Positive and negative pressure pulse electric arc welding and additive manufacturing method

Abstract

The invention provides a positive and negative pressure pulse electric arc welding and additive manufacturing method which comprises the following steps: inducing electric arc plasma to generate a negative pressure electric arc with an anti-gravity adsorption effect through a current-magnetic field-hollow tungsten electrode-gas collaborative design, and forming a time sequence coupling process with a positive pressure electric arc. The core of the method is that a magnetic control positive pressure and negative pressure electric arc welding external field is cooperated with a molten pool reconstruction forming mechanism, that is, the dynamic and thermodynamic states of a molten pool are accurately balanced by dynamically switching the electric arc pressure direction and regulating and controlling the action proportion and alternating frequency of negative pressure and positive pressure electric arcs. A self-adaptive magnetic field threshold model based on current intensity and a gas mode is combined with variable polarity power supply parameters and gas flow rate cooperative control, and the problems of thin plate welding fusion penetration and thin-wall additive molten pool instability are effectively solved. According to the method, a welding wire, powder or laser composite manufacturing mode can be integrated, the forming precision and performance of a complex structure are remarkably improved, and an innovative technical support is provided for high-quality and high-efficiency welding and additive manufacturing.

Description

Technical Field

[0001] The present invention relates to the field of welding and additive manufacturing technology, and specifically to a positive and negative pressure pulse arc welding and additive manufacturing method based on the synergistic effect of current, magnetic field, hollow tungsten electrode and gas. In particular, it relates to a process that utilizes a magnetic field to induce a hollow tungsten electrode arc to generate a negative pressure arc with an anti-gravity adsorption effect, and performs pulse timing coupling with a positive pressure arc, thereby achieving stable control of the molten pool by dynamically regulating the stress state of the molten pool. The process is suitable for solving the problem of molten pool instability during high-quality welding of thin plate components and additive manufacturing of thin-walled complex structures. Background Art

[0002] Arc welding and additive manufacturing technologies, with their advantages of high heat input, strong material adaptability, and high forming efficiency, are widely used in the fields of joining thin-plate components and directly manufacturing complex metal structures. However, during thin-plate welding and additive manufacturing of thin-walled complex structures, the molten pool is prone to instability such as flowing, collapsing, spattering, and even perforation due to the coupling of complex dynamic and thermodynamic factors such as gravity, surface tension, and arc pressure. This seriously compromises the weld quality and the dimensional accuracy and mechanical properties of the additively manufactured components.

[0003] Traditional arc processes have significant limitations in controlling melt pool stability. Conventional tungsten inert gas welding (GTAW) relies on downward positive arc pressure to maintain melt pool shape, but this pressure can easily exacerbate melt pool oscillation and liquid metal splashing, especially on thin plates or in overhanging positions, leading to melt pool instability. While pulsed current can be used to regulate heat input, this is essentially a single-direction positive pressure, with limited ability to dynamically control the melt pool's stress state. Existing magnetic field-assisted arc technologies (such as external transverse or longitudinal magnetic fields) primarily agitate the melt pool to refine grains or constrain arc shape. While these technologies can improve forming to some extent, they fail to fundamentally change the direction of the arc's force on the melt pool (which remains downward positive pressure). Furthermore, the dynamic matching mechanism between magnetic field parameters and arc / melt pool state is imperfect, making them ineffective in addressing melt pool instability.

[0004] Chinese patent application publication numbers CN115007974A and CN114713942A disclose a tungsten inert gas arc welding method and additive manufacturing method with arc negative pressure constraint. Although the arc force direction is reversed by applying an external longitudinal magnetic field to form a negative pressure arc, which realizes the adsorption effect on the molten pool during welding and additive manufacturing, 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 coupling mechanism, which cannot dynamically balance the stress state of the molten pool; (2) The magnetic field is only used to induce a static negative pressure effect, and the hollow tungsten electrode structure and gas collaborative design are not combined, 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 is not solved, and it is difficult to meet the dynamic stability requirements of multi-pass and multi-layer additive manufacturing.

[0005] The Chinese patent application publication number CN118023712A discloses a negative pressure hollow tungsten electrode arc-laser coaxial composite welding method. Although a negative pressure area (0 to -300 Pa) is formed in the center of the arc by a magnetic field or a magnetic field + exhaust to reduce the shielding of the laser energy by the metal vapor, thereby improving the laser energy utilization rate and the weld penetration depth, the technology still has the following limitations: (1) It only uses a unidirectional static negative pressure to assist laser welding, and does not design a positive and negative pressure pulse timing coupling mechanism, and cannot dynamically control the stress state of the molten pool to solve the instability problem; (2) The negative pressure effect focuses on reducing the metal vapor shielding effect, and does not involve the dynamic control of the molten pool. In particular, there is no targeted solution to the instability phenomena such as molten pool flow and collapse in thin plate / thin wall additive manufacturing; (3) Although a hollow tungsten electrode structure is adopted, the magnetic field-hollow tungsten electrode-gas flow collaborative design is not realized, and it is difficult to accurately control the range and intensity of the negative pressure effect; (4) The problem of molten pool oscillation caused by the accumulation of thermal cycles is not solved, and the stability is insufficient in multi-pass and multi-layer additive manufacturing.

