTION 
This invention relates to laser welding systems for welding sheets of 
material together. 
BACKGROUND OF THE INVENTION 
Laser welding has many well known advantages over conventional resistance 
welding. For example, laser welding provides low distortion, small heat 
affected zones (HAZ), improved mechanical/structural performance, 
increased speed of processing, improved process 
controllability/consistency and single sided access. However, one great 
disadvantage of laser welding is the requirement of tight gaps between the 
parts to be welded which in turn requires precise positioning of the laser 
beam relative to the parts to be welded. 
Typically, laser welding systems utilize welding clamps which clamp and fix 
the parts to be welded together. Robots are used to perform the welding 
operation. A laser beam generator or source generates or produces a laser 
beam. The laser beam is transmitted to a focusing head via a fiber optic 
cable. The focusing head is installed or mounted on the end of the robot 
arm. The robot is then programmed to accurately position the focusing 
head, and thus the laser beam focal point, relative to the parts to be 
welded. The welding is done sequentially as the robot must move from weld 
joint to weld joint. With a robotic-based laser welding system, time is 
wasted during non-welding motion from joint to joint. Also, accuracy and 
repeatability of positioning the laser beam focal point relative to the 
surface of the parts to be welded is difficult to accomplish at high 
speeds with a robot. Part dimensional variations and motion trajectory 
errors lead to difficulties in obtaining consistent weld quality. 
U.S. Pat. No. 4,654,505 issued Mar. 31, 1987 to Sciaky et al. discloses a 
multi-point laser welding system for vehicle bodies and the like which 
includes apparatus for positioning the pieces to be welded, apparatus for 
gripping the pieces to be welded, and apparatus for welding the positioned 
and gripped pieces at specific points. The '505 patent employs a laser 
beam delivery system using multiple motor driven optical mirrors 
controlled by a computer program to focus a laser beam upon a single point 
on the parts to be welded. The '505 patent does not disclose moving the 
laser beam across the parts to be welded to provide a linear or curved 
stitch, as opposed to a single point spot weld. Additionally, the '505 
patent does not disclose the use of a fiber optic cable for transmitting a 
laser beam from a laser beam source to a focusing head secured to a 
clamping fixture. Instead, the laser welding system disclosed in the '505 
patent employs multiple mirrors to transmit a laser beam from a laser beam 
source to the pieces or parts to be welded. 
The laser welding system disclosed in the '505 patent also does not 
disclose confining the laser beam within a clamp fixture as the laser beam 
is used to perform the welding. Instead, the laser beam travels outside of 
or externally from the fixture used to clamp the pieces to be welded 
together. Confining the laser beam so that the laser beam is directly 
transferred from a focusing head to the parts to be welded is critical 
since exposed laser beams may create hazardous conditions for those 
workers near the laser welding system. 
SUMMARY OF THE INVENTION 
The present invention provides a laser welding system for welding sheets of 
a material together. 
The present invention also provides a computer-controlled laser welding 
system, including a central computerized time-share installation, which 
distributes a laser beam, sourced from a single laser generator in a 
pre-programmed sequence, to remote modular clamps by means of a plurality 
of fiber optic cables. 
The present invention further provides a plurality of modular clamps which 
cooperate to grip and position sheets of material wherein each clamping 
unit, upon receiving a distributed laser beam, is adapted to deliver the 
laser beam to a sheet of material achieving multi-point, linear, and/or 
two-dimensional weld patterns. 
It is another aspect of the present invention to provide plurality of 
modular clamps adapted for selective tailored mounting and positioning on 
a common work surface for laser welding sheets of material together. 
It is another aspect of the present invention to provide each clamp with a 
laser beam focusing head which is movable relative to the clamping unit to 
focus and move a laser beam under computer control over a designated 
portion of the sheets of material to execute a linear edge joint weld, a 
linear lap joint stitch, a two-dimensional lap weld, or the like. 
It is still another aspect of the present invention to provide each clamp 
with a slot into which a portion of the laser beam focusing head is placed 
so as to confine the laser beam for direct transmission to the sheets of 
material to be welded. 
It is still another aspect of the present invention to provide a laser 
welding system for automobile vehicle body parts and the like, including a 
computerized time-share system which sequentially switches the laser beam, 
in a pre-programmed manner, from clamp to clamp to complete the welding. 
