The big weld

© Sigrid Rauchdobler

Weighing 20 tons and up to 200 millimeters thick. The sheets TRUMPF welds in Austria are the biggest ever tackled by a hybrid laser welding head from Fronius International GmbH. The TRUMPF plant in Austria uses a fully automatic process to produce huge frames for press brakes.

Ask people randomly what they associate with the word “sheet metal” and most people would probably respond with something like “baking sheet” or “fender”. Chances are they wouldn’t picture what Herbert Staufer, head of high-power welding at Fronius International, comes across every time he enters the production hall at TRUMPF Austria in Pasching. The steel sheets here are four meters long and so thick that the one on the bottom reaches to his ankle, measuring an impressive 200 millimeters. Staufer knows this material like the back of his hand — hardly surprising since Fronius is one of the leading suppliers of hybrid welding machines.

Safety-Cabin-for-hybrid-laser-welding-at-Trumpf-Austria

A fully welded frame in front of the “hall in a hall” where the welding machine does its work. Photo | Sigrid Rauchdobler

He generally visits Pasching as a customer, though he recently slipped into the supplier’s role for a project carried out jointly. His project partner and customer Thomas Reiter, who heads up sheet metal processing in Pasching, explains why they brought Staufer on board for the project. “We’re welding these sheets to make the frames for our press brakes, and that involves some very special welds indeed.” To show how it works, the two men leave the metal sheets behind and wander over to a gray wall. It resembles the windowless exterior wall of a production building, yet is clearly inside the hall. The TruDisk 8002 disk laser standing against the wall seems tiny in comparison.

320 tons of press force

Thick-sheet-to-build-maschine-frames-at-Trumpf

You need sheets this thick to build machine frames that can handle hundreds of tons of press force without any loss of precision. Photo | Sigrid Rauchdobler

On the other side of that wall, inside the enormous laser safety cabin, the hydraulic system lifts the 20 ton weight and tilts the clamped steel sheets to the correct angle. A portal moves into place above the apparatus and a robot arm descends, carrying the hybrid welding head. It slowly passes over the first seam welding points, using laser light to heat the material. Now it’s time for the fire-works to begin: the laser beam and the arc of the metal active gas (MAG) welding torch work together to weld the joint. These welds, which are up to eight millimeters deep, will eventually support loads stemming from up to 320 tons of press force. Over and over again, for the entire service life of the brake press.

The best of both worlds

TruDisk 8002

Due to its insensitivity to back reflections, the disk laser is the ideal laser tool for hybrid laser welding. For the compact fiber-guided TruDisk laser from TRUMPF, there are used energy-efficient diode lasers as the excitation source. After this, the disk results in a high beam quality. The TruDisk 8002 has a laser power of 8 kW.

Outside the cabin, Staufer and Reiter watch the process unfold on the monitor. “We used to send the frames out for welding — by hand !” That took an entire week, and we were determined to make things more efficient,” says Reiter. He immediately hit upon hybrid laser welding as a suitable solution. “The welding process is much quicker because you only need a single pass — instead of having to build it up bead by bead as you would in arc welding. We’re also able to use the laser to preheat the material, and quality assurance is much easier in this automated process.”

The welding process is much quicker because you only Need a single pass.

Thomas Reiter, Head of sheet metal processing at TRUMPF in Pasching

Outside the cabin, Staufer and Reiter watch the process unfold on the monitor. “We used to send the frames out for welding — by hand !” That took an entire week, and we were determined to make things more efficient,” says Reiter. He immediately hit upon hybrid laser welding as a suitable solution. “The welding process is much quicker because you only need a single pass — instead of having to build it up bead by bead as you would in arc welding. We’re also able to use the laser to preheat the material, and quality assurance is much easier in this automated process.”