[0006] U.S. patent application publication number US2016 / 0067811A1 discloses a central negative pressure arc welding device and method. Although the device forms a relatively low-pressure zone in the center area 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 the local area is lower than the surrounding environment. It does not form a true negative pressure with an adsorption effect in the anti-gravity direction, and cannot actively stabilize the molten pool through the upward adsorption force.

[0007] Liu Mingxu. Numerical Simulation of Droplet Transfer in a Short-Circuit Arc Under a Magnetic Field, 2015. This paper studies the effect of a magnetic field on droplet transfer, optimizing droplet behavior by generating an upward electromagnetic force component. However, the arc itself and its primary force on the molten pool remain downward (positive pressure). The upward component generated by the magnetic field is primarily used to facilitate droplet detachment, rather than to control the dynamic stability of the entire molten pool. Furthermore, the research context focuses on droplet transfer, not on molten pool instability.

[0008] In the existing technology, conventional arc processes and magnetic field-assisted methods are unable to achieve active, dynamic, and bidirectional regulation of the stress state of the molten pool. The fundamental defect is that there is a lack of a mechanism to generate an adsorption-type negative pressure arc in the opposite direction of gravity, and the temporal coupling of negative pressure and positive pressure arcs cannot be achieved to dynamically balance the combined force of the molten pool. The "positive and negative pressure pulse arc welding and additive manufacturing method" proposed in the present invention breaks through this technical bottleneck through the collaborative design of current-magnetic field-hollow tungsten electrode-gas. Negative pressure arc refers to an arc force vector that is directed upward, forming an adsorption force on the molten pool in the direction opposite to gravity, rather than being lower than vacuum. The core of positive and negative pressure pulses is that the arc pressure direction switches periodically over time. Its essence is the temporal alternation of the arc force vector direction, which is essentially different from traditional current pulses.

[0009] In response to the above-mentioned long-standing technical bottlenecks and the shortcomings of existing methods, the present invention proposes a positive and negative pressure pulse arc welding and additive manufacturing method based on the collaborative design of current-magnetic field-hollow tungsten electrode-gas. The core of this method is to use a specially configured longitudinal magnetic field to dynamically induce the hollow tungsten electrode arc plasma to produce a true negative pressure arc with anti-gravity and strong adsorption effect, and to perform precisely timed pulse alternating coupling with a positive pressure arc (a conventional positive pressure arc or a positive pressure arc induced by a magnetic field or a positive pressure arc with a synergistic effect of a magnetic field and gas supply). Through this innovative timing coupling process, dynamic and precise control of the positive and negative pressures on the molten pool is achieved, effectively balancing the dynamic and thermodynamic states of the molten pool, thereby completely solving the instability problems such as melt penetration, 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

[0010] The purpose of the present invention is to overcome the defects of the prior art and provide a positive and negative pressure pulse arc welding and additive manufacturing method, which utilizes the current-magnetic field-hollow tungsten electrode-gas collaborative design to induce the generation of a negative pressure arc with an anti-gravity adsorption effect, and through the pulse timing coupling process of the positive and negative pressure arc, dynamically regulates the dynamic and thermodynamic states of the molten pool, completely solving the problem of molten pool instability in thin plate welding and thin-walled complex structure additive manufacturing, and ensuring high-precision, high-performance and high-quality forming properties of components.

[0011] The above purpose is achieved through the following technical solutions:

[0012] The present invention relates to a positive and negative pressure pulse arc welding and additive manufacturing method, comprising the following steps:

[0013] Step 1: Fix the workpiece or additive manufacturing component on the platform, and fix the workpiece to be welded or the additive manufacturing substrate on the operating platform to ensure that the working surface is flat and stable;

[0014] Step 2: Set the hollow tungsten electrode structural parameters: outer diameter 1.6-8mm, inner diameter 0.4-4mm; select the gas flow mode (gas supply, gas extraction, or natural state) according to process requirements;

[0015] 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 achieve variable polarity or pulsed hollow tungsten arc welding or additive manufacturing; according to the material, structure and process requirements, adjust the electrode positive connection (EP) or pulse current duty cycle, welding current amplitude and frequency, and gas flow direction and size in the hollow tungsten electrode to coordinately adapt to form an arc welding or additive manufacturing process with alternating negative and positive arc pressures;

[0016] Step 4: Set key process parameters, including arc parameters and magnetic field parameters, where the arc current is 60-560A, the welding speed is 0.08-50cm / s, the electrode positive (EP) state duty cycle is 10%-30%, the outer diameter of the hollow tungsten electrode is 1.6-8mm, the inner diameter of the hollow tungsten electrode is 0.4-4mm, the magnetic field intensity is 0.025-0.08T, the gas flow rate in the hollow tungsten electrode is 0-10m / s, and the negative pressure arc magnetic field threshold is greater than 0.022T;

[0017] Step 5: Turn on the hollow tungsten arc power supply and the external magnetic field excitation device to form a hollow tungsten arc with negative pressure for welding or additive manufacturing.

