A wire current-carrying and follow-up magnetic field coordinated laser directed energy deposition device and method

Abstract

This invention discloses a laser-directed energy deposition apparatus and method that coordinates current carrying on the filament with a servo magnetic field. The apparatus includes a laser deposition head, a filament feeding mechanism, a conductive nozzle, a programmable current source, an electromagnetic device, a reflow fixture, and a controller. During deposition, current is applied to the filament through the conductive nozzle, forming a closed loop along the path of "filament—molten pool—substrate—reflow fixture," establishing a controllable current distribution within the molten pool. The electromagnetic device generates a transverse magnetic field, which couples the current with the magnetic field to produce a Lorentz force field, regulating the flow, heat transfer, and solidification of the molten pool. Switching the current type enables two modes: an electromagnetic braking mode coupling the magnetic field with DC current, suppressing molten pool convection and stabilizing the solidification front; and an electromagnetic oscillation mode coupling the magnetic field with AC current, inducing periodic electromagnetic forces to promote grain refinement and improve porosity and crack tendency. This invention eliminates the need for an independent external electrode inserted into the molten pool, simplifying the structure and making it suitable for long-term deposition on complex trajectories and precise control of crystal texture.

Description

Technical Field

[0001] This invention belongs to the field of metal additive manufacturing, specifically relating to a magnetoelectric coupling active control device and method for the laser powder-directed energy deposition (L-DED) process, and more particularly to a laser powder-directed energy deposition device and method that coordinates the current carrying capacity of the filament and the following magnetic field. Background Technology

[0002] Laser-directed energy deposition (LDED) is an additive manufacturing technology that uses a high-energy laser beam as a heat source and metal wires or powders as filler materials. This technology offers advantages such as high material utilization, high deposition efficiency, and unrestricted forming size, making it valuable for the manufacturing and repair of metal components in aerospace, energy equipment, and shipbuilding industries.

[0003] In laser-directed energy deposition (LDED), the flow within the molten pool and the stability of the solidification front directly affect the consistency of the deposited layer, its microstructure, and the formation of defects. For titanium alloys, stainless steel, and high-temperature alloys, during long-term continuous deposition, the temperature and flow fields of the molten pool are difficult to control, leading to defects such as molten pool fluctuations, splashing, unstable formation, porosity, cracks, high dilution rates, and coarsening of columnar crystals. These defects significantly reduce the deposition quality and service performance.

[0004] Existing technologies attempt to use external magnetic or electric fields to interfere with the flow and solidification of the molten pool, but there are still significant shortcomings:

[0005] The scheme of applying only an external magnetic field usually relies on the weak current (milliampere level) generated by the thermoelectric effect in the molten pool. A strong magnetic field (commonly >1T) is required to obtain sufficient Lorentz force, resulting in a large size and mass of the magnetic field device, the need for water cooling, difficulty in integration with the deposition head, and the strong magnetic field may affect the powder trajectory and deposition stability.

[0006] Fixed clamping electrode current diversion schemes (such as introducing applied current through lateral clamps or substrate electrodes) have the problem that the current path is unstable due to dynamic changes in the position of the molten pool, the resistance of the molten pool and the contact state. It is difficult to form a stable and repeatable volume force distribution inside the molten pool, and the electrodes are prone to burn-out and have poor spatial coordination with the deposition head.

[0007] One approach uses "hot-wire laser cladding," which involves heating the filler wire to near its melting point before laser irradiation by passing an electric current through it, thereby improving cladding efficiency. While preheating the welding wire helps reduce the main laser's energy consumption and improve cladding efficiency, it has limited control over the flow and solidification behavior of the molten pool, and cannot actively reduce defects such as porosity and cracks in the cladding layer, nor can it actively control the grain size and orientation of the molten pool.

[0008] Existing solutions attempt to combine electric and magnetic fields, but the magnetic fields used are mostly fixed magnetic fields, and the current introduction method is limited to indirect coupling far from the molten pool. They lack the ability to be coaxially aligned and follow up with the laser wire feeding / wire-powder co-feeding to the molten pool, which makes it impossible to accurately control and stably reproduce the current flow path and the spatial distribution of the Lorentz force field in the molten pool.

[0009] In existing external field control schemes, single magnetic field schemes are often limited by difficulties in magnetic field servoing or unstable control effects; schemes using independent electrodes to guide current to the laser molten pool have drawbacks such as complex equipment, difficulty in coupling with the wire / powder feeding system, and the risk of contamination and lifespan issues caused by electrodes being close to or entering the molten pool. Furthermore, existing schemes lack multiple switchable in-situ "magnetic-electric" control modes for laser wire / powder feeding directional energy deposition processes, and cannot achieve process switching between "convection suppression braking mode" and "stirring promotion oscillation mode" by switching current waveforms on the same equipment, making it difficult to simultaneously cover the two typical needs of directional crystal epitaxial growth and polycrystalline refinement.

[0010] Therefore, there is an urgent need for a new technical solution that can actively establish a strong, controllable and switchable Lorentz force field inside the laser wire feeding or laser wire feeding-powder co-feeding composite molten pool, while being able to be integrated with the lightweight deposition head in a dynamic manner without interfering with the wire feeding or wire feeding-powder co-feeding and the protective gas.

