Distortion of gears due to induction hardening with the gap-to-gap technique

The main goal of the European Commission Research project “WINDUCTION” is the design of an eco-friendly and low-energy consuming production route for the planet gears of the wind turbine gearboxes by the replacement of classical case hardening process with induction hardening.

Quantifying the distortions that occur during heat treatment is an important criterion when evaluating process chains. This paper compares the distortion of gears from different manufacturing processes after induction hardening and conventional case hardening. Gears with a module of 8 mm and a tip diameter of 220 mm were used. The gears were manufactured from the materials EN-50CrMo4 (AISI 4147), EN-56NiCrMoV7 (AISI 4150) and EN-56NiCrMoVBi7 (AISI L6). For induction hardening, the gap-to-gap technique was applied. Identical gears made of the material EN-18CrNiMo7-6 (AISI 4820) were used as a reference, consisting of gas carburizing with subsequent quenching in salt.

The focus is on the distortion of the gearing. As part of the measurement, three helix and three profile lines were measured on both flanks of each tooth. In addition, a pitch and runout measurement was carried out at two different positions in the axial direction of the gear. The resulting profile and helix deviations (slope and form) as well as the pitch deviations and runout error are analyzed.