The present invention relates to an apparatus 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 apparatus comprising an electron beam source emanating an electron beam for fusing the powder material in a build tank, a hollow construction having an upper opening and a lower opening, means for moving the hollow construction between a first position and a second position, a synchronising unit for synchronising the movement of a powder distributor for applying the individual layers of powder material on the work table with the movement of the hollow construction so that the hollow metal construction is at the first position when fusing and/or heating the powder layer and at the second position when the powder distributor is distributing the powder material for forming the individual powder layers.