[0011] In laser wire feeding or laser wire feeding-powder co-directed energy deposition processes, the metal wire is naturally conductive and continuously enters the molten pool. If an external current source is used to apply current to the wire through a conductive nozzle at the wire exit point of the deposition head, and the wire then introduces the current into the molten pool, creating a closed loop through the substrate and reflow fixture, while a servo magnetic field is applied in the molten pool region, a controllable Lorentz force field can be constructed within the molten pool using the coupling effect of the current and magnetic field. This allows for active control of the molten pool's flow and solidification behavior. Therefore, a device and method are needed that is compact, easily integrated, requires no independent external electrode inserted into the molten pool, and can achieve dual-mode control ("electromagnetic braking / electromagnetic oscillation") through current type switching. Summary of the Invention

[0012] The purpose of this invention is to overcome the shortcomings of the prior art and provide a laser-directed energy deposition device and method that coordinates wire current carrying and a follow-up magnetic field. The external current is stably introduced into the molten pool through the wire and coupled with a constant external magnetic field to generate a Lorentz force field. By switching the type of external current, an electromagnetic braking mode of "magnetic field + DC" and an electromagnetic oscillation mode of "magnetic field + AC" can be realized, thereby stabilizing the molten pool and solidification front, promoting grain refinement and improving the tendency of porosity and crack formation, and realizing free switching between the two modes.

[0013] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: In a first aspect, the present invention provides a laser-directed energy deposition apparatus that coordinates current carrying by a filament and a servo magnetic field, comprising: A laser deposition head is used to output laser light and form a molten pool on the surface of a substrate. The laser deposition head is provided with a wire feeding channel. A wire feeding mechanism is used to continuously feed metal wire into the molten pool through the wire feeding channel; A conductive tip is disposed at the wire exit section of the laser deposition head and is in electrical contact with the metal wire, for applying an external current to the metal wire; A programmable current source, electrically connected to the conductive nozzle, is used to output DC current or AC current, and its current mode can be switched. An electromagnetic device, fixed to the laser deposition head and moving synchronously with the laser deposition head, is used to apply an external magnetic field to the molten pool region. The external magnetic field is a transverse magnetic field that is constant in time and adjustable in intensity, and its magnetic induction lines are perpendicular to the direction of the deposition scanning path. A reflow fixture is electrically connected to the substrate or tooling fixture and electrically connected to the loop return end of the programmable current source to form a closed current loop through the conductive nozzle, wire, molten pool, substrate to the reflow fixture. The controller is connected to the laser deposition head, the programmable current source, and the electromagnetic device, respectively, and is used to coordinate the adjustment of laser power, wire feed speed, deposition scanning rate, applied current type and parameters, and applied magnetic field parameters, and is configured to switch between applied current DC mode and AC mode during the deposition process; The applied current establishes a controlled current distribution in the molten pool through the closed current loop, and the applied current and the applied magnetic field interact in the molten pool to generate Lorentz force, thereby regulating the flow, heat transfer and solidification behavior of the molten pool.

[0014] Preferably, the applied magnetic field is a time-constant magnetic field with adjustable intensity and direction, and the magnetic induction intensity is 0.05~0.1T.

[0015] Preferably, when the programmable current source outputs DC current, the DC current amplitude is 20~50A; when the programmable current source outputs AC current, the effective value of the AC current is 20~50A and the frequency is 50~100Hz.

[0016] Preferably, the diameter of the metal wire is 0.8~1.5mm; the metal wire is a weakly magnetic solid welding wire, including at least one of nickel-based high-temperature alloy wire, cobalt-based high-temperature alloy wire, stainless steel wire, titanium alloy wire or aluminum alloy wire.

[0017] Preferably, the return fixture is clamped in the non-deposition area of ​​the substrate or tooling fixture so that the current loop does not cross the air or protective gas gap.

[0018] Preferably, the controller is configured to provide at least two operating modes: an electromagnetic braking mode in which the magnetic field is coupled to a direct current, and an electromagnetic oscillation mode in which the magnetic field is coupled to an alternating current; in the electromagnetic braking mode, the direct current is coupled to a constant external magnetic field to generate a steady-state Lorentz force, which suppresses convective fluctuations in the molten pool and stabilizes the solidification front; in the electromagnetic oscillation mode, the alternating current is coupled to a constant external magnetic field to generate an alternating Lorentz force, which induces electromagnetic oscillations in the molten pool and promotes grain refinement.

[0019] Preferably, the device further includes a powder feeding mechanism and a powder nozzle; the laser deposition head is also provided with a powder feeding channel; the powder nozzle is connected to the powder feeding channel, and the powder feeding mechanism is used to provide metal powder to the molten pool while feeding the wire through the powder feeding channel and the powder nozzle, so as to realize wire feeding-powder feeding composite simultaneous feeding.

[0020] Secondly, the present invention provides a laser-directed energy deposition method that coordinates current carrying capacity of a filament with a servo magnetic field, implemented using the aforementioned apparatus, comprising the following steps: The substrate or tooling fixture is electrically connected to the return terminal of the programmable current source via a return fixture. The laser deposition head is activated to form a molten pool on the substrate surface, while the wire feeding mechanism feeds metal wire into the molten pool. An external current is applied to the metal wire by a conductive tip located at the wire exit point of the laser deposition head. The applied current forms a closed current loop through the conductive tip, the wire, the molten pool, the substrate, and the reflow fixture, thus establishing a controlled current distribution within the molten pool. An electromagnetic device applies a transverse magnetic field to the molten pool region. The direction of the magnetic induction lines of the transverse magnetic field is perpendicular to the direction of the deposition scanning path, causing the current in the molten pool to couple with the magnetic field and generate a Lorentz force. During the deposition scanning process, the Lorentz force is used to regulate the flow, heat transfer, and solidification behavior of the molten pool.

