In the automotive engineering world, weight saving is often a matter of reducing component mass by only a few percentage points. So achieving a reduction of 34% is extraordinary by any standards.
That is what Johnson Controls Automotive Experience has managed, as it completed development of a new rear-seat system at its European headquarters at Burscheid, Germany. But it is not the use of advanced composites that has made it possible; it is advances in adhesive bonding and its application to steel and aluminum.
Johnson Controls sees the use of its new technology as being particularly applicable to electric vehicles, for which weight saving is crucial to enhance range potential.
Traditionally, rear seatback frames have used steel, mainly for material stability reasons. A mix of aluminum and steel elements for seats has been under consideration by the company for some time. A hurdle, though, has been achieving a quality bond that would meet all safety requirements.
Dr. Andreas Eppinger, Vice President of Technology Management at Johnson Controls’ Automotive Experience, explained that bonding an all-steel seat frame was a relatively simple matter of welding its constituent parts. Introducing aluminum was an obvious route to reduced mass because its material properties and those of steel are similar, but the use of conventional welding was not possible if required criteria were to be met.
So Johnson Controls specialists developed an adhesive bonding technology that would join aluminum and steel while meeting safety and service life needs. “Aluminum is used for the upper and lower cross members of the seatback frame, but the side members and the reinforcing cross beam are steel, resulting in a 30% weight reduction,” Eppinger said.
By reducing the thickness of the steel back panel, from 0.6 to 0.4 mm (0.024 to 0.016 in), a further 4% weight saving was achieved. The seat’s modular design enables it to be easily adapted to meet packaging in a variety of models.
“Extensive testing has been conducted and this new rear-seat structure is as safe as traditional seat structures despite the thinner back panel,” said Eppinger.
He stated that at microscopic level, metals have a rough surface consisting of pores, crevices, and cracks where the adhesive can intrude. “It hardens in such a way that it keys into the surfaces and forms a strong bond. A multidisciplinary science, adhesive bonding demands expertise in material science, surface characterization, pretreatments, chemistry, and mechanical properties.”
Although full details of the Johnson Controls technology have not been released, Eppinger said the new adhesive was compatible not only with steel and aluminum but also with other metals, plastics, natural fibers, and further materials. It also is compatible with other bonding technologies including riveting, clinching, and welding, while meeting durability, structural strength, and crash stability standards.
Johnson Controls is therefore positioned to apply the technology to other components, bringing both mass and packaging advantages.
R&D work on the new adhesive was carried out at the company’s Burscheid center. The center, close to Cologne and Dusseldorf, houses product development, industrial design, consumer and market research, benchmarking, and prototyping departments plus a wide range of testing facilities. Many central functions are based there, including engineering and program management.