Plasma gas volumetric flow measurement and control system for metal-based wire-plasma arc additive manufacturing applications

Abstract

Systems and methods for adjusting the mass flow rate and monitoring the volumetric flow rate, adjusting the volumetric flow rate, monitoring the mass flow rate, and adjusting both the mass flow rate and the volumetric flow rate of gas to a plasma torch for a wire-plasma arc additive manufacturing process, and methods for producing metal objects by additive manufacturing using one or more of the systems are provided.

Description

Technical Field

[0001] Cross - Reference to Related Applications This patent application claims priority to U.S. Provisional Patent Application No. 62 / 948,148, filed on December 13, 2019, and also to U.S. Patent Application Publication No. 17 / 116,092, filed on December 9, 2020, both entitled "VOLUMETRIC PLASMA GAS FLOW MEASUREMENT AND CONTROL SYSTEM FOR METAL - BASED WIRE - PLASMA ARC ADDITIVE MANUFACTURING APPLICATIONS", the entire contents of which are incorporated herein by reference in their entirety.

[0002] The present invention generally relates to a system and method for controlling and consistently delivering a gas flow to a melting tool in an additive manufacturing process to provide a consistent force to a melt pool while the gas density varies due to mechanical and environmental factors.

Background Art

[0003] Structural metal parts made of titanium or titanium alloys have conventionally been made by casting, forging, or machining from billets. These techniques have many drawbacks, such as a large amount of expensive titanium metal material usage and a long lead time in shaping metal objects. In many cases, in casting, which can be used to produce objects that may be near - net - shape, the material quality typically degrades due to the inability to control the solidification and cooling rates. Tooling costs and the inability to produce objects with complex shapes are other drawbacks of the conventional methods.

[0004] A very dense physical object can be fabricated by additive manufacturing, a manufacturing technique also known as rapid prototyping, rapid manufacturing, freeform fabrication, and layered manufacturing. In additive manufacturing, near-net shape products are created by successively depositing materials layer by layer one at a time to yield a three-dimensional object. This additive manufacturing is in contrast to subtractive manufacturing, where a billet or block of material is machined by removing material to produce a final product.

[0005] In some additive manufacturing processes, a wire-arc welding process is used. This process is generally referred to as wire-arc additive manufacturing (WAAM). WAAM includes three different processes. In gas metal arc welding (GMAW), an electric arc formed between a consumable wire electrode that is substantially coaxial with the torch and the workpiece metal is used. Gas tungsten arc welding (GTWA) and plasma arc welding (PAW) differ from GMAW in that they can generate an ionized plasma using a non-consumable tungsten electrode and an inert gas to heat and melt a metallic material such as a metal wire for the purpose of forming a three-dimensional preform or workpiece. In gas tungsten arc welding and plasma arc welding, ionization can occur between the non-consumable negative (tungsten) electrode and the workpiece, either alone as a direct transfer arc or in combination with a pilot arc between the non-consumable negative (tungsten) electrode and the anode. The preform or substrate can function as the anode. Depending on the torch configuration and the relative position and orientation of the torch with respect to the workpiece, a plasma column that impinges on the molten pool can be produced.

[0006] In plasma arc welding applications for additive manufacturing, both the number of gas molecules per unit time and the gas volume per unit time are very important. The reason is that both factors affect the thermal characteristics of the plasma arc. In particular, the gas mass flow rate (the number of gas molecules per unit time) affects the ionization degree of the plasma arc (i.e., the number of ionized gas atoms relative to the total number of available gas atoms). The gas volume flow rate (the volume of gas per unit time) affects the kinetic energy of the plasma arc flow and the resulting pressure on the molten pool. The pressure that the plasma column can exert on the workpiece during formation can have a significant impact on layer uniformity and process reproducibility. The pressure of the plasma column can be affected by the control of the inert gas supplied to the torch. The gas flow control techniques currently used in metal-based wire-plasma arc additive manufacturing processes measure and control the mass flow rate, i.e., the number of gas molecules per unit time supplied to the plasma torch, by "assuming" standard conditions for the pressure and temperature of the supply gas. However, the density of the gas supplied to the torch can vary significantly due to environmental variations, either alone or in combination with factors that vary between machines.

[0007] As a result, the actual volume flow rate of the gas supplied at the torch and the resulting pressure that the plasma column can exert on the workpiece can vary significantly during manufacturing. These variations can lead to the formation of inconsistent products produced by metal-based wire-plasma arc additive manufacturing processes. SUMMARY OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION

[0008] Therefore, in the art, there is a need for an improved method of controlling the flow of an inert gas ionized into a plasma to a plasma torch for use in a metal additive manufacturing process. MEANS FOR SOLVING THE PROBLEM

[0009] Accordingly, the embodiments described herein are directed to systems and methods for controlling the flow of inert gas to a plasma torch, which can determine an actual volumetric flow rate and enable adjustment of the plasma arc pressure and melt pool dynamics for use in a metal-based wire-plasma arc additive manufacturing process. A system is provided for adjusting the mass flow rate of gas to the plasma torch and monitoring its volumetric flow rate. A system is provided for adjusting the volumetric flow rate of gas to the plasma torch and monitoring its mass flow rate. A system is provided for adjusting both the mass flow rate and the volumetric flow rate of gas to the plasma torch. The systems and methods can measure and / or control any gas density variations resulting from arc radiation disturbances, such as temperature variations in the gas hose or gas pipe, and can include a volumetric flow control element that can be located inside the production chamber near or at the plasma torch gas inlet for receiving the gas ionized into plasma by the plasma torch. The volumetric flow control element near or at the gas inlet of the plasma torch can also enable detection of a decrease in mass flow rate due to leaks or the like and can function as a secondary diagnostic sensor for mass flow rate.

[0010] The aim of the embodiments described herein is to provide a consistent force to the melt pool during a wire plasma arc additive manufacturing process, even if the gas density varies due to mechanical or environmental disturbances or both. In the embodiments, a consistent force can be achieved by controlling the volumetric flow rate of the gas in the plasma torch that forms the ionized gas or plasma. In some embodiments, the control of the volumetric flow rate of the gas in the plasma torch can be achieved by adjusting the mass flow rate of the gas ionized from the gas supply source, or by modifying the temperature or pressure of the gas or a combination thereof, or by adjusting the density of the gas ionized in the plasma torch by adjusting the temperature and / or pressure of the gas ionized in the plasma torch near or at the plasma torch gas inlet, or by a combination of adjusting the mass flow rate of the gas ionized by the gas supply in combination with the volumetric flow rate of the gas ionized by the plasma torch.

[0011] The object of the embodiments described in this specification is to improve the melt pool dynamics and thus the geometric shape and mechanical properties of the preforms produced by the metal-based wire-plasma arc additive manufacturing process, thereby improving the consistency and quality.

[0012] Another object of the embodiments provided in this specification is to exert a consistent plasma arc pressure (i.e., arc force per unit area of the melt pool) on the melt pool by maintaining the gas emission rate of the plasma arc from the nozzle of the plasma torch at the target emission rate at various density levels of the inert gas supplied to the plasma torch.

[0013] A system and method for controlling the flow of an inert gas ionized into a plasma to a plasma torch of an additive manufacturing apparatus are provided. This system can enable the adjustment of the plasma arc pressure exerted on the melt pool and thus can enable the correction of the melt pool dynamics during the shaping of an object using a metal-based wire-plasma arc additive manufacturing process.

[0014] A system for controlling the gas flow to the plasma torch of an additive manufacturing apparatus is provided. The system can include a source of inert gas, a supply manifold in fluid communication with the source of inert gas, a plasma torch including a gas inlet for receiving the inert gas from an inert gas line connected to the supply manifold and a gas ionization device electromagnetic field for ionizing the inert gas into a plasma. The system can include a sensing kit that can include a temperature measurement unit, a pressure measurement unit, and a mass flow measurement unit. Each unit can communicate with one or more sensing connectors connected to the position of the inert gas line between the supply manifold and the gas ionization device electromagnetic field. The system can also include a control valve in fluid communication with the gas supply manifold and for regulating the flow of the inert gas from the gas supply manifold.

[0015] The system can include a process master controller that communicates with a sensing kit. The system can include a part program that provides a mass flow setpoint or a volume flow setpoint or both a mass flow setpoint and a volume flow setpoint to the process master controller. The system can include a computing function executed by the process master controller, which can include a computing function for calculating the actual volume flow. The system can include a mass flow control function executed by the process master controller. The mass flow control function can compare the mass flow setpoint from the part program with the actual mass flow value from the mass flow measurement unit of the sensing kit, and can increase or decrease the mass flow of the inert gas and adjust either the control valve or the density control element or both the control valve and the density control element to reduce the difference between the mass flow setpoint and the actual mass flow value.

[0016] The system can include a volume flow control function executed by the process master controller. The volume flow control function can compare the volume flow setpoint from the part program with the calculated volume flow value from the computing function, and can increase or decrease the volume flow of the inert gas and adjust either the control valve or the density control element or both the control valve and the density control element to reduce the difference between the volume flow setpoint and the calculated volume flow value.

[0017] The system can include a mass flow control function and a volume flow control function executed by the process master controller. The mass flow control function can compare the mass flow setpoint from the part program with the actual mass flow value from the mass flow measurement unit of the sensing kit, and the volume flow control function can compare the volume flow setpoint from the part program with the calculated volume flow value from the computing function, and can adjust the control valve and the density control element to regulate both the mass flow and the volume flow of the inert gas fed to the gas ionization device electromagnetic field of the plasma torch.

[0018] The system can include combined mass flow rate and volume flow rate control functions executed by a process master controller. The mass flow rate and volume flow rate control functions compare the mass flow rate setpoint from the part program with the actual mass flow rate value from the mass flow rate measurement unit of the sensing kit, and the volume flow rate setpoint from the part program with the calculated volume flow rate value from the calculation function, and adjust the control valve and density control element to regulate both the mass flow rate and volume flow rate of the inert gas fed to the gas ionization device electromagnetic field of the plasma torch.

[0019] In the system provided herein, the mass flow rate control function can compare the mass flow rate setpoint from the part program with the actual mass flow rate value from the mass flow rate measurement unit of the sensing kit, and increase or decrease the mass flow rate of the inert gas to reduce the difference between the mass flow rate setpoint and the actual mass flow rate value of the inert gas fed to the gas ionization device electromagnetic field of the plasma torch by adjusting the control valve. Also, the volume flow rate control function can compare the volume flow rate setpoint from the part program with the calculated volume flow rate value from the calculation function, and adjust the density control element to control the volume flow rate of the inert gas fed to the gas ionization device electromagnetic field of the plasma torch.

[0020] In the provided system, the process master controller can further communicate with a) a mass flow rate controller processor in which the mass flow rate control function is executed, or b) a volume flow rate controller processor in which the volume flow rate control function is executed, or c) a calculation processor in which the calculation function is executed, or d) any combination of a), b), and c). Any one or combination of the process master controller, calculation processor, volume control processor, and mass flow rate control processor can further communicate with a data server. The mass flow rate and volume flow rate data can be transmitted to the data server.

[0021] In the system provided herein, each sensing connector of the temperature measurement unit, pressure measurement unit, and mass flow measurement unit of the sensing kit can be connected at any location between the gas manifold or any other type of gas distribution system and the electromagnetic field of the gas ionization device of the plasma torch. In some configurations, each sensing connector of the temperature measurement unit, pressure measurement unit, and mass flow measurement unit of the sensing kit can be connected in the vicinity of the plasma torch gas inlet. In some configurations, each sensing connector of the temperature measurement unit and pressure measurement unit of the sensing kit is located within the plasma torch.

[0022] The system provided herein can include a density control element that controls the temperature and / or pressure of the inert gas fed to the inlet of the plasma torch. In some configurations, the gas density modifier can include a) a temperature regulator and a temperature sensor, or b) a pressure regulator and a pressure sensor, or c) a temperature regulator, a temperature sensor, a pressure regulator, and a pressure sensor, or d) any combination of a), b), and c). In configurations where the gas density modifier includes a temperature regulator, the temperature regulator can include a heater. The heater can include, or can be, an induction heater, a resistance heater, a piezoelectric ceramic heating element, or a combination thereof. In some configurations, the temperature regulator can further include a cooling device. The cooling device can include a) a tube connected to a cryogenic fluid reservoir and a pump for forming a closed-loop cooling path for supplying a cooling fluid to the temperature regulator, or b) a conduit passing through the temperature regulator and a fan connected to a conduit for passing a cooling gas through the temperature regulator, or c) a combination of a) and b).

[0023] In a system configured to include a pressure regulator, the pressure regulator can include a movable plenum chamber that can increase the volume of the pressure regulator and thereby decrease the pressure of the inert gas exiting the pressure regulator, or decrease the volume of the pressure regulator and thereby increase the pressure of the inert gas exiting the pressure regulator. In the systems provided herein, a control element can be configured to control the velocity of the inert gas to the plasma torch.

[0024] In the systems provided herein, the temperature measurement unit of the sensing kit can include a temperature sensor. In the systems provided herein, the pressure measurement unit of the sensing kit can include a pressure sensor. In the systems provided herein, the mass flow measurement unit of the sensing kit can include a mass flow sensor. In some configurations, the sensing connector can be positioned inside the production chamber of the additive manufacturing system and at the plasma torch gas inlet to measure the disturbance of radiation from the plasma torch and / or the workpiece. The systems provided herein can include a mass flow meter located upstream of the control valve and communicating with the process master controller, the mass flow meter being capable of detecting a decrease in the mass flow rate of the inert gas from the manifold. The process master control transmits a signal to the data monitoring system to indicate a leak.

[0025] The system provided herein includes a source of inert gas, a supply manifold in fluid communication with the source of inert gas, a plasma torch including a gas inlet for receiving the inert gas, a control valve in fluid communication with the gas supply manifold and configured to regulate the flow of inert gas from the gas supply manifold, a sensing kit including a temperature measurement unit, a pressure measurement unit, and a mass flow measurement unit, wherein each unit communicates with a sensing connector connected at any location between the gas manifold or any other type of gas distribution system and the gas ionization device electromagnetic field of the plasma torch, a group of processors connected to the sensing kit and communicating with the control valve, including a process master controller communicating with the sensing unit, a computing processor communicating with the sensing kit and the process master controller and configured to calculate an actual volumetric flow rate, and a group of processors including a) a mass flow controller communicating with the process master controller, or b) a volumetric flow controller communicating with the process master controller, or c) a mass flow controller and a volumetric flow controller communicating with the process master controller, and a part program configured to provide a mass flow setpoint or a volumetric flow setpoint or both a mass flow setpoint and a volumetric flow setpoint to the process master controller. The mass flow controller compares the mass flow setpoint from the part program with the actual mass flow value from the sensing kit and adjusts the control valve to increase or decrease the flow of inert gas to reduce the difference between the mass flow setpoint and the actual mass flow value, or the volumetric flow controller compares the volumetric flow setpoint from the part program with the calculated volumetric flow value from the computing processor and adjusts the control valve to increase or decrease the flow of inert gas to reduce the difference between the volumetric flow setpoint and the calculated volumetric flow value. The sensing connector may be connected to or in the vicinity of the plasma torch gas inlet.

[0026] The components of the sensing kit can be separated. The elements can be embedded in different parts of the inert gas line. For example, the mass flow measurement unit of the sensing kit can be located along any part of the inert gas line. In addition, the temperature measurement unit and the pressure measurement unit can be located along the gas line or inside the plasma torch. A plurality of sensing connectors can be positioned along the inlet gas line.