The courage to change depth

The welding head developed by Fronius International | Photo: Sigrid Rauchdobler

The welding head developed by Fronius International | Photo: Sigrid Rauchdobler

Rewind two years to see Reiter and Staufer sitting in the Fronius development laboratory, a place where they spent a lot of time during that period. They are baffled by a series of micrographs showing a weld root showing numerous fine fissures and defects, making the seam unusable. And they had been so confident: “With eight kilowatts of laser power, we were easily penetrating 12 millimeters into the material. But down in the keyhole we had absolutely no control over the process,” Staufer recalls. The type of fissure suggested that the issue was preheating. “But no matter how much we varied the temperatures — and we had plenty of control for that parameter using the laser as a preheating tool — the fissuring didn’t change one bit.” Plan B was looking like the only alternative. But then in one of their meetings they hit on the idea of turning their welding strategy on its head, “maybe because we were so close to forsaking Plan A anyway,” says Reiter with a chuckle. “We asked ourselves: Do we really need such a deep weld seam to create a perfectly stable joint ?” he recalls. So Staufer and his team of laser experts at Fronius gradually began to reduce the weld depth. And when they got to 10 millimeters they were finally able to relax — the quality of the seam was improving continuously. “We finally got ideal welding results at eight millimeters,” says Staufer.

In the balance

A freshly made fillet weld, approximately eight millimeters deep. Photo | Sigrid Rauchdobler

A freshly made fillet weld, approximately eight millimeters deep. Photo | Sigrid Rauchdobler

With this partial victory in the bag, the project team could finally turn to the next problem. “To achieve the optimum welding process, you need the laser light to hit the material at the right angle,” says Staufer. “But the robot wasn’t maneuverable enough to reach every single weld point.” Luckily, Staufer knew exactly who to turn to. Raimund Geh relishes this type of challenge. His company, Femitec GmbH in Gersthofen near Augsburg, specializes in designing welding systems. He explains how he approached the problem: “If the robot arm with the laser hybrid welding head couldn’t reach the welding point, then we would simply have to take the part to the welding head.” The result was a tilting table with clamps to secure the part. “We were sure that this would let us weld in the downhand position.“ Geh and his team developed a complex simulation to test their theory — but the next step was to put it into practice.

 

It’s a clamping fixture on a tilting machine table — it’s just a bit bigger than usual.

Otwin Kleinschmidt, head of project management

Yaskawa Europe — a leading manufacturer in the fields of drive technology, industrial automation and robotics — was the company chosen to transform their vision into reality. Otwin Kleinschmidt, head of project management, tilts the palm of his hand to the crucial 45 degree angle and says: “In principle it’s pretty straightforward. It’s a clamping fixture on a tilting machine table — it’s just a bit bigger than usual,” he says with a grin. The first challenge the team ran up against was how to design a hydraulic system able to hold a part weighing several tons solidly in position, at precision down to the millimeter. “That’s what makes it possible for the welding robot to stay exactly on the welding path,” Kleinschmidt explains. The other challenge was how to harmonize the movements of the robot and the portal. But after four months of work everything was finally in place.

Thomas Reiter from TRUMPF (l.) and Herbert Staufer from Fronius International in Pasching. Photo | Sigrid Rauchdobler

Thomas Reiter from TRUMPF (l.) and Herbert Staufer from Fronius International in Pasching. Photo | Sigrid Rauchdobler

Frame by frame

Fronius

Headquartered in Austria, the company employs more than 3,300 people. It specializes in technologies and concepts to monitor and control energy, focusing in particular on welding technology, battery charging systems, and solar electronics.

Back in the shop in Pasching, Staufer and Reiter are once again strolling from one machine to another. In front of them the parts are waiting on pallets, and a crane is helping a production worker to position the sheets on the setup table. It takes two hours to get everything exactly in place. That sounds like a lot. But bearing in mind the parts he’s dealing with, it’s an extremely quick solution. Next, the table moves along rails into the laser safety cabin.

Once the welding robot is also on track, the worker moves to the other side of the safety cabin and starts clamping the next machine frame onto the second setup table. “Using this system, we can weld more than 20 machine frames a week,” says Reiter. And Staufer is equally pleased: “We’ve already been able to use the welding process for a different order.”

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