Patent Publication Number: US-2022219394-A1

Title: System and method for 3d printing

Description:
This application is a continuation-in-part of U.S. application Ser. No. 16/181,421, filed on Nov. 6, 2018, which is a continuation-in-part of U.S. application Ser. No. 15/954,062, filed on Apr. 16, 2018, the contents of each of which are incorporated herein by reference. 
    
    
     FIELD 
     The disclosure herein relates to systems and methods for 3D printing, in particular for continuous rotary 3D printing. 
     BACKGROUND 
     Three-dimensional (3D) printed parts result in a physical object being fabricated from a 3D digital image by laying down consecutive thin layers of material. 
     Typically these 3D printed parts can be made by a variety of means, such as selective laser sintering, selective laser melting or selective electron beam melting, which operate by having a powder bed onto which an energy beam of light or heat is projected to melt the top layer of the powder bed so that it welds onto a substrate or a substratum. This melting process is repeated to add additional layers to the substratum to incrementally build up the part until completely fabricated. 
     For each additional layer, powder is deposited onto the powder bed and then must be smoothed prior to application of energy for the melting/sintering of the next layer. In this regard, the powder beds typically have a rectangular configuration and require the powder applicator and a smoothing roller or the like to be linearly moved across the bed, often requiring a forward and reverse path to accomplish both depositing and smoothing. While some systems have accomplished depositing and smoothing in a single pass, such systems generally require a larger footprint to accomplish such. Whether in a single pass or a reciprocal pass, application of the energy, and thereby formation of the next layer, must be paused during such depositing and smoothing steps. 
     Since many 3D printed parts are comprised of thousands of layers, such delays between formation of each layer result in a time consuming process which has limited the full scale application of 3D printing. 
     SUMMARY 
     In at least one embodiment, the present disclosure provides an apparatus for fabricating a three-dimensional object from a representation of the object stored in memory. The apparatus includes a drum supported for rotation. A build platform is supported for linear movement within the drum from a first position adjacent a first end of the drum to a second position within the drum. The build platform is rotationally fixed relative to the drum such that the build platform rotates with the drum. A powder feed hopper is fixed at a position above a first portion of the build platform. At least one directed energy source is positioned above the build platform and is configured to apply directed energy to a majority of the remaining portion of the build platform excluding the first portion. 
     In at least one embodiment, the present disclosure provides an apparatus for fabricating a three-dimensional object from a representation of the object stored in memory. The apparatus includes an outer drum supported for rotation and an inner drum positioned within the outer drum and supported for rotation therewith. A powder receiving chamber is defined between the outer drum and the inner drum. A build platform is supported for linear movement within the powder receiving chamber from a first position adjacent a first end of the drums to a second position within the powder receiving chamber. The build platform is rotationally fixed relative to at least one of the inner or outer drums such that the build platform rotates with the drums. A powder feed hopper is positioned above the build platform. At least one directed energy source is positioned above the build platform and is configured to apply directed energy to at least a portion of the powder receiving chamber. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated herein and constitute part of this specification, illustrate the presently preferred embodiments of the disclosure, and, together with the general description given above and the detailed description given below, serve to explain the features of the disclosure. In the drawings: 
         FIG. 1  is a perspective view of a 3D printing system in accordance with an embodiment of the disclosure. 
         FIG. 2  is a perspective view of the 3D printing system with the housing panels removed and the frame structure shown in phantom. 
         FIG. 3  is a left side elevation view of the 3D printing system with the housing and frame structure removed. 
         FIG. 4  is a rear elevation view of the 3D printing system with the housing and frame structure removed. 
         FIG. 5  is a front elevation view of a portion of the 3D printing system with the housing panels removed and the frame structure shown in phantom. 
         FIG. 6  is a left side elevation view of a portion of the 3D printing system with the housing removed and the frame structure shown in phantom. 
         FIG. 7  is a top perspective view of the drum rotation assembly. 
         FIG. 8  is a bottom perspective view of the drum rotation assembly. 
         FIG. 9  is a top perspective view of the build assembly. 
         FIG. 10  is a front elevation view of the build assembly. 
         FIG. 11  is a left side elevation view of the build assembly. 
         FIG. 12  is a top perspective view of the build assembly and vertical control assembly. 
         FIG. 13  is a top perspective view of an alternative build assembly. 
         FIG. 14  is a perspective view of an alternative 3D printing system incorporating an alternative drum assembly and an alternative build assembly. 
         FIG. 15  is perspective view of the build platform of the drum assembly of  FIG. 14 . 
         FIG. 16  is a plan view of the drum assembly of  FIG. 14 . 
         FIG. 17  is a plan view similar to  FIG. 16  showing an alternative platform drive assembly. 
         FIG. 18  is a plan view similar to  FIG. 16  showing another alternative platform drive assembly. 
         FIG. 19  is a perspective view of the build assembly of  FIG. 14 . 
         FIG. 20  is a side elevation view of the build assembly of  FIG. 14 . 
         FIG. 21  is a top plan view of an example double-walled tube manufactured utilizing the printing system of  FIG. 14 . 
         FIG. 22  is a plan view of another embodiment of the drum assembly. 
