Patent Publication Number: US-11027491-B2

Title: Powder recirculating additive manufacturing apparatus and method

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to additive manufacturing, and more particularly to a powder recirculating additive manufacturing apparatus and method for producing a component or part. 
     Additive manufacturing is an alternative process to casting, in which material is built up layer-by-layer to form a component or part. Unlike casting processes, additive manufacturing is limited only by the position resolution of the machine and not limited by requirements for providing draft angles, avoiding overhangs, etc. as required by casting. Additive manufacturing is also referred to by terms such as “layered manufacturing,” “reverse machining,” “direct metal laser melting” (DMLM), and “3-D printing.” Such terms are treated as synonyms for purposes of the present invention. 
     Currently, powder bed technologies have demonstrated the best resolution capabilities of prior art metal additive manufacturing technologies. However, since the build needs to take place in the powder bed, conventional machines use a large amount of powder, for example a power load can be over 130 kg (300 lbs.). This is costly when considering a factory environment using many machines. The powder that is not directly melted into the part but stored in the neighboring powder bed is problematic because it adds weight to the elevator systems, complicates seals and chamber pressure problems, is detrimental to part retrieval at the end of the part build, and becomes unmanageable in large bed systems currently being considered for large components. 
     Accordingly, there remains a need for additive manufacturing apparatus and method capable of producing a component without the use of a powder bed. 
     BRIEF SUMMARY OF THE INVENTION 
     According to one aspect of the invention, a method of making a part by an additive manufacturing process includes the steps of: (a) supporting a build platform on a support surface; (b) traversing a powder dispenser positioned above the support surface across the build platform, while dispensing powder from the powder dispenser, so as to deposit the powder over the build platform; (c) traversing the build platform with a scraper to scrape the deposited powder, so as to form a layer increment of powder; (d) using a directed energy source to fuse the layer increment of powder in a pattern corresponding to a cross-sectional layer of the part; and (e) repeating in a cycle steps (b) through (d) to build up the part in a layer-by-layer fashion. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention may be best understood by reference to the following description taken in conjunction with the accompanying drawing figures, in which: 
         FIG. 1  is a right side elevation of an additive manufacturing apparatus constructed according to an aspect of the invention; 
         FIG. 2  is a left side elevation of the additive manufacturing apparatus of  FIG. 1 ; 
         FIG. 3  is a front cross-sectional view of the additive manufacturing apparatus of  FIG. 1  in a loading position; 
         FIG. 4  is a front cross-sectional view of the additive manufacturing apparatus of  FIG. 1  in a use position; 
         FIG. 5  illustrates powder being dispensed on a support platform; 
         FIG. 6  illustrates powder being scraped or leveled; 
         FIG. 7  illustrates the leveled powder of  FIG. 6  being fused by a laser to form a containment wall and component; and 
         FIG. 8  illustrates a containment wall and component built up after multiple passes of the process illustrated in  FIGS. 5-7 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to the drawings wherein identical reference numerals denote the same elements throughout the various views,  FIGS. 1-4  illustrate an apparatus  10  for carrying out a manufacturing method of the present invention. The basic components are a collection hopper  12  having a support surface  14  configured to support one or more build platforms  16 , a powder supply assembly  18  configured to supply powder, a powder dispenser  20  configured to receive powder from the powder supply assembly  18  and drop the powder onto the build platforms  16 , a scraper  22  to level the powder dropped onto the build platforms  16 , a blower  24  configured to blow powder contained in the collection hopper  12  into the powder supply assembly  18 , a directed energy source  26  to melt the leveled powder on the build platforms, and a beam steering apparatus  28 . For purposes of this application, the powder may be any powder which can be dispensed in layers and fused by a radiant energy source, for example, metal and plastic powders. Each of these components will be described in more detail below. While not shown, it will be understood that the entire apparatus  10  may be enclosed, in use, in an environment of inert gas or other suitable atmosphere to prevent undesired oxidation and/or contamination, and to provide secondary containment for the powder. 
