Patent Publication Number: US-2021187845-A1

Title: Variable height recoater blade

Description:
BACKGROUND 
     The present disclosure relates to additive manufacturing. More particularly, the present disclosure relates to methods and systems for monitoring an additive manufacturing build process. 
     Powder bed fusion additive manufacturing processes offer a technique capable of manufacturing a myriad of aerospace components and assemblies. Additive manufacturing processes operate application of multiple successive broad powder layers and then subsequent fusion of specific areas of powder to form a three dimensional workpiece. With additive powder bed fusion processes, certain build parameters and geometries can cause resulting thicknesses of solidified material to be greater than corresponding thicknesses of next powder layers, thus making contact with and potentially damaging a recoater blade as a new layer of powder is applied. This can cause interruptions in the build process as the recoater blade is repaired or replaced, often necessitating that the partially-built workpiece be scrapped. 
     SUMMARY 
     A method of controlling powder in an additive manufacturing process includes solidifying a portion of a first layer of powder to form a first layer of a workpiece. A first topology indicative of the first layer of powder and the first layer of the workpiece is captured. The recoater is moved across the second layer of powder. Heights of portions of the recoater are varied while moving the recoater, based on the first topology captured, to avoid contact of the recoater with solidified portions of the first layer that could stress the portions of the recoater if the heights of the portions were not varied. 
     An additive manufacturing system includes a powder bed with a build plate, a recoater, a plurality of pins supported by the recoater, and a sensor. The recoater positioned above the powder bed and disposed to wipe across a top of the powder bed. The plurality of pins are configured to be individually moved relative to the recoater while the recoater is being wiped across the top of the powder bed. The sensor is configured to capture a topology of the powder bed for use in moving the plurality of pins relative to the recoater. 
     A method of controlling a height of deposited powder includes depositing a first layer of powder onto a powder bed. A portion of the first layer of powder is solidified to form a first layer of a workpiece. A first topology dataset is captured. Any areas of discontinuity are identified. A first output dataset based is created on the identified areas of discontinuity. The first output dataset is converted to a first set of instructions for a recoater of the additive manufacturing system. A second layer of powder is deposited on the first layer of the workpiece and on top of the first layer of powder. The recoater is slid across the second layer of powder. The heights of individual pins of the pin array are varied based on the first set of instructions from the controller as the recoater is slid across the second layer of powder. 
     The present summary is provided only by way of example, and not limitation. Other aspects of the present disclosure will be appreciated in view of the entirety of the present disclosure, including the entire text, claims, and accompanying figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view of a powder bed additive manufacturing system. 
         FIG. 2  is a perspective view of a backside of the recoater blade and shows a pin array. 
         FIG. 3A  is a perspective view of a pin and a first leading edge element. 
         FIG. 3B  is a perspective view of the pin array and a second leading edge element. 
         FIG. 4  is a flowchart of a method of using the recoater to adjust a thickness of a powder layer. 
     
    
    
     While the above-identified figures set forth one or more embodiments of the present disclosure, other embodiments are also contemplated, as noted in the discussion. In all cases, this disclosure presents the invention by way of representation and not limitation. It should be understood that numerous other modifications and embodiments can be devised by those skilled in the art, which fall within the scope and spirit of the principles of the invention. The figures may not be drawn to scale, and applications and embodiments of the present invention may include features and components not specifically shown in the drawings. 
     DETAILED DESCRIPTION 
     The proposed system utilizes a recoater blade including an array of tightly spaced individually height adjustable square pins. The heights of these pins can be adjusted based upon measurements of variations in layer thickness from a height measurement and visual identification system. As layers of the solid workpiece are built up, the pins are controlled to be adjusted (each with an individual actuator) up or down based on the data from the measurement system so as to avoid areas of the formed workpiece with elevated solids coming into contact with the adjustable pins. 
       FIG. 1  is a side cross-section view of additive manufacturing system  10  and shows container walls  12 , powder bed  14 , build plate  16 , powdered material  18 , workpiece  20 , recoater  22  (with shield  24 , actuator  26 , driving arm  28 , and pin array  30 ), controller  32 , and sensor  34 . 