[0018] Furthermore, the negative pressure formed at the center of the arc is -12 to -680 Pa, the diameter of the negative pressure arc affected area is 1.2 to 38 mm, and the arc length is 1 to 10 mm;

[0019] Furthermore, the negative pressure arc in which the arc negative pressure and positive pressure alternately act accounts for 5% to 80%, the low frequency of the positive and negative pressure pulse frequency is 1 to 100 Hz, the medium frequency is 0.5 to 2 kHz, and the high frequency is 10 to 30 kHz;

[0020] Furthermore, the positive and negative pressure pulse arc welding and additive manufacturing method is characterized in that the magnetic field threshold for forming a negative pressure arc is as follows:

[0021] Mode 1: In the natural state of the hollow tungsten electrode, that is, without gas supply and exhaust, the negative pressure arc magnetic field threshold and the arc current satisfy the following functional relationship:

[0022] B(I)=0.15-3.87×10 -3 I+4.45×10 -5 I 2 -2.23×10 -7 I 3 +4.17×10 -10 I 4

[0023] Mode 2, in the hollow tungsten electrode exhaust mode, the negative pressure arc magnetic field threshold and the exhaust pressure satisfy the following functional relationship:

[0024] B(p)=0.04-0.02×exp(p / 9.18)

[0025] Mode 3, in the hollow tungsten electrode gas supply mode, the negative pressure arc magnetic field threshold and the arc current satisfy the following functional relationship:

[0026] B(I)=0.0588-8.348×10 -4 I+6.714×10 -6 I 2 -1.667×10 -8 I 3

[0027] Where: B represents the magnetic field threshold, the unit is Tesla (T), I represents the arc current, the unit is Ampere (A), p is the pumping pressure, the unit is Pascal (Pa);

[0028] Furthermore, in the positive and negative pressure pulse arc welding and additive manufacturing method, the negative pressure, range, and action time of the hollow tungsten electrode negative pressure arc can be flexibly adjusted by changing the magnetic field strength and frequency, the hollow tungsten electrode gas supply method and flow rate, and the arc current and action time. The hollow tungsten electrode negative pressure arc and the positive pressure arc cooperate with each other to complete the welding or additive manufacturing of complex structures in real time.

[0029] Furthermore, the hollow tungsten electrode, arc power supply and magnetic field parameters are adapted to different material properties:

[0030] (1) Q235 steel welding: hollow tungsten electrode outer diameter 2mm, inner diameter 0.6mm, arc current 60~80A, arc length 3mm, negative pressure arc proportion 20%~40%, EP state duty cycle 20%~30%, speed 0.6cm / s, applying longitudinal continuous alternating magnetic field, magnetic field strength 0.025~0.034T, arc negative pressure value -12~-120Pa, negative pressure arc affected area diameter 1.2~4mm, positive and negative pressure arc pulse frequency 12~20kHz; (2) 2195 aluminum alloy additive manufacturing: hollow tungsten electrode outer diameter 3mm, inner diameter 0.8mm, arc current 110~140A, arc length 5mm, negative pressure arc proportion 15%~20%, The EP state duty cycle is 15-25%, the speed is 1 cm / s, a longitudinal intermittent alternating magnetic field is applied, the magnetic field strength is 0.035-0.05 T, the arc negative pressure value is -150--280 Pa, the diameter of the negative pressure arc affected area is 5-10 mm, and the positive and negative pressure arc pulse frequency is 1-15 Hz; (3) ZK61 magnesium alloy additive: the hollow tungsten electrode has an outer diameter of 2.5 mm and an inner diameter of 0.7 mm, the arc current is 560 A, the arc length is 10 mm, the negative pressure arc accounts for 30%-80%, the EP state duty cycle is 10%, the speed is 3 cm / s, a longitudinal intermittent alternating magnetic field is applied, the magnetic field strength is 0.08 T, the arc negative pressure value is -680 Pa, and the pulse frequency is 0.6-1.2 kHz;

[0031] Furthermore, the gas delivered by the hollow tungsten electrode is CO2, or nitrogen, or argon, or helium, or a binary mixed gas of argon and helium, or a ternary mixed gas;

[0032] Furthermore, the process supports three composite manufacturing modes: metal powder is introduced into the hollow tungsten electrode to cooperate with the powder to realize powder cladding additive manufacturing, or welding wire is introduced into the hollow tungsten electrode to cooperate with the welding wire to realize wire cladding welding and additive manufacturing, or laser is introduced into the hollow tungsten electrode to cooperate with the laser to form hollow tungsten electrode coaxial composite welding and additive manufacturing.