[0021] Furthermore, when the programmable current source outputs DC current, it executes an electromagnetic braking mode. The DC current couples with the transverse magnetic field to generate a steady-state Lorentz force, which suppresses convective fluctuations in the molten pool and stabilizes the solidification front, and is used for the deposition or repair of single crystal or directional solidified alloys.

[0022] Furthermore, when the programmable current source outputs alternating current, it executes an electromagnetic oscillation mode. The alternating current couples with the transverse magnetic field to generate an alternating Lorentz force, which induces electromagnetic oscillation of the molten pool, breaks dendrites, and promotes the transformation of columnar crystals into equiaxed crystals, which is used for the deposition or repair of polycrystalline alloys.

[0023] Compared with the prior art, the present invention has at least the following beneficial effects: This invention uses metal wire as a current-carrying and guiding channel for the applied current, which not only plays the role of the filling material, but also allows the current to act directly on the molten pool. This avoids the limitations of traditional electromagnetic control that relies on weak thermocurrent (Seebeck effect), and significantly improves the electromagnetic force control effect. At the same time, this method does not require the insertion of independent external electrodes into the molten pool, has a compact structure, and is suitable for long-term continuous deposition operations.

[0024] In this invention, the current path is naturally coupled to the molten pool, and the circuit is closed through the substrate and the reflow fixture without crossing the air gap, ensuring stable current introduction. Simultaneously, the applied current mode can be switched between DC and AC. By switching the current type, it couples with a servo-steady magnetic field, achieving dual-mode control of electromagnetic braking and electromagnetic oscillation, thus accommodating both single-crystal / directional epitaxial growth and grain refinement requirements.

[0025] This invention employs a servo magnetic field covering the molten pool. Through synergy with the applied current introduced by the current-carrying filament, the resulting Lorentz force field is concentrated on the molten pool region, thereby achieving precise control of the molten pool flow field and temperature field. This "magnetic field + current" servo loading method allows for real-time active intervention in the deposition process. By adjusting the magnetic field strength and current parameters, the convection mode and solidification structure evolution of the molten pool can be directionally controlled.

[0026] The magnetoelectric assisted laser directional energy deposition device integrated in this invention provides two core operating modes: In the "DC + magnetic field" mode, a Lorentz force with a constant direction is generated. This constant force field mainly plays an electromagnetic braking and stabilizing role, which can effectively suppress disordered flow in the molten pool and improve the morphology of the molten pool, thereby creating more favorable conditions for the escape of bubbles and non-metallic inclusions in the molten pool. At the same time, electromagnetic braking helps to suppress Marangoni convection in the molten pool and promotes selective epitaxial growth of directional crystals. In the "AC + magnetic field" mode, an alternating Lorentz force with periodically alternating directions is generated, which forms a periodic disturbance and stirring effect on the molten pool, which can break dendrites, refine grains, and promote the floating and discharge of bubbles and inclusions, thereby significantly reducing porosity and inclusion content and optimizing solidification structure.

[0027] Based on the flexible configuration of the above-mentioned modes, this invention can meet the typical process requirements of both directional epitaxial growth and polycrystalline microstructure refinement using the same set of magnetoelectric assisted laser directional energy deposition equipment. This technology is applicable to additive manufacturing and remanufacturing repair of key materials such as titanium alloys, stainless steel, and high-temperature alloys. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the overall structure of the laser-directed energy deposition device with coordinated current carrying capacity of filament and servo magnetic field according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the current path and transverse magnetic field distribution within the molten pool in an embodiment of the present invention; Figure 3 This is a schematic diagram illustrating the effect of Lorentz braking force in the molten pool under DC electromagnetic braking mode in an embodiment of the present invention. Figure 4 This is a schematic diagram illustrating the effect of Lorentz oscillation force in the molten pool under AC electromagnetic oscillation mode in an embodiment of the present invention.

[0029] Explanation of reference numerals in the attached figures: 1-Laser deposition head; 2-Wire feeding mechanism; 3-Conductive nozzle; 4-Programmable current source; 5-Electromagnetic device; 6-Reflow fixture; 7-Controller; 8-Molten pool; 9-Wire material; 10-Powder nozzle; 11-Substrate; 12-Scanning direction; 13-Powder feeding mechanism. Detailed Implementation

[0030] The embodiments of this application will now be described in detail with reference to the accompanying drawings.

[0031] The following specific examples illustrate the implementation of this application. Those skilled in the art can easily understand other advantages and effects of this application from the content disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. This application can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this application. It should be noted that, in the absence of conflict, the following embodiments and features in the embodiments can be combined with each other. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0032] like Figure 1 As shown, the laser directional energy deposition device with filament current carrying and follow-up magnetic field coordination provided in this embodiment of the invention includes a laser deposition head 1, a filament feeding mechanism 2, a conductive nozzle 3, a programmable current source 4, an electromagnetic device 5, a return fixture 6, a controller 7, a filament 9, and a powder feeding mechanism 13.

