Abstract:
A method and apparatus for forming three dimensional objects by laser sintering that includes depositing the required quantities of powder for two successive layers on one side of the process chamber and simultaneously spreading the first layer while transporting the second layer quantity to the opposite side of the process chamber. The invention includes steps of parking the quantities of powder in sight of the part bed heater to pre-heat the powder and flattening the powder wave before the pre-heating step to improve pre-heat efficiency. This method and apparatus can result in reduction of the mechanisms, size, cost, and increase productivity of a laser-sintering device.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     This invention is in the field of freeform fabrication, and is more specifically directed to the fabrication of three-dimensional objects by selective laser sintering.  
         [0002]     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.  
         [0003]     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 an optics mirror system using 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 with the raster scanning, 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.  
         [0004]     Detailed description of the selective laser sintering technology may be found in U.S. Pat. No. 4,863,538, U.S. Pat. No. 5,132,143, and U.S. Pat. No. 4,944,817, all assigned to Board of Regents, The University of Texas System, and in U.S. Pat. No. 4,247,508, Housholder, all hereby incorporated by reference.  
         [0005]     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.  
         [0006]      FIG. 1  illustrates, by way of background, a rendering of a conventional selective laser sintering system, shown generally as the numeral  100  currently sold by 3D Systems, Inc. of Valencia, Calif.  FIG. 1  is a rendering shown without doors for clarity. A carbon dioxide laser  108  and its associated scanning system  114  are shown mounted in a unit above a process chamber  102  that includes a top layer of powder bed  132 , two powder feed systems  124 , 126 , and a spreading roller  130 . The process chamber maintains the appropriate temperature and atmospheric composition (typically an inert atmosphere such as nitrogen) for the fabrication of the article.  
         [0007]     Operation of this conventional selective laser sintering system  100  is shown in  FIG. 2  in a front view of the process with no doors shown for clarity. A laser beam  104  is generated by laser  108 , and aimed at target area  110  by way of optics-mirror scanning system  114 , generally including galvanometer-driven mirrors that deflect the laser beam. The laser and galvanometer systems are isolated from the hot process chamber  102  by a laser window  116 . The laser window  116  is situated interiorly of radiant heater elements  120  that heat the target area  110  and the powder bed  132  below. These heater elements  120  may be ring shaped (rectangular or circular) panels or radiant heater rods that surround the laser window. The deflection of the laser beam is controlled in combination with modulation of laser  108  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. Scanning system  114  may scan the laser beam across the powder in a raster-scan fashion, or in vector fashion. Scanning entails the laser beam  104  intersecting the powder surface in the target area  110 .  
         [0008]     Two feed systems ( 124 , 126 ) feed powder into the system by means of a push-up piston system. Target area  110  receives powder from the two feed systems as described hereinafter. 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 powder bed  132  in a uniform manner. The counter-rotating roller  130  passes completely over the target area  110  and powder bed  132  and then dumps any residual powder 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 surface of the powder bed  132 . Element  120  has a central opening which allows a laser beam to pass through the laser window or optical element  116 . After a traversal of the counter-rotating roller  130  across the powder bed  132 , the laser  108  selectively fuses the layer just dispensed. The roller  130  then returns from the area of the overflow receptacle  136 , the feed piston  125  pushes up a prescribed amount of powder, the roller  130  dispenses powder over the target area  110  in the opposite direction and roller  130  proceeds to the other overflow receptacle  138  to drop any residual powder. Before the roller begins each traverse of the system the center part bed piston  128  drops by the desired layer thickness to make room for additional powder.  
         [0009]     The powder delivery system in system  100  includes feed pistons  125  and  127 , controlled by motors (not shown) to move upwardly and lift, when indexed, a volume of powder into chamber  102 . Part bed 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 pistons  125  and  127  onto target area  110 . When traveling in either direction the roller  130  carries any residual powder not deposited on the target area into overflow receptacles ( 136 , 138 ) on either end of the process chamber  102 . Target area  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 dispensed on part bed piston  128  is referred to as part cake  106 . System  100  of  FIG. 2  also requires radiant heaters  122  over the feed pistons to pre-heat the powders to minimize any thermal shock as fresh powder is spread over the recently sintered and hot target area  110 . This type of dual push-up piston feed system, providing fresh powder from below the target area, with heating elements for both feed beds and the part bed or target area is implemented commercially in the Vanguard selective laser sintering system sold by 3D Systems, Inc. of Valencia, Calif.  
