The use of plastic-metal hybrid components in transmission housings opens up a new possibility
for lightweight construction. Closed housing structures made of a single material can be
replaced by open load-optimized housing structures that offer an otherwise unattainable weight
advantage through the use of plastics. The investigation of the bond strength between metal and
plastic is an essential part of this work. The adhesion promoters investigated make it clear
that there are currently no systems known to the author that can improve the bond strength of
not only freshly molded components in the long term. The shot peening process already used for
a large number of transmission housing types also opens up advantages for plastic-metal hybrid
components. The microstructured surface enables the plastic to fill in undercuts and cavities
in the molten state and thus to form an improved adhesive strength through microform closure.
If the adhesive strength is essentially based on a material-locking connection a blasted
surface can achieve considerable increases in the strength of the plastic-metal connection.
Force-fit and positive connections on the other hand benefit less from a blasted surface of
the metal. Investigations into the influence of the joining geometry on the bond strength
showed that geometries with pronounced joining characteristics achieve the greatest bond
strength. It could be shown that of all geometric features the increase of the undercut
surface in the pull-out direction has the greatest influence on the bond strength. A further
aim of this work is to investigate the tightness of the hybrid components. A test specimen
close to the component was developed for this purpose. The leakage tests were then carried out
on dry as molded and conditioned components under series test conditions. The adhesion promoter
systems which were disappointing in terms of bond strength were not convincing in this test
criterion either. Another approach to tighten the test specimen based on the modification of
the joining geometry also had to be accepted as impracticable. The expectations that the
shrinkage of the plastic resulting from the injection molding process could be used to improve
the tightness by a skillful choice of the joining geometry were not fulfilled. The use of
additional sealing elements which are inserted into the mold together with the aluminum part
and encapsulated by the plastic finally turned out to be the right way. The features of a
plastic-metal hybrid connection investigated in this paper were able to meet the expectations
for use in transmission housings. This could either be achieved with already proven means such
as a shot peened surface or after research work such as the insertion of an additional
sealing element.