[0033] The laser deposition head 1 outputs laser light and forms a molten pool 8 on the surface of the substrate 11. The laser deposition head 1 integrates a laser beam emission path, a powder feeding channel, and a wire feeding channel. The laser irradiation can be a ring laser or a multi-laser beam array. The wire feeding mechanism 2 continuously feeds a metal wire 9 into the molten pool 8 through the wire feeding channel. The wire 9 is preferably a metal alloy wire that is the same as or compatible with the deposition material, with a diameter of 0.8~1.5 mm, preferably 1.0 mm. The laser beam emission path guides the multi-laser beam array to focus on the surface of the substrate 11, forming a high-energy-density region to melt the substrate surface and the fed wire and powder. The powder feeding channel surrounds the laser beam path and connects to the powder nozzle 10. The powder feeding mechanism 13 provides metal powder to the molten pool 8 region through the powder feeding channel and the powder nozzle 10 below the laser deposition head, supplying powder to the molten pool 8 simultaneously with the wire feeding, achieving a combined wire and powder feeding. The laser deposition head 1 moves along the scanning direction 12, and the molten pool 8 moves synchronously with the laser deposition head 1.

[0034] The conductive nozzle 3 is located at the wire exit section of the laser deposition head 1 to guide the wire 9 and maintain electrical contact with it. The conductive nozzle 3 is connected to the output terminal of the programmable current source 4 via a wire. Its structure can adopt the form of a conventional copper conductive nozzle, so that the wire 9 has good frictional contact with it when passing through, ensuring that the current is efficiently transmitted through the wire to the molten pool 8.

[0035] The electromagnetic device 5 is fixed to the laser deposition head 1 and moves synchronously with it, used to apply an external magnetic field to the molten pool region 8. The electromagnetic device 5 is arranged around the periphery of the laser path and powder channel, and generates a magnetic field B in the molten pool region after being energized. The electromagnetic device 5 uses DC excitation to generate a transverse magnetic field that is constant in time and adjustable in intensity and direction, with the magnetic induction lines perpendicular to the deposition scanning path direction. The electromagnetic device 5 is preferably an electromagnetic coil with a magnetic induction intensity of 0.05~0.1T; the direction of the magnetic field can be switched by changing the direction of the excitation current.

[0036] The reflow fixture 6 is clamped in the non-deposition area of ​​the substrate or tooling fixture and is electrically connected to the return end of the programmable current source 4 to form a closed current loop through the conductive nozzle 3, wire 9, molten pool 8, substrate 11 to the reflow fixture 6.

[0037] The controller 7 is connected to the laser deposition head 1, the programmable current source 4, and the electromagnetic device 5, respectively, for coordinating the adjustment of laser power, wire feed speed, deposition scanning rate, applied current type and parameters, and applied magnetic field parameters (such as magnetic field strength), and is configured to switch between applied DC and AC modes during the deposition process. Preferably, the controller has a built-in programmable logic control unit, which dynamically adjusts the parameters of the programmable current source 4 and the electromagnetic coil according to the preset process program or sensor feedback signals, to achieve closed-loop control of the flow and solidification of molten metal in the molten pool.

[0038] In this embodiment of the invention, the metal wire 9 is preferably a weakly magnetic solid welding wire, including but not limited to nickel-based high-temperature alloy wires (such as GH3625, Inconel 625, Inconel 718, etc.), cobalt-based high-temperature alloy wires (such as CoCrMo, CoCrW, etc.), stainless steel wires (such as 316L, 304L, duplex stainless steel, etc.), titanium alloy wires (such as TC4, TA15, TC11, etc.), and aluminum alloy wires (such as 5A06, 6061, etc.). The term "weakly magnetic" refers to a material with a relative permeability ≤ 1.01. Under the action of a transverse magnetic field of 0.05~0.1T, the above materials exhibit weak hysteresis loss within the molten pool region, and the intensity and distribution of magnetic induction lines are not significantly disturbed, which is beneficial for the stable application and control of the Lorentz force field.

[0039] like Figure 2 As shown, one pole of the programmable current source 4 is connected to the conductive nozzle 3 via a wire, and the other pole is connected to the return clamp 6. When the wire 9 passes through the conductive nozzle 3 and comes into contact with the molten pool 8, the current I generated by the programmable current source 4 flows into the wire 9 through the conductive nozzle 3, then into the molten pool 8 and the substrate 11 through the wire 9, and finally returns to the programmable current source 4 through the return clamp 6, forming a closed loop. The applied current establishes a controlled current distribution within the molten pool 8.

[0040] like Figure 2 As shown, the magnetic field B generated by the electromagnetic device 5 runs from the N pole to the S pole, roughly horizontally traversing the molten pool region 8, and is perpendicular to the current I flowing vertically through the molten pool. According to Ampere's law, a Lorentz force F perpendicular to I and B is generated in the molten metal of the pool.

[0041] The working principle of the device is as follows: In this embodiment of the invention, the wire 9 is supplied with a current of a certain intensity through the conductive nozzle 3 before entering the molten pool 8. The current I is introduced into the molten pool 8 through the wire 9, forming a controlled current distribution within the molten pool 8. The transverse magnetic field B generated by the electromagnetic device 5 penetrates the region of the molten pool 8 and interacts with the current I to generate a Lorentz force F = I×B, thereby regulating the flow, heat transfer, and solidification behavior of the molten pool.

