When employing the laser welding process, there are 2 distinct means or modes that energy can be transferred from the laser to the weld metal. Dependent upon the power density, a factor of the laser's power and the area of the weld, the laser welding mode can be either conduction mode or keyhole mode. You might already be somewhat knowledgeable with the keyhole mode as it's often used in manual welding operations. It should be emphasized that the precise type of welding mode that is occurring is influenced by the quantity of power that's being passed to the base material, and the attributes of the metal being welded. The main difference between these two types of laser welding modes is the quantity of energy transferred to the metal being welded. You may regard the the conduction mode as the lower energy density, while the keyhole mode implies a higher energy density. Remember though that the energy density is what defines the mode. And since the energy density is specified by the power divided by the cross-sectional area of the weld, shifting either the size of the weld or the weld input power can impact the type of welding mode. Conduction mode welding is a low power density weld that basically heats the surface of the material being welded. When the surface heats up it then conveys heat further into the metal. Since this type of welding is a low energy density weld, the size of the weld on the top is generally larger, and the depth of penetration of the weld is typically a great deal more shallow. As you move from a small to a large energy density weld, the type of mode shifts from the conduction mode to the keyhole mode weld. Because of the definition of energy density, this can be reached by either lessening the area of the weld, or raising the power of the laser beam. In the simplest of terms, keyhole mode welding burns a keyhole or hole in the material being welded, due to the higher energy concentration transmitted to the material. This void is shaped by the vaporization of the material. As the beam travels ahead, the liquid material fills in behind it, and the actual fusion zone stretches from the face of the material to the base. This is different than the conduction mode where merely the face is heated, and so the weld doesn't penetrate as deeply.
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When laser welding, the sort of weld - a high energy density weld or a low energy density energy weld, determines whether or not the mode will be the keyhole mode or the conduction mode.
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