Additive manufacturing of three-dimensional articles

1. 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, said method comprising the steps of:

i) providing at least one electron beam source emitting an electron beam for at least one of heating or fusing said powder material, where said electron beam source comprises a cathode, an anode, and a grid between said cathode and anode;

ii) controlling the electron beam source in at least two modes during said formation of said three dimensional article, the at least two modes comprising a first mode and a second mode;

iii) applying a predetermined accelerator voltage between said cathode and said anode;

iv) applying at least one of a predetermined number of different grid voltages between said grid and said cathode for producing a corresponding predetermined number of electron beam current values while the electron beam source is in the first mode;

v) while applying the at least one of the predetermined number of different grid voltages, fusing the powder material;

vi) measuring an electron beam current during the second mode of the at least two modes;

vi) at least one of creating or updating a look-up table or mathematical function during the second mode of the at least two modes based on the measured electron beam current, wherein said look-up table or mathematical function defines a relationship between a desired electron beam current and an applied grid voltage; and

vii) subsequent to creating or updating the look-up table or mathematical function, repeating steps iv-v, wherein the at least one of the predetermined number of different grid voltages is selected from the look-up table or mathematical function.

2. The method according to claim 1 , wherein:

the first mode is utilized to control the electron beam source in a first process step;

the second mode is utilized to control the electron beam source in a second process step;

said first process step is said fusion of the powder material for forming said three-dimensional article; and

said second process step is one of the group of: preheating of the surface prior to applying a new powder layer onto said surface, preheating of a new powder layer, powder distribution, or post heat treatment of an already fused powder layer.

3. The method according to claim 1 , further comprising the steps of:

comparing a first actual electron beam current with a first desired electron beam current; and

updating the at least one of the look-up table or mathematical function if the difference between said first actual and first desired electron beam currents is greater than a predetermined value.

4. The method according to claim 3 , wherein the updating is performed after fusing a predetermined number of layers of the three-dimensional article.

5. The method according to claim 3 , wherein the updating is performed between the fusion process of each layer.

6. The method according to claim 1 , further comprising the steps of:

retrieving said predetermined grid voltage for producing said desired electron beam current from said look-up table or a mathematical function; and

changing said predetermined grid voltage from a first grid voltage to a second grid voltage during said first mode for changing said electron beam current from a first value to a second desired value during fusion of a predetermined layer.

7. The method according to claim 6 , wherein said predetermined grid voltage is changed from a first grid voltage to a second grid voltage during fusion of at least one individual scan line for changing said electron beam current in said scan line from a first value to a second desired value.