It is another aspect of the present invention to provide a laser welding 
system wherein selected ones of the clamps are adapted for producing a 
linear stitch laser weld for an edge joint or the like while other clamps 
are adapted for producing a two-dimensional laser weld for a lap joint or 
the like. 
More specifically, the present invention provides a laser welding system 
for welding sheets of material together comprising at least one clamp 
having a lower plate and an upper plate movable relative to the lower 
plate for squeezing together associated sheets of material positioned 
therebetween and a fiber optic cable for each of the clamps. The fiber 
optic cable includes a first end coupled to a laser beam source and a 
second end coupled to the clamp for transmitting a laser beam from its 
source to the clamp. The laser welding system further includes a focusing 
head secured to the clamp for coupling the second end of the cable to the 
clamp and for focusing the laser beam onto the material to be welded. 
In one embodiment of the invention, the focusing head is fixedly mounted 
within a slot, positioned between the upper and lower plates, for single 
spot welding together the edges of the sheets of material. 
In another embodiment of the invention, the focusing head is movably 
secured within a slot, positioned between the upper and lower plates, for 
linear stitch welding together the edges of the sheets of material. 
in another embodiment of the invention, the focusing head is mounted in a 
slot in one of the upper or lower plates for welding together opposing 
surfaces of the sheets of material. 
In another embodiment of the invention, the focusing head is movably 
secured in a slot in one of the upper or lower plates of a clamp for 
providing a two-dimensional weld on the opposed surfaces of the sheets of 
material. 
These and other features and advantages of the invention will be more fully 
understood from the following detailed description of the invention taken 
together with the accompanying drawings.

DETAILED DESCRIPTION OF THE INVENTION 
Referring now to the drawings, and in particular to FIGS. 1-4, numeral 10 
generally indicates a laser welding system for edge welding together a 
pair of upper 11 and lower 11' sheets of a material, such as automobile 
sheet metal body portions, by means of a plurality of modular clamps 12. 
Each clamp 12 includes a lower plate 14 and an upper plate 16, movable 
relative to lower plate 14, for squeezing together sheets of material 11, 
11' positioned therebetween. Each clamp 12 is formed with a horizontally 
disposed slot 28 extending through clamp 12. At least one clamp power 
actuator arm 30 is provided for each clamp 12 for moving upper plate 16 
relative to lower plate 14 between a first closed position, as seen in 
FIG. 2, and second opened position, as seen in FIG. 3. Actuator arm 30 may 
be a conventional hydraulic operated cylinder, an air cylinder, a movable 
ballnut driven screw or the like. 
As seen in FIG. 1, welding system 10 further includes a fiber optic cable 
18 for each clamp 12. Fiber optic cable 18 includes a first end fitting 20 
adapted to be coupled to a laser beam source 22 and a second end 24 
coupled to clamp 12 for transmitting a laser beam from laser beam source 
22 to clamp 12 at a remote work station 25. 
Referring to FIG. 4, the welding operation is carried out by a focusing 
head 26 secured to clamp 12 for coupling second end 24 of fiber optic 
cable 18 to clamp 12 and for focusing the laser beam onto sheets 11, 11'. 
Focusing head 26 includes an outer body 40, a recollimating lens 42, a 
focusing lens 44 and a protective transparent glass cover 46. 
Recollimating lens 42, focusing lens 44 and glass cover 46 are positioned 
within outer body 40 in a spaced apart relation. Focusing lens 44 is 
moveable relative to outer body 40 to vary the distance between 
recollimating lens 42 and focusing lens 44, thereby varying the position 
of the laser beam focal point relative to glass cover 46 and the distance 
of focal point to the edge weld. A motor (not shown) may be provided to 
drive or move focus lens 44 relative to recollimating lens 42. 
FIG. 1 illustrates work station 25 including a clamp support member 32, 
extending downwardly from lower plate 14 of each clamp 12, for elevating 
each clamp 12 above a work surface 34. Clamp support member 32 is adapted 
to be removably secured to work surface 34 as seen in FIG. 1A. Clamp 
support member 32 may be constructed of a resilient material, such as a 
hard rubber, for flexible clamp adjustment. Referring to FIG. 1A, lower 
plate 14 includes an elongated axial bore 36 adapted to receive clamp 
support member 32 in a snug-fit manner. Work surface 34 includes a 
plurality of apertures 38 for engagement with clamp support member 32 to 
thereby removably secure clamp support member 32 to work surface 34. 