[0042] By switching the output mode of the programmable current source 4 using the controller 7, this invention can achieve two operating modes: Electromagnetic braking mode (DC + transverse magnetic field): such as Figure 3 As shown, when the programmable current source 4 outputs a DC current I, the direction of the applied current is constant, and it couples with the transverse magnetic field B to generate a Lorentz braking force F in a constant direction. LThis braking force electromagnetically dampes the Marangoni convection driven by the surface tension gradient within the molten pool, suppressing disordered flow and eddies, and stabilizing the temperature gradient and solidification interface. This mode is suitable for the deposition or repair of single-crystal or directionally solidified superalloys, effectively avoiding impurity crystal nucleation and promoting epitaxial growth.

[0043] Electromagnetic oscillation mode (AC + transverse magnetic field): such as Figure 4 As shown, when the programmable current source 4 outputs AC current I AC When the direction of the applied current alternates periodically with time (e.g., using a 50Hz power frequency sinusoidal alternating current), it couples with the transverse magnetic field B to generate a periodically changing Lorentz oscillating force F. L Alternating Lorentz forces significantly agitate and turbulent the molten pool, essentially introducing an oscillating electromagnetic stirring mechanism within the pool. This stirring facilitates the escape of bubbles from the liquid phase and their rise to the surface, significantly reducing the porosity of the solidified deposit. Simultaneously, the molten pool experiences ample convection, resulting in a more uniform temperature field before solidification, which helps refine grains and suppresses solidification cracking caused by elemental segregation and thermal stress concentration. Specifically, the alternating Lorentz force drives forced oscillations and periodic shear flow in the molten metal, effectively breaking up growing primary dendrites, severing dendrite arms, and promoting new nucleation, thus inducing the transformation of columnar crystals to equiaxed crystals and refining the solidification structure. This mode is suitable for the deposition of polycrystalline alloys and can reduce hot cracking susceptibility.

[0044] It should be noted that the current applied to the wire in this invention is mainly used to generate a Lorentz force field to regulate the molten pool. During implementation, a lower open-circuit voltage and a suitable current can be selected as needed to avoid arc discharge, and current introduction is achieved solely through the conductive contact between the wire and the molten pool. The controller can switch to AC mode to enhance stirring after detecting that the molten pool has stabilized, or maintain DC mode when a more stable molten pool is required. The strength and direction of the magnetic field, as well as the current mode, direction, and magnitude, can also be adjusted according to specific applications to achieve specific molten pool flow patterns and solidification structure control.

[0045] This invention also provides a laser-directed energy deposition method that coordinates current carrying capacity of filament and a servo magnetic field, implemented using the aforementioned apparatus, and comprising the following steps: Establish a current loop: Connect the base or tooling fixture to the loop return terminal of the programmable current source 4 via the return fixture 6.

[0046] Start laser deposition and wire feeding: Start the laser deposition head 1 to form a molten pool 8 on the substrate surface, and at the same time, the wire feeding mechanism 2 continuously feeds the metal wire 9 into the molten pool 8.

[0047] Applying external current: Applying external current to the metal wire 9 through the conductive nozzle 3 located at the wire exit section of the laser deposition head 1, so that the applied current forms a closed current loop through the conductive nozzle 3, the wire 9, the molten pool 8, the substrate and the return fixture 6, and establishes a controlled current distribution in the molten pool 8.

[0048] Apply a follow-up transverse magnetic field: The electromagnetic device 5 applies a transverse magnetic field that is constant in time and adjustable in intensity in the molten pool 8 region. The direction of the magnetic induction lines is perpendicular to the direction of the deposition scanning path, and the magnetic induction intensity is 0.05~0.1T.

[0049] The coupling generates Lorentz force: the current in the molten pool 8 is coupled with the transverse magnetic field to generate Lorentz force, which continuously regulates the flow, heat transfer and solidification behavior of the molten pool during the deposition scanning process.

[0050] Based on the material selection mode: The applied current mode is selected via controller 7 according to the alloy material to be processed and the desired microstructure. When the material is a single crystal or a directionally solidified alloy, the DC mode (electromagnetic braking mode) is selected. The programmable current source 4 outputs DC current with an amplitude of 20~50A, preferably 40~50A. The DC current couples with the transverse magnetic field to generate a steady-state Lorentz force, which suppresses the convection fluctuations of the molten pool and stabilizes the solidification front.

[0051] When the material is polycrystalline or requires grain refinement, the AC mode (electromagnetic oscillation mode) is selected. The programmable current source 4 outputs AC current with an effective value of 20~50A, preferably 40~50A, and a frequency of 50~100Hz. The AC current couples with the transverse magnetic field to generate an alternating Lorentz force, which induces electromagnetic oscillation of the molten pool and promotes grain refinement.

[0052] Deposition complete: After deposition is complete, controller 7 cuts off the current and shuts off the magnetic field or maintains the magnetic field until the molten pool solidifies.

[0053] The present invention will now be described with reference to specific embodiments: Example 1: Additive manufacturing of TC4 titanium alloy (electromagnetic oscillation mode) In this embodiment, TC4 filament is used for laser-fed directional energy deposition additive manufacturing. The filament diameter is 0.8~1.2mm, preferably 1.2mm. The laser power is 800~1800W, preferably 1200W; the laser spot diameter is 1.0~2.0mm, preferably 1.5mm; the filament feed speed is 0.6~2.4m / min, preferably 1.6m / min; the deposition scanning rate is 300~900mm / min, preferably 600mm / min; the single-layer lift is 0.3~0.8mm, preferably 0.5mm; and the inter-pass overlap rate is 30%~50%, preferably 40%. Argon is used as the protective gas, with a flow rate of 10~20L / min, preferably 15L / min.

