Continuous seam welding apparatus and methods

A method of producing a continuous seam weld between two mating surfaces of a can includes the steps of supplying a bolus of laser energy at alternate spaced locations along the line of the mating surfaces to effect local melting of the mating surfaces. The bolus of energy is then allowed to dissipate initially by way of an enlargement in the size of the melt pool and subsequently by cooling to a level at which the pool solidifies. A further bolus of laser energy is supplied at intervening spaced locations along the line of the mating surfaces to effect local melting of the mating surfaces. This bolus of energy is allowed to dissipate initially by way of an increase in the size of the melt pool and subsequently by cooling. The spacing between the alternate and intervening locations and the power of the bolus of energy being of such magnitude that the size of each pool produced at each intervening location during its enlargement overlaps a solidified pool.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to continuous seam welding. 
2. Description of the Prior Art 
It has been previously proposed to weld an elongate seam by means of a 
laser beam and in particular to weld the side seam of a tubular can body 
made of sheet metal such as steel, black plate or steels coated with a 
metal such as tin, chromium, nickel or zinc, or steels coated with layers 
of chromium and chromium oxide. The steel or other sheet material to be 
welded may have an organic coating. 
In order to meet the commercial demand for welded cans it is desirable to 
weld can bodies at a rate in excess of 45 m/min. W M Steen and J Mazumder 
reported in the Welding Journal, June 1981, in an article entitled "The 
Laser Welding of Steels used in Can Making" that the welding of thin gauge 
steel (either coated or uncoated) was a possibility at speeds up to 7 or 8 
m/min. 
U.S. Pat. No. 4,315,132 (Saurin) describes a laser welding process which 
could weld cylinders at speeds up to 22 m/min but this process is not 
adaptable for use in the high speed welding of can bodies because high 
quality continuous wave (CW) laser welds cannot be consistently obtained 
at speeds above about 22 m/min regardless of laser power. 
European Patent Application No. 0 143 450 (SWS Incorporated/Sharp) 
describes a method and apparatus for pulsed high energy density welding. 
This patent specification teaches that if a pulsed laser is used so that a 
series of overlapping pulses are laid down one after another then, because 
of the slight pause between consecutive pulses of the beam, the melt pool 
has time to stabilise. Welding can then proceed without the instability in 
the melt pool that occurs with a continuous power laser at speeds up to 40 
m/min or more. This patent also gives an indication of the problems which 
beset the high speed welding of thin sheet metal and it indicates that the 
answer to high speed welding is not merely an increase in the power of the 
laser (this point is also made by Steen). Excessive power in the laser 
beam simply creates an unstable melt which may become a permanent hole if 
part of the melt is lost. 
The problems which need to be alleviated are: 
(a) the Sharp system only works at speeds up to 40 m/min because at greater 
speeds the melt becomes unstable and the weld is prone to such surface 
irregularities and undercutting as would be unacceptable in can making; 
(b) the weld produced by a laser beam is narrow so any deviation of the 
butt joint, between the parts to be welding can result in the beam missing 
the joint completely or striking at an out of focus position: 
(c) at high power levels there is a finite limit to the speed at which a 
laser can be pulsed: above this limited speed, a continuous laser beam may 
be used but problems (a) and (b) remain; and 
(d) The intense localised energy of the laser beam and conductivity of the 
sheet metal to be joined give rise to rapid heating and cooling of the 
melt and risk of martensitic transformation. 
Experience using such a welding process as Sharp's shows that there is a 
great difficulty in controlling the mechanical handling of the material to 
be welded at such high speeds. In addition at speeds in excess of about 45 
m/min instability once again occurs in the melt pool and welding becomes 
impracticable. 
In a paper entitled "The use of laser beam spinning to improve fit up and 
beam alignment tolerances when laser welding butt joints in sheet steel" 
by C J Dawes, published by the Welding Institute as Report 269; 1985 
various methods to overcome some of these problems are described. 
Discussing the welding of metals, thicker than those used in the can 
industry, at speeds much lower than appropriate to can making three 
methods of manipulating the laser beam are described. In one method a 
spinning laser beam was used which if scaled up to the requirements of the 
can making industry would be required to spin at speeds presently 
considered impracticable for can making. In another method the laser beam 
was directed to follow an oscillating path spanning the butt joint but 
this required the beam to follow a long path length shown in FIG. 1 at D 
so slowing down the welding process. In a further method the beam was 
defocussed to a broader zone width but lesser intensity. 
