P 1309 – Increase in the application limit and flexibility of one-sided mechanical joining processes by process-assisted heating for the steel-intensive lightweight construction
The aim of the research project was the extension of the application limits of flow drill screwing (FDS). To achieve this goal, a test setup for thermally assisted flow drill screwing was developed. At the beginning of the project, fundamental correlations were investigated by means of heating tests under variation of different influencing variables with regard to the local heating of the joint. Based on the findings, constructive boundary conditions for the process-integrated conditioning process could be determined. Using the developed test setup, suitable process parameters for joining were determined, taking into account the preceding heating of the joining partners. The influence of local conditioning on the process-related reaction variables of the FDS process was determined by means of screwing tests in the locally heated joining materials. In addition, a controlled conditioning process was implemented, so that programming of temperature-time profiles were possible and different heat treatment strategies could be investigated. Basically, the strategies of short-term tempering and austenitization were pursued.
For the entirety of the investigated material combinations suitable joining process parameters could be determined, so that the application limits of flow drill screwing could be significantly extended with regard to high-strength multiphase steels and ultrahigh-strength hot-forming steels. In addition, the joint formation of the thermally assisted FDS process was investigated metallographically. Microstructural changes were analyzed on the basis of contrasted microsections. In addition, hardness measurements were carried out to quantify the hardness and geometric expansion of the locally softened joint areas, taking into account different heat treatment strategies.
With regard to an industrial implementation of the thermally assisted FDS process, the properties of the joint formation were further investigated. The findings were used for the conception of an adapted process monitoring strategy, taking into account the preceding process parameter studies.
Prof. Dr.-Ing. G. Meschut