APRIL 2019 The FABRICATOR 79
expand them. Adhesives can be applied in areas that are inaccessible
to mechanical fastening during final assembly, allowing new designs
that further reduce weight, costs,
and labor. From an aesthetics
standpoint, adhesives can reduce
and eliminate unsightly screw and
rivet points and weld lines, leaving
a smooth, uninterrupted surface
without grinding after welding.
Adhesives can be used to bond
dissimilar materials, such as metal
to composites or plastics instead
of metal to metal. Di;erentiat-ing materials in assembly opens
up a multitude of design options,
and manufacturers can diversify
their product o;erings. Mechanical fasteners would not be a good
option for joining metal to many
composites, because drilling holes
for fasteners would likely crack the
material. When plastics are joined
to metal, thermal cycling can lead
to fractures within the plastic.
What type of adhesives are we
talking about? Adhesive sealants
provide high elongation, flexibility,
and gap filling. Toughened epoxies
work for applications that need a
more rigid, solid combination of
impact resistance and strength.
Industrial tapes are not only easy
to apply and convenient to handle,
but also are designed to provide
excellent impact load resistance
on thin substrates.
Adhesive Solutions to
With more manufacturers choosing substrates over traditional metals, the right adhesives can be the
answer for hard-to-bond materials.
Low surface energy (LSE) plastics like polyethylene, TPO, HDPE,
PP, and some powder topcoats
can be hard to bond because of
their chemical composition. Typically, these materials require extensive surface preparation before
the joining process even begins.
Thermal methods like friction
and ultrasonic welding are considered to be suitable for LSE plastics.
However, these methods typically
are expensive and require ongoing
tooling, which is not ideal for products that have short runs or need
frequent design changes.
Even adhesives don’t always solve the surface preparation issue. But some specialty adhesives have been
created to address this situation. These plastic adhesives can bond LSE materials and even reduce or eliminate the surface preparation steps.
Another challenge is trying to bond oily metal. Oily
metals often require extensive preparation and cleaning, which creates extra work for fabricators. Unfortunately, these steps are necessary because the oil can
interfere with robust bond formation.
That said, two-part structural acrylic adhesives are
able to absorb most oils from metal surfaces, allowing the metals to bond without extensive cleaning first.
This eliminates those tedious steps, saving the manufacturer time and money.
Adhesives: Going Beyond Strong
Though many manufacturers are comfortable with traditional fastening methods, modern design and sustainability factors render mechanical fasteners and welding
to be less e;ective than alternative joining methods for
Adhesives are an e;ective remedy for the issues mechanical fasteners present. They also allow manufacturers to choose from a wider variety of substrates,
bond dissimilar or hard-to-bond substrates, and explore di;erent design avenues to create unique and
Shari Loushin is senior technical service specialist, structural adhesives,
3M Company, Industrial Adhesives and Tapes Division, 3M Center, St.
Paul, MN 55144-1000, 888-364-3577, 3m.com/iatd.
It’s not where you are, it’s where you’re going.