Apparatus and Method for Cooling Part Cake in Laser Sintering

Abstract

A part cake defining a build produced by laser sintering and the surrounding unfused powder is contained in an enclosure, aid the enclosure includes displaceable wall portions for compressing the part cake to support the build against distortion during rapid cooling from a cooling fluid. The enclosure enables the part cake to be quickly and reliably cooled either within the laser sintering system or outside the laser sintering system. A source of cooling fluid connects to the enclosure and a lid holds the part cake in place as cooling fluid is forced through the pore volume of the cake. An inert gas blanket apparatus is also provided to reduce or prevent oxidation of the part cake and / or to cool the part cake. Once the part cake is cooled, the build produced by laser sintering may be removed from the part cake.

Description

FIELD OF THE INVENTION[0001]This invention relates to laser sintering for the formation of three-dimensional objects from fusible powders and more particularly relates to the cooling of such objects after the sintering has been completed.BACKGROUND OF THE INVENTION[0002]Laser sintering is a solid imaging process for building three-dimensional objects, layer-by-layer, from a working medium utilizing sliced data sets representing cross sections of the object to be formed. Typically an object representation is initially provided by a computer aided design (“CAD”) system. The laser sintering system dispenses a thin layer of heat-fusible powder, normally a fusible polymer powder, polymer coated metal, metal, or ceramic, over a bed of the powder commonly referred to as the “part cake.” The laser sintering system applies thermal energy to melt those portions of the powder corresponding to a cross-section of the article being built in that powder layer. Lasers typically supply the thermal e...

AI Technical Summary

Benefits of technology

[0008]In one embodiment, the invention is an apparatus for cooling a part cake that comprises an enclosure for containing the part cake in which the enclosure has opposed displaceable wall portions that can be displaced from a laser sintering position to a part cake compression position and provides for forced cooling fluid to pass through the compressed part cake. In another embodiment, the invention is a method for cooling a part cake in which an enclosure is provided for the part cake that has displaceable wall portions that can be moved from a laser sintering position to a compression position. The displaceable wall portions are moved to a compression position to compress the part cake, and cooling fluid is forced through the part cake to cool the part cake. In more specific embodiments, the part cake is compressed to from less than about 50% of full density to about 70% of full density, full density being defined as that density achieved by fusing the fusible powder. At this higher bed density the part build inside the part cake is held rigidly in place during the cooling phase and suffers little distortion due to the rapid cooling.

[0011]Further embodiments of the present invention comprise an inert gas blanket apparatus that is selectively used to cover the part cake and expose the part cake to an inert gas flow to prevent oxidation of the part cake while the part cake is removed from the laser sintering system. In the exemplary embodiments of the present invention the inert gas comprises nitrogen, while further embodiments comprise alternative inert gases (inert gas as defined herein is any gas that does not react chemically with the powder or fused powder of the part cake). The inert gas blanket apparatus of certain embodiments includes an inert gas supply, a controller with valve devices to selectively control the release of inert gas from the supply, and a lid with a passage to receive the inert gas from the supply and to allow the inert gas to generally expose the part cake to the inert gas to prevent oxidation of the part cake while the inert gas is supplied. Some embodiments of the present invention include a gas sensor capable of monitoring the concentration of inert gas and / or oxygen in the air proximate the part cake for purposes of personnel protection.

[0012]Thus, the invention provides, among other benefits, apparatus and methods for compressing a part cake to support a build against distortion and for speedier cooling with forced cooling fluid. The apparatus can be used with older laser sintering systems adapted for removal of the build and part cake enclosure or with more updated systems having a build and part cake enclosure adapted to be removable for cooling in a separate station.

Problems solved by technology

A newly formed build may require several hours or days to cool and, as a result, the laser sintering system may be inactive during the cooling time, which may cause the system to be unavailable for subsequent builds.

Images