High pressure multi-layer rolling is an effective method to reduce residual stress and distortion in metallic components built by wire arc additive manufacturing (WAAM). However, the mechanisms of the reduction in residual stress and distortion during multi-layer rolling are not well understood. Conventional finite element models for rolling are highly inefficient, hindering the simulation of multi-layer rolling for large WAAM components. This study aims to identify the most suitable modelling technique for finite element analysis of large WAAM component rolling. Four efficient rolling models were developed, and their efficiency and accuracy were compared with reference to a conventional large-scale rolling model (i.e., control model) for a WAAM built wall. A short-length transient model with fewer elements than the control model was developed to reduce computational time. Accurate predictions of stress and strain and a reduction in computational time by 96.5% were achieved using the short-length model when an implicit method for numerical solution was employed, while similar efficiency but less accurate prediction was obtained when an explicit solution method was adopted. A Eulerian steady-state model was also developed, which was slightly less efficient (95.91% reduction in computational time) but was much less accurate due to unrealistic representation of rolling process. The applicability of a 2D rolling model was also examined and it was found that the 2D model is highly efficient (99.52% time reduction) but less predictive due to the 2D simplification. This study also shows that the rigid roller adopted in the models is beneficial for improving efficiency without sacrificing accuracy.

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Wire arc additive manufacturing (WAAM) of large component is susceptible to residual stress and distortion, which are detrimental and need to be mitigated through high pressure rolling or other methods. In this study, an efficient modelling approach is developed to simulate both WAAM and rolling, and this approach can also be applied to other manufacturing processes to determine steady-state variables. For a clamped wall component, the computationally efficient reduced-size WAAM and rolling models (i.e., short models) can obtain steady-state solutions equivalent to those obtained by conventional full-size models. For the short models, the undesirable effect of reducing the length of the modelled component is counteracted by imposing additional longitudinal constraint as proper to specific processes. The steady-state solution obtained by the short model in clamped condition is then mapped to a long model for analysis of residual stress and distortion after removal of clamps. The WAAM model predictions of temperature, residual stress and distortion are in good agreement with experimental measurements. For the steady-state WAAM region, compressive longitudinal plastic strain is formed approximately uniformly in the wall, and the influential factors and implications of the plastic strain are analysed. The high pressure rolling on the WAAM-deposited wall introduces tensile plastic strain that compensates for the compressive plastic strain induced by the WAAM deposition, thereby mitigating the tensile residual stress in the clamped wall and alleviating the bending distortion after the removal of clamps. This study demonstrates an efficient approach for modelling large-scale manufacturing and provides insights into the steady-state strains and stresses generated by WAAM and rolling.