New technique will allow the joining of sheets made of different metallic materials

A team of INEGI researchers from is developing a new joining process, called hole hemming, to join hybrid metal-composite sheets.

The process increases the mechanical strength of the joints, and was designed for high-demand uses, such as vehicles and transport. That's why the team is partnered with Kobe Steel, a manufacturer and supplier of metal for the transport industry in Japan, and CG RAIL, a manufacturer of hybrid metal-composite structures for the transport industry in Germany.

Structures in this sector are increasingly multi-material and, "in recent years, mechanical joining processes by plastic deformation, such as the use of rivets, without casting or metallurgical bonding, is common", explains Lucas da Silva, responsible for the project at INEGI. "This technique, however, requires ductile materials and sometimes requires the use of an additional element, so it has limitations".

To solve this problem, the team conceived a method where only one of the sheets will have to be ductile enough, making it faster, more reliable and ecological. "The process is carried out in two stages, starting with flanging the hole in an outer sheet and bending this flange over the hole in an inner sheet, producing a mechanical interlock that can be made in any part of the sheets”, says Mehdi Kasaei, who is part of the team.

The team is now working to validate and optimize the new technique, namely by studying the mechanical strength and failure process of these dissimilar joints under different load conditions. In a next phase, the performance of the hybrid joints will be tested under conditions representative of those found in the transport industry, with the support of partner companies, allowing to validate the joining process under service conditions.

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