[0033] The beneficial effects of the present invention include:

[0034] A current-magnetic field-hollow tungsten electrode-gas synergistic design induces a negative-pressure arc with an anti-gravity adsorption effect, subverting the traditional unidirectional arc pressure model and proposing a mechanism for external-field coordinated melt pool reconstruction in magnetically controlled positive and negative pressure arc welding. The negative-pressure arc forms a rotating adsorption flow field at the center of the melt pool, counteracting the effects of gravity through upward suction. This fundamentally suppresses instabilities such as weld penetration in thin-plate welding and melt pool flow or collapse in thin-walled additive manufacturing, achieving a precise balance between the dynamic and thermodynamic states of the melt pool.

[0035] Through a sequentially coupled process of positive and negative pressure pulses, the stress state of the molten pool is dynamically controlled. The negative pressure phase attracts the liquid metal, enhancing the stability of the molten pool's surface tension, while the positive pressure phase provides deep penetration, ensuring efficient forming. The alternating action of positive and negative pressure pulses completely resolves the problem of oscillation and instability in the molten pool caused by the accumulation of force and heat from a single positive pressure arc. This approach is particularly suited to the dynamic, efficient, stable, and high-quality welding and additive manufacturing requirements of thin-walled, complex structures such as cantilevers and curved surfaces.

[0036] A dynamic matching model of the magnetic field threshold is created, and a functional relationship between the current or gas pattern and the critical magnetic field is established to achieve precise generation and range control of negative pressure arc pulses. Combined with the coordination of multiple parameters such as gas flow rate (0-10m / s) and EP duty cycle (10%-30%), the welding or additive manufacturing efficiency is increased by more than 30% and the defect rate is reduced by ≥30%.

[0037] In order to better demonstrate the implementation process, functional characteristics and advantages of the present invention, embodiments will be used below and further explained in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 (a) is a schematic diagram of the negative pressure arc principle of a positive and negative pressure pulse arc welding and additive manufacturing method of the present invention;

[0039] Figure 1 (b) is a schematic diagram of the positive pressure arc principle of a positive and negative pressure pulse arc welding and additive manufacturing method of the present invention;

[0040] Figure 2 The relationship between the arc force of the positive pressure pulse and the negative pressure pulse of the present invention and time;

[0041] Figure 3 The changing law of the positive and negative pressure pulse arc force distribution under the coordinated conditions of current, magnetic field, hollow tungsten electrode and gas supply in the present invention;

[0042] Figure 4 The invention shows the arc rotation adsorption effect during the negative pressure pulse stage under the conditions of current-magnetic field-hollow tungsten electrode-exhaust coordination.

[0043] Figure 5 The velocity field and flow field of the arc in the negative pressure pulse stage under the conditions of current-magnetic field-hollow tungsten electrode-no gas supply or exhaust;

[0044] Figure 6 The positive and negative pressure pulse arc temperature field of the present invention under the conditions of current-magnetic field-hollow tungsten electrode-gas coordination;

[0045] Figure 7 The positive and negative pressure pulse arc pressure field of the present invention is under the conditions of current-magnetic field-hollow tungsten electrode-gas coordination;

[0046] Figure 8 The Z-direction velocity of the center axis of the positive and negative pressure pulse arc under the coordinated conditions of current, magnetic field, hollow tungsten electrode and gas;

[0047] Among them, 1-tungsten electrode center hole, 2-tungsten electrode, 3-negative pressure area, 4-negative pressure arc, 5-molten pool, 6-substrate, 7-positive pressure arc. DETAILED DESCRIPTION

[0048] The following embodiments of the present invention are described in further detail with reference to the accompanying drawings and examples. The following examples are used to illustrate the present invention but are not intended to limit the scope of the present invention.

[0049] Solve the problem of molten pool instability during thin plate welding and thin-walled complex structure additive manufacturing, and ensure the high-quality forming properties of welded or additively manufactured components. Specifically, Figure 1 As shown, the present invention proposes a positive and negative pressure pulsed arc welding and additive manufacturing method. This method, based on a coordinated design of current, magnetic field, hollow tungsten electrode, and gas, utilizes a magnetic field to induce an anti-gravity adsorption effect in the hollow tungsten electrode arc plasma, enabling a sequentially coupled welding process involving a negative pressure arc (4) and a positive pressure arc (7). The alternating pulses of the positive and negative pressure arcs effectively control the kinetic and thermodynamic characteristics of the weld pool. Figure 2 The pulse relationship of arc pressure changing with time is shown. Figure 3 The results show the positive and negative pressures at different air flow rates, demonstrating that air flow rate can regulate arc pressure. At high airflow speeds, the airflow dominates, forming a positive pressure arc; at low airflow speeds, the magnetic field dominates, forming a negative pressure arc. Figure 4 It shows that increasing the air supply speed makes the reflux range decrease continuously. Figure 5 It also shows that the increase in air supply speed produces a significant compression effect on the reflow area, further confirming the above-mentioned regulation law.

