Method of controlling an irradiation system for use in an apparatus for producing a three-dimensional work piece and comprising a first and a second irradiation unit (22a, 22b), the method comprising the steps of: - defining a first irradiation area on a surface of a carrier adapted to receive a layer of raw material powder, - irradiating a layer of raw material powder applied onto the carrier in the first irradiation area by the first irradiation unit of the irradiation system, wherein the operation of the first irradiation unit is controlled in such a manner that the raw material powder is pre-heated, and - thereafter irradiating the layer of raw material powder applied onto the carrier in the first irradiation area by means of the second irradiation unit of the irradiation system, wherein the operation of the second irradiation unit is controlled in such a manner that the raw material powder is heated to a temperature which allows sintering and/or melting of the raw material powder in order to generate a layer of the three-dimensional work piece, characterized by the steps of: - defining a second irradiation area on the surface of the carrier, and - irradiating a layer of raw material powder applied onto the carrier in the second irradiation area by the second irradiation unit of the irradiation system, while the first irradiation unit irradiates a layer of raw material powder applied onto the carrier in the first irradiation area, or - irradiating a layer of raw material powder applied onto the carrier in the first irradiation area by the second irradiation unit of the irradiation system, while the first irradiation unit irradiates a layer of raw material powder applied onto the carrier in the second irradiation area. - defining a first irradiation area on a surface of a carrier adapted to receive a layer of raw material powder, - irradiating a layer of raw material powder applied onto the carrier in the first irradiation area by the first irradiation unit of the irradiation system, wherein the operation of the first irradiation unit is controlled in such a manner that the raw material powder is pre-heated, and - thereafter irradiating the layer of raw material powder applied onto the carrier in the first irradiation area by means of the second irradiation unit of the irradiation system, wherein the operation of the second irradiation unit is controlled in such a manner that the raw material powder is heated to a temperature which allows sintering and/or melting of the raw material powder in order to generate a layer of the three-dimensional work piece, - defining a second irradiation area on the surface of the carrier, and - irradiating a layer of raw material powder applied onto the carrier in the second irradiation area by the second irradiation unit of the irradiation system, while the first irradiation unit irradiates a layer of raw material powder applied onto the carrier in the first irradiation area, or - irradiating a layer of raw material powder applied onto the carrier in the first irradiation area by the second irradiation unit of the irradiation system, while the first irradiation unit irradiates a layer of raw material powder applied onto the carrier in the second irradiation area.