Patent Publication Number: US-2021170517-A1

Title: Scatter reduction in additive manufacturing

Description:
CROSS REFERENCE TO RELATED APPLICATION(S) 
     This application claims the benefit of U.S. application Ser. No. 15/582,493, entitled “SCATTER REDUCTION IN ADDITIVE MANUFACTURING” and filed on Apr. 28, 2017, the disclosure of which is expressly incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     Field 
     The present disclosure relates generally to additive manufacturing (AM), and more particularly, to reducing charged powder scattering in AM applications, such as powder-bed fusion (PBF). 
     Background 
     PBF systems can produce structures (referred to as build pieces) with geometrically complex shapes, including some shapes that are difficult or impossible to create with conventional manufacturing processes. PBF systems create build pieces layer-by-layer. Each layer or ‘slice’ is formed by depositing a layer of powder and exposing portions of the powder to an energy beam. The energy beam is applied to melt areas of the powder layer that coincide with the cross-section of the build piece in the layer. The melted powder cools and fuses to form a slice of the build piece. The process can be repeated to form the next slice of the build piece, and so on. Each layer is deposited on top of the previous layer. The resulting structure is a build piece assembled slice-by-slice from the ground up. 
     Some energy beams that are used to fuse the powder layer can also cause some of the particles of powder to scatter or fly away from the layer. For example, applying an electron beam to a powder layer can electrically charge some of the particles of powder. The electrical charges on the powder particles repel each other and cause some of the particles to fly off the powder layer, a phenomenon also known as ‘smoking.’ In some cases, the scattered powder interferes with the AM operation and can result in poor quality build pieces. 
     SUMMARY 
     Several aspects of apparatuses and methods for reducing powder scatter in PBF systems will be described more fully hereinafter. 
     In various aspects, an apparatus for powder-bed fusion can include a structure that supports a layer of powder material having a plurality of particles of powder, an energy beam source that generates an energy beam, and a deflector that applies the energy beam to fuse an area of the powder material in the layer. The energy beam can electrically charge the particles of powder. The apparatus can also include an electrical system that generates an electrical force between the structure and the charged particles of powder. 
     In various aspects, an apparatus for PBF can include one or more structures including a powder material support structure, an energy beam source directed to the powder material support surface, a deflector operationally coupled with the energy beam source, and a voltage source connected to at least one of the structures. 
     Other aspects will become readily apparent to those skilled in the art from the following detailed description, wherein is shown and described only several exemplary embodiments by way of illustration. As will be realized by those skilled in the art, concepts described herein are capable of other and different embodiments, and several details are capable of modification in various other respects, all without departing from the present disclosure. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not as restrictive. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various aspects will now be presented in the detailed description by way of example, and not by way of limitation, in the accompanying drawings, wherein: 
         FIG. 1A-D  illustrate an example PBF system during different stages of operation. 
         FIG. 2  shows a close-up view illustrating an example of particle scattering in PBF. 
         FIG. 3  illustrates another exemplary embodiment of an electrical system implementation for reducing powder scattering. 
         FIG. 4  shows a close-up view illustrating an exemplary embodiment of reducing particle scattering. 
         FIG. 5  illustrates another exemplary embodiment of an electrical system implementation for reducing powder scattering. 
         FIG. 6  illustrates another exemplary embodiment of an electrical system implementation for reducing powder scattering. 
         FIG. 7  illustrates an example beam error caused by an electric field. 
         FIG. 8  illustrates an exemplary embodiment of an electrical system including a beam compensation system. 
         FIG. 9  is a flow chart of an exemplary embodiment of a method of reducing powder scatter in a PBF system. 
     
    
    
     DETAILED DESCRIPTION 
     The detailed description set forth below in connection with the appended drawings is intended to provide a description of various exemplary embodiments of the concepts disclosed herein and is not intended to represent the only embodiments in which the disclosure may be practiced. The term “exemplary” used in this disclosure means “serving as an example, instance, or illustration,” and should not necessarily be construed as preferred or advantageous over other exemplary embodiments presented in this disclosure. The detailed description includes specific details for the purpose of providing a thorough and complete disclosure that fully conveys the scope of the concepts to those skilled in the art. However, the disclosure may be practiced without these specific details. In some instances, well-known structures and components may be shown in block diagram form, or omitted entirely, in order to avoid obscuring the various concepts presented throughout this disclosure. 
