Manufacturing
Industrial Use of Laser Welding
Dan Strawn
F.A.S.T. Test Pallet
Copyright © 2006 Department of Mechanical Engineering, Colorado State University
ABSTRACT
The use of lasers in the field of welding is not a new up
and coming technology, but it is finally becoming a main
stream welding technique. Laser welding has grown
exponentially over the past few years, and is widely used
in the production of electronic circuit boards, heavy
machinery and even the jewelry business. The use of
lasers in manufacturing is still young in terms of its
potential capability. Though, through continued
development, lasers will be able to re-define how
products are made. The principles behind laser welding
and related innovations with laser manufacturing are
described herein, along with the devices used to produce
these laser beams.
to generate light, which in turn is then focused in to a
high intensity beam. The actual entire process of the
laser is much more involved, but the focus of this paper
will be on solid state lasers. The solid state laser of
discussion is a Neodymium Yttrium Aluminum Garnet
(Nd: YAG) laser, specifically the Raytheon S550 Series
Precision Laser Welder/Driller.
Of the devices discussed, there will be an emphasis on
the machines that are capable of producing extremely
small and intricate welds on thin materials.
INTRODUCTION
A laser, Light Amplification by Stimulated Emission of
Radiation, is most commonly thought of as a science
fiction weapon, but the application of real world lasers is
as real as the sun or sky. Lasers are capable of
providing an immense amount of heat that is higher than
the temperature of the sun itself. With such a large
potential of power, the use of lasers in industry is rather
limitless.
In recent years, the use of lasers to perform complex or
difficult welds has grown. Lasers, utilizing the large heat
potential, make fusion welds of many different materials
in a variety of sizes possible. A fusion weld requires no
additional filler material to be added to the weld, which is
contrary to most common forms of welding. In laser
fusion welding there is a large reduction in the heat
affected zone (HAZ) around the weld, thus maintaining
the bulk material properties. In addition, the fusion weld
allows for unlike metals to be joined with much more
success than conventional methods.
Lasers are classified in two general categories: solid
state lasers and gaseous state lasers. The gaseous
state laser is created by passing a current through a gas
Figure 1: Raytheon S550 Laser Welder/Driller
As in any manufacturing process, there is great
consideration in the selecting a particular method to
create a weld. Thickness of material, material properties
of the weld and application of the welded part are three
key criteria to consider when choosing the proper
technique to create a weld. The diversity of a laser
welder allows for all three characteristics to be optimized
for the given situation.
PRINCIPLES OF WELDING
In order to gain insight to the extra dimension that laser
welding offers to the field of conventional welding, it is
important to address the basics of traditional welding.
The technique of welding involves bonding two materials
together through the use of intense heat. The metals are
joined together either through the use of a filler rod or
through the fusion of the metals.
There are many types of welds, but the butt, corner, fillet,
lap, and edge weld will be the focus. These are the most
common forms. Although there are many variations of
weld types, it is easiest to relate to these four welds.
When a butt weld is formed properly, the strength of the
weld is comparable to that of the plates being joined.
This relates to a weld efficiency of 100% under static
loading for a butt weld. In comparison, a fillet weld under
parallel static loading, as well as a fillet weld under
transverse static loading, is not as strong as the metals
themselves that are joined together.
Figure 2: Butt Weld
Figure 7: Fillet Weld Strength Potential
Figure 3: Corner Weld
Figure 4: Fillet Weld
Figure 5: Lap Joint Weld
The above equations illustrate that a fillet weld is much
weaker than the plates it joins. This is apparent in the
fact that the areas of the plates are (typically) much
larger than the weld. Also in addition to the area, the
plates do not have a correction factor of 0.58 imposed
upon it.
In relation, a corner weld and a lap joint weld are very
similar to a fillet weld, both in appearance and in their
physical properties. Whereas an edge weld is similar to
a butt joint weld, both in appearance and physical
properties. All four forms of these welds can be
performed in a variety of positions, meaning that the weld
can be performed vertically, horizontally, flat, and even
inverted.
Granted that the typical laser welder is
confined to the apparatus in which it is mounted, the
most common position for traditional laser welding would
be the flat position. In addition, it is important to note that
the corner, fillet, and lap joint welds require the laser
beam to be focused at the corner where the two pieces
meet. This allows for both materials to be fused
simultaneously.
When utilizing a laser welder, the same equations hold
true, in most cases. A laser uses a fusion weld and does
not impose a filler material into the metal being welded.
A laser weld maintains the material properties of the
plates, which is one of the main benefits of laser welding.
