Method and apparatus for producing parts by selective sintering

Abstract: A method and apparatus (10) for selectively sintering a layer of powder to produce a part comprising a plurality of sintered layers. The apparatus includes a computer (40) controlling a laser (12) 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. The powder may consist of a plastic, metal, ceramic, or polymer substance. In the preferred embodiment, the aim of the laser is directed in a continuous raster scan and the laser turned on when the beam is aimed within the boundaries of the particular cross-section being formed. Preferably, the powder dispensing mechanism includes a drum which is moved horizontally across the target area and counter-rotated to smooth and distribute the powder in an even layer across the target area. A downdraft system provides controlled temperature air flow through the target area to moderate powder temperature during sintering.

Description: This invention relates to a method and apparatus for distributing dispensed powder. The method and apparatus find application in apparatus which uses a directed energy beam to selectively sinter a powder to produce a part, for example, a computer aided laser apparatus which sequentially sinters a plurality of powder layers to build the desired part in a layer-by-layer fashion. Such an apparatus is described in EP-A-0287657. The present method and apparatus are not restricted to such application. In such apparatus it is necessary to distribute dispensed powder into a uniform layer. A known distributing apparatus makes use of a rotatable rotter and is described in DE-B-1146652. According to a first aspect of the present invention there is provided a device for distributing dispensed powder as a layer of powder over a region, comprising: drum means, and means for rotating the drum means; characterised in that the device includes means for moving the drum from one end of the region to another end of the region with a desired spacing between said region and drum; and said means is arranged to rotate the drum counter to the direction of movement of the drum from said one end to said other end; and wherein said drum means is operable when counter-rotated and moved from said one end to said other end to contact the dispensed powder such that the mechanical action of the drum on the powder ejects the powder in said direction of movement to leave a layer of powder over the region having a thickness of approximately said desired spacing. According to a second aspect of the present invention there is provided a method of applying a layer of powder over a region of a surface of an article being produced from the powder in layerwise fashion, comprising the steps of: providing powder to a location proximate said region; moving a drum across said region; rotating the drum counter to the direction of movement of said drum across said region; and contacting the powder with the counter-rotating drum as it moves across said region so that a layer of powder remains over said region after said moving step, wherein the moving step is carried out without transmitting substantial shear stress to previously applied layers and without disturbing the article produced in such previously applied layers. In an embodiment of the present invention the distributing device includes a drum, a mechanism for moving the drum across the region, and a mechanism for counter-rotating the drum as it is moved across the region. The drum moving mechanism preferably keeps the drum a desired spacing above the region to yield a layer of powder of a desired thickness. The drum is operable when counter-rotated and moved across the region to project powder forward in the direction of movement, leaving behind a layer of powder having the desired thickness. The invention will be described now by way of example only, with particular reference to the accompanying drawings. In the drawings: FIGURE 1 is a schematic representation of an apparatus in which the present method and apparatus can be used, FIGURE 2 is a schematic, vertical, sectional view of the powder dispensing device of the present invention distributing powder in a layer on the part being produced; and FIGURE 3 is a schematic, perspective view of the powder dispensing device of the present invention. Turning now to the drawings, FIGURE 1 broadly illustrates an apparatus 10 in which the present powder distributing apparatus can be used. Broadly speaking, the apparatus 10 includes a laser 12, powder dispenser 14, and laser control means 16. In more detail, the powder dispenser 14 includes a hopper 20 for receiving the powder 22 and having an outlet 24. The outlet 24 is oriented for dispensing the powder to a target area 26, which in FIGURE 1 is generally defined by the confinement structure 28. Of course, many alternatives exist for dispensing the powder 22. The components of the laser 12 are shown somewhat schematically in FIGURE 1 and include a laser head 30, a safety shutter 32, and a front mirror assembly 34. The type of laser used is dependent upon many factors, and in particular open the type of powder 22 that is to be sintered. In the embodiment of FIGURE 1, a Nd:YAG laser (Lasermetrics 9500Q) was used which can operate in a continuous or pulsed mode with a hundred-watt maximum outlet power in the continuous mode. The laser beam output of the laser 12 has a wavelength of approximately 1060 nM, which is near infrared. The laser 12 illustrated in FIGURE 1 includes an internal pulse rate generator with a selectable range of about one kiloHertz to forty kiloHertz, and an approximately six nanosecond pulse duration. In either the pulsed or continuous mode, the laser 12 can be modulated on or off to selectively produce a laser beam which travels generally along the path shown by the arrows in FIGURE 1. To focus the laser beam, a diverging lens 36 and converging lens 38 are disposed along the path of travel of the laser beam as shown in FIGURE 1. Using just the