Patent Publication Number: US-2022234286-A1

Title: Rotating relative recoater and part orientation

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 16/166,958, filed Oct. 22, 2018, the entire content of which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present disclosure relates to additive manufacturing, and more particularly to controlling geometries in additive manufacturing techniques such as laser powder bed fusion, electron beam additive manufacturing, and the like. 
     2. Description of Related Art 
     Laser powder bed fusion additive manufacturing and electron beam additive manufacturing use directed energy in conjunction with powder feedstock to form a sintered structure. The energy source, e.g., the laser beam or electron beam, excites the target material to the point of phase-change. This melt-pool process, coupled with an active toolpath effectively welds a single layer of powder feedstock into a solid state. Once one layer has been formed, a recoater pushes a thin layer of powder feedstock across the build surface and the process repeats. 
     Build quality is often dependent on the orientation of the part with respect to the recoater. Due to the movement of the recoater over recently fused layers of the build, the properties of the part build can be negatively affected by part orientation. The part is traditionally positioned on a build plate in such a way as to avoid risk of recoater crash during the additive manufacturing process. Certain geometries are very sensitive to recoater orientation relative to the part. As such, part designs have to be developed knowing that certain features may build poorly and this limits the design space. 
     The conventional techniques have been considered satisfactory for their intended purpose. However, there is an ever present need for improved additive manufacturing systems and methods. This disclosure provides a solution for this need. 
     SUMMARY OF THE INVENTION 
     A system for additive manufacturing includes a build chamber including a sidewall and a build plate cooperating to define a build volume, wherein the build chamber is configured to house a part and unfused feedstock powder during a build. An energy source is mounted for movement relative to the build chamber, wherein the energy source is configured to selectively sinter the feedstock powder. A recoater is mounted for movement relative to the build chamber, wherein the recoater is configured to deposit successive layers of the feedstock powder for sintering to the part. A rotational actuator is in operable communication with the build chamber and the recoater configured to rotate the build chamber relative to the recoater. 
     A gas flow manifold can be operatively connected to a machine body for controlling gas composition in the build chamber, wherein the rotational actuator is configured to rotate the build chamber relative to the gas flow manifold and relative to the machine body. A linear actuator can be configured to move the build plate relative to the sidewall of the build chamber. The linear actuator and the rotary actuator can each include a respective encoder, wherein the encoders are operatively connected to index part location and rotation to provide clearance between the part and the recoater for rotation of the build chamber. The rotational actuator can include an encoder configured to index rotational part position, wherein an index value from the encoder is used to confirm approach angle of the recoater. A controller can be operatively connected to the energy source, to the recoater, and to the rotational actuator for controlling additive manufacturing of a part in the build chamber, wherein the controller is configured to select an approach angle on a layer by layer basis for the recoater relative to a build in the build chamber. The approach angle for each layer can be selected based on which approach angles provide a predetermined build quality. 
     The recoater can a soft recoater which is configured to not make contact with a part in the build chamber during a build. The controller can be configured to select an approach angle on a layer by layer basis to reduce or eliminate ripples forming in the part due to interactions between the recoater and a melt pool formed in the part as the energy source sinters feedstock powder to the part. The controller can be configured to select an approach angle on a layer by layer basis to reduce or eliminate cumulative build errors forming in the part due to interactions between the recoater and a melt pool formed in the part as the energy source sinters feedstock powder to the part. 
     The build plate and the sidewall of the build chamber can be configured to rotate together with a part during a build in the build chamber, and to rotate the part and unfused feedstock powder together in the build chamber to avoid relative rotation of the part and unfused feedstock powder, e.g., so the feedstock powder in the build chamber remains undisturbed. The rotational actuator can be configured to rotate the build chamber clockwise and counter-clockwise. The build plate can have a non-circular shape, and the sidewall of the build chamber can conform to the non-circular shape. 
     A method of additive manufacturing includes depositing feedstock powder with a recoater in a build chamber, selectively sintering a portion of the feedstock powder deposited by the recoater to a part in the build chamber, rotating the part, the build chamber, and unsintered feedstock powder in the build chamber together relative to the recoater, and repeating the depositing, the selectively sintering, and the rotating to form an additively manufactured part layer by layer in the build chamber. 
     The method includes controlling gas composition in the build chamber using a gas flow manifold, wherein the rotational actuator is configured to rotate the build chamber relative to the gas flow manifold. The method includes indexing part location and rotation to provide clearance between the recoater and the part for rotation of the build chamber. The method includes using an index value from an encoder to confirm approach angle of the recoater. The method includes selecting an approach angle on a layer by layer basis for the recoater relative to a build in the build chamber, wherein the approach angle for each layer is selected based on which approach angles provide a predetermined build quality. 