         FIG. 23  is a top plan view of an example double-walled tube manufactured utilizing the drum assembly of  FIG. 22 . 
         FIG. 24  is a perspective view of another alternative drum assembly. 
         FIG. 25  is a cross-sectional view along the line  25 - 25  of  FIG. 24 . 
         FIG. 26  is a perspective view similar to  FIG. 24  showing the drums transparently. 
         FIG. 27  is a top perspective view of another alternative drum assembly. 
         FIG. 28  is a bottom perspective view of the drum assembly of  FIG. 27 . 
         FIG. 29  is an expanded view of a portion of the drum assembly of  FIG. 27 . 
         FIG. 30  is a schematic view of a control assembly in accordance with an embodiment of the disclosure. 
         FIG. 31  is a top plan view of a build platform with an embodiment of illustrative printing subregions illustrated thereon. 
         FIG. 32  is a top plan view of a build platform with another embodiment of illustrative printing subregions illustrated thereon. 
     
    
    
     DETAILED DESCRIPTION 
     In the drawings, like numerals indicate like elements throughout. Certain terminology is used herein for convenience only and is not to be taken as a limitation on the present disclosure. The following describes preferred embodiments of the present disclosure. However, it should be understood, based on this disclosure, that the disclosure is not limited by the preferred embodiments described herein. 
     Referring to  FIGS. 1-4 , a 3D printing system  10  in accordance with an embodiment of the disclosure will be described generally. In the illustrated embodiment, the printing system  10  includes a housing  12  which encloses a drum assembly  50  and a build assembly  80  and may optionally enclose gas supply tanks  40  and powder supply containers  46 . It is understood that the gas supply and/or powder supply may be external to the housing  12  and may be fed into the housing  12  via pipes, tubes or the like. The housing  12  is formed from various exterior panels secured to a support frame  20 . Various doors, removable panels or the like may be provided to facilitate access to different areas within the housing  12 . As illustrated in  FIG. 1 , a first door  14  provides access to the build assembly  80  while a second door  16  provides access to the drum assembly  50 , the doors  14 ,  16  having respective handles  15 ,  17 . While two doors are shown, it is understood that more or fewer doors may be utilized. 
     It is noted that due to the rotary motion of the drum assembly  50  and the build platform  70  while the build assembly  80  remains stationary, generally within the radius of the drum  54 , the housing  12  has a relatively small footprint. More specifically, because it is not necessary to move the powder applicator and/or smoothing roller clear of the build platform, such additional space within the housing which is usually required for X-Y printing systems is not required. 
     Referring to  FIG. 1 , a control panel  30  is supported on the housing  12  and is in communication with a control processor (not shown) within the housing  12 . The control panel  30  includes an input/output (I/O) interface  32 , for example, in the form of a touch screen, however other I/O devices may be utilized. A user can utilized the I/O interface  32  to enter control commands, data and the like to the control processor and receive information indicative of the operation of the system  10 . In the illustrated embodiment, the control panel  30  includes a face recognition sensor  34 , for example as described in US Appln. Pub. No. 2017/0228585, the contents of which are incorporated herein by reference. The face recognition sensor  34  is configured to regulate access to the control processor or physical access within the housing  12 . The face recognition system  34  may also be utilized to maintain a log of users accessing the system  10  and each individual&#39;s usage. While a face recognition system is described, the system  10  may incorporate additional or alternative access control, for example, other biometric sensors, control card sensors or password sensors. Alternatively, if utilized in a secure environment, the system  10  may not have any access control. 
     Referring to  FIGS. 2-4 , within the housing  12 , a lower support panel  21 , an intermediate panel  23  and an upper support panel  25  are supported by the frame  20 . The lower support panel  21  is configured to support the drum assembly  50 . The upper support panel  25  is configured to support portions of the build assembly  80 . The intermediate panel  23  is positioned between the lower and upper panels  21 ,  25  with a build chamber  82  defined therebetween the intermediate panel  23  and the upper support panel  25 . A vertical support panel  27  extends between the panels  23 ,  25  to support portions of the build assembly  80  within the build chamber  82 . A sealing wall  29 , which is illustrated in  FIG. 4  but is omitted in  FIGS. 2 and 3 , extends between the panels  23 ,  25  on the remaining three sides and in sealing engagement with the panels  23 ,  25 ,  27  such that the build chamber  82  is air-tight. The sealing wall  29 , or a portion thereof, may be removable to facilitate access within the build chamber  82  if necessary. 
     Turning to  FIGS. 5-12 , the drum assembly  50  and the build assembly  80  will be described in more detail. The drum assembly  50  generally includes a generally cylindrical drum  54  with a through passage extending from a lower end  51  to an upper end  53 . The lower end  51  of drum  54  is supported on a rotatable platform  52  in sealing engagement therewith. Clamps  56  or the like are utilized to releasably secure the drum  54  to the platform  52 . The upper end  53  of the drum  54  extends to the build chamber  82  through an opening  71  in the intermediate panel  23  (see  FIG. 2 ). The upper end  53  is in sealing engagement with the intermediate panel  23  while still being rotatable relative thereto. 