         [0010]     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.  
         [0011]     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 (either a roller or a wiper blade).  
         [0012]     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 improving the pre-heating of fresh powder to carry out the selective laser sintering process. A method and apparatus for pre-heating fresh powder for doing that is presented in concurrently filed co-pending application U.S. Ser. No. To Be Assigned, docket number USA.304, filed May 28, 2004 and assigned to 3D Systems, Inc. of Valencia, Calif. That application is hereby incorporated by reference.  
         [0013]     Briefly, this concurrently filed co-pending application provides for a method and apparatus with a depositing step for fresh powder wherein the depositing step includes at least depositing all of the powder required for two successive layers on the first side of target area in the process chamber which simultaneously spreads 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. The apparatus includes 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 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.  
         [0014]      FIGS. 3 &amp; 4  show a parked powder wave  184  initially being deposited from an overhead feed mechanism and subsequently positioned next to target area  186  during the laser scanning of the target area. The parked powder wave  184  is so placed to expose the powder wave to the radiant energy of heaters  160 . This allows the radiant heaters  160 , which are maintaining the proper temperature of the target area  186 , to also pre-heat the powder wave  184  that will be used in the next layer to reduce or eliminate the need to separately pre-heat the next layer of powder. This technique, while effective, suffers because of the poor thermal conductivity of polymer powders and its effect on the mound of powder in the parked wave that consequently heats more slowly than desired, resulting in a longer than desired delay before spreading the next layer. Additionally, there is the potential in this approach when feeding small particle size powders that a dust cloud can be generated when powder from feed mechanism  164  falls directly from the feed mechanism to the floor of the process chamber in forming parked powder wave  184 .  
         [0015]     There is thus a need to speed up the process of heating the parked wave of powder without increasing the temperature of the radiant heaters  160 , which would adversely affect the temperature of the target area  180 . There is also a need to significantly reduce the potential of dusting of the powders falling from the feed mechanism  164  onto the floor of the process chamber.  
       BRIEF SUMMARY OF THE INVENTION  
       [0016]     It is therefore an aspect of the present invention to provide a method and apparatus to rapidly heat the parked fresh powder wave.  
         [0017]     It is also an aspect of the instant invention to reduce the potential of dust being created by the falling of powder from an overhead feeder onto the floor of the process chamber.  
         [0018]     It is a feature of the present invention that the cover or cowling overlying the roller mechanism extends sufficiently far toward the powder bed surface to smooth or flatten the wave or mound of the fresh powder deposited adjacent the target area.  
         [0019]     It is another feature of the present invention that the cover or cowling overlying the roller mechanism is angled on opposing sides to permit the fresh powder to slide along it to the powder bed.  
         [0020]     It is an advantage of the present invention that the fresh powder wave is deposited on the powder bed surface and flattened out by the cover or cowling overlying the roller mechanism.  
         [0021]     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; flattening the first quantity of powder on the first side of the 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 second quantity of powder on a second side of the target area; flattening the second quantity of powder on the 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 simultaneously spreading the powder for the first successive layer while transporting the powder for the second successive layer to the second side of the target area.  
         [0022]     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 a 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 flattening a first quantity of powder on the first side of the target area; a means for spreading a first layer of powder over the target area while carrying a second quantity of powder to the second side of the target area to be used for a second layer of powder; a means for depositing the second quantity of powder on the second side of target area, a means for flattening the second quantity of powder on the second side of the target area; and a means for spreading the second quantity of powder over the target area.  
