Welcome to Part 2 of Flexible Assembly System’s
Fastening Theory educational video. In this video we will investigate friction
factors and how they affect tightening. First let’s look at where all the torque
we apply to a fastener goes. As discussed in part one, the goal of fastening
is to create clamp load. Clamp load is the force keeping two or more
parts from separating from each other. There is one giant factor that prevents all
the torque we apply from being translated into clamp force, and that is friction. Friction is the resistance that one surface
or object encounters when moving over another. About 90% of the applied torque is spent overcoming
friction, split between the threads and bearing surfaces of the bolted joint. Only about 10% of the applied torque in a
joint is creating clamp load. There are many friction factors to overcome
when fastening and a few ways to change where the torque goes. The first factor are the tolerances of the
parts involved. Bolts and nuts that are manufactured to a
tighter tolerance are more likely to fit together smoothly and offer more consistent results
than those made under looser standards. The next factor is alignment. When designing a joint the path the fasteners
take should be well aligned to prevent unnecessary rubbing or sheering when fastening the joint. A misaligned joint won’t provide a consistent
platform for tightening. Another factor is the surface finish on the
mating parts. A sanded or polished surface will produce
less friction than a brushed or textured surface would. The materials used also have a large impact
on friction. Plastics and soft metals are much less rigid
than steel or other hardened materials. Materials with lower frictional coefficients
will have less resistance to each other and consume less torque. The type of lubricant and the amount used
can help to alleviate friction that builds up between threads while tightening, if any
lubrication is used at all. Special fastener types such as thread forming
fasteners or nylon-insert lock nuts can introduce unique frictional factors that don’t exist
in standard fasteners. Other materials within the bolted joint such
as gaskets or soft objects will exert their own resistance to being compressed. When designing a joint all of these factors
should be taken in consideration. It’s important to maintain constant friction
within the joint while it’s being tightened. This will ensure the most accurate and reliable
results. That concludes part 2 of our Flexible Assembly
Fastening Theory educational video. Be sure to check out part 3 where we cover
different types of torque tools and safety concerns with using them. Thanks for watching this video, if you enjoyed
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