     A drum motor  58  is supported below the rotatable platform  52  in a fixed position relative to the lower support platform  21 . The drum motor  58  is configured to rotate the rotatable platform  52  and thereby the drum  54 . Bearings or the like (not shown), may be provided about the rotatable platform  52  and/or the drum  54  to facilitate smooth rotation thereof. The drum motor  58  is in communication with the control processor which controls the drum motor  58  to rotate the rotatable platform  52 , and thereby the drum  54  at a desired speed. 
     In the illustrated embodiment, the drum motor  58  is supported on a fixed plate  59  which is fixed relative to the lower support panel  21 . In the illustrated embodiment, a vacuum unit  60  is positioned between the fixed plate  59  and the lower support panel  21 . The vacuum  60  has an outlet port  61  which may be vented outside of the housing  12 . The vacuum  60  has an intake  63  which extends through the rotatable platform  52  such that the vacuum force may be applied into the drum  54  and into the build chamber  82  to remove heat and smoke generated during the printing process. 
     A support structure  64  is supported within the drum  54  and is configured to rigidly support a screw drive  66  relative to the drum  54 . The support structure  64  may have various configurations, for example, a plate, a spoke, cross straps, a cantilevered arm, or the like which fixedly supports the screw drive  66  relative to the drum  54 . Preferably the support structure  64  has some porosity to allow the vacuum force to pass thereby. A screw shaft  68  extends from the screw drive  66  to the build platform  70  (see  FIG. 9 ). The screw shaft  68  is fixed against rotation relative to the both the screw drive  66  and the build platform  70 . Since the screw drive  66  is fixed relative to the drum  54 , rotation of the drum  54  by the drum motor  58  will cause a corresponding rotation of the build platform  70 , as indicated by the arrows A in  FIGS. 9 and 10 . 
     The build platform  70  starts in an initial position just at or slightly above the upper end  53  of the drum  54  as shown in  FIG. 9 . The inner dimeter of the drum  54  and the outer diameter of the build platform  70  are maintained to close tolerances such that only a minimal gap  72  extends therebetween (see  FIG. 12 ). To facilitate the vacuum force reaching the build chamber  82 , the build platform  70  is preferably manufactured from a gas permeable material, for example, a gas permeable ceramic such as an ultra filtration ceramic membrane, which allows the heat and smoke to be vacuumed from the build chamber  82  but does not allow the powder to pass through. 
     Since the build assembly  80  is fixed in location, as each successive layer of the 3D printed objects is sintered or melted, it is necessary to move the build platform down by such layer thickness. Such downward movement is accomplished by the screw drive  66 . As the internal screw of the screw drive is rotated, as indicated by arrow B in  FIG. 12 , the internal screw engages the screw shaft  68 , causing the shaft  68  to move linearly as indicated by arrow C. The screw drive  66  does not rotate the screw shaft, but instead, the engagement of the respective threads and the rotationally fixed configuration of the screw shaft  68 , causes the shaft to move linearly. Rotation of the screw drive  66  is independent of rotation of the drum motor  58  which allows precise lowering in response to layer thickness regardless of the rotation speed of the drum  54  and thereby the build platform  70 . With this configuration, the completed object(s) will be lowered into the drum  54 . Upon completion, the drum  54  may be released via the clamps  56  or the like and the drum  54  removed from the housing to remove the completed object(s). A new, empty drum may be clamped on to the rotating platform  52  and a new process started. Alternatively, it is contemplated that a system may hold more than one drum and the drums may be selectively rotated into position in alignment with the build assembly  80 . It is further contemplated that post printing machinery, for example, a pressure cleaning system, a CNC machine or the like may be housed within the housing to finish the completed objects once they are removed from the drum. 
     The build assembly  80  includes a hopper  79  with a lower opening  81  configured to continuously deliver powder to the build platform  70 . The hopper  79  is supported by the vertical support panel  27 . In the illustrated embodiment, a slide mechanism  84  is supported along a rail  85  on the side of the hopper  79 . The slide mechanism  84  connects to an end of a delivery hose (not shown) extending from the powder containers  46 . A linear actuator  83  associated with the slide mechanism  84  moves the slide mechanism  84  back and forth along the rail  85  such that the delivery hose end moves back and forth along the hopper  79 , evenly distributing the powder. The powder may be any form of small particles typically used in laser or electron beam 3D printing. For example, the powder may be of plastic, metal, ceramic, glass or composites thereof. As non-limiting examples, the powder may include polymers such as nylon (neat, glass-filled, or with other fillers) or polystyrene, or metals including steel, titanium, alloy mixtures, for example, but not limited to, 17-4 and 15-5 stainless steel, maraging steel, cobalt chromium, inconel 625 and 718, aluminum AlSi10Mg, and titanium Ti6Al4V. 
     After the powder is delivered to the rotating build platform  70 , it is smoothed by a roller  86  on the trailing side of the hopper  79 . The roller  86  is supported by the vertical support panel  27  and is rotated by an actuator  87 . The roller  86  is rotated such that its lower edge moves toward the hopper  79 , i.e. toward the oncoming powder, thereby smoothing the powder. The smoothed powder is then ready for selective fusing via melting or sintering utilizing a targeted energy source. 