The Sharp patent showed that a way to increase speed was to allow the metal 
time to dissipate energy between welding pulses. However this has its 
limits in that if welding is fast enough there is insufficient time to 
cool down between welding pulses. In other words the practical effect is 
that there seems to be a limit to the amount of energy that can be pumped 
into the pieces to be welded over any particular time interval. We have 
discovered that this limit may be overcome by arranging for a series of 
non-overlapping weld pulses to be applied so that each weld pool has time 
to cool and possibly freeze before an overlapping pulse from a further, 
out-of-phase series, is applied. The longer the time lag between the first 
and subsequent adjacent weld pools the better. However, the time lag 
should not be too long in order to take advantage of the heat already 
supplied. By this means it should be possible to reach speeds of 100 m/min 
or more. The process does not have to be restricted to only two series of 
pulses, three or more could be used to fill the space between the welds 
formed by the first beam pulses. 
SUMMARY OF THE INVENTION 
According to the present invention there is provided a method of producing 
a continuous seam weld between two mating surfaces comprising the steps of 
supplying a bolus of energy at alternate spaced locations along the line 
of the mating surfaces to effect local melting of the mating surfaces, 
allowing the bolus of energy to dissipate initially by way of an 
enlargement in the size of the melt pool and subsequently by cooling to a 
level at which the pool solidifies, supplying a bolus of energy at 
intervening spaced locations along the line of the mating surfaces to 
effect local melting of the mating surfaces, and allowing the bolus of 
energy to dissipate initially by way of an increase in the size of the 
melt pool and subsequently by cooling, the spacing between the alternate 
and intervening locations and the power of the bolus of energy being of 
such magnitude that the size of each pool produced at each intervening 
location during its enlargement increases sufficiently to overlap a said 
solidifed pool. 
According to the present invention there is further provided a method of 
producing a continuous seam weld between two mating surfaces, the method 
comprising the steps of applying a first succession of spaced discrete 
energy pulses to the mating surfaces progressively along the line of the 
seam to be formed, to effect local melting of the mating surfaces, 
applying a second succession of spaced discrete energy pulses 
progressively along said line also to effect local melting of the mating 
surfaces, the point of application of each pulse of the second succession 
being such that the pool of melt which it produces overlaps an area 
previously melted by a pulse of the first succession of pulses and the 
timing of each pulse of the second succession being such that it occurs 
during the period when the temperature of the said previously melted area 
has dropped by not less than 1% but not more than 25% of the temperature 
difference betwen the melting point of the material of the mating surfaces 
and ambient temperature. 
According to the present invention there is still further provided a method 
of laser welding an elongate seam between seam materials said method 
comprising the steps of assembling the seam materials along the site of 
the eventual seam, causing relative motion as between the seam materials 
and a laser beam and controlling the delivery of laser energy to melt a 
plurality of overlapping zones, each zone being melted by a discrete pulse 
of laser energy characterised in that in the area of overlap between two 
zones a period of time elapses between the heating of the two zones 
sufficient to allow one said zone to stabilise or solidify before the 
other is melted. 
According to the present invention there is yet further provided apparatus 
for producing a continuous seam weld between two mating surfaces the 
apparatus comprising means for supporting the mating surfaces and aligning 
them along a predetermined axis defining the site for the seam, means for 
effecting relative displacement between the laser means and the support 
means to cause the beam of the laser means to scan the site, and control 
means for controlling the laser means to direct successive discrete laser 
energy pulses to impinge upon the seam site to effect local melting of the 
mating surfaces in a series of overlapping zones the control means being 
effective to ensure that at least every alternative pair of pulses 
produced do not impinge upon respective zones which overlap each other. 
According to the present invention there is still further provided a 
continuous seam weld between two mating surfaces and formed by local 
welding along a series of overlapping weld sites wherein the weld profile 
of the local weld produced at every alternate weld site overlaps and 
bridges the profiles of the local welds produced at every two adjacent 
intervening weld sites. 
