WINTER 2024

182
THE DISTRIBUTOR’S LINK
LAURENCE CLAUS HOW FASTENERS ARE MADE - PART 1: COLD HEADING from page 180
FIGURE 15: EXAMPLE OF BROACHED SLOTS AND FLATS
Thread Rolling
Like Cold Heading, Thread Rolling is a material
displacement process. In other words, material is moved
to create threads. This develops a strength advantage
over cut threads. As described earlier about the cold
forming process, thread rolling “curves” the grain making
it stronger (See Figure 18). Thus, rolled threads are
considered stronger than cut threads. In addition to
the strength advantage, thread rolling is fast, producing
parts at equal or greater speeds as cold heading.
FIGURE 18: ROLLED VERSUS CUT THREADS
FIGURE 16: EXAMPLE OF DRILLED BANJO BOLT
FIGURE 17: EXAMPLE OF PRECISION CENTERLESS-GROUND
SHOULDER
Parts that feature any of these secondary operation
processes are more costly to produce than parts made to
net shape. Therefore, net shape parts are always more
desirable than near net shape parts and even though
some forming technologies have been developed which
provide new forming techniques that negate the need for
secondary operations, there are still many cases where
secondary operations are simply unavoidable.
For most fasteners thread rolling is accomplished by
rotating and squeezing a part between two flat plates.
There are grooves in these plates that match the thread
profile and desired helix angle and as the blank rotates
between them, it is squeezed to form the threads.
In this process, there is only one part produced with
each repetition, although many of these machines are
operating at lightening speeds. Another method is to
squeeze the blank between either two or three rotating
dies. These are known as cylindrical rollers. Once again,
they produce one part per cycle and are slower than flat
die rollers. Finally, there are Planetary Thread Rollers. In
these machines there is a fully round rotating die and
a stationary hemispherical die. Parts rotate through the
length of the hemispherical die. A big advantage of these
machines is that they can accommodate several parts in
the die at one time, generating high part output.
Heat Treatment
Thermal treatments are used to generate desired
mechanical and/or physical properties, usually to make
the parts stronger, although there are several processes
that make parts less strong or restore workability.
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