Metal droplet formation using multiple plasma arcs

Abstract

Systems and methods for controlling droplet properties in an additive manufacturing process are disclosed. The systems may be used for 3D printing. The method includes setting at least one parameter for a plurality of plasma arcs, applying the plasma arcs in succession to the tip of a feedstock to form a metal droplet, and ejecting the metal droplet from the feedstock towards a build platform, the ejected metal droplet having at least one desired property based on the at least one set parameter.

Description

[0001] METAL DROPLET FORMATION USING MULTIPLE PLASMA ARCS

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS

[0003] The present application claims the benefit of and priority to United States Provisional Application No. 63 / 689,814, filed on September 2, 2024, and is a continuation in part of PCT Application No. PCT / US2025 / 036680, filed on July 7, 2025; U.S. Patent

[0004] Application No. 19 / 011,465, filed on January 6, 2025; and U.S. Patent Application No. 18 / 725,638, filed on June 28, 2024. The entire disclosure of each of these applications is hereby incorporated by reference as if set forth in its entirety herein.

[0005] FIELD

[0006] Embodiments of the present disclosure relate to devices, systems, methods and processes for controlling properties of molten metal droplets using multiple plasma arcs for additive manufacturing, layered creation of objects and parts, 3D printing or liquid metal printing.

[0007] BACKGROUND

[0008] Additive manufacturing encompasses a wide range of processes for producing objects layer-by-layer from digital models, enabling the fabrication of complex geometries and customized parts. Additive manufacturing may form parts using a variety of materials, including polymers, composites, ceramics, and metals. The properties of the fabricated objects, such as mechanical strength, thermal conductivity, surface finish, and chemical resistance, may be dependent on the properties of the constituent materials.

[0009] Various techniques may be used for forming metal parts using additive manufacturing. Conventional approaches often rely on sintering metal powders at elevated temperatures and / or under high pressures to fuse particles together into a solid obj ect . In such processes , the composition of the powder feedstock may significantly inf luence the quality and properties of the finished product . For example , controlled mixtures of different metal powders may be used to produce obj ects having targeted alloy compositions or graded material properties .

[0010] More recent advances involve liquid metal printing, in which molten metal droplets are used to build up 3 dimensional ( 3D) parts and obj ects by depositing droplets onto a build platform in layers . For example , feedstock material ( e . g . , metal wires ) may be heated to form metal droplets , which are then separated and deposited onto the build platform . A variety of heat sources may be used to heat the feedstock material . For example, a plasma arc may be formed between two electrodes and applied to the feedstock material , which may cause the feedstock material to melt and form a metal droplet .

[0011] Liquid metal printing offers several advantages over traditional manufacturing techniques such as machining, casting, and powder-based additive manufacturing . For example , forming metal droplets enables highly efficient material usage with minimal waste , as feedstock can be directly converted into part material without the formation of scrap . Additionally, the architecture of the manufacturing system can be simpler and more compact than traditional systems such as laser or electron beam machines , leading to lower equipment costs and energy consumption .

[0012] Accordingly, a need exists for controlling properties of molten metal droplets in liquid metal printing . SUMMARY

[0013] This summary is provided to introduce a selection of concepts in a simpli fied form that are further described below in the Detailed Description section . This summary is not intended to identi fy or exclude key features or essential features of the claimed subj ect matter, nor is it intended to be used as an aid in determining the scope of the claimed subj ect matter .

[0014] In one aspect, the techniques described herein relate to a method for controlling droplet properties in an additive manufacturing process , the method including : setting at least one parameter for a plurality of plasma arcs ; applying the plasma arcs in succession to the tip of a feedstock to form a metal droplet ; and ej ecting the metal droplet from the feedstock towards a build platform, the ej ected metal droplet having at least one desired property based on the at least one set parameter .

[0015] In some embodiments , the at least one set parameter controls the amount of energy imparted to the droplet .

[0016] In some embodiments , the parameter includes at least one of a number of the plasma arcs , a delay between successive plasma arcs , a duration of the plasma arcs , a polarity of the plasma arcs , an applied current of the plasma arcs , or an applied voltage of the plasma arcs .

[0017] In some embodiments , at least one plasma arc is applied after a delay from a preceding plasma arc .

[0018] In some embodiments , the method further includes imparting additional thermal energy to the droplet after it has been ej ected from the feedstock . In some embodiments , additional thermal energy is applied using at least one of a plasma arc, an arc bridging electrodes , a laser or a source of focused radiative energy .

[0019] In some embodiments , the method further includes applying additional thermal energy to the build platform prior to the landing of the droplet in an area where the droplet is expected to land .

