A method for forming a three dimensional article through successively depositing individual layers of powder material that are fused together with an electron beam from an electron beam sources so as to form the article. Providing a model of said three-dimensional article; a vacuum chamber having at least a first and a second section, powder material that are fused together is provided in said first section, at least one electron beam source is provided in said second section, wherein said first and second sections are openly connected to each other. Directing an electron beam from said at least one electron beam source over said work table to fuse in first selected locations according to said model to form a first cross section of said three-dimensional article while supplying a gas to said second section of said vacuum chamber.