Additionally, clamp support member 32 is adapted for axial movement 
relative to work surface 34 so as to vary the vertical distance between 
each clamp 12 and work surface 34. Clamp support member 32 may be movable 
in a vertical direction to raise or lower clamp 12 relative to work 
surface 34. By virtue of flexible support member 32, clamp 12 is adapted 
for limited horizontal positioning relative to work surface 34. In this 
manner, clamp 12 is adapted to accommodate sheet material having minor 
shape and size tolerance variations. 
Still referring to FIGS. 1-4, clamp 12 is shown with slot 28 positioned 
between lower and upper plates 14, 16 to thereby allow the edges of sheets 
11, 11' to be laser welded together. A portion of focusing head 26, shown 
in FIG. 4 positioned within slot 28, is fixedly mounted to clamp 12. In 
this manner, the laser beam is adapted to be focused normal to the sheet 
edges creating a single spot weld edge joint between sheets 11, 11'. 
As seen in FIG. 4, lower and upper clamp plates 14, 16 define opposed 
contoured surfaces 48 adapted to squeeze sheets 11, 11' therebetween. 
Contoured surfaces 48 are formed with semi-spherical opposed cavities 50 
defining a gas chamber 51 linking slot 28 to contoured surfaces 48. The 
system 10 provides a first air passage 52, extending through support 
member 32 and lower plate 14, to establish fluid flow communication with 
gas chamber 51. A second cover-gas passage 54 extends through clamp 
support member 32 and lower plate 14 to establish fluid flow communication 
with gas chamber 51. Pressurized air injected into air passage 52, exits 
chamber 51 by means of upper plate air exhaust passage 56, establishing a 
sheet of air flow passing between focusing head 26 and the edges of sheets 
11, 11' to be welded. In this manner, splattered sheet weld material is 
unable to pass through the shielding air flow, thereby preventing the 
splattered material from accumulating on cover glass 46. Cover gas passage 
54 may be used to inject a cover or shielding gas, such as helium, into 
gas chamber 51 to assist the laser welding process, as is well known in 
the art. 
Again referring to FIG. 1, system 10 further includes a computer 70 for 
controlling actuators 30, focusing head 26 and clamp support 32 to thereby 
control the respective motions of each. For example, computer 70 may 
remotely operate power arm actuators 30 to thereby control movement of 
upper plate 16 between its opened and closed positions. Further, computer 
70 may control movement of lens 44 for remotely focusing the laser beam on 
the material 11, 11' to be welded. Also, computer 70 may control the axial 
motion of clamp support 32, in addition to switching and/or sharing the 
laser beam. 
According to the present invention, laser beam source 22 may comprises a 
time-share distributor 72 of a known design, as disclosed in the October, 
1989 issue of "Photonics Spectra" magazine in an article entitled 
"Designer's Handbook, The Modern Industrial YAG Laser." In FIG. 1 
distributor 72 is shown incorporating a multi-positional switch 74 adapted 
to route a laser beam, received from a single laser beam generator, to any 
one of fiber optic cables 18 in a sequential manner in response to an 
electrical signal input from computer 70. Distributor 72 may also be used 
to couple a laser beam generator to multiple clamps 12 in a simultaneous 
fashion, wherein two or more weld joints may be produced at the same time. 
The preferred laser beam source or generator is a Nd:YAG laser, although 
other comparable laser generators may be used. 
Referring now to FIG. 5, numeral 110 generally indicates another embodiment 
of a laser welding system according to the invention. Because some of the 
details of laser welding system 110 have similar components or parts, as 
in laser welding system 10 shown in FIGS. 1-4, similarly ending numerals 
are used for like or similar parts. Additionally, laser welding system 110 
includes all the components, whether shown or not shown, of laser welding 
system 10 except for the differences set forth below. 
Whereas focusing head 26 of FIGS. 1-4 is fixedly secured to clamp 12, 
focusing head 126, as shown in FIG. 5, is movably secured to clamp 112. 