[0020] In some embodiments , additional thermal energy is applied using at least one of a plasma arc, an arc bridging electrodes , a laser or a source of focused radiative energy .

[0021] In some embodiments , the feedstock is moving relative to the plasma arcs .

[0022] In some embodiments , the parameter is set based on at least one of a property of the feedstock or a property of the ambient atmosphere .

[0023] In some embodiments , the parameter is updated based on at least one of the following being achieved : a desired sleeve length, a desired melting level , or a desired energy level .

[0024] In some embodiments , the desired property includes at least one of a desired droplet temperature , a desired droplet velocity, or a desired droplet si ze .

[0025] In some embodiments , at least one arc is applied using a variable current .

[0026] In some embodiments , at least one arc is applied before acceleration of the feedstock and at least one arc is applied during the acceleration of the feedstock . In some embodiments , the method further comprises applying additional thermal energy to the tip of the feedstock after ej ecting the metal droplet .

[0027] In another aspect, the techniques described herein relate to a system for controlling droplet properties in an additive manufacturing process , the system including : a controller configured to set at least one parameter for a plurality of plasma arcs ; and at least one electrode configured to apply the plasma arcs to the tip of a feedstock such that a metal droplet is formed and ej ected from the feedstock towards a build platform, wherein the ej ected metal droplet has at least one desired property based on the at least one set parameter .

[0028] In some embodiments , the at least one set parameter controls the amount of energy imparted to the droplet .

[0029] In some embodiments , the parameter includes at least one of a number of the plasma arcs , a delay between successive plasma arcs , a duration of the plasma arcs , a polarity of the plasma arcs , an applied current of the plasma arcs , or an applied voltage of the plasma arcs .

[0030] In some embodiments , at least one plasma arc is applied after a delay from a preceding plasma arc .

[0031] In some embodiments , the system further includes a source of thermal energy configured to impart additional thermal energy to the droplet after it has been ej ected by the feedstock .

[0032] In some embodiments , the source of thermal energy is a plasma arc generator, a pair of electrodes configured to generate a bridging arc, a laser or a source of focused radiative energy . In some embodiments , the system further includes at least one sensor configured to collect sensor data during the application of the plasma arcs .

[0033] In some embodiments , the sensor includes at least one of an optical sensor, a microphone , or an impact sensor .

[0034] BRIEF DESCRIPTION OF THE FIGURES

[0035] For a better understanding of the present disclosure , reference is made to the accompanying drawings , which are incorporated herein by reference and in which :

[0036] FIG . 1 shows a system for forming molten metal droplets according to one embodiment ;

[0037] FIG . 2 shows a printhead according to one embodiment ;

[0038] FIGs . 3A &3B show a printhead according to another embodiment ;

[0039] FIG . 4 shows a timeline of an arc sequence according to one embodiment ;

[0040] FIG . 5 shows a system for forming molten metal droplets according to another embodiment ; and

[0041] FIG . 6 shows a flowchart of a method for forming metal droplets according to an embodiment .

[0042] DETAILED DESCRIPTION

[0043] As described above, molten metal droplets may be formed to print a metal part in a liquid metal printing process . In some embodiments , the printing process may include melting feedstock, such as the tip of a feedstock wire, within the time window of a single droplet-making cycle . The droplet may be heated to a target temperature in a controlled manner and reliably separated from the feedstock material so that the droplet may be accurately positioned on a desired spot of a build bed .

[0044] FIG . 1 shows a system for forming molten metal droplets . The molten metal droplets may be used to build up 3 dimensional ( 3D) parts and obj ects by dispensing droplets onto a build platform in layers .

[0045] The system may comprise one or more metal wire sources 1 . The metal wire sources 1 may be metal microwire cartridges , spools and / or supplies . In embodiments where more than one metal wire source 1 is employed, the metal wire sources 1 may contain the same or dif ferent types of metal microwire . A printhead 2 may be in communication with the metal wire sources 1 . The printhead 2 may generate molten metal droplets 3 that are ej ected towards a build platform 4 on which metal parts are created from layers .

[0046] A controller 5 , such as a computer, server, dedicated microcontroller and / or other suitable processing unit , may supply instructions to the system . The controller 5 may be directly attached to the system or may communicate through a network or the internet .

[0047] The instructions from the controller 5 to the system may be derived from the desired part to be created . The desired part may be sliced into a plurality of cross-sectional areas , each corresponding to a respective one of the layers by which the apparatus will build up the part .

[0048] The metal microwire 7 may be in the range of 50 to 3000 micrometers in diameter . The advancement of the metal microwire 7 from the metal wire source 1 to the printhead 2 may be achieved using a piezo actuator, a stepper motor and / or a voice-coil . In some embodiments , there may be a single actuator to advance the metal microwire . In other embodiments , multiple actuators working together may be used .