     This disclosure is directed to reducing charged powder scattering, i.e., smoking, in PBF systems. The PBF system can be built, for example, such that one or more structures in the system can be charged to create an electrical force between the charged particles of powder and the powder layer. The electrical force can keep the charged particles of powder from flying off of the powder layer. For example, the build piece can be electrically charged such that the build piece is an anode, or pseudo-anode, to cause charge-accumulated powder particles to be attracted to the bed instead of repelled. Further, charged static shields can be placed with negative potential, with a near uniform field to reduce beam deflection, to prevent charge-accumulated particles from being attracted to the build chamber. Any deflections created by these mechanisms can be characterized by control systems of the PBF system, and compensations can be provided in the original beam deflection commands. 
       FIGS. 1A-D  illustrate an example PBF system  100  during different stages of operation. PBF system  100  can include a depositor  101  that can deposit each layer of metal powder, an energy beam source  103  that can generate an energy beam, a deflector  105  that can apply the energy beam to fuse the powder material, and a build plate  107  that can support one or more build pieces, such as a build piece  109 . PBF system  100  can also include a build floor  111  positioned within a powder bed receptacle. The walls of the powder bed receptacle are shown as powder bed receptacle walls  112 . Build floor  111  can lower build plate  107  so that depositor  101  can deposit a next layer and a chamber  113  that can enclose the other components. Depositor  101  can include a hopper  115  that contains a powder  117 , such as a metal powder, and a leveler  119  that can level the top of each layer of powder. 
     Referring specifically to  FIG. 1A , this figure shows PBF system  100  after a slice of build piece  109  has been fused, but before the next layer of powder has been deposited. In fact,  FIG. 1A  illustrates a time at which PBF system  100  has already deposited and fused slices in multiple layers, e.g., 50 layers, to form the current state of build piece  109 , e.g., formed of 50 slices. The multiple layers already deposited have created a powder bed  121 , which includes powder that was deposited but not fused. 
       FIG. 1B  shows PBF system  100  at stage in which build floor  111  can lower by a powder layer thickness  123 . The lowering of build floor  111  causes build piece  109  and powder bed  121  to drop by powder layer thickness  123 , so that the top of the build piece and powder bed are lower than the top of powder bed receptacle wall  112  by the powder layer thickness. In this way, for example, a space of with a consistent thickness equal to powder layer thickness  123  can be created over the top of build piece  109  and powder bed  121 . 
       FIG. 1C  shows PBF system  100  at a stage in which depositor  101  can deposit powder  117  in the space created over the top of build piece  109  and powder bed  121 . In this example, depositor  101  can cross over the space while releasing powder  117  from hopper  115 . Leveler  119  can level the released powder to form a powder layer  125  that has a thickness of powder layer thickness  123 . Thus, the powder in a PBF system can be supported by a powder material support structure, which can include, for example, a build plate, a build floor, a build piece, etc. It should be noted, that elements of  FIGS. 1A-D  and the other figures in this disclosure are not necessarily drawn to scale, but may be drawn larger or smaller for the purpose of better illustration of concepts described herein. For example, the illustrated thickness of powder layer  125  (i.e., powder layer thickness  123 ) is greater than an actual thickness used for the example 50 previously-deposited layers. 
       FIG. 1D  shows PBF system  100  at a stage in which energy beam source  103  can generate an energy beam  127  and deflector  105  can apply the energy beam to fuse the next slice in build piece  109 . In various embodiments, energy beam source  103  can be an electron beam source, energy beam  127  can be an electron beam, and deflector  105  can include deflection plates that can generate an electric field or a magnetic field that deflects the electron beam to scan across areas to be fused. In various embodiments, energy beam source  103  can be a laser, energy beam  127  can be a laser beam, and deflector  105  can include an optical system that can reflect and/or refract the laser beam to scan across areas to be fused. In various embodiments, the deflector can include one or more gimbals and actuators that can rotate and/or translate the energy beam source to position the energy beam. In various embodiments, energy beam source  103  and/or deflector  105  can modulate the energy beam, e.g., turn the energy beam on and off as the deflector scans so that the energy beam is applied only in the appropriate areas of the powder layer. For example, in various embodiments, the energy beam can be modulated by a digital signal processor (DSP). 