     The collection hopper  12  is carried by a first support  30  and includes a collection chamber  32  configured to collect and store unused powder that is dropped from the powder supply assembly  18 , powder dispenser  20 , and/or any powder that is removed from the build platforms  16  by the scraper  22 . The collection chamber  32  includes a sloped bottom wall  34  to promote movement of the collected powder to a low point and/or collection point  36  in the collection chamber  32 . The support surface  14  provides a planar work surface for the build platforms  16  to rest. The surface  14  includes a plurality of slots  38  or other openings formed therein to provide a grated surface and permit unused powder to drop through the slots  38  and into the collection chamber  32 . The collection hopper  12  may be fixed in place or slidably connected to the first support  30  to permit vertical movement of the collection hopper  12 . 
     The build platforms  16  are plate-like structures that provide a planar build surface configured to receive powder and permit the directed energy source  26  to form a containment wall  40  and a part  42  inside of the containment wall  40  thereon. The platforms  16  may be formed of any material capable of permitting the directed energy source to melt powder thereon and to permit the build platforms  16  to be reused for multiple additive manufacturing processes. For example, the build platform  16  may be formed of a metal or ceramic material. The build platforms  16  are sized to be slightly larger than the containment wall  40  to minimize the amount of powder needed to build a part  42  and to allow any powder not being used to fall into the collection hopper  12 . As shown, the build platforms  16  are positioned on the support surface  14  during a build process. 
     The powder supply assembly  18  is carried by a second support  44  and slidably connected thereto to permit the powder supply assembly  18  to move vertically. The powder supply assembly  18  includes a supply container  46  having a cyclone chamber  48 , a sieve  50 , and a storage chamber  52 . A powder feed tube  54  is connected between the collection hopper  12  and the powder supply assembly  18 . More particularly, a first end  56  of the powder feed tube  54  is connected to the collection point  36  of the collection chamber  32  and a second end  58  of the powder feed tube  54  extends through an annular side wall  60  of the cyclone chamber  48 . Additionally, an air return tube  62  is connected between the blower  24  and the powder supply assembly  18 . In more detail, a first end  64  of the air return tube  62  is connected to a suction side of the blower  24  and a second end  66  of the air return tube  62  is connected to a top wall  68  of the supply container  46 , at a central position. The blower  24  is connected to the collection chamber  32  at collection point  36  to blow powder out of the collection chamber  32  and into the cyclone chamber  48  via powder feed tube  54 . It should be appreciated that the blower  24  may be any device suitable to move powder from the collection hopper  12  to the powder supply assembly  18  via powder feed tube  54 , such as a fan or pump. Both the powder feed tube  54  and the air return tube  62  may be formed of two telescoping sections  54 A,  54 B and  62 A,  62 B or otherwise configured to permit vertical movement of the powder supply assembly  18  and/or collection hopper  12 . 
     The cyclone chamber  48  is generally cylindrical and configured to remove powder from powder entrained air entering the cyclone chamber  48  via powder feed tube  54 . As shown, the second end  58  of the powder feed tube  54  is positioned off-center to promote a cyclonic action. In other words, the powder feed tube  54  is positioned such that the powder entrained in air is spun along the cyclone chamber&#39;s side wall  60  to remove the powder from the air. The powder is dropped onto sieve  50  and the air is sucked out of the cyclone chamber  48  by the suction side of the blower  24  via the air return tube  62 . It is noted that the powder recirculation process, from collection point  36  to blower  24  to powder feed tube  54  to storage chamber  52 , and thence to the powder dispenser  20  or the collection chamber  32 , may occur either continuously or intermittently. 
     The sieve  50  includes a plurality of apertures  70  having a pre-determined size suitable to collect debris from the powder while allowing good powder to sift therethrough and into the storage chamber  52 . The storage chamber  52  includes a conically-shaped spout  72  configured to dispense powder from the storage chamber  52 . It should be appreciated that the spout  72  may have any shape suitable to dispense powder from the storage chamber  52 . 
