P 909 – Complementary approach for the bubble-free seam sealing of bonded hem flanges




P 909 – Complementary approach for the bubble-free seam sealing of bonded hem flanges

Inner and outer panel of automobile doors, trunks and hoods are joined via hem flange bonding. Air-filled cavities can form within the bonded hem flange and this can lead to blisters forming in the PVC seam seal during the further manufacturing process. The seam seal is visible to customers and the blisters adversely affect the optical quality.
There is also the risk that the defects are destroyed by mechanical effects during the
vehicle lifetime. This would allow direct access of electrolytes into the flange, with effective corrosion protection for the bonded hem flange being no longer guaranteed. This is why any defects in the seam seal during the production process have to be repaired and this involves time-consuming and costly finishing work.
In order to avoid the costs for this finishing work, the greater amount of quality assurance, and possibly loss of reputation should serious corrosion issues arise, this research project is investigating the mechanisms of defect formation and measures to minimize such defects and produce a blister-free seam seal.
The objective of this project was to develop the technological basis for the industrial
manufacture of blister-free bonded hem flanges. The project involved two complementary approaches: The minimization of cavities within the bonded hem flange, namely process optimization (minimization of the damage potential), and substitution of the defect-prone PVC plastisol by a blister-free seam sealant, namely material optimization (enhancement of the damage tolerance).
Within the material optimization, comparative tests of alternative sealant materials were carried out, which led to the qualification of an MS polymer as a potential PVC substitute.
Within the process optimization, the formation mechanism of cavities as well as the
influence of process and component tolerances on the degree of filling of the hem flange were investigated. Based on these findings, detailed recommendations for the optimization of the hem flange bonding and seam sealing process were developed.
The investigated joining technique of hem flange bonding is used both in mass, as well as in the production of small batches and individual parts. With the integration of the recommendations developed in the project in the series processes, the process increases security when joining steel components by means of hem flange bonding. The prevention of defects in the seam sealing means significant economic benefits for the automotive industry and its suppliers, as the higher costs due to rework as well as the risk of corrosion can be prevented.

Published in:
January 2019

Prof. Dr. rer. nat. B. Mayer, Dr. H. Fricke, B.Sc. Ivo F. Neumann, Prof. Dr.-Ing. D. Landgrebe, Dipl.-Ing. F. Jesche, Dipl.-Ing. (FH) S. Menzel