Abstract:
A powder delivery system for use in an additive manufacturing device includes a powder control valve configured to selectively divert at least a portion of an input fluid flow to a return line while a remainder of the input flow is delivered to a delivery nozzle. In some embodiments, the powder delivery valve may be modulated to alter the percentage of input flow diverted to the return line. Alternatively, the powder delivery valve may be either fully open or closed. In each embodiment, the powder delivery valve permits rapid changes in the amount of powder delivered to the nozzle.

Description:
BACKGROUND 
       [0001]    Technical Field 
         [0002]    The present disclosure generally relates to additive manufacturing, and more particularly, to powder delivery systems and methods used in additive manufacturing apparatus. 
         [0003]    Description of the Related Art 
         [0004]    Traditionally, materials are processed into desired shapes and assemblies through a combination of rough fabrication techniques (e.g., casting, rolling, forging, extrusion, and stamping) and finish fabrication techniques (e.g., machining, welding, soldering, polishing). Producing a complex assembly in final, usable form (“net shape”), which often may require not only forming the part with the desired materials in the proper shapes but also providing the part with the desired combination of metallurgical properties (e.g., various heat treatments, work hardening, complex microstructure), typically requires considerable investment in time, tools, and effort. 
         [0005]    One or more of the rough and finish processes may be performed using manufacturing centers, such as Computer Numerically Controlled (CNC) machine tools. CNC machine tools use precisely programmed commands to automate the manufacturing process. The commands may be generated using computer-aided design (CAD) and/or computer-aided manufacturing (CAM) programs. Examples of CNC machines include, but are not limited to, mills, lathes, mill-turns, plasma cutters, electric discharge machines (EDM), and water jet cutters. CNC machining centers have been developed which provide a single machine having multiple tool types that is capable of performing multiple different machining processes. Such machining centers may generally include one or more tool retainers, such as spindle retainers and turret retainers holding one or more tools, and a workpiece retainer, such as a pair of chucks. The workpiece retainer may be stationary or move (in translation and/or rotation) while a tool is brought into contact with the workpiece, thereby performing a subtractive manufacturing process during which material is removed from the workpiece. 
         [0006]    Because of cost, expense, complexity, and other factors, additive manufacturing techniques have been developed that would replace all or part of the conventional subtractive manufacturing steps. In contrast to subtractive manufacturing processes, which focus on precise removal of material from a workpiece, additive manufacturing processes add material, typically in a computer-controlled environment, by creating successive layers of material to form a three-dimensional object. Additive manufacturing techniques may improve efficiency and reduce waste while expanding manufacturing capabilities, such as by permitting seamless construction of complex configurations which, when using conventional manufacturing techniques, would have to be assembled from a plurality of component parts. For the purposes of this specification and the appended claims, the term ‘plurality’ consistently is taken to mean “two or more.” The opportunity for additive techniques to replace subtractive processes depends on several factors, such as the range of materials available for use in the additive processes, the size and surface finish that can be achieved using additive techniques, and the rate at which material can be added. Additive processes may advantageously be capable of fabricating complex precision net-shape components ready for use. In some cases, however, the additive process may generate “near-net shape” products that require some degree of finishing. 
         [0007]    Additive manufacturing techniques include, but are not limited to, powder bed fusion processes such as laser sintering, laser melting, and electron beam melting; direct energy deposition processes such as laser engineered net shaping direct metal/material deposition, and laser cladding; material extrusion such as fused deposition modeling; material jetting including continuous or drop-on-demand; binder jetting; vat polymerization; and sheet lamination including ultrasonic additive manufacturing. In some direct energy deposition processes, powder is injected from one or more nozzles into a focused beam of a laser to melt a small pool of the substrate material. Powder contacting the pool will melt to generate a deposit on the substrate. 
         [0008]    Material deposition systems used in additive manufacturing devices typically use open-loop control to provide a constant powder flow rate to the nozzle. This approach can introduce inconsistencies in deposition track morphology when the steady state is disturbed, such as acceleration or deceleration of the velocity of relative movement between the deposition head and the substrate. More recently, material deposition systems have been proposed that use a feedback system that may adjust the rate at which powder is delivered. Conventional powder delivery systems, however, may be slow to adjust to the change in powder demand, thereby slowing the additive manufacturing process and/or introducing inconsistencies in the deposited additive material. 
