FE modeling of orbital friction welding

Abstract

Within the European project WRIST (innovative Welding processes for new Rail InfraSTructure), an orbital friction welding (OFW) process for joining rails has been proposed. This process has potential benefits e.g. reduced heat affected zone, expulsion of impurities from the welded area and a fast welding process. To assist in the design of this welding process, finite element (FE) models will be developed within the WRIST project.This thesis concerns the initial development of a FE model for the OFW process, applied to two bars made of a R260 rail grade. The developed FE model consists of a thermal model and a mechanical model. These are further divided into three process steps: heating, forging and cooling.In the thermal model, two different friction models have been studied and compared against measured data from literature.Results regarding the heat generation in the faying surface (weld interface) are presented for the studied heat models. Furthermore, based on the cooling rates and a CCT-diagram for the proposed rail material, the micro-structural composition has been estimated. Results show that martensite will be created on the surface of the weld. The mechanical model uses the temperature history from the thermal model to predict residual stresses and deformations after cooling in an sequentially coupled approach. Results from the simulation show high residual stresses. A discussion concerning the sensitivity and accuracy of predicted residual stresses and deformations, with respect to material parameters,is given. Keywords: Heat affected zone, Orbital friction welding (OFW), residual stresses, Finite element method (FEM)