Nd: YAG LASERS
The use of solid state lasers, particularly the Nd: YAG
laser, has been around since the early 1960s. Even
though the technology is rather dated, it is important to
understand the principles that drive the operation of the
laser in order to recognize the potential of these welding
systems.
Figure 6: Edge Weld
An Nd: YAG laser operates by emitting a highly
concentrated beam of light from a crystal. The crystal is
made up of Neodymium Yttrium Aluminum Garnet, and
is the key to generating the laser beam. The crystal lies
within a highly reflective (typically gold plated) cavity and
is surrounded by krypton cathode lamps. The shape of
these cavities is critical to the power of the laser. The
krypton lamps emit an incoherent light, and the cavity
shape is designed to focus this light on to the crystal.
Figure 9: Partially Reflective Lens and Shutter
Control
Reflective Cavity
Krypton Lamps
Crystal
Figure 8: Nd: YAG Laser Internal Components
The krypton lamps, being the source of energy to the
crystal, are the limiting factor of a solid state laser. The
lamps require large amounts of power to be transmitted
through them in order to release a high strength
incoherent light. The light, after being focused by the
reflective cavity, strikes the Nd: YAG crystal. The photon
energy that strikes the crystal causes electrons within the
crystal to be placed in an excited state. These electrons
quickly drop back to their original energy state, in order
to maintain their energy balance within the system as a
whole. The “motion” of the electrons as they lower
energy states causes photons to be released from within
the crystal. These photons create the laser beam used
for welding.
Now that a beam of light has been created, it needs to
be focused and directed to the work piece. There are a
variety of methods to perform the focusing, and most
commonly it is done by using two main lenses and a
series of focus lenses. The light emitted from the crystal
does not come out in one direction, but rather from both
sides of the crystal. The dual beam makes it necessary
to reflect one portion of the beam back into the other half
of the beam. This process allows for a better efficiency
within the laser.
Figure 10: Rear Focus Lens
Beyond the actual laser, the support equipment required
to operate a laser effectively, is rather involved. In
particular, on the Raytheon S550 unit the laser head
requires a water to water heat exchanger. There is such
a great amount of heat being generated by the krypton
cathode lamps that the heat needs to be regulated and
dissipated effectively. This poses a critical problem
within the laser. In order to cool the laser, a working fluid
must be nearly perfect optical transparent. This allows
the lamps to maintain a constant temperature and still
emit the incoherent light that activates the Nd: YAG
crystal that produces the laser beam. An example of a
good working fluid for a typical water to water heat
exchanger would be glycol; however, due to the optical
constraints, de-ionized water is the best option. The deionized water is maintained at a safe level by use of the
heat exchanger which uses a constant flow of tap water
to keep the de-ionized water cool.
The laser beam then creates what is known as a key
hole (which penetrates the material). The key hole
causes internal refraction to occur within the weld and
increases the effectiveness by lowering the amount of
light that is reflected off the material.
Shielding Gas
Plasma
Cloud
Laser Beam
Keyhole
Melted Material
Weld
Material
Weld Direction
Figure 12: Weld Geometry
Figure 11: Water to Water Heat Exchanger
GENERAL PRINCIPLES OF LASER WELDING
The concept of a laser weld is very similar to a fusion
weld created by a torch. The overall general intent is to
super-heat the two parts at the joint above the materials’
melting points and then to force the molten material to
flow together into one uniform welded piece. However, a
laser is much more focused than a torch. The typical
diameter of a laser beam is on the order of tenths of
millimeters. This creates a very small, localized area of
incredibly intense heat. The beam is so minute that it
could create a weld about the diameter of the tip of a
needle. Precision and accuracy are the two driving
advantages of using a laser welding machine.
E( T)
1
3
2
2
  r( T) 
  r( T) 
2   r( T) 
0.365 
  
  0.006 

3   
  
  
Figure 13: Bramson Equation
In addition to the keyhole effect created by the laser as it
burns in to the material, the material that is burned off
creates a plasma cloud around the point of the weld.
The plasma cloud is extremely efficient at absorbing
incident light and acts to increase the effectiveness of
the laser. Add an inert shield gas to prevent weld sputter
to occur, and the laser weld practically enhances and
protects itself from negative effects caused by the
ambient environment.
THEORY OF LASER WELDING
Material Properties
As with any form of welding, the material to be welded is
critical to the weld’s ability to bond the two materials
together. In the consideration of laser welding it is critical
to understand the materials being welded. As stated
previously, a laser is an intense beam of light. Light can
easily be reflected, thus dissipating the energy it carries.
