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Laser Beam Welding Review
Laser welding is a commercial process used extensively to weld a wide range of materials. The laser beam is focused toward a seam or area which causes the materials to from change from solid to liquid and, as the laser energy is removed, back to solid. Laser welding is a type of fusion welding which may be used to produce selective area spot welds or linear continuous seam welds. There are two types of laser welding processes, conduction and penetration. Laser beam welding utilizes high power density (on the order of 1 MW/cm 2 ) resulting in small heat-affected zones and high heating and cooling rates. The spot size of the laser can vary between 0.2 mm and 13 mm, though only smaller sizes are used for welding. The depth of penetration is proportional to the amount of power supplied, but is also dependent on the location of the focal point : penetration is maximized when the focal point is slightly below the surface of the workpiece
A continuous or pulsed laser beam may be used depending upon the application. Millisecond-long pulses are used to weld thin materials such as razor blades while continuous laser systems are employed for deep welds.
LBW is a versatile process, capable of welding carbon steels , Nickel steels , stainless steel , aluminum , and titanium . Due to high cooling rates, cracking is a concern when welding high-carbon steels. The weld quality is high, similar to that of electron beam welding . The speed of welding is proportional to the amount of power supplied but also depends on the type and thickness of the workpieces. The high power capability of gas lasers make them especially suitable for high volume applications. LBW is particularly dominant in the automotive industry.
Some of the advantages of LBW in comparison to EBW are as follows:
- the laser beam can be transmitted through air rather than requiring a vacuum,
- the process is easily automated with robotic machinery ,
- x-rays are not generated, and
- LBW results in higher quality welds.
A derivative of LBW, laser-hybrid welding , combines the laser of LBW with an arc welding method such as gas metal arc welding . This combination allows for greater positioning flexibility, since GMAW supplies molten metal to fill the joint, and due to the use of a laser, increases the welding speed over what is normally possible with GMAW. Weld quality tends to be higher as well, since the potential for undercutting is reduced.
Laser conduction welding relies on the conductivity of
the material being welded. The laser beam is focused on a specific area on the
material which by proximity will conduct heat into the joint area to be welded.
By focusing laser beam at a location, heat is generated which is conducted into
the joint causing the material change from a solid to a liquid and combine to
the two separate liquid materials. After the material from the two material
change back to a solid the two material are joined or welded at that location.
Laser conduction welds are used for spot welding , continuous and partial
penetration seam welding.
Laser penetration welding is produced by focusing the
laser beam energy at a single location until the stacked materials are heated to
a liquid state and some of the material vaporizes creating a hole within the
material equal to the thickness of the material. When the stacked materials cool
from a liquid to a solid state the material has been joined at that location
through both stacked materials. Similar to the Spot / Lap weld joint
illustration shown below, except the weld is completely through both materials.
There are two common types of laser welding technologies in use,
- CO2 Gas laser
- Solid state lasers ( YAG type )
CO2 lasers use a mixture of high purity carbon dioxide with helium and
nitrogen as the lasing medium. Here are some of the key characteristics for CO2
- Infrared ( 10.6 micro-meters )
- Beam transmission by mirror only (not fiber optic)
- Cutting lasers are typically from 0.5 to 2 kw
- Can cut non-metallic materials
- High cutting speed
YAG lasers use a solid bar of yttrium aluminum garnet doped with neodymium as
the lasing medium. Here are some of the key characteristics for YAG lasers:
- Infrared (1.06 micro-meters)
- Beam transmission by optical fiber possible
- Available to 2 kw
- Wavelength absorbed well by metallic materials ( including Al & Cu )
- Not used for cutting non-metallic materials
Both CO2 and YAG lasers can operate in either continuous or pulsed operating