SUMMER 2023

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THE DISTRIBUTOR’S LINK
Laurence Claus
Laurence Claus is the President of NNi Training and Consulting, Inc. He has 25 years of
experience with a medium sized automotive fastener manufacturer, holding positions
including Vice President of Engineering, General Manager, Director of Quality, Director
of New Business Development and Applications Engineer. In 2012 he formed NNi
offering technical and business training courses as well as technical consulting, expert
witness and consultation work. He can be reached at 847-867-7363 or by email:
Lclaus@NNiTraining.com. You can learn more about NNi at www.NNiTraining.com.
DIFFICULT FASTENING APPLICATIONS - PART 2
THIN-WALLED PLASTIC BOSSES
Fasteners are often overlooked and “underconsidered”
when being designed into a product. It is for
this reason that even the simplest fastener can wreak
havoc for the unsuspecting or ill-prepared manufacturer.
The wrong choice can lead to serious headaches in
manufacturing, or worse yet, failures once the product
makes it into service.
Without trying to sound too dramatic, there isn’t
really a single fastener or fastener application that we
can take for granted. Even the screw that holds a cheap
child’s toy together is all important to a harried parent
if it should break leaving a frustrated and cranky child
in its wake. This means that there is no automatic
guarantee that things will work without some preplanning
and forethought. It also means that there are
some applications we must be especially careful with.
This three-part series investigates three particularly
challenging fastener applications. In the first part of this
series, we looked at thread forming into thin sheets. We
learned how thin sheet thickness only allows a couple
of pitches of thread engagement, making them very
vulnerable to threads stripping and placing them near
the top of the list of difficult fastening problems. In
this part of the series, we will investigate fastening into
thin-walled plastic bosses. The final segment will look
at the challenges of connecting two or more dissimilar
materials together.
To consider the challenges of fastening thin-walled
bosses, we must first consider plastics themselves.
There is a wide assortment of different plastic materials
TECHNICAL ARTICLE
available today which provide an even wider assortment
of mechanical and physical properties. Plastics are
polymers, meaning that they are comprised of long
chains of repeating molecules. Plastics broadly fall into
two categories, semi-crystalline and amorphous. Semicrystalline
polymers exhibit regions where these long
molecules arrange themselves in an orderly fashion (a
crystalline structure) and regions where they are simply
randomly intertwined (amorphous structure). Amorphous
plastics are entirely randomly intertwined, like a bowl of
spaghetti noodles.
This different molecular structuring has a dramatic
influence on the material’s performance characteristics.
Amorphous plastics tend to be more like glass. In fact,
the word “glass” is often part of the descriptive terms
associated with this category of plastics, and most
amorphous plastics are clear in their natural state.
Most amorphous plastics are considered “engineering
plastics”, or plastics that offer higher performance and
enhanced capabilities when compared with commodity
plastics. Engineering plastics are what designers choose
and manufacturers use to make high-end plastic parts
for multiple industries including automotive, consumer
products, electronics, aerospace, and medical to
name but a few. Typical engineering plastics that are
amorphous include Polycarbonate (PC), Acrylonitrile-
Butadiene-Styrene (ABS), and Polyphenylene Oxide
(PPO). Of course, not all engineering plastics are
amorphous, the polyamides being an excellent example
of a semi-crystalline engineering plastic.
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