     In the illustrated embodiment, the targeted energy source is a plurality of lasers  90   a - 90   d . Each laser  90   a - 90   d  has an associated beam deflection system  92 , e.g. Galvano scanner, which is used to focus the laser beam  96   a - 96   d  out the respective beam window  94  to the desired position on the build platform  70  in order to scan each layer, as illustrated in  FIGS. 11-12 . The lasers  90   a - 90   d  may have various configurations, for example, Nd:YAG and Yb-fiber optic lasers, CO lasers and He—Cd lasers. Because the hopper  79  and roller  86  provide continuously smooth powder and the target areas of the beams  96   a - 96   d  are the remainder of the build platform  70  other than the fixed position hopper  79  and roller  86 , the layers may be formed continuously along the rotating build platform  70  without any need to pause the fusing process. As such, the multiple lasers may print consecutive portions of the desired product, thereby stitching the product together as it travels along the complete rotational path of the build platform  70 . The number and position of the lasers  90   a - 90   d  may be selected to provide desired fusing at a desired rotation speed of the build platform  70 . It is also noted that the beam windows  94  are relatively close to the build platform  70 , the beams  96   a - 96   d  will have less distance to travel to accomplish fusing of a given layer, affording greater rotation speeds. Additionally, the beams  96   a - 96   d  contact the powder at less of an inclination resulting in less angled formation and accompanying roughness. 
     Such laser sintering or melting typically requires a tightly controlled atmosphere of inert gas, for example, argon or nitrogen at oxygen levels below 500 parts per million. The sealed build chamber  82  allows for such a controlled atmosphere with the required gas controllably supplied by the gas tanks  40 . 
     While the illustrated embodiment utilizes lasers, other energy sources may be utilized, for example, electron beam guns. In such a system, since electrons interact with the atmosphere, it is necessary to have a vacuum chamber which may be maintained in the sealed build chamber using a controlled helium inflow from the gas tanks  40 . In all other aspects, the system would operate in the same manner. 
     Referring to  FIG. 13 , a system incorporating an alternative build assembly  80 ′ is illustrated. The build assembly  80 ′ is similar to that described above and only the differences will be described herein. It is noted that any of the features described in the present embodiment may be separately incorporated into the previous embodiment and vice versa. In the present embodiment, the build assembly  80 ′ includes a pair of heating elements  88   a  and  88   b . Since in some applications it may be beneficial to heat the powder before fusing, the heating element  88   a  may be a heating bar positioned downstream from the roller  86  to heat the smoothed powder. Additionally, or alternatively, the heating element  88   b  may be a circular bar extending about a portion or the entirety of the build platform  70  to heat the powder over a larger area. The heating elements  88   a ,  88   b  may have various configurations, for example, an electronic heating bar, infrared heating bar, induction heating bar or the like. In an alternative embodiment, a portion of the lasers  90   a  and  90   b  may be utilized to preheat the material and the remaining lasers  90   c  and  90   d  may be utilized to fuse the powder. 
     Additionally, the build assembly  80 ′ includes a single laser  90 ′ which is self-contained. The laser  90 ′ is moveable along a rail  91  supported by a portion of the support frame. In the illustrated embodiment, the rail  91  has a linear configuration and the laser  90 ′ moves radially inward and outward as indicated by the arrow in  FIG. 13 . The rail may have other configurations, for example, an arcuate path or a structure that allows the laser  90 ′ to be moved in multiple coordinate planes. The moveable laser  90 ′ is not limited to a rail system, but may be otherwise moved, for example, utilizing a robotic arm (not shown). Additionally, the laser  90 ′ includes an extended cone  93 , for example, manufactured from glass, which extends from the laser beam window  94  to just above the build platform  70 . The extended cone  93  defines a laser specific gas chamber  82 ′ which would contain the inert gas necessary for the laser sintering or melting. The extended cone  93  would eliminate the need for a sealed build chamber. 
     Referring to  FIGS. 14-21 , a system incorporating an alternative drum assembly  150  and an alternative build assembly  180  will be described. In  FIG. 14 , the drum assembly  150  and the build assembly  180  are illustrated relative to the support platforms  21 ,  23 ,  25  the drum assembly  50  and the build assembly  80  will be described in more detail. As in the previous embodiments, the lower support panel  21  is configured to support the drum assembly  150 . The upper support panel  25  is configured to support portions of the build assembly  80 . The intermediate panel  23  is positioned between the lower and upper panels  21 ,  25  with a build chamber  82  defined therebetween the intermediate panel  23  and the upper support panel  25 . Except as described hereinafter, the system of  FIGS. 14-21  operates in a manner similar to that described with the above embodiments. 
     Referring to  FIGS. 14-16 , the drum assembly  150  generally includes a generally cylindrical outer drum  54  and a generally cylindrical inner drum  154 . Each drum  54 ,  154  extends from a lower end  51 ,  151  to an upper end  53 ,  153 . The lower end  51  of drum  54  is supported on a rotatable platform  152  in sealing engagement therewith. The lower end  151  of the inner drum  151  is also supported on the rotatable platform  152 . Clamps or the like (not shown) are utilized to releasably secure the drums  54 ,  154  to the platform  152 . The upper ends  53 ,  153  of the drums  54 ,  154  extend to the build chamber  82  through an opening in the intermediate panel  23 . The upper end  53  of the outer drum  54  is in sealing engagement with the intermediate panel  23  while still being rotatable relative thereto. 
