Porosity refers to the level of solidity achieved in an additively made metal part, that is, whether there are cavities or holes between the layers of a part.
In some metal additive manufacturing processes, a laser is used to melt a layer of metal powder to the point where the powder liquefies and adheres to an earlier melted layer. Usually, this process results in very dense parts, typically 98% dense or more. However, there are times when the melt is not complete, resulting in hollows or cavities, also referred to as porosity.
The incomplete melt can be the result of gas pockets that form within the metal powder, variations in powder granule size, or the 3D printing process itself.
Nearly 100% dense parts may be required in an application to reduce or eliminate the risk of cracks and fatigue fractures, which would weaken a part, or result in total part failure.
To reduce porosity, additive manufacturing vendors recommend using materials they have tested with their equipment. The machines have been set to accommodate laser power, the size and shape of the laser spot, and so on to ensure a dense build. Certain laser scanning patterns will also reduce the occurrence of cavities in a build.
Often to ensure a dense part, a post processing treatment, such as hot isostatic pressing, is used to eliminate any possible cavities in a part.