A Hollow Tungsten Electrode Positive and Negative Voltage Pulsed Arc Coaxial Wire Feeding Melting Welding and Additive Manufacturing Method

Abstract

This invention provides a method for coaxial wire feeding welding and additive manufacturing using a hollow tungsten electrode with positive and negative voltage pulsed arc. The method includes: fixing a workpiece or additive manufacturing substrate on a platform; setting hollow tungsten electrode parameters; configuring a variable polarity or pulsed arc power supply; setting key process parameters; and starting the coaxial wire feeding system, the hollow tungsten electrode arc power supply, and the external magnetic field excitation equipment. Through these steps, a pulsed timing synergistic process is constructed, synergistically controlling the magnetic field, the gas flow direction and velocity within the hollow tungsten electrode, and the arc current to form an external field with alternating positive and negative voltage arcs. The suction force of the negative voltage arc pulse phase directionally guides the molten wire droplets to a stable, impact-free transition into the molten pool, while the positive voltage arc pulse phase releases the molten pool pressure and spreads the liquid metal. This synergistic control of the droplet-molten pool system solves the problem of molten pool instability in thin-plate welding and thin-walled additive manufacturing, ensuring high-quality formability of welded or additively manufactured components.

Description

Technical Field

[0001] This invention relates to the fields of welding and additive manufacturing, specifically to a hollow tungsten electrode positive and negative voltage pulsed arc coaxial wire feeding welding and additive manufacturing method. Background Technology

[0002] Arc welding and additive manufacturing technologies are widely used in the joining of thin-plate components and the direct manufacturing of complex metal structures due to their advantages such as high heat input, strong material adaptability, and high forming efficiency. However, during the welding of thin plates and the additive manufacturing of thin-walled complex structures, the molten pool is prone to instability phenomena such as flowing, collapse, spattering, and even perforation due to the coupled effects of complex dynamic and thermodynamic factors such as gravity, surface tension, arc pressure, and droplet impact force. These phenomena severely impair the weld formation quality and the dimensional accuracy and mechanical properties of the additive components.

[0003] Traditional arc welding processes have significant limitations in controlling molten pool stability: conventional gas metal arc welding (GMAW) relies on the downward arc pressure and droplet impact force to maintain the molten pool shape and metal transition. However, this continuous downward pressure easily exacerbates molten pool oscillation, liquid metal splashing, and droplet impact on the molten pool. This is especially true in thin plate welding or additive manufacturing in overhanging positions, which can easily lead to molten pool instability, melt-through, or poor formation. Although pulsed GMAW processes can control the droplet transition mode and heat input by adjusting pulse current parameters (such as peak current, frequency, and duty cycle), thus improving molten pool stability to some extent, the force exerted by the arc on the molten pool is essentially a positive pressure in the same direction as gravity. Pulse adjustment mainly affects the refinement of droplet transition and heat input distribution, but cannot dynamically reverse the direction of the arc's force on the molten pool. The ability to actively control the overall stress state of the molten pool remains limited.

[0004] When existing magnetic field-assisted arc technology (such as applying an external transverse or longitudinal magnetic field) is applied to GMAW, it mainly refines grains, constrains arc morphology, or affects droplet transfer trajectory through electromagnetic stirring. Although it can improve weld formation and reduce spatter to some extent, it has failed to construct a pulse-sequence synergistic process that combines negative pressure arc adsorption and traction of droplet transfer with positive pressure arc spreading of liquid metal. Therefore, it is not effective enough in precisely addressing the problem of molten pool instability in thin-plate and thin-walled applications.

[0005] Chinese patents with application publication numbers CN115007974A and CN114713942A disclose a tungsten inert gas (TIG) welding method and an additive manufacturing method with arc negative pressure constraint. Although the negative pressure arc is formed by reversing the direction of the arc force through an external longitudinal magnetic field, and the adsorption effect on the molten pool is realized in the welding and additive manufacturing process, the above technology still has fundamental limitations: (1) It relies on a continuous unidirectional negative pressure arc and lacks a positive and negative pressure pulse timing coordination process, which makes it impossible to dynamically balance the stress state of the molten pool; (2) The magnetic field is only used to induce a static negative pressure effect and is not combined with the hollow tungsten electrode structure and gas synergistic design, making it difficult to accurately control the range and intensity of the negative pressure effect; (3) In thin plate welding and thin-walled complex structure additive manufacturing, unidirectional negative pressure may still cause molten pool oscillation or local collapse, especially for high curvature and overhanging structures, the forming stability control is insufficient; (4) The problem of molten pool instability caused by thermal cycle accumulation has not been solved, making it difficult to meet the dynamic stability requirements of multi-pass multi-layer additive manufacturing.

[0006] Chinese patent application CN118023712A discloses a negative pressure hollow tungsten electrode arc-laser coaxial composite welding method. Although a negative pressure region (0 ~ -300 Pa) is formed in the center of the arc by a magnetic field or magnetic field + pumping to reduce the shielding of laser energy by metal vapor and improve the utilization rate of laser energy and weld penetration, the technology still has the following limitations: (1) It only uses unidirectional static negative pressure to assist laser welding and does not design a positive and negative pressure pulse timing coupling mechanism, so it cannot dynamically control the stress state of the molten pool to solve the instability problem; (2) The negative pressure effect focuses on reducing the shielding effect of metal vapor and does not involve the dynamic control of the molten pool, especially for the instability phenomena such as molten pool flow and collapse in thin plate welding and thin-walled additive manufacturing, there is no targeted solution; (3) Although a hollow tungsten electrode structure is adopted, the current-magnetic field-hollow tungsten electrode-gas flow synergistic design is not realized, making it difficult to accurately control the range and intensity of the negative pressure effect; (4) The problem of molten pool oscillation caused by thermal cycling accumulation has not been solved, resulting in insufficient stability in multi-stage and multi-layer additive manufacturing.

[0007] US Patent Application Publication No. US2016 / 0067811A1 discloses a central negative pressure arc welding device and method. Although the device forms a relatively low pressure zone in the center region of the electrode, the overall direction of its core arc force is still downward (positive pressure). The so-called "negative pressure" is a relative concept that the pressure in a local area is lower than that in the surrounding environment. It does not form a true negative pressure with an anti-gravity adsorption effect and cannot actively stabilize the molten pool through upward adsorption force.

