Apparatus and method for forming a three-dimensional article

A method for operating an additive manufacturing apparatus in which a three-dimensional article is formed through successively depositing individual layers of powder material that are fused together according to a computer model so as to form the three-dimensional article, the method comprising the steps of:

• providing the computer model as a model of the three-dimensional article;
• distributing a layer of powder material on a work table in a first section of an apparatus comprising a chamber comprising the first section and a second section openly connected to each other, the second section comprising an electron beam source and an electromagnetic focus coil having an axially extending central axis;
• directing an electron beam from the electron beam source over the work table to fuse in first selected locations according to the computer model to form a first cross section of the three-dimensional article, such that drive current is supplied to the electromagnetic focus coil and to a reflector coil arranged radially outside the electromagnetic focus coil between the electromagnetic focus coil and an electron beam housing, and wherein a direction of windings of the reflector coil is opposite a direction of windings of the electromagnetic focus coil;
• and
• repeating the distributing and directing steps until the three-dimensional article is formed.