According to the present invention there is yet further provided a 
continuous seam provided by a succession of overlapping welding operations 
each over a generally circular site, the profile of the seam being such 
that each alternate weld is substantially circular and each intervening 
weld is substantially circular less the amount by which the or each 
adjacent alternate weld is in overlapping relationship with it.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In FIG. 1 a tubular article 10 has an elongate seam 11 defined by abutting 
edges of the side wall material 12. As shown in FIG. 1 the tubular article 
10 is moved under either laser beam "S" or alternatively laser beam "D" to 
progressively produce a butt weld. 
The laser beam "S" is operated in the manner and sequence taught in 
European patent application No. 0 143 450 so that, as the tubular article 
10 moves at high speeds (22 to 40 m/s or more) under the pulsed laser beam 
"S" a plurality of overlapping spot welds 1, 2, 3 is formed. One problem 
arising with this form of welding is that, if the tubular article 10 
twists as it travels the beam "S" will miss the abutting edges of the seam 
material 12. 
In order to overcome this problem C J Dawes described methods in which a 
laser beam, denoted "D" in FIG. 1, is caused to oscillate to and fro 
across the abutting edges either to trace a wave as depicted or 
alternatively a looped trajectory (not shown in FIG. 1). A problem arising 
with these "weaving" or "spinning" beams is that the path traced out is 
lengthy and so the speed of welding is reduced. 
FIG. 2 shows a butt weld 13 and a laser beam A impinging on it. By way of 
example, a 1 kW "ELECTROX" (trade name) carbon dioxide laser could have a 
focussed beam of width "B" at the seam, in the range of from 0.1 mm to 
0.15 mm (0.004 inch to 0.006 inch) so that if the tubular article twists a 
distance as little as 0.05 mm (0.002 inch) the beam A will miss the seam 
and an unsatisfactory weld 13 will be produced. Cans are currently made by 
welding cylindrical bodies formed from common sheet metals 12 of thickness 
"t" in the range of from 0.15 mm to 0.4 mm (0.006 inch to 0.016 inch). 
When using thin sheet metals such as tinplate blackplate or 
chromium/chromium oxide coated steels the dimensional tolerance in the 
location of the seam is difficult to maintain. Similar problems will arise 
when welding steels coated with nickel or zinc. 
FIG. 3 shows a tubular article having a lap seam 14 and a laser beam A 
impinging on the overlapping seam material 12. Early welded cans had an 
overlap "1" of about 3 mm but more recently this was reduced to 0.8 mm. 
However, in both cases the overlap exceeds the width "B" of the laser beam 
so the lap seam is a much easier target for a laser beam to hit. However, 
the lap seam is not preferred for can making because of the risk of 
corrosion in the crevice between the overlapping layers. 
FIG. 4 illustrates the distribution of the laser beam energy from a laser 
beam "A" into the melt pool via a keyhole 15 and thence into a heated zone 
16 from which it is drawn by the "heat sink" effect of the seam material 
12 and to a lesser extent into the newly created weld 17 made up of 
previous strikes. 
The cooling rates arising at a strike zone can be as much as 10.sup.6 
.degree. C./sec so that during welding of ferrous materials, martensite 
may be formed. As martensite is harder than the ferritic sheet metal, a 
weld having a martensitic structure represents a discontinuity of 
structure that may give rise to difficulty during the subsequent spinning 
or roll forming of a shoulder neck and flange on the welded cylinder. It 
is therefore desirable to abate the rapid cooling that causes the 
martensitic transformation so that a ferritic weld 17, properly centred in 
the seam material 12 is produced as shown in FIG. 5. 
It will be noted that in FIG. 5 the weld, about 0.4 mm wide, penetrates the 
thickness of the seam metal 12 without protruding. The degree of 
penetration is to some extent governed by the power of the laser beam used 
and the speed of travel of the beam across the seam. Typically a laser 
beam having an average density of at least 155.times.10.sup.9 W/m.sup.2 
(10.sup.6 watts/inch.sup.2) is used, such as can be provided by a carbon 
dioxide laser. However a dilemma arises because a high power laser is best 
able to deliver power quickly for rapid progression of the weld but high 
powered lasers (e.g. 3 Kilowatt) are capable of producing an unstable melt 
pool 15 which may collapse to leave a void or move to freeze as a 
protrusion or "stub". 
FIG. 6 reproduces a prior art weld sequence produced by laser beam S of 
FIG. 1 in a simple geometrical plan form. As can be seen each pulse of 
laser energy partially overlaps the previously heated zone to achieve a 
continuous weld from the succession of pulse induced spot welds. The arrow 
denotes the next pulse strike location. 