     The application of energy beam  127  can cause particles of powder to fly away from the powder layer, shown in  FIG. 1D  as scattered powder particles  129 . As noted above, scattered powder particles  129  can interfere with the printing operation and can result in poorer quality build pieces. 
       FIG. 2  shows a close-up view illustrating an example of particle scattering in PBF. 
     In particular,  FIG. 2  shows an energy beam  201  scanning across a powder layer  203  in the direction of the bold arrow (i.e., scanning to the right). As energy beam  201  is applied, powder is fused into fused powder  205  to form build piece  207 . In the view shown in  FIG. 2 , a top portion of the previous slice  209  can be seen, as well as the portion of the current slice  211  that has been fused so far. As energy beam  201  is applied to an area of powder layer  203  to heat and fuse the area, some of the powder particles can become charged. In this example, some of the powder particles can become negatively charged, and these charged powder particles are represented by a “−” symbol. For example, energy beam  201  can be an electron beam, which is a beam of electrons, i.e., negatively-charged particles. The electrons in the electron beam can be captured by powder particles, such that the powder particles become negatively charged. 
     Negatively-charged objects repel each other due to the electrostatic force. As illustrated in  FIG. 2 , if enough negatively-charged powder particles are in close proximity, the repulsive electrostatic force between them can overcome the force of gravity, causing some of the charged powder particles to fly upward from powder layer  203 . These powder particles are shown as scattered powder particles  213 . 
       FIG. 3  illustrates another exemplary embodiment of an electrical system implementation for reducing powder scattering. An electrical system  300  can include a voltage source  301  and a voltage source  303 . In this example, the positive terminal of voltage source  301  can be connected to a build plate  305  through an opening in a build floor  307 . Build plate  305  and build floor  307  can support a powder bed  309  and a conductive build piece  311 . For example, conductive build piece  311  can be formed of a metal or other conductive material. 
     In this example, build plate  305  can be electrically conductive and can be electrically connected to conductive build piece  311 . For example, conductive build piece  311  can be fused to build plate  305 . The connection of build plate  305  to voltage source  301  can cause positive charge to collect on the build plate and on the conductive build piece. The positive charge can create an electric field, shown by electric field lines  312 . In this example, because positive charge can collect at the top of conductive build piece  311 , the electric field through the powder layer on top of the build piece may be stronger compared to the electric field in the example of  FIG. 3 , particularly if the top of the build piece is far away from the build plate. This may allow electrical system  300  to more efficiently reduce powder scatter. 
     Voltage source  303  can be applied to an electron beam source  313  as the acceleration voltage used to create the electron beam, which can be scanned by a deflector  315  to fuse powder. In this case, the positive terminal of voltage source  303  is the anode of electron beam source  313 . Voltage source  301  is also connected to the anode of electron beam source  313 , such that voltage source  301  is applied between the anode and build plate  305 . In this way, for example, the voltage applied by voltage source  301  can help reduce powder scatter and increase beam modulation gain by further accelerating the beam for greater beam energy. 
       FIG. 4  shows a close-up view illustrating an exemplary embodiment of reducing particle scattering. In particular,  FIG. 4  illustrates the top of a conductive build piece  400 , such as conductive build piece  311  above. An energy beam  401  scanning across a powder layer  403  in the direction of the bold arrow (i.e., scanning to the right). As energy beam  401  is applied, powder is fused into fused powder  405  to form build piece  400 . In the view shown in  FIG. 4 , a top portion of the previous slice  409  can be seen, as well as the portion of the current slice  411  that has been fused so far. As energy beam  401  is applied to an area of powder layer  403  to heat and fuse the area, some of the powder particles can become charged. In this example, some of the powder particles can become negatively charged, as represented by the “−” symbol. For example, energy beam  201  can be an electron beam, and the electrons in the electron beam can be captured by powder particles, such that the powder particles become negatively charged. 
     In this example, conductive build piece  400  can be connected to an electrical system such as electrical system  300  in  FIG. 3  above, such that positive charge collects at the top of the conductive build piece. The positive charge can create an electric field, shown as electric field lines  413 , that can attract the negatively charge powder particles. The attraction is shown in  FIG. 4  by electric field lines  413  between the positive and negative charges. The attractive force exerted by the electric field on the negatively-charged powder particles can be greater than the repulsive force between the powder particles, and the negatively-charged powder particles can be prevented from flying upward, as illustrated by immobilized powder particle  415 . In this way, for example, powder scattering may be reduced or eliminated. 