     The powder dispenser  20  is configured to receive powder via the spout  72  from the powder supply assembly  18  and dispense the powder onto the build platforms  16 . The powder dispenser  20  is carried by a first rail  74  to permit the powder dispenser  20  to traverse the support surface  14 . Because the powder dispenser  20  traverses the support surface  14 , multiple build platforms  16  may be spaced about the support surface  14  to receive powder. The powder dispenser  20  includes a bottom wall  76 , a plurality of side walls  78  extending outwardly from the bottom wall  76 , and an open top  80  defined by a top edge  82  of the side walls  78 . The bottom wall  76  includes an aperture  84  extending therethrough and is sized to drop powder at a pre-determined flow rate from the powder dispenser  20  as it traverses the support surface  14 . The open top  80  is sized to receive powder from the spout  72  of the powder supply assembly  18  and the side walls  78  are configured to contain the powder in the powder dispenser  20  and direct the powder towards aperture  84 . Optionally, the powder dispenser  20  may also be vibrated using known techniques such as ultrasonic vibration to ensure that the powder flows through the aperture  84  at a specified rate. 
     The scraper  22  is a rigid, laterally-elongated structure configured to scrape powder disposed on a build platform  16 , thereby leveling the powder and removing any excess powder. The scraper  22  is carried by a second rail  86  to permit the scraper  22  to traverse the support surface  14 . The second rail  86  is carried by the first support  30  to permit the second rail  86  to permit vertical movement of the second rail  86 . 
     The directed energy source  26  is carried by the second rail  86  and may be raised or lowered with respect to the support surface  14  by moving the second rail along the first support  30 . The directed energy source  26  may comprise any known radiant energy source of suitable power and other operating characteristics to melt and fuse the powder during the build process, described in more detail below. For example, a laser source having an output power density having an order of magnitude of about 10 4  W/cm 2  may be used. Other directed-energy sources such as electron beam guns are suitable alternatives to a laser source. 
     The beam steering apparatus  28  comprises one or more mirrors, prisms, and/or lenses and is provided with suitable actuators, and arranged so that a beam “B” from the directed energy source  26  (see  FIG. 6 ) can be focused to a desired spot size and steered to a desired position in an X-Y plane coincident with the support surface  14 . 
     Actuators (not shown) may be used to move the components of the apparatus  10 . More particularly, actuators may be used to selectively move the second rail  86  and/or the collection hopper  12  along the first support  30 , the powder supply assembly  18  along the second support  44 , the powder dispenser  20  along first rail  74 , and the scraper  22  along second rail  86 . Actuators such as pneumatic or hydraulic cylinders, ballscrew or linear electric actuators, and so forth, may be used for this purpose. Additionally, the components may be keyed to the supports or rails to which they are carried by to provide a stable connection that allows the components to move. As illustrated, a dovetail-type connection is used; however, it should be appreciated that any suitable type of connection that is stable and allows a component to move relative to the support and/or rail may be used. 
     The build process using the apparatus  10  described above is as follows. The powder dispenser  20  and scraper  22  are moved to an initial position, shown in  FIG. 3 , to allow a build platform  16  to be secured to support surface  14 . As shown, the powder dispenser  20  and scraper  22  are moved along the first and second rails  74 ,  86  to permit the powder dispenser  20  to receive powder “P” ( FIG. 5 ) from the powder supply assembly  18  by aligning spout  72  with open top  80  of the powder dispenser  20 . Additionally, the first and second rails  74 ,  86  are moved along first and second supports  30  and  44  to position the powder dispenser  20  and scraper  22  at substantially the same elevation to prevent the powder dispenser  20  from interfering with the directed energy source  26  while traversing the support surface  14 . The initial position also places the directed energy source  26  at a suitable elevation to melt a first layer of powder P disposed on the build platform  16 ,  FIG. 7 . 
     The powder supply assembly  18  fills the powder dispenser  20  with powder P via the spout  72 . Once filled, the powder dispenser  20  drops a continuous flow of powder P at a controlled rate through the aperture  84 . Subsequent to filling, the powder dispenser  20  may traverse the support surface  14  and build platforms  16 , from the initial position to an end position,  FIG. 4 , while dropping a flow of powder P Powder P dropped on the support surface  14  falls through the slots  38  for recycling while powder P dropped onto the build platform  16  forms a first layer of powder P. 