By way of contrast a first embodiment of the method embodying the invention 
is shown in FIG. 7. In FIG. 7 the finished weld pattern is similar to that 
of FIG. 6 but it will be seen that before overlaying the overlapping 
strike (3) as arrowed, a pulse strike (2) is delivered one pitch ahead so 
that zone of the previous strike (1) has time to cool and start to 
stabilise before it is overlapped by the pulse strike (3), i.e. in FIG. 7 
the pulse denoted 1 has time to cool while pulse 2 is laid ahead of it 
before an additional pulse 3 is overlaid upon it. 
Each circle drawn in FIG. 7 represents a heated zone as described with 
reference to FIG. 4. As more heat is added then when an additional pulse 
overlaps a previous zone of heating it is possible to control the amount 
of heat introduced by increasing the amount of overlap. 
FIG. 8 shows how the amount of heat applied to each zone can be decreased 
by reducing the amount of overlap as will be understood by comparison with 
FIG. 7. Again the area heated by pulse 1 must have time to cool before the 
next pulse 3 is overlaid upon it. Whilst pulse 2 is shown as being applied 
one pitch ahead, it may, if desired be placed even further ahead as shown 
by the dashed circles 2a or 2b. A benefit of applying the distant strikes 
2a or 2b is that they make a spot weld which holds the seam steady for 
final welding. 
The pulse required to produce the zone 2 may be delivered by redirecting 
the beam from a single laser used to provide the pulse for zone 1 or 
alternatively a separate laser may be used to provide pulses for heating 
the zones denoted 1, 2a or 2b. 
The patterns of FIGS. 7 and 8 rely on a laser beam of adequate width to 
span any tolerable deviation of the seam 11. FIG. 9 shows a pattern of 
pulse strikes which increases the width of material heated by use of a 
staggered array of pulse strike zones. In FIG. 9 a pulse strike zone 2 is 
laid ahead of a previous strike zone 1 before an additional pulse strike 3 
is applied the pulse strikes 1 and 2 are centred to one side of the seam 
line 11 and the pulse strike 3 is about to be applied to the other side of 
the seam line 11 so that a double row of overlapping zones is 
progressively laid. The distant strikes 1a, 2b in FIG. 9 show again that 
there is some design choice as to the degree of prefixing and thermal 
control. 
FIG. 10 is presented to show that a pair of pulses may be applied 
simultaneously so that in FIG. 10 a first pair of pulses 1a, 1b is applied 
and has time to cool and stabilise while a second pair of pulses 2a, 2b is 
applied so that when the third pair of pulses 3a, 3b are applied the rate 
of cooling of pulses 1a is controlled. 
FIG. 11 shows how a staggered array of zones, centred on the seam line may 
be progressively developed using a pair of laser beams. A first laser beam 
A.sub.1 has created the top row of zones and is shown in the leading 
position in readiness for a next strike. A second laser beam A.sub.2 has 
created the lower row of zones and is shown in the position for its next 
strike at which the pulse delivered will overlay the two adjacent zones 
created by the laser A.sub.1. Thus the zones in the row created by laser 
A.sub.1 have time to stabilise before being struck by pulses from laser 
A.sub.2. 
FIG. 12 shows a pattern of zones laid along a wave form as proposed by 
Dawes in the prior art but, as in FIG. 7, there is a delay in time between 
the pulse striking zone 1 and being struck by an additional pulse 3 during 
which period the zone 2 is irradiated. The zone 1 is therefore able to 
stabilise before being restruck. The pattern shown in FIG. 12 may be made 
by use of two laser beams, one of which deflects from side to side across 
the seam 11 and the other of which fills in the overlap zones: in which 
case the sequence will not be as shown in FIG. 12. 
FIG. 13 shows a pattern of heated zones comprising three rows: one row 
centred on the seam line 11 and a row centred on each side of the seam 
line but encompassing the seam line 11. It will be seen that the 
overlapping zones of the outer rows and centre melt zones of the central 
row progressively make a nearly continuous band of irradiation greater in 
width than would be achieved by a single laser beam. Also the triple zone 
pattern provides heat laterally of the weld so abating the heat sink 
effect of the cold metal to each side of it. To a lesser extent the double 
zone patterns of FIGS. 9 and 11 yield a similar benefit. 
