Reliable electrical connections for drive systems

Microrelative movements can lead to crack formation and crack growth in press-fit connections. Together with the Institute of Materials Engineering and the Institute of Drive and Vehicle Technology, both at the University of Kassel, Fraunhofer EMFT researchers are working on a suitable accelerating model to better understand how these undesirable effects occur.

In the field of drive systems, press-fit technology presents an interesting alternative to other electrical contacting methods such as solder, screw or crimp connections. The benefits are minimal space requirements, repair capacity and a failure rate which is potentially between ten and hundred times lower. The press-fit procedure creates a touch zone between the pressfit contact and the copper sleeve in the circuit board. As a result of the pressure caused by the deformation of the press-fit contact when it is pressed in, this touch zone forms a gas-tight and corrosion-proof contact zone after about 24 hours. Inside this zone, the free electrons generate attraction forces that connect the two metal surfaces. In this way, a cold weld zone is formed within a few hours.

However, this process can also cause unwanted damage to the component. For example, vibration-induced microrelative motions between the press-fit contact and the copper sleeve in the blank lead to fatigue damage or fatigue failure of the cold weld zone.

The Fraunhofer EMFT team has established a test rig for these micro relative movements as part of the project. Furthermore, the Munich experts are carrying out precise electrical characterizations of the contact resistance of the cold weld zone. Following a detailed mechanical analysis and simulation, the team from the University of Kassel is working on the development of a gathering model. This model will then be validated in the Fraunhofer EMFT laboratories using a practical surface material combination of press-fit contact and copper sleeve that is of interest from an industrial perspective.

The research project is funded by the AiF Arbeitsgemeinschaft industrieller Forschungsvereinigungen "Otto von Guericke" e.V. (IGF application no.: N 09826/16, FVA no. 618 II "Raffungsmodelle II").