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, 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, varying an accelerator voltage between the cathode and the anode between at least a first and a second predetermined value during the forming of the three-dimensional article, applying the first predetermined value of the accelerator voltage between the cathode and the anode when the formation of the three dimensional article is in a first stage, and applying the second predetermined value of the accelerator voltage between the cathode and the anode when the formation of the three dimensional article is in a second stage, wherein the predetermined first value of the accelerator voltage differs from the second predetermined value of the accelerator voltage by at least 10kV, wherein: the first stage is a first process step used for a central melting spot and the second stage is a second process step used for at least one surrounding heating spot; the first stage is a first process step used for a central melting spot and the second stage is a second process step used for a concentric heating spot; the first stage is a first process step used for a central melting spot and the second stage is a second process step used for an at least partially overlapping heating spot; or the first stage is at least one portion of a first process step used for preheating of unfused powder and the second stage is at least one other portion of the first process step used for preheating of unfused powder. 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, varying an accelerator voltage between the cathode and the anode between at least a first and a second predetermined value during the forming of the three-dimensional article, applying the first predetermined value of the accelerator voltage between the cathode and the anode when the formation of the three dimensional article is in a first stage, and applying the second predetermined value of the accelerator voltage between the cathode and the anode when the formation of the three dimensional article is in a second stage, wherein the predetermined first value of the accelerator voltage differs from the second predetermined value of the accelerator voltage by at least 10kV, wherein: the first stage is a first process step used for a central melting spot and the second stage is a second process step used for at least one surrounding heating spot; the first stage is a first process step used for a central melting spot and the second stage is a second process step used for a concentric heating spot; the first stage is a first process step used for a central melting spot and the second stage is a second process step used for an at least partially overlapping heating spot; or the first stage is at least one portion of a first process step used for preheating of unfused powder and the second stage is at least one other portion of the first process step used for preheating of unfused powder. the first stage is a first process step used for a central melting spot and the second stage is a second process step used for at least one surrounding heating spot; the first stage is a first process step used for a central melting spot and the second stage is a second process step used for a concentric heating spot; the first stage is a first process step used for a central melting spot and the second stage is a second process step used for an at least partially overlapping heating spot; or the first stage is at least one portion of a first process step used for preheating of unfused powder and the second stage is at least one other portion of the first process step used for preheating of unfused powder.