Projects

Spot joining for stable hybrid joints

Load-bearing hybrid joints made of metals and thermoplastics are becoming increasingly important for industrial applications. Efficient joining processes are required with which firm joints can be produced quickly and reproducibly according to the specific load case. The HeatPressCool integrative technology (HPCi®) enables the process-reliable joining of different materials in just a few seconds without the use of additives such as adhesives, screws or rivets.

Functional principle

HPCi® joining gun for metal to plastic joining within seconds.
© Fraunhofer IWS
HPCi® joining gun for metal to plastic joining within seconds.

The combination of rapid local metal part heating and simultaneous pressing to a thermoplastic component causes the plastic to melt at the contact point. It wets the metal and solidifies right after the heating process. To improve the joint strength, the metal surface can be structured or coated with an adhesion promoter, if required. Even materials that are challenging with respect to adhesive technology, such as POM or AlMg3, are excellently qualified for the HPCi® process.

Flexible geometry

Joining of a test specimen made of glass fiber reinforced polyamide and aluminum.
© Fraunhofer IWS Dresden
Joining of a test specimen made of glass fiber reinforced polyamide and aluminum.
The multiphysical simulation enables joining on the spot.
© Fraunhofer IWS Dresden
The multiphysical simulation enables joining on the spot.

When using laser radiation, dynamic beam shaping can flexibly generate different heating profiles and can thus produce varying joint geometries. For higher production quantities, metal volume heating with adapted inductors ensures minimum joining times and high energy efficiency. Direct access to the metallic joining partner is not necessary. The inductors can be designed with regard to the geometry and material of the joined parts. For integration into fully automatic assembly processes, a joining gun has been developed that preferably creates spot-like connections. A ring inductor working in the outer field encloses the pressure die, which presses the joining partners. The process-integrated control, the monitoring of the traverse path and the local joining temperature enable both the minimization of the joining time and the inline documentation of the achieved joining quality. The HPCi® joining gun operates both with one-sided and two-sided accessibility and can be adapted to conventional industrial robots. The tool is thus suitable for use in car body construction to convert resistance spot-welded metal constructions into multi-material designs.

Application fields

Possible application: Joining of a hybrid B-pillar in car body construction.
© Fraunhofer IWS Dresden
Possible application: Joining of a hybrid B-pillar in car body construction.

In addition to applications of metal-thermoplastic compounds in lightweight construction (e.g. automotive industry, aviation or sports equipment industry), the focus of current research is on their implementation in electronics production. A further field is opening up in industrial and household goods as well as in the furniture industry.

Sustainability

SEM image of a destructively tested polypropylene-aluminum joint.
© Fraunhofer IWS Dresden
SEM image of a destructively tested polypropylene-aluminum joint.

Due to the fact that no additives are used, safety measures that are necessary when processing or storing reactive adhesives are no longer required. The technology also enables repeated detaching of the fundamentally stable HPCi® connection. Parts can thus be repaired more easily and separated according to type at the end of their life cycle. In combination with bio-based plastics, sustainable hybrid components can thus be created.