Abstract:
A device for providing uniform powder flow to the nozzles when creating solid structures using a solid fabrication system such as the directed light fabrication (DLF) process. In the DLF process, gas entrained powders are passed through the focal point of a moving high-power laser light which fuses the particles in the powder to a surface being built up in layers. The invention is a device providing uniform flow of gas entrained powders to the nozzles of the DLF system. The device comprises a series of modular splitters which are slidably interconnected and contain an integral flow control mechanism. The device can take the gas entrained powder from between one to four hoppers and split the flow into eight tubular lines which feed the powder delivery nozzles of the DLF system.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims priority from U.S. provisional application serial No. 60/131,827 filed on Apr. 29, 1999. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0002] This invention was made with Government support under Contract No. W-7405-ENG-36, awarded by the Department of Energy. The Government has certain rights in this invention. 
     
    
     
       REFERENCE TO A MICROFICHE APPENDIX  
         [0003]    Not Applicable  
         BACKGROUND OF THE INVENTION  
         [0004]    1. Field of the Invention  
           [0005]    This invention pertains generally to directed light fabrication processes, and more particularly to a device which provides uniform distribution of gas-carried material powder within a directed light fabrication system.  
           [0006]    2. Description of the Background Art  
           [0007]    Fabrication of three-dimensional solids by means of directed fabrication, such as directed light fabrication (DLF), involves injecting powders into a high energy density moving beam, such as a laser light beam. The powders are carried by a stream of gas, commonly argon, to the focal point of the laser beam wherein material fusing occurs. The gas provides a non-reactive carrier for the particles of the powder which are to be fused into a solid. In practice, though, the powder is often injected non-uniformly about the beam resulting in a build-up from the fused powder material that is also of non-uniform structure. The lack of uniformity is particularly noticeable when the laser beam changes direction, thereby causing a different orientation of powder injection relative to the beam motion. This lack of uniformity in the resultant solid due to the improperly distributed powders becomes even more pronounced when fabricating alloy solids from a combination of powders.  
           [0008]    Achievement of a uniform finished structure therefore requires uniformity of powder injection. The multiple feed powder splifter in accordance with the present invention when used with a multiple-outlet nozzle for powder disbursement satisfies that need, as well as others, and overcomes deficiencies in current powder feed techniques.  
         BRIEF SUMMARY OF THE INVENTION  
         [0009]    The present invention distributes controlled powder flow rates to a series of output lines for dispersing powder which is entrained within a gas through nozzles for use within the directed light fabrication (DLF) process. The device comprises a number of modular splitter blocks which can be slidably interconnected. The slidable connection incorporates an integral flow control means that requires no moving parts. A combination of splitter blocks are interconnected to receive a flow of gas entrained powder from one or more hoppers. The flow of gas entrained powder is split into a number of tubular lines which are connected to feed the powder delivery nozzles.  
           [0010]    An object of the invention is to split the flow of gas entrained powder into a series of output lines.  
           [0011]    Another object of the invention is to control the relative amount of powder flowing into each powder flow splitter block without the need of moving parts employed within separate valve assemblies.  
           [0012]    Another object of the invention is to provide a powder flow splitter system that allows configuration for various numbers of hoppers for supplying the powder material.  
           [0013]    Another object of the invention is to provide for modular mechanical block interconnections which allow for rapid assembly, flow adjustment, and tear-down.  
           [0014]    Another object of the invention is to provide an integrated flow control means for equalizing the flow of gas entrained powder.  
           [0015]    Another object of the invention is to provide gas entrained powder flow passageways that do not restrict powder flow or unduly clog up.  
           [0016]    Another object of the invention is to provide uniform distribution of incoming powder material among two outgoing passageways.  
           [0017]    Another object of the invention is to provide a flow control means with minimal susceptibility to failure.  
           [0018]    Further objects and advantages of the invention will be brought out in the following portions of the specification, wherein the detailed description is for the purpose of fully disclosing preferred embodiments of the invention without placing limitations thereon. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]    The invention will be more fully understood by reference to the following drawings which are for illustrative purposes only:  
         [0020]    [0020]FIG. 1 is a front view of a one-to-eight way gas entrained powder splitter according to the invention, with three tiers of interconnected splitter blocks shown.  
