Manufacturing chamber for an additive manufacturing machine , comprising an enclosure and comprising, in this enclosure : - a working plane comprising a central area having a flat surface, - a manufacturing platform for the deposition of the layers of additive manufacturing material and for supporting the part being manufactured, said platform being located in the central area of the working plane , said platform being moved in translation with respect to the working plane as the deposition and fusion of the layers of additive manufacturing powder proceed, - a circuit for circulating a gas flow over the manufacturing platform , characterized in that the enclosure and/or the working plane comprises an inlet opening for the gas flow, the geometry of this opening enabling the gas flow to be injected into the enclosure, in that the working plane comprises, upstream of the manufacturing platform with respect to the direction of circulation of the gas flow, an upstream ramp connected to the central area of the working plane where the manufacturing platform is located by a surface having a rounded convex profile, said upstream ramp being inclined with respect to the plane of the platform at an angle of between 10° and 25°; in that said inlet opening directs the gas flow onto said upstream ramp; and in that the surface with a rounded convex profile is configured for attaching the gas flow, by the Coanda effect, above the working plane along the central area of the working plane , said gas flow thus circulating in the form of a laminar flow over said manufacturing platform , the enclosure and/or the working plane also comprising, downstream of the platform , an outlet opening through which the gas flow is drawn, and the working plane comprising, downstream of the manufacturing platform with respect to the direction of circulation of the gas flow, a downstream ramp , connected to the area of the working plane where the manufacturing platform is located by a surface having a rounded convex profile. - a working plane comprising a central area having a flat surface, - a manufacturing platform for the deposition of the layers of additive manufacturing material and for supporting the part being manufactured, said platform being located in the central area of the working plane , said platform being moved in translation with respect to the working plane as the deposition and fusion of the layers of additive manufacturing powder proceed, - a circuit for circulating a gas flow over the manufacturing platform , characterized in that the enclosure and/or the working plane comprises an inlet opening for the gas flow, the geometry of this opening enabling the gas flow to be injected into the enclosure, in that the working plane comprises, upstream of the manufacturing platform with respect to the direction of circulation of the gas flow, an upstream ramp connected to the central area of the working plane where the manufacturing platform is located by a surface having a rounded convex profile, said upstream ramp being inclined with respect to the plane of the platform at an angle of between 10° and 25°; in that said inlet opening directs the gas flow onto said upstream ramp; and in that the surface with a rounded convex profile is configured for attaching the gas flow, by the Coanda effect, above the working plane along the central area of the working plane , said gas flow thus circulating in the form of a laminar flow over said manufacturing platform , the enclosure and/or the working plane also comprising, downstream of the platform , an outlet opening through which the gas flow is drawn, and the working plane comprising, downstream of the manufacturing platform with respect to the direction of circulation of the gas flow, a downstream ramp , connected to the area of the working plane where the manufacturing platform is located by a surface having a rounded convex profile. <EOS>