     A powder receiving chamber  160  is defined between the inner surface of the outer drum  54  and the outer surface of the inner drum  154 . As shown in  FIG. 16 , the outer drum  54  has an inner radius of R 1  and the inner drum  154  has an outer radius R 2 . The difference between R 1  and R 2  defines the width W of the powder receiving chamber  160 . As shown in  FIG. 15 , the build platform  170  of the present embodiment has a disc shaped body  172  with a central passage  173 . The build platform body  172  has an outer radius PR 1  which is slightly smaller than the outer drum inner radius R 1  and an inner radius PR 2  which is slightly larger than the inner drum outer radius R 2 . With such a configuration, the build platform  170  supports the powder within the powder receiving chamber  160  but is axially moveable up and down within the chamber  160 . 
     The radii R 1  and R 2  may be chosen to be any desired size with any desired width W to print the intended product. The build platform  170  will correspondingly be chosen with radii PR 1  and PR 2 . For example, to print the illustrative double-wall tube  200  shown in  FIG. 21 , the width W may be selected to be slightly larger than the thickness T of the double-wall tube  200 . If, for example, the tube  200  has a thickness T of 1 inch, the width W of the powder receiving chamber  160  could be selected to be 2 inches. In one exemplary embodiment, the radius R 2  is at least 25% the radius R 1 . In another exemplary embodiment, the radius R 2  is at least 50% the radius R 1 . In yet another exemplary embodiment, the radius R 2  is at least 75% the radius R 1 . In a further exemplary embodiment, the radius R 2  is at least 90% the radius R 1 . In each such embodiment, the volume of powder necessary to build the desired product is reduced compared to an assembly without an inner drum. Without the inner drum, the volume of required powder V R  would be equal to the volume of the outer drum, namely, V R =πR 1   2 h. However, by defining the powder receiving chamber  160  between the outer drum  54  and the inner drum  154 , the volume of required powder V R  will equal the volume of the outer drum V O  minus the volume of the inner drum V I , namely, V R =(πR 1   2 h)−(πR 2   2 h). 
     As a first example, if the double-wall tube has an outer diameter of 2 feet and a height of 2 feet, the outer drum  54  may have an R 1  of 12.25 inches (i.e. a diameter which is a half inch larger than outer diameter of the tube) and the inner drum  154  may have an R 2  of 11.25 inches (i.e. a diameter which is a half inch less than inner diameter of the tube). Without the inner drum, the volume of required powder V R  would equal V R =πR 1   2 h=π(12.25 in) 2 (24 in)=11,314.45 in 3 . With the inner drum of the present disclosure, the V R  is reduced to V R =(πR 1   2 h)−(πR 2   2 h)=(π(12.25 in) 2 (24 in))−(π(11.25 in) 2 (24 in))=11,314.45 in 3 −9542.59 in 3 =1771.86 in 3 . The same tube  200  may be manufactured utilizing only 1771.86 in 3  of material instead of 11,314.45 in 3 , or 15.66% volume of material. For larger scale objects, the material requirement may be even further reduced. For example, for a tube having a 12 foot diameter, a height of 5 feet and a thickness of 4 inches, the material requirement would be only 8.13% volume of material. More specifically, without the inner drum, the volume of required powder V R  would equal V R =πR 1   2 h=π(72.25 in) 2 (60 in)=983,958.6 in 3 . With the inner drum of the present disclosure, the V R  becomes V R =(πR 1   2 h)−(πR 2   2 h)=(π(72.25 in) 2 (60 in))−(π(69.25 in) 2 (60 in))=983,958.6 in 3 −903,942.24 in 3 =80,016.36 in 3 . The same tube  200  may be manufactured utilizing only 80,016.36 in 3  of material instead of 983,958.6 in 3 . Such a significant savings in material has many benefits, for example, reduced inventory, reduced waste and significantly less power required to rotate the drums  54 ,  154 . 
     Referring to  FIG. 16 , the rotatable platform  152  of the present embodiment includes an outer rim  155  and a center support  157  with a plurality of rails  156  extending therebetween. In the illustrated embodiment, the outer drum  54  is supported by the outer rim  155  and the inner drum  154  is supported by the rails  156 . It is contemplated that both the outer and inner drums  54 ,  154  may be supported by the rails  156 . Each of the drums  54 ,  154  will be connected to their respective support surface such that the drums  54 ,  154  rotate with the rotatable platform  152 . 
     In the embodiment illustrated in  FIG. 16 , a space  158  is defined between each pair of adjacent rails  156 . The spaces  158  allow linear actuators  164  to extend through the rotatable platform  152  and between the drums  54 ,  154  and into contact with the build platform  170 . In the illustrated embodiment, each of the linear actuators  164  includes a housing  166  mounted to a respective rail  156  and a rod  168  extendible relative to the housing  166 . The illustrated housings  166  are radially adjustable such that the position of the linear actuators  164  may be radially adjusted to properly align with the build platform  170 . 
