Article updated on 25 January 2021.
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Laser welding can be used to fuse metals or thermoplastics. Because it's such a concentrated heat source, a laser beam can weld thin materials at relatively high speeds, at rates of several meters per minute. To fuse thicker materials, laser beam welding can generate thin, deep welds.
Laser beam welding is primarily used for its high welding speeds, small seams, and relatively low amount of unwanted thermal distortion to the final product. Add in automated operation and the capacity to control a laser over an internet connection, and it's easy to see why laser welding has become a standard process in industrial fabrication today.
Laser welding has two fundamental modes; conduction-limited welding and keyhole welding, with mode depending largely on the power density across the laser beam.
Performed at lower power densities, conduction-limited welding involves the laser beam energy being absorbed solely at the target materials' exterior. This mode produces welds with a high width-to-depth ratio.
Typically done at greater power densities, keyhole welding involves concentrating a laser beam on a spot small enough to cause the materials at the target spot to melt, and then vaporize. The energy of the focused laser beam penetrates deep into the work surface(s), creating a cavity known as a 'keyhole' that is subsequently filled with metal vapor. In some cases, this vapor can ionize to create a plasma. This vapor (or plasma) expands and, in doing so, prevents the collapse of the keyhole's molten walls.
A deep weld can then be created by passing the keyhole-forming laser beam down the gap meant to be fused. Due to surface tension, some molten source material at the keyhole's front edge flows around the back of the cavity, where it cools and solidifies. This creates a weld cap with a chevron design that points towards the origin point of the process. This mode results on welds with a high depth-to-width ratio.
As with any fusion welding process, laser beam welding can contain defects, especially when done with steel. Without suitable preparation of source materials and the right welding parameters, some defects become more likely such as cracks, pores and general weakness.
The welding speed and weld shape are also critical factors. High welding speeds tend to create deep, narrow welds, with a single central boundary, while lower speeds lead to a broader, shallower weld, which may have a stronger, intricate solidification structure in place. The weld shape can be affected by raising heat and/or using a laser beam with a bigger focus diameter, both of which can broaden the weld.
Applications
Laser beam welding can be used for a wide range of applications, including for spot/seam welding, deposit welding, and scanner welding.
Laser welding can create spot welds with sub-millimeter diameters and a long weld seam just a few millimeters in width. As noted previously, these welds can be done at high speeds, making laser beam welding a highly efficient fusion welding process.
Deposit welding involves a filler material in the form of a powder or wire being melted and used to fuse a joint. This process allows for small-scale repairs and modifications with weld diameters as small as 0.1 mm. Using a powder source material, deposit welding can put down a protective metallic layer to guard against corrosion and wear. Compared to spot/seam welding, deposit welding produces a much smaller thermal load on the target materials.
Scanner welding is a welding process that avoids having to move either the laser device or the workpiece. This process involves a laser beam being directed via a rotating mirror(s), with the beam being guided by adjusting the angle of the mirror(s). This welding process can be used for two-dimensional and three-dimensional welding. The angular versatility of the system also means a much faster processing speed for three-dimensional welding jobs.
Sources and Further Reading
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