         [0021]    [0021]FIG. 2 is a top view of the three-tier gas entrained powder splitter of FIG. 1.  
         [0022]    [0022]FIG. 3 is a front view of the three-tier gas entrained powder splitter of FIG. 2.  
         [0023]    [0023]FIG. 4 is a side view of the gas entrained powder splitter of FIG. 2.  
         [0024]    [0024]FIG. 5 is a front view of a source feed connection block according to the invention.  
         [0025]    [0025]FIG. 6 is a side view of the source feed connection block of FIG. 5.  
         [0026]    [0026]FIG. 7 is a front view of a first-tier splitter block according to the invention.  
         [0027]    [0027]FIG. 8 is a side view of the first-tier splitter block of FIG. 7.  
         [0028]    [0028]FIG. 9 is a top view of a second-tier splitter block according to the invention.  
         [0029]    [0029]FIG. 10 is a front view of the second-tier splitter block of FIG. 9.  
         [0030]    [0030]FIG. 11 is a side view of the second-tier splitter block of FIG. 9.  
         [0031]    [0031]FIG. 12 is a top view of a third-tier splitter block according to the invention.  
         [0032]    [0032]FIG. 13 is a front view of the third-tier splitter block of FIG. 12, shown without output connectors in place.  
         [0033]    [0033]FIG. 14 is a side view of the third-tier splitter block of FIG. 12.  
         [0034]    [0034]FIG. 15 is a front view of a one-to-eight way gas entrained powder splitter with an attached reverse splitter for receiving and combining gas entrained powders from two hoppers.  
         [0035]    [0035]FIG. 16 is a front view of a reversing splitter according to the invention.  
         [0036]    [0036]FIG. 17 is a side view of the reversing splitter of FIG. 16. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0037]    Referring more specifically to the drawings for illustrative purposes, the present invention is embodied in the apparatus generally shown in FIG. 1 through FIG. 17. It will be appreciated that the apparatus may vary as to configuration and as to details of the parts, and that the method may vary as to the specific steps and sequence, without departing from the basic concepts as disclosed herein.  
         [0038]    Referring first to FIG. 1, a three-tier gas entrained powder splitter  10  according to the present invention is shown. The splitter shown has been modularly assembled from a source feed connection block  16 , a first-tier splitter block  20 , a pair of second-tier splitter blocks  32 ,  34 , and four third-tier splitter blocks  48 ,  50  (two of the third-tier splitter blocks are hidden in this view). The third-tier of splitter blocks within this embodiment incorporate output tubing connectors for communicating the gas entrained powder to a set of nozzles within the directed light fabrication (DLF) system.  
         [0039]    In use, an input source line  12  is connected to a hopper (not shown) which provides the powder that is entrained within a gas carrier, such as argon. The gas entrained powder enters the tubing of the input source line  12  and passes through a tubing connector  14  which is integral to a source feed connection block  16 , whose exit port  18  terminates at a slidable connection interface  28  with the first-tier splitter block  20 . An entry port  22  of the first-tier splitter block  20  has an enlarged entry chamber which allows the powder entering the splitter block to spacially disperse prior to reaching the dividing wall that separates the flow between two flow passageways  24   a ,  24   b  within the splitter block. Referring also to FIG. 7, on traversing a path toward exit, the passageways  24   a ,  24   b  taper down to straight, non-tapered sections  92   a ,  92   b , respectively, and then open up into chambers on the two exit ports  26   a ,  26   b , respectively, of the first-tier splitter block  20 .  
