L-PBF process control to reduce hot-cracking and residual stress

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Powder bed fusion (PBF) of metals is an additive manufacturing process in which thermal energy selectively fuses regions of a powder bed. In laser PBF, a focused laser beam melts the powder to produce parts, layer by layer. Due to its flexibility, laser PBF accounts for ~80% of all installed metal AM systems in the world today. However, current metal AM machines do not enable parts to be built 'right first time': significant part-specific print development is still required to validate the build strategy for a new production part and demanding applications require post-process part testing and verification before entering service. Hot-cracking and residual stresses are major causes of part failure and are related to the evolution of the temperature distribution in the powder bed. As the temperature increases during a build, the conditions for the interaction of the laser with the powder bed can produce an unsatisfactory build condition. The thermal history depends on the interaction of the scan strategy with the part cross-section in the layer being built. In principle, these thermal effects are predictable, but it is not currently possible to achieve that in less time than it takes to undertake the physical build.This project will understand the physical processes involved in hot-cracking and residual stress formation from the literature, in particular the role of the evolving temperature distribution. Control build experiments will be undertaken to confirm this understanding, requiring suitable thermal imaging to be incorporated into the build chamber. Strategies to reduce hot-cracking and the effects of residual stress will then be investigated.