[0054] The conductive tip 3 is positioned at the filament exit point of the laser deposition head 1 and makes electrical contact with the filament 9. The return clamp 6 holds the non-deposition area of ​​the substrate and is connected to the return terminal of the programmable current source 4. The electromagnetic device 5 moves with the laser deposition head 1 and uses DC excitation to form a constant transverse magnetic field with a magnetic induction intensity of 0.05~0.1T, preferably 0.05~0.06T. The direction of the magnetic induction lines is perpendicular to the direction of the deposition scanning path.

[0055] During the deposition process, an electromagnetic oscillation mode is selected, and a programmable current source 4 outputs an AC current with an effective value of 20~50A, preferably 40~45A; a frequency of 50~100Hz; and a preferred waveform of sine wave.

[0056] During deposition, alternating current coupled with a transverse magnetic field generates alternating Lorentz force, inducing molten pool oscillation and stirring, promoting grain refinement and reducing defect formation tendency. The specific steps of this embodiment are as follows: First, the substrate is connected to the return end of the programmable current source 4 circuit via a return fixture 6; the laser deposition head 1 and wire feeding mechanism 2 are started, with a wire feeding angle of 90°, and the wire end is fed into the laser action zone front or molten pool front, forming a molten pool 8 on the surface of the substrate 11; alternating current is applied to the wire 9 through a conductive nozzle 3, forming a closed loop; an electromagnetic device 5 is started to generate a 0.05~0.06T transverse magnetic field; during deposition scanning, alternating current coupled with the transverse magnetic field generates alternating Lorentz force, continuously inducing molten pool oscillation; the current is cut off after deposition. This parameter combination is used to weaken the continuous growth of columnar crystals, promote the formation of equiaxed crystals, and reduce the tendency for porosity and incomplete fusion defects in the wire-fed deposition layer.

[0057] Example 2: Repair / Welding of 316L Stainless Steel (Electromagnetic Braking Mode) In this embodiment, 316L solid core welding wire is used as the wire material for repair / surfacing on a 316L stainless steel substrate. The wire diameter is 0.8~1.2mm, preferably 1.2mm. The laser power is 1000~2200W, preferably 1600W; the laser spot diameter is 1.0~2.0mm, preferably 1.5mm; the wire feed speed is 0.8~3.5m / min, preferably 1.8m / min; the deposition scanning rate is 300~1000mm / min, preferably 700mm / min; the single-layer lift is 0.4~1.0mm, preferably 0.6mm; the interpass overlap rate is 35%~55%, preferably 45%; the distance from the contact tip to the front edge of the molten pool is 8~20mm, preferably 12mm; the wire extension length is 5~15mm, preferably 8mm. Argon is used as the shielding gas, with a flow rate of 12~25L / min, preferably 18L / min.

[0058] The conductive tip 3 is positioned at the filament exit point of the laser deposition head 1 and makes electrical contact with the filament 9. The return clamp 6 holds the non-deposition area of ​​the substrate and is connected to the return terminal of the programmable current source 4. The electromagnetic device 5 moves with the laser deposition head 1 and uses DC excitation to form a constant transverse magnetic field with a magnetic induction intensity of 0.05~0.1T, preferably 0.06~0.08T. The direction of the magnetic induction lines is perpendicular to the direction of the deposition scanning path.

[0059] During the deposition process, the electromagnetic braking mode is selected, and the programmable current source 4 outputs DC current, which is 20~50A, preferably 40~50A.

[0060] During deposition, the coupling of DC current and transverse magnetic field generates a steady-state Lorentz force, which suppresses molten pool convection fluctuations, improves the morphology of the weld bead, and reduces spatter. The specific steps of this embodiment are as follows: First, the substrate is connected to the return end of the programmable current source 4 circuit via the return fixture 6; the laser deposition head 1 and wire feeding mechanism 2 are started to form a molten pool 8 on the substrate surface; DC current is applied to the wire 9 through the conductive nozzle 3 to form a closed loop; the electromagnetic device 5 is started to generate a 0.06~0.08T transverse magnetic field; during the deposition scanning process, the coupling of DC current and transverse magnetic field generates a steady-state Lorentz force, continuously suppressing molten pool convection; the current is cut off after deposition. This steady-state Lorentz force is used to suppress molten pool surface fluctuations and spatter, reduce weld bead edge collapse and overlap ripples, and facilitate the escape of bubbles, improving the density and surface continuity of the repair / weld overlay layer.

[0061] Example 3: IN718 Additive Manufacturing and Repair (Dual-Mode Switching) In this embodiment, IN718 wire is used for multi-pass, multi-layer laser-guided energy deposition on a nickel-based alloy substrate. The wire diameter is 0.8~1.2mm, preferably 1.2mm. The laser power is 1200~2500W, preferably 1800W; the laser spot diameter is 1.0~2.0mm, preferably 1.5mm; the wire feed speed is 0.8~3.0m / min, preferably 1.6m / min; the deposition scanning rate is 300~900mm / min, preferably 600mm / min; the single-layer lift is 0.4~0.9mm, preferably 0.6mm; and the inter-pass overlap rate is 35%~50%, preferably 45%. Argon is used as the protective gas, with a flow rate of 10~25L / min, preferably 18L / min. The wire feed angle is 90°, and the wire end is fed into the leading edge of the laser action zone or the leading edge of the molten pool.

