Abstract:
Wire and Arc Additive Manufacturing (WAAM) is a promising technology for
manufacturing large-scale parts with low costs and short lead time. One of the
main challenges in applying WAAM in industry is the effective control of residual
stress and distortion. It has been found that high-pressure inter-layer rolling can
effectively mitigate the residual stress and distortion of WAAM components.
However, the mechanism behind the mitigation efficacy is of a complex nature
and has not been well understood. Finite element analysis (FEA) has proven to
be a reliable and accurate method for simulating the thermo-mechanical process.
The FEA simulation of large-scale inter-layer rolling is challenging due to the high
computational cost and complicated coupling between WAAM and rolling.
This research is based on efficient models for simulating WAAM deposition and
rolling processes, and their combination for large-scale structures. The efficient
modelling method is developed using a reduced-size model to determine the
steady-state solution, and then mapping the solution to a full-size structure for
further analysis. This method is successfully applied to study the evolution of
residual stress and plastic strain during the post-build and inter-layer rolling of
WAAM deposited walls. The numerical predictions are verified with experimental
results.
Cyclic formation of tensile residual stress occurs during the WAAM deposition,
whereas inter-layer rolling counteracts the development of the residual stress.
The effectiveness of roller designs is studied for reducing residual stress of the
WAAM process. Compared with a flat roller, a slotted roller can induce greater
longitudinal plastic strains and more effectively reduce the tensile residual stress
in the WAAM wall. Removal of the clamps only results in a slight redistribution of
residual stress in the post-build and inter-layer rolled WAAM components, since
the rolling mitigates most of the tensile residual stresses caused by WAAM. To
enhance the manufacturing efficiency, stacked-layers rolling can replace inter-
layer rolling for RS and distortion mitigation in tall WAAM parts. Influences of main
process parameters, such as rolling load and roller-to-component friction, on
mitigation of RS and distortion are also studied. Finally, based on the
understanding gained through the simulations, recommendation of an optimal
rolling strategy is made for future industrial application.