     The recoater can be a soft recoater and the method can include avoiding contact between the soft recoater with a part in the build chamber during a build, wherein avoiding contact includes selecting an approach angle on a layer by layer basis to reduce or eliminate ripples forming in the part due to interactions between the recoater and a melt pool formed in sintering feedstock powder to the part. The method can include selecting an approach angle on a layer by layer basis to reduce or eliminate cumulative build errors forming in the part due to interactions between the recoater and a melt pool formed in the part in sintering feedstock powder to the part. 
     Rotating the part, the build chamber, and unsintered feedstock can include rotating the part and unfused feedstock powder together to avoid relative rotation of the part and unfused feedstock powder, e.g., so the feedstock powder in the build chamber remains undisturbed. Rotating the part, the build chamber, and unsintered feedstock can include rotating the build chamber clockwise and counter-clockwise. 
     These and other features of the systems and methods of the subject disclosure will become more readily apparent to those skilled in the art from the following detailed description of the preferred embodiments taken in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that those skilled in the art to which the subject disclosure appertains will readily understand how to make and use the devices and methods of the subject disclosure without undue experimentation, preferred embodiments thereof will be described in detail herein below with reference to certain figures, wherein: 
         FIG. 1  is a schematic side elevation view of an exemplary embodiment of a system constructed in accordance with the present disclosure, showing a build in process within the build chamber; 
         FIG. 2  is a schematic plan view of a portion of the system of  FIG. 1 , showing one approach angle of the recoater; and 
         FIG. 3  is a schematic plan view of a portion of the system of  FIG. 1 , showing another approach angle of the recoater. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made to the drawings wherein like reference numerals identify similar structural features or aspects of the subject disclosure. For purposes of explanation and illustration, and not limitation, a partial view of an exemplary embodiment of a system for additive manufacturing in accordance with the disclosure is shown in  FIG. 1  and is designated generally by reference character  100 . Other embodiments of systems in accordance with the disclosure, or aspects thereof, are provided in  FIGS. 2-3 , as will be described. The systems and methods described herein can be used to control build quality and reduce cumulative build errors in additive manufacturing. 
     The system  100  includes an energy source  102 , e.g., a laser, electron beam, or any other suitable directed source of sintering energy, mounted for movement, e.g., linear or curved movement, relative to a machine body  104 , e.g., two-dimensional movement left and right and into and out of the viewing plane as oriented in  FIG. 1 . The energy source  105  is configured to selectively sinter feedstock powder  106 . A recoater  108  is mounted for movement, e.g., linear movement, relative to the machine body, e.g. for movement left and right as oriented in  FIG. 1 . The recoater  108  is configured to deposit successive layers of feedstock powder  106  for sintering to a part  110 , e.g., by sweeping a thin layer of feedstock powder from a dosing chamber  112  over the top of part  110  and the feedstock powder  106  in the build chamber  114  after each layer of the part  110  is sintered. The build chamber  114  includes a sidewall  116  and a build plate  118  cooperating with one another to define a build volume, e.g., the volume that is filled with feedstock powder  106  and the part  110  in  FIG. 1 . The build chamber  114  houses the part  110  and the unfused feedstock powder  106  during a build. After each layer of part  110  is sintered, a linear actuator  120  lowers the build plate  118 , the unfused feedstock powder  106 , and the part  110  slightly to create a clearance at the top of the part  110  for recoater  108  to deposit the next layer of feedstock powder over the part  110  for sintering the next layer of the part  110 . The movement direction of the build plate  118  is indicated by the vertical double arrow in  FIG. 1 . The linear actuator  120  is configured to move the build plate  118  relative to the sidewall  116  of the build chamber  114 . 
     A rotational actuator  122  operatively connects between the machine body  104  and the build chamber  114  for rotating the build chamber  114  relative to the machine body  104  and recoater  108 . The direction of rotation of the build chamber  114  due to the rotational actuator  122  is about the axis A and is indicated schematically in  FIG. 1  by the circular double arrow, wherein the axis A aligned to the build direction, i.e., the axis A is aligned with the direction in which the part  110  grows layer by layer during the build. As depicted in  FIG. 1 , the linear actuator  120  lifts or lowers the rotary actuator together with the build plate, however it also contemplated that mechanical order could be different, e.g., wherein the rotational actuator  122  rotates the linear actuator together with rotating the build chamber  114 . A gas flow manifold  124  is operatively connected to the machine body  104  for controlling gas composition in the build chamber  114 . The rotational actuator  122  is configured to rotate the build chamber  114  relative to the gas flow manifold  124 . 
