When using the laser welding process, there are two different ways or modes that energy can be transferred from the laser to the weld material. Depending on the power density, which is a factor of the laser’s power and the area of the weld, the laser welding mode can be either the conduction mode or the keyhole mode. You may be already somewhat familiar with the keyhole mode as it’s often used in manual welding processes. It should be stressed that the type of welding mode that is occurring is determined by the amount of power that’s being transferred to the base material, and the properties of the material being welded.

The main difference between these two laser welding modes is the amount of energy that is transferred to the metal. You can think of the conduction mode as the lower energy density, while the keyhole mode involves a higher energy density. Keep in mind though that the energy density is what most influences the mode. And since the energy density is defined by the power divided by the cross-sectional area of the weld, changing either the size of the weld or the power of the laser beam can affect the type of welding mode.

Conduction mode welding is a low energy density weld that basically heats the surface of the material being welded. Once the surface heats up it then conducts heat deeper into the material. Since this mode of welding is a low energy density weld, the size of the weld on the surface is generally larger, and the depth of penetration of the weld is generally much more shallow.

As you move from a low energy density weld to a high energy density weld, the type of mode changes from the conduction mode weld to the keyhole mode weld. Again, referring to the definition of energy density, this can be achieved by either decreasing the size of the weld, or increasing the power of the laser beam. In the simplest of terms, keyhole mode welding melts a keyhole or hole in the material being welded, due to the higher energy density delivered to the material. This hole is formed by the vaporizing the metal. As the beam moves forward, the molten metal fills in behind it, and the actual fusion zone reaches from the face of the material to the bottom. This is unlike the conduction mode where only the face is heated, and therefore the weld doesn’t penetrate as deeply.