       SUMMARY OF THE DISCLOSURE 
       [0009]    According to certain aspects of this disclosure, a powder delivery system is provided for an additive manufacturing device having a carrier gas source, a powder feeder, and a nozzle. The system includes a powder delivery line having an input section fluidly communicating with the carrier gas source and the powder feeder and an output section fluidly communicating with the nozzle. A powder control valve is disposed in the powder delivery line and has an inlet fluidly communicating with the input section of the powder delivery line, a first outlet fluidly communicating with the output section of the powder delivery line, and a second outlet, the powder control valve having a recirculation state configured to separate an input fluid flow entering the inlet into an output fluid flow supplied to the first outlet and a return fluid flow supplied to the second outlet. A return line fluidly communicates with the return port of the powder control valve, and a collector fluidly communicates with the return line. 
         [0010]    According to additional aspects of this disclosure, a method of delivering powder to a nozzle of an additive manufacturing device is provided that includes supplying an input fluid flow of carrier gas through an input section of a powder delivery line, entraining powder into the input fluid flow, and separating the input fluid flow into an output fluid flow through an output section of the powder delivery line and a return fluid flow through a return line. The method further includes communicating the output fluid flow to the nozzle, and communicating the return fluid flow to a collector. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    For a more complete understanding of the disclosed methods and apparatus, reference should be made to the embodiment illustrated in greater detail on the accompanying drawings, wherein: 
           [0012]      FIG. 1  is a schematic diagram of a material deposition apparatus including a powder transport system in accordance with one embodiment of the present disclosure. 
           [0013]      FIG. 2  is an enlarged schematic diagram of the powder transport system of  FIG. 1 . 
           [0014]      FIG. 3  is a schematic diagram of a material deposition apparatus including a powder transport system in accordance with another embodiment of the present disclosure. 
           [0015]      FIG. 4  a schematic diagram of a material deposition apparatus including a powder transport system in accordance with yet another embodiment of the present disclosure. 
           [0016]      FIG. 5  is a perspective view of one embodiment of a powder control valve for use in the powder transport systems disclosed herein. 
           [0017]      FIG. 6  is a perspective view of an alternative embodiment of a powder control valve for use in the powder transport systems disclosed herein. 
           [0018]      FIG. 7  is a perspective view of yet another alternative embodiment of a powder control valve for use in the powder transport systems disclosed herein. 
       
    
    
       [0019]    It should be understood that the drawings are not necessarily to scale and that the disclosed embodiments are sometimes illustrated diagrammatically and in partial views. In certain instances, details which are not necessary for an understanding of the disclosed methods and apparatus or which render other details difficult to perceive may have been omitted. It should be understood, of course, that this disclosure is not limited to the particular embodiments illustrated herein. 
       DETAILED DESCRIPTION 
       [0020]    Any suitable additive manufacturing apparatus may be employed in conjunction with the methods disclosed herein. In some embodiments, the methods are performed using a computer numerically controlled machine configured to perform additive manufacturing processes; however other types of systems, such as robotic systems, may be used. The machine may be an NT-series machine, versions of which are available from DMG/Mori Seiki USA, the assignee of the present application. Alternatively, DMG/Mori Seiki&#39;s DMU-65 (a five-axis, vertical machine tool) machine tool, or other machine tools having different orientations or numbers of axes, may be used in conjunction with the apparatus and methods disclosed herein. 
         [0021]      FIG. 1  schematically illustrates a powder delivery system  10  of an additive manufacturing system having a source of carrier gas  12 , a powder feeder  14 , and a nozzle  16 . The nozzle  16  may be disposed in a machining chamber  15  of the additive manufacturing system. The nozzle  16  may be directed at a substrate  17  upon which layers of additive material are to be built to create a build object. Accordingly, other components of the additive manufacturing system, such as an energy beam source and/or guide and focusing optics (not shown), may also be provided in the machining chamber  15 . 