       FIG. 5  illustrates another exemplary embodiment of an electrical system implementation for reducing powder scattering. An electrical system  500  can include a voltage source  501  and a voltage source  503 . In this example, the positive terminal of voltage source  501  can be connected to a build floor  505 , which supports a build plate  507 , a powder bed  509 , and a build piece  511 . In this implementation, build floor  505  can be electrically conductive. In other implementations, build plate  507  can also be electrically conductive. In other implementations, build plate  507  and build piece  511  can also be electrically conductive. Different electric fields can be generated in the different implementations to reduce or eliminate powder scatter. 
     Voltage source  503  can be applied to an electron beam source  513  as the acceleration voltage used to create the electron beam, which can be scanned by a deflector  515  to fuse powder. In this case, the positive terminal of voltage source  503  is the anode of electron beam source  513 . Voltage source  501  is also connected to the anode of electron beam source  513 , such that voltage source  501  is applied between the anode and build floor  505 . In this way, for example, the voltage applied by voltage source  501  can help reduce powder scatter and increase beam modulation gain by further accelerating the beam for greater beam energy. 
       FIG. 6  illustrates another exemplary embodiment of an electrical system implementation for reducing powder scattering. An electrical system  600  can include a voltage source  601  and a voltage source  603 . In this example, the positive terminal of voltage source  601  can be connected to a conductive plug  604  in a non-conductive build plate  605  through an opening in a build floor  607 . Non-conductive build plate  605  and build floor  607  can support a powder bed  609  and a conductive build piece  611 . For example, conductive build piece  611  can be formed of a metal or other conductive material. 
     In this example, when printing the first few layers of conductive build piece  611 , the PBF system also prints a conductive extension  612  that can connect the conductive build piece to conductive plug  604 . In this way, for example, voltage source  601  can be connected to conductive build piece  611  to cause positive charge to collect on the conductive build piece. The electric field (not shown) generated by the positive charge collected on conductive build piece  611  can help reduce or eliminate powder scatter from powder layers on top of the build piece. Because the positive charge is collected on conductive build piece  611 , but not on non-conductive build plate  605 , the electric field may be concentrated in the build piece without requiring the build plate to be charged. In this way, for example, the voltage generated by voltage source  601  may be reduced. 
     Voltage source  603  can be applied to an electron beam source  613  as the acceleration voltage used to create the electron beam, which can be scanned by a deflector  615  to fuse powder. In this case, the positive terminal of voltage source  603  is the anode of electron beam source  613 . Voltage source  601  is also connected to the anode of electron beam source  613 , such that voltage source  601  is applied between the anode and build plate  605 . In this way, for example, the voltage applied by voltage source  601  can help reduce powder scatter and increase beam modulation gain by further accelerating the beam for greater beam energy. 
     In various embodiments, one or more conductive extensions could be formed in various shapes and configurations to connect one or more build pieces to a voltage source. For example, multiple build pieces could be connected by a lattice of conductive extensions. In various embodiments, a conductive extension need not be directly connected between each build piece and the voltage source. For example, a first conductive extension could connect a first build piece to the voltage source (e.g., directly connect to a conductive plug, such as in  FIG. 6 ), and a second conductive extension could connect the first build piece directly to a second build piece. In this way, for example, the second build piece can be connected to the voltage source through the first build piece (i.e., not directly connected). 
       FIG. 7  illustrates an example beam error caused by an electric field. An electrical system  700 , including a voltage source  701  and a voltage source  703 . The positive terminal of voltage source  701  can be connected to a conductive build plate  705  through an opening in a build floor  707 . Conductive build plate  705  and build floor  707  can support a powder bed  709  and a conductive build piece  711 . Conductive build plate  705  can be electrically connected to conductive build piece  711 , such as being fused to the build piece, and accordingly, positive charge can collect on the build plate and on the conductive build piece to create an electric field similar to the example of  FIG. 3 . For the purpose of clarity, the electric field lines are not shown in  FIG. 7 . 
     Voltage source  703  can be applied to an electron beam source  713  as the acceleration voltage used to create an electron beam  715 , which can be scanned by a deflector  717  to fuse powder. In this case, the positive terminal of voltage source  703  is the anode of electron beam source  713 . Voltage source  701  is also connected to the anode of electron beam source  713 , such that voltage source  701  is applied between the anode and build plate  705 . In this way, for example, the voltage applied by voltage source  701  can help reduce powder scatter and increase beam modulation gain by further accelerating the beam for greater beam energy. 
