Welding the way you want

Joining coils is part of the steel industry's day-to-day business. For machines to work continuously, coil welding machines positioned at the beginning of the rolling mill connect the tail end of one coil to the beginning of the next, creating an endless ribbon. Yet not all steel is the same: the official Register of European Steels lists over 2,300 varieties.

This is a challenge for coil welding machines, because while some steel is best joined using laser welding, others do better with resistance welding. With this in mind, Belgian company Malex S.A. has developed a new kind of machine that can switch flexibly back and forth between the two methods depending on the kind of steel. The machine is specially designed for cold rolled coils with a thickness of 0.2 to 3 millimeters and a width of up to 1,600 millimeters.
"Laser welding has come to dominate in many areas, but resistance welding is still the most widely used. Our goal was to unite the two methods in one hybrid machine and also use the laser for weld preparation," company manager Alex Quaranta explains.

World premiere

The prototype of the machine, dubbed HybWeldCut, is standing in one of Malex's halls at the company headquarters in Charleroi, Belgium. For years now, the company has been recognized as an expert on coil joining solutions. In collaboration with Belgium's CEWAC (Wal loon Research Centre for Assembly and Control of Materials), Malex engineers developed the machine as part of an EU project designed to assist small and medium-sized enterprises on machining topics.

After all, no machine like this has ever existed before. As its name makes clear, the machine combines resistance and laser welding methods in one hybrid machine, and also cuts the coil ends in preparation for welding.

Just a laser source

Until now, if the steel industry used a laser for joining coils, then the CO2 laser was the laser of choice. But the HybWeldCut employs a solid state laser.

"It is far more efficient because metal can absorb it much more easily," explains Quaranta. "Unlike the CO2 laser, the beam of the solid-state laser can be easily transported via fiber optic cable, even over longer distances, and distributed to different work optics. Fiber optic cable also makes it easier to control the laser light, thus permitting more flexibility for welding.

The HybWeld Cut employs a TRUMPF TruDisk Laser, which offers a total of six outgoing lines for various applications. Using one to supply the welding optics and two to supply the cutting heads, the HybWeldCut uses three in total. The user can switch easily back and forth between the two techniques. The solid-state laser offers still another advantage: Malex devised the machine in such a way that even an existing resistance welding system can be retrofitted with the laser cutting and welding technology. "That would be almost impossible with a CO2 laser because of the beam guide with mirrors," explains Quaranta.

Everything in one go

In practice, it works like this: the coils are fed into the machine, and two laser cutting beams cut both coil ends in parallel. Depending on the type and thickness of the steel, the machine then joins the coils together using laser welding or resistance welding. If the operator selects laser welding, the TruDisk laser changes over in milliseconds from the outgoing lines for cutting to the fiber optic cable for the welding optic. In total, the combined cutting and welding process takes less than 30 seconds.

Quaranta believes he has another ace up his sleeve with resistance welding. "Resistance welding equipment can also be used to anneal steel, so for certain kinds of steel, we can avoid the self-quenching process you have with laser welding," Quaranta explains. Malex has patented the clever combination of techniques and it is ready for use.