Additive manufacturing of three-dimensional articles

A method for forming a three-dimensional article through successively depositing individual layers of powder material that are fused together so as to form the article, said method comprising the steps of:

• providing at least one electron beam source emitting an electron beam for at least one of heating or fusing said powder material, where said electron beam source comprises a cathode, an anode, and a grid between said cathode and anode;
• controlling the electron beam source in a first mode when said formation of said three dimensional article is in a first process step;
• and
• controlling said electron beam source in a second mode when said formation of said three dimensional article is in a second process step,
• wherein:
• the second process step comprises one of the group of:
• preheating the surface prior to applying a new powder layer onto said surface, preheating a new powder layer, preheating a powder distribution, and post heat treatment of an already fused powder layer;
• an electron beam current from said electron beam source is controlled in a feed-forward mode in said first mode;
• the first process step involves fusing said powder material;
• a predetermined grid potential provided to the grid is changed, during fusion of said powder material in the first process step, from a first predetermined grid potential to a second predetermined grid potential different from the first predetermined grid potential;
• said electron beam current is controlled in a feed-back mode in said second mode;
• and
• said feed-back mode comprises measuring said electron beam current.