Abstract:
An apparatus ( 20, 21 ) and method ( 80 ) operable to: feed ( 82 ) a granulated feedstock ( 26 ) into a chamber ( 22 ); apply ( 84 ) a melting or sintering energy ( 28 ) in programmable scans ( 30 ) producing a material deposit ( 32 ) overlaid with slag ( 34 ) in the chamber ( 22 ); position ( 86 ) a slag removal device ( 40, 52 ) such that its cutting surface ( 35 ) is coincident with a top surface ( 33 ) of the material deposit; cut or break the slag free ( 88 ) from the material deposit with the slag removal device; separate ( 92 ) the removed slag from a reusable portion of the granulated feedstock in a separator ( 42 ); and feed ( 94 ) the reusable portion of the granulated feedstock to the top surface of the material deposit for repeating ( 96 ) the above operations.

Description:
FIELD OF THE INVENTION 
     The invention relates generally to welding and materials joining technologies, and more particularly to machines and processes for slag removal after selective laser melting or sintering of granulated feedstocks. 
     BACKGROUND OF THE INVENTION 
     Melting and sintering processes often produce a slag overlay. Slag removal can be challenging, especially when the metal or other material being formed must be successively layered to form a repair, cladding, or layered fabrication. Manually removing slag between each layer is slow and unproductive. 
     Submerged arc welding (SAW), electroslag welding (ESW), selective laser melting (SLM) and selective layer sintering (SLS) have been used to produce welds, cladding, and parts by additive manufacturing. In submerged arc welding a granulated flux buries an arc between an electrode wire or strip and a substrate to protect the molten material from reaction with the atmosphere. The process leaves slag on the surface of the metal deposit that must be removed before subsequent welding passes are made over or beside the existing deposit. The slag is manually removed, and unused granulated flux is vacuumed and combined with new flux for further processing. This process is also used for submerged arc cladding. Electroslag welding or cladding avoids an arc by providing molten flux at the point of processing as a current conductor. Other processing technologies include laser cladding and selective laser melting (SLM) or selective laser sintering (SLS) of feedstock powder. 
     Vacuuming can be employed in submerged arc welding to recover both slag and unused flux if the slag is readily dislodged from the deposit surface. However, when physical engagement is required to dislodge the slag, vacuuming is not enough. For powder bed processing (e.g. SLM, SLS), vacuuming tends to remove feedstock powder together with, or in preference to, slag because the powder is lighter and is not adhered to the substrate. Not only does this fail in slag removal, but it removes unused feedstock needed for additional melting/sintering passes on or beside the previous deposit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is explained in the following description in view of the drawings that show: 
         FIG. 1  is a schematic sectional view of a chamber containing a substrate overlaid with a granular feedstock for processing according to an embodiment of the invention. 
         FIG. 2  is a view of the machine of  FIG. 1  after melting or sintering of the feedstock has formed a material deposit overlaid with slag on the substrate. 
         FIG. 3  is a view of the machine of  FIG. 1  repositioning the slag layer above a rim of the chamber for slag removal. 
         FIG. 4  is a view of a slag removal device disposed on the chamber of  FIG. 1  and raking slag from the material deposit and onto a separator that separates slag from reusable granular feedstock. 
         FIG. 5  is a view of the machine of  FIG. 4  recycling the recovered feedstock to a top surface of the material deposit for further layering or cladding. 
         FIG. 6  is a view of an embodiment of the invention with a vertically adjustable rotary slag removal device. 
         FIG. 7  shows an embodiment that rotates a component being repaired, welded, layered, or fabricated. 
         FIG. 8  illustrates steps in a method operable by the disclosed machine. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a machine  20  with a melting chamber  22  surrounding a component or substrate  24  for repair, cladding, welding, or fabrication. The chamber may have an upper rim  38 , which may be planar or curved, and may guide a slag removal device as later described. A movable positioner  25  may support the substrate  24  and move it vertically relative to the chamber  22 . A granular feedstock  26  is disposed on the substrate  24  for melting or sintering by an energy source  28  such as a laser. The energy source  28  may move across the feedstock  26  in a programmable path  30  to melt or sinter the granular material  26 , which may include alloy constituents and flux. For example, a laser beam may be directed to scan a programmable path  30  by means of movable mirrors or prisms to “paint” a predetermined area of the feedstock  26  with laser energy for heating. The feedstock  26  may be any type or combination of materials that can be melted or sintered to form a solid layer or body with a layer of slag thereon. 
       FIG. 2  shows a deposit  32  formed on the substrate  24  by melting or sintering of the feedstock  26 . A slag layer  34  is formed on an upper surface  33  of the deposit  32 . 
       FIG. 3  shows the substrate raised  36  by the positioner  25  so that, for example, the top surface of the deposit  32  is flush with the rim  38  of the chamber  22 . 
