Fraunhofer IWS develops laser-joining of low mass structures for manufacturing

03 Apr 2023

“Sandwich plating” offers tech and green potential for ships, railways and factories.

Making lightweight panels faster and cheaper than by conventional methods.

Modern lightweight construction has already been helping automotive and aerospace industry to save fuel and materials and to reduce environmental impact. Researchers at the Fraunhofer Institute for Material and Beam Technology (IWS) have recently found a way to transfer such proven design principles to other industries.

By using lasers, they weld filigree hollow chamber structures with cover sheets to form lightweight sandwich panels. Such metal structures can be produced particularly efficiently in the roll-to-roll process of the IWS. The new technology ensures higher production speeds and a wider range of uses for lightweight panels. This opens up new lightweight construction perspectives, as in the construction of ship superstructures, railroads and factory buildings.

The laser-based “sandwich plating” method offers a lot of technological, economic as well as ecological potential for industry, “With this technology, lightweight panels and profiles can be produced significantly faster and more cost-efficiently than with conventional methods,” said Andrea Berger, researcher at the IWS. “In addition, the new process eliminates the need for adhesives and other additional materials. This facilitates the recycling of the lightweight structures produced with it.”

Sandwich plates are used in lightweight construction instead of solid steel plates.

Instead of centimeter-thick heavy steel plates, many lightweight builders often use hollow sandwich plates. Despite their significantly lower weight compared with solid steel, these are strong enough for partition walls and ceilings in vehicles, aircraft or halls. Typical starting materials are thin steel, aluminum, or plastics. On these inner structures, manufacturers weld or glue thin sheets on both sides.

Classical extrusion at the limit

A large wagon manufacturing company from Saxony approached IWS with a challenge, which started the new laser rolling process: The manufacturer was already using lightweight aluminum profiles for its vehicle technology.

However, the applied extrusion process did not allow for arbitrarily thin inner webs. Approximately 1.5 mm constituted the technological lower limit. This was and still is opposed by the desire to save as much material and weight as possible or to use filigree internal structures.

The IWS researchers solved this problem with a laser welding rolling mill. Using this system, they guide a flexible core layer of light internal structures between two rollers, over which a cover sheet rolls at both top and bottom. Scanner-controlled lasers are directed obliquely from both sides precisely into the thin gap between the core layer and the cover sheet.

How laser-based sandwich cladding works. Click for info.

There they heat the metal surfaces with pinpoint accuracy. Depending on the sheet material selected, local temperatures of between 660 and 1400 deg C are generated. The rolls then press the slightly melted surfaces of core layer and cover sheet together so firmly that they bond permanently.

Green laser processing

Such particularly lightweight sheets can be produced in a single pass using a rolling process. Compared with conventional methods such as extrusion at high temperatures, laser welding saves a significant amount of energy because the energy-rich light only has to melt the metal surfaces locally to a wafer-thin thickness. It also suits low-cost mass production.

Even the laboratory prototype achieves a high production speed. Developed to industrial scale, such systems could produce more than ten meters of lightweight sheet per minute, estimates Andrea Berger. In addition, such machines can be quickly converted to new profile or sheet structures.