[0049] The printhead 2 may contain a single molten metal droplet generator or an array of molten metal droplet generators , each being supplied with the same type of metal microwire or di f ferent types of metal microwire . The molten metal droplet generators may generate metal droplets using any suitable heat source , such as lasers , induction coils , plasma arcs , electron beams , and / or electromagnetic fields .

[0050] In some embodiments , the printhead 2 may form a plasma arc between two electrodes by applying an electric potential across the gap of the electrodes . The voltage applied to the electrodes may be an AC or DC voltage . The magnitude of the voltage may be determined based on the distance between the electrodes , the thickness of the metal microwire 7 , and / or the type of metal used . The voltage may be applied to one electrode or both electrodes . Those skilled in the art may readily determine the appropriate magnitude of the voltage based on these parameters . The plasma arc may be hot enough to melt the metal microwire 7 from solid to liquid . The tip of the metal microwire 7 may be advanced into the plasma arc, which may heat and transition the metal microwire 7 to liquid state .

[0051] The printhead 2 may ej ect molten metal droplets 3 towards a build platform 4 through use of the molten metal droplet generators . The printhead 2 may be capable of ej ecting droplets at a maximum frequency . The minimum time between droplets may be referred to as a droplet generation cycle . The printhead 2 may be capable of skipping one or multiple droplets , also referred to as drop on demand . In the XY plane , the printhead 2 and build platform 4 may move relative to each other either in a vector, tool-path kind of traj ectory or in a rastering scanning type of motion . The ej ected molten metal droplets 3 may be laid down in a layer according to the instruction sent by the control ler 5 . As noted above, the 3-dimensional part or obj ect is built up from multiple layers . The printhead 2 and the build platform 4 may also more relative to each other in the Z direction .

[0052] In some embodiments , the controller 5 may set various parameters for the system . The controller 5 may send the set parameters to other components of the system for forming metal droplets in accordance with the set parameters . For example , the controller 5 may set parameters for the droplet generators and send the parameters as an instruction to the droplet generators for forming plasma arcs . The droplet generators may be digitally addressable droplet generators capable of generating controlled arcs with user-defined or programmatically determined parameters .

[0053] FIG . 2 shows an expanded view of the printhead 2 . The printhead 2 includes a carriage 6 , which holds the metal microwire 7 . The carriage 6 is held by linear guides 11 , disposed on opposite sides of the carriage 6. The carriage 6 may be able to move relative to the linear guides 11 , such as in an up and down direction . In certain embodiments , the linear guides 11 limit the movement of the carriage to only one direction, such as up and down, left and right, or forward and backward . For example , a rod

[0054] 15 or other rigid member may be used to connect the carriage 6 to a rotating component 16 , such as a cylinder . The rotating component 16 may be driven by a motor at a fixed or variable RPM . The rod 15 is coupled to the rotating component 16 at a location that is not the axis of rotation . The center of the rotating component 16 is fixed, such that rotation of the rotating component

[0055] 16 causes the rod 15 to move in a reciprocating fashion, causing the carriage 6 to move relative to the linear guides 11 . The rotating component 16 may rotate at the maximum frequency of the printhead, such that the carriage 6 moves up and down for the generation of each droplet . In certain embodiments , the carriage 6 may move in the X or Y directions relative to the linear guides 11 .

[0056] Within the carriage 6 may be one or more actuators 8 to advance the metal microwire 7 through the carriage 6 . In some embodiments , the actuators 8 may be located on the carriage 6 . In other embodiments , the actuators 8 may be locator of f the carriage 6, in which case a flexible drive shaft may connect the carriage 6 to the actuators 8 . The actuators 8 may be piezo electric devices or motors . The metal microwire 7 is advanced in a way such that the distance advanced can be controlled .

[0057] A variety of di f ferent heat sources may be used to heat the tip of the metal microwire 7 to form the metal droplet 13 .

[0058] In one embodiment , light conduit 9, such as a fiber optic cable, may be disposed proximate the carriage 6 . Light , in the form of a laser beam, may be transmitted through the light conduit 9 . The light conduit 9 may have a curved portion such that the laser beam is focused at the end of the metal microwire 7 . The fiber optic cable may include a lens 10 to focus the emergent beam at the tip of the metal microwire 7 . The energy from the laser beam may cause the tip of the metal microwire 7 to transition from a solid to a liquid, so as to form a droplet .