[0008] Liu, Mingxu. Numerical Simulation of Droplet Transfer in Short-Circuit Arc under Magnetic Field, 2015. This paper studies the influence of magnetic field on droplet transfer, optimizing droplet behavior by generating an upward electromagnetic force component through the magnetic field. However, the arc itself and its main force on the molten pool are still downward (positive pressure). The upward component generated by the magnetic field is mainly used for droplet detachment, rather than for dynamic stability control of the molten pool as a whole, and its research background is droplet transfer rather than molten pool instability. A negative pressure arc refers to an arc force vector direction that is upward, forming an adsorption force on the molten pool in the anti-gravity direction, rather than being below vacuum. The core of positive and negative pressure pulses lies in the periodic switching of the arc pressure direction over time. Its essence is the temporal alternation of the arc force vector direction, which is fundamentally different from traditional current pulses.

[0009] In the existing technology, conventional electric arc processes and magnetic field-assisted methods cannot achieve active, dynamic, and bidirectional control of the stress state of the molten pool. Their fundamental defects are: the lack of a mechanism to generate an adsorption-type negative pressure electric arc opposite to the direction of gravity, and the failure to achieve a time-coordinated process of negative pressure and positive pressure electric arcs to dynamically balance the combined force of the molten pool.

[0010] To address the long-standing technical bottlenecks and shortcomings of existing methods, this invention proposes a coaxial wire-feeding melting welding and additive manufacturing method based on a co-designed hollow tungsten electrode positive and negative pressure pulsed arc. The core of this method lies in: dynamically inducing a hollow tungsten electrode arc plasma with anti-gravity and strong adsorption effects using a specifically configured longitudinal magnetic field, and precisely timing the pulsed coupling with a positive pressure arc. This innovative pulse-timing co-process enables dynamic and precise control of the positive and negative pressures on the molten pool, effectively balancing the kinetic and thermodynamic states of the molten pool. This completely solves the instability problems such as weld penetration and flow in thin-plate welding, and molten pool collapse and poor forming in the additive manufacturing of thin-walled complex structures, ensuring high-quality and high-precision forming properties. Summary of the Invention

[0011] The purpose of this invention is to overcome the deficiencies of existing technologies and provide a method for coaxial wire feeding welding and additive manufacturing using a hollow tungsten electrode positive and negative pressure pulsed arc. Based on a current-magnetic field-hollow tungsten electrode-gas synergistic system, and a coaxially integrated wire feeding system, this method uses a magnetic field to induce a hollow tungsten electrode arc plasma to generate a negative pressure arc with an anti-gravity adsorption effect and a positive pressure arc with a magneto-controlled spreading and strengthening effect, constructing a pulsed timing synergistic process. The negative pressure arc pulse's adsorption force directionally guides the molten wire droplets to a stable, impact-free transition into the molten pool. Coupled with the positive pressure arc pulse stage, the molten pool pressure is released and the liquid metal is spread. The dual effects of electromagnetic stirring by the positive and negative pressure pulsed arc—refining grains and eliminating porosity—synergistically regulate the droplet-molten pool-weld structure system, solving the problem of molten pool instability during thin-plate welding and additive manufacturing of thin-walled complex structures, ensuring high-quality formability of welded or additively manufactured components.

[0012] The above objectives are achieved through the following technical solutions:

[0013] This invention relates to a method for coaxial wire feeding welding and additive manufacturing using hollow tungsten electrode positive and negative voltage pulsed arc welding, comprising the following steps:

[0014] Step 1: Fix the workpiece or additive manufacturing substrate onto the platform;

[0015] Step 2: Set the parameters of the hollow tungsten electrode, including its internally integrated coaxial wire feeding system. The outer diameter of the hollow tungsten electrode is 1.8 ~ 9 mm, and the inner diameter of the hollow tungsten electrode (i.e., the size of the coaxial wire feeding channel) is 0.8 ~ 5 mm.

[0016] Step 3: Set up a variable polarity or pulsed arc power supply, connect one end of the arc power supply to the hollow tungsten electrode, and the other end to the workpiece; set up a coaxial wire feeding system to precisely feed the welding wire into the coaxial wire feeding channel inside the hollow tungsten electrode; adjust the electrode positive polarity (EP) or pulse current duty cycle, welding current amplitude and frequency, wire feeding speed and position, and the direction and magnitude of gas flow inside the hollow tungsten electrode according to material, structure and process requirements, and coordinate to form an arc coaxial wire feeding melting welding and additive manufacturing process with alternating arc negative pressure and positive pressure;

[0017] Step 4: Set key process parameters, including arc parameters and magnetic field parameters. The arc current is 80 ~ 520A, the welding or additive deposition rate is 0.1 ~ 6 cm / s, the wire feed speed is 0.5 ~ 15 m / min, the duty cycle of the positive electrode (EP) state is 15% ~ 35%, the magnetic field strength is 0.026 ~ 0.15 T, the gas flow velocity inside the hollow tungsten electrode is 0 ~ 10 m / s, and the negative pressure arc magnetic field threshold is greater than 0.022 T.

[0018] Step 5: Turn on the coaxial wire feeding system, the hollow tungsten inert gas (TIG) power supply, and the external magnetic field excitation equipment to form an arc environment with a negative pressure arc with an anti-gravity adsorption effect and a positive pressure arc pulse with a spreading and strengthening effect, and perform welding or additive manufacturing based on coaxial wire feeding.

[0019] Furthermore, the negative pressure formed at the center of the electric arc is -20 to -840 Pa, the diameter of the negative pressure arc-affected area is 1.5 to 45 mm, and the arc length is 1 to 6 mm;

[0020] Furthermore, the proportion of negative pressure arc with alternating negative and positive pressure is 10% to 70%, and the low frequency of the positive and negative pressure arc pulse is 1 to 200 Hz, the medium frequency is 1 to 3 kHz, and the high frequency is 10 to 30 kHz.

[0021] Furthermore, the hollow tungsten electrode positive and negative voltage pulsed arc coaxial wire feeding melting welding and additive manufacturing method is characterized in that the magnetic field threshold for forming the negative voltage arc is as follows:

[0022] (1) Under the natural state of the hollow tungsten electrode, i.e., without gas supply or extraction, the negative pressure arc magnetic field threshold and the arc current satisfy the following functional relationship.