The pattern shown in FIG. 13 can be achieved by deflecting a single laser 
beam to the zone positions 1, 2, 3, 4 as shown. However it may be move 
convenient to use a first laser beam oscillating across the seam line 11 
to heat zones 1 and 2 and 3 whilst a second laser beam fills in the centre 
row at an appropriate later time. Instead three separate lasers could be 
used each timed to fire at the appropriate time to create a spaced array 
of zones which is finally completed but this would be costly. 
To recapitulate: the patterns of FIGS. 7 to 13 all allow each melt pool to 
stabilise before its peripheral zone is restruck by an adjacent zone. The 
patterns of FIGS. 9, 11, 12 and 13 increase the amount of heat to each 
side of the seam line so reducing the heat sink effect of the seam 
material giving an opportunity to prevent martensitic transormations and 
possibly more importantly permitting relaxation of the tolerance on 
location of the seam line under the or each beam. 
In the embodiments of the apparatus for performing the invention as will 
now be described the apparatus of FIGS. 14 to 18 is shown to effect a 
distribution of the zones along the line of the seam while a lateral 
distribution of zones is effected by the apparatus of FIGS. 9, 11, 12 and 
13. 
FIG. 14 shows a first embodiment of apparatus for welding an elongate seam 
according to the sequence described with reference to FIGS. 7, 8 and 11 
and adaptable, by slewing the conveyor, to make the seams of FIGS. 9 and 
11. 
The apparatus shown in FIG. 14 comprises a 2 Kw carbon dioxide laser 20 
emitting a continuous beam which is directed on to a reflecting chopper 21 
in the form of rotating blades. A laser beam when not intercepted by the 
blades, impinges upon a first fixed mirror 22 which reflects it, on to a 
second fixed mirror 23 which redirects the beam through a lens 24 on to 
the workpiece 25 which is located in the focal plane of lens 24. 
When the beam is intercepted by or strikes a blade of the reflecting 
chopper 21 it is directed on to a third mirror 26 which passes the chopped 
beam (denoted by dashed lines) to a fourth mirror from where the beam is 
redirected on to the mirror 23. The beam when reflected by the mirror 23 
passes through the lens 24 on to the workpiece 25 at a desired distance 
apart from the point of strike by the beam not intercepted by the chopper. 
The apparatus of FIG. 14 is therefore able to apply a series of pulse 
strikes each at a location set apart from the next. As the workpiece is 
conveyed by the conveying means 28 to pass across the beams, the desired 
pattern of strikes by each pulse is delivered. Each pulse has time to 
stabilise before being partially restruck. The apparatus of FIG. 14 
creates two intermittent beams spaced apart. Each beam delivers energy 
only when the other is not doing so. FIG. 15 shows a second embodiment of 
apparatus suitable for use in creating the sequence of strikes as shown in 
FIGS. 7 to 11. In FIG. 15 the apparatus comprises a pulsed laser 30 from 
which the pulsed beam is directed on to a stationary beam splitter 31 
which splits the beam into two beams one of which passes directly to a 
mirror 32 for reflection through a lens 33 on to a workpiece 34 located in 
the focal plane of lens 33. The second beam (shown by dashed lines) is 
deflected from the splitter 31 to strike a second mirror 35 which reflects 
the second beam on to mirror 32. The mirror 32 reflects the second beam 
through the lens 33 to be focussed on the workpiece 34 in a zone at a 
distance apart from the zone heated by the first beam. In the apparatus of 
FIG. 15 two simultaneous beams are created: any pulsing arises because a 
pulsed laser was chosen. 
A zinc selenium beam splitter with appropriate surface coatings may be 
used. The ratio of beam intensity may be varied by choice of an 
appropriate splitter, for example a 50:50 ratio of first beam intensity to 
second beam intensity can be selected. Alternatively a 70:30 ratio can be 
selected. With the latter alternative the reduced intensity beam "30" is 
useful if there is a risk of injecting too much heat in a pattern location 
such as the trailing edge of zone 2 in FIG. 7 or the centre line zones "4" 
of FIG. 13. 
If the desired zone pattern requires more beams another splitter may be 
added, for example after the first splitter on the main beam. 
FIG. 16 shows a third embodiment of apparatus for welding an elongate seam. 
