Abstract:
A metal powder reconditioning apparatus and method recondition contaminated residual powder from an additive manufacturing device. The apparatus and method include a reducing chamber that receives contaminated residual powder resulting from an additive manufacturing process and remove oxygen from the contaminated residual powder to produce reconditioned powder. The reconditioned powder may be reused in the additive manufacturing process, or may be stored in a non-oxidizing atmosphere for later reuse.

Description:
BACKGROUND 
       [0001]    Additive manufacturing is a process by which three-dimensional objects may be manufactured from a powder or liquid base. Examples of additive manufacturing processes include stereolithography, selective laser sintering (SLS), direct metal laser sintering (DMLS), electron beam melting (EBM), and laser powder deposition (LPD). Each of these methods may be used to create objects which are not possible to make using subtractive manufacturing or machining. 
         [0002]    Stereolithography is the process of filling a chamber with photosensitive liquid in layers. As each layer is filled, a light source hardens thin layers or slices of the desired three-dimensional object. When the desired object has been built up in a layerwise fashion, the unused photosensitive liquid is removed. 
         [0003]    SLS is a similar process to stereolithography, but with a powder base rather than a photosensitive liquid. For example, SLS may use a powdered polymer, or a polymer/metal blend. Furthermore, SLS uses a laser, often a CO2 laser, to sinter or melt the powder. SLS is often used to create so-called “green bodies” for use in subsequent molding. 
         [0004]    DMLS, like SLS, uses a powder base. However, DMLS uses only metal powders. A single metal or a blend of metals may be used. DMLS also uses a laser as a sintering or melting source. Once a three-dimensional object has been created using DMLS, residual powder is removed. Often, there is enough oxidized, contaminated powder in the residual powder that it is unusable for future additive manufacturing. 
         [0005]    EBM is similar to DMLS, but rather than using a laser beam an electron beam is used for heating the target powder. As with DMLS, unsintered residual powder may be too oxidized for use in future additive manufacturing. 
         [0006]    LPD uses a laser head to deposit powder only in those regions where it is to be melted. Thus, where other additive manufacturing techniques may have layers or slices of any geometry, each layer or slice in an LPD design must be supported by a sintered layer beneath it. Thus, LPD leaves fewer design options, but results in less contaminated powder. 
         [0007]    Each of the foregoing additive manufacturing techniques may be used to create complex three-dimensional structures that cannot be made using subtractive manufacturing (e.g. machining). However, these techniques either suffer from their own design limitations (as with LPD) or from large quantities of waste material (as with DMLS, SLS, stereolithography, or EBM). 
       SUMMARY 
       [0008]    A metal powder reconditioning apparatus and a method for reconditioning residual metal powder from an additive manufacturing process are disclosed. The metal powder reconditioning apparatus includes an additive manufacturing device, a reducing chamber, and a conveyor for transporting contaminated powder from the additive manufacturing device to the reducing chamber. The method includes additively manufacturing an object, and gathering for reconditioning the powder contaminated by additively manufacturing that object. After the contaminated powder is gathered, it is reconditioned by removal of oxides. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a schematic block diagram of a method incorporating the present invention. 
           [0010]      FIG. 2  is a schematic view of a metal reconditioning apparatus of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0011]      FIG. 1  shows a flow chart of cycle  10  for reconditioning and reusing contaminated pulverant material from an additive manufacturing process. Cycle  10  includes producing parts by additive manufacturing (step  12 ), collecting contaminated residual powder from the additive manufacturing process (step  14 ), transferring the contaminated powder to a reducing chamber (step  16 ), optionally storing the powder in a non-oxidizing environment (step  18 ), and reusing the powder for producing parts by additive manufacturing (step  12 ). 
         [0012]    Producing parts by additive manufacturing (step  12 ) includes producing a component by any additive manufacturing process that uses pulverant material for the base material and creates contaminated waste powder. For example, Direct Metal Laser Sintering uses pulverant metal granules to create an additively manufactured metal part. Finished parts are removed from the additive manufacturing apparatus, and unused, contaminated powder remains. 
         [0013]    Collecting contaminated powder (step  14 ) includes gathering residual powder which was used in producing parts by additive manufacturing (step  12 ), but which were not part of the finished part. Often a large percentage of the powder used in additive manufacturing is not sintered to become a finished part. This unused, contaminated residual powder may be oxidized or even partially sintered during the process of producing parts by additive manufacturing (step  12 ). Often, the residual powder is contaminated to such an extent that it would be unusable in future additive manufacturing processes. 