         [0022]    A powder delivery line  18  has an input section  18 A fluidly communicating with the carrier gas source  12  and the powder feeder  14 , and an output section  18 B fluidly communicating with the nozzle  16 . The carrier gas source  12  generates an input fluid flow of carrier gas through the input section  18 A and the powder feeder  14  introduces powder into the input fluid flow so that powder particles are entrained in and carried by the input fluid flow. The carrier gas may be argon, nitrogen, helium, carbon dioxide, or other gases, including blends thereof. 
         [0023]    The system  10  may further include a flow separator which divides the input fluid flow into an output fluid flow directed to the nozzle  16  and a return fluid flow. In the embodiment of  FIG. 1 , the flow separator is shown as a powder control valve  20 . More specifically, and as best shown in  FIG. 2 , the powder control valve  20  is disposed in the powder delivery line  18  and has an input port  22  fluidly communicating with the input section  18 A, an output port  24  fluidly communicating with the output section  18 B, and a return port  26 . 
         [0024]    The powder control valve  20  may be set to a recirculation state, in which the powder control valve  20  is configured to separate the input fluid flow entering the input port  22  into a desired output fluid flow supplied to the output port  24  and a desired return fluid flow supplied to the return port  26 . In some embodiments, the desired output and return fluid flows are fixed. For example, the desired output fluid flow may be fixed at two-thirds of the input fluid flow and the desired return flow may be fixed at one-third of the input fluid flow. Other fixed rates for the desired output and return fluid flows may be used. In embodiments providing fixed desired flows, the powder control valve  20  may have a single active position. Alternatively, the powder control valve  20  may be a binary valve having two active positions. In a first active position, the binary valve may deliver the desired fixed flows, while in the second active position, the binary valve may provide a default flow, such as directing 100% of the input fluid flow to the return port  26 . Alternatively, the binary valve may have a first active position which directs all of the input flow to the output port  24  and a second active position which directs all of the input flow to the return port  26 . 
         [0025]    In other embodiments, the desired output and return fluid flows are variable. For example, the desired output and return fluid flows may be expressed as percentages of the input fluid flow, and the particular percentages for the desired output fluid flow and the desired return fluid flow may change over time. In embodiments providing variable desired fluid flows, the powder control valve  20  may be an analog or metering valve that may be modulated to provide variable flow rates for the output fluid flow and the return fluid flow. More specifically, the powder control valve  20  may be modulated to change the percentages of input fluid flow that are directed to the output port  24  and the return port  26 . 
         [0026]    Exemplary valves that may be used to provide either fixed desired fluid flows or variable desired fluid flows include three-way valves, servo-valves, proportional valves, distribution valves, electronically controlled valves, or other type of fluid flow regulating devices. Still further, the powder control valve  20  may include multiple valves to achieve the desired fixed or variable fluid flows. 
         [0027]    Powder directed through the return port  26  of the powder control valve  20  may be routed through a return line  30  for collection and reuse. As shown in  FIGS. 1 and 2 , the return line  30  fluidly communicates with the return port  26  of the powder control valve  20 . The return line  30  directs the return fluid flow to a collector, which in the embodiment of  FIG. 1  is the powder feeder  14 . In other embodiments, the collector may be a dedicated powder return tank, as discussed below. 
         [0028]    In operation, the input fluid flow travels through the powder control valve  20 , at which point it may be separated into the output fluid flow and the return fluid flow. The return fluid flow may be set such that it maintains a minimum return flow rate that is sufficient to maintain suspension of the powder particles in the carrier gas, so that the powder in the return fluid flow may be collected for reuse. Furthermore, the input fluid flow may be selected such that it is sufficient to carry a mass flow rate of powder that is greater than that currently needed at the nozzle, with the excess being directed through the return line  30 . As a result, should a disturbance in the additive process or change in deposition parameters increase or decrease the amount of powder needed, the powder control valve  20  may be operated to quickly meet the increased or decreased powder demand. 
