The Fraunhofer Institute uses lasers to weld the filament empty ventricle structure to the cover plate to form a lightweight sandwich plate

Modern lightweight structures have long helped save fuel and materials and reduce the environmental burden of automotive engineering and the aircraft industry. Researchers at the Fraunhofer Institute for Materials and Beam Technology, IWS, have now found a way to transfer this proven design principle to other industries.

To do this, they used lasers to weld the filament empty ventricle structure to the cover plate to form a lightweight sandwich plate. These metal structures can be produced particularly efficiently using the roll-to-roll process of the Fraunhofer IWS. Innovative technologies ensure higher production rates and a wider range of applications for lightweight panels. This opens up the perspective of lightweight structures, such as those used to build ship superstructures, railways and factory halls.

The new laser-based "sandwich cladding" offers great technical, economic and ecological potential for industry: "With this technology, lightweight sheets and profiles can be produced faster and more cost effective than traditional methods such as extrusion," stresses Fraunhofer IWS researcher Andrea Berger. In addition, the new process does not require adhesives or other additives. This helps to recycle the lightweight structures produced from it.

Many lightweight manufacturers often use sandwich plates instead of heavy, centimeter-thick steel plates. Although significantly lighter in weight than solid steel, they are flexible enough to be used in partitions and ceilings in vehicles, aircraft or hangars. The sandwich plates and profiles consist of honeycomb, trapezoid, web or spherical hollow ventricle structures. Typical starting materials are thin steel, aluminum, plastic, or other materials. The manufacturer welds or bonds thin sheets to the sides of these internal structures.

Classical extrusion reaches its limit

The starting point for the new laser rolling process was a challenge approached by Fraunhofer IWS, a large truck manufacturing company that already uses lightweight aluminum profiles in its vehicle technology. However, the extrusion process used does not allow for arbitrarily thin inner rods. About 1.5 mm is considered the lower limit of technical determination. On the other hand, there was and still is a desire to save as much material and weight as possible or to use the internal structure of filaments.

Researchers at Fraunhofer IWS solved this challenge with a laser welding machine. Through the system, they guide a flexible core layer with a very light internal structure between two rollers, with the cover plate rolling off at the top and bottom. Scanner-controlled lasers are aimed diagonally from both sides at the thin gap between the core layer and the cover plate. There, they heat the metal surface with precise precision. Depending on the plate chosen, locally generated temperatures range from 660 to more than 1400 degrees. Rollers then press the core layer and the slightly melted surface of the ceiling together, making it permanently bonded.

Laser process can reduce energy consumption and promote recycling

This extra light sheet can be produced in a single batch during the rolling process. Compared to classical methods such as high-temperature extrusion, laser welding saves a lot of energy because the high-energy light only needs to partially melt the metal surface in a wafer-thin manner. It is also suitable for low cost mass production. Even laboratory prototypes have reached high production rates. Andrea Berger estimates that the system could produce more than ten kilometres of lightweight sheet metal per minute. In addition, such machines can be quickly converted to a new profile or sheet structure. On the other hand, when customers order new sheet models, extrusions require different tools for each application.

Laser sandwich plating can also be used to create stable structures only a few tenths of a millimetre thick. This, for example, alleviates the aforementioned difficulties in truck-making. Because laser roll coating enables an inexpensive lightweight solution made of pure heat-resistant steel, the plates can also be installed where many traditional lightweight structures were previously taboo for fire-proof reasons - for example at certain points in the shipbuilding industry. The wider use of such lightweight structures in turn reduces material consumption for supplier industries, which can reduce the weight of vehicles, aircraft and ships, thereby saving fossil fuels or electricity. Another ecological benefit comes at the end of a component's life cycle: the laser-connected sandwich boards contain neither adhesives nor solder or other foreign matter that must later be painstakingly separated again at a recycling plant.

Predictable shipbuilding, hall and vehicle building applications

Marko Seifert, head of the heat treatment and electroplating division at Fraunhofer IWS, believes suppliers to shipyards and automakers could be early adopters of the new process. A first application scenario could be, for example, a light staircase or a ship partition, where power cables could be laid invisibly due to the hollow internal structure of the panels. The new technology could also quickly gain a foothold in truck trailers and hall construction. In the next steps, the Fraunhofer researchers are looking for partners to put the idea into practice.

Source: IT House