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Düsseldorf, September 18, 2019

X-Pro® laser welder for coil to coil joining of high strength steel

The welding machine is a crucial piece of equipment in strip processing lines to maximize production. Our specialists describe latest trends in welding technology as well as the X-Pro® laser welder which was developed for the production of hard-to-weld strip materials. Further advantages are the automatic welding parameter calculation, the quality assurance system, the low cycle time and the exchangeable laser sources.

Flexibility and productivity

In the entry section of strip processing lines, strips of different and partially difficult-to-weld steel grades have to be connected to form an endless strip in a short time. Old flash butt welding machines or conventional laser welding machines are not able to weld modern grades in a reliable manner, since the high alloying contents have an influence on the weld ability of the materials. Furthermore, welding machines in existing lines need to be replaced as spare parts and ‘in house expertise’ availability dwindles. Maintenance-friendly machines with high availabilities are required, which operate automatically and adaptively with desired production results.

SMS group reacted on this change process and also on the impact of digitization with this new developed welding machine. Several digital solutions are implemented to operate this machine in a simple manner. Machine features create a “today” with reduced operating and maintenance staff to perform preventive maintenance by means of long time archives recording all relevant data. The documentation of the machine is digitally available and interlinked.

Requirements

The welding machine is not only a crucial technological piece of equipment in every strip processing line, but also an entry cycle time factor and one key component for utilized and maximized production. If coils are not joined properly, the whole process will stop. Every strip break or machine stoppage has the potential to affect upstream and downstream operations resulting in significant financial implications.

The requirements to the weld seam and a reliable welding process are very high. The entire process is fully automated and the sequences to join both strip ends successfully are always the very same. What changes is the material to be welded in regards to steel quality, strip thickness, strip width and thickness from one coil to the other.

The welding process takes place every 3 to 5 minutes. In a pickling line/tandem cold mill the weld seam is bent numerous times with high tension (up to 65 tons), it travels more than 1,000 meters through the line with high speed (up to 1,200 m/min) and it eventually gets rolled and significantly reduced in thickness with high forces in five mill stands (up to 1,800 tons). Modern high-strength grades with high contents of alloying elements tend to create extreme hardness increases in the weld seam area. Induction pre- and post-heat treatment or even additional buffering wire during laser welding are mandatory for these high-tech steel grades to improve the ductility of the weld in order to allow successful production without any weld seam breakages during line run. Another major requirement of the machine is a low cycle time. Since the lines are producing continuously, the needed stops for welding have to be as short as possible.

Read the full technical paper