     The linear actuators  164  may have various configurations, for example, screw drives, pneumatic cylinders, hydraulic cylinders, or any other desired configuration. Additionally, to facilitate manufacture of objects having a large height without significantly increasing the height of the system, the linear actuators of each of the embodiments described herein may have a telescoping or scissor configuration which allows a larger extension than the envelope of the actuator, for example, the T2—Telescoping Linear Actuator by Helix Linear Technologies or the I-Lock Spiralift 250 by Paco Spiralift. Such telescoping or scissor lifts may be electronically, pneumatically, hydraulically or otherwise controlled. As another alternative, the linear actuators may be positioned along the surface of one of the drums  54 ,  154  with pins extending through vertical slots in the respective drum into the chamber to support the build platform. An illustrative embodiment with such a configuration will be described hereinafter with reference to  FIGS. 27-29 . 
     The linear actuators  164  are configured for synchronized movement such that the build platform  170  is supported and raised or lowered in a controlled manner. In the embodiment illustrated in  FIG. 16 , each housing  166  houses a screw motor (not shown). The system control processor controls each of the screw motors such that the actuators  164  provide synchronized movement of the build platform  170 . Turning to the embodiment illustrated in  FIG. 17 , each of the linear actuators  164 ′ includes a drive gear  167  supported by the housing  166  and engaging the rod  168 . Rotation of the drive gear  167  causes linear motion of the rod  168 . In the illustrated embodiment, a platform drive motor  161  controllably drives a main gear  163 . A belt  165  or the like engages the main gear  163  and each of the drive gears  167  such that rotation of the platform drive motor  161  causes synchronized rotation of the drive gears  167 . The embodiment illustrated in  FIG. 18  is similar to the previous embodiment, however, instead of a separate drive motor, the main gear  163 ′ is connected to the drum motor  58  supported below the rotatable platform  152 . A belt  165  or the like engages the main gear  163 ′ and each of the drive gears  167  such that rotation of the drum motor  58  causes synchronized rotation of the drive gears  167 . Other synchronized drive assemblies may alternatively be utilized. The linear actuators  164  may be configured to raise or lower the build platform  170  in any desired manner. In one embodiment, the actuators  164  are configured such that the build platform  170  moves equally at all times such that the platform moves in an incremental, vertical manner even though the platform  170  is rotating. In another embodiment, the actuators  164  are configured to move differently from another such that the platform  170  moves in a spiral manner as it rotates and moves vertically. 
     Referring to  FIGS. 14, 19 and 20 , an exemplary build assembly  180 . While the build assembly  180  is described in conjunction with the present embodiment, it is understood that features of the build assembly  180  may be utilized with any of the embodiments described herein. The build assembly  180  includes a hopper  179 . As shown in  FIG. 14 , the hopper  179  may have a width such that it extends from the outer drum to the center axis thereof. Since the width W of the powder receiving chamber  160  is less than the width of the hopper  179 , the hopper  179  includes an adjustable wall  184  such that the width of the powder area  183  may be adjusted to approximately equal the width W of the powder receiving chamber  160 . In the illustrated embodiment, a telescoping rod  185  sets the position of the adjustable wall  184 , however, other mechanisms, for example, clips or the like may be utilized to fix the position of the adjustable wall  184 . 
     With reference to  FIGS. 19 and 20 , the hopper  179  has a lower opening  181  such that powder within the powder area  183  is delivered to the distribution roller  190 . The distribution roller  190  has a cylindrical body  192  rotatably supported on a shaft  191 . The shaft  191  may be supported by brackets  178  extending from the hopper  179  or otherwise supported below the hopper  179 . The cylindrical body  192  a plurality of small cavities  194  defined in the surface thereof. As one non-limiting example, the cavities  194  have a diameter of 2 mm and a depth of 2 mm. Rotation of the distribution roller  190  is controlled by an actuator  193 . As the distribution roller  190  is rotated, powder is pushed into the cavities  194  by an elastic blade  196  positioned adjacent the hopper opening  181  and contacting the distribution roller  190 . As the roller  190  rotates, the cavities  194  carry the powder toward the build platform  170 . A brush  198  with a plurality of bristles  199  is positioned adjacent the distribution roller  190  such that the bristles  199  engage the cavities  194  and cause the powder to be distributed onto the build platform  170 . Since the powder is carried by the cavities  194 , the rate of rotation of the distribution roller  190  will control the amount of powder delivered toward the build platform, i.e. the faster the distribution roller  190  is rotated, the more powder will be delivered. 
     After the powder is delivered to the rotating build platform  170 , it is smoothed by a roller  186  on the trailing side of the distribution roller  190 . The roller  186  is rotatably supported on a shaft  188  extending between the brackets  178  extending from the hopper  179 . The roller  186  will have a length approximately equal to or slightly less than the width W of the powder receiving chamber  160  such that a portion of the roller  186  is received within the chamber  160 . Since the length of the roller  186  is generally going to be less than the length of the shaft  188 , a clip  189  or the like may be positioned along the shaft  188  to fix the position of the roller  186 . If the drums  54 ,  154  are changed to define a different chamber width W, the roller  186  can be similarly changed to correspond to the new width W. The roller  186  is rotated by an actuator  187  such that its lower edge moves toward the hopper  179 , i.e. toward the oncoming powder, thereby smoothing the powder. The smoothed powder is then ready for selective fusing via melting or sintering utilizing a targeted energy source. 