[0059] In another embodiment , the heat source used to melt the tip of the metal microwire 7 might not be a laser or induction coil but a plasma arc . Embodiments that utili ze a plasma arc 19 are shown in FIGs . 3A-3B . Similar components have been given identical reference designators . In the embodiment shown in FIG . 3A, a plasma arc 19 is created between two electrodes 18 by applying an electric potential across the gap of the electrodes 18 which may or may not be filled with gas other than air, such as shield gas . The plasma arc 19 may be created by a pulse generator, which may comprise circuitry for generating a breakdown pulse . The voltage applied to the electrodes 18 may be an AC or DC voltage . The magnitude of the voltage may be determined based on the distance between the electrode 18 , the thickness of the metal microwire 7 and the type of metal used . The voltage may be applied to one electrode or both electrodes . Those skilled in the art may readily determine the appropriate magnitude of the voltage based on these parameters . The plasma arc 19 is hot enough to melt the metal microwire 7 from solid to liquid . The tip of the metal microwire 7 is advanced into the plasma arc 19 , which will heat and transition the metal microwire 7 to liquid state .

[0060] In the embodiment shown in FIG . 3B, the tip of the metal microwire 7 serves as one of the two electrodes 18 creating the plasma arc 19 which will also heat and transition the metal microwire 7 to liquid state . In certain embodiments , the metal microwire 7 is grounded and the electrode 18 is supplied with a voltage , which may be AC or DC voltage . Further, the voltage applied to the electrode 18 may be positive or negative . In other embodiments , this voltage may be applied to the metal microwire 7 . In yet other embodiments , voltages are applied to both the metal microwire 7 and the electrode 18 . These voltages may be AC or DC, positive or negative and may vary in magnitude .

[0061] In some embodiments , the heat source is designed such that the quantity and rate of heat energy applied to the tip of the metal microwire 7 is such that the metal microwire 7 above the tip remains a solid . In other embodiments , the metal microwire above the tip remains a solid due to active temperature management of the metal microwire 7 , such as via conduction or convection . In all embodiments, the droplet size is controlled by the distance the metal microwire 7 is advanced by the actuator 8. In some embodiments, the metal droplets 13 may have a diameter in the range of 150 to 3000 micrometers. Additionally, one or more droplets may be skipped by not advancing the metal microwire 7.

[0062] In certain embodiments, a hard stop 12 may be provided on the linear guide 11.

[0063] The metal droplet 13 may be separated from the tip of the metal microwire 7 through a momentum change. The momentum change may be achieved using a momentum change sequence. For example, the momentum change may be achieved by oscillating the carriage 6 in different directions. The droplet may separate after the carriage 6 moves in a first direction, decelerates, changes direction, and accelerates again in an opposite second direction. In some examples, the momentum change may be achieved using oscillation with a hard stop. The carriage 6 may move in a first direction and decelerate after striking a hard stop. The carriage 6 may then change direction and accelerate again. In some examples, the momentum change may be achieved using momentum transfer. The carriage 6 may receive a momentum in the desired direction of droplet movement and transfers that momentum to the molten metal droplet. The momentum change may impart a force to the metal droplet 13 that may be in excess of 10G. In some embodiments, the force is in excess of 100G. In some embodiments, the force applied to the metal droplet 13 may be on the order of 1000G or more, thus reducing the influence of gravity on the orientation of the droplet separation and subsequent trajectory to a minimum.

[0064] The properties of each individual droplet (e.g., size, temperature, velocity, drop path, kinetic energy, etc.) may significantly impact the properties of the formed part . For example , droplet properties may be selected based on the corresponding region in the printed part . Outer perimeter regions of the part may be formed from smaller or cooler droplets to improve surface finish . Interior regions may be formed from hotter, larger droplets to promote bonding strength and reduce porosity . In some embodiments , droplets may be cooled intentionally to create weaker metallurgical bonds , such as in support structures intended for easy removal . For example , weakly bonded interface layers for support structures may be formed using cooler metal droplets . Control over droplet properties may also be used to print complex geometries , such as overhangs or thin features , by adj usting adhesion and wetting behaviors at the impact site . As such, precise control over droplet formation and deposition may be beneficial for ensuring consistent and high- quality manufacturing processes .

[0065] One technique for forming the droplet includes applying a plasma arc to the feedstock to heat and melt the material ( e . g . , as shown in FIGs . 3A-3B ) . The droplet properties may depend on various factors related to the formation and separation of the droplets , including the parameters of the plasma arc such as the arc current, the arc duration, and the arc voltage established during breakdown of the surrounding atmosphere when the arc is initiated . The energy delivered by the plasma arc may be a function of the arc parameters .