[0027] In the system, the processor group can include a mass flow controller. The mass flow controller can further communicate with the control valve and adjust the control valve to increase or decrease the flow of the inert gas so as to reduce the difference between the mass flow set value and the actual mass flow value. In the system, the processor group can include a volume flow controller. The volume flow controller can further communicate with the control valve and adjust the control valve to increase or decrease the flow of the inert gas so as to reduce the difference between the volume flow set value and the calculated volume flow value. The processor group can be a set of processors that execute different tasks in parallel, or can be one master processor such as a process master controller that executes a set of tasks in parallel to support various functions.

[0028] A method for feeding an inert gas with a target volume flow rate to be ionized into plasma to a plasma torch is also provided. The method includes providing an inert gas from a gas supply manifold to the inlet of the plasma torch through a control valve attached to the inert gas supply manifold, measuring the temperature, mass flow rate and pressure of the inert gas at or near the inlet, calculating the actual volume flow rate of the inert gas at or near the inlet, comparing the actual volume flow rate with the target volume flow rate to generate a difference value. Based on the difference value, the control valve can be adjusted to increase or decrease the mass flow rate of the inert gas reaching the inlet of the plasma torch through the control valve, or the density of the inert gas can be adjusted by increasing or decreasing the pressure and / or temperature of the inert gas to provide a modified inert gas and guide the modified inert gas to the inlet of the plasma torch.

[0029] In this method, adjusting the control valve includes generating an adjustment signal based on a difference value and transmitting the adjustment signal to a drive unit attached to the control valve, and the drive unit can include increasing or decreasing the opening degree of the control valve based on the adjustment signal and transmitting. In this method, adjusting the density of the inert gas includes a) measuring the temperature of the inert gas and increasing or decreasing the temperature of the inert gas in response to the difference value, or b) measuring the pressure of the inert gas and increasing or decreasing the pressure of the inert gas in response to the difference value, or c) including both a) and b).

[0030] In this method, increasing the temperature of the inert gas can include guiding the inert gas to a temperature regulator including a heater and operating the heater. The heater can include an induction heater, a resistance heater, a piezoelectric ceramic heating element, or a combination thereof. In this method, decreasing the temperature of the inert gas can include guiding the inert gas to a temperature regulator that may include a cooling device and operating the cooling device. The cooling device can include a pipe connected to a cryogenic fluid reservoir and a pump for forming a closed-loop cooling path for supplying a cooling fluid to the temperature regulator, or a duct passing through the temperature regulator and a fan connected to a duct for passing a cooling gas through the temperature regulator, a pipe connected to a cryogenic fluid reservoir and a pump for forming a closed-loop cooling path for supplying a cooling fluid to the temperature regulator, or a duct passing through the temperature regulator and a fan connected to a duct for passing a cooling gas through the temperature regulator.

[0031] In this method, increasing or decreasing the pressure of the inert gas fed to the plasma torch can include guiding the inert gas to a pressure regulator. The pressure regulator can include a movable plenum chamber that can increase the volume of the pressure regulator and thereby decrease the pressure of the inert gas exiting the pressure regulator, or decrease the volume of the pressure regulator and thereby increase the pressure of the inert gas exiting the pressure regulator. In this method, the inert gas can be argon.

[0032] A method of feeding an inert gas having a target volumetric flow rate, which is ionized into plasma, to a plasma torch, the method including attaching the system provided herein to an inert gas source and operating the system, is also provided.

[0033] Additional features and advantages of the embodiments described herein are set forth in the following description, will be apparent in part from the description, or may be learned by practice of the invention. The objectives and other advantages of the exemplary embodiments will be realized and achieved by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.

[0034] It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the claimed invention.

[0035] The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention.

Brief Description of the Drawings

[0036]

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[0037] Here, embodiments of the present invention will be referred to in detail, and examples of the embodiments are illustrated in the accompanying drawings.

[0038] A. Definitions Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. All patents, patent applications, published applications and publications, websites and other published materials referred to throughout this specification are incorporated by reference in their entirety unless otherwise indicated. In the case of multiple definitions for terms herein, those in this section shall prevail.

[0039] As used herein, the singular forms "a", "an" and "the" include plural referents unless the context clearly dictates otherwise.

[0040] As used herein, ranges and amounts can be expressed as "about" a particular value or range. "About" includes the exact amount. Thus, "about 5 percent" means "about 5 percent" as well as "5 percent". "About" means within the typical experimental error range for the intended use or purpose.

[0041] As used herein, "optional" or "optionally" means that the subsequently described event or situation may or may not occur, and that the description includes both the case where the event or situation occurs and the case where the event or situation does not occur. For example, an optional component within a system means that the component may or may not be present within the system.

[0042] As used herein, "combination" refers to any relationship between two items or among three or more items. This relationship can be a spatial relationship or can refer to the use of two or more items for a common purpose.

[0043] As used herein, the terms "comprise", "comprising" and "include" are synonyms and are inclusive or non-limiting. Each term indicates that additional, unrecited elements or method steps can optionally be included.

[0044] As used herein, "and / or" means "either or both" of the elements so joined, i.e., elements that in some cases coexist conjunctively and in other cases disjunctively. A plurality of elements listed using "and / or" should likewise be construed as "one or more" of the elements so joined. Other elements other than those specifically identified by the "and / or" clause may optionally exist, whether or not they are related to those specifically identified elements. Thus, by way of non-limiting example, reference to "A and / or B", when used in conjunction with non-limiting terms such as "comprising", may in one embodiment refer to only A (optionally including elements other than B), in another embodiment refer to only B (optionally including elements other than A), and in yet another embodiment refer to both A and B (optionally including other elements).

[0045] As used herein, "additive manufacturing" or "AM", also known as "additive shaping" and "additive layer manufacturing", refers to an additive process for manufacturing an object layer by layer. In this process, a melting tool including 3D model data, a metal source such as wire or powder, and an energy source (such as a plasma arc, laser or electron beam) for melting the metal source or a combination thereof can be used.

[0046] As used herein, "additive manufacturing system" refers to a machine used for additive manufacturing.

[0047] As used herein, "directed energy deposition" or "DED" refers to an additive manufacturing process in which a heat source is used to melt a material, particularly a metal, by melting as the material is deposited.

[0048] As used herein, the term "metallic material" refers to any known or conceivable metal or metal alloy that can be used in an additive manufacturing process to form a three-dimensional object. Examples of suitable materials include, but are not limited to, titanium and titanium alloys, such as the Ti-6Al-4V alloy.

[0049] As used herein, "plasma gas" refers to an inert gas that is converted to plasma by the action of a plasma torch. The inert gas that is ionized into plasma can typically be argon or a combination of argon and helium.

[0050] As used herein, "plasma torch" refers to any welding torch that can be used in plasma arc welding.

[0051] As used herein, "plasma arc welding torch" or "PAW torch" refers to a welding torch that can be used in plasma arc welding. The torch is designed such that a gas is heated to a high temperature to form a plasma and become conductive, and then the plasma transfers an electric arc to the workpiece, and the intense heat of the arc can melt the metal and / or fuse two metal pieces together. The PAW torch can include a nozzle for constricting the arc, thereby increasing the output density of the arc. The inert gas that is ionized into plasma is typically argon. The PAW torch typically also has an outer nozzle for providing a shielding gas. The shielding gas can be argon, helium, or a combination thereof. The shielding gas helps to minimize oxidation of the molten metal. The PAW torch includes a plasma transfer type arc torch.

[0052] As used interchangeably herein, the terms "plasma transferred arc torch" or "PTA torch" mean any device capable of heating and exciting an inert gas stream into a plasma by an electric field, and then transferring, through a nozzle, a stream of plasma containing an electric arc outwardly to form a constricted plume that extends outwardly from the nozzle and transfers the intense heat of the plasma to a target area. The electrode and the target area are electrically connected to a power source, such as a DC power source, such that the electrode of the PTA torch can be the cathode and the target area can be the anode. Thereby, a plasma plume containing an electric arc can reliably deliver a heat flux that is highly concentrated on a small surface area of the target area with excellent control over the spread and magnitude of the area of the heat flux supplied from the PTA torch. The plasma transferred arc has the advantage of having little fluctuation, being highly resistant to length deviation between the cathode and the anode, being stable, and providing a consistent arc. Thus, the PTA torch may be suitable for both forming a molten pool in a base material and heating and melting a metal wire feedstock. The PTA torch may advantageously have an electrode made of tungsten and a nozzle made of copper, while various parts of the PTA torch can be water-cooled. However, the present invention is not restricted to any particular selection or type of PTA torch or any particular configuration of PTA torch. Any known or conceivable device that can function as a PTA torch can be used.

[0053] As used herein, "in the vicinity of the plasma torch gas inlet" means located at or near the gas inlet of the plasma torch where electromagnetic radiation from the plasma arc or the workpiece or temperature variations caused by such electromagnetic radiation can be measured. The location where a sample of the inert gas is taken to measure the gas flow and density may be several millimeters, several centimeters, or several meters away from the torch inlet.

[0054] As used herein, the term "base material" refers to a target material for heat from a melting tool, which is a target material on which a molten pool can be formed. The base material serves as a holding substrate when depositing the first layer of a metallic material. When one or more layers of a metallic material are deposited on the holding substrate, the base material becomes the upper layer of the deposited metallic material on which a new layer of the metallic material is to be deposited.

[0055] As used herein, the term "workpiece" refers to a metallic body produced using solid freeform fabrication.

[0056] As used herein, a "preform" is a workpiece produced by an additive manufacturing process, which is an intermediate or semi-finished part of a final finished part. The preform has a near-net shape for the final finished product, but requires at least some further processing, such as final finishing to a high-strength configuration, to result in the final finished product.

[0057] As used herein, a "melting tool" refers to a device including a heat source for melting part or both of the surface of a metallic material or a workpiece in an additive manufacturing process. Examples include a PTA torch that generates a plasma arc as the heat source, a laser device that generates a laser beam as the heat source, and an electron beam device that generates an electron beam as the heat source.

[0058] As used herein, the "gas discharge rate from the nozzle" refers to how fast the gas moves out of the nozzle of the plasma torch per unit time.

[0059] As used interchangeably herein, the terms "design model", or "computer-aided design model", or "CAD model" refer to any known or conceivable virtual vectorized layered three-dimensional representation of an object formed by an additive manufacturing process. The model can be obtained, for example, by first dividing the object into a set of virtual parallel layers and then dividing each of the parallel layers into a set of virtual quasi-one-dimensional segments that can be used by a controller of an additive manufacturing system to form the object by depositing or fusing metal layers according to the virtual parallel layers, thereby forming a virtual vectorized layered model of the three-dimensional object.

[0060] As used herein, "controller" refers to any logic circuit and / or processing element involved in communicating with and / or controlling one or more components of an additive manufacturing system and the associated software or program of the components of the additive manufacturing system. The controller can include a computer and / or computer memory.

[0061] As used herein, "computer" can include any program that can be programmed to communicate with and / or control, without limitation, hardware and / or software and one or more electronic devices or software-controlled mechanical devices that can capture and / or store data. The computer can include a non-transitory computer-readable medium that can include, without limitation, a CD-ROM, a removable flash memory card, a hard disk drive, or a magnetic tape.

[0062] As used herein, "computer memory" refers to a configurable storage element that can store digital data or information that can be obtained by a computer.

[0063] As used herein, "inert atmosphere" refers to any known or conceivable gas or gas mixture that can cover or surround an object and isolate the object from the ambient air. An inert atmosphere can protect an object from oxygen exposure or other undesirable chemical actions by the components of the ambient atmosphere. Exemplary inert atmospheres include one or more noble gases.

[0064] As used herein, "molten pool" refers to an amount of molten metal formed during additive manufacturing.

[0065] As used herein, "electromagnetic force" refers to the Lorentz force resulting from an electromagnetic field that is used to ionize a gas to generate a plasma.

[0066] As used herein, "electromagnetic axial pressure" refers to the electromagnetic force per unit area of the molten pool.

[0067] As used herein, "plasma flow force" refers to the mechanical disturbance resulting from the momentum of the plasma as a fluid flowing towards the molten pool.

[0068] As used herein, "plasma flow axial pressure" refers to the plasma flow force per unit area of the molten pool.

[0069] As used herein, "plasma arc pressure" or "total arc pressure" refers to the arc force per unit area of the molten pool.

[0070] As used herein, "total arc pressure" is equal to the sum of the electromagnetic axial pressure and the plasma flow axial pressure.

[0071] As used herein, "arc force" refers to the Lorentz force resulting from the electromagnetic field, i.e., the electromagnetic force used to ionize a gas to generate a plasma, in addition to the mechanical disturbance resulting from the mass of the plasma as a fluid flowing towards the molten pool.

[0072] As used herein, "mass flow rate" refers to the number of gas molecules supplied to the plasma torch per unit time.

[0073] As used herein, "volume flow rate" refers to the volume of gas supplied to the plasma torch per unit time.

[0074] As used herein, "stagnation point pressure" or "pitot pressure" is used interchangeably to refer to the static pressure at the stagnation point of a fluid flow. At the stagnation point, the fluid velocity is zero and all kinetic energy has been converted to pressure energy.

[0075] As used herein, "molten pool temperature" refers to the temperature characterizing the molten pool, and the molten pool temperature can be the volume average temperature of the molten pool, the time average temperature of the molten pool, the surface temperature of the molten pool, or the peak temperature of the molten pool (the highest temperature reached by any surface or region in the molten pool).

[0076] For any range described herein, unless otherwise explicitly defined, the range includes all values within the range and all sub-ranges within the range. For example, if a range of 1 to 10 is described, the range includes 1 and 10, all values between 1 and 10, such as 1.1, 2.5, 3.333, 6.26, 7.9989, etc., and all sub-ranges between them, such as 1 to 3.5, 2.75 to 9.33, 1.5 to 9.999, etc.

[0077] B. System for Controlling Gas Flow The directed energy deposition technique can use a local heat source such as a plasma arc to heat and melt a metal raw material that can be provided in the form of a wire to a plasma torch. An exemplary plasma transferred arc (PTA) configuration using one PTA torch is shown in FIG. 1. This figure shows a plasma torch 600 that generates a plasma arc 625 positioned above a workpiece 650. The metal wire melted by the plasma arc 625 is not shown. This plasma arc 625 melts the wire and results in molten metal droplets that are deposited layer by layer on the workpiece 650 by an additive manufacturing process to form a three-dimensional object. FIG. 1 depicts a single plasma torch 600. However, other configurations can be considered that may include two or more plasma torches, or two or more wire feeders, or multiple wires, or a wire feeder with a head capable of handling multiple metal wires and can be included in the systems provided herein. FIG. 1 illustrates a gas supply manifold 120 connected to a gas volume flow and mass flow control system 800 via a gas hose 160. The control system 800 is connected to the plasma torch via a gas hose 196.

[0078] In an exemplary embodiment, the workpiece can be included in an electrical circuit. The plasma is formed between the workpiece and the plasma torch due to the ionization effect of the electromagnetic field generated between the torch and the workpiece by connecting a power source, for example, a reversing terminal, to the torch and the workpiece.