It is important to understand the absorptivity of the
material to be welded.
In order to calculate the
absorptivity the Bramson Equation is utilized. The
equation relates the electrical conductivity as a function
of temperature to the wavelength of light to be imparted
on the surface.
For example, a typical absorptivity of aluminum using the
Bramson Equation is 2-3%. The reflective loss is rather
significant. Therefore, in the aluminum case, additional
measures must be implored to minimize these losses,
such as an absorbent powder or an anodized film. The
surface finish of any material greatly affects the
absorptivity of the laser.
It is important to note that there are alternative ways to
circumvent the problems associated with absorptivity
issues. The laser will function properly at the desired
power level once the keyhole has been created. A
simple test to create the initial key hole is to pulse the
laser very briefly at a higher than normal operating
intensity. This will usually overcome the absorptivity
issues discussed above and allow the operator to make
the weld as desired.
Perhaps the most intriguing ability of laser welding lies in
the lasers potential to weld practically any metal. The
laser creates a fusion weld with the two metals with no
filler rod, as previously stated. Due to this nature, exotic
metals can now be welded. Traditional methods were
either unable to perform the weld or required too much
complexity/difficulty thus nullified the practicality.
The laser’s exotic capability is also a feature of the laser
beam’s energy density with the beam. The beam is
capable of producing heat that is comparable and/or
higher than that of the surface of the sun. No known
material is capable of surviving such heat. This means
that almost any metal, that will go molten before
vaporizing, is capable of being laser welded.
Material Geometry
While lasers can be used to produce a wide variety of
welds, perhaps the most unique ability is to weld on
miniscule parts with great precision. In terms of the
energy density the beam imparts on the material, there is
a large potential for fine tuning on a laser welder. The
agility of the laser allows for extremely thin materials to
be welded together, as shown below.
Figure 14: 16 Gage Stainless Steel Sheet Metal Weld
By pulsing the beam of the laser, a more controlled
amount of energy can be directed to the weld. This
technique allows the operator to greatly affect the weld
penetration depth. In the use of the Raytheon S550, the
following charts dictate how changing the pulse rate and
pulse width change the laser output to the work piece.
Table 1-1: Maximum Pulse Rate
Leading
Edge
(ms) 0 ms
200
0.3
Hz
200
0.5
Hz
200
0.9
Hz
200
1
Hz
150
1.1
Hz
150
1.4
Hz
PFN Tail Settings
1 ms 2 ms 3 ms 4 ms
100 60
60
45
Hz
Hz Hz Hz
100 60
60
45
Hz
Hz Hz Hz
100 60
60
45
Hz Hz Hz Hz
100 60
60
45
Hz Hz Hz Hz
86
55
55
42
Hz Hz Hz Hz
86
55
55
42
Hz
Hz Hz
Hz
5 ms 6 ms
45
30
Hz Hz
45
30
Hz Hz
45
30
Hz Hz
45
30
Hz Hz
42
29
Hz Hz
42
29
Hz Hz
Table 2-2: Rated Maximum Pulse Energy
Total
Pulse
Width
(ms)
1
2
3
4
5
6
7
7.4
Maximum
Pulse
Energy (J)
6.3
12.6
19
25.3
31.6
37.9
44.2
50.5
Through the understanding of pulse times of the laser, it
is possible to estimate the weld penetration depth and
correctly size the required power input to the weld, which
permits proper weld penetration depth. Understanding
the weld depth for a given set-up allows one to correctly
size the laser to function on whatever size metal is
needed to be welded. Adequate penetration depth in a
weld is a driving feature required to properly manufacture
a structurally sound weld.
Figure 15: Weld Properties
Through the understanding of weld geometric properties
and the understanding of how to obtain them, it is
possible to see how a laser welder is capable of welding
complex geometries. The parameters of are all internal
to the laser. This allows for computer numerical control
to be used in laser welding. Also with the addition of
fiber optic weld tips, complex welds can be made even
easier.
After using the Raytheon S550 and consulting the
manual, calculating parameters theoretically and
obtaining specimens, the results demonstrated that no
matter how much theory was involved; the best welds
were obtained through an iterative trial and error
methodology. There are so many parameters on the
laser to adjust that it is extremely difficult to account for
all factors and compute the exact settings to weld with
theoretically.
In the particular study of thin plate welds, it was
observed through experiment that the best way to make
quality welds was to perform most everything wrong.
When making a weld, it usually requires that the laser to
be focused directly on the surface of the metal and then
pulsed to a given setting to accommodate the material
thickness, feed rate, and desired pulse width of the weld.
