Patent ID: 7807947

Claim:
In an apparatus for forming a three-dimensional object layer-by-layer from a powder material by laser sintering comprising in combination: a. a process chamber having a floor, a movable support platform co-operative with the floor, two opposing ends and a ceiling; b. a powder material feeder to controllably feed a powder material to the process chamber from a source of material; c. a powder spreader movably mounted to the apparatus and cooperative with the material feeder to spread powder material across the floor to form a powder bed between the two opposing ends; d. a laser energy source effective to selectively deliver laser energy to material in the powder bed supported by the support platform to fuse the powder material to form a three-dimensional object; e. at least one laser window having a surface exposed to the process chamber and being mounted in a window frame, wherein the laser energy source delivers the laser energy through the laser window; f. a source of inert gas feeding the inert gas in a direction of flow to the exposed surface of the laser window; and g. an inert gas dispenser comprising a discharge orifice that is mounted to at least one of the exposed surface and the window frame, wherein the discharge orifice dispenses an inert gas in a laminar flow at an effective velocity across the exposed surface to form a curtain of inert gas across the exposed surface and at a flow rate having a Reynolds number characteristic of the flow geometry of less than 200 effective to minimize the build-up of chemical by-product from the powder material on the exposed surface of the laser window during laser sintering.