     In some cases, the electric field generated by various embodiments can cause an energy beam to bend. In this example, the electrons in electron beam  715  can be attracted to the positively-charged conductive build piece  711  and can bend.  FIG. 7  shows a zero field beam  719 , which represents the path the electron beam would take in a zero electric field to hit a target spot  721 . The amount of bending of energy beam  715  can be determined from the strength of the electric field. Therefore, deflector  717  can compensate for the predicted amount of beam bending and can hit target spot  721  by aiming energy beam in a different direction than zero field beam  719 , as shown in  FIG. 7 . 
       FIG. 8  illustrates an exemplary embodiment of an electrical system including a beam compensation system. Like the example of  FIG. 7 , an electrical system  800  can include a voltage source  801  and a voltage source  803 . Voltage source  803  can be applied to an electron beam source  813  as the acceleration voltage used to create an electron beam  815 , which can be applied by a deflector  817  to fuse powder. Voltage source  801  can apply a voltage between an anode of electron beam source  813  and a conductive build plate  805  through an opening in a build floor  807 . Conductive build plate  805  and build floor  807  can support a powder bed  809  and a conductive build piece  811 . Conductive build plate  805  can be electrically connected to conductive build piece  811 , such as being fused to the build piece, and accordingly, positive charge can collect on the build plate and on the conductive build piece to create an electric field similar to the example of  FIG. 3 . For the purpose of clarity, the electric field lines are not shown in  FIG. 8 . 
     Electrical system  800  can include a system with additional structures that can be charged to provide further scatter reduction. In this example, the additional structures can include shields  819  and  820 , which can be connected to the negative terminal of voltage source  801 . A negative voltage can cause negative charge to collect on shields  819  and  820 , which can repulse the negatively charged powder particles in the powder layer of powder bed  809 . In other words, the additional charged structures can create an electric field that causes a force between the charged powder particles and the powder layer that pushes the charged powder particles toward the powder layer. In this way, for example, charged powder particle scatter may be further reduced. In various embodiments, the additional structures can be arranged symmetrically around a normal axis extending between the deflector and the powder material support structure. In this way, for example, a deflection of electron beam  815  may be minimized. In various embodiments, for example, a single shield can include a ring of conductive material symmetrically surrounding a normal axis extending between the deflector and the build plate. A constant voltage source can be applied to the ring. The shape of the ring can be, for example, circular, rectangular, a torus, etc. In various embodiments, the shape of the ring can mimic the shape of the surface of the powder bed. 
       FIG. 9  is a flow chart of an exemplary embodiment of a method of reducing powder scatter in a PBF system. The PBF system can support ( 901 ) a layer of powder material on a structure. For example, a powder layer can be deposited on the top surfaces of a powder bed and one or more build pieces, and the powder bed and the one or more build pieces can be supported by a build plate. The PBF system can generate ( 902 ) an energy beam. For example, the PBF system can include an electron beam source that generated an electron beam. The PBF system can scan ( 903 ) the energy beam to fuse an area of the powder material in the layer. For example, the PBF system can include a deflector that deflects the electron beam to scan the beam across the powder layer. The energy beam can electrically charge the particles of powder. The PBF system can generate an electrical force between the structure and the charged particles of powder. For example, the PBF system can include an electrical system that applies a voltage between an electron beam source and a structure, such as the build floor, the build plate, the build piece, etc., that creates an electric field resulting in an electrostatic force that attracts the charged particles of powder to the powder layer. In this way, for example, charged powder scatter may be reduced or eliminated. 
     The previous description is provided to enable any person skilled in the art to practice the various aspects described herein. Various modifications to these exemplary embodiments presented throughout this disclosure will be readily apparent to those skilled in the art. Thus, the claims are not intended to be limited to the exemplary embodiments presented throughout the disclosure, but are to be accorded the full scope consistent with the language claims. All structural and functional equivalents to the elements of the exemplary embodiments described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are intended to be encompassed by the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. No claim element is to be construed under the provisions of 35 U.S.C. § 112(f), or analogous law in applicable jurisdictions, unless the element is expressly recited using the phrase “means for” or, in the case of a method claim, the element is recited using the phrase “step for.”