     
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0023]     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:  
         [0024]      FIG. 1  is a diagrammatic view of a conventional prior art selective laser-sintering machine;  
         [0025]      FIG. 2  is a diagrammatic front elevation view of a conventional prior art selective laser-sintering machine showing some of the mechanisms involved;  
         [0026]      FIG. 3  is a diagrammatic front elevation view of the system of the co-pending application showing the metering of the powder in front of the roller;  
         [0027]      FIG. 4  is a diagrammatic front elevation view of the system of the co-pending application showing the retraction of the roller mechanism and the parking of it under the feed mechanism while the laser is selectively heating the target area and the radiant heater is pre-heating the parked powder wave;  
         [0028]      FIG. 5  is a partial diagrammatic front elevation view of the system of the present invention showing a design aspect of modified cover of the roller mechanism;  
         [0029]      FIG. 6  is a partial diagrammatic front elevation view of the system of the present invention showing the depositing of powder using the cover of the roller mechanism;  
         [0030]      FIG. 7  is a partial diagrammatic front elevation view of the system of the present invention showing the parking of the first powder quantity near the part bed;  
         [0031]      FIG. 8  is a partial diagrammatic front elevation view of the system of the present invention showing the method of flattening of the parked powder wave;  
         [0032]      FIG. 9  is a diagrammatic front elevation view of the system of the present invention showing the metering of the first quantity of powder;  
         [0033]      FIG. 10  is a diagrammatic front elevation view of the system of the present invention showing the parking of the powder wave near the part bed;  
         [0034]      FIG. 11  is a diagrammatic front elevation view of the system of the present invention showing the retraction of the spreading mechanism, the flattening of the parked powder wave, and the parking of the spreading mechanism under the feed mechanism while the laser is selectively heating the target area and the radiant heater is pre-heating the flattened parked powder wave;  
         [0035]      FIG. 12  is a diagrammatic front elevation view of the system of the present invention showing the dispensing of the second layer of powder onto the top of the roller mechanism and the radiant heater is pre-heating the flattened parked powder wave;  
         [0036]      FIG. 13  is a diagrammatic front elevation view of the system of the present invention showing the first layer of powder being distributed across the target area and the second layer of powder being carried on top of the roller mechanism to the opposing second side of the target area;  
         [0037]      FIG. 14  is a diagrammatic front elevation view of the system of the present invention showing the depositing of the second layer of powder in front of the roller and depositing of residual powder from the first layer in the overflow receptacle;  
         [0038]      FIG. 15  is a diagrammatic front elevation view of the system of the present invention showing the parking of the second powder wave near the target area;.  
         [0039]      FIG. 16  is a diagrammatic front elevation view of the system of the present invention showing the parking of the roller to the side and the flattening of the second parked powder wave while the laser is selectively heating the target area and the radiant heater is pre-heating the flattened parked powder wave;  
         [0040]      FIG. 17  is a diagrammatic front elevation view of the system of the present invention showing the second layer of powder being distributed across the target area;  
         [0041]      FIG. 18  is a diagrammatic front elevation view of the system of the present invention showing the roller completing one cycle by depositing residual powder in the overflow receptacle; and  
         [0042]      FIG. 19  is a diagrammatic front elevational view of an alternative embodiment of the system of the present invention showing a second stationary blade for dislodging and depositing of the first layer of powder in front of the roller on the opposing side of the target area from the first stationary blade.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0043]     The concept of the present invention includes a redesign of the overlaying structure or cowling covering the roller mechanism. Referring to  FIG. 5  the new roller assembly is shown overall by the numeral  200 . Over roller mechanism  180  is a flat top powder support or carrying surface  208  that is used by the process to carry the powder quantity needed for the second side of the chamber. A cover  204  is added to the structure that is angled outwardly on each side to provide adequate clearance for the powder wave created by the roller. The cover  204  extends downwardly at an angle on opposing sides leaving a small clearance between the roller in roller mechanism  180  and the floor  206  of the process chamber  152 . In operation, as seen in  FIG. 6 , the process begins with the roller mechanism  180  parked below and slightly to the side of the overhead feed mechanism  164 . The first quantity of powder is discharged to fall on the exterior of cover  204  and slides down forming a powder wave  184  on the floor  206  adjacent to roller mechanism  180 . By dropping the powder onto the exterior cover of roller assembly  200  in this manner the creation of a dust cloud is substantially reduced. The powder falls a shorter distance before its vertical fall is interrupted than previously by striking cover  204  at an angle, thereby reducing its terminal velocity, and sliding gently down onto the floor  206  of the process chamber  152 . The deposited quantity of powder will be referred to as a parked powder wave.  
