Laser welding Joining sandwich structures and sheets using laser

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Researchers from the Fraunhofer Institute IWS have developed a laser process that welds delicate hollow chamber structures with cover sheets into lightweight sandwich panels.

Modern lightweight construction has long been helping in the automotive and aircraft industries to save fuel and material and to reduce environmental impact. Instead of heavy steel plates, many engineers often use sandwich panels. Despite their significantly lower weight compared to solid steel, these are durable enough for partitions and ceilings in vehicles, aircraft, or halls.

Such sandwich panels and profiles consist of honeycomb-, trapezoidal-, web-, or spherical-like hollow chamber structures. Typical starting materials are thin steel, aluminum, plastics, or other materials. Manufacturers weld or glue thin sheets onto these inner structures on both sides.

Traditional extrusion reaches its limits

A railway wagon construction company has used lightweight aluminum profiles for its vehicle technology. Until now, the extrusion process has been used for this purpose. Disadvantage: It does not allow for arbitrarily thin inner webs. About 1.5 millimeters were considered the technological lower limit. Faced with this challenge, the company approached the Fraunhofer IWS. The request: to save as much material and weight as possible and to use delicate inner structures.

This technology allows the production of lightweight panels and profiles much faster and more cost-effectively than with conventional methods such as extrusion.

Andrea Berger, researcher at Fraunhofer IWS

The employees of the Fraunhofer IWS solved this challenge with a laser welding roller machine. Through this machine, they guide a flexible core layer made of very lightweight inner structures between two rollers, over which a cover sheet unrolls on the top and bottom. Scanner-controlled lasers aim obliquely from both sides into the thin gap between the core layer and the cover sheet.

There, they heat the metal surfaces with pinpoint accuracy. Depending on the chosen sheet material, temperatures locally reach between 660 and over 1,400 degrees Celsius. The rollers then press the slightly molten surfaces of the core layer and cover so firmly together that they permanently bond.

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The new, laser-based "sandwich plating" offers significant technological, economic, and ecological potential for the industry, emphasize the researchers: "With this technology, lightweight panels and profiles can be produced much faster and more cost-effectively than with conventional methods such as extrusion," says Andrea Berger, researcher at Fraunhofer IWS. "Moreover, the new process does not require adhesives and other additional materials. This facilitates the recycling of the lightweight structures produced with it."

Laser process reduces energy consumption and facilitates recycling

Such particularly lightweight panels can be produced in a continuous process using the rolling method. Compared to traditional methods such as extrusion at high temperatures, laser welding saves a lot of energy, as the high-energy light only needs to melt the metal surfaces locally and very thinly.

It is also suitable for cost-effective mass production. Even the laboratory prototype achieves a high production speed. "Developed to an industrial scale, such facilities could produce more than ten running meters of lightweight sheet metal per minute," estimates Andrea Berger. Moreover, such machines can be quickly retooled for new profile or plate structures.

In contrast, extrusion requires a different tool for each application when the customer orders a new plate model. The laser sandwich plating also allows for the production of stable structures that are only a few tenths of a millimeter thin. This mitigates, for example, the mentioned dilemma in wagon construction.

This broader application of lightweight construction:

• reduces material consumption in the supply industry

• can reduce the weight of vehicles, aircraft, and ships and

• save fossil fuels or electricity

Another ecological benefit arises at the end of the component lifecycle: Laser-joined sandwich panels contain neither adhesive nor solder or other foreign substances that would have to be laboriously separated later in recycling plants.

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Applications in vehicle construction foreseeable

Marko Seifert, head of the Heat Treatment and Coating department at Fraunhofer IWS, sees suppliers for shipyards and vehicle manufacturers as possible early adopters of the new process. First application scenarios could be, for example, lightweight stairs or ship partitions, in which, thanks to the hollow inner structures of the panels, power cables can be laid invisibly.

The new technology could also quickly establish itself for truck trailers and hall construction. For the next steps, the Fraunhofer researchers are looking for partners to bring the idea into application.