Implementierung ausgewählter Kriechmodelle in die numerische Simulation des WAAM-Prozesses

Research output: ThesisMaster's Thesis

Organisational units

Abstract

The present master thesis investigates the influence of creep in the course of process simulation of Wire and Arc Additive Manufacturing (WAAM). WAAM is a generative manufacturing process that uses a wire-shaped feed material in combination with an arc welding process to economically produce components of larger dimensions and medium complexity by applying material layer by layer. Creep is a viscoplastic material behavior that can occur with certain materials such as the titanium alloy Ti6Al4V investigated in this thesis, especially at elevated temperatures and stress levels greater than zero. Due to the thermo-mechanical WAAM process, significant residual stress and distortion states can occur, which can be influenced by possible creep. Therefore, this effect acts as the focus of this study. The beginning of the work deals with a literature research of the WAAM process and its numerical simulation as well as the creep behaviour of Ti6Al4V. An experimental part includes creep tests to investigate the short term creep behaviour of the material and to further derive selected creep models, which will subsequently be implemented into the numerical WAAM process simulation. With a simple simulation model consisting of a three-layer WAAM structure welded onto a base plate, simulations are performed using the developed creep models. Additionally, the influence of pre-heating of the base plate during the process is investigated. The simulation results are compared with each other and validated with measurement results of experimental investigations. It is shown that in a numerical analysis without the use of a creep model, a significant difference between simulation and measurement, when considering the local residual stress state of the base plate, can occur. By implementing the creep models this difference is reduced up to 35%, thus the prediction accuracy of the numerical simulation is improved. In general, it is shown that the local residual stress state in the WAAM structure is reduced by up to 51% by creep effects. No significant impact on the distortion of the base plate, mainly caused by the use of a relatively small, simple model geometry, could be evaluated. As a result of this work, besides the knowledge about the influence of creep on the residual stress and deformation state, a primary creep model for Ti6Al4V is available, which can be implemented in the WAAM process simulation and can be further used for the numerical analysis of larger, more complex WAAM structures.

Details

Translated title of the contributionImplementation of selected creep models in the numerical simulation of the WAAM process
Original languageGerman
QualificationDipl.-Ing.
Awarding Institution
Supervisors/Advisors
Award date23 Oct 2020
Publication statusPublished - 2020