[0023]

[0024] (2) Under the hollow tungsten electrode pumping method, the negative pressure arc magnetic field threshold and the pumping pressure satisfy the following functional relationship.

[0025]

[0026] (3) Under the hollow tungsten electrode gas supply method, the negative pressure arc magnetic field threshold and the arc current satisfy the following functional relationship.

[0027]

[0028] In the formula: B represents the magnetic field threshold, in Tesla (T), I represents the arc current, in Ampere (A), and p is the pumping pressure, in Pascal (Pa).

[0029] The hollow tungsten electrode negative pressure arc with anti-gravity adsorption effect and the positive pressure arc with magnetron spreading strengthening effect are constructed in the following way: an excitation coil is set on the welding torch, and an excitation current is applied to generate a longitudinal magnetic field that coincides with or is parallel to the central axis of the arc; by dynamically adjusting the intensity of the longitudinal magnetic field to exceed the critical threshold for the formation of negative pressure in the hollow tungsten electrode arc, negative pressure and its appropriate range of action are formed at the center of the arc; in combination with a conventional positive pressure arc, or with a magnetic field-induced positive pressure arc, or with the direction and speed of gas flow in the hollow tungsten electrode induced by the magnetic field, a coaxial wire-feeding arc melting welding and additive manufacturing process with alternating negative and positive pressure of the arc is formed.

[0030] Furthermore, the hollow tungsten electrode positive and negative pressure pulsed arc coaxial wire feeding welding and additive manufacturing method precisely feeds the welding wire into the center region of the arc through a coaxial wire feeding channel. A negative pressure region is formed at the center of the arc, generating a rotational adsorption effect and creating a local low-pressure region. This local low-pressure region acts directionally on the coaxially fed wire droplets, enabling them to achieve a stable and controlled transition from the droplets to the molten pool under the synergistic effect of negative pressure adsorption force and electromagnetic stirring. Simultaneously, the liquid metal in the molten pool flows synchronously and stably under the action of negative pressure adsorption force, achieving bidirectional stable control of the welding wire-molten pool system, significantly improving the forming accuracy and quality of welding or additive manufacturing.

[0031] The described hollow tungsten electrode positive and negative pressure pulsed arc coaxial wire feeding welding and additive manufacturing method utilizes a dynamic control mechanism of the negative pressure arc pulse on the molten droplets fed coaxially into the wire. During the negative pressure arc pulse stage, the negative pressure region formed at the center of the arc generates a rotational adsorption effect, causing the molten droplets to be in a buffer zone after detaching from the end of the welding wire, significantly reducing the impact kinetic energy of the molten droplets on the molten pool and forming a stable transition from the molten droplets to the molten pool without impact. During the positive pressure arc pulse stage, the magnetically controlled arc pressure is released and spreads the liquid metal in the molten pool. The molten droplets smoothly integrate into the molten pool under the action of gravity. At the same time, under the electromagnetic stirring action of the external field, the weld grains are refined, the internal pores of the molten pool are eliminated, and the segregation of the weld microstructure is reduced, forming a high-quality joint. Through the alternating action of the positive and negative pressure arcs, the buffering process of the molten droplet transition and the leveling process of the molten pool are independently controlled, ensuring stable forming and high-quality properties of the welded or additively manufactured structure.

[0032] Furthermore, in the hollow tungsten electrode positive and negative pressure pulsed arc coaxial wire feeding melting welding and additive manufacturing method, the negative pressure magnitude, range of action and duration of the hollow tungsten electrode negative pressure arc can be dynamically controlled by adjusting the magnetic field strength and frequency, the gas flow direction and flow rate inside the hollow tungsten electrode, and the arc current parameters. At the same time, it is necessary to coordinate and match the coaxial wire feeding speed and wire feeding position. The hollow tungsten electrode negative pressure arc and positive pressure arc act alternately, combined with the precise material supply of coaxial wire feeding, to jointly ensure the real-time shape control of the weld pool or the additive manufacturing deposition layer.

[0033] The hollow tungsten electrode positive and negative voltage pulsed arc coaxial wire feeding melting welding and additive manufacturing method uses a solid welding wire, a flux-cored welding wire, or a powder-cored welding wire with a diameter of 0.6 ~ 4.8 mm and a wire feeding speed of 0.3 ~ 18 m / min.

[0034] Furthermore, the hollow tungsten electrode, arc power supply, and magnetic field parameters are adapted to the characteristics of different welding wire materials:

[0035] (1) Solid alloy steel welding wire is fed through a hollow tungsten electrode coaxial wire feeding system. The hollow tungsten electrode has an outer diameter of 2 mm and an inner diameter of 0.8 mm. The welding wire diameter is 0.6 mm. The arc current is 80 ~ 300 A, the arc length is 1 ~ 6 mm, the negative pressure arc ratio is 10% ~ 30%, the EP duty cycle is 15% ~ 20%, the welding speed is 0.4 cm / s, and the wire feeding speed is 12 ~ 18 m / min. A longitudinal continuous alternating magnetic field is applied with a magnetic field strength of 0.026 ~ 0.035 T to form a negative pressure region of -20 ~ -150 Pa. The diameter of the negative pressure arc influence region is 1.5 ~ 4.5 mm, and the pulse frequency is 12 ~ 20 kHz. The conductive welding wire droplets are adsorbed and directionally transferred during the negative pressure stage, and the molten pool is spread during the positive pressure stage.

[0036] (2) Aluminum alloy flux-cored welding wire is fed through a hollow tungsten electrode coaxial wire feeding system. The hollow tungsten electrode has an outer diameter of 5 mm and an inner diameter of 2 mm. The welding wire diameter is 1.6 ~ 1.8 mm. The arc current is 140 ~ 200 A. The arc length is 1 ~ 3 mm. The negative pressure arc ratio is 25% ~ 50%. The duty cycle of the EP state is 18 ~ 25%. The deposition rate is 2 cm / s. The wire feeding rate is 1.3 ~ 4.5 m / min. A longitudinal intermittent alternating magnetic field is applied. The magnetic field strength is 0.04 ~ 0.065 T. The arc negative pressure value is -160 ~ -280 Pa. The diameter of the negative pressure arc influence area is 5 ~ 10 mm. The positive and negative pressure arc pulse frequency is 1 ~ 15 Hz. The negative pressure arc suppresses aluminum alloy droplet splashing. The positive pressure arc improves the surface leveling of the deposited layer.

