M. Maalekian, H. Cerjak, Graz University of Technology, Graz, Austria
The heat generation term is the key issue in the analysis and modelling of friction welding processes. The major unknown value for estimation of heat flux is the friction coefficient (μ). Often, a constant μ is used to approximate the heat generation by friction. However, many factors, e.g., temperature, magnitude of relative velocity, material properties and applied forces, affect frictional behavior and the forces that resist sliding between the two surfaces. Therefore, it is rather impossible to find the exact coefficient of friction, particularly for friction welding processes, by looking up values in published tables of friction coefficients. Because the conditions used to obtain those values are usually diverse from the friction welding conditions. Consequently, this assumption, i.e. constant μ, does not represent the nature of the process properly. Another widely used approach to define the heat flux at the weld interface is the conversion from experimentally measured power data. This method is, however, also not sufficiently accurate, since the recorded power is not entirely converted into the heat at the weld interface and a correction factor (efficiency) is required, which is usually not known. A convenient means for numerical analysis of the frictional heat generation is the inverse heat conduction approach, which is used in the present work. The Orbital friction welding of pearlitic steel bars is modeled using a 3-D FEM model. Based on the estimated heat generation obtained from an inverse heat transfer analysis, two FE simulations are carried out. First, in the coupled thermal-mechanical FE model, thermal history, flash formation and axial shortening are analyzed. Then, with the thermal phase transformation FE analysis, the final microstructure constituents after welding and the size of the HAZ are predicted.
Summary: The orbital friction welding of eutectoid steel bars is modeled using a 3-D FE model. Based on the estimated heat generation obtained from an inverse heat transfer analysis, two FE simulations, thermal-mechanical and thermal-phase transformation analyses are carried out. Thermal history, flash formation, axial shortening and the HAZ width are predicted.