[0066] One challenge in applying plasma arcs for forming metal droplets is oxidation of the molten droplet , which can prevent bonding to adj acent drops and degrade the integrity of the printed obj ect . While oxidation may be mitigated by using a pure noble metal or a noble metal alloy as the feedstock, such materials may limit the range of potential properties of the printed obj ect . Oxidation may also be mitigated by carrying out the arcing process in an inert atmosphere, such as an argon or nitrogen atmosphere . However, di f ferences in atmospheric properties may lead to premature or uncontrolled arcing to the base of the feedstock instead of its tip, thereby frustrating droplet formation .

[0067] Although the droplet formation rate may influence the throughput of the printing process , maximi zing the rate of energy delivery may not necessarily result in optimal print speed or quality . Energy delivery beyond a certain threshold may cause over-melting of the feedstock, leading to the formation of multiple uncontrolled droplets or even vapori zation of the feedstock .

[0068] To address these challenges , embodiments described herein include applying a controlled sequence of multiple plasma arcs to form metal droplets . Various arc parameters may be set to affect the properties of the formed metal droplets , such as a number of the plasma arcs , a delay between successive plasma arcs , a duration of the plasma arcs , a polarity of the plasma arcs , an applied current of the plasma arcs , and / or an applied voltage of the plasma arcs . By controlling the duration of an arc, for example, the arc may be maintained at the tip of the feedstock and kept away from the base of the feedstock . The application of multiple arcs may allow delivery of a desired amount of energy to the feedstock, thereby enabling melting without overmelting or vapori zation . Controlling the timing between arcs may allow the droplet to assume a desired geometry prior to deposition .

[0069] In some embodiments , the length of the sleeve ( defined as the sheath of ions generated by the plasma arc) may be controlled to influence the length of the melted feedstock and the resulting droplet size and geometry . The sleeve length can be controlled by setting any of the parameters described herein . Once a portion of the feedstock has melted, the molten zone may act as a sink for subsequent arcs , limiting sleeve growth and focusing thermal energy into a reduced volume , thereby enabling higher melt temperatures and / or faster melting cycles .

[0070] In some embodiments , the feedstock may be delivered through a ceramic carrier, a shaped carrier, and / or an electrostatically charged carrier to influence the sleeve length, rate of sleeve formation, melt temperature , droplet geometry, and / or arc termination point on the feedstock . For example , a ring electrode charged with the same polarity as the sleeve may halt sleeve formation at the electrode .

[0071] In some embodiments , at least three arcs may be applied to form a droplet . The first arc may be directed to the tip of the feedstock to melt a predetermined portion and form a sleeve . The first arc may be paused before the arc can dri ft toward the feedstock base or extend excessively into the feedstock body . The sleeve may begin to assume a droplet shape as a protodroplet before the second arc is applied . The second arc may be applied after a first delay to heat the protodroplet to a desired temperature while limiting further melting of the feedstock . A second delay after the second arc may permit surface tension and other forces to refine the geometry of the protodroplet . The droplet may be fully formed during the second delay . A third arc may be applied after the second delay to the fully formed droplet prior to its mechanical detachment .

[0072] In some embodiments , the arcs in the sequence may have di f ferent energy levels . For example, the second arc may have the largest energy level and the third arc may have the smallest energy level . An exemplary energy ratio among the arcs may be , for example , 1 : 2 . 5 : 0 . 5 . To illustrate, FIG. 4 shows a timeline of an arc sequence. The x-axis represents time and the y-axis represents the applied current strength for generating the plasma arcs in the arc sequence. The current strength may determine the energy level of each arc. The arc sequence may be divided into multiple time periods, such as time periods for applying a plasma arc and / or delays between plasma arcs. As shown, for example, the arc sequence may begin with a first arcing period 400 for applying a first arc. The first arcing period may be followed by a first delay 402, which in turn may be followed by a second arcing period 404 for applying a second arc. The current strength for the second arc may be different from that of the first arc. The second arcing period 404 may be followed by a second delay 406, which may be followed by a third arcing period 408 for applying a third arc. The current strength for the third arc may be different from that of the first arc and / or second arc.

[0073] In some embodiments, additional arcs may be applied (e.g., after the third arc) to adjust the drop path. In some embodiments, additional arcs may be used (e.g., before the first arc) to remove surface contaminants, stabilize the plasma attachment point, and / or partially preheat the feedstock to reduce the energy required in subsequent arcs.

[0074] In some embodiments, the arc parameters may be adjusted to form self-separating droplets. The droplets may be formed and detached through controlled surface tension. By adjusting the arc parameters and timing, the droplets may be induced to detach from the feedstock without requiring high momentum change. This may reduce stress on the printhead and improve droplet trajectory. In some embodiments, the self-separation may be controlled by adjusting mechanical parameters, such as the orientation of the printhead and / or feedstock, feedstock tension, and / or damping control .

