Keyhole welding

A big plus of Laserline's diode lasers at keyhole welding is the calm molten pool that minimizes the amount of metal splashes on the workpiece and laser optic which leads to smoother and cleaner welding seams.

Besides the aluminum welding or the joining of tailored blanks, applications for welding thick steel with a laser power of 50 kW are also realized.

Keyhole welding - the method

With keyhole laser welding, the material is processed with very high beam intensities. Different to heat conduction welding, here a metal vapor is created additionally to the metal melt that partially displaces the melt, thereby leading to the creation of a vapor capillary (keyhole). This also applies for welding thick steel. The keyhole welding technique is characterized by a high process speed. The heat-affected zone is always limited, hence material distortion is accordingly low. What remains is a narrow, evenly structured welding seam with a depth-gauge that is often bigger than its width.

The advantages of a diode laser using the keyhole welding technique

A big plus of Laserline's diode lasers is the calm molten pool that minimizes the amount of metal splashes on the workpiece and laser optic which leads to smoother and cleaner welding seams. With a protection class of IP54, the lasers guarantee, even without protecting enclosures, process stability in tough application environments. Their high electrical efficiency of up to 50 percent and the robust technology make Laserline’s systems a reliable and very economical tool for keyhole welding. Designed for more than 30,000 operation hours, they are also very durable with low maintenance effort.

Application examples

Welding thick sheets with 50 kW laser power

Processes for welding sheets with thicknesses between 10 mm and 25 mm are becoming increasingly popular for different industrial applications. For the laser-based process, the seam preparation currently poses a key challenge in this area. Variable gap dimensions are often unavoidable and must be bridged reliably and efficiently. With 50 kW laser power and spot sizes of up to 4 mm, with its LDF high-power diode lasers, Laserline offers a suitable system solution for these applications.

Journal

About welding thick metal sheets

To date, whoever wants to weld thick-walled metal sheets has to put up with long processes, not to mention annoying material distortions. Keyhole welding with fiber-coupled high power diode lasers from Laserline save time and costs.

In a German expression, ”drilling of thick planks” has long since become a popular metaphor for persistence. Rarely mentioned is the welding of thick metal sheets even though persistence is also required for this, at least when established methods are used. But users know this all too well, especially those who decide to use submerged-arc welding (SAW) or metal active gas (MAG) welding. For example, to join the thick steel walls of ships with butt-joint using both methods, a welding seam preparation must be made, and when using the typical laser MAG hybrid technique, multilayers have to be welded. This takes time. When the sheets are thicker than 20 millimeters, often there is no other way than to weld them from two sides or to use a backing technique. It does not get any quicker and the next time-eater is waiting already, and this is because the high-heat input of the conventional welding methods leaves its traces. It influences the steel structures of the sheets beyond the seam area and can lead to a distortion in the components. This requires intensive post processing.

Now, seams created by MAG or SAW welding are undoubtedly very solid and can also tolerate a suboptimal seam preparation. In practice, they have proven themselves over many years. However, this does not mean that we cannot do it better, because the comparatively slow processes and material distortions that must be accepted at MAG welding pose an economic challenge. And this does not apply only to ship construction, because the task of welding thick sheets is also given in other areas, as, for example, in pipe systems for oil and natural gas pipelines or at the foundations of off-shore wind turbines.

On each of these application fields, one question keeps presenting itself: how can the welding processes be made more efficient and thus more economical?

Aluminum welding

Aluminum claddings that are mounted in a visible area require smooth and optically appealing welding seams. Here, Laserline's diode lasers achieve excellent results, as the created joints are uniform in shape and require no post-processing. Always requiring filler material out of aluminum silicon (ALSi), with which hot cracks can be avoided, these can be applied during the welding process with Laserline's diode lasers in one of two ways: either over a tactile process optic or with triple spot method using a supplementary wire that was developed by Laserline. In this method, there are two side-spots positioned in front of the main spot, which first ablate the coating at the edge of the wire melting zone. Because of this preparatory work, the result is a controlled melting process without material transfer to adjacent areas.

In close collaboration with Audi and other plant suppliers, triennial process investigations were conducted and diode laser requirements for aluminum welding were defined.