converging lens 38, the location of the true focal point is not easily controlled by varying the distance between the converging lens 38 and the laser 12. The diverging lens 36 placed between the laser 12 and converging lens 38 creates a virtual focal point between the diverging lens 36 and the laser 12. Varying the distance between the converging lens 38 and the virtual vocal point, allows control of the true focal point along the laser beam path of travel on the side of the converging lens 38 remote from the laser 12. In recent years there have been many advances in the field of optics, and it is recognised that many alternatives are available to efficiently focus the laser beam at a known location. In more detail, the laser control means 16 includes computer 40 and scanning system 42. In a preferred embodiment, the computer 40 includes a microprocessor for controlling the laser 12 and a CAD/CAM system for generating the data. In the embodiment illustrated in FIGURE 1, a personal computer is used (Commodore 64) whose primary attributes includes an accessible interface port and a flag line which generates a nonmaskable interrupt. As shown in FIGURE 1, the scanning system 42 includes a prism 44 for redirecting the path of travel of the laser beam. Of course, physical layout of the apparatus 10 is the primary consideration in determining whether a prism 44, or a plurality of prisms 44, are needed to manipulate the path of travel of the laser beam. The scanning system 47 also includes a pair of mirrors 46, 47 driven by respective galvonometers 48, 49. The galvonometers 48, 49 coupled to their respective mirrors 46, 47 to selectively orientate the mirrors 46, 47. The galvonometers 46, 47 are mounted perpendicular to each other such that the mirrors 46, 47 are mounted nominally at a right angle to each other. A function generator driver 50 controls the movement of the galvonometer 48 (galvonometer 49 is slaved to the movement of galvonometer 48) so that the aim of the laser beam (represented by the arrows in FIGURE 1) can be controlled in the target area 26. The driven 50 is operatively coupled to the computer 40 as shown in FIGURE 1. It will be appreciated that alternative scanning methods are available for use as the scanning system 42, including acousto-optic scanners, rotating polygon mirrors, and resonant mirror scanners. A more detailed description can be found in EP-A--287657. Turning to FIGURES 2 and 3, a powder dispenser 20 in accordance with the present invention. Broadly speaking, a support defines a target area 102 where the aim of the beam 64 is directed (see FIG. 1). A hopper 104 dispenses the powder 106 through opening 108 into the target area 102. A metering roller (not shown) is disposed in the opening 108, such that when rotated the metering roller deposits a metered mound of powder in a line at end 110 of the target area 102. A levelling mechanism 114 spreads the mound of powder 106 from end 110 to the other end 112 of the target area. The levelling mechanism 114 includes a cylindrical drum 116 having an outer knurled surface. A motor 118 mounted on bar 120 is coupled to the drum 116 via pulley 122 and belt 124 to rotate the drum. The levelling mechanism 114 also includes a mechanism 126 for moving the drum 116 between end 110 and end 112 of the target area. The mechanism 126 comprises an X/Y table for moving the bar 120 horizontally and vertically. That is, table 128 is fixed while plate 130 is selectively movable relative to plate 130. The dispensing mechanism 114 has been found to provide a controlled level layer of powder in the target area 102 without disturbing the part being produced. A metered amount of powder 106 is deposited at end 110 of the target area 102. The drum 116 is spaced away from end 110 when the powder 106 is dispensed. In the system illustrated in FIGURE 3, the plate 130 and bar 120 (and attached mechanisms) are raised vertically after the powder is dispensed in the mound. Travel of the plate 130 towards the hopper 104 brings the drum 116 into position adjacent the mound of powder lined up along end 110. The drum 116 is lowered to contact the mound of powder and brought horizontally across the target area 102 to spread the mound of powder in a smooth even layer. Of course, the precise location of plate 130 relative to table 128 can be controlled, so that the spacing between drum 116 and target area 102 can be precisely controlled to yield the desired thickness to the layer of powder. Preferably, the spacing between the drum 116 and target area 102 is constant to give a parallel motion, but other spacing options are available. As the drum 116 is moved horizontally across the target area 102 from end 110 to end 112, motor 118 is activated to counter-rotate the drum 116. As shown in FIGURE 2, "counter-rotation" means the drum 116 is rotated in the direction R counter to the direction of movement M of the drum 116 horizontally across the target area 102. In more details (FIG. 2), the drum 116 is counter-rotated at high speed to contact the mound of powder 106 along the trailing edge 160. The mechanical action of the drum on the powder ejects the powder to the direction of movement M so that the ejected particles fall in the region of the leading edge of the powder 162. As illustrated in FIGURE 2, a smooth, level layer of powder is left behind the drum 116 (between drum 116 and end 110) as depicted at 164. FIGURE 2 also illustrated schematically that the powder 106 can be distributed over the target area without disturbing previously sintered powder 166 of unsintered powder 168. That is, the drum 116 is moved across the target area 102 without transmitting shear stress to the previously built up layers and without disturbing the article as it is being produced. The absence of such sheer stress permits a smooth layer of powder 106 to be distributed on the fragile substrate in the target area, which includes both the sintered particles 166 and the unsintered particulars 168.

