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 metals surface condition. (Ivan Griffin pp. 12) Laser welding studies of Al alloys containing Mg have found that Mg is the predominant

…….component in the black coating deposited near the weld, even though Mg was a small fraction of the overall alloy………

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.

…….Laser welding of magnesium did not appear to increase the oxygen level in the weld above 50 ppm which was the detectabiltiy limit of the Leco technique…….

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. …. Chemical analysis of the weld beads revealed changes in the metallic composition but no increase in the oxygen content. Due to the low boiling points and high vapor pressures of magnesium and zinc, these elements were preferentially evaporated during welding……..

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. (Ivan Griffin pp. 15)……. A sound weld is defined here as a full penetration weld with no significant cracks or porosity and good weld surface quality……..

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 ...