[0037] (3) High-temperature alloy powder-cored welding wire is fed through a hollow tungsten electrode coaxial wire feeding system. The hollow tungsten electrode has an outer diameter of 9 mm and an inner diameter of 5 mm. The welding wire diameter is 4.6 ~ 4.8 mm. The arc current is 300 ~ 520 A. The arc length is 1 ~ 3 mm. The negative pressure arc accounts for 45% ~ 70%. The duty cycle of the EP state is 24 ~ 35%. The deposition rate is 3 ~ 6 cm / s. The wire feeding speed is 0.3 ~ 2 m / min. A longitudinal intermittent alternating magnetic field is applied. The magnetic field strength is 0.07 ~ 0.15 T. The arc negative pressure value is -300 ~ -840 Pa. The diameter of the negative pressure arc influence area is 12 ~ 45 mm. The positive and negative pressure arc pulse frequency is 1 ~ 1.5 kHz. The non-conductive welding wire droplets are strongly adsorbed in the negative pressure stage to overcome the high viscosity characteristics of the high-temperature alloy. The spreading time is extended in the positive pressure stage to prevent cracking.

[0038] Furthermore, the gas supplied to the hollow tungsten electrode is CO2, or nitrogen, or argon, or helium, or a binary mixture of argon and helium, or a ternary mixture of argon, helium and nitrogen.

[0039] The beneficial effects of this invention include:

[0040] Based on a current-magnetic field-hollow tungsten electrode-gas synergistic system, a coaxial integrated wire feeding system dynamically controls the stress state of the molten droplet and the molten pool through a positive and negative pressure pulse timing synergistic process. The negative pressure phase pulls the coaxially fed wire droplet, placing it in a buffer zone after it falls off, significantly reducing the impact kinetic energy of the droplet on the molten pool, suppressing spatter, and achieving a stable and controlled transition of the droplet to the molten pool. The positive pressure phase releases the arc pressure, effectively spreading the liquid metal in the molten pool, improving surface leveling and forming accuracy, while providing the necessary penetration depth. This solves the problem of molten pool instability in thin plate welding and additive manufacturing of thin-walled complex structures, ensuring high-quality formability of welded or additively manufactured components.

[0041] The negative pressure electric arc creates a rotating adsorption flow field at the center of the molten pool, and the resulting upward swirling suction effectively counteracts the influence of gravity. This mechanism fundamentally suppresses instability phenomena such as weld penetration in thin-plate welding and molten pool flow or collapse in thin-walled additive manufacturing, achieving a precise balance between molten pool dynamics and thermodynamic state, and significantly improving the stability and reliability of the forming process of complex structures such as thin walls, cantilever, and curved surfaces.

[0042] A dynamic matching model for magnetic field thresholds was established, clarifying the functional relationship between the critical magnetic field strength (B) required to form a negative pressure arc and the arc current (I) or the pumping pressure (p) under three working conditions: natural state, pumping state, and pumping state. By adjusting multiple parameters such as magnetic field strength and frequency, coordinated gas flow direction and velocity, and electrode positive connection (EP) duty cycle, the performance of the negative pressure arc can be optimized in real time.

[0043] To better demonstrate the process of achieving the objectives, functional characteristics, and advantages of this invention, the following will use embodiments and further explain them in detail with reference to the accompanying drawings. Attached Figure Description

[0044] Figure 1 (a) is a schematic diagram of the negative pressure arc principle of a hollow tungsten electrode positive and negative pressure pulsed arc coaxial wire feeding melting welding and additive manufacturing method of the present invention;

[0045] Figure 1 (b) is a schematic diagram of the positive pressure arc principle of a hollow tungsten electrode positive and negative pressure pulsed arc coaxial wire feeding melting welding and additive manufacturing method of the present invention;

[0046] Figure 2 This is a pulse relationship graph showing the change of arc pressure over time according to the present invention.

[0047] Figure 3 This invention illustrates the variation law of positive and negative voltage pulsed arc force distribution under the coordinated conditions of current-magnetic field-hollow tungsten electrode-gas supply.

[0048] Figure 4 This invention relates to the rotational adsorption effect of the electric arc during the negative pressure pulse stage under the synergistic conditions of current-magnetic field-hollow tungsten electrode-air extraction.

[0049] Figure 5 This invention describes the velocity field and flow field of the electric arc during the negative pressure pulse stage under the conditions of current-magnetic field-hollow tungsten electrode-no gas supply and no gas extraction.

[0050] Figure 6 This invention relates to the temperature field of a positive and negative voltage pulsed electric arc under the synergistic conditions of current-magnetic field-hollow tungsten electrode-gas.

[0051] Figure 7 This invention relates to a positive and negative pressure pulsed electric arc pressure field under the synergistic conditions of current-magnetic field-hollow tungsten electrode-gas;

[0052] Figure 8 The present invention relates to the velocity in the Z-direction of the central axis of a positive and negative voltage pulsed arc under the synergistic conditions of current-magnetic field-hollow tungsten electrode-gas;

[0053] Among them, 1-welding wire, 2-tungsten electrode, 3-negative pressure zone, 4-negative pressure arc, 5-molten pool, 6-substrate, 7-positive pressure arc. Detailed Implementation

[0054] The embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and should not be construed as limiting the scope of the invention.

[0055] This addresses the challenge of molten pool instability during thin-plate welding and additive manufacturing of complex thin-walled structures, ensuring high-quality formability of welded or additively manufactured components. Specifically, for example... Figure 1 As shown, this invention proposes a method for coaxial wire feeding melting welding and additive manufacturing using hollow tungsten electrode positive and negative pressure pulsed arcs. This method is based on a synergistic design of current-magnetic field-hollow tungsten electrode-gas, utilizing the magnetic field to induce an anti-gravity adsorption effect in the hollow tungsten electrode arc plasma, achieving a pulsed timing synergistic process between the negative pressure arc 4 and the positive pressure arc 7. Through the alternating pulsed action of the positive and negative pressure arcs, the droplet transfer behavior, the molten pool spreading process, and the dynamic and thermodynamic characteristics of molten pool stability can be effectively controlled. Figure 2 The pulse relationship between arc pressure and time is shown. Figure 3 The diagram shows the positive and negative pressure conditions under different air delivery speeds, indicating that the air delivery speed can regulate the arc pressure. Under high-speed airflow, the airflow dominates the formation of a positive pressure arc; under low-speed airflow, the magnetic field dominates the formation of a negative pressure arc. Figure 4 The results show that increasing the air supply speed causes the recirculation range to continuously decrease. Figure 5 This also shows that the increase in gas delivery speed has a significant compression effect on the recirculation region, further confirming the above-mentioned regulation law.

