Patent Application
20050263933
This invention relates to the field of freeform fabrication, and more specifically is directed to the fabrication of three-dimensional objects by selective laser sintering.
The field of freeform fabrication of parts has, in recent years, made significant improvements in providing high strength, high density parts for use in the design and pilot production of many useful articles. Freeform fabrication generally refers to the manufacture of articles directly from computer-aided-design (CAD) databases in an automated fashion, rather than by conventional machining of prototype articles according to engineering drawings. As a result, the time required to produce prototype parts from engineering designs has been reduced from several weeks to a matter of a few hours.
By way of background, an example of a freeform fabrication technology is the selective laser sintering process practiced in systems available from 3D Systems, Inc., in which articles are produced from a laser-fusible powder in layerwise fashion. According to this process, a thin layer of powder is dispensed and then fused, melted, or sintered, by laser energy that is directed to those portions of the powder corresponding to a cross-section of the article. Conventional selective laser sintering systems, such as the Vanguard system available from 3D Systems, Inc., position the laser beam by way of galvanometer-driven mirrors that deflect the laser beam. The deflection of the laser beam is controlled, in combination with modulation of the laser itself, to direct laser energy to those locations of the fusible powder layer corresponding to the cross-section of the article to be formed in that layer. The computer based control system is programmed with information indicative of the desired boundaries of a plurality of cross sections of the part to be produced. The laser may be scanned across the powder in raster fashion, with modulation of the laser affected in combination therewith, or the laser may be directed in vector fashion. In some applications, cross-sections of articles are formed in a powder layer by fusing powder along the outline of the cross-section in vector fashion either before or after a raster scan that “fills” the area within the vector-drawn outline. In any case, after the selective fusing of powder in a given layer, an additional layer of powder is then dispensed, and the process repeated, with fused portions of later layers fusing to fused portions of previous layers as appropriate for the article, until the article is complete.
Detailed description of the selective laser sintering technology may be found in U.S. Pat. Nos. 4,863,538; 5,132,143; and 4,944,817, all assigned to Board of Regents, The University of Texas System, and in U.S. Pat. No. 4,247,508 to Housholder, all hereby incorporated by reference.
The selective laser sintering technology has enabled the direct manufacture of three-dimensional articles of high resolution and dimensional accuracy from a variety of materials including polystyrene, some nylons, other plastics, and composite materials such as polymer coated metals and ceramics. Polystyrene parts may be used in the generation of tooling by way of the well-known “lost wax” process. In addition, selective laser sintering may be used for the direct fabrication of molds from a CAD database representation of the object to be molded in the fabricated molds; in this case, computer operations will “invert” the CAD database representation of the object to be formed, to directly form the negative molds from the powder.
Operation of this conventional selective laser sintering system is shown in
Two feed systems (124,126) feed powder into the system by means of push-up piston systems. A part bed 132 receives powder from the two feed pistons as described immediately hereafter. Feed system 126 first pushes up a measured amount of powder and a counter-rotating roller 130 picks up and spreads the powder over the part bed in a uniform manner. The counter-rotating roller 130 passes completely over the target area 110 and part bed 132. Any residual powder is deposited into an overflow receptacle 136. Positioned nearer the top of the chamber are radiant heater elements 122 that pre-heat the feed powder and a ring or rectangular shaped radiant heater element 120 for heating the part bed surface. Element 120 has a central opening which allows a laser beam to pass through the laser window 116. After a traversal of the counter-rotating roller 130 across the part bed 132 the laser selectively fuses the layer just dispensed. The roller then returns from the area of the overflow receptacle 136, after which the feed piston 124 pushes up a prescribed amount of powder and the roller 130 dispenses powder over the target area 110 in the opposite direction and proceeds to the other overflow receptacle 138 to deposit any residual powder. Before the roller 130 begins each traverse of the part bed 132 the center part bed piston 128 drops by the desired layer thickness to make room for additional powder.
The powder delivery system in system 100 includes feed pistons 125 and 127. Feed pistons 125 and 127 are controlled by motors (not shown) to move upwardly and lift, when indexed, a volume of powder into chamber 102. Part piston 128 is controlled by a motor (not shown) to move downwardly below the floor of chamber 102 by a small amount, for example 0.125 mm, to define the thickness of each layer of powder to be processed. Roller 130 is a counter-rotating roller that translates powder from feed systems 124 and 126 onto target surface 110. When traveling in either direction the roller carries any residual powder not deposited on the target area into overflow receptacles (136,138) on either end of the process chamber 102. Target surface 110, for purposes of the description herein, refers to the top surface of heat-fusible powder (including portions previously sintered, if present) disposed above part piston 128; the sintered and unsintered powder disposed on part piston 128 will be referred to herein as part cake 106. System 100 of
Another known powder delivery system uses overhead hoppers to feed powder from above and either side of target area 110 in front of a delivery apparatus such as a wiper or scraper.
There are advantages and disadvantages to each of these systems. Both require a number of mechanisms, either push-up pistons or overhead hopper systems with metering feeders to effectively deliver metered amounts of powder to each side of the target area and in front of the spreading mechanism which typically is either a roller or a wiper blade.