[0062] During wire feeding deposition, the conductive nozzle 3 maintains stable electrical contact with the wire 9. The wire 9 is conductive and in contact with the molten pool 8. The applied current forms a closed loop through the conductive nozzle 3, the wire 9, the molten pool 8, the substrate 11, and the return fixture 6. During deposition, the initial section, the arc-ending section, the path corner section, or the thin-walled edge section adopts a DC electromagnetic braking mode to improve the stability of the molten pool. In the steady-state filling section, the AC electromagnetic oscillation mode is switched to promote microstructure refinement and improve the tendency of porosity, segregation, and crack defects.

[0063] Specifically, during the dual-mode switching, the electromagnetic braking mode is preferably used in the starting segment, ending segment, path corner segment, or thin-walled edge segment, with a DC current of 20~50A, preferably 40~50A, and a transverse magnetic field strength of 0.05~0.1T, preferably 0.06~0.08T, to stabilize the molten pool morphology and reduce the tendency of overheating and collapse; the steady-state filling segment is preferably switched to the electromagnetic oscillation mode, with an effective value of AC current of 20~50A, preferably 45~50A, a frequency of 50~100Hz, and a sine wave waveform, to promote dendrite fragmentation, solute homogenization, and refinement of the microstructure in the interlayer overlap zone.

[0064] The specific steps of this embodiment are as follows: First, the substrate is connected to the return end of the programmable current source 4 circuit through the return fixture 6; the laser deposition head 1 and the wire feeding mechanism 2 are started to form a molten pool 8 on the substrate surface; the electromagnetic device 5 is started to generate a 0.06T transverse magnetic field; in the initial stage, a DC current (40A) is applied to the wire 9 through the conductive nozzle 3 to stabilize the molten pool by executing the electromagnetic braking mode; after entering the steady-state filling stage, the controller 7 switches the output of the programmable current source 4 to AC current (RMS 50A, frequency 100Hz) to execute the electromagnetic oscillation mode to promote tissue refinement; in the arc-ending stage, it is switched back to DC mode; the current is cut off after deposition is completed.

[0065] In the steady-state electromagnetic oscillation stage, the applied alternating current couples with the transverse magnetic field to form an alternating Lorentz force, which is used for grain refinement, interlayer overlap homogenization, element segregation reduction and crack suppression during the wire feeding deposition process of polycrystalline high-temperature alloys such as IN718. In the electromagnetic braking transition stage, the direct current couples with the transverse magnetic field to form a steady-state Lorentz force, which can suppress excessive convection and surface fluctuations in the molten pool, and improve the forming consistency of the path start and end positions, corner positions and thin-walled edges.

[0066] Furthermore, during the IN718 multilayer deposition process, higher laser power and lower scanning rates can be used in the first layer or at stages with lower heat accumulation to ensure substrate wetting, for example, laser power of 1800~2200 W and scanning rate of 400~600 mm / min; in the middle and upper stable deposition stages, laser power of 1600~2000 W and scanning rate of 600~800 mm / min can be used; in the tail layer or thin-walled edge region, the wire feed speed can be reduced to 0.8~1.2 m / min and DC braking can be used to stabilize the molten pool for a short time. The above segmentation parameters can be combined with AC oscillation mode to take into account the forming stability, grain refinement, and interlayer metallurgical bonding quality.

[0067] In any of the above embodiments, the powder nozzle 10 can be used to supply powder to the molten pool simultaneously with the wire feeding for composite deposition. Under the condition of simultaneous wire and powder feeding, the wire still serves as the primary current-carrying channel, while the powder only serves as a supplement for composition fine-tuning, transition layers, or functional enhancement phases. The selectable powder particle size is 45~150μm, preferably 53~106μm; the powder feeding rate is 1~8g / min, preferably 3~5g / min; the carrier gas is argon with a flow rate of 2~6L / min, preferably 4L / min; the outer protective gas flow rate is 12~25L / min, preferably 18L / min. The wire-to-powder mass input ratio can be set to 90:10~60:40, preferably 80:20. The applied current is still applied to the wire 9 by the programmable current source 4 via the conductive nozzle 3 and then returned to the molten pool and substrate to close the current path, thus avoiding the influence of powder flow stability on the current path.

[0068] Table 1: Typical Materials and Recommended Parameter Window To facilitate implementation, a recommended window for typical materials is shown in Table 1 below:

[0069] In addition to the current and magnetic field windows listed in Table 1, the optional process parameters for wire-fed laser-directed energy deposition also include: laser power 800~2500W, spot diameter 1.0~1.5mm, wire feed speed 0.8~2.0m / min, scanning rate 300~1000mm / min, single-layer lift 0.3~1.0mm, inter-pass overlap 30%~55%, and shielding gas flow rate 10~25L / min. Specific values ​​can be selected by combining electromagnetic braking mode and electromagnetic oscillation mode based on the melting point, viscosity, hot cracking sensitivity, and microstructure control targets of materials such as TC4, 316L, and IN718.

