Title : Thermomechanical analysis of wire arc additive manufacturing of the bell mouth component of offshore facilities
The design freedom provided by Additive Manufacturing (AM) in the production of metallic parts represents a big step in the modern method of rapid manufacturing. These AM attributes can be used to great advantage in offshore facilities in the oil and gas sector, as parts inventory can be reduced, as well as equipment maintenance operations can be better managed. Among the AM techniques, Wire Arc Additive Manufacturing (WAAM), based on a welding process, stands out for enabling the manufacture of largescale metallic parts or adding material to pre-made workpieces with a high deposition rate and low feed material cost. However, the large amount of energy and material added during metallic deposition causes residual stress and distortion that can compromise the product’s functionality and structural integrity. Numerical simulation using finite element method (FEM) offers a tool for stress and distortion predictions that occur during arc welding thermal cycles. The simulation results can be used to identify the optimized material deposition strategies as well as the manufacturing parameters that minimize part defects. In this work, a FEM model is proposed to simulate the WAAM process in order to predict the temperature field, residual stresses and distortions in offshore facilities equipment parts. The influence of microstructural transformation on mechanical analysis is included through the mechanical properties of the filler material. The numerical simulation is implemented in a three-dimensional model of a thin wall by a transient thermal analysis coupled in series with mechanical analysis. The material deposition is modeled by element birth and death techniques (B&DT) combined with homogeneously distributed heat in the activating elements. The double ellipsoid model is adopted for heat generation on already activated elements. The material deposition and heat source modeling were developed by an integrated routine in the commercial finite element software ANSYS. The model evaluation is accomplished by comparing the results obtained in the part temperature field and distortion, layer by layer, from numerical analysis. Finally, numerical simulations with different deposition strategies are carried out to investigate the influence of each layer’s deposition direction on the final defects in the parts.