[0075] In some embodiments, at least one arc parameter (e.g., the arc durations, arc delays, etc.) may be determined based on the feedstock properties and / or atmospheric properties. The feedstock properties may include, but are not limited to, material composition, hardness, thermal conductivity, electrical conductivity, melting temperature, oxidation rate, and / or surface condition. The atmospheric properties may include, but are not limited to, gas composition, breakdown voltage, thermal conductivity, temperature, humidity, and / or pressure.

[0076] In some embodiments, the arc parameters may be adjusted manually (e.g., by a user) and / or automatically (e.g., by a controller or other processing unit) . For example, a user may directly select a value for the arc parameter at an interface for a printing system. In some examples, the user may select a value for a property, such as a feedstock property or atmospheric property. The system may automatically adjust any arc parameter affected by the property.

[0077] In some embodiments, atmospheric properties may be automatically controlled, such as by regulating an enclosed build chamber. The system may use atmospheric control units (e.g., gas supply lines, valves, and / or sensors) to maintain a desired atmosphere, such as an inert atmosphere (e.g., argon, nitrogen, etc.) at a desired purity level. The system may adjust the atmospheric properties based on desired arc parameters and / or droplet properties.

[0078] In some embodiments, the desired atmosphere may be varied during different stages of the printing process. For example, the system may maintain an inert atmosphere for a portion of the printing process and a controlled, reactive atmosphere for another portion. The reactive atmosphere may be introduced before deposition of selected layers to promote surface oxide formation, alloying, and / or other desired surface modifications.

[0079] In some embodiments, feedstock properties may be determined without user input, such as by reading scannable indicia on feedstock spools to identify material type and adjust arc parameters accordingly.

[0080] In some embodiments, the arc parameters may be dynamically adjusted based on feedback received during the printing process. For example, a sensor may determine at least one property of the printing process in real time, such as arc properties, protodroplet properties, droplet properties, movement and vibration properties, and / or atmospheric properties. In some embodiments, if the property is outside an acceptable range, the arc parameters may be adjusted. For example, the collected property values may be compared to expected property values. If a deviation is detected, then the arc parameters may be adjusted. In some embodiments, if the property falls within a desired value or range, the arc parameters may be adjusted.

[0081] Any suitable sensor modality may be used to monitor the printing process, such as optical sensors, thermal sensors, photodiodes, accelerometers, gyroscopes, encoders, impact sensors, and / or vibration sensors. For example, a sensor (e.g., an optical sensor) directed towards the feedstock and / or electrode may detect the initiation of an arc and the formation of a sleeve. The system may terminate the arc once a desired property is achieved, such as a desired sleeve length, desired melting level, and / or desired energy output. For example, the sensor may determine that a desired energy output has been achieved based on known voltage and current values . The sensor may measure any subsequent arcs and terminate any of the subsequent arcs after a desired property is achieved . This closed-loop monitoring may allow for any number of arcs to be used to achieve the desired energy output .

[0082] In some embodiments , various sensors may be used to detect carriage movement and / or droplet delivery, such as microphones , accelerometers , gyroscopes , encoders , impact sensors , and / or vibration sensors . The system may dynamically adj ust arc parameters based on the detection . For example, microphones may detect acoustic signatures generated by plasma arc initiation, droplet detachment , and / or impact events on the build platform . Such acoustic data may be compared to expected data values corresponding to successful droplet formation and delivery . Deviations in the acoustic profi le may indicate arc instability, premature droplet detachment , and / or incomplete melting .

[0083] FIG . 5 shows another system for forming molten metal droplets . The system may include the printhead 2 , the controller 5 , a sensor array 500 , a user device 502 , and a user interface 504 . As described above , the printhead 2 may be configured to melt feedstock to form metal droplets and the controller 5 may be configured to supply instructions to the system .

[0084] The sensor array 500 may include various sensors for monitoring the system, such as sensors 506a and 506b. The sensors 506 may include any of the sensor modalities described herein . The sensor array 500 may be configured to collect sensor data during the printing process . The sensor data may be supplied to the controller 5, which may adj ust system parameters based on the sensor data, such as arc parameters .

[0085] The user device 502 may be any suitable device capable of presenting the user interface 504 to a user, such as an administrator . The user device 102 may be a smartphone , tablet

[0086] PC, laptop, smart TV, smartwatch, and / or any other type of device whether available now or invented hereafter . The user interface 504 may allow the user to input data for the system, such as user preferences , instructions , updates , and / or observations . For example , the user may input preferred arc parameters via the user interface 504 . The controller 5 may receive the input data from the user device 502 via the user interface 504 .

