Reactor for production of an object of a weldable material by solid freeform fabrication, where the reactor comprises: - a reactor chamber which is closed to the ambient atmosphere, where the reactor is filled with argon as inert gas, so that the atmosphere of the reactor chamber has an oxygen concentration of 50 ppm or less, - an actuator controlling the position and movement of a support substrate placed inside the reactor chamber, - an actuator controlling the position and movement of a high energy plasma transferred arc welding torch with a wire feeder, - a control system able to read a virtual three dimensional vectorized layered model of the object which is to be formed and employ the virtual model to control the position and movement of the actuators (2, 4), operation of the welding torch and wire feeder such that a physical object is build by welding a layered structure of quasi one-dimensional pieces of the weldable material onto the supporting structure according to the virtual three dimensional vectorized layered model of the object which is to be formed, wherein: - all adjacent wall elements of the walls of the reactor chamber are joined with an obtuse angle (larger than 90°), - the actuator extends from below the reactor chamber and protrudes into the reactor chamber through an opening in the reactor chamber wall holding the support substrate inside the reactor chamber, - the opening is sealed by at least one elastic gas impermeable membrane which is gas tight attached to the reactor wall at the opening and to the actuator, - the actuator extends from the outside of the reactor chamber and protrudes into the reactor chamber through an opening of the wall of reactor chamber holding the high energy plasma transferred arc welding torch with wire feeder of the weldable material inside the reactor chamber, - the opening is sealed by the at least one elastic gas impermeable membrane which is gas tight attached to the reactor wall at the opening and to the actuator, - the reactor is equipped with at least one closable gas inlet located in the lower part the reactor chamber and at least one closable gas outlet located at the upper part of the reactor chamber, - where the gas inlet is equipped with means for regulating the argon pressure to about 100 Pa above the ambient atmospheric pressure, and - the reactor is equipped with means for measuring the oxygen content of the inert atmosphere inside the reactor chamber, and means to engage the flushing of the chamber with fresh inert gas in case the oxygen concentration rises above a preset maximum value. - a reactor chamber which is closed to the ambient atmosphere, where the reactor is filled with argon as inert gas, so that the atmosphere of the reactor chamber has an oxygen concentration of 50 ppm or less, - an actuator controlling the position and movement of a support substrate placed inside the reactor chamber, - an actuator controlling the position and movement of a high energy plasma transferred arc welding torch with a wire feeder, - a control system able to read a virtual three dimensional vectorized layered model of the object which is to be formed and employ the virtual model to control the position and movement of the actuators (2, 4), operation of the welding torch and wire feeder such that a physical object is build by welding a layered structure of quasi one-dimensional pieces of the weldable material onto the supporting structure according to the virtual three dimensional vectorized layered model of the object which is to be formed, - all adjacent wall elements of the walls of the reactor chamber are joined with an obtuse angle (larger than 90°), - the actuator extends from below the reactor chamber and protrudes into the reactor chamber through an opening in the reactor chamber wall holding the support substrate inside the reactor chamber, - the opening is sealed by at least one elastic gas impermeable membrane which is gas tight attached to the reactor wall at the opening and to the actuator, - the actuator extends from the outside of the reactor chamber and protrudes into the reactor chamber through an opening of the wall of reactor chamber holding the high energy plasma transferred arc welding torch with wire feeder of the weldable material inside the reactor chamber, - the opening is sealed by the at least one elastic gas impermeable membrane which is gas tight attached to the reactor wall at the opening and to the actuator, - the reactor is equipped with at least one closable gas inlet located in the lower part the reactor chamber and at least one closable gas outlet located at the upper part of the reactor chamber, - where the gas inlet is equipped with means for regulating the argon pressure to about 100 Pa above the ambient atmospheric pressure, and - the reactor is equipped with means for measuring the oxygen content of the inert atmosphere inside the reactor chamber, and means to engage the flushing of the chamber with fresh inert gas in case the oxygen concentration rises above a preset maximum value.