Patent Publication Number: US-2021178520-A1

Title: Composite forming system combining additive manufacturing and forging and methods for same

Description:
TECHNICAL FIELD 
     The invention relates to the field of additive manufacturing technology, and in particular to a composite forming system and method combining additive manufacturing and forging. 
     BACKGROUND 
     Additive manufacturing technology is an emerging technology for material processing that is rapidly developing. At present, the mainstream additive manufacturing usually achieves metallurgical bonding of metal materials through the “melting-solidification” method, which is characterized by using a high-energy beam such as a laser beam, an electron beam or an arc beam as a heat source to melt the synchronously fed metal material, such as metal powder, metal wire, and so on, which are stacked in layers, whereby parts are manufactured by surfacing, and the internal microstructure of the obtained parts is a solidified structure. 
     Compared with the conventional forged structure, the solidified structure obtained by the above-mentioned “melting-solidification” method produces crystals that are very coarse with obvious directionality, therefore in a general sense, it is difficult to achieve comprehensive performance comparable to that of a forged material. In order to improve the mechanical properties of the obtained parts and reduce internal defects, a method of combining the molten deposition additive with thermomechanical processing has been gradually developed, that is, material deposition and metallurgical bonding are achieved by melting-solidification, thereafter rolling, shock processing and other treatments are used to refine the grains and improve internal quality. 
     Although the method of melting combined with forging can improve the internal quality as well as enhance performance to some extent, in this composite processing method, due to the high complexity of the process and the equipment, as well as due to the rapid solidification and cooling rate, the forging condition which includes the temperature and other parameters cannot be effectively controlled, thus affecting the scope of application of the materials as well as the effect of forging. 
     Therefore, new technologies are needed to solve at least one of the above problems. 
     SUMMARY 
     The objective of the present invention is to provide a composite forming system combining additive manufacturing and forging as well as its methods. 
     In one aspect, embodiments of the present invention relate to an additive manufacturing system comprising a material conveyor, an energy source, and a micro-forging device. The material conveyor is configured to convey material. The energy source is configured to direct an energy beam toward the material, the energy beam fuses at least a portion of the material to form a solidified portion. The micro-forging device is movable along with the material conveyor for forging the solidified portion, wherein the micro-forging device comprises a first forging hammer and a second forging hammer, the first forging hammer is configured to impact the solidified portion to generate a first deformation, and the second forging hammer is configured to impact the solidified portion to generate a second deformation greater than the first deformation. 
     In another aspect, embodiments of the present invention relate to an additive manufacturing method. The method comprises: feeding a material via a material conveyor to a platen; directing an energy beam towards the material to fuse at least a portion of the material to form a solidified portion; and forging the solidified portion by: moving a micro-forging device comprising a first forging hammer and a second forging hammer, along with the material conveyor; impacting the solidified portion with the first forging hammer to generate a first deformation; and impacting the solidified portion with the second forging hammer to generate a second deformation greater than the first deformation. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       To read the following detailed description with reference to the accompanying drawings can help understand the features, aspects and advantages of the present invention, where: 
         FIG. 1  is a schematic view of a composite forming system in accordance with one embodiment of the present invention. 
         FIG. 2  shows a hammer device suitable for use in the real-time micro-forging device of the composite forming system in  FIG. 1 . 
         FIG. 3  shows a simple rail structure suitable for use with the hammer assembly in  FIG. 2 . 
         FIG. 4  shows a linear guide structure suitable for use with the hammer assembly in  FIG. 2 . 
         FIG. 5  shows a transmission mechanism that can drive two of the eccentrics of the hammer assembly in  FIG. 2  using a single motor. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     “Comprise”, “include”, “have”, and similar terms used in the present application are meant to encompass the items listed thereafter and equivalents thereof as well as other additional items. Approximating language in the present application is used to modify a quantity, indicating that the present invention is not limited to the specific quantity, and may include modified parts that are close to the quantity, acceptable, and do not lead to change of related basic functions. 
     In the specifications and claims, unless otherwise clearly indicated, no limitation is imposed on singularity and plurality of all items. Unless otherwise clearly indicated, the terms “OR”, “or” do not mean exclusiveness, but mean at least one of the mentioned item (such as ingredients), and include a situation where a combination of the mentioned exists. 
