The University of Texas System

Dtm Corporation

Udaykumar Lakshminarayan

Harris L Marcus

David L Bourell

Kevin P McAlea

Richard B Booth

A method of fabricating articles, such as prototype parts and prototype tooling for injection molding, is disclosed. The method begins with the fabrication of the article in a 'green' state by the selective laser sintering, or another additive thermal process, applied to a composite powder, preferably a powder of metal particles coated with a thermoplastic polymer. Both the green article and also an aqueous emulsion of a thermosetting material are then preheated to a temperature below the glass transition temperature of the thermoplastic polymer, and the green article is then infiltrated with the aqueous emulsion. The thermosetting material may be a thermosetting polymer with an appropriate cross-linking agent, or may be a cross-linking agent that will react with the thermoplastic binder polymer. After infiltration, the article is dried, and a rigid skeleton of a thermosetting material is now present within the structure of the article. Further processing may now be performed. The article may be heated beyond the decomposition temperature of the polymers so as to drive off the polymer and sinter the metal particles to one another; alternatively, a resin may be added to the article to form a metal-polymer composite article. High strength articles may thus be formed in a manner which preserves the dimensional accuracy of the article relative to its CAD representation.

Method of forming three-dimensional articles using thermosetting

A method and apparatus for selectively sintering a layer of powder to produce a part comprising a plurality of sintered layers. The apparatus includes a computer controlling a laser to direct the laser energy onto each layer of the powder to produce a sintered mass corresponding to a cross-section of the part. For each cross-section, the aim of the laser beam is scanned over a layer of powder and the beam is switched on to sinter only the powder within the boundaries of the cross-section. Powder is applied and successive layers sintered until a completed part is formed. Also disclosed is a method of forming a part by interaction of material in the powder layer with reactants in the surrounding atmosphere, at locations of the powder irradiated by the energy, or laser, beam. The reaction may be nitridation, oxidation or carburization of the powder, with the product being a chemical compound of one or more constituents in the powder with one or more gases in the atmosphere. Alternatively, reduction of the powder may be so enabled by the energy beam so that a metallic phase product is formed at the irradiated locations. Particular benefits of the invention include the densification of the material of the part as a result of the reaction, and the ability to form high temperature materials by way of a relatively low temperature process.

Method of producing parts by selective beam interaction of powder with

A method and apparatus for selectively sintering a layer of powder to produce a part comprising a plurality of sintered layers. The apparatus includes a computer controlling a laser to direct the laser energy onto the powder to produce a sintered mass. The computer either determines or is programmed with the boundaries of the desired cross-sectional regions of the part. For each cross-section, the aim of the laser beam is scanned over a layer of powder and the beam is switched on to sinter only the powder within the boundaries of the cross-section. Powder is applied and successive layers sintered until a completed part is formed. Preferably, the powder comprises a plurality of materials having different dissociation or bonding temperatures. The powder preferably comprises blended or coated materials, including precursor materials which are formed into a mass at the irradiated locations, and which either react due to the laser thermal energy or in a later heat treatment to form a compound with properties different than the precursors. Examples are disclosed wherein a compound is formed which has a significantly higher melting point than that of one or more of the precursor powders. A ceramic part, such as a mold for investment casting, may be formed according to the method, where a first material (e.g., ammonium dihydrogen phosphate) has a melting point sufficiently low that it is melted so as to bind the second material (e.g., alumina). Subsequent heat treatment enables chemical reaction of the two materials to form a ceramic (e.g., aluminum phosphate) capable of withstanding high temperatures.

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Austin, TX, United States of America

Udaykumar Lakshminarayan