[0079] Noble gases such as argon can be gases that are ionized by a plasma torch, such as by using arc electrodes. However, instead of argon, alternative inert gases, ions, molecules or atoms can be used in combination with the plasma torch. These alternative carriers of plasma energy can contain positive and / or negative ions, or can contain electrons alone or together with ions. Further, reactive elements can be combined with an inert gas such as argon to optimize the performance of the torch. The plasma generation process can excite argon gas to a high gas temperature such as a temperature of 5,000K to 30,000K. As a result, there only needs to be a small amount of excited argon gas in order to melt the metal feed wire into molten metal for deposition on the workpiece. The plasma torch can include one or more nozzles. For example, nozzles with various openings can be used to provide a specific geometry and / or alignment of the plasma for shaping different components. The plasma torch can include one or more openings. Exemplary openings include direct beam nozzle holes and fan-shaped openings. These openings can also be used to effect the desired geometry and / or alignment of the plasma column.

[0080] Regardless of whether the plasma stream exiting the plasma torch is directed to a metal feed wire, a workpiece, or a combination thereof, it can impinge on the surface of or in the vicinity of the molten pool. Thus, the volumetric flow rate of the plasma column can affect the molten pool dynamics, such as by the pressure exerted on the molten pool by the plasma column. The systems and methods provided herein can enable adjustment of the plasma arc pressure and thus enable modification of the molten pool dynamics during the shaping of an object using a metal-based wire-plasma arc additive manufacturing process.

[0081] A plasma torch can be designed to heat a gas to a high temperature so as to form a plasma and to make the gas electrically conductive. The plasma can then move an electric arc to the workpiece. The intense heat of the arc can melt the metal and / or fuse two metal pieces together. The plasma torch heats and excites the flow of an inert gas into the plasma by means of an electric arc discharge, and then transfers the flow of the plasma containing the electric arc outside through an opening (such as a nozzle), and extends outside from the opening to form a constricted plume that transmits the intense heat of the arc to a target area, such as a metal wire or the workpiece or both, and can be a "plasma transfer arc torch" or a "PTA torch". The plasma can be supplied along the electrode and ionized and accelerated near the cathode. The arc can be directed towards the workpiece and is more stable than a free-burning arc (such as in a TIG torch). The current typically reaches about 500 A DC (direct current). The voltage typically ranges from about 10 to 70 V. By adjusting the flow of the inert gas such as the mass flow rate and / or the inlet pressure and the volume flow rate, and / or by adjusting the plasma output (such as by adjusting the plasma voltage and current), various plasma arc configurations can be generated for a given plasma torch or plasma head shape.

[0082] In addition, the pressure and temperature distribution of the plasma arc may be affected by factors such as the relative position of the plasma torch with respect to the workpiece, the presence of a transfer voltage between the workpiece and the plasma head, etc. Generally, compared with non-plasma transfer arcs, more energy of the plasma transfer arc can be guided, and a more concentrated transfer of thermal energy to the material deposited on the workpiece can be achieved. The total arc pressure exerted on the molten pool by the plasma arc during manufacturing can be a function of plasma output, gas density and temperature, and gas flow rate (velocity). For example, it has been observed that a variation of X% in the flow of the inert gas at the torch inlet can result in a variation of more than 2X% in the melting area of the plasma arc. For example, in some configurations, by increasing the flow of the inert gas to the plasma torch from 2.5 L / min to 2.75 L / min, the melting area of the plasma arc can increase by about 10% while all other process variables are kept constant. This is the effect of the increase in the kinetic energy of the plasma flow.

[0083] The plasma arc pressure on the molten pool can be one of the most important factors defining the molten pool dynamics. The plasma arc pressure can affect the geometric shape, mechanical properties, or both the geometric shape and mechanical properties of the deposited metal layer, which can affect the consistency and quality of the additive manufacturing process. The systems and methods provided herein can be used to exert a consistent plasma arc pressure on the molten pool by adjusting and maintaining the gas discharge velocity from the plasma torch over various density levels of the ionized gas supplied to the plasma torch at a desired level.

[0084] The gas flow control technology currently used in the metal-based wire-plasma arc additive manufacturing process measures and controls the mass flow rate of the welding gas, that is, the number of gas molecules per unit time supplied to the plasma torch, by "assuming" the standard conditions of the supply gas pressure and temperature. A typical plasma welding gas control system adjusts the standard volume flow rate in NL / min, where N represents the standard state. In the standard volume flow rate, for example, a gas temperature of 0 °C (273.15 K, although other temperatures such as 20 °C or 25 °C are also used in the art) and a gas pressure of 1 atmosphere (atm, that is, 1.013 bar) are assumed. These reference conditions can be referred to as normal temperature and pressure conditions, that is, NTP conditions. Therefore, the actual volume flow rate (L / min) varies depending on the temperature and pressure of the gas. The change in the volume flow rate under non-standard conditions, such as the changes that occur during the additive manufacturing process compared to the standard conditions, can be obtained using the following formula.

Number

[0085] Here,

Number

Number

[0086] Normal measurements are performed at the gas supply source without considering the possibility of changes in the cross-section of the hoses and connectors throughout the system, nor the environmental factors near the plasma torch. The density of the gas supplied to the torch can vary significantly at locations far from the gas supply source due to environmental variations, either alone or in combination with mechanical tolerance factors, such as variations in the diameters of hoses, pipes, and connections. As a result, the actual volume flow rate of the gas supplied to the plasma torch can vary widely regardless of the conditions that may exist at the gas supply source.

[0087] The actual volume flow rate is an important factor in defining the plasma arc pressure on the melt pool, which has a significant impact on the driving force of the melt pool and thus the melt pool dynamics. The volume flow rate can be measured as the volume occupied by the gas as it flows through a conduit such as a hose or a plasma torch, and thus can be regarded as a measure of the space occupied by the gas molecules. In contrast, the mass flow rate measures the number of molecules flowing through the conduit. By using the systems and methods provided herein to generate a consistent volume flow rate of the supply gas in the plasma torch, the robustness of the manufacturing process is improved, resulting in a consistent final product quality of the workpiece produced using the additive manufacturing deposition process regardless of different environmental and / or mechanical variations.

[0088] The robustness of an additive manufacturing process can be improved using the systems and methods provided herein by controlling the effect of the actual plasma volume flow rate on the melt pool dynamics. This control can be achieved by adjusting and controlling the volume flow rate either alone or in combination with simultaneous mass flow control. By controlling the volume flow rate of the gas either alone or in combination with the mass flow, the effects of environmental disturbances, mechanical variations, or combinations thereof on the melt pool and the workpiece being formed can be mitigated. For example, when the deposition process is performed using the same machine, variations in gas density due to environmental disturbances can be controlled. Thus, the environmental disturbances either have no effect on the dynamic behavior of the melt pool or have only a negligible effect. When the deposition process is performed on "different" machines, environmental variations and mechanical variations between the machines can be mitigated, regardless of whether they have the same, similar, or different designs or configurations. Thus, these variations either have no effect on the dynamic behavior of the melt pool or have only a negligible effect.

[0089] The flow rate of the gas ionized into plasma can be one of the important process parameters in a wire - plasma arc additive manufacturing process. The gas ionized by the plasma torch is supplied to the plasma torch through a supply line, tube, or hose. In the plasma torch, the gas can be ionized and accelerated within an electromagnetic field generated by a power source such as an inverter to form a plasma arc, which is a heat source for the additive manufacturing process. This arc can then be used to heat / melt metal raw materials such as titanium wire and a titanium substrate, which are the basis for metal - based additive manufacturing. In metal - based additive manufacturing, the aim is to generate a three - dimensional shape by successively adding layers of solidified material to bring about the desired workpiece shape.

[0090] When describing the flow rate of the gas ionized by the plasma torch, the flow rate can be presented as a mass flow rate (the number of gas molecules supplied to the plasma torch per unit time) or a volume flow rate (the volume of gas supplied to the plasma torch per unit time).

[0091] In metal-based wire-plasma arc additive manufacturing applications, conventional gas flow control techniques rely on the measurement and control of the mass flow rate. As a result, the number of gas molecules supplied to the plasma torch to form the plasma arc is maintained at the desired level. However, due to variations in the gas density (i.e., gas pressure and temperature) that affect the average distance between gas molecules, the system may provide different gas volume flow rates to the torch in order to keep the mass flow rate constant. That is, the control system adjusts the gas velocity to compensate for variations in the gas density.

[0092] One of the most dominant driving forces of melt pool dynamics can be the total plasma arc pressure, which is the sum of the electromagnetic axial pressure and the plasma flow axial pressure. In some additive manufacturing processes, the electromagnetic axial pressure can be controlled by the arc current at a given arc length. The arc current is generated by a power source with the negative electrode connected to the consumable electrode in the plasma torch and the positive electrode connected to the workpiece. Then, the intensity of the resulting electric field is controlled to maintain the desired level of the main current by ionizing a predetermined number of gas atoms.

[0093] To achieve accurate total arc pressure under various conditions of an additive manufacturing process, it is necessary to accurately control the plasma flow axial pressure. The total arc pressure can be described in the form of "stagnation point pressure" or Pitot pressure as a function of gas density and gas flow rate (velocity). As a result, fluctuations in the density of the gas (which can be affected by temperature and pressure) can lead to fluctuations in the plasma flow axial pressure and, consequently, fluctuations in the dynamic behavior of the molten pool. Thus, the systems and methods provided herein can achieve a consistent force on the molten pool by the plasma arc, even if the gas density of the gas ionized in the plasma varies due to mechanical disturbances or environmental factors or perturbations or combinations thereof, by controlling the volume flow rate alone or in combination with the mass flow rate of the gas ionized in the plasma by the plasma torch.

[0094] In some configurations of the systems and methods provided herein, a plasma torch can be provided that houses a pressure sensor capable of measuring the pressure of the inert gas within the plasma torch. In some configurations, a plasma torch can be provided that includes a temperature sensor capable of measuring the temperature of the inert gas within the plasma torch. In some embodiments, a plasma torch that houses both a pressure sensor and a temperature sensor can be used. By including a pressure sensor and / or a temperature sensor in the plasma torch, the system can confirm the pressure and / or temperature of the inert gas within the plasma torch, respectively, before the inert gas is ionized into plasma. This data can be used by the system to adjust the mass flow rate and / or volume flow rate of the inert gas to the plasma torch.

[0095] Figure 2 is a schematic diagram showing an exemplary embodiment of a flow of an inert gas to be ionized through a plasma torch that includes a temperature sensor and a pressure sensor within the plasma torch, from a gas supply manifold through the flow control system provided herein. The inert gas passes through a region of an ionization electromagnetic field to generate a plasma arc and the pressure of the inert gas can be controlled. As shown in the embodiment depicted in Figure 2, the inert gas from gas supply 100 flows to gas supply manifold 120 and reaches a control valve 130 that can adjust the flow of the inert gas to plasma torch 600. The inert gas flows through a flow meter 265 located at or near torch inlet 605. The flow meter 265 enables measurement of the mass flow rate of the inert gas under the conditions received in the region of torch inlet 605. The inert gas flows through plasma torch 600 from torch inlet 605. This plasma torch 600 houses a pressure sensor 245 that can measure the pressure of the inert gas within plasma torch 600. The inert gas also flows through a temperature sensor 225 that can measure the temperature of the inert gas within plasma torch 600. The inert gas flows across tungsten electrode 610 and into a region of an ionization electromagnetic (EM) field where the inert gas is ionized into plasma and exits plasma torch 600 as plasma arc 625.

[0096] The mass flow rate and / or the volume flow rate, or both, can be controlled or modified using a gas volume flow rate and mass flow rate control system 800. The gas volume flow rate and mass flow rate control system 800 can be system 1000. Exemplary embodiments of system 1000 are illustrated in FIGS. 3A and 3B. System 1000 adjusts the mass flow rate of the gas ionized by the plasma torch and monitors the volume flow rate of this gas. The gas volume flow rate and mass flow rate control system 800 can be system 2000. Exemplary embodiments of system 2000 are illustrated in FIGS. 4A and 4B. System 2000 adjusts the volume flow rate of the gas ionized by the plasma torch and monitors the mass flow rate of this gas. The gas volume flow rate and mass flow rate control system 800 can be system 3000. Exemplary embodiments of system 3000 are illustrated in FIG. 7. System 3000 adjusts the mass flow rate and the volume flow rate of the gas ionized by the plasma torch. In the figures presented in FIGS. 3A, 3B, 4A, 4B, and 7, the dashed lines indicate data connection paths, the solid lines indicate fluid connection paths such as pipes and hoses through which the fluid can flow, and the dash-dot lines enclose different groups of components such as sensing kits or groups of processors.

[0097] In a conventional system, a source of gas to be ionized can be connected to a manifold that can direct the gas to two or more end uses, such as multiple plasma torches, to be ionized into a plasma, or for use as a shielding gas, or to maintain an inert environment, such as within a cabinet. The manifold can simultaneously provide the gas to meet these requirements. In some configurations, the system can include an inert gas supply line of a facility that can supply an inert gas directly to various elements of the system or through the manifold. An exemplary inert gas is a noble gas. In some embodiments, the inert gas is selected from among helium, neon, argon, krypton, xenon, and combinations thereof. In some embodiments, the inert gas is argon. For example, the inert gas supply line of the facility can be an argon gas supply that can be in fluid communication with the manifold. The density of the argon gas supplied to the manifold can be controlled within the gas supply line by use of pressure control elements, such as a pressure regulator, and temperature control elements, such as a heater and a temperature sensor. The inert gas from the gas manifold or any other type of gas distribution system can be directed to a mass flow unit that can measure and adjust the flow of the inert gas under standard conditions to provide the inert gas to the plasma torch of an additive manufacturing machine.

[0098] However, since conventional systems rely on standard conditions, the density of the inert gas supplied through the gas supply manifold can vary significantly due to several factors. One factor can be the different lengths and cross-sections of the piping lengths for supplying the inert gas to different regions of the components of the additive manufacturing system. Another factor can be the variation in the consumption of the inert gas at different stages of the additive manufacturing process and the variation between the components and machines of different additive manufacturing systems. Another factor affecting the density of the supplied inert gas can be the large variations in temperature and pressure in various components of the additive manufacturing process system. For example, the gas hoses and piping supplying the inert gas to the plasma torch can be exposed to a wide spectrum of electromagnetic radiation from the plasma arc and the workpiece, and the variations during the deposition process depending on the thickness or mass of the workpiece. As a result, the temperature of these hoses and piping changes, affecting the temperature of the ionized inert gas supplied to the plasma torch, and thus potentially affecting the pressure of the resulting plasma directed towards the melt pool by the plasma torch.

[0099] While the mass flow rate is maintained, fluctuations in the density of the plasma can affect the volumetric flow rate of the plasma in the plasma torch, and as a result, potentially affect the arc pressure on the melt pool. To address this, the system provided herein can monitor, adjust, or monitor and adjust the mass flow rate, volumetric flow rate, or both the mass flow rate and the volumetric flow rate. The system provided includes a sensing kit that includes a temperature measurement unit, a pressure measurement unit, and a mass flow measurement unit. The sensing kit includes sensors in the vicinity of the plasma torch gas inlet so as to be able to measure fluctuations in temperature, pressure, and mass flow rate due to environmental or mechanical variations.