     “Some embodiments” and the like mentioned in the present application specification represent that specific elements (such as a characteristic, structure, and/or feature) related to the present invention are included in at least one embodiment described in the specification, and may or may not appear in another embodiment. In addition, it should be understood that the invention elements can be combined in any manner. 
     Embodiments of the present invention relate to an additive manufacturing system and its methods, comprising an additive manufacturing device for forming an object layer-by-layer by additive manufacturing techniques, and a micro forging device used for real-time micro-forging by matching the object being formed by the additive manufacturing device synchronously layer-by-layer. Wherein the additive manufacturing device may comprise: a platen provided to support the object being formed, a material conveyor configured to feed material onto the platen or the object being formed, and an energy source configured to provide an energy beam, which directs the energy beam toward the material when it is being fed and melts it to form a solidified portion. Specifically, the real-time micro-forging device is movable synchronously with the material conveyor for forging the solidified portion after the material conveyor. The real-time micro-forging device comprises a first forging hammer and a second forging hammer, the first forging hammer being configured to pre-forge the solidified portion and generate a first deformation, the second forging hammer being configured to forge the pre-forged solidified portion and generate a second deformation greater than the first deformation 
       FIG. 1  shows a schematic diagram of a composite forming system  100  in accordance with one embodiment of the present invention. As shown in  FIG. 1 , the composite forming system  100  comprises an additive manufacturing device  110  and a real-time micro-forging device  140 . Of which, the additive manufacturing device  110  is used to form a target object layer-by-layer, specifically comprising a platen  112 , a material conveyor  114 , and an energy source  116 . The platen  112  is used to support the object  200  being formed. The material conveyor  114  is used to feed material  115  to the platen  112  or the object  200  being formed. The energy source  116  is used to provide an energy beam  118  that, when the material  115  is sent to the platen  112  or object  200 , causes the energy beam  118  to be directed toward the material  115  and melt it, whereby the molten material rapidly solidifies to form a solidified portion and become part of the object being formed. The real-time micro-forging device  140  is movable synchronously with the material conveyor  114  for forging the formed solidified portion in real-time after the material conveyor  114 . 
     The energy source  116  can be any device or equipment capable of providing an energy beam suitable for additive manufacturing. Specific examples of the energy beam include, but are not limited to, a laser beam, an electron beam, and an arc beam. The material  115  is typically delivered in the form of a powder or wire (e.g., metal powder, wire, etc.). The material conveyor  114  may comprise a powder feed nozzle for conveying powder material, or a wire feeding device for conveying the wire. In some embodiments, the material conveyor  114  comprises a powder feed nozzle or wire feed device that is coaxial with the energy beam. For example, in the embodiment illustrated in  FIG. 1 , the material conveyed by the material conveyor  114  is in powder form and comprises a powder feed nozzle  120  coaxial with the energy beam  118 . Specifically, the powder feed nozzle  120  is provided with a coaxial powder feeding passage and an energy beam passage, and a central axis of the powder flow formed by the powder material flowing in the powder feeding passage substantially coincides with a central axis of the energy beam. By coaxial arrangement, it is possible to provide a stable and uniform concentration of powder flow while reducing mechanical interference during processing. In other embodiments, the material conveyed by the material conveyor  114  may be in the form of a wire, and the material conveyor  114  may comprise a wire feeding device that is coaxial the with energy beam  118 . 
     In some embodiments, the real-time micro-forging device  140  comprises two or more forging hammers, the hammers are able to control parameters such as respective forging force and hammering frequency independently of each other. In the embodiment shown in  FIG. 1 , the real-time micro-forging device  140  comprises a first forging hammer  141  and a second forging hammer  142 , the first forging hammer  141  being configured to pre-forge the solidified portion and generate a first deformation, the second forging hammer  142  being configured to forge the pre-forged solidified portion and generate a second deformation. The second deformation may be made by controlling parameters of the first and second forging hammers, such as causing at least one of the forging force and the hammering frequency of the second forging hammer  142  to be greater than the first forging hammer  141 , resulting in the second deformation being greater than the first deformation. In some embodiments, the second forging hammer  142  may be made higher in frequency compared to the first forging hammer, for example, the first forging hammer  141  may have a pre-forging frequency of 2 Hz to 10 Hz, while the second forging hammer  142  has a forging frequency of 10 Hz to 50 Hz. 