[0050] The specific implementation steps are as follows:

[0051] Step 1: Fix the workpiece or additive manufacturing component on the platform, fix the workpiece to be welded or the additive manufacturing substrate on the operating platform, and ensure that the working surface is level;

[0052] Step 2: Set the hollow tungsten electrode parameters according to the material and structure requirements;

[0053] 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 achieve variable polarity or pulsed hollow tungsten arc welding or additive manufacturing; according to the material, structure and process requirements, adjust the electrode positive connection (EP) or pulse current duty cycle, welding current amplitude and frequency, and gas flow direction and size in the hollow tungsten electrode to coordinately adapt to form an arc welding or additive manufacturing process with alternating negative and positive arc pressures;

[0054] Step 4: Set key process parameters, including arc parameters and magnetic field parameters, where the arc current is 60-560A, the welding speed is 0.08-50cm / s, the electrode positive (EP) state duty cycle is 10%-30%, the outer diameter of the hollow tungsten electrode is 1.6-8mm, the inner diameter of the hollow tungsten electrode is 0.4-4mm, the magnetic field intensity is 0.025-0.08T, the gas flow rate in the hollow tungsten electrode is 0-10m / s, and the negative pressure arc magnetic field threshold is greater than 0.022T;

[0055] Step 5: Turn on the hollow tungsten arc power supply and the external magnetic field excitation device to form a hollow tungsten arc with negative pressure for welding or additive manufacturing.

[0056] The hollow tungsten pole negative pressure arc and positive pressure arc with anti-gravity spinning effect are constructed in the following manner: an excitation coil is set on the welding gun, and an excitation current is applied to generate a longitudinal magnetic field that coincides with or is parallel to the arc center axis; by dynamically adjusting the longitudinal magnetic field intensity to exceed the critical threshold for the formation of negative pressure in the hollow tungsten pole arc, negative pressure is formed in the arc center and its range of action is affected; in combination with a conventional positive pressure arc, or a magnetic field-induced positive pressure arc, or the magnetic field and the gas flow direction and speed in the hollow tungsten pole, an arc welding and additive manufacturing process with alternating arc negative pressure and positive pressure is formed.

[0057] The negative pressure formed at the center of the arc is -12 to -680 Pa, the diameter of the negative pressure arc affected area is 1.2 to 38 mm, and the arc length is 1 to 10 mm.

[0058] The negative pressure arc with alternating negative and positive pressures accounts for 5% to 80%, the low frequency of the positive and negative pressure pulses is 1 to 100 Hz, the medium frequency is 0.5 to 2 kHz, and the high frequency is 10 to 30 kHz.

[0059] The positive and negative pressure pulse arc welding and additive manufacturing method is characterized in that the magnetic field threshold for forming a negative pressure arc is as follows:

[0060] (1) Under the natural state of the hollow tungsten electrode, that is, without gas supply and exhaust, the negative pressure arc magnetic field threshold and the arc current satisfy the following functional relationship:

[0061] B(I)=0.15-3.87×10-3 I+4.45×10 -5 I 2 -2.23×10 -7 I 3 +4.17×10 -10 I 4

[0062] (2) Under the hollow tungsten electrode pumping mode, the negative pressure arc magnetic field threshold and the pumping pressure satisfy the following functional relationship:

[0063] B(p)=0.04-0.02×exp(p / 9.18)

[0064] (3) Under the hollow tungsten electrode gas supply mode, the negative pressure arc magnetic field threshold and the arc current satisfy the following functional relationship:

[0065] B(I)=0.059-8.35×10 -4 I+6.71×10 -6 I 2 -1.67×10 -8 I 3

[0066] Where: B is the magnetic field threshold, the unit is Tesla (T), I is the arc current, the unit is Ampere (A), and p is the exhaust pressure, the unit is Pascal (Pa).

[0067] The positive and negative pressure pulse arc welding and additive manufacturing method forms a negative pressure area at the center of the arc, has a rotating adsorption effect, and forms a local low-pressure area. The liquid metal in the molten pool is stably and high-quality formed under the action of the negative pressure arc adsorption force and electromagnetic stirring, thereby improving the welding or additive manufacturing efficiency and quality.