     Referring to  FIGS. 14 and 21 , as in the previous embodiments, the targeted energy source may be a plurality of lasers  90   a - 90   c , however, other sources, for example, electron beam guns, may be utilized. While three lasers  90   a - 90   c  are illustrated, it is understood that any number of lasers, including more or fewer than three, may be utilized. Each laser  90   a - 90   c  has an associated beam deflection system, e.g. Galvano scanner, which is used to focus the laser beam  96   a - 96   c  onto a desired position on the build platform  170  in order to scan each layer. In one embodiment, each laser  90   a - 90   c  may be utilized to complete a distinct portion of the desired product. For example, with the example double-walled tube  200  of  FIG. 21 , one of the lasers  90   a  may focus on the thicker outer wall  202  while one of the lasers  90   b  focuses on the thicker inner wall  204  and the other laser  90   c  focuses on the thinner honeycomb interior  206  and interior conduits  208 . Such a focused system allows for rapid rotational production of the desired product. It is also contemplated, as in the previous embodiments, that the multiple lasers may print consecutive portions of the desired product, thereby stitching the product together as it travels along the complete rotational path. It is noted that while the example tube has a cylindrical configuration, the disclosure is not limited to such and other shapes may be manufactured with a desired chamber width W chosen to accommodate such structure. 
     Additionally, the disclosure is not limited to a single powder receiving chamber. Referring to  FIGS. 22 and 23 , an embodiment utilizing two powder receiving chambers  160 ,  160   a  will be described, however, the number of chambers may be increased above the illustrated two by utilizing more drums. In the present embodiment, an intermediate drum  154   a  is positioned between the outer drum  54  and the inner drum  154  to define an outer chamber  160  and an inner chamber  160   a . The powder deposited into each chamber  160 ,  160   a  may be the same or different. Additionally, the products in each chamber may be independent of one another, or as illustrated in  FIG. 23 , may form an integrated product with the intermediate drum  154   a  forming a part of the product. The double-wall drum  200 ′ illustrated in  FIG. 23  includes an outer wall  202  and an inner wall defined by the intermediate drum  154   a . A honeycomb structure  206  extends between the outer wall  202  and the inner wall  154   a . The honeycomb structure  206  and the outer wall  202  are formed in the outer chamber  160 . The tube  200 ′ also includes a ceramic insulation layer  210  formed on the inside of the inner wall  154   a . The ceramic insulation layer  210  is formed in the inner chamber  160   a . Other integrated products of different or similar materials may also be manufactured utilized multiple chambers  160 ,  160   a.    
     Referring to  FIGS. 24-26 , a drum assembly  150 ′ in accordance with another embodiment of the disclosure will be described. The drum assembly  150 ′ is similar to the drum assembly  150  and only the differences will be described herein. The drum assembly  150 ′ includes an outer drum  54  and an inner drum  154 ′. As in the previous embodiment, the drums  54  and  154 ′ define a powder receiving chamber  160  in which the build platform  170  is positioned. The build assembly  180 ′ of the present embodiment is substantially the same as the previous embodiment but does not extend to the center axis of the drums. 
     Referring to  FIG. 25 , in the present embodiment, the inner drum  154 ′ is shorter than the outer drum  54  and includes a bottom surface  254  which extends across the inner drum  154 ′ and across the chamber  160  as shown at  254   a . The bottom surface  254  may be secured to the outer drum  54  to fix the inner drum  154 ′ relative to the outer drum  54  such that they rotate together. 
     For rotation, the outer drum  54  is fixed in a groove  222  of track  220 . The track  220  has a plurality of outwardly extending gear teeth  224 . A plurality of drum motors  230  are positioned about the track  220  which may increase efficiency and reliability of the rotational motion. Each drum motor  230  includes a motor  232  configured to rotate a drive gear  234 . As the motors  232  rotate the drive gears  234 , the drive gears  234  engage the gear teeth  224  such that the track  220  and outer drum  54  are rotated. 
     As in the previous embodiment, a plurality of linear actuators  164  are positioned below the platform  170  to controllably raise and lower the platform  170 . In the present embodiment, the linear actuators  164  are positioned within the chamber  160  and are supported by the bottom surface  254  of the inner drum  154 ′. In all other aspects, the linear actuators  164  are as described above. 
     Referring to  FIGS. 27-29 , a drum assembly  150 ″ in accordance with another embodiment of the disclosure will be described. The drum assembly  150 ″ is similar to the drum assembly  150 ′ and only the differences will be described herein. The drum assembly  150 ″ includes an outer drum  54 ′ and an inner drum  154 ′. As in the previous embodiment, the drums  54 ′ and  154 ′ define a powder receiving chamber  160  in which the build platform is positioned. The build assembly  180 ′ of the present embodiment is substantially the same as the previous embodiment. 
