Laser Welding

Laser Beam Welding

Introduction:
Laser Beam Welding (LBW) is a modern welding process; it is a high energy beam process that continues to expand into modern industries and new applications because of its many advantages like deep weld penetration and minimizing heat inputs. The turn by the manufacturers to automate the welding processes has also caused to the expansion in using high technology like the use of laser and computers to improve the product quality through more accurate control of welding processes.

Major Difference:
The main difference between traditional electric arc welding processes is in the mode of energy transfer. Unlike electric arc energy transfer, laser energy absorption by a material is affected by many factors like the type of the laser, the incident power density and the base metal’s surface condition.
Two important factors to help characterizing laser welding are:
1- The energy transfer efficiency, which is the ratio of the heat observed by the workpiece to the incident laser energy.
2- The melting efficiency, which is the ratio of the heat to just melt the fusion zone to the heat observed by the workpiece.
The laser output is not electrical, does not require electrical continuity, is not influenced by magnetism, is not limited to electrically conductive materials, can contract with any material and its function doesn’t require a vacuum nor does it produce x-rays.

How it works:
The focal spot is targeted on the workpiece surface which will be welded. At the surface the large concentration of light energy is converted into thermal energy. The surface of the workpiece starts melting and progresses through it by surface conductance. For welding, the beam energy is maintained below the vaporization temperature of the workpiece material, because hole drilling or cutting vaporization is required.
Because the penetration of the workpiece depends on conducted heat, the thickness of the materials to be welded is generally less than 0.80 inches if the ideal metallurgical and physical characteristics of laser welding must be realized.
Concentrated energy produces melting and coalescence before a heat affected zone is developed and when the materials to be welded are thick and have high thermal conductivity like for example aluminum the advantage of having a minimal heat affected zone can be seriously affected.
Because the heat source in this type of welding process is the energy of light, the workpiece will be welded purely which means the fatigue strength of the welded joint will be excellent.
Energy distribution across the beam is generated by the design of the resonant cavity, including mirror curvatures or shape and their relative arrangement. This combination results in photon oscillation within the cavity specific output beam energy patterns, these patterns are called Transverse Energy Modes (TEMs).
The function of all laser beam welding processes whether they be gas (carbon dioxide, helium, neo, etc.) or other lasing sources is based on the principles of the excitation of atoms using intense light, electricity, electron beams, chemicals, etc., and the spontaneous and stimulated release of photons.
The role of focusing lenses in this process is really important because it concentrates the beam energy into a focal spot as small as 0.005 in diameters or even less.

Like mentioned above there are many types of Laser Beam Welding (LBW) but the most popular types in the industry are:
1-Nd:YAG (neodymium-yttrium aluminum garnet) Laser:
The Nd:YAG laser uses a man-made crystal as its active medium and produces light with a 1.06-micron wavelength.
2-Carbon Dioxide Lasers:
The CO2 laser uses a mixture of gases including CO2 as the active medium and produces light with a 10.6-micron wavelength.
3-The Diode Laser:
The diode laser uses a semi-conductor diode material as its active medium can be manufactured to produce one of several wavelengths.

Industries Served:
1- Aerospace.
2- Defense/military.
3- Electronics.
4- Research & development.
5- Medical.
6- Sensors & instrumentation.
7- Petrochemical refining.
8- Communications & energy.

Advantages:
1-Deep and narrow welds can be done.
2-Absence of distortion in welds created.
3-Minimal heat affected zones in welds created.
4-Excellent metallurgical quality will be established in welds.
5-Ability to weld smaller, thinner components.
6-Increased travel speeds.
7-Non-contact welding.