[0070] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, various modifications and variations can be made to the embodiments of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A laser-directed energy deposition device that coordinates current carrying by a filament and a servo magnetic field, characterized in that, include: A laser deposition head is used to output laser light and form a molten pool on the surface of a substrate. The laser deposition head is provided with a wire feeding channel. A wire feeding mechanism is used to continuously feed metal wire into the molten pool through the wire feeding channel; A conductive tip is disposed at the wire exit section of the laser deposition head and is in electrical contact with the metal wire, for applying an external current to the metal wire; A programmable current source, electrically connected to the conductive nozzle, is used to output DC current or AC current, and its current mode can be switched. An electromagnetic device, fixed to the laser deposition head and moving synchronously with the laser deposition head, is used to apply an external magnetic field to the molten pool region. The external magnetic field is a transverse magnetic field, and the direction of its magnetic induction lines is perpendicular to the direction of the deposition scanning path. The return fixture is electrically connected to the substrate or tooling fixture and to the return terminal of the programmable current source to form a closed current loop through the conductive nozzle, wire, molten pool, substrate to the return fixture. The controller is connected to the laser deposition head, the programmable current source, and the electromagnetic device, respectively, and is used to coordinate the adjustment of laser power, wire feed speed, deposition scanning rate, applied current type and parameters, and applied magnetic field parameters, and is configured to switch between applied current DC mode and AC mode during the deposition process; The applied current establishes a controlled current distribution in the molten pool through the closed current loop, and the applied current and the applied magnetic field interact in the molten pool to generate Lorentz force, thereby regulating the flow, heat transfer and solidification behavior of the molten pool.

2. The apparatus according to claim 1, characterized in that: The applied magnetic field is a time-constant magnetic field with adjustable magnetic induction intensity and direction, and the magnetic induction intensity is 0.05~0.1T.

3. The apparatus according to claim 1, characterized in that: When the programmable current source outputs DC current, the DC current amplitude is 20~50A; when the programmable current source outputs AC current, the effective value of the AC current is 20~50A, and the frequency is 50~100Hz.

4. The apparatus according to claim 1, characterized in that: The diameter of the metal wire is 0.8~1.5mm; the metal wire is a weakly magnetic solid welding wire, including at least one of nickel-based high-temperature alloy wire, cobalt-based high-temperature alloy wire, stainless steel wire, titanium alloy wire or aluminum alloy wire.

5. The apparatus according to claim 1, characterized in that: The return fixture is held in the non-deposition area of ​​the substrate or tooling fixture, so that the current loop does not cross the air or protective gas gap.

6. The apparatus according to claim 1, characterized in that: The controller is configured to provide at least two operating modes: an electromagnetic braking mode in which the magnetic field is coupled to a direct current, and an electromagnetic oscillation mode in which the magnetic field is coupled to an alternating current. In the electromagnetic braking mode, the direct current is coupled to a constant external magnetic field to generate a steady-state Lorentz force, which suppresses convective fluctuations in the molten pool and stabilizes the solidification front. In the electromagnetic oscillation mode, the alternating current is coupled to a constant external magnetic field to generate an alternating Lorentz force, which induces electromagnetic oscillations in the molten pool and promotes grain refinement.

7. The apparatus according to claim 1, characterized in that: The device also includes a powder feeding mechanism and a powder nozzle; the laser deposition head is also provided with a powder feeding channel; the powder nozzle is connected to the powder feeding channel, and the powder feeding mechanism is used to provide metal powder to the molten pool while feeding the wire through the powder feeding channel and the powder nozzle, so as to realize the combined feeding of wire and powder.

8. A laser-directed energy deposition method for coordinating current carrying capacity of a filament and a servo magnetic field, implemented using the apparatus described in any one of claims 1-7, characterized in that, Includes the following steps: The substrate or tooling fixture is electrically connected to the return terminal of the programmable current source via a return fixture. The laser deposition head is activated to form a molten pool on the substrate surface, while the wire feeding mechanism feeds metal wire into the molten pool. An external current is applied to the metal wire by a conductive tip located at the wire exit point of the laser deposition head. The applied current forms a closed current loop through the conductive tip, the wire, the molten pool, the substrate, and the reflow fixture, thus establishing a controlled current distribution within the molten pool. An electromagnetic device applies a transverse magnetic field to the molten pool region. The direction of the magnetic induction lines of the transverse magnetic field is perpendicular to the direction of the deposition scanning path, causing the current in the molten pool to couple with the magnetic field and generate a Lorentz force. During the deposition scanning process, the Lorentz force is used to regulate the flow, heat transfer, and solidification behavior of the molten pool.

9. The method according to claim 8, characterized in that: When the programmable current source outputs DC current, it executes the electromagnetic braking mode. The DC current couples with the transverse magnetic field to generate a steady-state Lorentz force, which suppresses the convection fluctuations of the molten pool and stabilizes the solidification front, thereby realizing the growth of impurity-free epitaxial growth in the deposition / repair process of single crystal or directional solidification alloy.

10. The method according to claim 8, characterized in that: When the programmable current source outputs alternating current, it executes an electromagnetic oscillation mode. The alternating current couples with the transverse magnetic field to generate an alternating Lorentz force, which induces electromagnetic oscillation in the molten pool, breaks dendrites, and promotes the transformation of columnar crystals into equiaxed crystals, thereby achieving grain refinement and crack suppression during the deposition or repair of polycrystalline alloys.

Images