Abstract: A laser power control system (150; 150') having a first pulse stretch capability, as may be used in a rapid prototyping system (100), is disclosed. According to one disclosed embodiment, a one-shot multivibrator (156) generates a pulse responsive to a gate signal (LON/LOFF.sub.--) indicating that the laser (110) is to be turned on. The pulse, which is of a selected duration suitable for achieving population inversion, is applied to the laser (110); upon the end of this pulse, pulse-width-modulation (PWM) control of the laser begins. According to another disclosed embodiment, a first pulse stretch store (166) retains a digital value corresponding to the duration by which the first PWM pulse is to be lengthened; adders (176; 178) add this digital value to the parameters indicated by the desired laser power signal (DLP) to ensure population inversion and laser output of the laser (110) in the first pulse.

Abstract: A laser-sinterable powder product has been prepared having unique properties which allow the powder to be sintered in a selective laser sintering machine to form a sintered part which is near-fully dense. For most purposes, the sintered part is indistinguishable from another part having the same dimensions made by isotropically molding the powder. In addition to being freely flowable at a temperature near its softening temperature, a useful powder is disclosed that has a two-tier distribution in which substantially no primary particles have an average diameter greater than 180 .mu.m, provided further that the number average ratio of particles smaller than 53 .mu.m is greater than 80%, the remaining larger particles being in the size range from 53 .mu.m to 180 .mu.m. A powder with slow recrystallization rates, as evidenced by non-overlapping or slightly overlapping endothermic and exothermic peaks in their differential scanning calorimetry characteristics for scan rates of on the order of 10.degree. C. to 20.

Abstract: A selective laser sintering apparatus and method is disclosed, in which the laser power is controlled according to the scan velocity. The scanning system, which includes a pair of galvanometer-controlled mirrors for directing the aim of the laser beam, generates signals indicative of either the position or scan velocity of the aim of the beam, in either one or two directions. The signals are gated in the laser power control system so as to pass the signals only during those times at which the laser is to be turned on. A laser power control system receives the signals and, in the case of position signals, differentiates the signals to generate velocity signals. The velocity signals are used to derive a scan velocity, and the scan velocity is multiplied by the desired laser power at full scan velocity to produce a laser power control signal.

Abstract: A laser-sinterable powder product has been prepared having unique properties which allow the powder to be sintered in a selective laser sintering machine to form a sintered part which is near-fully dense. For most purposes, the sintered part is indistinguishable from another part having the same dimensions made by isotropically molding the powder. In addition to being freely flowable at a temperature near its softening temperature, a useful powder is disclosed that has a two-tier distribution in which substantially no primary particles have an average diameter greater than 180 .mu.m, provided further that the number average ratio of particles smaller than 53 .mu.m is greater than 80%, the remaining larger particles being in the size range from 53 .mu.m to 180 .mu.m. A powder with slow recrystallization rates, as evidenced by non-overlapping endothermic and exothermic peaks in their differential scanning calorimetry characteristics for scan rates of on the order of 10.degree. C. to 20.degree. C.

Abstract: A powder for use in selective laser sintering, from which prototype articles and masters for molds may be formed, is disclosed. The powder is formed by spray drying a polymer emulsion to yield a distribution of particles of substantially spherical shape. The powder is then air classified to remove excessively small particles from the distribution; the powder may also be screened to remove large particles therefrom, as well. The resulting distribution of particle sizes, by volume, preferably has a mean particle size of between about 20.mu. and about 50.mu., with preferably less than about 5% (by volume) of its particles with a size of less than about 15.mu. and less than about 2% (by volume) of its particles with a size of greater than about 75.mu.. The powder is subjected to selective laser sintering to produce an article of approximately 55% to 75% of theoretical density. The article may be used as a prototype article or part, or as a pattern or master for a mold.

Abstract: 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.

Abstract: A composite powder specially adapted for use in selective laser sintering is disclosed. The composite powder includes a polymer powder dry mixed with a reinforcement powder, where the polymer powder has a melting temperature substantially lower than that of the reinforcement powder. In the case where nearfully dense parts are to be formed, the first constituent powder is preferably a semi-crystalline powder, for example nylon 11, of a composition suitable for forming near-fully dense parts when used unblended in selective laser sintering; if porous parts are desired, the polymer powder is an amorphous powder, such as polycarbonate, polystyrene, acrylates, and styrene/acrylate copolymers. The reinforcement powder is preferably microspheres of glass, preferably coated to enhance wetting and adhesion with the polymer powder when selective laser sintering is performed.