[0100] The system may also include a group of processors or controllers that can monitor, correct, and maintain the volumetric flow rate / velocity of the gas to a desired consistent level, regardless of any fluctuations in gas density due to any of the reasons described above. The group of controllers can include a controller for calculating the actual volumetric flow rate based on the equation described above. The group of controllers can include a mass flow controller and / or a volumetric flow controller for monitoring, adjusting, and maintaining the mass flow rate and volumetric flow rate, respectively. In such a configuration, the system can include separate or distinct central processing units (CPUs) for performing the functions of a calculation processor, a mass flow controller, a volumetric flow controller, and a process master controller. The process master controller can communicate with each of the separate calculation processor, volumetric flow controller, and mass flow controller. This configuration can enable the process master controller to control the functions of each of the separate processors that control the calculation processor, mass flow controller, and volumetric flow controller. Also, each of the calculation processor, mass flow controller, and volumetric flow controller can be provided as a separate microcontroller that communicates with the process master controller. An exemplary configuration of the system provided herein that includes a group of processors is shown in FIGS. 3, 4, and 7. Separate processors or CPUs (e.g., microcontrollers) can be used for the calculation processor, mass flow controller, and volumetric flow controller to embed control tasks in several CPUs. However, a group of processors is not necessary for system functionality. The controllers do not have to be in the form of separate CPUs.

[0101] Instead of a separate group of processors, the system may also include a process master controller, which is a function or software code that is executed (e.g., integrally) by a process master controller rather than by individual processors or a separate central processing unit (CPU), for a calculation processor, a mass flow controller, and / or a volume flow controller. The functions of the mass flow controller and the volume flow controller can be incorporated into an integrated controller such as a process master controller. In this configuration, the process master controller can communicate with a control valve and a density control element, and use the data generated by the mass flow controller and the volume flow controller to modify and control the mass flow rate and / or the volume flow rate of the inert gas ionized by the plasma torch, thereby adjusting the plasma arc pressure exerted on the molten pool. Exemplary embodiments showing a system in which the calculation processor, the mass flow controller, and / or the volume flow controller are functions or software codes executed by a process master controller are depicted in FIGS. 8-11.

[0102] System for adjusting mass flow rate and monitoring volume flow rate An exemplary embodiment of a system 1000 for regulating mass flow rate and monitoring volume flow rate is illustrated in FIG. 3A. The embodiment shown in FIG. 3 includes a group of processors 300 that includes a separate calculation processor 320, a process master controller 340, and a mass flow controller 380. The process master controller communicates with the calculation processor 320 and the mass flow controller. The process master controller 340 also communicates with a part program 400, a sensing kit 200, and a data monitoring system 500. The mass flow controller further communicates with a control valve to effect the generation of a controlled mass flow rate of inert gas to the plasma torch.

[0103] An alternative embodiment of system 1000 for mass flow adjustment and volume flow monitoring is illustrated in FIG. 3B. In the exemplary system depicted in FIG. 3B, a single process master controller 340 includes a computing processor and the control tasks of a mass flow controller. These control tasks are software code or functions that are integrally executed in the process master controller. The process master controller communicates with the density control element and the control valve and transmits a mass flow control command to the control valve and / or the density control element to result in the generation of a controlled mass flow of inert gas to the plasma torch.

[0104] These configurations can help solve problems in the system. For example, these configurations can help detect leaks in the system. In the depicted configuration, the mass flow and gas density are measured directly at the plasma torch inlet or in the vicinity of the plasma torch inlet. This can make it possible to detect and compensate for any leaks in the pipes, hoses or connections that may occur between the gas supply 100 and the sensing connector 195 and that could potentially reduce the mass flow, by the operation of the control valve. Moreover, density measurements in any of these configurations can make it possible to take into account density variations due to environmental factors, mechanical tolerances and absorbed heat due to arc radiation when adjusting the flow of inert gas.

[0105] In the exemplary embodiments illustrated in FIGS. 3A and 3B, the gas supply 100 is connected to the gas supply manifold 120 via a hose 110. The inert gas of the gas supply 100 can be a noble gas. In some embodiments, the gas supply 100 provides a gas selected from helium, neon, argon, krypton, xenon, and combinations thereof. In some embodiments, the gas supply 100 provides argon to the system. The gas supply manifold 120 can provide gas to several different components of the additive manufacturing machine or to different additive manufacturing machines, as well as or in addition to maintaining a desired environment in the vicinity of the plasma arc or the workpiece. For example, the gas supply manifold 120 can provide gas to the chamber housing the additive manufacturing machine. FIGS. 3A and 3B illustrate only the gas line 125 connecting the gas supply manifold 120 to the control valve 130 for clarity. The control valve 130 can be operated to increase or decrease the valve opening to increase or decrease the amount of gas flowing through the control valve 130.

[0106] In the configuration shown in FIG. 3A, the inert gas can flow from the control valve 130 through the hose 185 to the plasma torch 600. The plasma torch 600 ionizes the gas to form a plasma arc 625. The plasma arc 625 can be used to melt a wire metal source and deposit the molten metal from the molten metal wire source onto the workpiece 650. In the configuration shown in FIG. 3B, the inert gas can flow from the control valve 130 through the hose 135 to the density control element 140 and then through the hose 190 to the plasma torch 600. The plasma torch 600 ionizes the gas to form a plasma arc 625. The plasma arc 625 can be used to melt a wire metal source and deposit the molten metal from the molten metal wire source onto the workpiece 650.

[0107] The sensing kit 200 of FIGS. 3A and 3B includes a sensing connector 195 to the gas line 185 to enable measurement of the temperature, pressure, and flow of the gas to the plasma torch. The sensing kit can include a temperature measurement unit 220, a pressure measurement unit 240, and a mass flow measurement unit 260. The temperature measurement unit 220 can include a temperature sensor 225 (not shown). The pressure measurement unit 240 can include a pressure sensor 245 (not shown). The mass flow measurement unit 260 can include a flow meter 265 (not shown) for measuring the mass flow under standard conditions. Other environmental measurement devices can also be included.

[0108] The sensing connector 195, which can be a gas sampling hose or tube of the sensing kit 200, can be connected to the inert gas supply line at any location between (i) the gas manifold or any other type of gas distribution system and (ii) the electromagnetic field of the gas ionization device. The arrangement can be selected to address any spatial limitations on the arrangement system hardware, such as the sensing kit, due to the various configurations of different deposition machines. As the placement of the sensing connector 195 moves farther away from the ionization field, some external disturbances to the controlled gas flow, such as gas leakage or fluctuations in gas temperature due to plasma arcs and radiation from the workpiece, may not be detected and thus may not be compensated for by the gas flow controller. When physical constraints permit, it may be advantageous to position the sensing connector 195 as close as possible to the torch to detect external disturbances, such as leaks in the hose that reduce the mass flow or radiation absorption by the hose that increases the gas flow temperature. In some embodiments, the sensing connector 195 is located 10 mm to 15 cm or 2 cm to 2 m or more away from the plasma torch gas inlet. In the figures, it is depicted as a single element 195 for clarity, but each of the components of the sensing connector, such as the temperature sensor, pressure sensor, and / or flow meter, can be arranged at separate physical locations and provide data to the sensing kit from different locations.

[0109] In the exemplary embodiments shown in FIGS. 3A and 3B, the sensing connector 195 can be directly connected to the torch inlet. The advantage of this configuration is that all external disturbances to the controlled gas flow up to the torch inlet, such as gas leaks or fluctuations in gas temperature due to radiation from the arc and workpiece, are detected and compensated for by the gas flow controller. In this configuration, external disturbances to the gas flow introduced into the torch assembly, such as pressure fluctuations due to mechanical tolerances of the torch or temperature fluctuations due to malfunction of the cooling circuit, are not captured and compensated for by the gas flow controller. In an exemplary embodiment, the sensing connector 195 can be connected to the inside of the production chamber at just the gas flow inlet of the plasma torch or to the gas supply line in the vicinity of the plasma torch gas inlet.

[0110] In an exemplary embodiment, the pressure sensor and / or temperature sensor of the sensing kit can be located inside the torch. FIG. 2 illustrates an exemplary embodiment of a plasma torch that houses both a pressure sensor and a temperature sensor. The advantage of this configuration is that all external disturbances to the gas flow, including the effects of mechanical tolerances of the torch, radiation from the plasma arc, and leaks, are measured and compensated for by the gas flow controller. The placement of the pressure sensor and temperature sensor of the sensing kit inside the torch can provide the most accurate control of the inert gas flow fed into the ionization electromagnetic field within the torch. The disadvantages associated with modifying the torch to include the pressure and temperature sensors of the sensing kit can include limitations in introducing the hardware for the pressure and temperature sensors of the sensing kit into the torch, such as space limitations. Another disadvantage is the increased cost of the torch with this configuration.

[0111] In some embodiments, a plurality of sensing connectors 195 connected at different positions can be used. Exemplary positions can include any combination of (a) within the inert gas supply line between the gas manifold and the torch inlet, (b) the torch inlet, and (c) inside the torch. Multiple sampling by the plurality of sensing connectors 195 can enable the sensing kit 200 to more accurately measure and control gas density variations throughout the system. The sensors of each of the separate components of the sensing kit can be spaced apart and arranged at different positions separately. For example, the mass flow measurement 260 of the sensing kit 200 can be positioned along multiple portions of the inert gas line 175 or 185. Separate temperature sensors and / or pressure sensors can be positioned along the inert gas line 175 or 185 or further within the plasma torch 600.

[0112] The sensing kit 200 illustrated in FIGS. 3A, 3B, 4, and 7 can be separated. Each of the elements can be embedded in different portions of the inert gas lines (125 and 185). In particular, the grouping of the sensors 220, 240, and 260 is shown only for clarity of presentation in FIGS. 3A, 3B, 4, and 7. The sensors can be separated from each other as described above. None of the sensors are intended to limit the generality of the control scheme as any of them can be placed anywhere between the gas manifold and the gas ionization device electromagnetic field.

[0113] By using the information generated by the elements of the sensing kit 200 (e.g., temperature, pressure, and mass flow rate in the embodiment illustrated in FIG. 3A), the processor group 300 can calculate and adjust the actual volumetric flow rate of the gas to be ionized. The processor group 300 can include a calculation processor 320 for calculating the actual volumetric flow rate and a mass flow controller 380 that can operate the control valve 130 based on the data received from the process master controller 340. For example, the process master controller 340 can receive the calculated volumetric flow rate from the calculation processor 320 and the measured gas mass flow rate from the sensing kit 200. The processor group 300 can be a set of processors that execute different tasks in parallel or a single processor that executes a set of tasks in parallel to support various functions. Depending on the computing power of the processor, the processor group 300 can be embedded in different physical processors (FIG. 3A) or represent parallel calculations of logical processes that can be incorporated into one process master controller in the form of logical functions (FIG. 3B). In particular, processes 320, 360, and 380 can be implemented in different functional forms by one physical processor, which can be 340 as shown in FIG. 3B, or, similarly, can be executed in parallel by different processors as shown in FIG. 3A.

[0114] A part program 400, which includes the path of the plasma torch, the gas flow, and the gas setpoint signal for the plasma torch to form a layer on a layer of molten metal to form a preform, contains the data necessary for an additive manufacturing system to prepare a given preform and can communicate with a process master controller. The process master controller can then provide the mass flow setpoint obtained from the part program 400 and the actual mass flow value obtained from the sensing kit 200 to the mass flow controller 380. The mass flow controller 380 can compare the mass flow setpoint with the actual mass flow value, send a signal to the control valve 130, and gradually open the control valve 130 to increase the mass flow rate of the gas to the plasma torch. The mass flow controller 380 can send a signal to the control valve 130 and gradually close the control valve 130 to decrease the mass flow rate of the gas to the plasma torch. Based on the data received from the sensing kit 200 via the sensing connector 195, the operation performed by the process master controller 340 adjusts the mass flow rate of the gas from the gas supply manifold 120 to the plasma torch 600, enabling a controlled mass flow rate of gas to be fed to the plasma torch. This makes it possible to control the number of gas molecules supplied to the plasma torch per unit time (i.e., control the mass flow rate). The system can also monitor the volume flow rate of the inert gas. The calculated volume flow rate data received by the process master controller 340 from the calculation processor 320 can be sent to the data monitoring system 500 for operator evaluation. By monitoring the actual volume flow rate data, the operator or the system can determine the plasma arc pressure and make any necessary adjustments to the mass flow rate of the inert gas to adjust the plasma arc pressure. In this configuration, the volume flow rate data can be used for positioning process analysis, machine state analysis, and detection and removal (or compensation) of leaks.

[0115] Data generated by any one or a combination of a sensing kit, a computing processor, a mass flow controller and a volume flow controller, a control valve, and a density control element can be recorded in a data server or other forms of data monitoring systems and / or presented to the user in real time or as a data file. This enables the system or the user to evaluate the data for system operation, quality control, diagnosis, or detection and / or resolution of problems. Optionally, previous recorded data can be used to update the part program to adjust the flow setpoint. Optionally, real-time data can be monitored during manufacturing to enable flow regulation such as providing flow parameters controlled according to the flow setpoint for the production of workpieces.

[0116] Optionally, daily operation data can be compared to determine the requirements for inert gas for the production demand of a given workpiece to enable resource allocation. Optionally, the data can be compared with information from the quality control analysis of the completed workpiece to determine whether the flow parameters need adjustment or to reset the flow setpoint to achieve similar quality control results in subsequent workpieces. The collected data, such as a combination of mass flow control and volume flow control, can be used to create a flow setpoint that realizes the desired characteristics in the final workpiece by controlling the plasma arc pressure in the melting pool during the production of the workpiece. The collected data can also be compared with the archived data to minimize the differences in daily production or production between different manufacturing machines or systems. Any one or a combination of a process master controller, a computing processor, a volume control processor, and a mass flow control processor can communicate with the data server. The mass flow and volume flow data can be transmitted to the data server.

[0117] The control valve 130 can be operated by a drive unit in response to a setpoint signal. The setpoint signal can be generated by a process master controller 340. The setpoint can correspond to a desired inert gas mass flow rate. The process master controller 340 can receive a mass flow rate setpoint from a part program 400. The process master controller 340 can be connected to a drive unit connected to the control valve 130, either directly or via a mass flow controller 380. The process master controller 340 can compare the actual mass flow rate value with the mass flow rate setpoint and generate an adjustment signal. The adjustment signal can adjust the opening degree of the control valve 130 to change the flow rate of the inert gas passing through the control valve 130, and thereby transmit to the drive unit of the control valve 130 to reduce the difference between the set mass flow rate value and the measured actual mass flow rate value.

[0118] The mass flow controller 380 can include a sensor attached to the control valve 130 that can detect the open position of the valve. The sensor can transmit the valve position to the mass flow controller 380. This mass flow controller 380 communicates with the process master controller 340 to adjust the valve position based on the valve position feedback received from the sensor.

[0119] The signal transmitted from the mass flow controller 380 or the control valve 130 to the process master controller 340 can be a digital signal such as a high voltage, low voltage, or zero voltage indicating whether the measured value is higher than, lower than, or at the preferred level. Similarly, any output transmitted from the process master controller 340 to the control valve 130, either directly or via the mass flow controller 380, can be an open signal, a closed signal, or a neutral signal. Alternatively, the signal can transmit an analog value.

[0120] The process master controller 340 can be configured to output a valve control signal as a high voltage, a low voltage, or a zero voltage to the control valve 130 or the mass flow controller 380, and can also include options for outputting an error signal. When the valve control signal is a high signal or a low signal, the control valve 130 can be gradually opened or closed respectively until a zero signal is achieved. When the valve control signal is zero, the valve does not change its position. When the valve control signal is an error, the valve can be fully blocked or the error output can be interpreted as a zero output depending on the type of error. For example, if the flow rate is too low to maintain the desired flow rate, the control valve 130 can be fully opened to maximize the flow. Alternatively, if the sensor detects an insufficient inert gas flow or no inert gas flow at all, the error signal can be interpreted as closing the valve and sending a warning signal to the data monitoring system 500.

