Solution to the processing problem of steel aluminum composite lightweight materials

The composite of steel and aluminum materials has great potential for lightweight design in the automotive industry. They have been widely used in the field of automobile manufacturing, but they are not used as a "composite" material.

Within the framework of the collaboration project on "High Pressure Deformation Processing Technology for Steel Aluminum Hybrid Laser Splicing Welded Pipes for Automotive Lightweight Design (IHU-THT)", the partners aim to manufacture lightweight, customized hollow pipes - using high-strength steel for the parts with higher load-bearing capacity and aluminum for the parts with lower load-bearing capacity. They attempted to use the Internal High Pressure Deformation Processing (IHU) technology to complete the deformation processing of steel aluminum laser welded pipes.

The Institute of Process Technology Integration (IPH) and the Laser Technology Center (LZH) in Hanover, Germany plan to attempt to achieve this goal. The R&D team promises that this new technology will reduce the weight of automotive components by an additional 20% based on their specific conditions in the lightweight design and manufacturing of automobiles. Many companies are also interested in this collaborative project. Johnson Controls, Qihao Automotive Co., Ltd., Laser on Demang, LMB, and SET Scientific participated in this project.

Johnson Controls has developed a specific plan: engineers have designed a complete set of seat backrests. On the one hand, we want to significantly reduce the weight of seat backrests by using laser welded pipes. We not only rely on the combination of lightweight designed steel and aluminum alloy materials to reduce the weight of seats, but also try to reduce the number of parts in seat components. What we are trying is the direct integration of high-strength parts for seat recliner components. This way, we can omit some accessories that have been necessary so far, fundamentally accelerating our global production and manufacturing, "said Dr. Andreas Eppinger, Vice President of Technology at Johnson Controls.

On the other hand, the design of seat back components that accurately meet load-bearing requirements has also opened up a new design method: the space behind the ultra-thin seat frame is more spacious, leaving more space for the knees of rear seat passengers, making it more convenient to get in and out of the car, and significantly improving the comfort during riding.

Brazing replaces laser welding

An important connection technology in the automobile production process is laser welding. Aluminum and steel will produce brittle intermetallic compounds after melting; their presence greatly reduces the deformation processing performance of the material. Therefore, in the IHU-THT cooperation project, we replaced laser welding with brazing because compared with laser welding technology, brazing conducts significantly less heat to the welded material, and the metal material does not melt, only the brazing material melts. ”Ms. Sarah Nothdurft, the project administrator of LZH company, said. Due to the high pressure deformation processing in IHU, the pressure of the pressure deformation processing system can reach up to 100MPa, so it is also required that the steel aluminum brazed pipes can also deform together under this high pressure. This eliminates the need for using laser welding equipment. Laser brazing technology is also a welding technique suitable for large-scale, industrial production. This connection technology uses welded joints with butt joints, as lap joints are not suitable joint forms in IHU's high-pressure processing technology. In addition, the different deformation and processing properties of the brazing material and the brazing material should also be considered. ”Ms. Sarah Nothdurft continued.

Another task of LZH Hanover's Laser Technology Research Institute is to design a set of brazing heads required for laser brazing. This brazing head should ensure the back and forth movement of the laser beam, reliably ensuring the delivery of traditional brazing wire, "said Ms. Sarah Nothdurft. The synthesized motion of laser beam and feed rate assisted by the scanner, as well as the power adjustment related to brazing temperature, should ensure a more optimized brazing process.

The combination of two different materials, steel and aluminum, poses many challenges for researchers: most aluminum alloy materials are much softer than steel, so they are also very prone to deformation. Therefore, the high-pressure deformation processing inside the IHU with this hybrid structure is much more complex than the semi-finished deformation processing of a single material. Before starting the deformation process, the steel part of the composite steel should be slightly heated to ensure that the deformation performance of the steel section is consistent with that of the aluminum section. Through relatively simple equipment and short-term internal high-pressure deformation pre testing, we obtained relevant data from the earlier batch. The specimens used in the pre testing were laser welded steel, "said Mr. Jonathan Ross.

Purposefully reducing weight

Based on the preliminary test results, participants in the IHU internal high-pressure deformation machining research and development project developed a FEM finite element simulation scheme suitable for the internal high-pressure deformation machining process. Based on the simulation results, deformation processing experiments can be conducted on real laser brazed composite pipes using IHU internal high-pressure deformation processing technology. ”Mr. Jonathan Ross summarized. Through the application of such material combinations, it is possible to purposefully utilize internal high-pressure deformation processing technology in the local area of laser brazed pipes according to the material strength characteristics and weight requirements, in order to achieve the goal of reducing the weight of parts, components, and assemblies, more effectively than traditional laser welded parts. Due to the combination of multiple traditional deformation processing steps into one process using internal high-pressure deformation processing technology, it can save a lot of production costs due to its high processing speed and few processes and steps. According to Mr. Jonathan Ross's estimation, based on the current experimental results, it seems that no new equipment technology is needed yet. It is estimated that a slight modification of the existing internal high-pressure deformation processing equipment can be completed.

Laser brazed composite pipes are suitable for use in the production and manufacturing of vehicle frames, such as the connection between vehicle C-pillars and roofs, seat frames, and dashboard brackets, but can also be used in the support components of axle parts. This composite pipe can also be used in the collision protection of car seats and doors, as well as in the connection of door panels.