Paul Janiak

Abstract

This project was focused on investigating the limitations with the Flow drill screw
(FDS) process in terms of thickness of material stack-ups, strength of materials to be joined and combination of mixed materials (Al, CFRP and steel).

There was also a secondary aim of investigating gap bridgeability of the FDS,
i.e. if it was possible to join a material combination with varying gap in between
the sheets.

FDS was feasible to use up to DP800 1,5mm material in the lower sheet of a material stack-up. Joining of e.g. DP800 1,5mm - aluminium to was possible with a clearance hole in the upper DP800 sheet.

Clearance hole in the upper sheet of a material stack-up were necessary in most
cases to achieve sound joints in this project. Worth mentioning is that the limits
of the FDS was tested in this project, meaning that almost no material
combinations were considered easy.

It was also possible to join Usibor 1500P AS boron steel with the FDS, however
only in a softened state (~240HV). Sound joints were achieved in CFRP – Usibor
1500P AS boron steel stack-ups with clearance hole in the CFRP material. This
joint was also possible without clearance hole in the CFRP material, however this
might cause health issues during production due to formation of fumes and
particles due to local melting of the polymer matrix material.

Results also showed that it was possible to both bridge gaps to some extent with the FDS as well as mount an FDS in a stiff structure that does not allow for any plastic deformation or bending of the sheets. Worth mentioning is that if this is to be used in a production case where the gap between sheets is varying, the time to mount the FDS needs to be optimized for the worst case i.e. the case with largest gap. This will affect the productivity negatively. With small variations in gap between sheets the FDS process can be optimized in a better way.

A small investigation of the EJOWELD process was also included in this project.
EJOWELD is a friction joining technique adapted for high volume, thin sheet
joining. Results were promising, showing good results in aluminium to steel joining. Even joining of Usibor 1500P AS boron
steel material was possible.