[0087] In some embodiments , a machine learning model may be configured to predict droplet properties based on input arc parameters . For example , the model may predict the geometry and si ze of a droplet based on selected arc parameters . In some embodiments , the model may be configured to output a set of recommended arc parameters based on input data, such as desired droplet properties , atmospheric properties , and / or feedstock properties . The model may be trained on historical printing data .

[0088] In some embodiments , the arc sequence may be applied during a momentum change sequence . As described above, momentum change sequences may be used to ej ect metal droplets towards the build platform . The arcs may be timed so that each arc is applied during a certain stage of a momentum change sequence . For example, the arc sequence may start before the feedstock begins moving . An initial arc may be applied to the stationary feedstock to begin forming a protodroplet . A second arc may be applied during the momentum change sequence , such as during a downward stage moving the feedstock towards the build platform . The second arc may be a higher energy arc that is applied while the droplet is not fully formed . This may prevent the movement from having unwanted ef fects on the geometry of the droplet . A third arc may be applied during a later stage , such as a deceleration stage . In some embodiments, the arc sequence may allow for selective drop-on-demand configurations. In such configurations, droplets may be formed only when required to (e.g., by a print pattern) . A printhead may forgo droplet formation during certain cycles, during which the feedstock may cool significantly. This may delay the time required to form the next droplet. Accordingly, in some embodiments, additional thermal energy may be applied to the feedstock after ejecting a metal droplet to maintain a steady thermal state, thereby reducing latency when droplet generation resumes. For example, a low-energy arc may be applied to feedstock during retraction stages (e.g., when the feedstock moves away from the build platform) and / or idle periods. The low-energy arc may not have sufficient energy to form a new droplet. The low-energy arc may prevent the feedstock from fully cooling between successive droplet cycles, thus increasing the throughput of the printing process .

[0089] In some embodiments, at least one arc may have a variable current. For example, a high initial current may be applied to form the arc (e.g., for the breakdown phase) . The current may then be reduced to a lower steady state to maintain a controlled melt at the tip of the feedstock. In some embodiments, a single arc with a variable current may be applied to function as a multiarc sequence without any delay overhead.

[0090] In some embodiments, multiple circuits may be used to generate the variable current. It may be difficult to use a single circuit to modulate a current across a wide ampere range. To address this, the system may use combinations of circuits in parallel, with each circuit handling within a narrower ampere range. For example, a first circuit may handle lower currents (e.g., 1-20 mA) , a second circuit may handle intermediate currents (e.g., 20-500 mA in parallel with the first circuit) , and a third circuit may handle higher currents ( e . g . , above 500 mA in parallel with the first circuit and second circuit ) . The required current value may be determined based on a printing pattern or arc parameter, and / or in real time based on feedback sensor data .

[0091] Other parameters af fecting droplet properties may include the spatial configuration of the printhead, the feed rate of the feedstock, the position ( e . g . , orientation, proximity) of the feedstock tip relative to the electrode , and / or motion of the feedstock relative to the electrode during the formation of the metal droplet . Such parameters may be adj usted to af fect droplet properties , either in combination with arc parameters or as an alternative to the arc parameters . In some embodiments , additional subsystems or actuators may further af fect droplet properties , such as mechanical vibration mechanisms or flow shaping devices .

[0092] In some embodiments , additional thermal energy may be imparted to the droplet using secondary heating mechanisms after the droplet has separated from the feedstock . For example , at least one arc or heating field may be positioned in the drop path of the droplet, such that the droplet traverses the arc and absorbs further thermal energy prior to impact . In some examples , a droplet may pass between a pair of electrodes that establish an arc across the drop path, allowing the droplet to bridge the arc and acquire additional energy . In some examples , focused radiation sources such as lasers or high-intensity lamps may be used to provide additional energy to droplets . The energy trans fer may be controlled by adj usting electrical and / or arc parameters . The energy trans fer may allow the droplet to maintain and / or raise its temperature while in-flight .

[0093] In some embodiments , the landing spot of the droplet at the build platform may undergo localized heating, such as by using additional arcs , lasers , resistive heating elements , and / or other heat sources . This may promote metallurgical bonding, particularly when the substrate temperature would otherwise be insufficient to promote fusion .

[0094] FIG . 6 shows a flowchart of a method for forming metal droplets in accordance with one embodiment . While FIG . 6 shows illustrative operations according to one embodiment , other embodiments may omit , add to , reorder, and / or modify any of the operations shown in FIG . 6 . Moreover, each of the operations depicted in FIG . 6 may be performed in any of the ways described herein . The operations shown in FIG . 6 may be performed by any of the illustrative systems described herein, such as the system shown in FIG . 1 .