     In the present embodiment, the linear actuators  164 ′ are defined along the exterior surface of the drum  54 ′. It is understood that the actuators  164 ′ could be defined along the interior surface of the drum  154 ′ or along both surfaces. Each linear actuator  164 ′ includes a rail  240  extending between ends  241 ,  243  which are secured relative to the outer drum  54 ′. Each rail  240  is aligned with a vertical slot  244  through the outer drum  54 ′. A pin member  242  is configured to ride along each rail  240 . The pin member  242  includes a pin (not shown) which extends through the vertical slot  244  and into the powder receiving chamber  160  below the build platform such that the build platform is supported on the pins of each linear actuator  164 ′. The pin members  242  are controllably moved along the rails  240  to raise and lower the build platform. Each of the linear actuators  164 ′ are synchronized to move the pin members  242 , and thereby the build platform, at a desired rate. 
     Each pin may extend through a flexible gasket  246  or the like along the vertical slot  244  such that the gasket  246  prevents powder from exiting through the vertical slot  244 . The gasket  246  has a slot which allows the pin to pass through but is otherwise closed. As the pin moves downward, the gasket  246  seals as the build platform moves along the gasket  246 . Other mechanisms may alternatively be utilized to seal the slot  244 . For example, in one embodiment, a coiled flat strip is positioned at the top of each slot  244  with a free end connected to the respective pin. As the pin moves downward, the strip is pulled along the slot  244 , thereby sealing the slot  244  as the pin moves downward. 
     Referring to  FIGS. 30 and 31 , a schematic diagram of an illustrative control assembly  270  is shown. The control assembly  270  is discussed in conjunction with the printing system  10  of the first embodiment, but may be utilized with any of the embodiments described herein. The control assembly  270  includes a controller  272 , for example, a microprocessor, which receives layer information  274  from the 3D object model. The controller  272  also receives information from a rotation sensor  276  which provides information regarding the rotational speed and angular position of the build platform  70 . The controller  272  is configured to send a signal to the drum motor  58  to rotate the build platform  70  at a desired speed. 
     The controller  272  is configured to synchronize each of the lasers  90   a ,  90   b , . . .  90   n  to print within a given subregion  282  of the printing layer which extends about the entire circumference of the build platform  70 , except for the subregion  280  below the hopper  79 . In the embodiment illustrated in  FIG. 31 , five subregions  282   a ,  282   b ,  282   c ,  282   d ,  282   e  are defined with five corresponding lasers  90   a ,  90   b ,  90   c ,  90   d ,  90   e . Each subregion  282   a - 282   e  extends over an arcuate portion of the build platform  70  circumference. More specifically, subregion  282   a  extends from the hopper subregion  280  at S0 approximately 70° to S1, subregion  282   b  extends from S2 approximately 70° to S3, subregion  282   c  extends from S4 approximately 70° to S5, subregion  282   d  extends from S6 approximately 70° to S7, and subregion  282   e  extends from S8 approximately 70° to S9 proximate the hopper subregion  280 . While the subregions  282  are illustrated as each having the same size, the regions may have different sizes from one another. It is also note that the subregions overlap one another slightly, for example, by 5%, such that continuous printing may be achieved, however, such overlap may not be needed. The controller  272  is configured to control each of the lasers  90   a  . . .  90   n  in a synchronized fashion such that one layer of the object will be printed as it passes through all of the subregions  282 . The controller  272  is configured to utilize the height adjustment mechanism to lower the build platform  70  by one layer thickness in conjunction with the object a rotation from one side of the hopper subregion  280  to the opposite side of the hopper subregion  280 . 
     In the embodiment illustrated in  FIG. 32 , four subregions  282   a ′,  282   b ′,  282   c ′,  282   d ′ are defined with five corresponding lasers  90   a ,  90   b ,  90   c ,  90   d . Each subregion  282   a ′- 282   d ′ extends over a radial portion of the build platform  70  and makes a complete circumference except for the hopper subregion  280 . More specifically, subregion  282   a  from a central location S0 to a radius at S1, subregion  282   b  extends radius S2 to radius S3, subregion  282   c  extends from radius S4 to radius S5, and subregion  282   d  extends from radius S6 to radius S7. As illustrated, the subregions  282  have different radial sizes from one another, however, the radial sizes may be equal. It is also note that the subregions overlap one another slightly, for example, by 5%, such that continuous printing may be achieved, however, such overlap may not be needed. The controller  272  is configured to control each of the lasers  90   a  . . .  90   n  in a synchronized fashion such that one layer of the object will be printed as it passes through all of the subregions  282 ′. The controller  272  is configured to utilize the height adjustment mechanism to lower the build platform  70  by one layer thickness in conjunction with the object a rotation from one side of the hopper subregion  280  to the opposite side of the hopper subregion  280 . 
     These and other advantages of the present disclosure will be apparent to those skilled in the art from the foregoing specification. Accordingly, it will be recognized by those skilled in the art that changes or modifications may be made to the above-described embodiments without departing from the broad inventive concepts of the disclosure. It should therefore be understood that this disclosure is not limited to the particular embodiments described herein, but is intended to include all changes and modifications that are within the scope and spirit of the disclosure as defined in the claims.