Induction hardening of gear teeth is a well known for its challenges, but also for its potential for improved
quality and process control. For complex geometric parts like gears, the power density and induction
frequency need to be adjusted very precisely to achieve the required hardening pattern. Since the 1940s, itis
well known that working with two simultaneous frequencies is the optimal way to heat a geared part up to
hardening temperature. The key point in this process is that the medium frequency (about 10 kHz) affects
primarily the tooth root and the high frequency affects first of all the tip of the tooth and the flanks. The right
combination of the power densities of medium- and high frequency energy values and the heating time are the
crucial factors to reach a contour true heating pattern and, thereby, a contour true hardening pattern. Short
heating times and high power densities are critical relevant factors in order to achieve contour true hardened
gears.