         [0029]    Exemplary embodiments of powder control valves  20  are illustrated in  FIGS. 5-7 . For example,  FIG. 5  shows the powder control valve  20  as a slide valve assembly  50  having an input tube  52  that is slidable relative to an output tube  54  and a return tube  56 . The output tube  54  may fluidly communicate with the output section  18 B of the powder delivery line  18 , while the return tube  56  may fluidly communicate with the return line  30 . A slide actuator  58  is coupled to the input tube  52  to position the input tube  52  relative to the output and return tubes  54 ,  56 . The slide actuator  58  may position the input tube  52  so that all of the input fluid flow enters the output tube  54 , all of the input fluid flow enters the return tube  56 , or portions of the input fluid flow enter both the input tube  52  and the return tube  56 . 
         [0030]      FIG. 6  illustrates the powder control valve  20  as a peristaltic pump assembly  60 . The input section  18 A of the powder delivery line  18  is connected to an inlet end of a T-branch  62 , while the output section  18 B of the delivery line  18  and the return line  30  are connected to outlet ends of the T-branch  62 . An output peristaltic pump  64  engages a flexible portion of the output section  18 B and a return peristaltic pump  66  engages a flexible portion of the return line  30 . Rotors having shoes (not shown) are provided in the peristaltic pumps  64 ,  66  that are configured to pinch and roll the flexible portions as the shoes are rotated, thereby to advance fluid flow through the output section  18 B and return line  30 , respectively. The pumps  64 ,  66  may be independently controlled to operate sequentially or simultaneously to produce the desired fluid flow through the output section  18 B and return line  30 . By using peristaltic pumps, the powder and carrier gas are completely contained within the delivery line  18  and return line  30 , thereby avoiding any potential cross-contamination between the powder and the peristaltic pump assembly  60 . 
         [0031]    Optionally, the powder delivery system  10  may provide carrier gas makeup to the nozzle  16 , thereby to provide a constant delivery velocity from the nozzle. As shown in  FIG. 1 , a carrier gas makeup line  40  may fluidly couple a source of carrier gas, such as the carrier gas source  12 , to the nozzle  16 . A makeup valve  42  is disposed in the makeup line  40  for controlling flow of makeup carrier gas to the nozzle  16 . The makeup valve  42  may be controlled to provide makeup carrier gas to the nozzle  16  based on the state of the powder control valve  20 . For example, if the powder control valve  20  is configured to deliver 20% of the input fluid flow to the output section  18 B of the powder delivery line  18  (and therefore 80% of the input fluid flow is directed to the return line  30 ), the makeup valve  42  may be actuated to provide a flow of pure carrier gas equal to 80% of the input fluid flow so that the nozzle  16  effectively receives a carrier gas flow that is equal to 100% of the input fluid flow. As a result, total gas flow through the nozzle, and thus nozzle velocity, remain constant regardless of the state of the powder control valve  20 . 
         [0032]      FIG. 7  illustrates an alternative powder control valve  20  in the form of an inverted peristaltic pump assembly  70 . In this embodiment, the input section  18 A of the powder delivery line  18  is connected to an inlet end of a Y-branch  72 , while the output section  18 B of the delivery line  18  and the return line  30  are connected to outlet ends of the Y-branch  72 . The Y-branch  72  is oriented so that the inlet end is positioned below the outlet ends, as shown. An output peristaltic pump  74  engages a flexible portion of the output section  18 B and a return peristaltic pump  76  engages a flexible portion of the return line  30 . The peristaltic pumps  74 ,  76  operate similar to those noted above with respect to the embodiment of  FIG. 6 , with rotors rotating shoes (not shown) that pinch and roll the flexible portions of the tubes to advance fluid flow through the output section  18 B and return line  30 , respectively. 
