Apparatus for additive manufacturing of three-dimensional articles

An apparatus for forming at least one three-dimensional article through successive fusion of parts of a powder bed, which parts correspond to successive cross sections of the three-dimensional article, said apparatus comprising:

• a control unit having stored thereon a computer model of said at least one three-dimensional article;
• and
• at least one energy beam from at least one energy beam source, the at least one energy beam source being at least one of an electron beam or a laser beam,
• wherein the control unit is configured to:
• determine a length of at least one of two adjacent of two or more parallel scan lines either applied to the first powder layer or to be applied to the first powder layer;
• set a distance between the two adjacent of two or more parallel scan lines as a function of the determined length, wherein the function of the determined length is such that as the determined length increases:
• (a) the distance increases while the determined length is less than a predetermined value, and (b) the distance is a constant value while the determined length is equal to or greater than the predetermined value;
• and
• direct the at least one energy beam over said work table so as to cause said first powder layer to fuse in first selected locations according to a corresponding model of said at least one three-dimensional article so as to form a first cross section of said three-dimensional article, where the at least one energy beam is configured to fuse at least a first region of a first cross section either with said two adjacent of said two or more parallel scan lines extending in a first direction and separated by said set distance, or with at least one additional parallel scan line extending in said first direction and separated from said two adjacent of said two or more parallel scan lines by said set distance.