As European manufacturing continues 
to evolve, plastic materials are playing 
an increasingly important role across 
industries including automotive, 
electronics and consumer goods. 
Lightweighting, miniaturisation and 
changing material requirements 
are contributing to the wider use of 
engineered plastics, but these materials 
also introduce different considerations 
when it comes to assembly. 
Drawing on its experience in fastening 
applications for plastics, PSM CELADA 
Fasteners looks at the factors engineers 
should consider when selecting the most 
appropriate fastening method.
Unlike metals, plastics can respond 
differently to load, temperature, vibration 
and repeated use. The fastening method 
therefore needs to be considered 
alongside the properties of the plastic 
itself, the manufacturing process and 
the demands of the finished application. 
Inserts, self-tapping screws, press-
in fasteners and other systems each 
approach these challenges differently.  
Understanding the main 
fastening methods
PSM CELADA Fasteners works with 
a range of fastening approaches for 
thermoplastics and thermosets, each 
A Guide to Fastening in Plastics 
with PSM CELADA
Italian distributor, PSM CELADA Fasteners, discusses how material properties, installation 
methods and end-use requirements influence fastener selection, and why the choice of 
method matters.
suited to different material properties, 
installation processes and performance 
requirements. Understanding how these 
methods work can help engineers make 
a more informed choice during the 
design stage.
Heat and ultrasonic installation:
Threaded inserts can be installed 
into thermoplastics using heat or 
ultrasonic energy. During installation, the 
surrounding plastic is softened, allowing 
it to flow around the external features 
of the insert before solidifying. Knurl 
geometry can influence resistance to 
torque and pull-out, while rounded profiles 
may be preferable for some amorphous 
thermoplastics where localised material 
stress needs to be considered.
Heat staking:
Thermal insertion is commonly used 
where threaded inserts need to be 
installed repeatedly and consistently 
during production. Parameters such as 
insertion temperature, pressure, depth 
and cycle time all influence the quality 
of the finished joint. Material behaviour 
should therefore be taken into account 
when defining the installation process.
Self-tapping screws:
Self-tapping fasteners form their own 
thread directly within the plastic. Thread 
geometry is particularly important, as it 
affects engagement with the material 
and the amount of stress generated 
around the hole. Different designs may 
be required for softer thermoplastics and 
harder thermoset or reinforced materials.
Press-in and expansion fasteners:
These systems rely on friction, 
interference or expansion to secure 
the fastener within the component. 
As they can often be installed without 
pre-threading, they can simplify the 
assembly process. Hole dimensions, 
plastic hardness and the geometry of the 
fastener all affect retention.
Insert moulding:
Fasteners can also be positioned within 
the mould before the plastic component 
is formed around them. This integrates 
the insert into the moulding process 
rather than adding it during a secondary 
assembly stage. Accurate positioning 
is important to maintain alignment and 
prevent movement during moulding.
Compression limiters:
Where plastic components are clamped 
using a bolt or screw, compression 
limiters can help control the forces 
applied to the plastic. They are commonly 
considered in assemblies exposed to 
repeated tightening, vibration or sustained 
14

View this content as a flipbook by clicking here.