     Additive manufacturing system  10  is a machine configured to produce objects with layer-by-layer additive manufacturing. In some non-limiting embodiments, additive manufacturing system  10  can be configured for laser additive manufacturing, laser powder bed fusion, electron beam powder bed fusion, laser powder deposition, electron beam wire, and/or selective laser sintering to create a three-dimensional object out of powdered material  18 . Container walls  12  are containment walls that help to contain the four sides of powder bed  14 . Powder bed  14  includes build plate  16 , powdered material  18 , and workpiece  20 . Build plate  16  is a platform that is configured to move in a vertical direction (up and down as shown in  FIG. 1 .). Powdered material  18  is feedstock material in powdered form. In some non-limiting embodiments, powdered material  18  can be or include titanium alloys, nickel alloys, aluminum alloys, steel alloys, cobalt-chrome alloys, copper alloys, or other types of powdered metal alloys. In some embodiments, powdered material can include polymer powder. Workpiece  20  is an article being constructed by the layer-by-layer additive manufacturing process of additive manufacturing system  10 . 
     Recoater  22  is a powder wiping device. Shield  24  is a panel or wall. Actuator  26  is a device for causing movement. In this example, actuator  26  includes a plurality of individual actuators  26  (see e.g.,  FIG. 2 ). Also in this example, actuator  26  can include a circular or linear actuator. A type of actuator  26  can include an electric, hydraulic, or pneumatic actuator. Driving arm  28  is an elongate piece of solid material such as a rod or shaft. Pin array  30  is a plurality of individual pins (see e.g.,  FIG. 2 ). In this example, a shape of each pin of pin array  30  is polyhedral and generally in the shape of a rectangular box. Controller  32  is an electronic control device. In this non-limiting embodiment, controller  32  is a computer. Sensor  34  is an instrument for sensing a surface profile or topography. As referred to hereinafter sensor  34  can be a structured light or a laser scanner, but a person skilled in the art will recognize that other forms of topographic sensors can alternatively be used. 
     Container walls  12  are disposed on the sides of and are in contact with powdered material  18  of powder bed  14 . Powder bed  14  is positioned below sensor  34 . Build plate  16  is positioned between container walls  12  and is in contact with the bottom sides of powdered material  18  and workpiece  20 . Powdered material  18  is disposed on build plate  16  and between container walls  12 . Workpiece  20  is disposed in and surrounded by a portion of powdered material  18  and sits upon build plate  16 . Recoater  22  is positioned above build plate  16  and is configured to move relative to powdered material  18 . In this example, recoater  22  is electrically connected to controller  32  via wires. 
     Shield  24  is mounted to a front of recoater  22  (with the front of recoater  22  being on the right side of recoater  22  as shown in  FIG. 1 ). Actuator  26  is attached and mounted to a backside of shield  24 . Driving arm  28  extends between and is connected to actuator  26  and to pin array  30 . Pin array  30  is mounted on and slideably engaged with shield  24 . Controller  32  is positioned away from powder bed  14  and is in data communication with recoater  22  and sensor  34 . In this example, sensor  34  is mounted above powder bed  14 . In this example, sensor  34  is electrically connected to controller  32  via wires. 
     Container walls  12  contain powdered material  18  within powder bed  14 . Powder bed  14  is used to form workpiece  20  from powdered material  18  by way of selectively solidifying portions of powdered material  18 . Build plate  16  functions as a base upon which powdered material  18  is placed and that supports workpiece  20 . As workpiece  20  is formed, build plate  16  lowers after each layer of workpiece  20  is iteratively formed. Powdered material  18  serves as feedstock or raw material from which workpiece  20  is solidified and formed. After a layer powder spreading step, recoater  22  is drawn across a top surface of powder bed  14  to wipe or scrape a portion of powdered material  18  from powder bed  14 . In this example, recoater  22  moves from left to right (as shown in  FIG. 1 ). 
     During use of recoater  22 , shield  24  acts as a support to which actuator  26  and pin array  30  are mounted. As recoater  22  is drawn across powder bed  14 , shield  24  pulls actuator  26 , driving arm  28 , and pin array  30  across powder bed  14 . Actuator  26  drives up and down motion of driving arm  28 . As driving arm  28  is driven up and down by actuator  26 , driving arm  28  pushes pin array  30  up and down relative to shield  34 . Pin array  30  moves up and down relative to shield  24  as recoater  22  is drawn across powder bed  14 . 
     Controller  32  controls and receives communications from the various components of additive manufacturing system  10 . In this example, controller  32  also stores a machine learning algorithm that is used, in conjunction with the data from sensor  34 , to actively monitor the additive manufacturing build-process layer by layer. The machine learning algorithm is configured to continually monitor the topographical data from sensor  34  and adjust the heights of each pin of pin array  30  based on height measurements powdered material  18  and workpiece  20 . In this example, sensor  34  emits a signal that is reflected off of powdered material  18  and workpiece  20 . The reflected beam is then captured by a detector on sensor  34 . Based on an angle and time of return of the beam and a location on sensor  34 , sensor software can determine how far the surface of powder bed  14  is away from sensor  34 . In this way, sensor  34  can capture a three-dimensional map (e.g., topographical profile) of various surface heights of powder bed  14  after a layer of workpiece  20  has been incrementally solidified and/or as powder bed  14  is recoated with powder. 