         [0040]    A slidable track engagement mechanism  28  at the input side of the first-tier splitter block  20 , and slidable track engagements  30   a ,  30   b  on the output end of the splitter block providing inter-modular connections on the splitter block. The slidable track engagements are slotted retention mechanisms which hold the blocks to one another, wherein an exit port of one module can be slid into alignment with an entry port of another module. The alignment of passageways can be slidably varied so as to control the flow of gas entrained powder between the modular sections of the invention. Connected at right angles to the first-tier splitter block  20  are two second-tier splitter blocks  32 ,  34 , each similarly having an entry port  36 ,  40  with a chamber and pairs of exit ports  38   a ,  38   b  (hidden in this view),  42   a , and  42   b  (hidden in this view), respectively. Slidable track engagements  44 ,  46  connect these second-tier splitter blocks  32 ,  34  with a group of four third-tier splitter blocks  48 ,  50  (two blocks are hidden in this view). As with the other modular sections, each of the third-tier splitter blocks is connected orthogonally to the preceding modular section, and contain entry ports  52 ,  54 , with flow passageways  56   a ,  56   b ,  58   a ,  58   b , along with exit ports  60   a ,  60   b ,  62   a ,  62   b . The exit ports of these third-tier splitter blocks have terminations to connect with tubing for routing the gas entrained powder to the nozzle of the DLF system. Four of the eight tubing connectors  64 ,  66 ,  68 ,  70 , are shown connecting to their respective output nozzle feed lines  72 ,  74 ,  76 ,  78 , for moving the material powder to the nozzles which are directed to the point of focus of the laser beam.  
         [0041]    [0041]FIG. 2 shows previously hidden third-tier splitter blocks  80 ,  82  within the three-tier, eight-way splitter embodiment  10 , along with the first and second third-tier splitter blocks  32 ,  34  which are shown in FIG. 3. In FIG. 4, the three tier splitter block is shown with first and third tiers of the splitter blocks in profile.  
         [0042]    The splitter block modules for this embodiment may be produced by machining channels within the faces of a pair of block halves (or a split block) by the use of, for example, CNC machining equipment. The splitter blocks can be fabricated from any suitably hard material, although metals are preferred. The two sections are then joined together to form a splitter block that contains integral passageways. The tracks can likewise be machined into the blocks to provide for modular attachment and flow regulation between sections.  
         [0043]    Note that the two separate flow passageways shown within each tier of splitter blocks gradually taper down in diameter from a corresponding chambered entry port and separate laterally in distance to provide room for the exit ports to connect to the next tier. Preferably, the passageways are directed downward at approximately a 45° angle to the vertical, and gradually taper in diameter to a smaller constant diameter vertical straight section before reaching the exit port. The diameter of the separate passageways at the split is preferably approximately one-half of the cross sectional area of the combined passageways prior to the split, so that the velocity of the gas entrained powder remains constant during that portion of the splitter block. The straight section transfers the gas entrained powders to the larger diameter chamber of the exit port just prior to flowing into the entry port of a succeeding splitter block. By straightening the flow path, the stream of particulates is not affected by changes in tube diameter or curvature changes in the passageways which can otherwise distort the flow path in the division chamber. The smaller diameter straight section serves to straighten the flow path, increase the velocity of gas and particulates, and disperse the particulates to lower aerial density as they enter the enlarged volume of the chamber prior to division into channels in the next block. The effect of increasing the velocity may be secondary to creating increased uniformity of the dispersion effect as the gas entrained powder leaves the straight section and enters the area of lower aerial density within the chamber of the exit port. The lower aerial particulate density produces a higher resolution of adjustment to try to equalize the mass of powder going down each passageway in the new tier. The enlarged chambers at the entry and exit ports also provide a higher resolution for the control of the flow of gas entrained powder. The higher resolution simplifies making balancing adjustments to the flow of gas entrained powder through the output tubes (typically eight) to the laser focal zone of the solids fabrication system.  
         [0044]    [0044]FIG. 5 and FIG. 6 show the source feed connection block  16  in more detail. Standard swaged tubing fittings (7/16-20 swaged tube fittings containing an O-ring) or the like can be used for interfacing the tubing with the modular blocks of the inventive embodiment. The tube fittings connect with ¼ inch Polyflow™ tubing or the like. It is generally preferable that the inlet tubes should have a larger diameter than the output tubes, for instance the use of inlet tubing with an inside diameter of 0.170 inches and output tubing with an inside diameter of 0.118 inches. Various alternative mechanisms for providing fluid communication to and from the splitter blocks of the present invention will be obvious to one of ordinary skill in the art.  