[0068] In the positive and negative pressure pulse arc welding and additive manufacturing method, the negative pressure size, range and action time of the hollow tungsten electrode negative pressure arc can be flexibly adjusted by changing the magnetic field strength and frequency, the gas supply method and flow rate of the hollow tungsten electrode, the arc current size and action time. The hollow tungsten electrode negative pressure arc and the positive pressure arc work together to complete the welding or additive manufacturing of complex structures to ensure real-time shape.

[0069] The positive and negative pressure pulse arc welding and additive manufacturing method is characterized in that the gas delivered by the hollow tungsten electrode is CO2, or nitrogen, or argon, or helium, or a binary mixed gas of argon and helium, or a ternary mixed gas.

[0070] The positive and negative pressure pulse arc welding and additive manufacturing method is characterized in that: metal powder is introduced into the hollow tungsten electrode to cooperate with the powder to realize powder cladding additive manufacturing, or welding wire is introduced into the hollow tungsten electrode to cooperate with the welding wire to realize wire cladding welding and additive manufacturing, or laser is introduced into the hollow tungsten electrode to cooperate with the laser to form hollow tungsten electrode coaxial composite welding and additive manufacturing.

[0071] The positive and negative pressure pulses and their frequencies refer to the alternating positive and negative pressure pulses and their frequencies, and are not the current pulses and their frequencies of conventional arc welding processes. There is an essential difference between the two.

[0072] Example 1

[0073] The present embodiment provides a positive and negative pressure pulse arc welding and additive manufacturing method, wherein the welding sample material is Q235, and specifically includes the following steps:

[0074] Step 1: Fix the 1mm thick Q235 steel plate on the welding platform to ensure horizontal positioning;

[0075] Step 2, set the parameters of the hollow tungsten electrode 2, the outer diameter of the tungsten electrode is 2 mm, and the inner diameter of the tungsten electrode center hole 1 is 0.6 mm;

[0076] 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 achieve variable polarity or pulsed hollow tungsten arc welding or additive manufacturing; according to the material, structure and process requirements, the positive and negative voltage arc pulse frequency is 12 to 20 kHz;

[0077] Step 4: Set key process parameters, including arc parameters and magnetic field parameters, where the arc current is 60-80A, the arc length is 3mm, the negative pressure arc ratio is 20%-40%, the welding speed is 1cm / s, the electrode positive (EP) state duty cycle is 20%-30%, a longitudinal intermittent alternating magnetic field is applied, the magnetic field strength is 0.025-0.034T, a negative pressure area 3 of -12--120Pa is formed, a negative pressure arc adsorption force 4 is generated, the diameter of the negative pressure arc affected area is 1.2-4mm, and the hollow tungsten electrode inlet flow rate is 0-6m / s;

[0078] Step 5: Turn on the hollow tungsten pole arc power supply and the external magnetic field excitation device to form a hollow tungsten pole negative pressure arc. Figure 2 The pulse relationship diagram of arc pressure changing with time is shown for positive and negative pressure pulse welding.

[0079] Example 2

[0080] This embodiment provides a positive and negative pressure pulse arc welding and additive manufacturing method, wherein the additive manufacturing structural material is 2195 aluminum alloy plate, and specifically includes the following steps:

[0081] Step 1: Fix the 1.5mm thick 2195 aluminum alloy plate on the platform and ensure it is horizontally positioned;

[0082] Step 2, set the parameters of the hollow tungsten electrode 2, the outer diameter of the tungsten electrode is 3 mm, and the inner diameter of the tungsten electrode center hole 1 is 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 achieve variable polarity or pulsed hollow tungsten arc welding or additive manufacturing; according to the material, structure and process requirements, the positive and negative voltage arc pulse frequency is 1 to 15 Hz;

[0084] Step 4: Set key process parameters, including arc parameters and magnetic field parameters, where the arc current is 110-140A, the arc length is 5mm, the negative pressure arc ratio is 15%-20%, the speed is 1cm / s, the variable polarity current EP state duty cycle is 15-25%, and a longitudinal intermittent alternating magnetic field is applied with a magnetic field strength of 0.035-0.05T to form a negative pressure area 3 with a negative pressure value of -150-280Pa, generate a negative pressure arc adsorption force 4, the diameter of the negative pressure arc affected area is 5-10mm, and the hollow tungsten electrode inlet flow rate is 0-8m / s;

[0085] Step 5: Turn on the hollow tungsten pole arc power supply and the external magnetic field excitation device to form a hollow tungsten pole negative pressure arc. Figure 2 The pulse relationship diagram of arc pressure changing with time is shown for positive and negative pressure pulse welding.