[0121] Due to variations in pipe length and / or diameter or fluctuations in inert gas consumption and requirements on the gas supply manifold 120 by different components of the additive manufacturing machine or related systems, in addition to the influence of environmental factors such as the production ambient temperature (deposition chamber temperature or production hall temperature), the density of the gas supplied from the gas supply manifold 120 varies significantly (with respect to temperature and pressure). Embodiments of the systems provided herein, configured as the system 1000 shown in FIG. 2, enable the provision of a controlled mass flow of inert gas to the plasma torch despite the various requirements on the gas supply manifold 120.

[0122] In a conventional gas flow measurement and control system in an additive manufacturing system, it is usually located in a control cabinet that can be positioned far from the torch due to space limitations within the production chamber of the additive manufacturing machine. This means that the regulated flow within the control cabinet is subject to the influence of disturbances introduced by the distance between the control cabinet and the torch. However, by placing the flow collection hose of the sensing kit at or near the inlet of the torch, it is possible to achieve detection of all disturbances to the mass flow rate (e.g., due to leaks in pipes or connectors or hoses) and the volumetric flow rate (e.g., due to mechanical tolerances of pipe and hose diameters and temperature variations caused by absorption of radiant heat from the arc and workpiece by the gas hose or temperature variations within the production cell). By positioning the sensing connector 195 adjacent to or near the gas inlet of the plasma torch 600, it is possible to enable detection of a decrease in the mass flow rate of the gas supplied to the plasma torch, such as a decrease in the plasma flow due to a leak. Thus, the sensing kit 200 can serve as a secondary diagnostic sensor for the mass flow rate of the plasma from the gas manifold 120 to the plasma torch 600.

[0123] The temperature measurement unit 220 of the sensing kit 200 can include a temperature sensor for measuring the temperature of the inert gas. The temperature sensor of the temperature measurement unit 220 is not limited. Exemplary temperature sensors can include thermocouples, thermistors, resistance temperature devices, infrared detectors, bimetal devices, liquid expansion devices, and any combination thereof.

[0124] The pressure measurement unit 240 of the sensing kit 200 can include a pressure sensor for measuring the pressure of the inert gas. The pressure sensor of the pressure measurement unit 240 is not limited. Exemplary pressure sensors can include piezoelectric strain gauges, capacitive sensors, strain gauges, resistive pressure sensors, piezoresistive strain gauges, metal thin film sensors, sensing elements of titanium alloys, ceramic thick film sensors, optical sensors, accelerometers, microelectromechanical system sensors, and combinations thereof.

[0125] The mass flow measurement unit 260 of the sensing kit 200 can include a flow meter for measuring the mass flow. The mass flow meter can have any configuration. For example, the mass flow meter can measure the mass of the substance that has passed through the mass flow meter over a given time, regardless of the space occupied by the molecules of the substance. The mass flow can be calculated from that information. Exemplary mass flow meters include thermal mass flow meters and Coriolis mass flow meters. Such measuring instruments are known in the art (see, for example, U.S. Patent No. 4,542,650 (Renken et al., 1985); U.S. Patent No. 4,934,196 (Romano, 1990); U.S. Patent No. 5,497,665 (Cage et al., 1996); U.S. Patent No. 7,032,462 (Barger et al., 2006); U.S. Patent No. 7,181,982 (Christian et al., 2007); U.S. Patent No. 7,905,139 (Lull, 2011); U.S. Patent No. 8,356,623 (Isobe et al., 2013); and U.S. Patent No. 8,504,318 (Mendelson et al., 2013)).

[0126] System for adjusting volumetric flow rate to monitor mass flow rate In the systems provided herein, the gas flow to the plasma torch can be corrected and controlled by selecting either mass flow control or volumetric flow control as described above, based on the requirements and advantages and disadvantages of the process. In an exemplary embodiment, the data generated by the sensing kit of the system provided herein can be used to adjust the gas volumetric flow rate (i.e., compensate for density variations) by comparing the setpoint and actual value of the volumetric flow rate to control the gas flow to the plasma torch. The mass flow rate of the plasma column can be adjusted to achieve the actual volumetric flow rate that reaches the target level across the full range of gas density variations to achieve the target plasma discharge rate in the plasma torch.

[0127] An exemplary configuration is shown as system 2000 in FIGS. 4A and 4B. The embodiment shown in FIG. 4A includes a group of processors including separate calculation processors, a process master controller, and a volumetric flow controller. The volumetric flow controller communicates with a control valve and a density control element. In the exemplary system shown in FIG. 4B, a single process master controller controls the tasks of the calculation processor and the volumetric flow controller. These tasks are software code or functions that are integrally executed by the process master controller. The process master controller communicates with the density control element and the control valve, and transmits a volumetric flow control command to the control valve and / or the density control element. In the systems of FIGS. 4A and 4B, the fluid flow path of the inert gas from the gas supply 100 to the plasma torch 600 in system 2000 is similar to the fluid flow path of system 1000 illustrated in FIG. 3A. The difference is that there is a density control element 140 between the control valve 130 and the sensing connector 195. The density control element 140 can modify or control the temperature and / or pressure of the inert gas. The density control element 140 can include a temperature regulator 150 (not shown) or a pressure regulator 160 (not shown) or both the temperature regulator 150 and the pressure regulator 160. The density control element 140 can be used in a controlled manner to vary or modify the temperature or pressure or both the temperature and pressure of the gas for the purpose of controlling the gas volumetric flow / gas velocity to the plasma torch to achieve and maintain a target plasma discharge level from the plasma torch. In the configuration shown in FIG. 4A, the density control element 140 communicates with the volumetric flow controller 360 of the group of processors 300. The volumetric flow controller 360 also communicates with the control valve 130. In the configuration shown in FIG. 4B, the density control element 140 communicates with the processor master controller 340 which also communicates with the control valve 130.

[0128] By adjusting the temperature and / or pressure, the inert gas density is controlled to maintain a certain average distance between inert gas molecules due to environmental and mechanical disturbances that may affect the distance between inert gas molecules, thereby achieving the target volumetric flow rate of the plasma. The gas density corrector can assist in adjusting all parameters that can define the volumetric flow rate, which can result in a consistent application of the plasma arc in the molten pool even if external conditions or disturbances change. The density control element can include a temperature regulator, a pressure regulator, or both a temperature regulator and a pressure regulator.

[0129] The density control element 140 can include a temperature regulator. The types of temperature regulators that can be included in the density control element are not limited. The temperature control regulator can include elements that can increase the temperature of the gas passing through the density control element. The temperature control regulator can include elements that can decrease the temperature of the gas passing through the density control element. The temperature control regulator can include a first element that can increase the temperature of the gas passing through the density control element and a second element that can increase the temperature of the gas passing through the density control element.

[0130] The temperature regulator can include a heater. The heater can increase the temperature of the inert gas within the density control element 140, thereby increasing the volume occupied by the same number of gas molecules. The heater can include an induction heater, a resistance heater, a piezoelectric ceramic heating element, or a combination thereof.

[0131] The temperature regulator can include a cooling device. The cooling device can lower the temperature of the inert gas within the density control element 140, thereby reducing the volume occupied by the same number of gas molecules. The cooling device can include a tube connected to a cryogenic fluid reservoir and a pump for forming a closed-loop cooling path for supplying the cooling fluid to the temperature regulator within the density control element 140. The cooling device can include a closed conduit passing through the temperature regulator and a fan connected to a closed conduit for passing the cooling gas to the temperature regulator within the density control element 140. A combination of the closed-loop cryogenic cooling path and the conduit for passing the cooling gas to the temperature regulator can be used. The density control element 140 can include a closed-loop cooling path for supplying the cooling fluid to the temperature regulator within the density control element 140 and a heater for increasing the temperature of the gas flowing through the density control element to enable independent regulation of the temperature using either device individually.

[0132] An exemplary density control element 140 for controlling the pressure of the inert gas at the inlet of the plasma torch, and thus the average distance between gas molecules, is shown in FIG. 5. In the exemplary embodiment shown in FIG. 5, the density control element 140 adjusts the pressure of the inert gas by changing the temperature of the gas. For a given volume of gas, increasing the temperature can increase the pressure, and conversely, decreasing the temperature can decrease the pressure. In the exemplary embodiment shown in FIG. 5, the density control element 140 includes a temperature regulator 150 that includes a liquid temperature regulator 151. The liquid temperature regulator 151 can increase or decrease the temperature of the fluid. The liquid temperature regulator 151 is in fluid communication with a heat exchanger 154 within the density control element 140 through a conduit 153 connected to an outlet 152 of the liquid temperature regulator 151. The heat exchanger 154 is positioned to be in thermal communication with the inert gas flowing through the density control element 140. When the liquid from the liquid temperature regulator 151 flowing through the heat exchanger 154 is at a temperature lower than the temperature of the inert gas flowing through the density control element 140, the liquid can absorb thermal energy from the inert gas, resulting in a decrease in the temperature of the inert gas as it passes through the heat exchanger 154 towards the inlet of the plasma torch. When the liquid from the liquid temperature regulator 151 flowing through the heat exchanger 154 is at a temperature higher than the temperature of the inert gas flowing through the density control element 140, the liquid can impart thermal energy to the inert gas, resulting in an increase in the temperature of the inert gas as it passes through the heat exchanger 154 towards the inlet of the plasma torch.

[0133] In the embodiment illustrated in FIG. 5, the liquid temperature regulator 151 includes an outlet 152 connected to a conduit 153 connected to the heat exchanger 154 to enable fluid to flow from the liquid temperature regulator 151 to the heat exchanger 154. In the illustrated embodiment, the temperature regulator 150 includes a pump 170 that can pump liquid from the heat exchanger 154, through a conduit 155 connected to the inlet 176 of the pump 170, through the outlet 174 of the pump 170, and through a conduit 156 back to the inlet 158 of the liquid temperature regulator 151 to complete a fluid flow circuit. The conduits 153, 155, and 156 can be hoses or tubes. The pump 170 is shown connected between the heat exchanger 154 and the liquid temperature regulator 151 behind the heat exchanger 154. The pump 170 can also be connected between the liquid temperature regulator 151 and the heat exchanger 154 in front of the heat exchanger 154. The pump 170 can enable the circulation of the liquid of the liquid temperature regulator 151 back to the liquid temperature regulator 151 through the fluid flow circuit.

[0134] To achieve a more rapid temperature change, the pump can be configured to include a discharge port 178 to enable the liquid received from the heat exchanger 154 to be discharged from the fluid flow circuit instead of being recirculated back to the liquid temperature regulator 151. The pump 170 can also include a suction port 172 to enable replacement fluid from an external liquid supply source 175 to be introduced into the fluid flow circuit and directed to the liquid temperature regulator 151 for temperature regulation of the liquid.

[0135] The density control element 140 can include a pressure regulator. The pressure regulator can include any mechanical pressure regulator. For example, the pressure regulator can include a movable plenum chamber that can increase the volume of the pressure regulator and thereby decrease the pressure of the plasma column exiting the pressure regulator, or decrease the volume of the pressure regulator and thereby increase the pressure of the plasma column exiting the pressure regulator.

[0136] An exemplary embodiment of a density control element 140 including a pressure regulator is illustrated in FIG. 6. In the illustrated embodiment, the pressure regulator 160 includes a plenum chamber 162. The volume of the plenum chamber 162 can be adjusted by adjusting the position of a sealing element 164 using a position adjuster 166. The position adjuster 166 can raise at least a portion of the sealing element 164, thereby increasing the volume of the plenum chamber 162, or lower at least a portion of the sealing element 164, thereby decreasing the volume of the plenum chamber 162. By increasing the volume of the plenum chamber 162, the effective volume within the pressure regulator 160 increases, and thus the distance between the molecules of the inert gas decreases. By decreasing the volume of the plenum chamber 162, the effective volume within the pressure regulator 160 decreases, and thus the distance between the molecules of the inert gas increases. The sealing element 164 can be a solid disk that can be raised or lowered to increase or decrease the volume of the plenum chamber 162. The sealing element 164 can be a flexible or elastic diaphragm fixed to the wall of the plenum chamber 162. The position corrector 166 can push the center of the sealing element 164 towards the gas flow pipe to decrease the volume of the plenum chamber 162, or the position corrector 166 can pull the center of the sealing element 164 away from the gas flow pipe to increase the volume of the plenum chamber 162. The illustrated embodiment shows a single plenum chamber. However, the pressure regulator 160 can include two or more plenum chambers.

[0137] In an exemplary embodiment of the system illustrated in FIG. 4, a volume flow controller 380 that communicates with a control valve 130 and a density control element 140 is included. In system 2000, a gas supply 100 is connected to a gas supply manifold 120 via a hose 110. The inert gas of the gas supply 100 can be a noble gas. In some embodiments, the gas supply 100 provides a gas selected from among helium, neon, argon, krypton, xenon, and combinations thereof. In some embodiments, the gas supply 100 provides argon to the system. The gas supply manifold can provide gas to several different components of the additive manufacturing machine or to different additive manufacturing machines, as well as or in addition to maintaining a desired environment in the vicinity of the plasma arc or the workpiece. FIGS. 4A and 4B illustrate only the gas line 125 that connects the gas supply manifold 120 to the control valve 130. The control valve 130 can be operated to increase or decrease the valve opening to increase or decrease the amount of gas flowing through the control valve 130. The gas can flow from the control valve 130 through a hose 135 to the density control element 140 and then through a hose 190 to the plasma torch 600. The plasma torch 600 ionizes the gas to form a plasma arc 625. The plasma arc 625 can be used to melt a wire metal source and deposit the molten metal from the molten metal wire source onto the workpiece 650.

[0138] The sensing kit 200 includes a sensing connector 195 to the gas line 190 to enable measurement of the temperature, pressure, and flow of the gas to the plasma torch. The sensing kit can include a temperature measurement unit 220, a pressure measurement unit 240, and a mass flow measurement unit 260. The temperature measurement unit 220 can include a temperature sensor. The pressure measurement unit 240 can include a pressure sensor. The mass flow measurement unit 260 can include a flow meter for measurement of the mass flow at standard conditions. Other environmental measurement devices can also be included in the sensing kit 200.

[0139] The sensing connector 195 of the sensing kit 200 can be located just inside the production chamber at the plasma torch gas inlet or in the vicinity of the plasma torch gas inlet. Such positioning enables the sensing kit 200 to measure and control gas density fluctuations caused by, for example, disturbances in arc radiation such as temperature changes directly resulting from the action of the plasma column, heat contributions from the workpiece such as radiant heat from the molten pool, or combinations thereof. Also, such positioning can enable the mass flow meter to detect flow variations that may occur due to leaks in the gas line between the gas supply and the plasma torch. In some embodiments, the sensing connector 195 can be located 10 mm to 15 cm away from the plasma torch gas inlet.

[0140] By using the information generated by the elements of the sensing kit 200 (e.g., temperature, pressure, and mass flow rate in the embodiments illustrated in FIGS. 4A and 4B), the processor group 300 (FIG. 4A) or the process master controller 340 (FIG. 4B) can calculate the actual volumetric flow rate of the gas to be ionized. The processor group 300 in FIG. 4A can include a calculation processor 320 for calculating the actual volumetric flow rate and a volumetric flow controller 360 that can operate the control valve 130 based on the data received from the process master controller 340. For example, the process master controller 340 can receive the calculated volumetric flow rate from the calculation processor 320 and the measured gas mass flow rate from the sensing kit 200. The process master controller 340 in FIG. 4B can include a software function that performs the task of the calculation processor for calculating the actual volumetric flow rate and a software function that performs the functionality of the volumetric flow controller 340. The process master controller 340 can operate the control valve 130 based on the data generated by the software function for calculating the actual volumetric flow rate and the functionality of the volumetric flow controller.