     Additive manufacturing system  10  utilizes sensor  34  to scan powder bed  14  as powder bed  14  is being formed by the additive manufacturing layer powder spreading process. Sensor  34  allows for capture of a topography of the surface of powder bed  14 . For example, sensor  34  captures an image of powder bed  14  after solidification of a layer of powdered material  18  is complete. After sensor  34  captures a topological profile of powder bed  14 , controller  32  measures deviations from a nominal model and determines relative height data. The height data is then used to monitor and adjust positions of each pin in pin array  30  based on the topology of powder bed  14 . As layers of powdered material  18  and workpiece  20  are built up, the pins of pin array  30  are controlled to move up or down to avoid areas of powder bed  14  with elevated solids (e.g., portions of workpiece  20 ) in response to the topographical data of powder bed  14 . 
       FIG. 2  is a perspective view of a backside of recoater  22  and shows shield  24 , actuators  26 , driving arms  28 , and pin array  30  with pins  36 . Here, recoater  22  is shown as including pin array  30  with a plurality of pins  36 . In alternative embodiments, pin array  30  can include more or fewer pins  36  than shown in  FIG. 2 . In this example, there are approximately eight pins  36  per inch. In other words, a width of each of pins  36  can be approximately 0.125 inches. Each of pins  36  is individually replaceable as wear occurs. Each of pins  36  is connected to and slideably engaged with both shield  24  and with an adjacent pin  36 . 
     In order to prevent powder flow between adjacent pins, recoater  22  can include one or more of the following features (alone or in combination). In one non-limiting embodiment, individual pins  36  can be ship-lapped to each other. In another non-limiting embodiment, a seal element can be provided between each of pins  36 . Additionally, interfaces between each individual pins  36  can be angled. Recoater  22  can also include one or more of the following features (alone or in combination) to limit or prevent non-linear motion of pins  36  relative to shield  24 . For example, pins  36  can interface with grooved bearing surfaces in shield  24  to limit forward and backward and/or side-to-side motion. In another example, pins  36  can include tracks (e.g., tongue and groove) to limit forward and backward and/or side-to-side motion. In yet another example, additive manufacturing system  10  can contain a sealing gas pressurizing pin (e.g., a retention connection) above the build chamber to limit contamination of powdered material  18 . These and other features can be incorporated to maintain long wear life, minimize required maintenance, and to limit contamination of the manufacturing process. 
     A vertical position of each individual pin  36  is provided by recoater  22 . For example, each individual actuator  26  drives an individual driving arm  28  which drives the vertical motion of an individual pin  36 . In this way, pin array  30  with pins  36  enables a resolution across pin array  30  of powder bed topology as pin array  30  is drawn across powder bed  14 . For example, the vertical heights of pins  36  can be adjusted so as to create a contour with varying valleys and apexes to control a height (e.g., topology) of powdered material  18  as recoater  22  is drawn across powder bed  14 . The desired resolution of the powder bed topology can be based on one or more of the following factors: powder material, length and width of powder bed  14 , powder size distribution, component surface finish of workpiece  20 , and build rate. 
     The adjustability of pins  36  of pin array  30  allows recoater  22  to avoid areas of powder bed  14  with elevated solids (e.g., elevated portions of workpiece  20 ) that could otherwise damage recoater  22 . 
       FIG. 3A  is a perspective view of an individual pin  36  of pin array  30  and shows leading edge  38 A, bottom face  40 A, and covering  42 A. Leading edge  38 A is a face of pin  36  that faces towards shield  24  (see e.g.,  FIGS. 1-2 ). Bottom face  40 A is a face of pin  36  that is located on an end of pin  36 . Covering  42 A is a piece of solid material. In this example, a material of covering  42 A can be elastomer or metal. Leading edge  38 A is positioned so as to be on a leading edge of pin  36  as recoater  22  is drawn across powder bed  14 . Bottom face  40 A is disposed on a bottom end of pin  36  (with top-bottom orientation shown as up-down in  FIG. 3A ). 
     In this example, covering  42 A is attached to and extends across both of leading edge  38 A and bottom face  40 A of pin  36 . In other non-limiting embodiments, covering  42 A can be attached to and extend across just one of either leading edge  38 A or bottom face  40 A of pin  36 . As shown in  FIG. 3A , covering  42 A extends a width of pin  36 . In such an example, each of pins  36  of pin array  30  can include their own respective, discrete covering  42 A mounted to each pin  36  (different from a continuous covering as shown in  FIG. 3B ). 
