Apparatus for Layerwise Producing an Object Using Laser Sintering

The present invention relates to an apparatus for layerwise producing an object using laser sintering.

The applicant is aware of an apparatus for layerwise producing an object using laser sintering, the apparatus comprising a support for positioning the object in relation to a working plane and a device for applying a powder which can be solidified by electromagnetic radiation. The apparatus further comprises a laser. The laser beam produced by the laser is focused onto a point within the working plane by means of a focusing device comprising a lens and solidifies the powder. Especially in case that polyamide is used as the powder material, monomers escape from the powder and precipitate on the lens, whereby the transparency thereof is progressively reduced in the course of the building process. This causes a progressive absorption of the laser beam, whereby its intensity at the working plane decreases. Owing to the decreasing intensity the quality of the object to be formed is reduced. In order to overcome this problem a protecting glass is arranged in front of the lens and nitrogen is blown out of a plurality of nozzles onto the protecting glass. However, since the nitrogen flows over part of the protecting glass only and no flow exists between the nozzles, the monomers precipitate at these places. Thus, the protecting glass must be removed and cleaned after each building process of an object.

It is the object of the invention to provide an apparatus for layerwise producing an object by laser sintering wherein the focusing unit is effectively protected against contamination.

This object is achieved by the apparatus comprising a device for producing an electromagnetic beam and a focusing device for focusing the beam onto the material within a working plane, whereby the focusing device comprises a lens and a mount supporting the lens, a ring nozzle arranged adjacent to the image-side surface of the lens facing the working plane, the ring nozzle having an outlet directed in relation to the image-side surface so that an outflowing stream strokes tangentially along the image-side surface towards the center, the inlet of the nozzle being selectively connected to a source of pressurized gas.

The apparatus is advantageous in that the nitrogen blown through the ring nozzle flows over the entire lens surface facing the working plane. Since the nitrogen is blown in a tangential direction of the lens surface, the flow produced is directed from the outer side of the lens towards the center thereof and therefrom towards the working plane. This flow efficiently prevents the precipitation of monomers on the lens surface. Hence, cleaning of the lens is required at considerably longer intervals.

Further features and advantages of the invention will be apparent from the description of embodiment with reference to the Figures. In the FIGS.

FIG. 1 is a schematic block diagram of the apparatus; and

FIG. 2 shows a section through the ring nozzle.

As shown in FIG. 1 the apparatus for layerwise production of an object comprises a support 2 which supports the object to be formed and which is movable in vertical direction within a tank 1 having an open top. The support 2 is vertically adjusted so that the respective layer of the object to be solidified is in a working plane 7. Moreover, a coating device 3 is provided for applying the powderous building material which can be solidified by electromagnetic radiation. The apparatus comprises a laser 5. The laser beam 6 produced by the laser 5 is focused onto a predetermined point within the working plane 7 by means of a focusing device 8.

As shown in FIG. 2, the focusing device 8 comprises a lens 9 and a mount 10 supporting the lens 9. The lens 9 comprises an image-side surface 11 facing the working plane 7. A ring nozzle 12 having an inlet connection 13 is provided in the mount 10. A reservoir containing a pressurized gas is coupled to the inlet connection 13 through a valve. Preferably, nitrogen is used for the gas. The ring nozzle 12 is arranged in the mount 10 adjacent to the image-side surface 11. The nozzle outlet orifice 14 is directed towards the image-side surface 11 so that the discharged gas stream flows tangentially across the image-side surface.

In operation the valve is opened and nitrogen flows through the inlet connection 13 into the ring nozzle 12 and out through the nozzle outlet orifice 14. The outflowing gas strokes across the entire image-side surface 11 of the lens 9 in a direction tangentially thereto. The gas flows radially towards the center of the lens 9 and therefrom in direction towards the working plane 7 so that monomers produced when solidifying the powder can not precipitate on the lens 9.