Apparatus and method for producing a three-dimensional work piece

1. An apparatus for producing a three-dimensional work piece comprising:

an irradiation unit comprising at least one scanning unit configured to scan a radiation beam over an uppermost layer of raw material powder to predetermined sites of the uppermost layer of the raw material powder in order to solidify the raw material powder at the predetermined sites,

wherein an axis corresponding to the radiation beam when it impinges on the uppermost layer of the raw material powder at an angle of 90° is defined as a central axis for the at least one scanning unit; and

a control unit configured to

receive work piece data indicative of at least one layer of the three-dimensional work piece to be produced, and

assign at least a part of a contour of the at least one layer of the three-dimensional work piece to the at least one scanning unit,

characterized in that

the control unit is configured to generate control data for controlling the irradiation unit, the control data defining a scan strategy of the radiation beam such that for more than 70% of a predefined length, the radiation beam moves away from the central axis,

the predefined length being defined as a length the radiation beam moves along the contour assigned to the at least one scanning unit, excluding sections concentric with regard to the central axis,

wherein the control unit is configured to generate the control data for controlling the irradiation unit, the control data defining the scan strategy of the radiation beam such that an irradiation power of the radiation beam and/or a scan speed of the radiation beam is adapted based on an angle between the radiation beam and the central axis, such that the irradiation power is increased when the angle increases and/or the scan speed is decreased when the angle increases; and

wherein the control unit is configured to, based on the work piece data, determine a thickness of the work piece in at least one region where the radiation beam is to be irradiated, decide whether the thickness is below a predefined threshold value, and, when the thickness is below the predefined threshold value, generate the control data for the at least one region such that the irradiation power is not increased in this region.

2. The apparatus according to claim 1 , wherein the predefined length is defined as an entire length the radiation beam moves along the contour assigned to the at least one scanning unit.

3. The apparatus according to claim 1 ,

wherein the irradiation unit comprises a further scanning unit configured to scan a further radiation beam over the uppermost layer of the raw material powder to predetermined sites of the uppermost layer of the raw material powder in order to solidify the raw material powder at the predetermined sites,

wherein an axis corresponding to the further radiation beam when it impinges on the uppermost layer of the raw material powder at an angle of 90° is defined as a further central axis for the further scanning unit;

wherein the control unit is configured to assign a section of the contour of the at least one layer of the three-dimensional work piece to the at least one scanning unit, such that an angle between the radiation beam and the central axis stays below a predefined value smaller than a maximum possible deflection angle of the at least one scanning unit, and to assign a further section of the contour to the further scanning unit, such that an angle between the further radiation beam and the further central axis stays below a further predefined value smaller than a maximum possible deflection angle of the further scanning unit.

4. The apparatus according to claim 1 , wherein the control unit is configured to generate the control data such that for more than 80% or for more than 90% of the predefined length, the radiation beam moves away from the central axis.

5. The apparatus according to claim 3 , wherein the predefined value and/or the further predefined value is a value in a range between 10° to 25°.

6. The apparatus according to claim 3 , wherein an overlap region is defined between the at least one scanning unit and the further scanning unit, wherein the overlap region can be irradiated by both the at least one scanning unit and the further scanning unit when the angles between the respective radiation beam and the respective central axis are below the respective predefined value.

7. The apparatus according to claim 3 , wherein the control unit is further configured to assign a portion of the at least one layer of the three-dimensional work piece that is not the contour to the at least one scanning unit, such that said portion is irradiated, at least in part, by the radiation beam under an angle larger than the predefined value.

8. The apparatus according to claim 3 , wherein the predefined value and/or the further predefined value is a value in a range between 15° and 20°.