Although a design such as system 100 has proven to be very effective in delivering both powder and thermal energy in a precise and efficient way there is a need to do so in a more cost effective manner by reducing the number of mechanisms and improve the pre-heating of fresh powder to carry out the selective laser sintering process.
It is an aspect of the present invention to provide a method and apparatus for fabricating objects by selective laser sintering employing fewer mechanisms.
It is another aspect of the present invention to provide a method and apparatus for fabricating objects by selective laser sintering which deposits all of the powder from an overhead feed system that is needed to form two successive cross-sectional layers on one side of a target area and which concurrently levels the powder for the first successive layer while transporting the powder for the second successive layer to an opposing second side of the target area.
It is a feature of the present invention that a method and apparatus for fabricating objects via selective laser sintering are provided without sacrificing good thermal control and good powder delivery.
It is another feature of the present invention that a modified process and an apparatus that utilize only one overhead feed hopper and no feed pistons with radiant heaters are provided.
It is another feature of the present invention that the second powder wave used to form the second layer of powder is preheated in a parked position within the process chamber while the laser beam scans the first layer of powder.
It is an advantage of the present invention that an apparatus and a method for employing that apparatus are provided for fabricating objects with a selective laser sintering system having a smaller machine footprint.
It is another advantage of the present invention that the method and apparatus are achieved at a lower cost than prior laser sintering systems.
The invention includes a method for forming a three dimensional article by laser sintering that includes at least the steps of: depositing a quantity of powder on a first side of a target area; spreading the powder with a spreading mechanism to form a first smooth surface; directing an energy beam over the target area causing the powder to form an integral layer; depositing a quantity of powder on an opposing second side of the target area; spreading the powder with the spreading mechanism to form a second smooth surface; directing the energy beam over the target area causing powder to form a second integral layer bonded to the first integral layer; and repeating the steps to form additional layers that are integrally bonded to adjacent layers so as to form a three-dimensional article, wherein the depositing step includes at least depositing all of the powder required for two successive layers on the first side of the target area and concurrently spreading the powder for the first successive layer while transporting the powder for the second successive layer to the opposing second side of the target area on the spreading mechanism, the powder for the second successive layer being dislodged by an appropriate device during a second depositing step.
The invention also includes an apparatus for producing parts from a powder comprising a chamber having a target area at which an additive process is performed, the target area having a first side and an opposing second side; a means for fusing selected portions of a layer of the powder at the target area; a powder feed hopper located above and on the first side of the target area for feeding desired amounts of the powder; a means for spreading a first layer of powder over the target area while carrying a second quantity of powder to the opposing second side of the target area to be used for a second layer of powder; and a means for depositing the second quantity of powder on the opposing second side of target area.
These and other aspects, features and advantages of the invention will become apparent upon consideration of the following detailed disclosure, especially when taken in conjunction with the accompanying drawings wherein:
An apparatus for carrying out the present invention can be seen in
A single powder feed hopper 162 is shown with a bottom feed mechanism 164 controlled by a motor (not shown) to control the amount of powder dropped onto the bed below. The feed mechanism can be of several types including, for example, a star feeder, an auger feeder, or a rotary drum feeder. A preferred feeder is a rotary drum. A part piston 170 is controlled by a motor 172 to move downwardly below the floor of the chamber 152 by a small amount, for example 0.125 mm, to define the thickness of each layer of powder to be processed.
Roller mechanism 180 includes a counter-rotating roller driven by motor 182 that spreads powder from powder wave 184 across the laser target area 186. When traveling in either direction the roller mechanism 180 carries any residual powder not deposited on the target area into overflow receptacles 188 on opposing ends of the chamber. Target area 186, for purposes of the description herein, refers to the top surface of heat-fusible powder, including any portions previously sintered, disposed above part piston 170. The sintered and unsintered powder disposed on part piston 170 will be referred to as part bed 190. Although the use of counter-rotating roller mechanism 180 is preferred, the powder can also be spread by other means such as a wiper or a doctor blade.
Operation of the selective laser sintering system of this invention is shown beginning in
In a second step, shown in
In a next step, shown in
In the next step, shown in
This inventive design concept reduces a laser sintering machine in both footprint (the horizontal width of the build chamber) and in mechanical mechanisms. The present invention now employs only one feed hopper, one piston, and preferably only one set of radiant heater elements. The reduced size of the build chamber improves the temperature control and temperature response of the system.
While the invention has been described above with references to specific embodiments, it is apparent that many changes, modifications and variations in the materials, arrangement of parts and steps can be made without departing from the inventive concept disclosed herein. Accordingly, the spirit and broad scope of the appended claims is intended to embrace all such changes, modifications and variations that may occur to one of skill in the art upon a reading of the disclosure. For example any suitable device such as a skive, roller or brush can be used to dislodge or remove the quantity of powder in the second powder wave from the powder carrying surface or structure of the specific spreading mechanism employed, whether a roller, wiper blade or other suitable device. All patent applications, patents and other publications cited herein are incorporated by reference in their entirety.