         [0044]     In the next step, as seen in  FIG. 7 , roller mechanism  180  is activated and moves to push powder wave  184  and park it on the edge of target area  186 . The powder wave  184  is flattened by the leading edge of roller cover  204  as it passes over the powder wave but is built up again by the action of the roller mechanism  180 . When roller mechanism  180  reverses direction though (see  FIG. 8 ) and returns to its position under the feed mechanism  164  the inside edge of the roller cover  204  cleanly flattens the powder wave  184  into a thinner wave that allows much more rapid heating of parked powder wave  184  by radiant heaters  160 . This design and process reduces heating time of powder wave  184  before the ensuing process steps that include advancing roller mechanism  180  across target area  186  to spread the next layer of pre-heated powder across the target area.  
         [0045]     The same sequence of steps on the opposing second side of the process chamber  102  will flatten the parked powder wave on that side of the chamber once the second powder wave is dislodged from the top powder support or carrying surface  208 , as will be explained hereafter. Although the roller mechanism  180  described is a preferred one, it should be evident that a number of variations of shapes of the roller assembly  200  could accomplish the twin goals of providing a gentle landing of the disbursed powder and flattening of the powder wave prior to pre-heating the wave.  
         [0046]     A laser sintering system employing the present invention is shown in  FIG. 9  indicated generally by the numeral  150 . The process chamber is shown as  152 . The laser beam  154  passing from laser  108  through the optics mirror scanning system  114  enters the chamber  152  through a laser window  156  that isolates the laser and optics (not shown) from the higher temperature environment of the process chamber  152 . The optics mirror scanning system  114  is similar to the one described in the prior art, but any suitable design may be employed. Radiant heating elements  160  provide heat to the target area  186  and to the powder in areas immediately next to the target area  186 . These radiant heaters can be any number of types including, for example, quartz rods or flat panels or combinations thereof. A preferred design employs fast response quartz rod heaters.  
         [0047]     A single overhead 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 process chamber floor  206  below. The feed mechanism  164  can be of several types including, for example, a star feeder, an auger feeder, a belt feeder, a slot 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  206  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.  
         [0048]     Still referring to  FIG. 9 , 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 carries any residual powder not deposited on the target area into overflow receptacles  188  on opposing ends of the chamber  152 . Target area  186 , 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  170 . The sintered and unsintered powder disposed on part piston  170  will be referred to herein as part cake  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.  
         [0049]     Operation of the selective laser sintering system of this invention is shown beginning in  FIG. 9 . In a first powder dispensing step powder is metered from above from feed mechanism  164  onto cover structure  204  and then slides to a position on the floor  206  in front of roller mechanism  180 . The quantity of powder metered will depend upon the size of target area  186  and the desired layer thickness to be formed.  
         [0050]     In a second step, shown in  FIG. 10 , the counter-rotating roller mechanism is activated to move the powder wave slightly forward and park it at the edge of target area  186  in view of radiant heater elements  160 . In a third step, shown in  FIG. 11 , roller mechanism  180  is moved back and roller cover structure  204  flattens parked powder wave  184 . Roller mechanism  180  is then parked under feed mechanism  164 . In iterations other than the first quantity of powder metered from feed mechanism  164 , the laser is then turned on and laser beam  154  scans the current layer to selectively fuse the powder on that layer. While the laser is scanning, roller mechanism  180  remains parked directly under the powder feeder mechanism. Also while the laser is scanning, flattened parked powder wave  184  is pre-heated by the action of radiant heater elements  160 . This step can eliminate the need for separate radiant heaters to pre-heat the powder.  
