Perfect welding wire

© Angelika Grossmann / Gernot Walter

Solid or powder filled, open type or laser welded. The comany Bühler Würz Kaltwalztechnik sees a huge market for welding wires.

It holds the world together and yet remains completely inconspicuous. Welding wire comes in countless variations and combinations. It comes as either solid wire or powder filled, and the latter is becoming increasingly popular among welders. It’s impossible to assess the global market. But one thing is certain: the market is big, and getting bigger.

“It’s very hard to say exactly how much powder core welding wire is even used each year,” says Stefan Nixdorf, Managing Director at Bühler Würz Kaltwalztechnik GmbH in Pforzheim, Germany. “Estimates start at a million tons a year.” And the goal is for his production machinery for laser-welded, coldrolled wire to secure a decent slice of that pie.

Open-type welding wires come with one major disadvantage

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Stefan Nixdorf, Managing Director at Bühler Würz Kaltwalztechnik GmbH

Stefan Nixdorf, Geschäftsführer Bühler Würz Kaltwalztechnik GmbH

Currently, the market is still dominated by open-type welding wire, which works fine but has one major disadvantage: the longitudinal seam is closed, but not sealed. Because the edges are simply overlapped or pressed together during forming to encase the powder in the hollow wire, over time the surrounding air makes its way in, which allows the powder to absorb the hydrogen in the air. This causes the quality to deteriorate, and can cause the wire to become unusable.

What’s more, open-type wire can withstand only minimal torsion stress. The wires twist in the feed, which in turn jeopardizes process reliability in automated applications such as the robotic welding lines in the automotive industry.

We require very good and constant penetration — to almost 100 percent of the wall thickness, but without scorching the thin sheet, which would destroy the powder,” 

The way to completely seal the seam

4 steps from sheet to coil

Click once and have a look at the whole machine.

  1. Ribbons of steel are turned into powder – filled, laser-welded tubes with custom mixtures.
  2. With a diameter of 12 millimeters and a wall thickness of 2 millimeters, it is fed into the cold rolling mill.
  3. Afterwards: at 1.2 millimeters on through the drawing die – the weld takes it all in stride.
  4. Now onto the coil, and the torsion-free welding wire with its perfectly straight, gastight seam is finished.

“There has to be another solution,” thought Stefan Nixdorf. And so he looked for a way to completely seal the seam in a torsion-free wire. Tungsten inert gas (TIG) welding was out — it is simply too slow. High-frequency welding failed too. “The powder should have the highest possible percentage of metal particles,” says Nixdorf, “and high-frequency welding would draw the particles back out magnetically.”

In the end, the laser was most persuasive — it is faster than TIG welding by a factor of two to three, it doesn’t affect the metal particles in the powder, and it produces a weld seam that can reliably withstand the enormous stresses in later processing steps.

And so the laser joined the production lines. The wire-making process is continuous. It begins with two-millimeter-thick ribbons of non-alloy, low-carbon steel. These are formed in the plant’s tube shaper into a trough and filled with metal powder. Then the trough is closed to form a cylinder just 12 millimeters in diameter. The wire-to-be is then worked by a beam guide — the TRUMPF TruLaser Cell 1100. Fully integrated into the line, it welds the longitudinal seam. The weld depth is critical: “We require very good and constant penetration — to almost 100 percent of the wall thickness, but without scorching the thin sheet, which would destroy the powder,” explains Nixdorf. With a laser, that doesn’t happen.

The ideal dose of laser

Welded gastight, the wire continues on to the rolling mill and is passed through a drawing die. In a single step, the rolls reduce the diameter to 1.2 millimeters. “And that’s the key advantage of our core technology, cold rolling,” Nixdorf emphasizes.

“Typically, an intermediate annealing step is required beyond a certain degree of reduction, but we don’t need that.” This saves customers an extremely energy-intensive process and gives them torsion-free wire with perfectly straight seams and a gastight seal.

That’s how sheet metal becomes a flux-cored welding wire. (Video: Bühler Würz Kaltwalztechnik.)

Faster welding process due to the variable proportion of powder

Nixdorf knows his machines won’t be used to produce cheap, mass-market wire. “Our technology pays off only for very high-quality wire. But with demand for welding wire amounting to a million tons worldwide, if ten percent of that is powder-filled and laser welded in the future, then that’s still 100,000 tons a year,” calculates Nixdorf. He’s confident that’s how it will work out, too.

This is particularly important when it comes to special alloys. Customers generally don’t need five tons. More likely, they need 100 kilograms,”

Bühler Würz Kaltwalztechnik

in Pforzheim, Germany, employs more than 100 people. They produce state-of-the-art cold rolling mills, as for example reduction, flat, profile and strip rolling mills and also complete production lines as well as FCW plants.

An added advantage is that laser-welded wire can be stored indefinitely without any quality losses, even under the harshest conditions, like those found in the shipbuilding industry. Wire manufacturers can also use the production line to tailor the composition of the power, making it economical to produce even small batches.

It’s even easy to vary the fill rates and consequently the proportion of powder in the wire. “The more powder there is, the thinner the sheet metal strip. This makes for an increase in current density and that lets the end user weld faster.” Working time is reduced — providing Nixdorf with yet another argument with which to win the welding wire market for his machinery.

Kontakt:

Bühler Würz Kaltwalztechnik
Stefan Nixdorf,
Telephone: +49 7231 7755-527
E-mail: nixdorf@buehler-wuerz.de

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