[0141] A part program 400 including the path of a plasma torch, a gas flow, and a gas setpoint signal for forming a layer on a molten metal layer to form a preform, which contains the data necessary for an additive manufacturing system to prepare a given preform, can communicate with a process master controller. Then, the process master controller can provide the volume flow setpoint obtained from the part program 400 and the actual volume flow value calculated from the calculation processor 320 to a software function that executes the functionality of the volume flow controller 360 (FIG. 4A) or the volume flow controller 340 (FIG. 4B). The volume flow controller 360 can compare the volume flow setpoint with the calculated volume flow value regardless of whether it is configured as a separate processor or as a software function. In the configuration shown in FIG. 4A, when the calculated volume flow value is below the volume flow setpoint, the processor including the volume flow controller 360 sends a signal to the control valve 130 and gradually opens the control valve 130 to increase the mass flow rate of the gas to the plasma torch. In the configuration shown in FIG. 4B, the process master controller receives data from the software function of the volume flow controller 360. When the calculated volume flow value exceeds the volume flow setpoint, the process master controller 340 can send a signal to the control valve 130 and gradually close the control valve 130 to reduce the mass flow rate of the gas to the plasma torch.

[0142] Based on the data received from the sensing kit 200 via the sensing connector 195, the process master controller 340 performs operations to adjust the volumetric flow rate of the gas from the gas supply manifold 120 to the plasma torch 600, either directly or through a separate volumetric flow rate controller, enabling the supply of a gas with a controlled volumetric flow rate to the plasma torch. This makes it possible to control the volume of gas molecules supplied to the plasma torch per unit time (i.e., control the volumetric flow rate). The system can also monitor the mass flow rate of the inert gas. The mass flow rate data received by the process master controller 340 from the mass flow rate measurement unit 260 of the sensing kit 200 can be transmitted to the data monitoring system 500 for evaluation by the operator or the system. In this configuration, the mass flow rate data can be used for the analysis of the deposition process, the calibration of the control system, and the detection and removal (or compensation) of leaks.

[0143] The control valve 130 can be operated by a drive unit in response to a setpoint signal. The setpoint signal can be generated by a volumetric flow rate controller 360 (configuration shown in FIG. 4A) or a process master controller 340 (configuration shown in FIG. 4B). The setpoint can correspond to the desired volumetric flow rate of the inert gas. The process master controller 340 can receive a volumetric flow rate setpoint from the part program 400. The process master controller 340 can be connected to the drive unit connected to the control valve 130, either directly or via the volumetric flow rate controller 360. The process master controller 340 can compare the calculated actual volumetric flow rate value with the volumetric flow rate setpoint to generate an adjustment signal. The adjustment signal can adjust the opening degree of the control valve 130 to change the flow rate of the inert gas passing through the control valve 130 and can be transmitted to the drive unit of the control valve 130 to reduce the difference between the set volumetric flow rate value and the calculated actual volumetric flow rate value.

[0144] The volume flow controller 360 can include a sensor attached to the control valve 130 that can detect the open position of the valve, whether configured as a separate processor or as a software function executed by the process master controller. The sensor can communicate the valve position to the volume flow controller 360. This volume flow controller 360 communicates with the process master controller 340 to adjust the valve position based on the valve position feedback received from the sensor.

[0145] The signal transmitted from the volume flow controller 360 or the control valve 130 to the process master controller 340 can be a digital signal such as a high voltage, low voltage, or zero voltage indicating whether the measured value is higher than, lower than, or at the preferred level. Similarly, any output transmitted by the process master controller 340 to the control valve 130 directly or via the volume flow controller 360 can be an open signal, a closed signal, or a neutral signal. Alternatively, the signal can transmit an analog value.

[0146] The process master controller 340 can be configured to output a valve control signal to the control valve 130 or the volume flow controller 360 as a high voltage, low voltage, or zero voltage, and can also include options for outputting an error signal. When the valve control signal is a high signal or a low signal, the control valve 130 can gradually open or close respectively until a zero signal is achieved. When the valve control signal is zero, the valve does not change position. When the valve control signal is an error, the valve can either completely shut off or interpret the error output as a zero output depending on the type of error. For example, if the pressure is too low to maintain the desired flow rate, the control valve 130 can fully open to maximize the flow. Alternatively, if the sensor detects an insufficient inert gas flow or no inert gas flow at all, the error signal can be interpreted as closing the valve and sending a warning signal to the data monitoring system 500.

[0147] Due to variations in pipe length or fluctuations in inert gas consumption, and requirements for the gas supply manifold 120 due to different components of the additive manufacturing machine or related systems, as well as temperature disturbances resulting from radiant heat from the arc, production chamber variations, and ambient temperature disturbances, the density of the gas supplied from the gas supply manifold 120 varies significantly (with respect to temperature and pressure). Embodiments of the systems provided herein, configured as system 2000 as shown in FIGS. 4A and 4B, enable the provision of a controlled volumetric flow rate of inert gas to the plasma torch despite the various requirements for the gas supply manifold 120.

[0148] System for adjusting volumetric flow rate and mass flow rate In another embodiment of the systems provided herein, the inert gas flow fed to the plasma torch can be controlled with respect to both the number of gas molecules over time and the gas volume over time. An exemplary configuration of a system 3000 for adjusting both mass flow rate and volumetric flow rate is shown in FIGS. 7A, 7B, and 7C. System 3000 can maintain the volumetric flow rate / velocity of the gas at a desired relatively consistent level regardless of any variations in inert gas density. The embodiment shown in FIG. 7A includes a group of processors including a separate computational processor, a process master controller, a volumetric flow rate controller, and a mass flow rate controller. The volumetric flow rate controller communicates with a density control element. The mass flow rate controller communicates with a control valve.

[0149] Instead of using separate processors, the system provided herein can include a single process master controller in which the control tasks of the computational processor, the mass flow controller, and the volumetric flow controller are software code or functions that are integrally executed by the process master controller. For example, the mass control function and the volumetric flow control function can be two single-input single-output (SISO) controllers operating in parallel. An exemplary configuration is illustrated in FIG. 8A. In this configuration, the mass flow error from the sensing kit unit is sent to the SISO mass flow controller function. The SISO mass flow controller function sends a commanded valve position to the control valve. The volumetric flow error from the sensing kit unit is sent to the SISO volumetric flow controller function. In response, the SISO mass flow controller function sends a density control command to the density control element. The use of parallel SISO controllers can enable simplification of the control design. The two parallel SISO controllers ignore any coupling between the mass flow error and the volumetric flow error.

[0150] The exemplary embodiment shown in FIG. 7B illustrates a single process master controller in which the control tasks of the computational processor, the mass flow controller, and the volumetric flow controller are software code or functions that are integrally and separately executed by the process master controller. The process master controller communicates with the density control element and the control valve to transmit a volumetric flow control command to the density control element and a mass flow control command to the control valve. In this configuration, SISO controllers operating in parallel can be used.

[0151] Alternatively, a mass and volume control function using a multivariable controller (multiple input multiple output, MIMO) can be used. The multivariable controller can have two inputs (mass flow error and volume flow error) and can have two outputs (command valve position and command operation to the density control element). The MIMO controller can consider the coupling dynamics between or within the variables. Such considerations between or within multiple variables can be included in the control algorithm. For example, variable X can be adjusted to a certain set point, variable Y can be adjusted to another set point, and it can be confirmed that each of variable X and variable Y is stabilized when operating separately. When the coupling between variable X and variable Y in the dynamic system is moderately weak, the system as a whole may not be disturbed by the influence of variable X on variable Y. However, when the coupling between variable X and variable Y in the dynamic system is strong, the system as a whole may be disturbed by the influence that variable X and variable Y exert on each other, and in a very strong coupling situation, the influence of variable X on variable Y may cause the destabilization of the system (i.e., variable X and variable Y "interfere" with each other). Under these conditions, the MIMO controller may be superior to a single SISO controller operating in parallel because it can consider the "coupling dynamics" of different variables. By using the MIMO controller, the stability of an interconnected system where variable coupling occurs can be maximized. One integrated MIMO controller can take into account the coupling terms between variables and adjust the system accordingly.

[0152] An exemplary configuration of the MIMO controller of the system provided in this specification is illustrated in FIG. 8B. As shown in FIG. 8B, the multivariable MIMO controller has two inputs (the mass flow rate error and the volume flow rate error received from the sensing kit unit) and a control algorithm that can take into account any coupling dynamics of the two variables, and has two outputs (the commanded valve position and the commanded operation to the density control element) that are sent to the control valve and the density control element respectively. With this configuration, it is possible for the system to stabilize individual values and for the system to handle or compensate for disturbances that one variable exerts on the other variable. Therefore, this configuration can stabilize the entire system.

[0153] The exemplary embodiment shown in FIG. 7C shows a single process master controller that uses a MIMO controller, shown as a combined mass flow rate and volume flow rate controller. The control tasks of the computing processor and the combined mass flow rate and volume flow rate controller are software code or functions that are integrally executed by the process master controller. The process master controller communicates with the density control element and the control valve to transmit the mass flow rate and volume flow rate control commands to the density control element and the control valve. In the configurations shown in FIGS. 7B and 7C, the inert gas with the controlled mass flow rate is fed from the control valve 130 to the density control element 140. The density control element feeds the inert gas with the controlled mass flow rate and volume flow rate to the plasma torch.

[0154] In the embodiment illustrated as system 3000 in FIGS. 7A, 7B, and 7C, the mass flow rate and volumetric flow rate of the inert gas to the plasma torch can be measured and adjusted. For example, the mass flow rate data can be converted to a volumetric flow rate by assuming standard conditions (e.g., a temperature of 0°C and a pressure of 1 atmosphere). This volumetric flow rate can differ from the actual volumetric flow rate of the inert gas due to density fluctuations. In an exemplary embodiment, the data generated by the sensing kit 200 of the system 3000 can be used to regulate the gas flow to the plasma torch by measuring the mass flow rate of the gas and calculating the volumetric flow rate of the gas, and the final volumetric flow rate of the inert gas can be adjusted to compensate for density fluctuations by comparing the setpoint and actual values of the mass flow rate and volumetric flow rate. The mass flow rate of the inert gas and the temperature and / or pressure of the inert gas can be adjusted to achieve the actual volumetric flow rate that reaches the target level across the range of gas density fluctuations in order to achieve the target plasma column discharge rate in the plasma torch.

[0155] The fluid flow path of the gas from the gas supply 100 to the plasma torch 600 in the system 3000 is the same as the fluid flow path of the system 2000 illustrated in FIGS. 4A and 4B. The difference is that there is a mass flow controller 380. This mass flow controller 380 is shown in FIG. 7A in communication with the process master controller 340 and the control valve 130. The density control element 140 can modify or control the temperature and / or pressure of the inert gas. The density control element 140 can include a temperature regulator or a pressure regulator or both a temperature regulator and a pressure regulator. The density control element 140 can be used in a controlled manner to modify the temperature or pressure or both the temperature and pressure of the gas in order to control the gas volume flow rate / gas velocity to the plasma torch to achieve and maintain the target plasma discharge level from the plasma torch. In the embodiment illustrated in FIG. 7A, the density control element 140 communicates with the volume flow controller 360 of the processor group 300. The control valve 130 communicates with the mass flow controller 380. In the embodiments illustrated in FIGS. 7B and 7C, the density control element 140 and the control valve 130 communicate with the process master controller 340.

[0156] By adjusting the temperature and / or pressure, the density of the inert gas is controlled to maintain a certain average distance between the inert gas molecules due to environmental and mechanical disturbances that may affect the distance between the inert gas molecules, thereby achieving the target volume flow rate of the inert gas to the plasma torch. The gas density modifier can assist in adjusting all parameters that can define the volume flow rate that can result in a consistent application of the plasma arc in the molten pool even when external conditions or disturbances change.

[0157] The density control element 140 can include a temperature regulator. The temperature regulator can include a heater. The heater can increase the temperature of the inert gas within the density control element 140, thereby increasing the volume occupied by the same number of gas molecules. The heater can include an induction heater, a resistance heater, a piezoelectric ceramic heating element, or a combination thereof.

[0158] The temperature regulator can include a cooling device. The cooling device can lower the temperature of the inert gas within the density control element 140, thereby reducing the volume occupied by the same number of gas molecules. The cooling device can include a pipe connected to a cryogenic fluid reservoir and a pump for forming a closed-loop cooling path for supplying a cooling fluid to the temperature regulator within the density control element 140. The cooling device can include a closed conduit passing through the temperature regulator and a fan connected to a closed conduit for passing a cooling gas to the temperature regulator within the density control element 140. A combination of the closed-loop cryogenic cooling path and the conduit for passing the cooling gas to the temperature regulator can be used.

[0159] The density control element 140 can include a pressure regulator. The pressure regulator can include a movable plenum chamber that can increase the volume of the pressure regulator and thereby reduce the pressure of the inert gas exiting the pressure regulator, or can decrease the volume of the pressure regulator and thereby increase the pressure of the inert gas exiting the pressure regulator.

[0160] In the exemplary embodiments illustrated in FIGS. 7A, 7B, and 7C, the gas supply 100 is connected to the gas supply manifold 120 via a hose 110. The inert gas of the gas supply 100 can be a noble gas. In some embodiments, the gas supply 100 provides a gas selected from helium, neon, argon, krypton, xenon, and combinations thereof. In some embodiments, the gas supply 100 provides argon to the system. The gas supply manifold can provide gas to some different components of the additive manufacturing machine or to different additive manufacturing machines, as well as or in addition to maintaining a desired environment in the vicinity of the plasma arc or the workpiece. FIGS. 7A-7C illustrate only the gas line 125 connecting the gas supply manifold 120 to the control valve 130. The control valve 130 is shown connected to the density control element 140 via a hose 135. The control valve 130 can be operated to increase or decrease the valve opening to increase or decrease the amount of gas flowing through the control valve 130 to the density control element 140. The gas can flow from the control valve 130 through the hose 135 to the density control element 140 and then through the hose 190 to the plasma torch 600. The plasma torch 600 ionizes the gas to form a plasma arc 625. The plasma arc 625 can be used to melt a wire metal source and deposit the molten metal from the molten metal wire source onto the workpiece 650.

[0161] The sensing kit 200 includes a sensing connector 195 to the gas line 190 to enable measurement of the temperature, pressure, and flow of the gas to the plasma torch. The sensing kit can include a temperature measurement unit 220, a pressure measurement unit 240, and a mass flow measurement unit 260. The temperature measurement unit 220 can include a temperature sensor. The pressure measurement unit 240 can include a pressure sensor. The mass flow measurement unit 260 can include a flow meter for measuring the mass flow or volumetric flow under standard conditions. Other environmental measurement devices can also be included in the sensing kit 200.

[0162] The sensing connector 195 of the sensing kit 200 can be located inside the production chamber at just the gas inlet of the plasma torch or near the plasma torch gas inlet. With such positioning, the sensing kit 200 can measure and control gas density fluctuations caused by disturbances in arc radiation such as temperature changes directly resulting from the action of the plasma column, heat contributions from the workpiece such as radiant heat from the molten pool, or combinations thereof. Also, with such positioning, the mass flow meter can detect flow fluctuations that may occur due to leaks in the gas line between the gas supply and the plasma torch. In some embodiments, the sensing connector 195 is located 10 mm to 15 cm or 2 cm to 2 m away from the plasma torch gas inlet.