     The linear actuator  120  and the rotary actuator  122  each include a respective encoder  124 ,  126 . The encoders  124 ,  126  are operatively connected to index part location and rotation of the part  110 , e.g. relative to the machine body  104  and recoater  108 , to provide clearance between the part  110  and the recoater  108  for rotation of the build chamber  114  relative to the recoater  108 . The encoder  126  of the rotational actuator  122  is configured to index rotational part position of the build chamber  114  and the part  110 , wherein an index value from the encoder  126  is used to confirm approach angle θ of the recoater (the approach angle θ is identified in  FIGS. 2-3 ). A controller  128  is operatively connected to the energy source  102 , to the recoater  108 , to the gas flow manifold  124 , to the linear actuator  120 , to the encoders  124 ,  126 , and to the rotational actuator  122  for controlling additive manufacturing of the part  110  in the build chamber  114 . 
     With reference to  FIGS. 2-3  the controller  128  (shown in  FIG. 1 ) is configured, e.g., with machine readable instructions that cause the controller to select an approach angle θ on a layer by layer basis for the recoater  108  relative to a build or part  110  in the build chamber  114 . The approach angle θ for each layer of the part  110  is selected based on which approach angles provide a predetermined build quality for the part  110 . For example, at each layer of the part  110 , the approach angle θ for the part  110  relative to the recoater  108  can be selected to minimize cumulative build errors that would otherwise result from having a constant relative orientation of the part  110  to the recoater  108 . As shown in  FIG. 1 , the controller  128  can control the rotational actuator  122  to rotate the build chamber  114  and the part  110  to the given approach angle θ (shown in  FIGS. 2-3 ) at a given layer of the part  110  before the recoater  108  deposits the next layer of feedstock powder  106 . 
     With continued reference to  FIGS. 1-3 , the recoater  108  is a soft recoater which is configured to not make contact with the part  110  in the build chamber  114  during a build. The controller  128  can be configured, e.g., with a build quality algorithm in machine readable instructions, to select the approach angle θ on a layer by layer basis for the part  110  to reduce or eliminate ripples forming in the part  110  due to interactions between the recoater  108  and a melt pool formed in the part  110  as the energy source  102  sinters feedstock powder  106  to the part  110 . It is also contemplated that the controller  128  can be configured, e.g., with a build quality algorithm in machine readable instructions, to select an approach angle θ on a layer by layer basis for the part  110  to reduce or eliminate cumulative build errors forming in the part  110  due to interactions between the recoater  108  and the melt pool formed in the part  110  as the energy source  102  sinters feedstock powder  106  to the part  110 . 
     With reference to  FIGS. 2-3 , the build plate  118  and the sidewall  116  of the build chamber  114  are configured to rotate together with the part  110  during a build in the build chamber  114 . This rotates the part  110  and the unfused feedstock powder  106  in the build chamber  114  together to avoid relative rotation of the part  110  and the unfused feedstock powder  106 , e.g., so the feedstock powder  106  in the build chamber  114  remains undisturbed during rotation. The rotational actuator  122  (shown in  FIG. 1 ) is configured to rotate the build chamber  114  clockwise relative to the recoater  108  as shown in  FIG. 3  and counter-clockwise relative to the recoater  108  as shown in  FIG. 2 , and the approach angle θ between the recoater  108  and the part  110  can be any angle from 0° to 360°. The build plate  118  has circular shape, but as shown in  FIGS. 2 and 3  in the dotted lines, this is a rectangle with rounded corners, however, any suitable shape can be used without departing from the scope of this disclosure. The sidewall  116  of the build chamber  114  conforms to the shape of the build plate  118 . If a circular build plate  118  is used, the build plate  118  and sidewall  116  can be mechanically registered to keep them from rotating relative to one another. 
     While disclosed herein in the exemplary context of having the build chamber  114  rotate relative to the machine body  104 , those skilled in the art will readily appreciate that it is possible to rotate the recoater relative to the machine body  104  to change the approach angle of the recoater  108 , without departing from the scope of this disclosure. 
     The ability to rotate the part after each layer of feedstock powder is sintered to the part allows designers to avoid the traditional problems when the sintered melt pool pulling in more feedstock powder material than intended. Traditionally in soft recoater systems, this melt pool phenomenon in one layer causes ripples in the surfaces of parts, and the errors in the part can be cumulative as the part is built layer by layer. The ability to change the approach angle for the recoater on each layer can disrupt the ripple patterns and thus avoid cumulative errors. Since the powder and part can be rotated together, errors arising from disturbing the unsintered feedstock powder can be avoided. Potential advantages of systems and methods as disclosed herein include the following. By reducing build failure risk with respect to part orientation, additive manufacturing part designers can be enabled to develop more complex part designs. For example, heat exchangers with complex internal fins and passages can benefit from this capability, whereas with traditional techniques such builds would have a much higher risk of build failure. 
     The methods and systems of the present disclosure, as described above and shown in the drawings, provide for additive with superior properties including improved build quality and reduced cumulative error relative to traditional techniques. While the apparatus and methods of the subject disclosure have been shown and described with reference to preferred embodiments, those skilled in the art will readily appreciate that changes and/or modifications may be made thereto without departing from the scope of the subject disclosure.