     In one example, covering  42 A acts as a squeegee (or squilgee) to wipe powdered material  18 . Covering  42 A also provides a protective barrier between pin  36  and powdered material  18  and workpiece  20 . Covering  42 A prevents the wearing down of pin  36  throughout the lifecycle of recoater  22 . For example, covering  42 A can provide a material hardness that is different from that of the material of pin  36  and such that the hardness of covering  42 A improves the durability of recoater  22  as pins  36  are drawn across powdered material  18 . Covering  42 A also provides a coefficient of friction that is different from that of a material of pin  36  and such that the coefficient of friction of covering  42 A improves the behavior (e.g., flowability) of powdered material  18  as pins  36  are drawn across powdered material  18  by recoater  22 . In another example, covering  42 A can be detachable so as to allow for replacement of covering  42 A as covering  42 A wears or becomes damaged. 
       FIG. 3B  is a perspective view of pin array  30  and shows pins  36 , leading edges  38 B, bottom faces  40 B, and covering  42 B. In contrast to covering  42 A shown in  FIG. 3A , covering  42 B in  FIG. 3B  is shown as extending across the entire expanse (or width) of pin array  30 . Covering  42 B is connected and mounted to each individual pin  36  of pin array  30 . In this example, covering  42 B can be attached to each of pins  36  at a single point of each pin  36  such that a minor rotation of a localized portion of covering  42 B is permitted with respect to each pin  36 . This minor rotation of covering  42 B enables covering  42 B to bend and flex in response to the position adjustments of pins  36 . The minor localized rotations of covering  42 B also enable covering  42 B to occupy a continuous curved shape along the width of pin array  30 . This flexibility of covering  42 B provides improved resolution and smoother topology of powder bed  14  thereby allowing for improved quality (e.g., surface finish, dimensional accuracy, etc.) of workpiece  20 . 
       FIG. 4  is a flowchart of method  100  of controlling a height of deposited powder in an additive manufacturing process. Method  100  includes steps  102  through  136 . 
     Step  102  includes depositing a first layer of powder onto powder bed  14  of additive manufacturing system  10 . Step  104  includes solidifying a portion of the first layer of powdered material  18  to form a first layer of workpiece  20 . Step  106  includes capturing a first topology dataset of the first layer of powdered material  18  and the first layer of workpiece  20 . Step  106  also includes step  108  of scanning the first layer of powdered material  18  and the first layer of workpiece  20  with sensor  34  (e.g., a structured light or a laser scanner). Step  110  includes sending the first topology dataset to a first portion of controller  32 . Step  110  also include step  112  of calculating an area of discontinuity based on previously collected topologies of solidified layers of powdered material  18  and solidified layers of workpiece  20 . 
     Step  114  includes identifying any areas of discontinuity in the first topology dataset. Step  114  also includes step  116  of predicting areas of concern of the layers of powdered material  18  based on an analysis of a nominal model of powder bed  14  and workpiece  20 . Step  118  includes creating a first output dataset based on the identified areas of discontinuity in the first topology dataset. Step  120  includes sending the first output dataset to a second portion of controller  32 . Step  122  includes converting the first output dataset to a first set of instructions for recoater  22  of the additive manufacturing system. Step  124  includes depositing a second layer of powdered material  18  on top of the first layer of workpiece  20  and on top of the first layer of powdered material  18 . Step  126  includes sliding recoater  22  across the second layer of powdered material  18 . 
     Step  128  includes varying heights of individual pins of the pin array based on the first set of instructions from controller  32  as recoater  22  is slid across the second layer of powdered material  18 . Step  128  also includes steps  130 ,  132 , and  134 . Step  130  includes moving one of pins  36  of pin array  30  in a linear motion relative to shield  24  and relative to other pins  36  of pin array  36 . Step  132  includes moving individual pins  36  with actuator  26 . Step  134  includes adjusting pin array  30  to avoid recoater  22  from coming into contact with an elevated solid region of the first layer of workpiece  20 . Step  136  includes adjusting a topology of the second layer of powdered material  18  with pins  36  of pin array  30  as recoater  22  is slid across the second layer of powdered material  18 . In another example, during solidification, the parameters related to melting can be adjusted based on the varying thickness of the deposited powdered material  18 . 