     The scraper  22  then traverses the support surface  14  and build platform  16  to spread the first layer of powder P horizontally across the build platform  16 , thereby leveling the powder P to form a first layer increment of powder P,  FIG. 6 . The layer increment affects the speed of the additive manufacturing process and the resolution of the part  42 . As an example, the layer increment may be about 10 to 50 micrometers (0.0003 to 0.002 in.). Any excess powder P drops through the slots  38  and into the collection chamber  32  for recycling as the scraper  22  passes from left to right. Subsequently, the scraper  22  and powder dispenser  20  may be retracted back to the initial position where the powder dispenser  20  may be refilled with powder P. The return traverse may be delayed until after the laser melting step described below. As described above, excess powder P that falls into collection chamber  32  is blown by blower  24  back into powder supply assembly  18 . 
     The directed energy source  26  is used to melt a two-dimensional cross-section of the containment wall  40  and part  42  being built,  FIG. 7 . As noted above, the containment wall  40  is built on the build platform  16  along with the part  42 . The directed energy source  26  emits a beam “B” and the beam steering apparatus  28  is used to steer the focal spot “S” of the beam B over the exposed powder surface in an appropriate pattern. The exposed layer of the powder P is heated by the beam B to a temperature allowing it to melt, flow, and consolidate. 
     The powder supply assembly  18  and powder dispenser  20  may be moved vertically upward along second support  44  at a distance substantially equal to the first layer increment to position the powder dispenser  20  for spreading a second layer of powder P of similar thickness to the first layer. The second rail  86  also moves vertically upward along first support  30  at a distance substantially equal to the first layer increment to position the scraper  22  for spreading the second layer of powder P and to position the directed energy source  26  for melting the exposed second layer of powder P. Optionally, the collection hopper  12  may be moved vertically downward along the first support  30  at a distance substantially equal to the first layer increment, or a combination of upward and downward vertical movement (downward for the collection hopper  12  and upward for the powder supply assembly  18 , powder dispenser  20 , scraper  22 , and directed energy source  26 ) of the components may be performed to increase the distance between the collection hopper  12  and the powder supply assembly  18 , powder dispenser  20 , scraper  22 , and directed energy source  26  by a distance substantially equal to the first layer increment. 
     Once in position, the powder dispenser  20  traverses the support surface  14  and build structure  16  from the initial position to the end position and applies the second layer of powder P. The scraper  22  then traverses the support surface  14  and build platform  16  to spread the applied second layer of powder P at a similar thickness to that of the first layer increment. Alternatively, depending on the capacity of the powder dispenser  20  and the flow rate from the aperture  84 , a second application of powder P may be applied as the powder dispenser  20  traverses back from the end position to the end position (without having had to execute a return trip to re-fill). The directed energy source  26  again emits a beam B and the beam steering apparatus  28  is used to steer the focal spot S of the beam B over the exposed powder surface in an appropriate pattern. The exposed layer of powder P is heated to a temperature allowing it to melt, flow, and consolidate both within the top layer and with the lower, previously-solidified layer. 
     This cycle of moving the components, applying powder P, and the directed energy source melting the powder P is repeated until the entire part  42  is complete. The containment wall  40  is built up along with the part  42 . 
     As seen in  FIGS. 7 and 8 , the build platform  16  may be made wider than the overall width of the containment wall  40 , creating a lateral overhang  100 . This overhang  100  permits powder P to build up on the build platform  16  around the exterior of the containment wall  40  during the build process. This powder P, lacking exterior support, tends to slope off at the natural angle of repose of the powder P. The remaining powder P defines a buttress “b” which provides exterior lateral support for the containment wall  40 , so that its integrity and wall thickness can be maintained during the build (i.e. the wall thickness can be uniform as the containment wall  40  extends upwards). The lateral width of the overhang  100  may be selected, knowing the angle of repose of the specific powder P, so that a minimum width “W” of powder P remains to support the containment wall  40 , even at the maximum height “H” of the part  42  and containment wall  40 . 
     The apparatus and process described above provide a means for additive manufacturing of parts without the need for fixed powder containers and the associated excess powder requirements. This will save time and money in the build process, reduce the size and complexity of fixed equipment, and increase the flexibility of the build process. 
     The foregoing has described a powder recirculating additive manufacturing apparatus and method. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. 
     Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features. 
     The invention is not restricted to the details of the foregoing embodiment(s). The invention extends any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.