[0086] Example 3

[0087] This embodiment provides a positive and negative pressure pulse arc welding and additive manufacturing method, wherein the additive manufacturing structural material is ZK61 magnesium alloy, and specifically includes the following steps:

[0088] Step 1: Fix the 2mm thick ZK61 magnesium alloy plate on the platform to ensure horizontal positioning;

[0089] Step 2, set the parameters of the hollow tungsten electrode 2, the outer diameter of the tungsten electrode is 2.5 mm, and the inner diameter of the tungsten electrode center hole 1 is 0.7 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 achieve variable polarity or pulsed hollow tungsten arc welding or additive manufacturing; according to the material, structure and process requirements, the positive and negative voltage arc pulse frequency is 0.6 to 1.2 kHz;

[0091] Step 4: Set key process parameters, including arc parameters and magnetic field parameters, where the arc current is 560A, the arc length is 10mm, the negative pressure arc ratio is 30% to 80%, the speed is 3cm / s, the variable polarity current EP state duty cycle is 10%, a longitudinal intermittent alternating magnetic field is applied, the magnetic field strength is 0.08T, a negative pressure area 3 with a negative pressure value of -680Pa is formed, a negative pressure arc adsorption force 4 is generated, the diameter of the negative pressure arc affected area is 38mm, and the flow rate at the hollow tungsten electrode inlet is 0 to 10m / s;

[0092] Step 5: Turn on the hollow tungsten pole arc power supply and the external magnetic field excitation device to form a hollow tungsten pole negative pressure arc. Figure 2 The pulse relationship diagram of arc pressure changing with time is shown for positive and negative pressure pulse welding.

[0093] It should be noted that the above embodiments are intended only to illustrate the technical principles of the present invention and are not intended to limit the scope of protection. Those skilled in the art may, without departing from the core concept of the present invention, make adaptive modifications or equivalent substitutions to the technical solutions, and such modifications and improvements shall fall within the scope of protection defined in the claims.

Claims

1. A positive and negative pressure pulse arc welding and additive manufacturing method, characterized by: Utilizing a coordinated design of current, magnetic field, hollow tungsten electrode, and gas, the magnetic field induces a time-coupled welding process of negative-pressure arc and positive-pressure arc to produce an anti-gravity and adsorption effect in the hollow tungsten electrode arc plasma. The dynamic and thermodynamic characteristics of the molten pool are controlled by the alternating pulses of positive and negative pressure arcs, solving the problem of molten pool instability during thin-plate welding and additive manufacturing of thin-walled complex structures, thereby ensuring high-quality forming properties of welded or additively manufactured components. The hollow tungsten electrode negative pressure arc and positive pressure arc with anti-gravity vortex suction effect are constructed in the following manner: an excitation coil is provided on the welding gun, and an excitation current is applied to generate a longitudinal magnetic field that is coincident with or 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, a negative pressure is formed in the center of the arc and its range of action; in combination with a conventional positive pressure arc, or a positive pressure arc induced by a magnetic field, or in combination with the magnetic field and the direction and speed of gas flow in the hollow tungsten electrode, an arc welding and additive manufacturing process with alternating arc negative pressure and positive pressure is formed; The negative pressure formed at the center of the arc is -12 to -680 Pa, the diameter of the negative pressure arc affected area is 1.2 to 38 mm, and the arc length is 1 to 10 mm; The negative pressure arc with alternating negative and positive pressures accounts for 5% to 80%, the positive and negative pressure arc pulses have a low frequency of 1 to 100 Hz, a medium frequency of 0.5 to 2 kHz, and a high frequency of 10 to 30 kHz.

2. The positive and negative pressure pulse arc welding and additive manufacturing method according to claim 1, characterized in that: The magnetic field threshold for forming a negative pressure arc is as follows: Mode 1: In the natural state of the hollow tungsten electrode, that is, without gas supply and exhaust, the negative pressure arc magnetic field threshold and the arc current satisfy the following functional relationship: B(I)=0.15-3.87×10 -3 ·I+4.45×10 -5 ·I 2 -2.23×10 -7 ·I 3 +4.17×10 -10 ·I 4 Mode 2, in the hollow tungsten electrode exhaust mode, the negative pressure arc magnetic field threshold and the exhaust pressure satisfy the following functional relationship: B(p)=0.04-0.02×exp(p / 9.18) Mode 3, in the hollow tungsten electrode gas supply mode, the negative pressure arc magnetic field threshold and the arc current satisfy the following functional relationship: B(I)=0.059-8.35×10 -4 ·I+6.71×10 -6 ·I 2 -1.67×10 -8 ·I 3 Where: B is the magnetic field threshold, the unit is Tesla (T), I is the arc current, the unit is Ampere (A), and p is the exhaust pressure, the unit is Pascal (Pa).

