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Experience shows that each laser welding application is unique

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onsdag 31. oktober 2012

Laser welding has been used for decades in serial productions of small components. Experience shows that not only component tolerances and fixtures are critical. The right choice of raw materials can also be crucial. But once the setup works it can be repeated perfectly millions of times.

By Kent Krøyer
Laser welding is common practice in many industrial productions, small as well as regular mass productions. Plastics as well as numerous metals are joined using lasers all over the world.

“Almost all of the automobile industry has been using lasers for many years. The German shipyard Meyer Werft is using them for 20m by 20m deck-sections in cruise ships. The plate thickness is at least 6-8 mm. The main reasons for using lasers at Meyer Werft are an increased speed and most of all a better quality in terms of less deformation,” says project manager Michel Honoré of Force Technology, Denmark.

Offhand he can mention several other companies which use laser welding – Siemens Flow Instruments, Broen and a cooperation between Volvo Aero Corporation and Force Technology, producing exhaust nozzles for rockets. There are numerous examples.

Manual laser welding The laser beam is invisible and comes from above. The blue flexible tube supplies shielding gas and the operator supplies filler wire to the hot melt. Photo: iStockphoto

A rule of thumb for small applications
The international pump manufacturer Grundfos has a long history of laser welding. The first laser-welded component was made in 1995 and new applications have been added regularly. Today more than 25 lasers are joining various metal objects in serial productions. The penetration depth is 2 mm maximum but some of the weldings are quite advanced, e.g. joining of rounded and bended objects.

“The challenge is to secure sufficient precision, not only in the fixtures but also in the objects to be welded. My rule of thumb is that the welded gap cannot be wider than 10 percent of the minimal plate thickness,” says senior engineer Jens Vestergaard Boll, who is responsible for welding processes at Grundfos.

This rule of thumb is particular demanding as some objects have plate thicknesses of merely 0.15 mm meaning that welding is only possible if strict tolerances are met. This does not deter Grundfos however.

“We are always looking for new welding technologies that offer new product opportunities or improve our ability to compete,” he says.

30 years of experience
Another long time user of laser welding technology is Danfoss, the international producer of valves, industrial automation and energy technologies.

“We were one of the first companies to begin using laser welding more than 30 years ago. We took this step because it gave us new opportunities in production,“ says engineering adviser Birthe Nørgaard Laursen.

The goal was to use a laser in an automatized serial production of a million valves per year. A small capillary tube had to be welded to a hole in a plate. The geometry was unique, but the limited heat from a laser welding made this technology optimal for the purpose.

Another product made use of a small membrane that had to be mounted without any damage. The laser technology did it in a very delicate and uniform way.

“It is very important to choose the right equipment from the beginning to make the product competitive with a superior quality and at the right price,” she says.

The very first attempts with laser welding gave problems with cracks, she remembers. This was solved through a PhD project that shed light on the causes. The solution was to use a specific type of stainless steel, pointing to the close interrelation between production technologies and materials selection.

A general challenge for laser welding is the high cooling rate that causes solidification to occur faster than alternative techniques. Another characteristic is minimal roughness on the surface which may be important in some applications.

At present Danfoss has around 10 laser welding units at different international manufacturing sites.

“We keep an eye on the development of new laser types. Our engineers always have laser solutions in mind as they develop new products,” she says.

An inexpensive shortcut to laser welding
Many companies which could benefit from laser welding technology are hesitating despite the possible advantages. One serious drawback could be the large investment, but there are shortcuts to overcome this.

“Laser cutting is being used in general. It is in fact very common. An economic shortcut is that the laser cutting equipment can relatively easily be converted into welding equipment by changing the cutting head to a welding head. Laser cutting production already has the necessary robotics and safety guards,” says Michel Honoré of Force Technology.

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