Recyclable metal-plastic hybrid construction for sustainable use of raw materials
KreisHybrid develops new joining technologies for metal–plastic hybrid components based on atmospheric plasma coatings. This enables lightweight, dense, and durable components with reduced material usage. At the same time, the recyclability of hybrid structures is considered from the outset.
Hybrid materials enable application-optimized resource utilization through the targeted combination of different materials. In particular, hybrid joints made of metal and plastic have become established across industries as a design principle for functionally integrated structures. However, the form-fitting joining techniques currently in use are increasingly reaching their limits in terms of load-bearing capacity, sealing performance, and design freedom. Especially in housing structures and in media- and current-carrying components, durable material-bonded joints are required that cannot be realized with conventional joining technologies.
The goal of the KreisHybrid project is therefore the industrial implementation of material-bonded metal-plastic joints using atmospheric plasma coating. Due to its compact system design, standardized interfaces for automation, and the ability to quickly change precursors, this technology offers high industrial adaptability. It allows the production of high-strength, media-tight and leak-proof connections with reduced material usage and without the need for complex protective measures, which is of particular interest to small and medium-sized enterprises (SMEs) in the plastics processing industry. However, currently available precursors are almost exclusively limited to the combination of steel and polyamides. To significantly increase the potential of hybrid structures, the material spectrum must be expanded to include additional material combinations. The focus is therefore on developing new precursor formulations, particularly for the combination of aluminum and polypropylene, in order to replace existing die-cast components with energy-efficiently manufactured deep-drawn and injection-molded components, thus promoting lightweight design and CO₂ reduction. The use of polypropylene offers ecological advantages over polyamides, as lower CO₂ equivalents are generated during production. In addition, non-ferrous metals and cathodic dip coating (CDC)-coated surfaces will be addressed to broaden the range of applications. The development goal is to significantly increase both the structural bond strength and the media-tightness of the hybrid connections.
A significant technological obstacle lies in the necessary heating of the metal inserts to joining temperatures above 250°C, which can lead to structural changes and loss of strength, especially with aluminum. The project is therefore developing a method for chemically modifying the precursors, enabling joining temperatures below 150°C. In parallel, a digitally supported virtual development methodology for component-specific, induction-based heating handling system is being developed. This is intended to replace the previously time-consuming experimental adaptation of induction heating to complex component geometries.
A key quality criterion for hybrid joints is the homogeneity of the adhesive strength across the entire component. In industrial practice, however, temperature-related inhomogeneities are unavoidable, which can lead to critical stress scenarios in certain areas. Therefore, the project is developing a data-based inline analysis that allows a real-time assessment of the strength by incorporating process-specific temperature data and failure models. This will enable the identification of components with potential weaknesses and allow them to be subjected to targeted, extended non-destructive testing. For this purpose, a fully digitized and networked process chain is being established, enabling the seamless recording and analysis of all process- and component-specific data.
In the interest of the sustainable development of hybrid structural components, aspects of the circular economy are also being considered. In addition to the use of virgin materials, single-grade recycled materials are being included in the investigations to evaluate the applicability of the developed precursors in the context of a future circular economy. A further development goal is the repairability of hybrid structures. For this purpose, a process for the direct thermal joining of repair structures using plasma and induction technology is being developed. At the end of the components’ service life, single-stream separation is being pursued to ensure high-quality material recycling of the materials used. Component removal should be quick, contamination-free, and energy-efficient using inductive heating.
The technological development is accompanied by life cycle assessments (LCAs), which systematically evaluate the environmental impact of the new joining and manufacturing technologies. The project thus contributes to the sustainable transformation of industrial manufacturing processes, increased resource efficiency, and the development of new fields of application for function-integrated lightweight structures in a wide range of technical areas – from electromobility and the consumer goods industry to medical technology.