Claims: A device for distributing dispensed powder (106) as a layer (164) of powder over a region (102), comprising: drum means (116), and means (118, 122) for rotating the drum means; characterised in that the device includes means (130) for moving the drum (116) from one end (110) of the region (102) to another end (112) of the region with a desired spacing between said region and drum; and said means (118, 122) is arranged to rotate the drum (116) counter to the direction of movement of the drum (116) from said one end (110) to said other end (112); and wherein said drum means (116) is operable when counter-rotated and moved from said one end (110) to said other end (112) to contact the dispensed powder (106) such that the mechanical action of the drum (116) on the powder ejects the powder in said direction of movement to leave a layer (164) of powder over the region (102) having a thickness of approximately said desired spacing. A device according to claim 1, wherein said desired spacing is constant. A device according to claim 1, wherein said region (102) is flat and the desired spacing constant with the drum means (116) being moved parallel to the region (102). A device according to claim 1, wherein said drum means comprises a cylinder (116) having a substantially uniform cross-section. A device according to claim 4, wherein said cylinder (116) has a knurled outer surface. A device according to claim 1, including means (104) for depositing a volume (106) of powder proximate said one end. A method of applying a layer (164) of powder over a region (102) of a surface of an article (166) being produced from the powder in layerwise fashion, comprising the steps of: providing powder (106) to a location proximate said region; moving a drum (116) across said region (102); rotating the drum (116) counter to the direction of movement of said drum (116) across said region (102); and contacting the powder (106) with the counter-rotating drum (116) as it moves across said region (102) so that a layer (164) of powder remains over said region (102) after said moving step, wherein the moving step is carried out without transmitting substantial shear stress to previously applied layers (166, 168) and without disturbing the article (166) produced in such previously applied layers. A method according to claim 7, wherein said moving step includes the substep of maintaining the drum (116) a desired spacing from said region (102). A method according to claim 8, wherein said desired spacing is a constant distance from said region (102) and said region (102) is flat. A method according to claim 7, wherein the surface of said drum (116) has a rough texture. A method according to claim 7, wherein the surface of said drum (116) is knurled. A method according to claim 7, wherein said providing step comprises: depositing a mound (106) of powder at said location proximate said region (102). A method according to claim 7, wherein said powder is sinterable. A method according to claim 13, wherein said region of said surface comprises said powder having a portion (166) in a sintered state and having a portion (168) in an unsintered state. A method according to claim 7, wherein powder is ejected in the direction of movement as a result of contact between said drum (116) and said powder in said contacting and moving steps. A method according to claim 7, wherein the location from which said drum (116) is moved in said moving step is outside of said region (102). A method according to claim 7, wherein said providing step provides a metered volume (106) of powder at said location proximate said region (102).

Inventors: DECKARD CARL R, DECKARD, CARL R.
Applicants: UNIV TEXAS, BOARD OF REGENTS THE UNIVERSITY OF TEXAS SYSTEM
Application year: 1987
Main classification: B05C19
IPC codes: G05B19, B05C19, B23K26, B22F7, B22F3, B29C35, C23C24, B29C67, B29C41, C23C26