         [0033]      FIG. 3  illustrates an alternative embodiment of a powder delivery system  100  capable of quickly switching the rate of output fluid flow to a nozzle  116  across a wider range of flow rates. The system  100  includes first, second, and third delivery lines  118 A,  118 B,  118 C fluidly communicating with a carrier gas source  112  and a powder feeder  114 . While a single carrier gas source  112  and powder feeder  114  are shown in  FIG. 3 , each deliver line  118 A,  118 B,  118 C may have a dedicated gas source and powder feeder, which may permit varying blends of alloys to be deposited. First, second, and third powder control valves  120 A,  120 B,  120 C may be disposed in the first, second, and third delivery lines  118 A,  118 B,  118 C, respectively. Output sections of the delivery lines  118 A,  118 B,  118 C, respectively located downstream of the powder control valves  120 A,  120 B,  120 C, fluidly communicate with a mixing chamber  140 . The mixing chamber  140 , in turn, fluidly communicates with the nozzle  116 . The powder control valves  120 A,  120 B,  120 C also fluidly communicate with a return line  130  that leads to a powder return tank  135 . In some embodiments, the powder return tank  135  may be maintained at atmospheric pressure or less to ensure proper operation of the system. The nozzle  116  is disposed in a machining chamber  115  of the additive manufacturing system and directed at a substrate  117  upon which layers of additive material are to be built to create a build object. Accordingly, other components of the additive manufacturing system, such as a power source and focusing optics (not shown), may also be provided in the machining chamber  115 . 
         [0034]    The first, second, and third delivery lines  118 A,  118 B,  118 C may be sized to provide different input flows. For example, the first delivery line  118 A may be sized to provide a first flow rate A to the first powder control valve  120 A. The second delivery line  118 B may be sized to provide a second flow rate B to the second powder control valve  120 B that is different than the first flow rate A. For example, the second flow rate “B” may be twice the first flow rate A. Still further, the third delivery line  118 C may be sized to provide a third flow rate C that is different than the first and second flow rates A and B. For example, the third flow rate C may be four times the first flow rate A. By providing delivery lines having different flow rates, the powder delivery system of  FIG. 3  may quickly switch the amount of powder delivered to the nozzle  116 . In some embodiments, the powder control valves  120 A,  120 B,  120 C are binary and therefore movable between an off position, in which all input flow is directed to the return line  130 , and an active position, in which portions of the input flow are directed to both the return line  130  and the mixing chamber  140 . When using binary valves, therefore, the system is capable of providing an instantaneous change in the amount of powder delivered to the nozzle  116 . In these binary valve embodiments, it will be appreciated that up to seven different, precise flow rates may be provided by opening various individual or combinations of powder control valves  120 A,  120 B,  120 C, and that switching flow rates is virtually instantaneous. Alternatively, the powder control valves  120 A,  12 B,  120 C may be modulating valves that provide more gradual or gradient changes in output flow rate to the return line  130  and mixing chamber  140 . 
         [0035]      FIG. 4  illustrates a further embodiment of a powder delivery system  200  that permits the use of different powder materials and provides more direct recovery of powder routed through the return circuit. The system  200  includes first and second delivery lines  218 A,  218 B fluidly communicating with the same or different carrier gas sources  212 . First and second powder feeders  214 A,  214 B respectively communicate with the first and second delivery lines  218 A,  218 B. 
         [0036]    A first powder control valve  220 A is disposed in the first delivery line  218 A and fluidly communicates with a first nozzle  216 A through an output section of the first delivery line  218 A. The first powder control valve  220 A also communicates with a first powder return tank  235 A through a first powder return line  230 A. 
         [0037]    A second powder control valve  220 B is disposed in the second delivery line  218 B and may fluidly communicate with the first nozzle  216 A through an output section of the second delivery line  218 A. Alternatively, as shown in phantom line, the second powder control valve  220 B may fluidly communicate with a second nozzle  216 B separate from the first nozzle  216 A. If both the first and second powder control valves  220 A,  220 B communicate with the first nozzle  216 A, a mixing chamber  240  may be provided to combine the output fluid flows prior to reaching the nozzle  216 A. The second powder control valve  220 B also communicates with a second powder return tank  235 B through a second powder return line  230 B. 
         [0038]    The first and second nozzles  216 A,  216 B may be disposed in a machining chamber  215  of the additive manufacturing system and directed at a substrate  217  upon which layers of additive material are to be built to create a build object. Accordingly, other components of the additive manufacturing system, such as a power source and focusing optics (not shown), may also be provided in the machining chamber  215 . 
