Abstract: Before performing additive manufacturing of an article to be formed, a first scale plate is scanned in a first scanning speed so that a trace of the electron beam is depicted. An electric current value through a focusing coil with which the trace of the electron beam becomes narrowest is found and set as a melting electric current value. Then, a second scale plate is scanned similarly in the first scanning speed so that a trace of the electron beam is depicted. An electric current value through the focusing coil with which the trace of the electron beam cannot be seen is found and set as a preheating focusing electric current value. Dispersed metal powder is scanned with electron beam of the preheating electric current value as set before in a second scanning speed 20 to 30 times of the first scanning speed. Thereafter, the additive manufacturing is performed.

Abstract: In an additive manufacturing apparatus using electron beam melting for manufacturing three-dimensional structures by laminating layers in which metal powder is selectively molten-solidified with electron beam, defect in current apparatus is to be removed such that electrons accelerated with a constant accelerating voltage are irradiated irrespective of filling rate or density of metal powder to be used for additive manufacturing. Voltage of power supply applied between a grid and an anode provided in an electron gun for generating electron beam is varied corresponding to filling rate and/or density of metal powder. With this, velocity of electron such that a position where thermal energy becomes maximum is taken as most suitable can be obtained.