[0056] The specific implementation steps are as follows:

[0057] Step 1: Fix the workpiece to be welded or the additive manufacturing substrate to the operating platform, ensuring that the working surface is level;

[0058] Step 2: Set the parameters of the hollow tungsten electrode, including its internally integrated coaxial wire feeding system. The outer diameter of the hollow tungsten electrode is 1.8 ~ 9 mm, and the inner diameter of the hollow tungsten electrode (i.e., the size of the coaxial wire feeding channel) is 0.8 ~ 5 mm.

[0059] Step 3: Set up a variable polarity or pulsed arc power supply, connect one end of the arc power supply to the hollow tungsten electrode, and the other end to the workpiece; set up a coaxial wire feeding system to precisely feed the welding wire into the coaxial wire feeding channel inside the hollow tungsten electrode; adjust the electrode positive polarity (EP) or pulse current duty cycle, welding current amplitude and frequency, wire feeding speed and position, and the direction and magnitude of gas flow inside the hollow tungsten electrode according to the material, structure, and process requirements.

[0060] Step 4: Set key process parameters, including arc parameters and magnetic field parameters. The arc current is 80 ~ 520A, the welding or additive deposition rate is 0.1 ~ 6 cm / s, the wire feed speed is 0.5 ~ 15 m / min, the duty cycle of the positive electrode (EP) state is 15% ~ 35%, the magnetic field strength is 0.026 ~ 0.15 T, the gas flow velocity inside the hollow tungsten electrode is 0 ~ 10 m / s, and the negative pressure arc magnetic field threshold is greater than 0.022 T.

[0061] Step 5: Turn on the coaxial wire feeding system, hollow tungsten inert gas (TIG) power supply, and external magnetic field excitation equipment to form an arc environment with negative pressure arc with anti-gravity adsorption effect and positive pressure arc pulse with spreading and strengthening effect, and perform welding or additive manufacturing based on coaxial wire feeding.

[0062] The hollow tungsten electrode negative pressure arc with anti-gravity adsorption effect and the positive pressure arc with magnetron spreading strengthening effect are constructed in the following way: an excitation coil is set on the welding torch, and an excitation current is applied to generate a longitudinal magnetic field that coincides with or is parallel to the central axis of the arc; by dynamically adjusting the intensity of the longitudinal magnetic field to exceed the critical threshold for the formation of negative pressure in the hollow tungsten electrode arc, negative pressure and its appropriate range of action are formed at the center of the arc; in combination with a conventional positive pressure arc, or with a magnetic field-induced positive pressure arc, or with the direction and speed of gas flow in the hollow tungsten electrode induced by the magnetic field, a coaxial wire-feeding arc melting welding and additive manufacturing process with alternating negative and positive pressure of the arc is formed.

[0063] The negative pressure formed at the center of the electric arc is -20 to -840 Pa, the diameter of the negative pressure arc-affected area is 1.5 to 45 mm, and the arc length is 1 to 6 mm.

[0064] The negative pressure arc, which alternates between negative and positive pressure, accounts for 10% to 70% of the total arc. The low frequency of the positive and negative pressure arc pulses is 1 to 200 Hz, the medium frequency is 1 to 3 kHz, and the high frequency is 10 to 30 kHz.

[0065] The hollow tungsten electrode positive and negative voltage pulsed arc coaxial wire feeding melting welding and additive manufacturing method is characterized by the following magnetic field threshold for forming the negative voltage arc:

[0066] (1) Under the natural state of the hollow tungsten electrode, i.e., without gas supply or extraction, the negative pressure arc magnetic field threshold and the arc current satisfy the following functional relationship.

[0067]

[0068] (2) Under the hollow tungsten electrode pumping method, the negative pressure arc magnetic field threshold and the pumping pressure satisfy the following functional relationship.

[0069]

[0070] (3) Under the hollow tungsten electrode gas supply method, the negative pressure arc magnetic field threshold and the arc current satisfy the following functional relationship.

[0071]

[0072] In the formula: B represents the magnetic field threshold, in Tesla (T), I represents the arc current, in Ampere (A), and p is the pumping pressure, in Pascal (Pa).

[0073] The aforementioned hollow tungsten electrode positive and negative pressure pulsed arc coaxial wire feeding melting welding and additive manufacturing method precisely feeds the welding wire into the center region of the arc through a coaxial wire feeding channel. A negative pressure region is formed at the center of the arc, generating a rotational adsorption effect and creating a local low-pressure region. This local low-pressure region acts directionally on the coaxially fed wire droplets, enabling them to achieve a stable and controlled transition from the droplets to the molten pool under the synergistic effect of negative pressure adsorption force and electromagnetic stirring. Simultaneously, the liquid metal in the molten pool flows synchronously and stably under the action of negative pressure adsorption force, achieving bidirectional stable control of the welding wire-molten pool system, significantly improving the forming accuracy and quality of welding or additive manufacturing.

[0074] The described hollow tungsten electrode positive and negative pressure pulsed arc coaxial wire feeding welding and additive manufacturing method utilizes a dynamic control mechanism of the negative pressure arc pulse on the molten droplets fed coaxially into the wire. During the negative pressure arc pulse stage, the negative pressure region formed at the center of the arc generates a rotational adsorption effect, causing the molten droplets to be in a buffer zone after detaching from the end of the welding wire, significantly reducing the impact kinetic energy of the molten droplets on the molten pool and forming a stable transition from the molten droplets to the molten pool without impact. During the positive pressure arc pulse stage, the magnetically controlled arc pressure is released and spreads the liquid metal in the molten pool. The molten droplets smoothly integrate into the molten pool under the action of gravity. At the same time, under the electromagnetic stirring action of the external field, the weld grains are refined, the internal pores of the molten pool are eliminated, and the segregation of the weld microstructure is reduced, forming a high-quality joint. Through the alternating action of the positive and negative pressure arcs, the buffering process of the molten droplet transition and the leveling process of the molten pool are independently controlled, ensuring stable forming and high-quality properties of the welded or additively manufactured structure.

