The present invention relates to a methods, computer program products, program elements, and apparatuses for forming a three-dimensional article through successively depositing individual layers of powder material that are fused together so as to form the article. The method comprising the steps of providing at least one electron beam source emitting an electron beam for at least one of heating or fusing the powder material, where the electron beam source comprises a cathode and an anode, and varying an accelerator voltage between the cathode and the anode between at least a first and second predetermined value during the forming of the three-dimensional article.