         [0045]    Referring to FIG. 5, the input source line  12  connects to a source of gas entrained powder from a hopper (not shown). In FIG. 5 the tubing of the input source line  12  is shown retained by tubing connector  14 . In FIG. 6 the source feed connection block  16  module is shown in a side view configured with a connector receptacle  84  into which the tubing connector  14  has been press-fit. The female track slot  86 , which can be easily seen in this view, connects with a mating section of male track to provide block-to-block slidable interconnection.  
         [0046]    [0046]FIG. 7 and FIG. 8 show an individual first-tier splitter block  20 . In FIG. 8 the male track  88  can be seen which mates with the female track  86  of the source feed block  16  as shown in FIG. 6. The first-tier splitter block  20  (FIG. 7) is configured for the attachment of two modular block sections by means of the female track slots  90   a ,  90   b . Flow passageway  24   a  can be seen in FIG. 8 with entry port  22  providing an expansion chamber within the passageway that tapers down to section  92   a  which, as described previously, is a short straight section that opens up again near exit port  26   a . Note again that, as the cross-sectional area of the passageway decreases, the gas/powder velocity increases proportionally. Thus, on each side of the tier interface the powder moves from a narrow passageway where velocity is highest to a larger opening defined by the size of the dual channel on the opposite side of the tier boundary. By transitioning from one passageway into two, the area is roughly cut in half and the velocity stays approximately the same as the velocity in the larger area prior to splitting. The gradual decrease in diameter to a minimum in the straight vertical section helps increase particular velocity prior to splitting again.  
         [0047]    [0047]FIG. 9 through FIG. 11 are three views of a second-tier splitter block  32 . FIG. 9 is a top view showing entry port  36  as a generally circular hole on the slidable connection edge of the block. When connected with another module, the circular hole is generally positioned in alignment with the circular hole of the passageway in the preceding module where through gas entrained powder may be communicated. The slidable connection can be intentionally mis-aligned to achieve a controllable flow restriction between modules which is introduced to balance the flow emitted at the nozzles. In FIG. 10 a second-tier splitter block  32  is shown with female track slots  96   a ,  96   b  which provide for attachment of subsequent modules. It should be recognized that succeeding modules may comprise splitters, or tubing connectors similar to the source connector  16  with either male or female track connections. In FIG. 11 the male track  94  of this second-tier splitter block is clearly shown.  
         [0048]    [0048]FIG. 12 through FIG. 14 show a third-tier splitter block  48 . In FIG. 12 the passageway  52  and longitudinal track  98  can be seen. In FIG. 13 and FIG. 14 the connector receptacles  100   a ,  100   b  are shown on the exit portions of the passageways beyond the straight sections  56   a ,  56   b , which follows the curving tapered sections from the entry port  52 . The connector receptacles  100   a ,  100   b  are configured for receiving a pair of tubing connection fittings (not shown).  
         [0049]    The preferred tapering and chambers within the channels of the splitter blocks are included to improve the flow of gas-entrained powder through the splitter system. The larger channel diameter within the curved section of the channel reduces flow path distortion, while the straight constricted sections preceding the chambered exit ports act to straighten the flow path while increasing the velocity of the gas and particulates. The particulates then become dispersed more evenly as they enter the area of lower aerial density within the chamber. The lower aerial density at the exits of the splitter block improve the ease with which the splitter blocks may be adjusted to achieve the desired flow balancing within the system.  
         [0050]    When using the two-way splitters of the described embodiment, a set of three tiers (layers) are employed to split one input line into eight output lines. The splitter block modules can also accommodate receiving source feed inputs from more than one hopper, such as might be used in the DLF process when building up alloys. When building up an alloy, it is often desirable to introduce materials from symmetrically opposite ports around the laser beam axis to reduce compositional build-up that may occur if the material was introduced from a single point. Materials may also be changed “on the fly”, wherein material is fed from a single hopper at any one time and the selection of hopper is changed during the build up process so as to form a sharp interface of dissimilar metals in the part being built up. For example, to create a sharp interface instead of a mixed alloy, a fraction of a solid being built up can be made with nickel while the remainder is built up from copper. Alternatively, a composite can be formed by layering alternating materials. It is preferable, therefore, that the splitter blocks according to the invention provide the ability to receive material input from a number of hoppers so that different materials may be fed into the head of the solids fabrication system. Use of inputs from multiple hoppers may be accommodated in numerous ways. The first-tier splitter block can be eliminated, wherein a pair of separate hoppers are connected by tubing connections to source feed connection blocks which are connected directly to the second-tier splitter blocks. Four hoppers can be accommodated by making similar tubular connections with the third-tier splitter blocks. Three hoppers can be accommodated by connection of one hopper source line to the second-tier splitter blocks and a pair of hopper source lines to the third-tier splitter blocks (if appropriate balancing is set for the incoming feed rates).  