     Method  100  allows pin array  30  to avoid coming into contact with higher than usual solidified portions of workpiece  20  so as to prevent damage to recoater  22 . In addition to avoiding higher than usual solid portions of powdered material  18 , method  100  can be used to vary the thickness of powdered material  18  across build plate  16  allowing multiple layer thicknesses in varying areas of the build to create specific surface finishes, material properties, or increase build speed in areas of reduced concern. 
     Discussion of Possible Embodiments 
     A method of controlling powder in an additive manufacturing process includes solidifying a portion of a first layer of powder to form a first layer of a workpiece. A first topology indicative of the first layer of powder and the first layer of the workpiece is captured. The recoater is moved across the second layer of powder. Heights of portions of the recoater are varied while moving the recoater, based on the first topology captured, to avoid contact of the recoater with solidified portions of the first layer that could stress the portions of the recoater if the heights of the portions were not varied. 
     The method of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following steps, features, configurations and/or additional components. 
     The first topology can be sent to a first portion of a controller after the first topology is captured; and/or a first output dataset can be sent to a second portion of the controller after the first output dataset is created. 
     A topology of the second layer of powder can be adjusted with the pins of the pin array as the recoater is moved across the second layer of powder. 
     The recoater can comprise: a front shield; an array of pins that can be slideably mounted to the front shield; and an actuator that can be mounted to the front shield and/or operably connected to the array of pins; and/or a pin of the array of pins can be moved in a linear motion relative to the front shield and/or relative to the other pins of the pin array. 
     Individual pins can be moved with the actuator. 
     An area of discontinuity can be calculated based on previously collected topologies of solidified layers of powder and/or solidified layers of the workpiece. 
     Areas of concern of the powder layer can be predicted based on an analysis of a nominal model of the powder bed and the workpiece. 
     The first layer of powder and/or the first layer of the workpiece can be scanned with a structured light or a laser scanner. 
     The recoater can be adjusted to avoid the recoater from coming into contact with an elevated solid region of the first layer of the workpiece. 
     An additive manufacturing system includes a powder bed with a build plate, a recoater, a plurality of pins supported by the recoater, and a sensor. The recoater positioned above the powder bed and disposed to wipe across a top of the powder bed. The plurality of pins are configured to be individually moved relative to the recoater while the recoater is being wiped across the top of the powder bed. The sensor is configured to capture a topology of the powder bed for use in moving the plurality of pins relative to the recoater. 
     The system of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components. 
     The recoater can comprise: a shield that can be disposed to move relative to the powder bed; an actuator that can be mounted to the shield; and/or a pin array that can comprise a plurality of pins, wherein each pin of the pin array can be connected to the actuator by a driving arm, wherein each pin of the pin array can be slideably engaged with the shield; and/or a controller can be electrically connected to the sensor and/or to the actuator, wherein the controller can be configured to send and/or receive electrical signals to and/or from the sensor and the actuator. 
     The controller can control actuation of each pin of the pin array via corresponding driving arm based on the captured topology of the powder bed. 
     A covering can be attached to a bottom face or to a leading edge of one of the pins of the pin array. 
     A covering can be attached to a bottom face or to a leading edge of the pin array. 
     The driving arm can comprise a plurality of driving arms extending between the actuator and the pins of the pin array, wherein one of the driving arms of the plurality of driving arms can be connected to the actuator and to one of the pins, wherein the actuator can be disposed to drive motion of the driving arms. 
     Each pin of the pin array can be slideably engaged with an adjacent pin of the pin array. 
     A method of controlling a height of deposited powder includes depositing a first layer of powder onto a powder bed. A portion of the first layer of powder is solidified to form a first layer of a workpiece. A first topology dataset is captured. Any areas of discontinuity are identified. A first output dataset based is created on the identified areas of discontinuity. The first output dataset is converted to a first set of instructions for a recoater of the additive manufacturing system. A second layer of powder is deposited on the first layer of the workpiece and on top of the first layer of powder. The recoater is slid across the second layer of powder. The heights of individual pins of the pin array are varied based on the first set of instructions from the controller as the recoater is slid across the second layer of powder. 
     The method of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following steps, features, configurations and/or additional components. 
     The first topology dataset can be sent to a first portion of a controller after the first topology dataset is captured; and/or the the first output dataset can be sent to a second portion of the controller after the first output dataset is created. 
     An area of discontinuity can be calculated based on previously collected topologies of solidified layers of powder and solidified layers of the workpiece; and/or areas of concern of the powder layer can be predicted based on an analysis of a nominal model of the powder bed and the workpiece. 
     The pin array can be adjusted to avoid the recoater from coming into contact with an elevated solid region of the first layer of the workpiece. 
     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.