[0163] By using the information generated by the elements of the sensing kit 200 (e.g., temperature, pressure, and mass flow rate in the embodiments illustrated in FIGS. 7A - 7C), the software function that performs the function of the calculation processor 320 executed by the calculation processor 320 in the processor group 300 (FIG. 7A) or the process master controller processor (FIGS. 7B and 7C) can calculate the actual volumetric flow rate of the ionized gas. In the exemplary configuration shown in FIG. 7A, the processor group 300 can include a calculation processor 320 for calculating the actual volumetric flow rate, a volumetric flow controller 360 that can communicate with and operate the density control element 140, and a mass flow controller 380 that can communicate with the control valve 130 and operate the control valve 130 based on the data received from the process master controller 340. For example, the process master controller 340 can receive the measured gas mass flow rate data from the sensing kit 200, the calculated volumetric flow rate from the calculation processor 320, and the flow rate set value from the part program 400.

[0164] In the exemplary configuration shown in FIG. 7B, the computational processor 320, the volumetric flow controller 360, and the mass flow controller 380 for the calculation of the actual volumetric flow rate are software functions executed by the process master controller 340, respectively. The process master controller 340 can communicate with the control valve 130 and the density control element 140 to operate the control valve 130 and the density control element 140. The process master controller 340 receives the measured gas mass flow rate data from the sensing kit 200 and uses not only the flow rate setpoint from the part program 400 but also the calculated volumetric flow rate from the software function of the computational processor 320, and can determine not only the difference between the set mass flow rate value and the actual mass flow rate value from the mass flow rate measurement 260 from the sensing kit 200, but also the difference between the set volumetric flow rate value and the calculated actual flow rate value. Based on the differential mass flow rate value, the process master controller 340 communicates with the control valve 130 and increases or decreases the mass flow rate of the inert gas so that the mass flow rate difference value approaches or becomes zero, resulting in a controlled mass flow rate from the control valve 130 to the density control element 140. Based on the differential volumetric flow rate value, the process master controller 340 communicates with the density control element 140 and increases or decreases the temperature and / or pressure of the inert gas so that the differential volumetric flow rate value approaches or becomes zero, resulting in a controlled volumetric flow rate and a controlled mass flow rate from the density control element 140 to the plasma torch 600.

[0165] The exemplary configuration shown in FIG. 7C differs from the configuration shown in FIG. 7C in that the process master controller 340 includes a software function 385 executed by the process master controller 340. The software function 385 performs the functions of the mass flow controller and the volume flow controller of the process master controller 340 in FIG. 7B. The mass flow and volume flow controller 385 of the configuration shown in FIG. 7C utilizes the calculated actual volume flow rate from the software function that performs the function of the calculation processor 320 to determine the difference between the volume flow rate set value from the part program 400 and the calculated volume flow rate value. This difference is transmitted to the process master controller 340. The process master controller compares the set mass flow rate value from the part program 400 with the actual mass flow rate value from the mass flow rate measurement 260 of the sensing kit 200 to also determine the difference between the mass flow rate set value and the actual mass flow rate value. Based on the differential mass flow rate value, the process master controller 340 communicates with the control valve 130 and increases or decreases the mass flow rate of the inert gas so that the mass flow rate difference value approaches or becomes zero, resulting in a controlled mass flow rate from the control valve 130 to the density control element 140. Based on the differential volume flow rate value, the process master controller 340 communicates with the density control element 140 and increases or decreases the temperature and / or pressure of the inert gas so that the differential volume flow rate value approaches or becomes zero, resulting in a controlled volume flow rate and mass flow rate from the density control element 140 to the plasma torch 600.

[0166] A part program 400 that includes the path of a plasma torch, a gas flow, and a gas setpoint signal for the plasma torch to form a layer on a layer of molten metal to form a preform, and includes the data necessary for an additive manufacturing system to prepare a given preform, can communicate with a process master controller. The process master controller 340 can provide a mass flow setpoint and a measured actual gas mass flow value to the mass flow controller 380. The process master controller 340 can provide a volume flow setpoint obtained from the part program 400 and a volume flow actual value calculated from the calculation processor 320 to the volume flow controller 360.

[0167] Without loss of generality, the mass flow controller can be a separate processor, such as a controller, or a software function executed by the process master controller processor. The mass flow controller 380 compares the gas mass flow setpoint with the actual mass flow value. If the measured mass flow value is below the mass flow setpoint, it can send a signal to the control valve 130 and gradually open the control valve 130 to increase the mass flow of gas to the density control element 140. If the measured mass flow value is above the mass flow setpoint, the mass flow controller 380 can send a signal to the control valve 130 and gradually close the control valve 130 to decrease the mass flow of gas to the density control element 140.

[0168] The volume flow controller 360 compares the volume flow setpoint with the volume flow calculated value. When the calculated volume flow value is below the volume flow setpoint, it sends a signal to the density control element 140 to gradually increase the temperature to increase the volume of the gas or decrease the pressure to increase the volume. When the calculated volume flow value is above the volume flow setpoint, the volume flow controller 360 sends a signal to the control valve 130 to gradually decrease the temperature to decrease the volume of the gas or increase the pressure to decrease the volume of the gas. Based on the data received from the sensing kit 200 via the sensing connector 195, the process master controller 340 adjusts the volume flow of the gas from the gas supply manifold 120 through the density control element 140 to the plasma torch 600, enabling an inert gas with a controlled volume flow and adjusted mass flow to be fed to the plasma torch 600. This makes it possible to control both the volume and the number of gas molecules supplied to the plasma torch. The system can also monitor the mass flow of the inert gas. The mass flow data and volume flow data received by the process master controller 340 can be sent to the data monitoring system 500 for evaluation by the operator or the system. The data on mass flow and actual volume flow can be used, for example, in the analysis and development of deposition processes, leak detection and removal (or compensation), and calibration of the gas control system.

[0169] The control valve 130 can be operated by a drive unit in response to a mass setpoint signal. The mass setpoint signal can be generated by a process master controller 340 and transmitted to a mass flow controller 380. The process master controller 340 can receive a mass flow setpoint from a part program 400. The mass flow controller 380 can be connected to a drive unit connected to the control valve 130. The process master controller 340 can compare the calculated actual volumetric flow rate value with the volumetric flow rate setpoint to generate an adjustment signal. The adjustment signal can be transmitted to the drive unit of the control valve 130 through the mass flow controller 380 to adjust the opening degree of the control valve 130, change the flow rate of the inert gas passing through the control valve 130, and thereby reduce the difference between the set mass flow rate value and the measured actual mass flow rate value. Then, the adjusted gas of the mass flow can be sent to the density control element 140 through the hose 135.

[0170] The process master controller 340 can also receive a volumetric flow rate setpoint from the part program 400. The process master controller 340 can be connected to the density control element 140 directly or through a volumetric flow controller 360. Without loss of generality, the volumetric flow controller can be a separate processor, such as a controller, or a software function executed by the process master controller processor. The process master controller 340 can compare the calculated actual volumetric flow rate value with the volumetric flow rate setpoint to generate an adjustment signal. The adjustment signal can be transmitted to the density control element 140 to adjust the volume of the gas by modifying the temperature and / or pressure, changing the volumetric flow rate of the inert gas passing through the density control element 140, and thereby reducing the difference between the set volumetric flow rate value and the calculated actual volumetric flow rate value.

[0171] The mass flow controller 380 can include a sensor attached to the control valve 130 that can detect the open position of the valve. The sensor can transmit the valve position to the mass flow controller 380. This mass flow controller 380 communicates with the process master controller 340 to adjust the valve position based on the valve position feedback received from the sensor.

[0172] The signal transmitted from the sensor of the mass flow controller 380 or the control valve 130 to the process master controller 340 can be a digital signal such as a high voltage, a low voltage, or a zero voltage, indicating whether the measured value is higher than, lower than, or at the preferred level. Similarly, any output transmitted from the process master controller 340 to the control valve 130 directly or via the mass flow controller 380 can be an open signal, a closed signal, or a neutral signal. Alternatively, the signal can transmit an analog value.

[0173] The process master controller 340 can be configured to output a valve control signal to the control valve 130 or the mass flow controller 380 as a high voltage, a low voltage, or a zero voltage, and can also include options for outputting an error signal. When the valve control signal is a high signal or a low signal, the control valve 130 can gradually open or close respectively until a zero signal is achieved. When the valve control signal is zero, the valve does not change its position. When the valve control signal is an error, the valve can either completely shut off or interpret the error output as a zero output depending on the type of error. For example, if the pressure is too low to maintain the desired flow rate, the control valve 130 can fully open to maximize the flow. Alternatively, if the sensor detects an insufficient inert gas flow or no inert gas flow at all, the error signal can be interpreted as closing the valve and sending a warning signal to the data monitoring system 500.

[0174] Variations in pipe length and / or diameter, and / or mechanical tolerances of pipes and hoses, connector diameters, and / or variations in inert gas consumption and requirements on the gas supply manifold 120 by different components of an additive manufacturing machine or related systems, and variations in gas temperature due to thermal disturbances such as heat absorption from the arc and workpiece by the gas hose and environmental temperature disturbances such as temperature variations in the production hall and production chamber, result in significant variations in the density of the gas supplied from the gas supply manifold 120 (with respect to temperature and pressure). Embodiments of the systems provided herein, configured as shown as system 3000 in FIGS. 7A, 7B, and 7C, enable the provision of a controlled mass flow rate and volume flow rate of inert gas to the plasma torch, despite various requirements on the gas supply manifold 120, or gas leaks in the system between the gas supply 100 and the plasma torch 600, or gas temperature variations due to radiation from the plasma arc and workpiece.

[0175] Any wire-based additive manufacturing system can be modified for use with any of the inert gas flow control systems provided herein.

[0176] C. Flow Control Method Also provided is a method for controlling the flow of an inert gas ionized in a plasma to a plasma torch in order to produce a workpiece by an additive manufacturing process. The methods provided herein can feed a target mass flow rate or a target volume flow rate or both a target mass flow rate and a target volume flow rate of an inert gas to the plasma torch. The method can include integrating one of the systems provided herein into a DED manufacturing system and using the system to adjust and control the inert gas flow to the plasma torch. The plasma arc pressure on the melt pool can be one of the most important factors that define melt pool dynamics and thus the geometric shape and mechanical properties of the bead. The geometric shape and mechanical properties of the bead can characterize the consistency and quality of the additive manufacturing process. The methods provided herein can exert a consistent plasma arc pressure (i.e., arc force per unit area of the melt pool) on the melt pool by maintaining the gas discharge rate from the plasma torch at a desired level over various density levels of the inert gas supplied to the plasma torch. The methods provided herein can calculate the actual volume flow rate that has a significant impact on the driving force of the melt pool, i.e., melt pool dynamics. Since the method can provide a consistent volume flow rate of inert gas to the plasma torch, a significantly improved and more robust deposition process can be achieved for different environmental and mechanical variations that can affect gas density.

[0177] The methods provided herein enable control of the actual volumetric flow rate of the inert gas to the plasma torch. For example, because fluctuations in gas density due to environmental disturbances do not affect the dynamic behavior of the melt pool, the deposition process becomes more consistent. When the deposition process is performed on different machines, environmental variations due to mechanical part tolerances and mechanical variations between machines do not affect the dynamic behavior of the melt pool, and more consistent preform formation on different machines is achieved. The sensing connector, which can be a gas sampling hose / tube, can be connected to the inert gas flow line anywhere between the gas manifold and the gas ionization device electromagnetic field. In some embodiments, the sensing connector can be attached directly to or in the vicinity of the torch inlet. In some embodiments, the temperature sensor and pressure sensor of the sensing connector can be incorporated within the torch. In some embodiments, the actual volumetric flow control element can be located inside the production chamber at just the inlet of the inert gas to the plasma torch so as to be able to measure and control gas density variations resulting from arc radiation disturbances or heat radiation disturbances caused by the workpiece.

[0178] The method can include adding a mass flow measurement element at the inlet of the inert gas to the plasma torch. The mass flow measurement element can enable detection of a decrease in mass flow rate due to leaks, etc., and can be used as a secondary diagnostic sensor for the mass flow rate of the inert gas. The method can include the use of a torch that includes a temperature sensor and / or a pressure sensor inside the plasma torch to measure the temperature and / or pressure of the inert gas.

[0179] The methods provided herein can enable the actual volumetric flow rate to be achieved across the full range of fluctuations in gas density in order to achieve a targeted value for the gas emission rate in a plasma torch. The methods and systems provided herein can also enable an inert gas stream to be fed to the plasma torch with respect to both the number of gas molecules over time and the gas volume over time. The volume control of the inert gas can be achieved by changing the temperature and / or pressure of the inert gas, thereby controlling the gas density to maintain a constant average distance between gas molecules due to environmental and mechanical disturbances that can affect the distance between gas molecules.

[0180] The method can include communicating a target mass flow rate or a target volumetric flow rate or both a target mass flow rate and a target volumetric flow rate of the inert gas to a process master controller, measuring the mass flow rate of the inert gas, determining a volumetric flow rate calculated based on the mass flow rate of the inert gas, comparing the calculated volumetric flow rate to the target volumetric flow rate, calculating a difference between the calculated volumetric flow rate and the target volumetric flow rate, and adjusting the inert gas flow to the plasma torch by a) adjusting a mass flow control valve to increase or decrease the mass flow rate of the inert gas to the plasma torch, or b) adjusting the gas density of the inert gas by adjusting the temperature and / or pressure of the inert gas supplied to the plasma torch.

[0181] This method can also include positioning a gas density corrector within the inert gas flow line of an additive manufacturing system, and measuring and adjusting gas density variations of the inert gas caused by radiation disturbances from a plasma torch or a workpiece or a combination thereof. The gas density corrector can be positioned inside the production chamber. The gas density corrector can be positioned outside the production chamber. The gas density corrector can communicate with a sensing kit that communicates with a position at or near the position of the plasma torch gas inlet, or a position within the plasma torch, or a position connected anywhere between the gas manifold and the electromagnetic field of the gas ionization device. The sensing kit can communicate with a plurality of flow meters, temperature sensors, pressure sensors, or any combination thereof. The sensing kit can detect external disturbances that affect the inert gas flow to the plasma torch. Adjusting the gas density can include increasing or decreasing the gas temperature. Adjusting the gas density can include increasing or decreasing the gas pressure. Adjusting the gas density can include modifying the gas temperature and pressure.

[0182] In a method in which the flow of an inert gas ionized within a plasma torch is adjusted by a control valve, the method includes adjusting the control valve by generating an adjustment signal based on a difference value representing the difference between a set value and an actual value, and transmitting the adjustment signal to a drive unit attached to the flow control valve, the drive unit increasing or decreasing the opening degree of the control valve based on the adjustment signal. In some methods, the inert gas can be directed to a gas density modifier capable of adjusting the density of the inert gas. Adjusting the density of the inert gas can include a) measuring the temperature of the inert gas and increasing or decreasing the temperature of the inert gas in response to the difference value, or b) measuring the pressure of the inert gas and increasing or decreasing the pressure of the inert gas in response to the difference value, or c) including both a) and b). Increasing the temperature of the inert gas can include directing the inert gas to a temperature regulator including a heater and operating the heater. Decreasing the temperature of the inert gas can include directing the inert gas to a temperature regulator including a cooling device and operating the cooling device. Increasing or decreasing the pressure of the inert gas supplied to the plasma torch can include directing the inert gas to a pressure regulator.