[0075] The hollow tungsten electrode positive and negative pressure pulsed arc coaxial wire feeding melting welding and additive manufacturing method describes a method where the negative pressure magnitude, range, and duration of the hollow tungsten electrode negative pressure arc can be dynamically controlled by adjusting the magnetic field strength and frequency, the gas flow direction and flow rate inside the hollow tungsten electrode, and the arc current parameters. At the same time, it is necessary to coordinate and match the coaxial wire feeding speed and wire feeding position. The hollow tungsten electrode negative pressure arc and positive pressure arc act alternately, combined with the precise material supply of coaxial wire feeding, to jointly ensure the real-time shape control of the weld pool or additive manufacturing deposition layer.

[0076] The hollow tungsten electrode positive and negative voltage pulsed arc coaxial wire feeding melting welding and additive manufacturing method uses a solid welding wire, a flux-cored welding wire, or a powder-cored welding wire with a diameter of 0.6 ~ 4.8 mm and a wire feeding speed of 0.3 ~ 18 m / min.

[0077] The gas supplied to the hollow tungsten electrode is CO2, nitrogen, argon, helium, a binary mixture of argon and helium, or a ternary mixture of argon, helium, and nitrogen.

[0078] The positive and negative pressure pulses and their frequencies refer to the pulses and frequencies of alternating positive and negative pressure, which are not the current pulses and frequencies of conventional arc welding processes. The two are fundamentally different.

[0079] Example 1

[0080] This embodiment of a hollow tungsten inert gas (TIG) positive and negative voltage pulsed arc coaxial wire feeding welding and additive manufacturing method involves feeding a solid alloy steel welding wire with a diameter of 0.6 mm through a hollow tungsten inert gas (TIG) coaxial wire feeding system. The method specifically includes the following steps:

[0081] Step 1: Fix the workpiece to be welded on the welding platform and ensure that the working surface is level;

[0082] Step 2: Set the parameters of the hollow tungsten electrode 2: outer diameter of tungsten electrode 2 mm, inner diameter of tungsten electrode 0.8 mm;

[0083] Step 3: Set up a variable polarity or pulsed arc power supply, connect one end of the arc power supply to the hollow tungsten electrode, and the other end to the workpiece to realize variable polarity or pulsed hollow tungsten electrode arc welding or additive manufacturing; depending on the material, structure and process requirements, the positive and negative voltage arc pulse frequency is 12 ~ 20 kHz.

[0084] Step 4: Set key process parameters, including arc parameters and magnetic field parameters. The arc current is 80 ~ 300A, the arc length is 1 ~ 6 mm, the negative pressure arc ratio is 10% ~ 30%, the EP duty cycle is 15% ~ 20%, the welding speed is 0.4 cm / s, and the wire feed speed is 12 ~ 18 m / min. Apply a longitudinal continuous alternating magnetic field with a magnetic field strength of 0.026 ~ 0.035 T to form a negative pressure region of -20 ~ -150 Pa, generating a negative pressure arc adsorption force 4. The diameter of the negative pressure arc influence region is 1.5 ~ 4.5 mm.

[0085] Step 5: Turn on the coaxial wire feeding system, the hollow tungsten electrode arc power supply, and the external magnetic field excitation equipment to form an arc environment with a negative pressure arc with an anti-gravity adsorption effect and a positive pressure arc pulse with a spreading and strengthening effect. According to... Figure 2 The pulse relationship graph of arc pressure changing with time shown is used for positive and negative pressure pulse welding based on coaxial wire feeding.

[0086] Example 2

[0087] This embodiment describes a hollow tungsten electrode positive and negative voltage pulsed arc coaxial wire feeding welding and additive manufacturing method. The method involves feeding an aluminum alloy flux-cored welding wire with a diameter of 1.6 to 1.8 mm via a hollow tungsten electrode coaxial wire feeding system. The specific steps include:

[0088] Step 1: Fix the additive manufacturing substrate to the operating platform, ensuring the working surface is level;

[0089] Step 2: Set the parameters of the hollow tungsten electrode 2: outer diameter of tungsten electrode 5 mm, inner diameter of tungsten electrode 2 mm;

[0090] Step 3: Set up a variable polarity or pulsed arc power supply, connect one end of the arc power supply to the hollow tungsten electrode and the other end to the workpiece to realize pulsed hollow tungsten electrode arc coaxial wire feeding melting additive manufacturing; depending on the material, structure and process requirements, the positive and negative voltage arc pulse frequency is 1 ~ 15 Hz.

[0091] Step 4: Set key process parameters, including arc parameters and magnetic field parameters. The arc current is 140 ~ 200A, the arc length is 1 ~ 3 mm, the negative pressure arc ratio is 25% ~ 50%, the EP state duty cycle is 18 ~ 25%, the deposition rate is 2 cm / s, and the wire feed rate is 1.3 ~ 4.5 m / min. Apply a longitudinal intermittent alternating magnetic field with a magnetic field strength of 0.04 ~ 0.065 T, an arc negative pressure value of -160 ~ -280 Pa, generating a negative pressure arc adsorption force 4, and the diameter of the negative pressure arc influence area is 5 ~ 10 mm.

[0092] Step 5: Turn on the coaxial wire feeding system, the hollow tungsten electrode arc power supply, and the external magnetic field excitation equipment to form an arc environment with a negative pressure arc with an anti-gravity adsorption effect and a positive pressure arc pulse with a spreading and strengthening effect. According to... Figure 2 The pulse relationship graph of arc pressure changing with time shown is used for positive and negative pressure pulse additive manufacturing based on coaxial wire feeding.