         [0039]    The first and second powder return tanks  235 A,  235 B may be configured to separate carrier gas from the return fluid flow, thereby depressurizing the tanks  235 A,  235 B and permitting return powder to accumulate in the tanks  235 A,  235 B. For example each tank may include a vent or exhaust port in fluid communication with the surrounding environment, as illustrated by exhaust port  236 B, thereby venting the return carrier gas to atmosphere. Alternatively, the return carrier gas may be reused in the additive manufacturing system, such as by fluidly coupling the exhaust port to the machining chamber  215 , as illustrated by exhaust port  236 A. In either embodiment, the exhaust port depressurizes the powder return tanks  235 A,  235 B and separates return carrier gas from the return fluid flow to permit powder to accumulate in the tanks. 
         [0040]    The first and second powder return tanks  235 A,  235 B may be further configured to facilitate reuse of the powders they collect by permitting transfer of powder from the tanks  235 A,  235 B to the feeders  214 A,  214 B. As shown in  FIG. 4 , the first and second powder return tanks  235 A,  235 B fluidly communicate with the first and second powder feeders  214 A,  214 B, respectively, via connection lines  237 A,  237 B. During operation of the powder delivery system, the first and second powder feeders  214 A,  214 B are pressurized by the carrier gas source(s)  212  while the powder return tanks  235 A,  235 B are depressurized, which may prevent transfer of powder from the tanks to the feeders. Return valves  238 A,  238 B may be disposed in the connection lines  237 A,  237 B to permit powder to flow from the tanks to the feeders. More specifically, the return valves  238 A,  238 B may open when the powder feeders  214 A,  214 B are unpressurized or at a reduced pressure, thereby permitting powder to flow from the return tanks  235 A,  235 B. The return valves  238 A,  238 B may be operated by automatic mechanical actuation (i.e., as check valves or gravity driven valves that open when the mass of powder overcomes the pressure force in the feeder), manual mechanical actuation (i.e., opened directly by a user), manual electrical actuation (i.e., by triggering an actuator coupled to the valve), automatic electrical actuation (i.e., by a sensor triggering an actuator coupled to the valve), or other operation scheme. 
         [0041]    When two different powders are respectively provided in the first and second powder feeders  214 A,  214 B, the alloy blend may be changed on the fly. That is, the ratio of first powder to second powder provided to the first nozzle  216 A may be adjusted by modulating the first and second powder control valves  220 A,  220 B. 
         [0042]    Alternatively, if the same powder is provided in both the first and second powder feeders  214 A,  214 B, the powder delivery system  200  may be operated continuously by switching between the powder feeders  214 A,  214 B. That is, while the first powder feeder  214 A is supplying powder to the nozzle, the second powder feeder  214 B may be taken off line and replenished, and vice versa. By toggling between the two powder feeders  214 A,  214 B, powder may be continuously supplied to the nozzle. 
       INDUSTRIAL APPLICABILITY 
       [0043]    The powder delivery systems and methods described herein may be used to provide a flow of powder to the nozzle of an additive manufacturing device, such as a 3D printer. 
         [0044]    All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference. The description of certain embodiments as “preferred” embodiments, and other recitation of embodiments, features, or ranges as being preferred, is not deemed to be limiting, and the claims are deemed to encompass embodiments that may presently be considered to be less preferred. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended to illuminate the disclosed subject matter and does not pose a limitation on the scope of the claims. Any statement herein as to the nature or benefits of the exemplary embodiments is not intended to be limiting, and the appended claims should not be deemed to be limited by such statements. More generally, no language in the specification should be construed as indicating any non-claimed element as being essential to the practice of the claimed subject matter. The scope of the claims includes all modifications and equivalents of the subject matter recited therein as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the claims unless otherwise indicated herein or otherwise clearly contradicted by context. Additionally, aspects of the different embodiments can be combined with or substituted for one another. The description herein of any reference or patent, even if identified as “prior,” is not intended to constitute a concession that such reference or patent is available as prior art against the present disclosure.