[0183] An exemplary method of feeding an inert gas having a target volumetric flow rate and a target mass flow rate, which is ionized in a plasma, to a plasma torch is to provide the inert gas from a gas supply manifold to an inlet of the plasma torch through a control valve attached to an inert gas supply manifold via an inert gas line, measuring a) the temperature, mass flow rate, and pressure of the inert gas between the inert gas supply manifold and the gas ionization device electromagnetic field of the plasma torch, or b) the temperature, mass flow rate, and pressure of the inert gas at or near the plasma torch gas inlet, or c) the temperature and pressure of the inert gas inside the plasma torch and the mass flow rate at or near the plasma torch gas inlet, or d) any combination of a), b), and c), calculating the actual volumetric flow rate of the inert gas to the plasma torch at i) a location at or near the plasma torch inlet, or ii) inside the plasma torch, or iii) a location of the inert gas supply line between the gas manifold and the plasma torch gas inlet, comparing the actual volumetric flow rate with the target volumetric flow rate to generate a volumetric flow rate difference value, comparing the actual mass flow rate with the target mass flow rate to generate a mass flow rate difference value, and based on the mass flow rate difference value and / or the volumetric flow rate difference value, a) adjusting the control valve to increase or decrease the mass flow rate of the inert gas reaching the plasma torch gas inlet through the control valve, or b) adjusting the density of the inert gas by increasing or decreasing the pressure and / or temperature of the inert gas to result in a modified inert gas volumetric flow rate and guiding the modified inert gas to the inlet of the plasma torch, or c) adjusting the control valve and the density of the inert gas by increasing or decreasing the pressure and / or temperature of the inert gas to control the mass flow rate and volumetric flow rate of the inert gas to the ionization electromagnetic field of the plasma torch.

[0184] In this method, adjusting the control valve includes generating an adjustment signal based on the mass flow rate difference value and / or the volume flow rate difference value, and transmitting the adjustment signal to a drive unit attached to the control valve, where the drive unit increases or decreases the opening degree of the control valve based on the adjustment signal. Adjusting the density of the inert gas in this method can include a) measuring the temperature of the inert gas and increasing or decreasing the temperature of the inert gas in response to the volume flow rate difference value, or b) measuring the pressure of the inert gas and increasing or decreasing the pressure of the inert gas in response to the volume flow rate difference value, or c) including both a) and b).

[0185] Increasing the temperature of the inert gas includes guiding the inert gas to a temperature regulator including a heater and operating the heater. Any heater can be used as long as it can raise the temperature of the inert gas. Exemplary heaters include induction heaters, resistance heaters, piezoelectric ceramic heaters, and any combination thereof.

[0186] Decreasing the temperature of the inert gas can include guiding the inert gas to a temperature regulator including a cooling device and operating the cooling device. Any cooling device can be used as long as it can lower the temperature of the inert gas. The cooling device can include a cryogenic cooling system or a heat exchanger that can lower the temperature of the inert gas. The cooling device can include a cryogenic fluid that can remove thermal energy from the inert gas. In some methods, the cooling device can include a) a pipe connected to a cryogenic fluid reservoir and a pump for forming a closed-loop cooling path for supplying a cooling fluid to the temperature regulator, or b) a conduit passing through the temperature regulator and a fan connected to a conduit for passing a cooling gas through the temperature regulator, or c) a combination of a) and b).

[0187] In the method provided herein, increasing or decreasing the pressure of the inert gas includes directing the inert gas to a pressure regulator. Any pressure regulator can be used as long as it can increase or decrease the pressure of the inert gas. For example, the pressure regulator can include a movable plenum chamber that increases the volume of the pressure regulator and thereby decreases the pressure of the inert gas exiting the pressure regulator, or decreases the volume of the pressure regulator and thereby increases the pressure of the inert gas exiting the pressure regulator. In the method provided herein, the inert gas can be argon.

[0188] It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit and scope of the invention. Accordingly, the invention is intended to cover such modifications and variations provided they are within the scope of the appended claims and their equivalents.

[0189] The following is a list of reference numbers used in this specification and the accompanying drawings.

Description of the Signs

[0190] 100 Gas supply 110 Hose or pipe between the gas supply and the gas supply manifold 120 Gas supply manifold 125 Hose or pipe between the gas supply manifold and the control valve 130 Control valve 135 Hose or pipe between the control valve and the density control element 140 Density control element 150 Temperature regulator 151 Liquid temperature regulator 152 Outlet 153 Conduit 154 Heat exchanger 155 Conduit 156 Conduit 158 Inlet 160 Pressure regulator 162 Plenum chamber 164 Sealing element 166 Position corrector 170 Pump 172 Suction port 174 Outlet 175 External liquid supply source 176 Inlet 178 Discharge port 181 Hose or pipe between the gas supply manifold and the gas volume / mass flow control system 185 Hose or pipe between the control valve and the plasma torch 190 Hose or pipe between the density control element and the plasma torch 195 Sensing connector between the gas supply line and the sensing kit Intermediate hose or pipe 200 Sensing kit 220 Temperature measurement unit 225 Temperature sensor 240 Pressure measurement unit 245 Pressure sensor 260 Mass flow measurement 265 Mass flow meter 300 Processors (controllers) group 320 Calculation processor for calculating the actual volume flow 340 Process master controller 360 Volume flow controller 385 Mass flow and volume flow controller 400 Part program 500 Data monitoring system 600 Plasma torch 605 Inert gas inlet of the plasma torch 610 Tungsten electrode 615 Region of the ionization device electromagnetic field 625 Plasma arc (ionized gas) 650 Workpiece

Claims

Claim 1 A system for controlling the flow of gas to a plasma torch of an additive manufacturing apparatus, comprising a source of inert gas, a supply manifold in fluid communication with the source of inert gas, a plasma torch including a gas inlet for receiving the inert gas from an inert gas line connected to the supply manifold, and a gas ionization device electromagnetic field for ionizing the inert gas into plasma, a sensing kit including a temperature measurement unit, a pressure measurement unit, and a mass flow measurement unit, each unit communicating with one or more sensing connectors connected at a position of the inert gas line between the supply manifold and the gas ionization device electromagnetic field, a control valve in fluid communication with the gas supply manifold and for regulating the flow of the inert gas from the gas supply manifold to the plasma torch, a process master controller communicating with the sensing kit, a part program providing a mass flow setpoint and a volume flow setpoint to the process master controller, a computer function executed by the process master controller for calculating an actual volume flow, a) a mass flow control function and a volume flow control function executed by the process master controller, or b) a combined mass flow and volume flow control function executed by the process master controller and the system further comprising a density control element for controlling the temperature and / or pressure of the inert gas fed to the inlet of the plasma torch. Claim 2 The mass flow control function compares the mass flow setpoint from the part program with the actual mass flow value from the mass flow measurement unit of the sensing kit and increases or decreases the mass flow of the inert gas to reduce the difference between the mass flow setpoint and the actual mass flow value by adjusting either the control valve or the density control element or both the control valve and the density control element, according to the system of claim 1. Claim 3 The volume flow rate control function compares the volume flow rate set value from the part program with the calculated volume flow rate value from the calculation function, and increases or decreases the volume flow rate of the inert gas to reduce the difference between the volume flow rate set value and the calculated volume flow rate value by adjusting either the control valve or the density control element or both the control valve and the density control element. The system according to claim 1.

4. The mass flow rate control function and the volume flow rate control function are executed by the process master controller, The mass flow rate control function is adapted to compare the mass flow rate set value from the part program with the actual mass flow rate value from the mass flow rate measurement unit of the sensing kit, and The volume flow rate control function compares the volume flow rate set value from the part program with the calculated volume flow rate value from the calculation function, and The control valve and the density control element are adjusted to adjust both the mass flow rate and the volume flow rate of the inert gas fed to the gas ionization device electromagnetic field of the plasma torch. The system according to claim 1.

5. The combined mass flow rate and volume flow rate control function compares the mass flow rate set value from the part program with the actual mass flow rate value from the mass flow rate measurement unit of the sensing kit, and the volume flow rate set value from the part program with the calculated volume flow rate value from the calculation function, and The control valve and the density control element are adjusted to adjust both the mass flow rate and the volume flow rate of the inert gas fed to the gas ionization device electromagnetic field of the plasma torch. The system according to claim 1.

6. The mass flow rate control function compares the mass flow rate set value from the part program with the actual mass flow rate value from the mass flow rate measurement unit of the sensing kit, and Increases or decreases the mass flow rate of the inert gas to reduce the difference between the mass flow rate set value and the actual mass flow rate value of the mass flow rate of the inert gas fed to the gas ionization device electromagnetic field of the plasma torch by adjusting the control valve, and The volume flow rate control function compares the volume flow rate set value from the part program with the calculated volume flow rate value from the calculation function, and The system according to claim 1, adapted to adjust a density control element so as to control a volumetric flow rate of the inert gas fed to the electromagnetic field of the gas ionization device of the plasma torch. **Claim 7** Each of the sensing connectors of the temperature measurement unit, the pressure measurement unit, and the mass flow measurement unit of the sensing kit is connected in the vicinity of the plasma torch gas inlet, Each of the sensing connectors of the temperature measurement unit and the pressure measurement unit of the sensing kit is located within the plasma torch, the system according to any one of claims 1 to 6. **Claim 8** The density control element is a) a temperature regulator and a temperature sensor, or b) a pressure regulator and a pressure sensor, or c) a temperature regulator, a temperature sensor, a pressure regulator and a pressure sensor, or d) any combination of a), b) and c) The system according to any one of claims 1 to 7, comprising. **Claim 9** The density control element includes the temperature regulator, and the temperature regulator includes a heater, The heater includes an induction heater, a resistance heater, a piezoelectric ceramic heating element, or a combination thereof, The temperature regulator further includes a cooling device, the system according to claim 8. **Claim 10** The cooling device is a) a pipe connected to a cryogenic fluid reservoir and a pump for forming a closed-loop cooling path for supplying a cooling fluid to the temperature regulator, or b) a conduit passing through the temperature regulator and a fan connected to the conduit for passing a cooling gas through the temperature regulator, or c) a combination of a) and b) The system according to claim 9, comprising. **Claim 11** Including the pressure regulator, The pressure regulator is Increasing the volume of the pressure regulator and thereby reducing the pressure of the inert gas exiting the pressure regulator, or Reducing the volume of the pressure regulator and thereby increasing the pressure of the inert gas exiting the pressure regulator The system according to any one of claims 8 to 10, comprising a movable plenum chamber capable of. **Claim 12** The density control element is configured to control the velocity of the inert gas to the plasma torch, the system according to any one of claims 8 to 11. **Claim 13** The sensing connector is positioned inside the production chamber of the additive manufacturing system and at the plasma torch gas inlet to measure the disturbance of the radiation from the plasma torch and / or the workpiece, according to any one of claims 1 to 12.

14. A mass flow meter located upstream of the control valve and communicating with the process master controller, the mass flow meter capable of detecting a decrease in the mass flow rate of the inert gas from the manifold, and the process master control transmitting a signal to a data monitoring system to indicate leakage, according to any one of claims 1 to 13.

15. The sensing connector is connected to the gas inlet or in the vicinity of the gas inlet. The system further includes a group of processors connected to the sensing kit and communicating with the control valve. The group of processors includes the process master controller communicating with the sensing kit, a calculation processor communicating with the sensing kit and the process master controller for calculating the actual volumetric flow rate, a mass flow controller and a volumetric flow controller communicating with the process master controller, and the part program for providing a mass flow set value or a volumetric flow set value or both a mass flow set value and a volumetric flow set value to the process master controller. The system according to any one of claims 1 to 14.

16. A method of feeding an inert gas with a target volumetric flow rate and a target mass flow rate ionized into plasma to a plasma torch, comprising: providing an inert gas from a gas supply manifold to an inlet of the plasma torch through a control valve attached to an inert gas supply manifold via an inert gas line; a) measuring the temperature, mass flow rate and pressure of the inert gas between the inert gas supply manifold and the gas ionization device electromagnetic field of the plasma torch; or b) measuring the temperature, mass flow rate and pressure of the inert gas at or near the plasma torch gas inlet; or c) measuring the temperature and pressure of the inert gas inside the plasma torch and the mass flow rate at or near the plasma torch gas inlet; or d) any combination of a), b) and c). i) calculating the actual volumetric flow rate of the inert gas to the plasma torch at or near the plasma torch inlet, or ii) inside the plasma torch, or iii) at the location of the inert gas supply line between the gas manifold and the plasma torch gas inlet; comparing the actual volumetric flow rate with a target volumetric flow rate to generate a volumetric flow rate difference value; comparing the actual mass flow rate with a target mass flow rate to generate a mass flow rate difference value; based on the mass flow rate difference value and the volumetric flow rate difference value; x) adjusting the control valve to increase or decrease the mass flow rate of the inert gas reaching the plasma torch gas inlet through the control valve, or y) adjusting the density of the inert gas by increasing or decreasing the pressure and / or temperature of the inert gas to provide a modified inert gas volumetric flow rate and guiding the modified inert gas to the inlet of the plasma torch, or z) adjusting the control valve and the density of the inert gas by increasing or decreasing the pressure and / or temperature of the inert gas to control the mass flow rate and volumetric flow rate of the inert gas to the ionization electromagnetic field of the plasma torch A method comprising the steps of: **Claim 17** Adjusting the control valve comprises: generating an adjustment signal based on the mass flow rate difference value and / or the volumetric flow rate difference value; transmitting the adjustment signal to a drive unit attached to the control valve, the drive unit increasing or decreasing the opening degree of the control valve based on the adjustment signal; The method according to claim 16, comprising the steps of: **Claim 18** Adjusting the density of the inert gas comprises: a) measuring the temperature of the inert gas and increasing or decreasing the temperature of the inert gas in response to the volumetric flow rate difference value, or b) measuring the pressure of the inert gas and increasing or decreasing the pressure of the inert gas in response to the volumetric flow rate difference value, or c) both a) and b) The method according to claim 16 or 17, comprising the steps of: **Claim 19** Increasing the temperature of the inert gas comprises guiding the inert gas to a temperature regulator including a heater and operating the heater. The method according to claim 18, comprising the steps of: **Claim 20** The heater includes an induction heater, a resistance heater, a piezoelectric ceramic heating element, or a combination thereof, the method according to claim 19.

21. Reducing the temperature of the inert gas includes guiding the inert gas to a temperature regulator including a cooling device and operating the cooling device, the method according to claim 18.

22. The cooling device a) a pump for forming a closed-loop cooling path for connecting a pipe connected to a low-temperature fluid reservoir and supplying a cooling fluid to the temperature regulator, or b) a conduit passing through the temperature regulator and a fan connected to the conduit for passing a cooling gas through the temperature regulator, or c) a combination of a) and b) including, the method according to claim 21.

23. Increasing or decreasing the pressure of the inert gas includes guiding the inert gas to a pressure regulator, the method according to claim 20.

24. The pressure regulator includes a movable plenum chamber capable of increasing the volume of the pressure regulator and thereby decreasing the pressure of the inert gas exiting the pressure regulator, or decreasing the volume of the pressure regulator and thereby increasing the pressure of the inert gas exiting the pressure regulator, the method according to claim 23.

25. The inert gas is argon, the method according to any one of claims 16 to 24.

26. The target volume flow rate and the target mass flow rate are provided by a part program, the method according to any one of claims 16 to 25.

27. A method of feeding an inert gas with a target volume flow rate to be ionized into plasma to a plasma torch, comprising: attaching the system according to any one of claims 1 to 15 to an inert gas supply source; and operating the system. A method including.

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