     In some embodiments, the deformations generated by each forging hammer can be controlled, and the total deformation generated by the entire real-time micro-forging device  140  can also be controlled, for example, the total deformation can be controlled to be no greater than a range of 50%. In some specific embodiments, the first deformation can be controlled within the range of 5% to 15%, and the second deformation can be controlled within the range of 15% to 35%. 
     In some embodiments, the real-time micro-forging device  140  may further comprise more forging hammers, for example, further comprising a third forging hammer (not shown) configured to perform further forging after the solidified portion being forged by the second forging hammer  142 , and generate a third deformation greater than the second deformation. 
     In some embodiments, the real-time micro-forging device  140  is movable relative to the additive manufacturing device  110 , thereby adjusting its distance from the center of the molten pool (the location at which the material is melted). For example, in some specific embodiments, the real-time micro-forging device  140  is movable relative to the material conveyor  114  between a hot forging position and a cold forging position, wherein, when the real-time micro-forging device  140  is located at the hot forging position, the first forging hammer  141  performs pre-forging at a position of 2 mm to about 9 mm from a molten pool, and when the real-time micro-forging device  140  is located at the cold forging position, the first forging hammer  141  performs pre-forging at a position greater than 9 mm from the molten pool. In some embodiments, when the real-time micro-forging device  140  is located at the cold forging position, the real-time forging (including the pre-forging performed by the first forging hammer  141  and the forging performed by the second forging hammer  142 ) is performed at a temperature ranging from 30% to 50% of the melting point of the material. When the real-time micro-forging device  140  is located at the hot forging position, the real-time forging is performed at a temperature ranging from 60% to 80% of the melting point of the material. 
     The composite forming system  100  may comprise control devices (not shown) to realize control of the additive manufacturing device  110 , the real-time micro-forging device  140 , and other devices in the system, including but not limited to: control of the relative position of the real-time micro-forging device  140 , control of the motion parameters of multiple forging hammers. 
     In some specific embodiments, the control device can adaptively adjust the distance to the center of the molten pool based on the energy beam used by the additive manufacturing device  110 . When the energy beam is an arc beam, the real-time micro-forging device  140  is located at the cold forging position, the first forging hammer head  141  performs pre-forging at a position greater than 9 mm from the molten pool, the real-time forging (including the forging performed by the first forging hammer  141  and the forging performed by the second forging hammer  142 ) is performed at a temperature ranging from 30% to 50% of the melting point of the material. When the energy beam is a laser beam or an electron beam, the first forging hammer  141  performs pre-forging at a position 2 mm to 9 mm from the molten pool, the real-time micro-forging device  140  is located at the hot forging position, the real-time forging is performed at a temperature ranging from 60% to 80% of the melting point of the material. For example, for a nickel-based alloy having a melting point of about 1,600° C., the cold forging is generally performed at a temperature ranging from 480° C. to 800° C., and the hot forging is generally performed at a temperature ranging from 960° C. to 1,280° C. 
     The composite forming system  100  may further comprise a real-time polishing device  160  that can be moved synchronously with the real-time micro-forging device  140  by following the real-time micro-forging device  140 , to perform real-time polishing of the solidified portion after being forged by the real-time micro-forging device  140  and eliminate unevenness resulting from forging, thereby facilitating material stacking and additive manufacturing for the subsequent layer. The polishing device may comprise a micro-grinding wheel or a micro-milling cutter to smooth the forged portion. In some specific embodiments, the additive manufacturing device  110 , the real-time micro-forging device  140 , and the real-time polishing device  160  are sequentially arranged, such that the materials melted at the molten pool may be forged by a plurality of hammers arranged in sequence after solidification, to repeat the steps of melting-solidification-multiple forging-polishing after polishing to obtain the next layer. 
     In some embodiments, the additive manufacturing device  110 , the real-time micro-forging device  140 , and the real-time polishing device  160  are connected by a certain connecting mechanism  180 . The arrangement of the connecting mechanism  180  enables relative motion and synergy between the devices  110 ,  140 ,  160 . The connecting mechanism comprises, but is not limited to, a connecting rod, a bracket, a sliding device, and so on. 