3. The positive and negative pressure pulse arc welding and additive manufacturing method according to claim 1, characterized in that: The sequential collaborative process of positive and negative pressure pulsed arc welding and additive manufacturing methods is performed as follows: Step 1: Fix the workpiece or additive manufacturing component on the platform; Step 2, set the hollow tungsten electrode parameters; Step 3: Set 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 achieve variable polarity or pulsed hollow tungsten arc welding or additive manufacturing; according to the material, structure and process requirements, adjust the electrode positive connection (EP) or pulse current duty cycle, welding current amplitude and frequency, and gas flow direction and size in the hollow tungsten electrode to coordinately adapt to form an arc welding and additive manufacturing process with alternating negative and positive arc pressures; Step 4, setting key process parameters, including arc parameters and magnetic field parameters, wherein the arc current is 60-560A, the welding speed is 0.08-50cm / s, the electrode positive (EP) state duty cycle is 10%-30%, the outer diameter of the hollow tungsten electrode is 1.6-8mm, the inner diameter of the hollow tungsten electrode is 0.4-4mm, the magnetic field strength is 0.025-0.08T, the gas flow rate in the hollow tungsten electrode is 0-10m / s, and the negative pressure arc magnetic field threshold is greater than 0.022T; Step 5: Turn on the hollow tungsten pole arc power supply and the external magnetic field excitation device to form a hollow tungsten pole negative pressure arc for welding or additive manufacturing; The positive and negative pressure pulse arc welding and additive manufacturing method described herein forms a negative pressure area at the center of the arc, which has a rotating adsorption effect and forms a local low-pressure area. Under the action of the negative pressure arc adsorption force and electromagnetic stirring, the liquid metal in the molten pool is stably formed with high quality, thereby improving the welding or additive manufacturing efficiency and quality. In the positive and negative pressure pulse arc welding and additive manufacturing method, the negative pressure size, range and action time of the hollow tungsten electrode negative pressure arc can be flexibly adjusted by changing the magnetic field strength and frequency, the gas supply method and flow rate of the hollow tungsten electrode, the arc current size and action time. The hollow tungsten electrode negative pressure arc and the positive pressure arc work together to complete the welding or additive manufacturing of complex structures to ensure real-time shape.

4. The positive and negative pressure pulse arc welding and additive manufacturing method according to claim 1, characterized in that: The welding sample material is Q235, the outer diameter of the hollow tungsten electrode is 2mm, the inner diameter is 0.6mm, the arc current is 60~80A, the arc length is 3mm, the negative pressure arc accounts for 20%~40%, the EP state duty cycle is 20%~30%, the speed is 0.6cm / s, and a longitudinal continuous alternating magnetic field is applied with a magnetic field strength of 0.025~0.034T, forming a negative pressure area of ​​-12~-120Pa. The diameter of the negative pressure arc affected area is 1.2~4mm, and the positive and negative pressure arc pulse frequency is 12~20kHz.

5. The positive and negative pressure pulse arc welding and additive manufacturing method according to claim 1, characterized in that: The additive manufacturing structural material is 2195 aluminum alloy plate, the outer diameter of the hollow tungsten pole is 3mm, the inner diameter is 0.8mm, the arc current is 110~140A, the arc length is 5mm, the negative pressure arc accounts for 15%~20%, the EP state duty cycle is 15~25%, the speed is 1cm / s, and a longitudinal intermittent alternating magnetic field is applied. The magnetic field strength is 0.035~0.05T, the arc negative pressure value is -150~-280Pa, the diameter of the negative pressure arc affected area is 5~10mm, and the positive and negative pressure arc pulse frequency is 1~15Hz.

6. The positive and negative pressure pulse arc welding and additive manufacturing method according to claim 1, characterized in that: The additive manufacturing structural material is ZK61 magnesium alloy, the outer diameter of the hollow tungsten pole is 2.5mm, the inner diameter is 0.7mm, the arc current is 560A, the arc length is 10mm, the negative pressure arc accounts for 30% to 80%, the EP state duty cycle is 10%, the speed is 3cm / s, and a longitudinal intermittent alternating magnetic field is applied with a magnetic field strength of 0.08T. The arc negative pressure value is -680Pa, the diameter of the negative pressure arc affected area is 38mm, and the positive and negative pressure arc pulse frequency is 0.6 to 1.2kHz.

7. The positive and negative pressure pulse arc welding and additive manufacturing method according to claim 1, characterized in that: The gas delivered by the hollow tungsten pole is CO2, or nitrogen, or argon, or helium, or a binary mixed gas of argon and helium, or a ternary mixed gas.

8. The positive and negative pressure pulse arc welding and additive manufacturing method according to claim 1, characterized in that: Metal powder is passed into the hollow tungsten electrode to realize powder cladding additive manufacturing in combination with the powder, or welding wire is passed into the hollow tungsten electrode to realize wire cladding welding and additive manufacturing in combination with the welding wire, or laser is passed into the hollow tungsten electrode to realize hollow tungsten coaxial composite welding and additive manufacturing in combination with the laser.

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