Slot 128 defines a path of motion. Focusing head 126 is adapted to travel 
the path of motion moving the laser beam across material 111 thereby 
forming a linear stitch weld joint, as opposed to a spot weld joint. 
Welding system 110 further includes a drive assembly 158 operably 
associated with focusing head 126, for moving focusing head 126 along the 
path of motion. Focusing head 126 is mounted to a reciprocal table 160 by 
a bracket 162. Table 160 is movable in a linear horizontal path along an 
"X" axis 168 relative to a base 164 which is fixedly secured to lower 
plate 114. Drive assembly 158 includes a motor and gear assembly 166, 
secured to base 164 for moving table 160 along "X" axis 168 thereby moving 
focusing head 126 along the path of motion. Drive assembly 158, which may 
be of a known design as manufactured by Parker and sold under the name 
"Daedal Positioning Systems and Controls," is adapted to be remotely 
controlled by computer 170. 
Referring now to FIGS. 6-8, another embodiment of a laser welding system 
according to the present invention is shown and is generally indicated by 
numeral 210. Because some of the details of system 210 are similar to 
those of systems 10, 110, shown in FIGS. 1-5 and described above, 
similarly ending numerals are used for like or similar parts. Whereas 
clamp slots 28 and 128 are positioned between their associated lower and 
upper clamp plates, slot 228 is formed in upper plate 216 to thereby allow 
the opposed face-to-face flush surfaces of the sheets 211, 211' to be 
laser welded together. Focusing head 226 is fixedly mounted to clamp 212, 
partially within slot 228, as shown best in FIGS. 7-8. Air passage 252 and 
cover or shielding gas passage 254 extend through upper plate 216, as 
opposed to lower plate 214, as in FIGS. 1-5. Also, air passage 252 and 
cover gas passage 254 include tubes 253, 255 extending from upper plate 
216 and support member 232, respectively. Actuators 230 are mounted to 
upper plate 216 via a pair of L-shaped brackets 231. 
Referring now to FIG. 9, another embodiment of a laser welding system, 
according to the present invention, is shown and generally indicated by 
numeral 310. Because some of the details of laser welding system 310 have 
similar components or parts, as in laser welding system 210 shown in FIGS. 
6-8, similarly ending numerals are used for like or similar parts. 
Additionally, laser welding system 310 includes all the components, 
whether shown or omitted, of the laser welding system 210, except for the 
differences set forth below. 
Whereas focusing head 226 of FIGS. 6-8 is fixedly secured to clamp 212, the 
FIG. 9 focusing head 326 is movably secured to clamp 312. A slot 328 
defines a path of motion. Focusing head 326 may be moved along the path of 
motion thereby moving the laser beam across sheet material 311 to form a 
linear stitch weld joint or two-dimensional lap weld joint as opposed to a 
spot weld joint. Welding system 310 further includes a drive assembly 358, 
operably associated with focusing head 326, for moving focusing head 326 
along the path of motion. Focusing head 326 is mounted to a table 360 by a 
bracket 362. Table 360 is movable in a linear horizontal path along an "X" 
axis 368 and a "Y" axis 374 relative to a base 364 which is fixedly 
secured to upper plate 316. Drive assembly 358 thereby moves the focusing 
head 326 along "X" axis 368 and "Y" axis 374. It will be noted that drive 
assembly 358 includes two motor and gear assemblies 366 secured to base 
364 for moving table 360 along the horizontal path of "X" axis 368 and "Y" 
axis 374 to thereby move focusing head 326 along the path of motion. Drive 
assembly 358 is of a known design, as manufactured by Parker, and sold 
under the name "Daedal Positioning Systems and Controls." As in the above 
described embodiments, drive assembly 358 may be remotely controlled by a 
computer 370. 
Although not shown, clamps 12, 112, 212, 312 may be used together in any 
combination for laser welding material 11, 111, 211, 311 to thereby 
provide multiple types of weld joints, such as spot weld joints, linear 
stitch weld joints, two-dimensional lap weld joints, or the like. 
Although the invention has been described by reference to a specific 
embodiment, it should be understood that numerous changes may be made 
within the spirit and scope of the inventive concepts described. 
Accordingly, it is intended that the invention not be limited to the 
described embodiment, but that it have the full scope defined by the 
language of the following claims.