Having clarified at the start of our small series what exactly a diode laser is, today we look at the application fields. These are, as already mentioned, broadly diversified even though there are certain key areas in which diode lasers can clearly attract attention. One of them is the metal welding process. Diode lasers play a decisive role in various industrial areas, from the wafer-thin electric contact-sheet to the centimeter-thick side of ships made of steel and countless metal components joined by welding. Today, diode lasers cover a complete array of joining spectrum and offer suitable tools for different welding applications. Compared to classic arc welding methods like MIG/MAG or WIG welding as well as other laser-based welding techniques, welding with diode lasers is often superior.
In fact, diode lasers are actually meant for industrial welding processes. This are several reasons for it. First, the combination of high power output and comfortable spot sizes allows for an optimal gap bridgeability. Second, the energetic homogeneity of the spot and the high absorption capacity of a typical wavelength mix generate unusual calm melt pools that leave almost no impurities by spatters or wavelets at the adjoining areas of the seams. This guarantees excellent seam qualities. Third, diode lasers provide the highest energy efficiency of any industry lasers, which also qualifies them along with their low maintenance costs – for welding in series production. Fourth, with these lasers, heat conduction as well as keyhole welding applications can be executed.
Using components with medium to substantial material thicknesses, keyhole welding is a typical laser welding method. The joining partners are irradiated with high intensity so that a vapor capillary is created in the direction of the beam - a tube-like one with a metal vapor filled hollow (keyhole). Thus, the material is molten up to the deeper layers; the depth of the melt zone is usually higher than its width. The inner walls of the vapor capillary also reflect the laser beam so that the absorption of the yielded energy is strengthened, thereby causing a sizable melting volume. Between the joining partners, highly stable connections are created that withstand even the most demanding stress. Typical applications are, for example, the joining of tailored blanks in the automotive assembly or thick-sheet welding. As combined diode laser systems today can reach powers of up to 60 kW, even ships’ sides of 50 mm thickness made of massive steel braces in foundations or offshore wind turbines can all be welded with only two welding runs (layer and opposite side).
When workpieces of a low material thickness have to be joined, keyhole welding is no longer automatically suitable. The high energy input could cause material separations instead of joining, but definitely with heavy deformations. Thus, in such cases, heat conduction welding is almost always used. With its welding penetration depth at a maximum of 2 to 3 millimeters, the method is also suitable for thin sheets or metal foils. The diode laser fuses the joining partners along the planned seam; the melts merge and then solidify towards the desired weld seam. The material distortion is low, while the joining is totally uncomplicated and clearly quicker than WIG-welding, for example. Because of the homogeneous and even heat exposure of the diode laser, the seams are smooth and non-porous and do rarely need post-processing. This high seam quality makes the method especially for visible areas interesting, as, for example, in the joining of metallic sinks. Besides, it has also proven itself quite apart from design-related spheres, even at geometrically very demanding components such as gaiters for pipes.
With the development of the LDMblue, a laser with 450 nm and hence the blue light wavelength, meanwhile even the world’s first high-power diode laser is now available, which allows for a controlled spatter-free heat conduction welding of very thin non-ferrous components made of copper or precious metals such as gold. Here, with the classical infrared lasers, heat conduction welding is not feasible due to the infrared radiation being strongly reflected by non-ferrous metals, such that the surface can only be molten with a high-intensity beam. However, blue laser light is very well absorbed by non-ferrous metals so that the workpieces can be molten with clear lower energy input as well. In this, even wafer-thin electrical contacts made of copper, e.g. those used in electromobility, can be reliably joined. Here as well, very smooth and visually pleasing seams are created that can additionally prove themselves with their excellent electrical conductivity.
You see: for metal welding, the diode laser is a real universal tool that has no equal. And because work will continue on optimizing the relation between laser power and beam quality on all types of diode lasers, the spectrum of application fields in welding will probably grow.