[0095] Operation 600 may include setting at least one parameter for a plurality of plasma arcs . The parameter may be set by a controller, such as the controller 5 .

[0096] Operation 602 may include applying the plasma arcs in succession to the tip of a feedstock to form a metal droplet .

[0097] Operation 604 may include ej ecting the metal droplet from the feedstock towards a build platform . The ej ected metal droplet may have at least one desired property based on the set parameter, such as any of the properties described herein .

[0098] The present disclosure is not to be limited in scope by the specific embodiments described herein . Indeed, other various embodiments of and modi fications to the present disclosure , in addition to those described herein, will be apparent to those of ordinary skill in the art from the foregoing description and accompanying drawings . Thus , such other embodiments and modifications are intended to fall within the scope of the present disclosure . Furthermore , although the present disclosure has been described herein in the context of a particular implementation in a particular environment for a particular purpose , those of ordinary skill in the art will recognize that its usefulness is not limited thereto and that the present disclosure may be beneficially implemented in any number of environments for any number of purposes . Accordingly, the claims set forth below should be construed in view of the full breadth and spirit of the present disclosure as described herein .

Claims

CLAIMSWhat is claimed is:

1. A method for controlling droplet properties in an additive manuf cturing process, the method comprising: setting at least one parameter for a plurality of plasma arcs; applying the plasma arcs in succession to the tip of a feedstock to form a metal droplet; and ejecting the metal droplet from the feedstock towards a build platform, the ejected metal droplet having at least one desired property based on the at least one set parameter.

2. The method of claim 1 wherein the at least one set parameter controls the amount of energy imparted to the droplet.

3. The method of claim 1 wherein the parameter comprises at least one of a number of the plasma arcs, a delay between successive plasma arcs, a duration of the plasma arcs, a polarity of the plasma arcs, an applied current of the plasma arcs, or an applied voltage of the plasma arcs.

4. The method of claim 1 wherein at least one plasma arc is applied after a delay from a preceding plasma arc.

5. The method of claim 1 further comprising imparting additional thermal energy to the droplet after it has been ejected from the feedstock .

6. The method of claim 5 wherein additional thermal energy is applied using at least one of a plasma arc, an arc bridging electrodes, a laser or a source of focused radiative energy.7 . The method of claim 1 further comprising applying additional thermal energy to the build platform prior to the landing of the droplet in an area where the droplet is expected to land .8 . The method of claim 7 wherein additional thermal energy is applied using at least one of a plasma arc, an arc bridging electrodes , a laser or a source of focused radiative energy .9 . The method of claim 1 wherein the feedstock is moving relative to the plasma arcs .10 . The method of claim 1 wherein the parameter is set based on at least one of a property of the feedstock or a property of the ambient atmosphere .11 . The method of claim 10 wherein the parameter is updated based on at least one of the following being achieved : a desired sleeve length, a desired melting level , or a desired energy level .12 . The method of claim 1 wherein the desired property comprises at least one of a desired droplet temperature , a desired droplet velocity, or a desired droplet size .13 . The method of claim 1 wherein at least one arc is applied using a variable current .14 . The method of claim 1 wherein at least one arc is applied before acceleration of the feedstock and at least one arc is applied during the acceleration of the feedstock .15 . The method of claim 1 further comprising applying additional thermal energy to the tip of the feedstock after ej ecting the metal droplet .16 . A system for controlling droplet properties in an additive manufacturing process , the system comprising : a controller configured to set at least one parameter for a plurality of plasma arcs ; and at least one electrode configured to apply the plasma arcs to the tip of a feedstock such that a metal droplet is formed and ej ected from the feedstock towards a build platform, wherein the ej ected metal droplet has at least one desired property based on the at least one set parameter .17 . The system of claim 16 wherein the at least one set parameter controls the amount of energy imparted to the droplet .18 . The system of claim 16 wherein the parameter comprises at least one of a number of the plasma arcs , a delay between successive plasma arcs , a duration of the plasma arcs , a polarity of the plasma arcs , an applied current of the plasma arcs , or an applied voltage of the plasma arcs .19 . The system of claim 16 wherein at least one plasma arc is applied after a delay from a preceding plasma arc .20 . The system of claim 16 further comprising a source of thermal energy configured to impart additional thermal energy to the droplet after it has been ej ected by the feedstock .21 . The system of claim 20 wherein the source of thermal energy is a plasma arc generator, a pair of electrodes configured togenerate a bridging arc, a laser or a source of focused radiative energy .22 . The system of claim 16 further comprising at least one sensor configured to collect sensor data during the application of the plasma arcs .23 . The system of claim 22 wherein the sensor comprises at least one of an optical sensor, a microphone, or an impact sensor .

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