fastening & assembly solutions and technology - Approved Business

Advanced fastener
design for plastic
applications
For many years now inserts used in
plastics have traditionally be manufactured
from brass because of its combination
of free machining characteristics,
thermal conductivity and corrosion resistance.
However, the cost of brass has
escalated in the last two years to its highest
ever recorded now making it very
prohibitive. This has been the catalyst for
PSM to address the situation and has
resulted in them designing an insert made
from aluminium.
By the selection of aluminium, it not
only offers the benefit of low cost of
inserts compared to brass but it also has
weight and process improvements advantages.
Many tests have been carried out to
ensure that the type of aluminium used
for the PSM Tri-step insert offers similar
performance requirements to the brass
inserts that are currently in use today.
With regard to weight improvements,
aluminium is some 60% lighter than
brass material. This helps designers significantly
in meeting weight reduction
targets that most companies are looking
to achieve in the current economic climate.
From a process point of view where
inserts are installed by heat or ultrasonic
methods, the aluminium Tri-step insert
has 40% better thermal conductivity
compared to brass or steel. This reduces
the heating preparation time prior to
installation of the insert and cools more
rapidly once installed. Better production
efficiencies and lower use of power to
install the insert all add to in-place cost
improvements.
Further performance improvements
have been made by the geometry of the
insert and hole combination. The Tri-step
insert has three diameters reducing from
the top face of the insert to the leading
edge at the bottom of the insert. This corresponds
with three stepped holes in the
plastic moulding that accommodate each
diameter of the insert. The first advantage
is that because the smallest diameter of
the insert enters the largest of the stepped
holes in the plastic moulding ensures
excellent positioning and alignment of
the insert in the hole. The second advan-
FAST OCTOBER 2011
PRODUCT REVIEW: ALUMINIUM INSERTS
The high cost of brass used for special inserts in plastics components has led to the development of
an aluminium alternative
tage is that the insert enters the hole by
66% of its length before it meets resistance
making the installation faster than
other types of insert by some 30%. The
saving on the process can easily be calculated
to add to the in-place cost savings.
The design of the insert and hole
ensure that the minimum amount of pressure
is applied when installing the insert,
resulting in extremely low levels of stress
being transferred to the plastic material.
This combined with the stepped parallel
insert design results in the elimination of
spring back, a condition where the insert
can move out of the hole to some degree
before the plastic material has the chance
to cool sufficiently. This can occur if
pressure is not applied for a short time
after the insert is fully installed.
The Aluminium Tri-Step insert will
be showcased by PSM at
the upcoming FAST
exhibition in October.
PSM INTERNATIONAL
01902 407370
Three stepped aluminium inset and hole design
Left: Location has 0.6mm clearance between hole and vanes
Centre: Insert free fits into hole for more than two thirds of its length
Right: 3.1mm of insert travel to install an M6 insert fully
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