[0093] Example 3

[0094] This embodiment describes a hollow tungsten electrode positive and negative voltage pulsed arc coaxial wire feeding welding and additive manufacturing method. The method involves feeding a high-temperature alloy powder-cored welding wire with a diameter of 4.6 ~ 4.8 mm via a hollow tungsten electrode coaxial wire feeding system. The specific steps include:

[0095] Step 1: Fix the additive manufacturing substrate to the operating platform, ensuring the working surface is level;

[0096] Step 2: Set the parameters of the hollow tungsten electrode 2: outer diameter of tungsten electrode 9 mm, inner diameter of tungsten electrode 5 mm;

[0097] Step 3: Set up a variable polarity or pulsed arc power supply, connect one end of the arc power supply to the hollow tungsten electrode and the other end to the workpiece to realize pulsed hollow tungsten electrode arc coaxial wire feeding melting additive manufacturing; according to material, structure and process requirements, the positive and negative voltage arc pulse frequency is 1 ~ 1.5 kHz;

[0098] Step 4: Set key process parameters, including arc parameters and magnetic field parameters. The arc current is 300 ~ 520A, the arc length is 1 ~ 3 mm, the negative pressure arc accounts for 45% ~ 70%, the EP state duty cycle is 24 ~ 35%, the deposition rate is 3 ~ 6 cm / s, and the wire feed speed is 0.3 ~ 2 m / min. Apply a longitudinal intermittent alternating magnetic field with a magnetic field strength of 0.07 ~ 0.15 T, an arc negative pressure value of -300 ~ -840 Pa, generating a negative pressure arc adsorption force 4, and the diameter of the negative pressure arc influence area is 12 ~ 45 mm.

[0099] Step 5: Turn on the coaxial wire feeding system, the hollow tungsten electrode arc power supply, and the external magnetic field excitation equipment to form an arc environment with a negative pressure arc with an anti-gravity adsorption effect and a positive pressure arc pulse with a spreading and strengthening effect. According to... Figure 2 The pulse relationship graph of arc pressure changing with time shown is used for positive and negative pressure pulse additive manufacturing based on coaxial wire feeding.

[0100] It should be noted that the above embodiments are only used to illustrate the technical principles of the present invention and are not intended to limit the scope of protection. Those skilled in the art can make adaptive modifications or equivalent substitutions to the technical solutions without departing from the core concept of the present invention, and all related modifications and improvements fall within the scope of protection defined by the claims.

Claims

1. A method for hollow tungsten electrode positive and negative voltage pulsed arc coaxial wire feeding melting welding or additive manufacturing, characterized in that: Based on a current-magnetic field-hollow tungsten electrode-gas synergistic system and a coaxial integrated wire feeding system, a pulse-sequential synergistic process is constructed by using a magnetic field to induce a negative pressure arc with an anti-gravity adsorption effect and a positive pressure arc with a magneto-controlled spreading and strengthening effect in the hollow tungsten electrode arc plasma. The adsorption force of the negative pressure arc pulse is used to directionally guide the wire droplet to the molten pool for a stable transition without impact. The positive pressure arc pulse stage releases the molten pool pressure and spreads the liquid metal. The dual effects of positive and negative pressure pulse arc electromagnetic stirring refine the grains and eliminate pores, synergistically regulating the droplet-molten pool-weld microstructure system to ensure high-quality formability of welded or additively manufactured components. The negative pressure arc with anti-gravity adsorption effect and the positive pressure arc with magnetron spreading enhancement effect are constructed in the following way: an excitation coil is set on the welding torch, and an excitation current is applied to generate a longitudinal magnetic field that coincides with or is parallel to the central axis of the arc; by dynamically adjusting the intensity of the longitudinal magnetic field to exceed the critical threshold for the formation of negative pressure in the hollow tungsten electrode arc, negative pressure and its appropriate range of action are formed at the center of the arc; in combination with a conventional positive pressure arc, or with a magnetic field-induced positive pressure arc, or with the direction and speed of gas flow in the magnetic field-induced hollow tungsten electrode, a coaxial wire feeding melting welding or additive manufacturing process with alternating negative and positive pressure is formed. The negative pressure formed at the center of the electric arc is -20 to -840 Pa, the diameter of the negative pressure arc-affected area is 1.5 to 45 mm, and the arc length is 1 to 6 mm. The negative pressure arc, which alternates between negative and positive pressure, accounts for 10% to 70% of the total arc. The low frequency of the positive and negative pressure pulses is 1 to 200 Hz, the medium frequency is 1 to 3 kHz, and the high frequency is 10 to 30 kHz. The pulse timing coordination process is performed according to the following steps: Step 1: Fix the workpiece or additive manufacturing substrate onto the platform; Step 2: Set the parameters of the hollow tungsten electrode, including its internally integrated coaxial wire feeding system. The outer diameter of the hollow tungsten electrode is 1.8 ~ 9 mm, and the inner diameter of the hollow tungsten electrode is the size of the coaxial wire feeding channel, which is 0.8 ~ 5 mm. Step 3: Set up a variable polarity or pulsed arc power supply, connect one end of the arc power supply to the hollow tungsten electrode, and connect the other end to the workpiece or additive manufacturing substrate. A coaxial wire feeding system is set up to precisely feed the welding wire into the coaxial wire feeding channel inside the hollow tungsten electrode. According to the material, structure and process requirements, the duty cycle of the positive electrode or pulse current, the amplitude and frequency of the welding current, the wire feeding speed and position, and the direction and magnitude of the gas flow inside the hollow tungsten electrode are adjusted to form an arc coaxial wire feeding melting welding or additive manufacturing process with alternating arc negative pressure and positive pressure. Step 4: Set key process parameters, including arc parameters and magnetic field parameters. The arc current is 80 ~ 520 A, the welding or additive deposition rate is 0.1 ~ 6 cm / s, the electrode positive duty cycle is 15% ~ 35%, the magnetic field strength is 0.026 ~ 0.15 T, the gas flow velocity inside the hollow tungsten electrode is 0 ~ 10 m / s, and the negative pressure arc magnetic field threshold is greater than 0.022 T. Step 5: Turn on the coaxial wire feeding system, hollow tungsten inert gas (TIG) power supply, and external magnetic field excitation equipment to form an arc environment with negative pressure arc with anti-gravity adsorption effect and positive pressure arc pulse with magnetic spread enhancement effect, and perform welding or additive manufacturing based on coaxial wire feeding. The welding wire is precisely fed into the center of the electric arc through a coaxial wire feeding channel, forming a negative pressure area at the center of the arc and generating a rotational adsorption effect, creating a local low-pressure area. This local low-pressure area acts directionally on the coaxially fed wire droplets, enabling them to achieve a stable and controlled transition from the droplets to the molten pool under the combined action of negative pressure adsorption force and electromagnetic stirring. At the same time, the liquid metal in the molten pool flows synchronously and stably under the action of negative pressure adsorption force, realizing bidirectional stable control of the welding wire-molten pool system. The dynamic control mechanism of negative pressure arc pulses on the molten droplets fed coaxially into the wire involves the following steps: During the negative pressure arc pulse phase, the negative pressure region formed at the center of the arc generates a rotational adsorption effect, causing the molten droplets to be in a buffer zone after detaching from the end of the welding wire, forming a stable transition from the droplets to the molten pool without impact. During the positive pressure arc pulse phase, the magnetically controlled arc pressure is released and spreads the liquid metal in the molten pool. The molten droplets smoothly integrate into the molten pool under the action of gravity. At the same time, under the electromagnetic stirring action of the external field, the weld grains are refined, pores inside the molten pool are eliminated, and the segregation of weld microstructure is reduced, forming a high-quality joint. Through the alternating action of positive and negative pressure arcs, the buffering process of droplet transition and the leveling process of the molten pool are independently controlled, ensuring stable forming and high-quality properties of welded or additive manufacturing structures. The magnitude, range, and duration of the negative pressure of the hollow tungsten electrode negative pressure arc can be dynamically controlled by adjusting the magnetic field strength and frequency, the gas flow direction and flow rate inside the hollow tungsten electrode, and the arc current parameters. At the same time, it is necessary to coordinate and match the coaxial wire feeding speed and wire feeding position. The hollow tungsten electrode negative pressure arc and positive pressure arc work alternately, and combined with the precise material supply of coaxial wire feeding, they jointly ensure the real-time shape control of the weld pool or additive manufacturing deposition layer. The welding wire can be solid, flux-cored, or powder-cored, with a diameter of 0.6 to 4.8 mm and a wire feeding speed of 0.3 to 18 m / min.

