Build orientation optimisation method and system for producing an article by additive manufacturing

A method of making an article by additive manufacturing from first and second powders of the same material which have been recycled to different extents where more of the less recycled (or virgin) powder has to be used in the more stressed regions of the article and less can be used in the less stressed regions of the article. The stress the article will experience is predicted, an optimal build orientation is identified which minimises the amount of the less recycled powder used to make the article and then the article is made in this orientation using the minimum amount of the less recycled powder. Each layer is made from a mixture of the first and second powders, their ratio depending upon the predicted stress experienced in that layer. The build orientation can be further optimised to minimise support structure volume.