Innovative Stainless Steel Applications in transport ... - Euro Inox

There are three basic variants of resistance welding: resistance spot, projection and
seam welding. In spot welding, the electrodes are typically rod-shaped round bars that
produce round, molten “nuggets”, that join the materials together. In projection welding,
projections, embossments or other raised features on one of the workpieces define the
final joint-location and area. With this technique, the electrodes have a large contact
surface with the workpiece and the projections ensure that the current is concentrated in
a small, controlled area. This process can be used to make multiple weld spots in one
go, or it can be used for non-flat or complex shapes. In seam welding, the electrode is a
rotating disk that produces a series of individual but overlapping spot welds, using
current pulsing. This results in an apparently continuous, leak-tight weld seam. A
typical application area for all these resistance-welding processes is the lap joining of
thin sheets of up to about 3 mm thick.
4.3.4 Adhesive bonding
Unlike fusion processes, where bonding and joint formation is based on melting and the
resulting metallurgical mixing or even reactions, adhesive bonding relies only on
secondary atomic forces – i.e. van der Waals forces at molecular level, formed between
the base material and the adhesive on each individual surface of the joint. Since these
secondary forces are much weaker than a metallurgical bond, the joint area required for
a given load-bearing capability is usually much larger than in a fusion weld. In practice,
this means that instead of the butt or fillet joints typical of fusion welding, adhesive
joints are usually lap joints, where one flat surface overlaps the other and the
overlapping area is dimensioned according to the required strength properties.
Since the base materials remain in solid state and adhesive bonding is carried out at or
close to room temperature, no distortions related to melting-resolidification or even to
thermal expansion occur. In addition, any surface coatings usually remain intact during
bonding. There is a vast variety of commercially available adhesives for various
metallic materials and their combinations, loading and service conditions, processing
routes, etc.
Weldbonding
Adhesive bonding is increasingly used in combination with resistance spot welding,
especially in the automotive and transport-vehicle industries. Once the adhesive has
been applied between the joint surfaces, the component is welded using conventional
spot welding equipment. The resulting joint usually shows better mechanical properties
than either an adhesive-bonded or spot-welded joint alone and the adhesive seals the
crevice between the base materials, thus eliminating the risk of crevice corrosion in
long-term use. The spot welds also have the advangtage of fixing the parts to be joined
during the setting of the adhesive.
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