Mesure et prédiction des distorsions des engrenages traités par induction

Abstract

The present study concerns the measurement of distortions on induction hardened gear. Induction heat treating of gear is used in the industry to allow the surface hardening of the gear teeth while its core stays ductile. This treatment increases the contact strength and insures a good fatigue behavior. But this heat treatment induces geometrical modifications which imposes a final step of machining. To quantify these distortions, measuring method on a coordinate measurement machine has been developed. First, the study focuses on AISI4340 steel gear with a simple geometry: right teeth geometry, involutes flanks. Results show homogeneous distortions around the gear, and for a giving induction recipe, they are repeatable within ±2μm for flanks and external radius, until ±5μm for lateral surfaces. The comparison between the four recipes has permitted to study their influence on distortions. The scale of distortions obtained extends from few micrometers to a maximum of 25 μm. Thus, the distortions can be anticipated and do not justify alone the necessity of final machining step, at least for this kind of geometry. The second part of the work concerns different gear geometry, more complex, in AISI4340 steel too. It is composed of a right teeth associated to a plate, linked to the rest of the part by a thin section. The results show that the global geometry of the part which was heat treated by induction can have a major influence on distortions level which can increase up to several hundred micrometers. Distortions are not only due to metallurgical transformations of the part. The study of the effect of different induction and material parameters has permitted to determine some tendencies to reduce distortions. But it is difficult to find one induction recipe to obtain minimal distortions because of the interactions between the different parameters studied and the reactions of each geometrical area of the part.

Date	14 Dec 2012
Original language	French
Awarding Institution	École de technologie supérieure
Supervisor	Philippe Bocher (Supervisor)