In FIG. 16 the apparatus comprises a laser 40 (which may be pulsed or 
continuous), a chopper 41 which receives the beam from the laser 40 and 
passes it on each alternate occasion to a mirror 42 and lens 43 which 
focusses it on a workpiece 44 and on each intervening occasion to a second 
mirror 45 which directs the beam on to mirror 42 for focussing by the lens 
43 on to the workpiece. 
In FIG. 16 the chopper 41 is connected to a servo controlled device 46 
which is electronically controlled by means 47 so that the chopping action 
by the chopper 41 is synchronised with the laser pulses if pulsed laser is 
used. 
As shown by the pulse graphs adjacent each beam the pulses of each beam are 
phase displaced so that when one beam is delivering power the other is 
not. The intensity of each beam may be varied, as either by controlling 
the laser or alternatively by choice of an appropriate chopper. 
FIG. 17 shows a fourth embodiment of the apparatus for use in welding 
cylindrical can bodies 50, 51 having a butt seam uppermost to receive a 
plurality of laser beams. A conveyor 52 has spaced drive dogs 53 which 
drive the can bodies 50, 51 within the restraint of guide means for 
example guide rails 54. As in the previous examples the seam is 
substantially in the focal plane of a lens 59 which focusses the laser 
beams received from a mirror 58. 
In contrast to the previously described examples of apparatus FIG. 17 shows 
a separate laser used to provide each beam. A first laser 55 of relatively 
low power and located upstream of the lens 59, directs its beam on to the 
seam material as the can body 50 is conveyed beneath it (from left to 
right in FIG. 17). The beam from the laser 55 serves to volatilise any 
coating materials on the seam margins adjacent the butt joint. As can 
coatings are usually inorganic pigments in an organic vehicle the heat 
acts to drive off the carbon bearing organic polymers in order to prevent 
carbon reaching the subsequent melt pool. Should it be found that any 
particular can coating chars or stubbornly adheres it may be brushed off 
by a rotating brush (not shown). 
The cleaned can 51 is depicted during welding. Depending on the laser power 
used for edge cleaning of the butt seam it may still have useful preheat 
so that less power is required at the welding station. 
As shown the can body 51 is receiving irradiation from two lasers 56 and 
57. The beam from each of the two lasers 56 and 57 is delivered to the can 
body 51 via a mirror 58 and a lens 59 of focal length such that the seam 
is substantially in the focal plane of the lens as previously explained. 
The lasers 56 and 57 are timed by control means 60 to direct their pulses 
so that one of the patterns of FIGS. 7 to 13 is developed at the seam as 
the can body moves across the beams. 
If required a fourth laser 61 (shown in broken lines) may be included to 
facilitate the formation of a pattern requiring a triple row of heated 
zones such as shown in FIG. 13. Alternatively this optional third laser 
may be used for edge cleaning or preheating to adjust the heat 
distribution in the weld. 
If desired a further beam may be directed to heat the weld after the 
formation in order to further control the rate of cooling for example 
prevent martensitic transformations or perform some degree of annealing or 
normalising of the welding structure. 
The various features of the apparatus described may be transposed as 
desired to achieve useful results without exceeding the scope of the 
invention. For example, the lasers 56 and 61 of FIG. 17 could be directed 
at the can without the mirror 58. 
It will be appreciated that with the methods described where a continuous 
seam is produced by creating overlapping melt zones it is important to 
allow each melt zone to cool (to dissipate energy) before an overlapping 
portion is remelted. 
It is preferable that each zone should cool to below the freezing point of 
the material before a reheating is effected. However with high speed 
welding where one zone is often caused to overlap with two others this is 
not always possible if high speeds are to be maintained. As a compromise 
therefore at least one of the two zones to be partially remelted should 
have cooled to below freezing before being partially remelted. 
Advantageously that zone should have cooled by not less than 1% and not 
more than 25% of the temperature difference between the melting point of 
the seam materials and the ambient temperature. Preferably this range 
should be between 5 and 15%. 
While the description has been directed to producing a continuous seam weld 
in ferrous materials, it will of course be apprecaited that any other 
materials including other metals and even plastics materials can be welded 
in a similar manner. 
While the presently preferred embodiments of the present invention have 
been illustrated and described, modifications and variations thereof will 
be apparent to those skilled in the art given the teachings herein, and it 
is intended that all such modifications and variations be encompassed 
within the scope of the appended claims.