2. The hollow tungsten electrode positive and negative voltage pulsed arc coaxial wire feeding melting welding or additive manufacturing method according to claim 1, characterized in that, The magnetic field threshold for forming a negative pressure electric arc is as follows: Method 1: Under the natural state of the hollow tungsten electrode, i.e., without gas supply or extraction, the magnetic field threshold of the negative pressure arc and the arc current satisfy the following functional relationship. ； In Method 2, under the hollow tungsten electrode pumping method, the magnetic field threshold of the negative pressure arc and the pumping pressure satisfy the following functional relationship: ； In Method 3, under the hollow tungsten electrode gas supply method, the magnetic field threshold of the negative pressure arc and the arc current satisfy the following functional relationship: ； In the formula: B represents the magnetic field threshold, in Tesla (T), I represents the arc current, in Ampere (A), and p is the pumping pressure, in Pascal (Pa).

3. A method for hollow tungsten electrode positive and negative voltage pulsed arc coaxial wire feeding melting welding or additive manufacturing according to claim 1 or 2, characterized in that: Solid alloy steel welding wire is fed through a hollow tungsten electrode coaxial wire feeding system. The hollow tungsten electrode has an outer diameter of 2 mm and an inner diameter of 0.8 mm. The welding wire diameter is 0.6 mm. The arc current is 80 ~ 300 A, the arc length is 1 ~ 6 mm, the negative pressure arc accounts for 10% ~ 30%, the electrode positive duty cycle is 15% ~ 20%, the welding speed is 0.4 cm / s, and the wire feeding speed is 12 ~ 18 m / min. A longitudinal continuous alternating magnetic field with a magnetic field strength of 0.026 ~ 0.035 T is applied to form a negative pressure region of -20 ~ -150 Pa. The diameter of the negative pressure arc influence region is 1.5 ~ 4.5 mm, and the pulse frequency is 12 ~ 20 kHz. During the negative pressure stage, the conductive welding wire droplets are adsorbed and directionally transferred, and during the positive pressure stage, the molten pool is spread.

4. A method for hollow tungsten electrode positive and negative voltage pulsed arc coaxial wire feeding melting welding or additive manufacturing according to claim 1 or 2, characterized in that: Aluminum alloy flux-cored welding wire is fed through a hollow tungsten electrode coaxial wire feeding system. The hollow tungsten electrode has an outer diameter of 5 mm and an inner diameter of 2 mm. The welding wire diameter is 1.6 ~ 1.8 mm. The arc current is 140 ~ 200 A, the arc length is 1 ~ 3 mm, the negative pressure arc ratio is 25% ~ 50%, the electrode positive duty cycle is 18 ~ 25%, the deposition rate is 2 cm / s, and the wire feed speed is 1.3 ~ 4.5 m / min. A longitudinal intermittent alternating magnetic field is applied with a magnetic field strength of 0.04 ~ 0.065 T. The arc negative pressure value is -160 ~ -280 Pa. The diameter of the negative pressure arc influence area is 5 ~ 10 mm, and the positive and negative pressure arc pulse frequency is 1 ~ 15 Hz. The negative pressure arc suppresses aluminum alloy droplet spatter, and the positive pressure arc improves the surface leveling of the deposited layer.

5. A method for hollow tungsten electrode positive and negative voltage pulsed arc coaxial wire feeding melting welding or additive manufacturing according to claim 1 or 2, characterized in that: High-temperature alloy powder-cored welding wire is fed through a hollow tungsten electrode coaxial wire feeding system. The hollow tungsten electrode has an outer diameter of 9 mm and an inner diameter of 5 mm. The welding wire diameter is 4.6 ~ 4.8 mm. The arc current is 300 ~ 520 A. The arc length is 1 ~ 3 mm. The negative pressure arc accounts for 45% ~ 70%. The electrode positive duty cycle is 24 ~ 35%. The deposition rate is 3 ~ 6 cm / s. The wire feeding speed is 0.3 ~ 2 m / min. A longitudinal intermittent alternating magnetic field is applied with a magnetic field strength of 0.07 ~ 0.15 T, an arc negative pressure value of -300 ~ -840 Pa, a negative pressure arc influence area diameter of 12 ~ 45 mm, and a positive and negative pressure arc pulse frequency of 1 ~ 1.5 kHz. During the negative pressure stage, non-conductive welding wire droplets are strongly adsorbed to overcome the high viscosity characteristics of high-temperature alloys, and during the positive pressure stage, the spreading time is extended to prevent cracks.

6. A method for hollow tungsten electrode positive and negative voltage pulsed arc coaxial wire feeding melting welding or additive manufacturing according to claim 1 or 2, characterized in that: The gas supplied to the hollow tungsten electrode is CO2, nitrogen, argon, helium, a binary mixture of argon and helium, or a ternary mixture of argon, helium, and nitrogen.

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