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3. RIVETING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133
4. SNAP-LOCK & CLIPPING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
129
EUROPEAN ALUMINIUM ASSOCIATION
1.1. Definition
Adhesive bonding is defined as
a process of joining parts using a
non-metallic substance (adhesive)
which undergoes a physical
or chemical hardening and by
thus leading to a joining of the
parts through surface forces
(adhesion) and internal forces
(cohesion).
Adhesion can be physical attraction
between the adhesive and
the metal surface, real chemical
bonding between the adhesive
molecules and the metal atoms
or mechanical interlocking
between the adhesive and the
surface roughness of the metal.
Cohesion is the inner strength
of the adhesive itself as a result
of physical and/or chemical
forces between the components
of the adhesive.
1. Adhesive bonding
Physical attraction forces
between adhesive and
metal surface
Chemical bonding
between adhesive
molecules and metal
atoms
Mechanical interlocking
between adhesive and
surface roughness of
the parts to be joined
Physical and/or chemical interaction
between the adhesive molecules
PRINCIPLE OF ADHESIVE BONDING
FIGURE IX.1
ADHESION
COHESION
Source: Talat lectures
130
ALUMINIUM IN COMMERCIAL VEHICULES CHAPTER IX OTHER JOINING TECHNIQUES 130 | 131
1.2. ADVANTAGES AND DISADVANTAGES
Advantages
1. Load distributed uniformly at right
angle to loading direction
2. Microstructure unaffected
3. Distortion-free joining
4. Different materials can be joined
5. Very thin parts can be joined
6. Weight saving
7. Heat-sensitive materials can be joined
8. Metals with different electrochemical
potentials can be joined (insulating
effect of adhesive)
9. High strength joining in combination
with other methods (screwing,
welding…)
10. High fatigue strength and good
vibration damping
Disadvantages
1. Influence of time on process properties
2. Pre-treatment of joined surfaces
necessary
3. Limited form stability
4. Process parameters must be held in
narrow ranges
5. Change of the properties in time
(ageing of the adhesive)
6. Complicated control of process
7. Low peeling strength
8. Low adhesive layer strength requires
large joining areas
9. Limited repair possibilities
10. Difficult strength calculation
Source: Talat lectures
1.3. Types of adhesives
Adhesives can be divided into 3 subgroups
depending on their forming
reaction and polymer structure:
• Polymerisation: An exothermic
process in which monomers link
together to form macromolecules
(polymers). Thermoplastics like
methylacrylates, polyvinyl chlorides,
polyvinyl acetates and rubber
polymers belong to this group
• Polycondensation: Water is produced
as a result of the chemical
reaction. Thermoplastics like
polyamides and polysulfones as
well as duromers like phenol
formaldehyde resins, urea resins,
melamine resins and polymides, are
all produced by polycondensation.
• Polyaddition: During this
process the hydrogen atoms are
rearranged. Very common adhesives
for metal bonding like
epoxy resins and polyurethanes
are produced by polyaddition.
Combination of adhesive bonding
and mechanical joining (e.g. riveting
or bolting) can eliminate some
of the above-listed disadvantages.
131
EUROPEAN ALUMINIUM ASSOCIATION
1.4. Application
of adhesives
As adhesive bonding is working
by surface forces, prerequisites
for a well functioning adhesive
joint are
a) the choice of an appropriate
adhesive for the materials to be
combined
b) the existence of a suitable
material surface
A suitable surface means, that
the surface area must be large
enough to transfer the applied
forces and that it is capable to
ensure a proper bonding. This
can be achieved through a
suitable pre-treatment. Any
residues of dirt like moisture,
oils, dust etc. must be removed
prior to application of the adhesive.
This can be done by chemical
means with the use of
detergents, degreasers or etching
agents or mechanically by
grinding. In any case the surface
must be absolutely clean before
gluing. It might be favourable to
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