         [0051]    In addition, to mix different materials from a series of hoppers, splitter blocks may be adapted to perform a reverse split, such that multiple streams of gas entrained powder from the hoppers are combined into a single stream of material before being divided up and traveling to the head of the solids fabrication system. FIG. 15 shows a powder splitter  110  which includes a reverse splitter  112  that is fed gas entrained powder from two separate powder hoppers. This reverse splitter  1   12  forms the interface to the first level splitter block  20 . The reverse splitter  112  has input chambers  114   a ,  114   b  with entry passageways  116   a ,  116   b  that narrow down to passageways  118   a ,  118   b  that are received within a combiner chamber  120  whose singular output flow is received by the splitter  20 . The reverse splitter  112  is attached coplanar with the first level splitter block at output connection  122 . Inputs  124 , 126  of the reverse splitter  112  is configured for attachment of the source feed connections  128 ,  130 . The remaining blocks  20 ,  32 ,  34 ,  48 ,  50  are conventional splitter blocks which divide the incoming gas entrained powder after it has been combined within reverse splitter block  112 . Additional reverse splitter blocks may be disposed between the source feed connections  128 , 130  and the first reverse splitter block  112  so that the flow from additional hoppers may be combined. FIG. 16 is a detailed view of reverse splitter block  112  showing the inputs  124 , 126  and the passageway profiles  114   a ,  114   b ,  116   a ,  116   b ,  118   a ,  118   b  leading into the combiner chamber  120  which terminates at the output connection  122 . FIG. 17 is the reverse splitter block  112  showing the side profile of the passageways from entry ports  114   a ,  116   a ,  118   a , through the output connection  122 .  
         [0052]    It will be appreciated that the invention can be implemented in a variety of ways without departing from the inventive principles. Although various channel shapes may be used within the splitter blocks, the particular profile shape described in the embodiment is preferred due to its flow characteristics.  
         [0053]    The embodiment describes the preferred use of two-way splitting within each splitter block, however the incoming flow within a splitter block can be divided into more than two channels. The number of outputs for a given number of tiers using two-way (binary) splitters is given by 2 n  where n is the number of tiers used. The symmetrical nature of the passageway division within a binary splitter assures a generally even distribution of the gas entrained powder between the two resultant passageways regardless of pressure, speed, and flow characteristics of the material. The binary splitters are preferred and are used as the basis of this embodiment. Alternatively the splitter blocks can be configured to split in more than two ways, such as trinary splitters. The number of tiers required for a given number of splits may then be reduced (number of splits being given then by 3 n ); however the distribution of material between three planar passageways would generally be dependent on the speed and flow within the system due to the unsymmetrical nature of a three-way (or four-way, five-way, six-way, etc.) planar split. On the other hand, non-planar splitting, wherein flow splitting is performed into a set of non-planar three-dimensionally-arranged passageways, increases manufacturing difficulty and complexity with regard to providing proper interconnection of the splitter block modules.  
         [0054]    Accordingly, it will be seen that the invention of a multiple feed powder splitter provides a readily manufactured solution which can provide uniform feeding of gas entrained powder to the nozzles of a directed light fabrication system. The invention provides a simple yet rugged flow control mechanism for balancing powder flow and is modularly configurable for a variety of input to output ratios and hopper systems. Although the description above contains many specificities, these should not be construed as limiting the scope of the invention but as merely providing illustrations of some of the presently preferred embodiments of this invention. Thus the scope of this invention should be determined by the appended claims and their legal equivalents.