Abstract: A laser-sinterable powder product has been prepared having unique properties which allow the powder to be sintered in a selective laser sintering machine to form a sintered part which is near-fully dense. For most purposes, the sintered part is indistinguishable from another part having the same dimensions made by isotropically molding the powder. In addition to being freely flowable at a temperature near its softening temperature, a useful powder is disclosed that has a two-tier distribution in which substantially no primary particles have an average diameter greater than 180 .mu.m, provided further that the number average ratio of particles smaller than 53 .mu.m is greater than 80%, the remaining larger particles being in the size range from 53 .mu.m to 180 .mu.m. A powder with slow recrystallization rates, as evidenced by non-overlapping or slightly overlapping endothermic and exothermic peaks in their differential scanning calorimetry characteristics for scan rates of on the order of 10.degree. C. to 20.

Abstract: A laser-sinterable powder product has been prepared having unique properties which allow the powder to be sintered in a selective laser sintering machine to form a sintered part which is near-fully dense. For most purposes, the sintered part is indistinguishable from another part having the same dimensions made by isotropically molding the powder. In addition to being freely flowable at a temperature near its softening temperature, a useful powder is disclosed that has a two-tier distribution in which substantially no primary particles have an average diameter greater than 180 .mu.m, provided further that the number average ratio of particles smaller than 53 .mu.m is greater than 80%, the remaining larger particles being in the size range from 53 .mu.m to 180 .mu.m. A powder with slow recrystallization rates, as evidenced by non-overlapping endothermic and exothermic peaks in their differential scanning calorimetry characteristics for scan rates of on the order of 10.degree. C. to 20.degree. C.

Abstract: A method and apparatus for calibrating the scan of a laser over a planar surface that includes defining an error table having x-dimension and y-dimension correction factors, and also a scale factor, for each of a plurality of regions of the planar target surface. The scale factor is initially set to a value to account for differences in the size of the image field to be scanned and the overall scan field in the CAD data base. Adjustment is performed to each scale factor to account for theoretical differences due to the use of a perpendicular galvanometer-driven mirror scanning system. A sheet with a large number of square cells is then placed over the target surface, after rotational alignment, and the laser marks each cell. The sheet is then converted into digital form by scanning, and the location of the laser mark relative to the centroid of the cell is used to update the correction factors for that cell.

Abstract: A method and apparatus for fabricating three-dimensional objects according to the selective laser sintering process are disclosed. In order to reduce inconsistencies in structural and textural integrity, and in thermal effects that can cause distortion, methods for ensuring that overlapping laser scans are accomplished in a consistent manner relative to the thermal flow from the sintered locations are utilized. Methods are disclosed for achieving this by limiting the extent to which the laser scans object areas in the powder layers so that the time-to-return for adjacent overlapping scans is minimized; such minimization results in significantly less variation in the time-to-return overall.

Abstract: A laser-sinterable powder product has been prepared having unique properties which allow the powder to be sintered in a selective laser sintering (SLS) machine to form a sintered part which is near-fully dense. For most purposes, the sintered part is indistinguishable from another part having the same dimensions made by isotropically molding the powder. In addition to being freely flowable at a temperature near its softening temperature, the powder has a two-tier distribution in which substantially no primary particles has an average diameter greater than 180.mu.m, provided further that the number average ratio of particles smaller than 53.mu.m is greater than 80%, the remaining larger particles being in the size range from 53.mu.m to 180.mu.m. When the powder is a semicrystalline synthetic resin having a number average molecular weight in the range from about 30,000 to 500,000; a molecular weight distribution M.sub.w /M.sub.

Abstract: An apparatus and method for producing parts by fusing selected portions of a layer of powder at a target area, including the systems for delivering the powder to the target area, is disclosed. Multiple powder pistons are included in the apparatus, each of which lift a volume of powder above a surface in an alternating manner relative to one another. Powder delivery begins by the lifting of a volume of powder at a first location on one side of the target area. A counter-rotating roller moves across the lifted powder, distributes it over the target area, and rests beyond a second powder lifting location on the other side of the target area. Portions of the powder layer are then fused at the target area according to a cross-section of the part to be produced, and is followed by lowering a part cylinder at the target area in order to accept the next layer of powder.

Abstract: A radiant heater, and an apparatus for performing selective laser sintering using the same, are disclosed. The radiant heater is ring-shaped with its dimensions and distance from the target surface preferably defined to provide radiant energy to a target surface, with the rate of energy received per unit area of the target surface being substantially uniform. A frusto-conical ring-shaped radiant heater is also disclosed, which may be disposed closer to the surface to provide improved efficiency of heat transfer in a uniform fashion. A cooling element similarly shaped is also disclosed, which operates in the same manner to uniformly transfer radiant heat from the target surface. Zoning of the ring-shaped radiant heaters, to allow for non-uniform radiant energy emission to the target surface, is also disclosed. Monitoring of the temperature of the target surface is done by way of infrared sensors.