Plastic gears are everywhere
today - throughout your car, at
the oceans' lowest depths, in deep
space. The question, when is a
metal gear a candidate for plastic
conversion, can be addressed in
three words, i.e. what's the application?
Cracks initiated at the surface of case-hardened gears may lead to typical life-limiting fatigue failure
modes such as pitting and tooth root breakage. Furthermore, the contact load on the flank surface
induces stresses in greater material depth that may lead to crack initiation below the surface if the
local material strength is exceeded. Over time the sub-surface crack propagation may lead to gear
failure referred to as “tooth flank fracture” (also referred to as “tooth flank breakage”). This paper explains the mechanism of this subsurface fatigue failure mode and its decisive influence factors, and presents an overview of a newly developed calculation model.
Since we began publishing in 1984, Gear Technology's mission has been to educate our readers. For 31 years, we've shown you the basics of gear manufacturing as well as the cutting edge. We take our educational mission quite seriously, and we go through steps that most publishers don't have time for or wouldn't consider.
At the dawn of the Industrial
Revolution, so-called mechanics
were tasked with devising the precise methods that would make mass production possible. The result was the first generation of machine tools, which in turn required improved tooling and production methods.
It has long been known that the skiving
process for machining internal gears is
multiple times faster than shaping, and
more flexible than broaching, due to skiving's continuous chip removal capability. However, skiving has always presented a challenge to machines and tools. With the relatively low dynamic stiffness in the gear trains of mechanical machines, as well as the fast wear of uncoated cutters, skiving of cylindrical gears never achieved acceptance in shaping or hobbing, until recently.