Abstract
Due to the layer-by-layer nature of the process, parts produced by laser-based powder bed fusion (LPBF) have high residual stresses, causing excessive deformations. To avoid this, parts are often post-processed by subjecting them to specially designed heat treatment cycles before or after their removal from the base plate. In order to investigate the effects of the choice of post-processing steps, in this work the entire LPBF process chain is modelled in a commercial software package. The developed model illustrates the possibilities of implementing and tailoring the process chain model for metal additive manufacturing using a general purpose finite element (FE) solver. The provided simplified computational example presents an idealised model to analyse the validity of implementing the LPBF process chain in FE software. The model is used to evaluate the effect of the order of the process chain, the heat treatment temperature and the duration of the heat treatment. The results show that the model is capable of qualitatively capturing the effect of the stress relaxation that occurs during a heat treatment at elevated temperature. Due to its implementation, the model is relatively insensitive to duration and heat treatment temperature, at least as long as it is above the relaxation temperature. Furthermore, the simulations suggest that, when post-processing, it is necessary to perform the stress relaxation before the part is removed from the base plate, in order to avoid a significant increase of the deformation. The paper demonstrates the capability of the simulation tool to evaluate the effects of variations in the process chain steps and highlights its potential usage in directing decision-making for LPBF process chain design.
Highlights
Additive manufacturing (AM) allows the manufacturing of parts with high complexity.relatively short lead times, near-net-shape production and low material waste contribute to the increasing interest in AM
The results show that the model is capable of qualitatively capturing the effect of the stress relaxation that occurs during a heat treatment at elevated temperature
The model is relatively insensitive to duration and heat treatment temperature, at least as long as it is above the relaxation temperature
Summary
Additive manufacturing (AM) allows the manufacturing of parts with high complexity. relatively short lead times, near-net-shape production and low material waste contribute to the increasing interest in AM. The mesh is fine where the laser surface heat flux interacts with the part and coarser in previously built layers, which effectively smears out the temperature and stress field in these layers This strategy results in a high resolution simulation of a single cuboid, both thermally and mechanically. Yakout et al [24] investigated the effect of the thermal expansion coefficient and the thermal diffusivity on the residual stress after the LPBF To achieve this, they simulated different materials and validated the model for one of them. Process chain modelling of other manufacturing chains, such as welding, can be found in the work by Yan et al [34] They use an Arrhenius-type equation to simulate the reduction of the stress during a post-weld heat treatment. The goal of the current paper is to evaluate the capabilities of the finite element model to assess the effect of the different process steps on the final part quality
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