       FIG. 4  shows a slag removal device  40 , exemplified as a scraper, mounted on a drive mechanism  39 , exemplified by a screw that moves the slag removal device across the top surface of the deposit  32 . This removes the slag  34  above a cutting surface  35  of the slag removal device  40 . Herein, “cutting surface” means a surface geometry, such as a plane or a surface of rotation, beyond which the slag removal device removes material during relative motion between the deposit  32  and the slag removal device  40 . The top surface  33  of the deposit  32  has been positioned at the cutting surface  35 , so that the slag  34  is removed. Also removed is at least a portion of reusable feedstock  27  remaining above the level of the upper surface  33  of the deposit. A separation device  42  may be provided that separates the slag from the reusable feedstock based on particle size or other criteria. This separation may be implemented for example by a perforated conveyor belt, a shaker screen, or a vibratory sieve. A conveying device  44  may transfer the recovered feedstock  27  to a collector  46 , or the collector may be directly filled by the separation device  42 . 
     The slag removal device  40  may be embodied especially by a device such as a scraper or planer, which may optionally be embodied as a rotating cylinder with tines or blades, for example a rotary planer head. A preferred type of slag removal device breaks or cuts the slag free from the deposit, and breaks the slag  34  into pieces larger than a maximum size of granules of the reusable feedstock  27  for ease of separation therefrom. The slag removal device  40  may be guided by the upper rim  38  of the chamber after positioning the upper surface of the deposit flush with the rim  38  or flush with the cutting surface  35 , which may be coplanar with the rim  38  as shown. 
       FIG. 5  shows a feedstock feeder  48  distributing recovered feedstock  27  along with new feedstock  26  on the deposit  32  to create a further deposit thereon by further scans  30  of the energy source  28  of  FIG. 1 . The positioner  25  may lower  50  the substrate  24  so that the chamber rim  38  retains the further layer of feedstock  26 ,  27 . 
       FIG. 6  shows an embodiment  21  with a rotary brush or blade  52  moving on a guide track  54  from a starting position  56  to an ending position  58  to remove slag  34  and reusable feedstock  27  at and above the level of the upper surface of the deposit. The guide track  54  may be vertically adjustable  55  to position the cutting surface  35  at the upper surface  33  of the deposit  32 . In this embodiment, the cutting surface  35  is approximately or exactly tangent to the surface of rotation of the rotary brush or blade. The cylindrical rotary brush or blade  52  may be embodied with wire bristles, tines, or as a planer head. 
     The slag removal device  40 ,  52  may be mounted on or moved by a drive mechanism, especially a position translating mechanism such as a motor-driven chain or screw drive or a motor-driven or hydraulic piston. The drive mechanism may include or operate against a guiding device, such as a track  54  or the chamber rim  38  that guides the slag removal device to move along a predetermined cutting surface  35  relative to the chamber  22 . 
     A machine  20 ,  21  configured with apparatus herein, includes for example a chamber  22 , a feedstock feeder  48 , an energy source  28  with programmable scanning  30 , a slag removal device  40  or  52 , a drive mechanism  39 , and a separation device  42 . It may be controlled automatically by an electronic process controller to perform slag removal and separation as described. Such machine is operable to automatically repair or clad a substrate with one or more layers of material deposits, and to automatically remove slag after each deposit. Controllers, motors, actuators, and interconnections for machine automation are not shown in the drawings since such elements are known in the field of process automation and controls. 
       FIG. 7  shows an embodiment  60  with a feedstock chamber  62  containing a feedstock  64 , which may granular and/or in a liquefied or fluidized form. A component  66  for repair, cladding, or welding, or fabrication, or more generally, a form for fabrication, is positioned to receive a flow of the feedstock  64  on a surface  67  thereof. The component  66  is rotated by a drive mechanism  71  relative to an energy source  69  such as a laser. The energy source  69  may be stationary, or it may move across the component  66  in a programmable path to melt or sinter the granular material  64 , which may include alloy constituents and flux. For example, a laser beam may be directed to scan a programmable path back and forth along a rotation axis  70  of the component  66  as the component rotates. The energy source  69  forms a localized melt pool  68  on the component surface  67  from which a deposit  32  is drawn on the surface  67  as it rotates under the melt pool. As the deposit  32  hardens with a slag  34  overlay, it rotates under a slag removal device  62  such as a stationary scraper or cutter as shown, or a moving device such as a rotary device as previously shown. Removed reusable feedstock  27  may be separated from the removed slag  34  as previously described. 
       FIG. 8  illustrates a method  80  operable by the disclosed machine. The method  80  may be implemented by control logic in software or hardware to execute the below steps and/or subsets thereof as claimed. The steps may include: 
       82  Feed a granular feedstock material into a chamber; 
       84  Scan the feedstock with an energy source that selectively melts or sinters the feedstock to create a material deposit overlaid with slag; 
       86  Position the top surface of the material deposit at a cutting surface of a slag removal device, or position the cutting surface of the slag removal device at the top surface of the material deposit; 
       88  Pass the slag removal device across the top surface of the deposit or move the deposit relative to the slag removal device, cutting or breaking the slag free from the top surface; 
       90  Receive the removed slag and a reusable portion of the granular feedstock into a separation device; 
       92  Separate the removed slag from the reusable portion of the granular feedstock with the separation device; 
       94  Recycle the reusable portion of the granular feedstock to the top surface of the material deposit; and 
       96  Repeat one or more times from step  82 . 
     While various embodiments of the present invention have been shown and described herein, it will be obvious that such embodiments are provided by way of example only. Numerous variations, changes and substitutions may be made without departing from the invention herein. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.