Integrierte Wärmebehandlungssimulation und Berechnung der Fußtragfähigkeit von Sinterzahnrädern

  • Integrated simulation of the heat treatment and calculation of the tooth root load bearing capacity of sintered gears

Rajaei, Ali; Broeckmann, Christoph (Thesis advisor); Schulze, Volker (Thesis advisor)

Aachen : RWTH Aachen University (2023)
Dissertation / PhD Thesis

Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2023

Abstract

Traditional powder metallurgy has the ability to produce gears with less energy input while conserving resources. However, the remaining porosity after sintering reduces the load-bearing capacity of the sintered gear. Studies show that the load-bearing capacity of sintered gears can be significantly increased by the subsequent cold rolling and case hardening. Currently, the design of heat treatment for sintered gears is based on investigations of conventional gears since specific guidelines for sintered gears are not available. Therefore, an integrated method for case hardening simulation and calculation of the load carrying capacity of the sintered gear was developed in this work, which con-siders the influence of the hardness profile and residual stresses on the load carrying capacity in combination with the local density. The developed finite element modeling of the heat treatment describes the hardness and residual stresses quantitatively according to process parameters such as carburizing temperature and duration as well as the quenching medium. The material model for the heat treatment simulation is mainly based on own experimental material investigations and partly on adopting model parameters from the literature. Following the heat treatment simulation, the loading of the gear is modeled according to the standard bench tests to determine the load bearing capability. This provides a three-dimensional description of the superposition of the load and residual stresses for different loading scenarios. The analysis of the probability of survival of the sintered gear integrates a strength model for the sintered steel and several failure hypotheses in an extended failure model. The load-bearing capacity of the sintered gear corresponds to the maximum load amplitude for a given probability of survival. The simulation model was validated by component characterizations and used in a computational study to investigate the influence of heat treatment on the load bearing capacity. It was shown that trends can be observed through the simulation that are very difficult or costly to identify experimentally. For example, it was found that increasing the case hardening depth affects the residual stresses of the surface zone and also the depth of compressive stresses at the tooth root and flank. Slightly higher compressive stresses due to the increased case depth led to an increase in tooth root load bearing capacity in the simulation. Furthermore, the simulation of the tooth flank pressure showed a risk of damage both in the near-surface edge region below the pitch circle and in the tooth volume approximately parallel to the densification profile of the surface layer.

Institutions

  • Internet of Production [080067]
  • Chair and Institute for Materials Applications in Mechanical Engineering [418110]

Identifier

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