12
800-826-3045
FASTENER TECH
engineering and manufacturing source for specialty and custom
fasteners for use in motorsports.
It is important to realize that simply quoting an AMS
(Aerospace Material Specification) number without strength and
percentage of elongation numbers is meaningless. Statements that
the use of a particular material will, in itself, result in extreme
strength and resistance to fatigue can be misleading. In the world
of high strength alloys, whether they are used for bolts or for
landing gears, the manufacturing processes are at least as impor-
tant as the material specification.
Some in our industry claim to inspect materials at the “molec-
ular” level. In metallurgical terms, molecules are not necessarily
part of the vocabulary. Our engineers tell us that talking about
molecules is misleading. When reference is made to metal, it is
typically in terms of atom structures. We routinely check metal-
lurgical features microscopically. By the way, the same is true for
claims of manufacturing to “zero tolerance.”
“Our engineers tell us that this is technically unrealistic.”
Smith: “How does the actual process work at ARP?”
“For each new design, we produce a number of prototype
parts using different design aspects and sometimes different
methods.
We inspect and test after each process, choose the best design
and method of manufacture, and then freeze the design and write
the manufacturing specification.”
Smith: “You have mentioned the importance of fatigue
resistance. Is there a difference in the procedures for
strength and fatigue testing between aerospace and the
specialty racing industry?”
“Yes. While the ultimate tensile strength testing is the same,
fatigue testing is different. Aerospace fasteners are fatigue tested
to the relevant specification of fluctuating tension load and
number of cycles typically 130,000 cycles with the high tension
load at 50% of the UTS and the low load at 10% of the high
load. If all of the test samples last 85,000 cycles (per AMS 5842-
D), the lot is accepted.
Even though racing fasteners are not continuously subjected
to their maximum design load, at 18,000 rpm, 100,000 cycles
takes just 5 minutes, thirty-four seconds. Except for drag racing,
measured in seconds, no race lasts just 5 minutes. Therefore we
consider this Aerospace Standard to be inadequate. At ARP, we
fatigue test to elevated loads (10% above aerospace requirements)
and to a minimum cycle life that exceeds 350,000 cycles. The
majority of samples are routinely tested to one million cycles.
During material development...and in the case of extremely criti-
cal new designs, we test to destruction.
Thread rolling is the last mechanical operation in our manu-
facturing process. For each production run the thread rolling
machine is shut down after a few parts. These parts are inspected
for dimensional accuracy and thread quality, and are physically
tested for both strength and fatigue before the run is continued.
Random samples are inspected and tested throughout the run.
Extremely critical components are individually inspected for
dimensional integrity.”
Smith: “What about out sourcing?”
“Economics often dictate that many processes in the manu-
facture of aerospace fasteners are out sourced or farmed out. In
fact, 30 plus years ago, ARP began as an out source thread rolling
shop.
Over the years, however, we have found, through experience,
that the only way to maintain the quality we require is to keep
everything in-house. From heading through machining, grind-
ing, heat-treat, thread rolling, and shot-peening to black oxide
treatment we perform every operation in house on our own
equipment with our own employees.”
Smith: “Gary, One of the things that I am hearing is that
every aspect of the manufacture of racing engine fasteners
is more expensive than that of similar aerospace items.”
“True, but the bottom line is that we have to look at the cost
aspect of the very best fastener versus the cost aspect of a blown
engine and a lost race. In the end, the manufacturing of fasteners
for racing comes down to a matter of attitude; a refusal to accept
published standards and procedures as the best that can be done
and most of all a determination to learn and to make still better
products.”