When welding thin material, it is extremely difficult to
control the power intensity of the laser on the surface. It
is possible to power the laser extremely low (which is
detrimental to the operating life of the krypton cathode
lamps) and to adjust the pulse and feed rate to weld thin
material. However, even after making these adjustments
the laser typically will melt right through the material.
The easiest thing to do in order to overcome this problem
is to un-focus the laser on the material. For the thin
stainless steel cylinder shown below, the beam was
unfocused by 0.150”. It is important that the focal point
be slightly below the metal pieces. By understanding
how the convex lenses focus the beam, it is easy to
understand that raising or lowering the piece will make a
much wider laser beam. The beam is much wider above
and below the focal point; however, below the focal point
the beam is still at too high of an energy intensity. By unfocusing the beam above the focal point, the laser’s
intensity on the part is lower, but this still allows the
krypton cathode lamps to operate at a safe level (safe to
the lamps operating life). When using this technique it is
extremely important that the correct shielding gas is used
in order to prevent weld splatter from hitting the lens.
There is no exact science to how much the beam needs
to be unfocused, and it is again a trial and error process.
EMPIRICAL STUDY OF LASER WELDING
The theory behind a laser welder is very detailed and
extremely precise, but there is still a great deal of “art”
required to use a laser welder. The net operation of a
laser requires a great deal of variability in order to
operate the laser at peak efficiency. The best way to
make a proper weld is to experiment with a variety of
settings in order to get the desired weld penetration, weld
width, weld strength, etc.
Figure 16: 0.020" Cylinder Laser Welded Butt Joint
INDUSTRIAL USE OF LASERS
Laser welding technology has been around for a long
time, but the use in industry is still rather new. Initially,
there was no need to use lasers over traditional welding
methods.
As technology has progressed and the
manufacturing market fuses in with the “high tech” fields,
laser welding is making a strong presence.
Even in the obscure fields, such as the jewelry business,
laser welders have made an appearance. The precision
along with the ability to weld virtually any metal have
made the use of laser welding a valuable tool to the
industry.
SAFETY
It is important to understand the inherent danger of any
welding process, especially for a laser welder. Laser
welders operate in a wavelength of light that is invisible
to the human eye, but is extremely dangerous to the eye.
For the Raytheon S550, the wavelength of light utilized is
1060 nm. This wavelength of light will pass through
most common welding shields and can severely damage
the eye. Specially designed optical protection gear must
be worn at all times when operating a laser welder.
The laser beam is capable of producing an extremely
intense heat. Combine this heat with the fact that the
beam is invincible, makes the laser extremely
hazardous. If a person were to place there hand under
the laser beam, there would be extreme burning of the
appendage. Be safe.
The last safety precaution has less to do with the laser
beam itself, but rather with the power supply that powers
the laser. Typical lasers use up to 480V of potential.
The systems are often water cooled, and the
combination of high voltage and water should always
make the operator attentive of what is occurring at all
times.
Refer to the American National Standard for the Safe
Use of Lasers for further instruction on the safe use of
laser welding.
CONCLUSION
Figure 17: Industrial CNC Laser
In large scale welding functions the use of lasers is
extremely beneficial in robotic welding. The size of the
torch required to produce the amount of energy that
comes out of a laser beam can be contained in a fiber
optic cable. This factor allows for welds, which are
usually extremely difficult to reach with traditional
welders, to be easily performed using a laser welder.
Laser welding in the high-tech field allows for a level of
precision that was previously unattainable. Delicate
electronics can now be fused together using a laser
welder with extreme precision. Laser welding technology
is helping make electronics smaller and much more
precise. The high power required for larger materials is
not required at this small level, and the laser unit can be
contained in a much smaller unit, which makes the laser
welder at this level much easier to use.
Welding is an important metal joining process. In order
to properly create a weld, it is important to keep in mind
of the material being welded, the size of the weld and the
functionality expected of the weld. The use of laser
welding allows for complex welds to be created when the
weld used to be extremely difficult or even impossible.
ACKNOWLEDGMENTS
I would like to thank Greg Jackson and the entire staff of
Alpha Engineering and Design for all of their time,
assistance with the assembly and for the donated
machine time of the Raytheon SS550 Precision Laser
Welder.
NOMENCLATURE
F = static force
Sy = yield strength
Ssy = yield stress in shear
A = area
E = absorptivity
ρr = electrical resistivity
d = spot size of the laser
f = focal length of the lens
Θ = full angle of beam divergence
P = input power to the laser
k = thermal diffusivity
t = pulse time
λ = wavelength of light
T = temperature
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