INDIRECT PROJECTION WELDING
FOR AESTHETIC METALLIC SURFACES
This process is used when one of the two metal sheets must not
present any kind of deformation or imperfection after they have been welded
together.
It is mainly used in the automotive industry and in the household applicances in
which, for the visible sheets, strict aesthetic rules must be observed in order
to meet customer satisfaction.
To perform an indirect projection welding it is necessary to create a specific
dimple on one of the 2 sheets, in relation to the normal plane of the sheet
itself, by a moulding operation.
Just this dimple (on the not visible sheet) will be fused and amalgamated on the
second sheet (the visible one) by using a well known process of resistence
indirect projection welding.
In the contact area between the dimple and the upper sheet, a small fin shaped
to exactly match the protrusion itself must be created by moulding. These are
the fundamentals of this technology.
This particular process is used for the mobile components of a car (ie. doors,
hoods, trunks) and it takes place in the perimeter hemming station
(electromechanical or robotized with roller tool) or in the next station.
It is important to take into consideration that the hemming blades must be
"unloaded" within the covering fin/frame work dimple coupling areas, in order to
avoid the crushing of the dimple itslef, which might compromise the welding
operation.
As shown in the figure,
the welding process involves just 2 of the 3 superimposed layers.
The presence of the structural adhesive does not damage, in any way, the welding results.
