SPRING 2022

184
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LAURENCE CLAUS HOT FORGING FASTENERS from page 180
is heated up in an induction coil and then introduced to
the thread roller. Rolled threads are stronger and have
an advantage in fatigue applications over cut threads.
For this reason, some customers will dictate the process
method for developing the threads.
Threads
FIGURE 8: PARTS COOLING AFTER FORMING
Threads on large diameter, externally threaded
fasteners may be cut or formed. Unlike smaller diameter
parts which most often employ flat thread roll die
technology, large diameter, externally threaded fasteners
that have formed threads usually use large twin die
cylindrical rollers. The unthreaded parts are positioned
between two cylindrical roll dies rotating in opposing
directions. The part is squeezed between these two
dies as they rotate. This is a progressive process with
each rotation forming a little more of the thread. With a
cylindrical roller there are no limits to how many rotations
the part can receive until the thread is finished.
Threads can also be cut by drawing the cylindrical
blank through a rotating set of cutters. This equipment
feeds the part through the center of the cutting head so
that it can generate very long threaded sections. Take,
for example, long anchor rods. These products can be
many feet in length with a six inch to one foot threaded
section on one end. Cutting those threads using this
process is easy.
Parts that utilize hard to form materials may also
need to add heat for thread rolling. The process is very
similar to forming. The area to be threaded on the blank
Typical Uses
Warm and hot formed parts can find their way into
many different products. However, they tend to be in
products that use large diameter fasteners, very long
fasteners or hard to form metals.
Large diameter fasteners are often used in
construction projects and on large industrial machinery.
Very long fasteners, such as anchor rods, are used mostly
in construction. Small and large diameter fasteners that
utilize hard to form metals such as stainless steel, A286,
Inconel, Hasteloy, and Titanium are commonly found in
aerospace, defense, and harsh industrial applications.
Summary
Warm and hot forming are common fastener
manufacturing processes when parts are very large or
the materials they are made from are extremely difficult
to form. Like smaller, cold formed fasteners, large
diameter, hot headed fasteners must pass rigorous
inspections and purchasing requirements. These
components play an integral part of the fastener
supply chain and serve in many critical applications.
The manufacturing process, whether conducted on a
high speed hot header or individually on a horizontal
upsetter, the process is fascinating and well worth the
time to understand and witness first-hand if given the
opportunity.
Acknowledgements
The author wishes to extend his grateful appreciation
to Atsushi Hashimoto of Unytite, Inc . and Rich Giusti
of Haydon Bolt for sharing images 1 through 7 for this
article.
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