     The composite forming system  100  is widely applicable to various materials for additive manufacturing, and is particularly suitable for high-temperature alloy materials such as nickel-based and cobalt-based alloys, whose mechanical properties are not substantially degraded in a use environment below 650° C. 
       FIG. 2  shows a hammer assembly  244  suitable for use in the real-time micro-forging device of the composite forming system  100 , comprising a forging hammer  245  and corresponding auxiliary mounts and drive mechanisms. As shown in  FIG. 2 , the hammer  245  is mounted to the base  247  by a hammer mount that is coupled to a pair of symmetrically disposed slidable brackets  248 ,  249 . The slidable brackets  248 ,  249  are able to slide up and down respectively along the guide rails (not visible in  FIG. 2 , only one side of the rail is visible in  FIG. 3 ) formed on the fixed bracket  252  when being driven by the eccentrics connected thereto (not visible in the drawings, respectively under the outer covers  250 ,  251 ), thereby causing the hammer  245  to vibrate up and down at a certain frequency and amplitude. The eccentrics under the outer covers  250 ,  251  are respectively driven by motors  253 ,  254  that act as power sources, and the motors  253 ,  254  may be stepper motors or servo motors. In the embodiment shown in  FIG. 2 , the drive mechanism comprising the slidable bracket  248 , the eccentric under the outer cover  250 , the motor  253  and the guide rail (not visible in  FIG. 2, 255  in  FIG. 3 ) as well as the drive mechanism comprising the slidable bracket  249 , the eccentric under the outer cover  251 , the motor  254  and the guide rail (not visible in the drawing) are symmetrically disposed on both sides of the fixed bracket  252 , and the symmetrically arranged driving mechanisms act together to drive and generate a stable and controllable vibration. 
       FIG. 3  shows a simple rail structure, the rails (only one side of the rail  255  is visible) are directly in contact with the slidable brackets  248 ,  249 , the structure is simple and suitable for the vibration of the hammer at a small frequency and amplitude. In other embodiments, a sliding member such as a slider may be provided on the guide rail to mount the slidable bracket to the sliding member, and to cause the sliding member to slide along the guide rail. For example,  FIG. 4  shows a linear guide rail  356  having a slider  357  along which it can slide, the slidable bracket  248  or  249  can be mounted on the slider  357 , such a linear guide rail with the slider is more stable and reliable, therefore it is more suitable for the case where the hammer vibrates at a higher frequency and a greater amplitude. 
     The hammer assembly  244  can be used as any of the forging hammers in the composite forming system  100  shown in  FIG. 1 , comprising but not limited to the first hammer  141  and the second forging hammer  142 , and the hammer assembly  244  can be connected to other devices in the system, such as additive manufacturing devices and real-time polishing devices, through a structure such as a connecting rod. 
       FIG. 5  shows a transmission mechanism  400  that can drive two of the eccentrics of the hammer assembly  244  in  FIG. 2  using a single motor, the transmission mechanism  400  comprising a worm  401 , a main turbine  403  that engages with the worm  401 , the slave turbines  405  and  406  that engage with the main turbine  403 , the forward turbine  407  that engages with the slave turbine  405 , and the reverse turbine  408  that engages with the slave turbine  406 . Of which, the main turbine  403  comprises gears that engage with the worm  401 , as well as left and right hand gears that engage with the slave turbines  405  and  406 , respectively. The worm  401  can be coupled to and driven by a motor, the forward turbine  407  and the reverse turbine  408  can be respectively coupled to two eccentrics of the hammer assembly  244  shown in  FIG. 2 , and thus is able to drive the two eccentrics through the single motor connected to the worm  401 , which avoids synchronization problems that may occur with the use of two motors. 
     Since the real-time micro-forging device comprises two or more forging hammers, each of the layers formed by the additive manufacturing can be hammered by the hammers several times, which can solve the problem of the previous layer remelting due to the heat input from the forming process of the subsequent layer to a certain extent, which may occur during the layer-by-layer stack forming process. 
     While the present invention has been described with reference to specific embodiments thereof, it will be understood by those skilled in the art that many modifications and variations can be made thereto. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and variations insofar as they are within the true spirit and scope of the invention.