X-ray diffraction measurements and computational prediction of residual stress mitigation scanning strategies in powder bed fusion additive manufacturing

The repeated localised heating-melting-cooling-solidification processes during laser beam powder bed fusion (PBF-LB) additive manufacturing (AM) induce intricate thermal residual stress (RS) in manufactured parts. Non-destructive characterisation using X-ray diffraction was used to measure the RS of Ti-6Al-4V square plates that were manufactured by using six different scanning strategies. Computational modelling was used to interpret the experimental stress measurement results. It was revealed that an inclined scanning strategy is beneficial for reducing the average through-thickness RS because the inclined scanning strategy can mitigate the non-uniform thermal profile and corresponding residual thermal stresses in successive layers of material. Among all the different scanning strategies that were analysed in this work, the 45° inclined 90° rotation scanning resulted in the lowest RS. The thicker parts have a greater gradient of RS than the thinner parts, after base plate removal. This research outcome can help the AM industry to design or optimise the process parameters of the PBF-LB aiming to minimise the RS of metal parts.