         [0051]     In a next step, shown in  FIG. 12 , a second powder wave  185  is fed onto top powder support or carrying surface  208  of roller mechanism  180 . After scanning of the current layer of powder the next step, shown in  FIG. 13 , begins. Roller mechanism  180  is activated and traverses across the process chamber  152 , spreading the first layer of pre-heated powder  184  across the target area  186 , while carrying the second layer of powder in second powder wave  185  on top powder support surface  208  of roller mechanism  180 . In the next step, shown in  FIG. 14 , a mounted stationary blade  192  dislodges the second powder wave  185  off the top powder support surface  208  of roller mechanism  180  as the roller passes under the blade  192 . The dislodged powder slides down the inboard side of angled cover  204 , depositing the second powder wave  185  on the floor  206  of process chamber  152  while the roller mechanism  180  proceeds to feed any excess powder into overflow receptacle  188 . The apparatus is not limited to a stationary blade for dislodgement, but could encompass any mechanism that would dislodge the powder from the top powder supporting or carrying surface  208  of roller mechanism  180  such as a skive, roller or brush.  
         [0052]     In the next step, shown in  FIG. 15 , roller mechanism  180  immediately reverses and moves to park the second powder wave  185  near the target area  186  and in sight of the radiant heater elements  160  sufficiently close to receive heating effects from them. In the next step ( FIG. 16 ) of this preferred embodiment, roller mechanism  180  moves back and flattens parked powder wave  185 , with the inboard side of angled cover  204  contacting and leveling the mound of second powder wave  185 . Roller mechanism  180  then parks while the laser scanning action is completed and the flattened second quantity of powder in second powder wave  185  is being pre-heated by the radiant heating elements  160 . After the laser scanning action is completed, roller mechanism  180  is then activated and moves to spread the second quantity of powder in second powder wave  185  over target area  186  as shown in  FIG. 17 . After spreading the powder roller mechanism  180 , as seen in  FIG. 18 , proceeds to the end of its run and drops any excess powder into overflow receptacle  188 . This completes the cycle and the next cycle is ready to proceed as in  FIG. 9 .  
         [0053]     An alternative design can include a second mounted stationary blade  193  shown in  FIG. 19  outboard of the bottom feed mechanism  164  on the opposing side from blade  192  so that a quantity of powder to be deposited on the powder support surface  208  is always present and being preheated for each traversal of the roller mechanism  180  across the target area  186 . In this approach, the iterative cycle has the first parked powder wave  184  be deposited on the top powder support surface  208  of the roller mechanism  180 . The roller mechanism  180  is moved a short distance toward blade  193  so that the blade dislodges the quantity of powder that forms parked powder wave  184 . The roller mechanism  180  moves forward and then reverses direction a short distance so what is now the inboard side of angled cover  204  of roller mechanism  180  flattens parked powder wave  184  to promote faster preheating. Roller mechanism  180  reverses its direction to pull away from the leveled mound of powder and remains stationary while pre-heating occurs for the first quantity of powder metered in the first iteration and in subsequent iterations while laser scanning occurs. For the first iteration roller mechanism  180  is repositioned under the bottom of feed mechanism  164  and the powder carrying surface  208  is refilled with the second powder wave  185 .  
         [0054]     This inventive design achieves rapid and efficient pre-heating of distributed powder before it is spread across the target area of a selective laser sintering system and reduces the potential of dust clouds forming from dropped powder striking the floor of the process chamber.  
         [0055]     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, the pre-heating of the parked powder waves may employ the use of the laser beam, either on low power or with a fast scan speed to assist in elevating the powder temperature but not initiate melting or softening of the powder to the extent that even spreading across the powder bed is hampered. Additionally, additional radiant heating panels, such as Watlow flat panel heaters, can be positioned above the parked powder locations on opposing sides of the process chamber suitably mounted, such as in the roller mechanism&#39;s traversing assembly or other suitable arrangement. All patent applications, patents and other publications cited herein are incorporated by reference in their entirety.