         [0014]    After collecting contaminated powder (step  14 ), the contaminated powder is transferred to a reducing chamber (step  16 ). The contaminated residual powder may be conveyed in any of a number of ways, such as on a conveyor belt, a screw, in a batch, or carried by hand. The reducing chamber is any chamber which includes a reducing fluid, such as hydrogen gas or a reducing liquid. Optionally, the reducing chamber may be heated to accelerate reduction of the contaminated powder. The contaminated residual powder may be left in the reducing chamber for sufficient time to remove oxidation incurred during production of parts by additive manufacturing (step  12 ). In some embodiments, transferring contaminated residual powder to a reducing chamber includes using a screw or other mechanism to generate turbulence and mixing of the contaminated powder. Generating turbulence and mixing of the contaminated residual powder exposes all of the contaminated powder to the reducing fluid. After transferring contaminated powder to a reducing chamber (step  16 ), the contaminated powder becomes reconditioned powder, and may be used in subsequent production of parts (step  12 ). 
         [0015]    After the contaminated powder has gone through the reducing chamber, cycle  10  optionally includes storing the reconditioned powder in a non-oxidizing environment (step  18 ). The non-oxidizing environment could be, for example, a hermetically sealed container purged with an inert gas. Alternatively, the non-oxidizing environment could be a hermetically sealed container purged with a reducing gas, or one under vacuum. Storing powder in a non-oxidizing environment  18  allows for use of the reconditioned powder at a later time. Storing powder in a non-oxidizing environment  18  is not necessary if cycle  10  includes producing parts  10  immediately upon removal of the reconditioned powder from the reducing chamber. In that scenario, the reconditioned powder may be used immediately in step  12  for producing parts by additive manufacturing. 
         [0016]    Cycle  10  reduces waste in additive manufacturing. Often, materials used for additive manufacturing are difficult to create and expensive to purchase. Discarding all or a large portion of contaminated residual powder after producing parts, or even recycling contaminated metal powder into non-powder metals, results in waste and expense. Cycle  10  allows for very high rates of recovery of contaminated residual powder for use in subsequent additive manufacturing. 
         [0017]      FIG. 2  shows a simplified schematic of apparatus  20  for reconditioning a contaminated residual powder from an additive manufacturing process. Apparatus  20  includes hopper  22  for collecting contaminated residual powder  24 , conveyor  26 , reducing chamber  28 , and inert storage chamber  33 . Hopper  22  is any container suitable for holding powder, and has an outlet (not shown) for selectively dispensing powders therein. Contaminated residual powder  24  is powder generated during additive manufacturing, such as metallic powder, at least some of which has been oxidized during additive manufacturing. Conveyor  26  is any system for conveyance. As shown in  FIG. 2 , conveyor  26  is a conveyor belt. However, in alternative embodiments, conveyor  26  may be a screw or other mechanical means of conveyance, or conveyor  26  may be eliminated and contaminated residual powder  24  may be deposited directly into reducing chamber  28 . Hopper  22  may deliver contaminated residual powder  24  to conveyor  26 , and conveyor  26  may transfer contaminated residual powder  24  to reducing chamber  28 . 
         [0018]    Reducing chamber  28  accepts contaminated residual powder  24  and also includes reducing fluid inlet  30  and reducing chamber screw  32 . While in reducing chamber  28 , contaminated residual powder  24  is subjected to a reducing atmosphere. The fluid that makes up the reducing atmosphere is provided by reducing fluid inlet  30 . In order to accelerate reduction of contaminated residual powder  24 , reducing chamber  28  includes reducing chamber screw  32 . Reducing chamber screw  32  agitates and/or mixes contaminated residual powder  24  as it passes through reducing chamber  28  in order to promote contact between the reducing atmosphere of reducing chamber  28  and all of contaminated residual powder  24 . In alternative embodiments, reducing chamber screw  32  may not be necessary, or may be any other device which mixes contaminated residual powder  24  in such a way as to promote contact between all of contaminated residual powder  24  and the reducing atmosphere. 
         [0019]    Upon exiting reducing chamber  28 , contaminated residual powder  24  has been sufficiently reduced that it is now reconditioned powder  40 . Further steps may be taken to ensure that reconditioned powder  40  is suitable for use in subsequent additive manufacturing processes. For example, reconditioned powder  40  may be sieved in order to ensure that reconditioned powder  40  is made of granules of an appropriate size. 
         [0020]    Reconditioned powder  40  is transferred to inert storage container  33 . Inert storage container  33  in the embodiment shown in  FIG. 2  includes hermetically sealed housing  38 , inert gas inlet  34 , and inert gas outlet  36 . Hermetically sealed housing  38  prevents contamination of reconditioned powder  40  by oxidants. Inert gas inlet  34  and inert gas outlet  36  admit and remove gas from hermetically sealed housing  38  in order to ensure that the atmosphere surrounding reconditioned powder  40  is either inert or reducing. In alternative embodiments, inert storage container  33  may be under vacuum. When reconditioned powder  40  is used in subsequent production of additively manufactured parts ( FIG. 1 , step  12 ), inert storage container  33  may be transferred to the additive manufacturing apparatus and unsealed. In yet other embodiments, inert storage container  33  may be eliminated and reconditioned powder  40  may be delivered directly to an additive manufacturing device (not shown). 
         [0021]    While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.